Wavelet transform analytics for RF-based UAV detection and identification system using machine learning & nbsp;
}, volume={82}, ISSN={["1873-1589"]}, url={https://doi.org/10.1016/j.pmcj.2022.101569}, DOI={10.1016/j.pmcj.2022.101569}, abstractNote={In this work, we performed a thorough comparative analysis on a radio frequency (RF) based drone detection and identification system (DDI) under wireless interference, such as WiFi and Bluetooth, by using machine learning algorithms, and a pre-trained convolutional neural network-based algorithm called SqueezeNet, as classifiers. In RF signal fingerprinting research, the transient and steady state of the signals can be used to extract a unique signature from an RF signal. By exploiting the RF control signals from unmanned aerial vehicles (UAVs) for DDI, we considered each state of the signals separately for feature extraction and compared the pros and cons for drone detection and identification. Using various categories of wavelet transforms (discrete wavelet transform, continuous wavelet transform, and wavelet scattering transform) for extracting features from the signals, we built different models using these features. We studied the performance of these models under different signal-to-noise ratio (SNR) levels. By using the wavelet scattering transform to extract signatures (scattergrams) from the steady state of the RF signals at 30 dB SNR, and using these scattergrams to train SqueezeNet, we achieved an accuracy of 98.9% at 10 dB SNR.}, journal={PERVASIVE AND MOBILE COMPUTING}, publisher={Elsevier BV}, author={Medaiyese, Olusiji . O. and Ezuma, Martins and Lauf, Adrian P. and Guvenc, Ismail}, year={2022}, month={Jun} } @article{funderburk_kesler_sridhar_sichitiu_guvenc_dutta_zajkowski_marojevic_2022, title={AERPAW Vehicles: Hardware and Software Choices}, DOI={10.1145/3539493.3539583}, abstractNote={AERPAW (Aerial Experimentation and Research Platform for Advanced Wireless) is an advanced wireless research platform centered around fully programmable radios and fully programmable vehicles. In this paper we detail the vehicle aspects of the testbed, including the AERPAW UAVs, UGVs, as well as the hardware and software choices made by the team, as well as our experience earned in the past few years.}, journal={PROCEEDINGS OF THE 2022 EIGHTH WORKSHOP ON MICRO AERIAL VEHICLE NETWORKS, SYSTEMS, AND APPLICATIONS, DRONET 2022}, author={Funderburk, Mark and Kesler, John and Sridhar, Keshav and Sichitiu, Mihail L. and Guvenc, Ismail and Dutta, Rudra and Zajkowski, Thomas and Marojevic, Vuk}, year={2022}, pages={37–42} } @article{namuduri_fiebig_matolak_guvenc_hari_maattanen_2022, title={Advanced Air Mobility: Research Directions for Communications, Navigation, and Surveillance}, url={https://doi.org/10.1109/MVT.2022.3194277}, DOI={10.1109/MVT.2022.3194277}, abstractNote={Advanced air mobility (AAM) is an emerging industry focus as well as a research and development discipline. Innovations and technologies resulting from AAM will change the way that we move cargo and people in and around cities. Industry is moving fast with excitement to deploy AAM solutions. However, there are multiple technical challenges that need to be overcome before AAM becomes a reality. This article takes a closer look at the technology readiness level of AAM solutions in the area of communications, navigation, and surveillance (CNS) and identifies open research problems as well as directions to address them. In particular, we discuss current approaches and future research challenges in air corridor design, air-to-air (AA) communications, 3rd Generation Partnership Project (3GPP) support for navigation, and detect and avoid (DAA)/collision avoidance, among other areas, for supporting future AAM operations.}, journal={IEEE Vehicular Technology Magazine}, author={Namuduri, Kamesh and Fiebig, Uwe-Carsten and Matolak, David W. and Guvenc, Ismail and Hari, K.V.S. and Maattanen, Helka-Liina}, year={2022}, month={Dec} } @article{samal_dutta_guvenc_sichitiu_floyd_zajkowski_2022, title={Automating Operator Oversight in an Autonomous, Regulated, Safety-Critical Research Facility}, ISSN={["1095-2055"]}, DOI={10.1109/ICCCN54977.2022.9868858}, abstractNote={The deployment at scale of Unmanned Aerial Systems have become increasingly imminent in the last few years, even as concerns regarding the dependability and predictability of their command and control channels remain fully to be addressed. The intersection of ground-to-air wireless communications, aerial networking, and trajectory control has become a research area of sharp interest. The validation of such research, beyond the theoretical/simulation stage, requires a facility that is both realistic, and admits of potentially risky or unsafe operation, while in the end guaranteeing personnel and equipment safety. The AERPAW project is an ambitious project, funded by the PAWR program of the US NSF, to create a remote accessible research platform for a research facility to enable such validation. To enable remote usage of such a testbed, yet provide the researcher with complete experimental freedom, the AERPAW facility includes a combination of architectural mechanisms that balance freedom of experimentation with regulatory compliance and safety. In this paper, we articulate the challenges and considerations of designing such mechanisms, and present the architectural features of AERPAW that attempt to realize these lofty goals.}, journal={2022 31ST INTERNATIONAL CONFERENCE ON COMPUTER COMMUNICATIONS AND NETWORKS (ICCCN 2022)}, author={Samal, Tripti and Dutta, Rudra and Guvenc, Ismail and Sichitiu, Mihail L. and Floyd, Brian and Zajkowski, Thomas}, year={2022} } @article{ezuma_anjinappa_semkin_guvenc_2022, title={Comparative Analysis of Radar-Cross-Section-Based UAV Recognition Techniques}, volume={22}, ISSN={["1558-1748"]}, url={https://doi.org/10.1109/JSEN.2022.3194527}, DOI={10.1109/JSEN.2022.3194527}, abstractNote={This work investigates the problem of unmanned aerial vehicle (UAV) recognition using their radar cross section (RCS) signature. The RCS of six commercial UAVs is measured at 15 and 25 GHz in an anechoic chamber for both vertical–vertical (VV) polarization and horizontal–horizontal (HH) polarization. The RCS signatures are used to train 15 different recognition algorithms, each belonging to one of three different categories: statistical learning (SL), machine learning (ML), and deep learning (DL). The study shows that, while the average accuracy of all the algorithms increases with the signal-to-noise ratio (SNR), the ML algorithm achieved better accuracy than the SL and DL algorithms. For example, the classification tree ML achieves an accuracy of 98.66% at 3-dB SNR using the 15-GHz VV-polarized RCS test data from the UAVs. We investigate the recognition accuracy using the Monte Carlo analysis with the aid of boxplots, confusion matrices, and classification plots. On average, the accuracy of the classification tree ML model performed better than the other algorithms, followed by Peter Swerling’s statistical models and the discriminant analysis ML model. In general, the accuracy of the ML and SL algorithms outperformed the DL algorithms (Squeezenet, Googlenet, Nasnet, and Resnet 101) considered in the study. Furthermore, the computational time of each algorithm is analyzed. The study concludes that, while the SL algorithms achieved good recognition accuracy, the computational time was relatively long when compared to the ML and DL algorithms. Also, the study shows that the classification tree achieved the fastest average recognition time of about 0.46 ms.}, number={18}, journal={IEEE SENSORS JOURNAL}, author={Ezuma, Martins and Anjinappa, Chethan Kumar and Semkin, Vasilii and Guvenc, Ismail}, year={2022}, month={Sep}, pages={17932–17949} } @article{maeng_anjinappa_guvenc_2022, title={Coverage Probability Analysis of Passive Reflectors in Indoor Environments}, volume={26}, ISSN={["1558-2558"]}, url={https://doi.org/10.1109/LCOMM.2022.3193810}, DOI={10.1109/LCOMM.2022.3193810}, abstractNote={Since millimeter wave (mmWave) and sub-terahertz bands are highly vulnerable to blockage and penetration loss effects, wireless coverage enhancement is one of the critical challenges in indoor mmWave deployments. In particular, when the line-of-sight (LoS) link is blocked, a strong non-LoS (NLoS) path can provide a stable link quality. One of the efficient ways to improve the NLoS link is the use of strategically placed passive reflectors. In this letter, we study the indoor coverage improvement by using a transparent passive reflector attached on a wall. We consider an indoor open-door scenario, where the LoS link is blocked by the walls for receivers inside the room, and the coverage can only be achieved via an NLoS link through a passive reflector. We analytically derive closed-form equations of the reflection visibility probability and the coverage probability. By simulation and analytical results, we show the coverage dependency on the location and size of the reflector.}, number={10}, journal={IEEE COMMUNICATIONS LETTERS}, author={Maeng, Sung Joon and Anjinappa, Chethan K. and Guvenc, Ismail}, year={2022}, month={Oct}, pages={2287–2291} } @article{rahmati_hosseinalipour_yapici_he_guvenc_dai_bhuyan_2022, title={Dynamic Interference Management for UAV-Assisted Wireless Networks}, volume={21}, ISSN={["1558-2248"]}, url={https://doi.org/10.1109/TWC.2021.3114234}, DOI={10.1109/TWC.2021.3114234}, abstractNote={We investigate a transmission mechanism aiming to improve the data rate between a base station (BS) and a user equipment (UE) through deploying multiple relaying UAVs. We consider the effect of interference incurred by another established communication network, which makes our problem challenging and different from the state of the art. We aim to design the 3D trajectories and power allocation for the UAVs to maximize the data flow of the network while keeping the interference on the existing communication network below a threshold. We utilize the mobility feature of the UAVs to evade the (un)-intended interference caused by (un)-intentional interferers. To this end, we propose an alternating-maximization approach to jointly obtain the 3D trajectories and the UAVs transmission powers. We handle the 3D trajectory design by resorting to spectral graph theory and subsequently address the power allocation through convex optimization techniques. We also approach the problem from the intentional interferer’s perspective where smart jammers chase the UAVs to effectively degrade the data flow of the network. We also extend our work to the case for multiple UEs. Finally, we demonstrate the efficacy of our proposed method through extensive simulations.}, number={4}, journal={IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Rahmati, Ali and Hosseinalipour, Seyyedali and Yapici, Yavuz and He, Xiaofan and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2022}, month={Apr}, pages={2637–2653} } @article{chapnevis_guvenc_bulut_2022, title={IMSI Sharing-Based Dynamic and Flexible Traffic Aggregation for Massive IoT Networks}, volume={9}, ISSN={["2327-4662"]}, url={https://doi.org/10.1109/JIOT.2022.3155923}, DOI={10.1109/JIOT.2022.3155923}, abstractNote={International mobile subscriber identity (IMSI) sharing-based aggregated communication aims to connect multiple Internet of Things (IoT) devices to the mobile operator’s core network over the same subscriber line. IoT devices with low data rates and long data sending intervals are first grouped together and assigned the same subscriber identity. They then take turns to perform their data exchanges using the same cellular connection, yielding huge savings in resource (e.g., number of active bearers) usage. Current solutions however do not consider different device traffic characteristics, the flexibility in traffic patterns, and dynamic network environments where new IoT devices join and existing ones leave the network. In this article, we study the problem of the grouping of IoT devices that will share the same subscriber identity based on their traffic patterns which can also be slightly shifted. We also study the efficient regrouping of these devices as the set of devices in the network changes. We first solve the optimal grouping and traffic aggregation problem for the initial and updated network states using integer linear programming (ILP). Then, to avoid the high complexity of ILP solutions, we develop heuristic-based solutions. Through extensive simulations, we show that heuristic-based algorithms can provide close to optimal ILP-based results while running much faster. The results also show that shifting-based grouping provides more resource saving compared to no-shifting-based aggregation and the proposed solution for dynamic environments can maintain the resource saving with a much lower complexity.}, number={19}, journal={IEEE INTERNET OF THINGS JOURNAL}, author={Chapnevis, Amirahmad and Guvenc, Ismail and Bulut, Eyuphan}, year={2022}, month={Oct}, pages={18221–18237} } @article{sinha_guvenc_2022, title={Impact of Antenna Pattern on TOA Based 3D UAV Localization Using a Terrestrial Sensor Network}, volume={71}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2022.3164423}, DOI={10.1109/TVT.2022.3164423}, abstractNote={In this article, we explore the fundamental limits of the 3-dimensional (3D) localization of unmanned aerial vehicles (UAVs) in conjunction with the effects of 3D antenna radiation patterns. Although localization of UAVs has been studied to some extent in the literature, effects of antenna characteristics on 3D localization remains mostly unexplored. To study such effects, we consider a scenario where a fixed number of radio-frequency (RF) sensors equipped with single or multiple dipole antennas are placed at some known locations on the ground, and they derive the time-difference-of-arrival (TDOA) measurements from the time-of-arrival (TOA) data collected for the UAV that is also equipped with a dipole antenna. We then use these measurements to estimate the 3D location of the UAV, and to derive the Cramer-Rao lower bounds (CRLBs) on the localization error for various orientations of the dipole antennas at the transmitter and the receiver. Namely, we consider vertical-vertical (VV), horizontal-horizontal (HH), and vertical-horizontal (VH) radiation patterns in a purely line-of-sight (LoS) environment and a mixed LoS/Non-line-of-sight (NLoS) environment. We show that the localization accuracy changes in a non-monotonic pattern with respect to the UAV altitude and identify the respective critical altitudes for each of the VV, VH and HH orientations. Subsequently, we propose a multi-antenna signal acquisition technique that mitigates the accuracy degradation due to the antenna pattern mismatches, and we derive the localization CRLB for the multi-antenna scenario. Our numerical results characterize achievable localization accuracy for various antenna configurations, UAV heights, and propagation conditions for representative UAV scenarios.}, number={7}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sinha, Priyanka and Guvenc, Ismail}, year={2022}, month={Jul}, pages={7703–7718} } @article{anjinappa_ganesh_ozdemir_ridenour_khawaja_guvenc_nomoto_ide_2022, title={Indoor Propagation Measurements with Transparent Reflectors at 28/39/120/144 GHz}, ISSN={["2164-7038"]}, DOI={10.1109/ICCWorkshops53468.2022.9814550}, abstractNote={One of the critical challenges of operating with the terahertz or millimeter-wave wireless networks is the necessity of at least a strong non-line-of-sight (NLoS) reflected path to form a stable link. Recent studies have shown that an economical way of enhancing/improving these NLoS links is by using passive metal-lic reflectors that provide strong reflections. However, despite its inherent radio advantage, metals can dramatically influence the landscape's appearance - especially the indoor environment. A conceptual view of escaping this is by using transparent reflectors. In this work, for the very first time, we evaluate the wireless propagation characteristics of passive transparent reflectors in an indoor environment at 28 GHz, 39 GHz, 120 GHz, and 144 GHz bands. In particular, we investigate the penetration loss and the reflection characteristics at different frequencies and compare them against the other common indoor materials such as ceiling tile, clear glass, drywall, plywood, and metal. The measurement results suggest that the transparent reflector, apart from an obvious advantage of transparency, has a higher penetration loss than the common indoor materials (excluding metal) and performs similarly to metal in terms of reflection. Our experimental results directly translate to better reflection performance and preserving the radio waves within the environ-ment than common indoor materials, with potential applications in controlled wireless communication.}, journal={2022 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS)}, author={Anjinappa, Chethan K. and Ganesh, Ashwini P. and Ozdemir, Ozgur and Ridenour, Kris and Khawaja, Wahab and Guvenc, Ismail and Nomoto, Hiroyuki and Ide, Yasuaki}, year={2022}, pages={1118–1123} } @article{deshmukh_lin_lou_kamel_yang_guvenc_2022, title={Intelligent Feedback Overhead Reduction (iFOR) in Wi-Fi 7 and Beyond}, DOI={10.1109/VTC2022-Spring54318.2022.9860553}, abstractNote={The IEEE 802.11 standard based wireless local area networks (WLANs) or Wi-Fi networks are critical to provide internet access in today’s world. The increasing demand for high data rate in Wi-Fi networks has led to several advancements in the 802.11 standard. Supporting MIMO transmissions with higher number of transmit antennas operating on wider bandwidths is one of the key capabilities for reaching higher throughput. However, the increase in sounding feedback overhead due to higher number of transmit antennas may significantly curb the throughput gain. In this paper, we develop an unsupervised learning-based method to reduce the sounding duration in a Wi-Fi MIMO link. Simulation results show that our method uses approximately only 8% of the number of bits required by the existing feedback mechanism and it can boost the system throughput by up to 52%.}, journal={2022 IEEE 95TH VEHICULAR TECHNOLOGY CONFERENCE (VTC2022-SPRING)}, author={Deshmukh, Mrugen and Lin, Zinan and Lou, Hanqing and Kamel, Mahmoud and Yang, Rui and Guvenc, Ismail}, year={2022} } @article{ahmad_narmeen_becvar_guvenc_2022, title={Machine Learning-Based Beamforming for Unmanned Aerial Vehicles Equipped with Reconfigurable Intelligent Surfaces}, volume={29}, ISSN={["1558-0687"]}, DOI={10.1109/MWC.004.2100694}, abstractNote={Unmanned aerial vehicles (UAVs) equipped with reconfigurable intelligent surfaces (RISs) have emerged as a promising technology for numerous applications involving aerial networks. However, the UAV-RIS concept faces challenges related to the deployment of the UAV-RIS, especially in cases, where UAV-RIS is combined with emerging technologies, such as beamforming, sensitive to propagation channel variation. In this article, we first overview various use-cases of UAV-RIS beam-forming considering practical scenarios. Aiming to improve the performance of communication channels, we propose a machine learning-based beamforming policy for UAV-RIS by employing prioritized experience replay (PER) based deep Q-Network (DQN). Compared to traditional approaches, the proposed PER DQN-based beamforming for UAV-RIS communication provides significant enhancements in performance. Finally, we highlight some potential directions for future research.}, number={4}, journal={IEEE WIRELESS COMMUNICATIONS}, author={Ahmad, Ishtiaq and Narmeen, Ramsha and Becvar, Zdenek and Guvenc, Ismail}, year={2022}, month={Aug}, pages={32–38} } @article{maeng_guvenc_sichitiu_floyd_dutta_zajkowski_ozdemir_mushi_2022, title={National Radio Dynamic Zone Concept with Autonomous Aerial and Ground Spectrum Sensors}, ISSN={["2164-7038"]}, DOI={10.1109/ICCWORKSHOPS53468.2022.9814648}, abstractNote={National radio dynamic zone (NRDZs) are intended to be geographically bounded areas within which controlled experiments can be carried out while protecting the nearby licensed users of the spectrum. An NRDZ will facilitate research and development of new spectrum technologies, waveforms, and protocols, in typical outdoor operational environments of such technologies. In this paper, we introduce and describe an NRDZ concept that relies on a combination of autonomous aerial and ground sensor nodes for spectrum sensing and radio environment monitoring (REM). We elaborate on key characteristics and features of an NRDZ to enable advanced wireless experimentation while also coexisting with licensed users. Some preliminary results based on simulation and experimental evaluations are also provided on out-of-zone leakage monitoring and real-time REMs.}, journal={2022 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS)}, author={Maeng, S. J. and Guvenc, I and Sichitiu, M. L. and Floyd, B. and Dutta, R. and Zajkowski, T. and Ozdemir, O. and Mushi, M.}, year={2022}, pages={687–692} } @article{sinha_krim_guvenc_2022, title={Neural Network Based Tracking of Maneuvering Unmanned Aerial Vehicles}, ISSN={["1058-6393"]}, DOI={10.1109/IEEECONF56349.2022.10052072}, abstractNote={The motion model of an unmanned aerial vehicle (UAV) is a time-varying function that is often unknown to the tracking entity, which makes accurate tracking of highly maneuvering UAVs a challenging problem. Most state-of-the-art tracking techniques employ a fixed set of parametric models that approximate the possible maneuvers along the target trajectory to a reasonable accuracy. However, such predetermined motion models might not be adequate for frequent and aggressive maneuvers performed by small UAVs. To this end, we build a data driven adaptive filtering algorithm that improves the tracking accuracy by using a recurrent neural network (RNN)-based motion model that is trained on realistic simulated data generated from a medium fidelity simulink model of a fixed-wing UAV. We then train another feed-forward neural network in conjunction with the pretrained RNN-based motion model, to adaptively combine the incoming current measurement with the predicted state based on the output of a change detection algorithm that detects any increase/decrease in the uncertainty in the predicted states. Our analysis and results show that the proposed tracking algorithm outperforms the state-of-the-art interactive multiple model (IMM) algorithm for highly maneuvering trajectories.}, journal={2022 56TH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS}, author={Sinha, Priyanka and Krim, Hamid and Guvenc, Ismail}, year={2022}, pages={380–386} } @article{maeng_guvenc_sichitiu_ozdemir_2022, title={Out-of-Zone Signal Leakage Sensing in Radio Dynamic Zones}, ISSN={["1550-3607"]}, DOI={10.1109/ICC45855.2022.9838534}, abstractNote={Radio dynamic zones (RDZs) are geographically bounded areas where novel advanced wireless technologies can be developed, tested, and improved, without the concern of interfering to other incumbent radio technologies nearby the RDZ. In order to operate an RDZ, use of a real-time spectrum monitoring system carries critical importance. Such a monitoring system should detect out-of-zone (OoZ) signal leakage outside of the RDZ, and if the interference to nearby receivers is intolerable, the monitoring system should be capable of mitigating such interference. This can e.g. be achieved by stopping operations inside the RDZ or switching to other bands for RDZ operation. In this paper, we introduce a spectrum monitoring concept for OoZ signal leakage detection at RDZs, where sensor nodes (SNs) are installed at the boundary of an RDZ and monitor the power leakage from multiple transmitters within the RDZ. We propose a prediction algorithm that estimates the received interference at OoZ geographical locations outside of the RDZ, using the measurements obtained at sparsely located SNs at the RDZ boundary. Using computer simulations, we evaluate the performance of the proposed algorithm and study its sensitivity to SN deployment density.}, journal={IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC 2022)}, author={Maeng, Sung Joon and Guvenc, Ismail and Sichitiu, Mihail L. and Ozdemir, Ozgur}, year={2022}, pages={5579–5584} } @article{maeng_yapici_guvenc_bhuyan_dai_2022, title={Precoder Design for Physical-Layer Security and Authentication in Massive MIMO UAV Communications}, volume={71}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2022.3141055}, DOI={10.1109/TVT.2022.3141055}, abstractNote={Supporting reliable and seamless wireless connectivity for unmanned aerial vehicles (UAVs) has recently become a critical requirement to enable various different use cases of UAVs. Due to their widespread deployment footprint, cellular networks can support beyond visual line of sight (BVLOS) communications for UAVs. In this paper, we consider cellular connected UAVs (C-UAVs) that are served by massive multiple-input-multiple-output (MIMO) links to extend coverage range, while also improving physical layer security and authentication. We consider Rician channel and propose a novel linear precoder design for transmitting data and artificial noise (AN). We derive the closed-form expression of the ergodic secrecy rate of C-UAVs for both conventional and proposed precoder designs. In addition, we obtain the optimal power splitting factor that divides the power between data and AN by asymptotic analysis. Then, we apply the proposed precoder design in the fingerprint embedding authentication framework, where the goal is to minimize the probability of detection of the authentication tag at an eavesdropper. In simulation results, we show the superiority of the proposed precoder in both secrecy rate and the authentication probability considering moderate and large number of antenna massive MIMO scenarios.}, number={3}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Maeng, Sung Joon and Yapici, Yavuz and Guvenc, Ismail and Bhuyan, Arupjyoti and Dai, Huaiyu}, year={2022}, month={Mar}, pages={2949–2964} } @article{ezuma_anjinappa_funderburk_guvenc_2022, title={Radar Cross Section Based Statistical Recognition of UAVs at Microwave Frequencies}, volume={58}, ISSN={["1557-9603"]}, url={https://doi.org/10.1109/TAES.2021.3096875}, DOI={10.1109/TAES.2021.3096875}, abstractNote={This article presents a radar cross-section (RCS)-based statistical recognition system for identifying/classifying unmanned aerial vehicles (UAVs) at microwave frequencies. First, the article presents the results of the vertical (VV) and horizontal (HH) polarization RCS measurement of six commercial UAVs at 15 and 25 GHz in a compact range anechoic chamber. The measurement results show that the average RCS of the UAVs depends on shape, size, material composition of the target UAV as well as the azimuth angle, frequency, and polarization of the illuminating radar. Afterward, radar characterization of the target UAVs is achieved by fitting the RCS measurement data to 11 different statistical models. From the model selection analysis, we observe that the lognormal, generalized extreme value, and gamma distributions are most suitable for modeling the RCS of the commercial UAVs while the Gaussian distribution performed relatively poorly. The best UAV radar statistics forms the class conditional probability densities for the proposed UAV statistical recognition system. The performance of the UAV statistical recognition system is evaluated at different signal noise ratio (SNR) with the aid of Monte Carlo analysis. At an SNR of 10 dB, the average classification accuracy of 97.60% or better is achievable.}, number={1}, journal={IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS}, author={Ezuma, Martins and Anjinappa, Chethan Kumar and Funderburk, Mark and Guvenc, Ismail}, year={2022}, month={Feb}, pages={27–46} } @article{ozturk_erden_du_anjinappa_ozdemir_guvenc_2022, title={Ray Tracing Analysis of Sub-6 GHz and mmWave Indoor Coverage with Reflecting Surfaces}, ISSN={["2164-2958"]}, DOI={10.1109/RWS53089.2022.9719917}, abstractNote={Indoor coverage and channel modelling is crucial for network planning purposes at mmWave bands. In this paper, we analyzed received power patterns and connectivity in an indoor office environment for sub-6 GHz and mmWave bands using ray tracing simulations and theoretical models over different scenarios. We discussed the effect of using metallic walls instead of regular drywall, base station (BS) location, and open/shut doors. Our results showed that ray tracing solutions are consistent with theoretical calculations, and using reflective walls significantly improves average received power and connectivity at mmWave bands, e.g., for the given floor plan, coverage increases from 86% to 97.5% at 60 GHz band.}, journal={2022 IEEE RADIO AND WIRELESS SYMPOSIUM (RWS)}, author={Ozturk, Ender and Erden, Fatih and Du, Kairui and Anjinappa, Chethan K. and Ozdemir, Ozgur and Guvenc, Ismail}, year={2022}, pages={160–163} } @article{yang_kang_park_guvenc_kim_jeong_2022, title={Stepped-Carrier OFDM With a Nonlinear Hopping Pattern for Joint Radar and Communications}, volume={22}, ISSN={["1558-1748"]}, url={https://doi.org/10.1109/JSEN.2022.3219244}, DOI={10.1109/JSEN.2022.3219244}, abstractNote={In this article, a stepped-carrier orthogonal frequency-division multiplexing (OFDM) system with a nonlinear hopping pattern is developed for joint radar and communication (RadCom). In the proposed OFDM-based RadCom system, the carrier frequencies of OFDM symbols for multiple RadCom nodes are orthogonally switched to avoid interference while also maximizing the signal-to-radar interference ratio (SRIR). Differently from conventional linear stepped-carrier OFDM radar that does not consider the communication performance, we first develop a subband allocation method that considers both the radar and the communication performance for multiple RadCom nodes. Channel state information (CSI) of multiple nodes is shared with a centralized server, which then computes the subband allocation strategy that gives the maximum SRIR. Furthermore, a distributed subband allocation strategy based on stateless Q-learning is also proposed, which is suitable when the RadCom nodes do not share their CSI. We also develop the radar signal processing algorithm for range and velocity estimation when the stepped-carrier OFDM waveforms are transmitted through multiple subbands with a nonlinear hopping pattern. Through computer simulations, we confirm that the proposed stepped-carrier OFDM with the nonlinear hopping pattern exhibits a higher achievable sum rate than conventional linear stepped OFDM while not sacrificing the radar performance of target parameter estimation.}, number={24}, journal={IEEE SENSORS JOURNAL}, author={Yang, Yunji and Kang, Jong-Sung and Park, Jaehyun and Guvenc, Ismail and Kim, Hyungju and Jeong, Byung Jang}, year={2022}, month={Dec}, pages={24619–24633} } @article{mushi_joshi_dutta_guvenc_sichitiu_floyd_zajkowski_2022, title={The AERPAW Experiment Workflow - Considerations for Designing Usage Models for a Computing-supported Physical Research Platform}, ISSN={["2159-4228"]}, DOI={10.1109/INFOCOMWKSHPS54753.2022.9798061}, abstractNote={The AERPAW project is an ambitious project, funded by the PAWR program of the US NSF, to create a remote accessible research platform for a research facility with some distinct features that makes its usage model unique, and non-obvious to many researchers desirous of making use of this platform. AERPAW is primarily a physical resource (not a computing or cyber-resource) - the RF enviroment, and the airspace. Experimenters can explore them through radio transceivers and Unmanned Aerial Vehicles, both under the Experimenter’s programmatic control. Since the entire workflow of the user is through the mediation of virtual computing environments, users often tend to think of AERPAW as a computing resource, and find some of the experiment workflow counter-intuitive. In this paper, we articulate the challenges and considerations of designing an experiment workflow that balances the need for guaranteeing safe testbed operation, and providing flexible programmatic access to this unique resource.}, journal={IEEE INFOCOM 2022 - IEEE CONFERENCE ON COMPUTER COMMUNICATIONS WORKSHOPS (INFOCOM WKSHPS)}, author={Mushi, Magreth and Joshi, Harshvardhan P. and Dutta, Rudra and Guvenc, Ismail and Sichitiu, Mihail L. and Floyd, Brian and Zajkowski, Thomas}, year={2022} } @misc{khawaja_semkin_ratyal_yaqoob_gul_guvenc_2022, title={Threats from and Countermeasures for Unmanned Aerial and Underwater Vehicles}, volume={22}, ISSN={["1424-8220"]}, DOI={10.3390/s22103896}, abstractNote={The use of unmanned aerial vehicles (UAVs) for different applications has increased tremendously during the past decade. The small size, high maneuverability, ability to fly at predetermined coordinates, simple construction, and affordable price have made UAVs a popular choice for diverse aerial applications. However, the small size and the ability to fly close to the terrain make the detection and tracking of UAVs challenging. Similarly, unmanned underwater vehicles (UUVs) have revolutionized underwater operations. UUVs can accomplish numerous tasks that were not possible with manned underwater vehicles. In this survey paper, we provide features and capabilities expected from current and future UAVs and UUVs, and review potential challenges and threats due to use of such UAVs/UUVs. We also overview the countermeasures against such threats, including approaches for the detection, tracking, and classification of UAVs and UUVs.}, number={10}, journal={SENSORS}, author={Khawaja, Wahab and Semkin, Vasilii and Ratyal, Naeem Iqbal and Yaqoob, Qasim and Gul, Jibran and Guvenc, Ismail}, year={2022}, month={May} } @article{liu_matolak_guvenc_mehrpouyan_2022, title={Tropospheric attenuation prediction for future millimeter wave terrestrial systems: Estimating statistics and extremes}, volume={5}, ISSN={["1099-1131"]}, DOI={10.1002/dac.5240}, abstractNote={Tropospheric attenuations can be significant in the millimeter wave (mmWave) frequency bands; hence, accurate prediction modeling of tropospheric attenuation is important for reliable mmWave communication. Several models have been established by the International Telecommunication Union (ITU), yet estimation accuracy is limited due to the large spatial scales used for model input parameters. In this paper, we address this and apply local precipitation data to analyze tropospheric attenuation statistics and compare to results when using ITU regional input rain data. Specifically, tropospheric attenuation is predicted via simulations using the ITU method at 30, 60, and 90 GHz in four distinct geographic locations with different climate types. From our simulations, we gather statistics for annual average rain attenuation, worst month rain attenuation, and rain attenuation per decade. Our results indicate that when using local measured rain data, for 1 km link distance, mean rain event attenuation increases from 0.5 to 2 dB. Local rain data yield larger attenuations at essentially all percentages of time not exceeded (essentially corresponding to all probability values): for example, for 0.1% of time not exceeded, in Columbia, SC, rain attenuation for 30 GHz frequency increases to 9 dB with local rain data, compared to 5 dB with ITU's regional data, corresponding to rain rates of 38.2 and 17.5 mm/h, respectively; at the same probability and location, the 90 GHz attenuation increases by 10 dB, from 10 to 20 dB when local rain data are used. Fog attenuations are also appreciable, reaching 8 dB for the 90 GHz frequency. Moreover, for the example locations, peak rain attenuations have increased at a rate of approximately 2 dB/decade over the past 50 years. Our results indicate that actual tropospheric attenuations may be substantially larger than that predicted by the ITU model when using regional rain rate data.}, journal={INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS}, author={Liu, Jinwen and Matolak, David W. and Guvenc, Ismail and Mehrpouyan, Hani}, year={2022}, month={May} } @article{du_ozdemir_erden_guvenc_2021, title={28 GHz Indoor and Outdoor Propagation Measurements and Analysis at a Regional Airport}, DOI={10.1109/PIMRC50174.2021.9569260}, abstractNote={In the upcoming 5G communication, the millimeter-wave (mmWave) technology will play an important role due to its large bandwidth and high data rate. However, mmWave frequencies have higher free-space path loss (FSPL) in line-of-sight (LOS) propagation compared to the currently used sub-6 GHz frequencies. What is more, in non-line-of-sight (NLOS) propagation, the attenuation of mmWave is larger compared to the lower frequencies, which can seriously degrade the performance. It is therefore necessary to investigate mmWave propagation characteristics for different deployment scenarios of interest, to understand coverage and rate performance in such scenarios. In this paper, we focus on 28 GHz wideband mmWave signal propagation characteristics at Johnston Regional Airport (JNX), a local airport near Raleigh, NC. To collect data, we use an NI PXI-based channel sounder at 28 GHz for indoor, outdoor, and indoor-to-outdoor scenarios. Results on LOS propagation, reflection, penetration, signal coverage, and multipath components (MPCs) show a lower indoor FSPL, a richer scattering, and a better coverage compared to outdoor. We also observe high indoor-to-outdoor propagation losses.}, journal={2021 IEEE 32ND ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC)}, author={Du, Kairui and Ozdemir, Ozgur and Erden, Fatih and Guvenc, Ismail}, year={2021} } @article{chowdhury_anjinappa_guvenc_sichitiu_ozdemir_bhattacherjee_dutta_marojevic_floyd_2021, title={A Taxonomy and Survey on Experimentation Scenarios for Aerial Advanced Wireless Testbed Platforms}, volume={2021-March}, ISSN={["1095-323X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85111405299&partnerID=MN8TOARS}, DOI={10.1109/AERO50100.2021.9438449}, abstractNote={There are various works in the recent literature on fundamental research and experimentation on unmanned aerial vehicle (UAV) communications. On the other hand, to our best knowledge, there is no taxonomy and survey on experimentation possibilities with a software-defined aerial wireless platform. The goal of this paper is first to have a brief overview of large-scale advanced wireless experimentation platforms broadly available to the wireless research community, including also the Aerial Experimentation and Research Platform for Advanced Wireless (AERPAW). We then provide a detailed taxonomy and a comprehensive survey of experimentation possibilities that can be carried out in a platform such as AERPAW. In particular, we conceptualize and present eleven different classes of advanced and aerial wireless experiments, provide several example experiments for each class, and discuss some of the existing related works in the literature. The paper will help to develop a better understanding of the equipment and software resources that can be available for experimentation in mid-scale wireless platforms, as well as the capabilities and limitations of such platforms.}, journal={2021 IEEE AEROSPACE CONFERENCE (AEROCONF 2021)}, author={Chowdhury, Md Moin Uddin and Anjinappa, Chethan K. and Guvenc, Ismail and Sichitiu, Mihail and Ozdemir, Ozgur and Bhattacherjee, Udita and Dutta, Rudra and Marojevic, Vuk and Floyd, Brian}, year={2021} } @article{panicker_ozdemir_sichitiu_guvenc_dutta_marojevic_floyd_2021, title={AERPAW emulation overview and preliminary performance evaluation}, volume={194}, ISSN={["1872-7069"]}, url={https://doi.org/10.1016/j.comnet.2021.108083}, DOI={10.1016/j.comnet.2021.108083}, abstractNote={The Aerial Experimentation and Research Platform for Advanced Wireless (AERPAW) has been recently funded by the National Science Foundation (NSF)’s Platforms for Advanced Wireless Research (PAWR) program. The AERPAW platform will enable experiments with programmable radios and programmable unmanned aerial vehicles (UAVs), conducted in a safe and repeatable manner. Several architectural components are crucial for enabling the envisioned capabilities of the testbed. In this paper, after providing a high level overview of AERPAW, we first present the emulation design of AERPAW vehicles. Subsequently, we describe various different options for wireless channel emulation in AERPAW. We start with a generalized model for wireless emulation, and expand that model to packet-level emulation, I-Q level emulation, and radio-frequency (RF)-level emulation. A discussion on the trade-offs among these various different emulation possibilities is also provided.}, journal={COMPUTER NETWORKS}, publisher={Elsevier BV}, author={Panicker, Ashwin and Ozdemir, Ozgur and Sichitiu, Mihail L. and Guvenc, Ismail and Dutta, Rudra and Marojevic, Vuk and Floyd, Brian}, year={2021}, month={Jul} } @article{namuduri_fiebig_hari_matolak_guvenc_maattanen_2021, title={Advanced Air Mobility}, volume={16}, ISSN={["1556-6080"]}, DOI={10.1109/MVT.2021.3091797}, abstractNote={Advanced air mobility (AAM) aims at shifting a major part of today’s ground-based urban transportation of people and goods into the third (vertical) dimension. Aerial transport routes lead to shorter transport times and relieve ground traffic. Opening up the third dimension for transport in densely populated urban areas requires reliable and alwaysavailable communication to coordinate the multitude of unmanned aerial vehicles (UAVs) to optimize flight trajectories and avoid collisions. As the industry is enthusiastically making progress toward unmanned air transportation, further research and development are needed in this domain.}, number={3}, journal={IEEE VEHICULAR TECHNOLOGY MAGAZINE}, author={Namuduri, Kamesh and Fiebig, Uwe-Carsten and Hari, K. V. S. and Matolak, David W. and Guvenc, Ismail and Maattanen, Helka-Liina}, year={2021}, month={Sep}, pages={87-+} } @article{hosseini_khatun_guo_du_ozdemir_matolak_guvenc_mehrpouyan_2021, title={Attenuation of Several Common Building Materials: Millimeter-Wave Frequency Bands 28, 73, and 91 GHz}, volume={63}, ISSN={["1558-4143"]}, url={https://doi.org/10.1109/MAP.2020.3043445}, DOI={10.1109/MAP.2020.3043445}, abstractNote={Future cellular systems will make use of millimeter-wave (mm-wave) frequency bands. Many users in these bands are located indoors, i.e., inside buildings, homes, and offices. The typical building material attenuations in these high-frequency ranges are of interest for link budget calculations. In this article, we report on a collaborative measurement campaign to find the attenuation of several typical building materials in three potential mm-wave bands (28, 73, and 91 GHz). Using directional antennas, we took multiple measurements at multiple locations using narrow-band and wideband signals and averaged out residual small-scale fading effects. The materials include clear glass, drywall (plasterboard), plywood, acoustic ceiling tile, and cinder blocks. The specific attenuations range from approximately 0.5 dB/cm for ceiling tile at 28 GHz to approximately 19 dB/cm for clear glass at 91 GHz.}, number={6}, journal={IEEE ANTENNAS AND PROPAGATION MAGAZINE}, author={Hosseini, Nozhan and Khatun, Mahfuza and Guo, Changyu and Du, Kairui and Ozdemir, Ozgur and Matolak, David W. and Guvenc, Ismail and Mehrpouyan, Hani}, year={2021}, month={Dec}, pages={40–50} } @article{anjinappa_erden_guvenc_2021, title={Base Station and Passive Reflectors Placement for Urban mmWave Networks}, volume={70}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2021.3065221}, DOI={10.1109/TVT.2021.3065221}, abstractNote={The use of millimeter-wave (mmWave) bands in 5G networks introduces a new set of challenges to network planning. Vulnerability to blockages and high path loss at mmWave frequencies require careful planning of the network to achieve a desired service quality. In this paper, we propose a novel 3D geometry-based framework for deploying mmWave base stations (gNBs) in urban environments by considering first-order reflection effects. We also provide a solution for the optimum deployment of passive metallic reflectors (PMRs) to extend radio coverage to non-line-of-sight (NLoS) areas. In particular, we perform visibility analysis to find the direct and indirect visibility regions, and using these, we derive a geometry-and-blockage-aided path loss model. We then formulate the network planning problem as two independent optimization problems, placement of gNB(s) and PMRs, to maximize the coverage area, minimize the deployment cost, and maintain a desired quality-of-service level. We test the efficacy of our proposed approach using a generic map and compare our simulation results with the ray tracing solution. Our simulation results show that considering the first-order reflections in planning the mmWave network helps reduce the number of PMRs required to cover the NLoS area. Moreover, the gNB placement aided with PMRs require fewer gNBs to cover the same area, which in turn reduces the deployment cost.}, number={4}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Anjinappa, Chethan Kumar and Erden, Fatih and Guvenc, Ismail}, year={2021}, month={Apr}, pages={3525–3539} } @article{khawaja_ozdemir_guvenc_2021, title={Channel Prediction for mmWave Ground-to-Air Propagation Under Blockage}, volume={20}, ISSN={["1548-5757"]}, url={https://doi.org/10.1109/LAWP.2021.3078268}, DOI={10.1109/LAWP.2021.3078268}, abstractNote={Ground-to-air (GA) communication using unmanned aerial vehicles (UAVs) has gained popularity in recent years and is expected to be part of 5G networks and beyond. However, the GA links are susceptible to frequent blockages at millimeter-wave (mmWave) frequencies. During a link blockage, the channel information cannot be obtained reliably. In this letter, we provide a novel method of channel prediction during the GA link blockage at 28 GHz. In our approach, the multipath components (MPCs) along a UAV flight trajectory are arranged into independent path bins based on the minimum Euclidean distance among the channel parameters of the MPCs. After the arrangement, the channel parameters of the MPCs in individual path bins are forecasted during the blockage. An autoregressive model is used for forecasting. The results obtained from ray-tracing simulations indicate a close match between the actual and the predicted mmWave channel.}, number={8}, journal={IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Khawaja, Wahab and Ozdemir, Ozgur and Guvenc, Ismail}, year={2021}, month={Aug}, pages={1364–1368} } @article{chapnevis_guvenc_njilla_bulut_2021, title={Collaborative Trajectory Optimization for Outage-aware Cellular-Enabled UAVs}, DOI={10.1109/VTC2021-Spring51267.2021.9448776}, abstractNote={Cellular-enabled unmanned aerial vehicles (UAVs) require almost continuous cellular network connectivity to fulfill their missions successfully. However, the area (e.g., rural) they fly over may have partial coverage, making the path planning of such UAV missions a challenging task. Recently a tolerable outage duration is taken into account for such UAVs, and the trajectory optimization under this outage duration is studied. However, these existing studies consider only a single UAV and focus on optimization of each UAV’s own path separately even in multi-UAV scenarios. In this paper, we study the trajectory optimization problem for cellular-enabled UAVs by taking into account the collaboration among UAVs. That is, for a given set of UAVs, each with a mission to fly from a starting point to an ending point, we aim to optimize the total mission completion time for all UAVs such that none of them has a connection outage more than a threshold. We let UAVs collaborate and provide connectivity as relays to each other to solve their outage problem and shorten their trajectories. We first model and solve this problem using nonlinear programming after discretization of the problem. Since it takes longer to solve the problem with such an approach, we then provide a graph-based approximate solution that runs fast. Numerical results show that the proposed approximate solution provides close to optimal results and performs better than state-of-the-art solutions that consider each UAV separately without collaboration among UAVs.}, journal={2021 IEEE 93RD VEHICULAR TECHNOLOGY CONFERENCE (VTC2021-SPRING)}, author={Chapnevis, Amirahmad and Guvenc, Ismail and Njilla, Laurent and Bulut, Eyuphan}, year={2021} } @article{cui_guan_guvenc_oestges_zhong_2021, title={Coverage Analysis of Cellular-Connected UAV Communications with 3GPP Antenna and Channel Models}, ISSN={["2576-6813"]}, DOI={10.1109/GLOBECOM46510.2021.9685078}, abstractNote={For reliable and efficient communications of aerial platforms, such as unmanned aerial vehicles (UAVs), the cellular network is envisioned to provide connectivity for the aerial and ground user equipment (GUE) simultaneously, which brings challenges to the existing pattern of the base station (BS) tailored for ground-level services. Thus, we focus on the coverage probability analysis to investigate the coexistence of aerial and terrestrial users, by employing realistic antenna and channel models reported in the 3rd Generation Partnership Project (3GPP). The homogeneous Poisson point process (PPP) is used to describe the BS distribution, and the BS antenna is adjustable in the down-tilted angle and the number of the antenna array. Meantime, omnidirectional antennas are used for cellular users. We first derive the approximation of coverage probability and then conduct numerous simulations to evaluate the impacts of antenna numbers, down-tilted angles, carrier frequencies, and user heights. One of the essential findings indicates that the coverage probabilities of high-altitude users become less sensitive to the down-tilted angle. Moreover, we found that the aerial user equipment (AUE) in a certain range of heights can achieve the same or better coverage probability than that of GUE, which provides an insight into the effective deployment of cellular-connected aerial communications.}, journal={2021 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM)}, author={Cui, Zhuangzhuang and Guan, Ke and Guvenc, Ismail and Oestges, Claude and Zhong, Zhangdui}, year={2021} } @article{anjinappa_guvenc_2021, title={Coverage Hole Detection for mmWave Networks: An Unsupervised Learning Approach}, volume={25}, ISSN={["1558-2558"]}, url={https://doi.org/10.1109/LCOMM.2021.3106251}, DOI={10.1109/LCOMM.2021.3106251}, abstractNote={The utilization of millimeter-wave (mmWave) bands in 5G networks poses new challenges to network planning. Vulnerability to blockages at mmWave bands can cause coverage holes (CHs) in the radio environment, leading to radio link failure when a user enters these CHs. Detection of the CHs carries critical importance so that necessary remedies can be introduced to improve coverage. In this letter, we propose a novel approach to identify the CHs in an unsupervised fashion using a state-of-the-art manifold learning technique: uniform manifold approximation and projection. The key idea is to preserve the local-connectedness structure inherent in the collected unlabelled channel samples, such that the CHs from the service area are detectable. Our results on the DeepMIMO dataset scenario demonstrate that the proposed method can learn the structure within the data samples and provide visual holes in the low-dimensional embedding while preserving the CH boundaries. Once the CH boundary is determined in the low-dimensional embedding, channel-based localization techniques can be applied to these samples to obtain the geographical boundaries of the CHs.}, number={11}, journal={IEEE COMMUNICATIONS LETTERS}, author={Anjinappa, Chethan K. and Guvenc, Ismail}, year={2021}, month={Nov}, pages={3580–3584} } @article{singh_lee_tran_zhou_sichitiu_guvenc_bhuyan_2021, title={FPV Video Adaptation for UAV Collision Avoidance}, volume={2}, ISSN={["2644-125X"]}, url={https://doi.org/10.1109/OJCOMS.2021.3106274}, DOI={10.1109/OJCOMS.2021.3106274}, abstractNote={First person view (FPV) technology for unmanned aerial vehicles (UAVs) provides an immersive experience for pilots and enables various personal and commercial applications such as aerial photography, drone racing, search and rescue operations, agricultural surveillance, and structural inspection. While real time video streaming from a UAV and vision-based collision avoidance strategies have been studied in literature as separate topics, in this paper we tackle collision avoidance in FPV scenarios, taking into account network delays and real time video parameters. We present a theoretical model for obstacle collisions that considers the current communication channel conditions, the real time video parameters, and the UAV’s position relative to the closest obstacle. A video adaptation algorithm is then designed, using this metric, to tune the FPV video resolution, number of re-transmission attempts, and the modulation scheme to maximize the probability of avoiding collisions. This algorithm also takes into account specific latency constraints of the application. This video algorithm was evaluated in various scenarios and its ability to respond to both distances to the obstacle as well as the communication channel conditions was demonstrated. It was found that, for the considered scenarios, the performance of the proposed adaptive algorithm was, on an average, 58.63% higher than the closest non-adaptive one in terms of maximizing the probability of avoiding collision. Such collision avoidance strategies could be used to make UAV FPV applications safer and more reliable.}, journal={IEEE OPEN JOURNAL OF THE COMMUNICATIONS SOCIETY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Singh, Simran and Lee, Hee Won and Tran, Tuyen X. and Zhou, Yu and Sichitiu, Mihail L. and Guvenc, Ismail and Bhuyan, Arupjyoti}, year={2021}, pages={2095–2110} } @article{sinha_guvenc_gursoy_2021, title={Fundamental Limits on Detection of UAVs by Existing Terrestrial RF Networks}, volume={2}, ISSN={["2644-125X"]}, url={https://doi.org/10.1109/OJCOMS.2021.3109105}, DOI={10.1109/OJCOMS.2021.3109105}, abstractNote={Detection of drones carries critical importance for safely and effectively managing unmanned aerial system traffic in the future. Given the ubiquitous presence of the drones across all kinds of environments in the near future, wide area drone detection and surveillance capability are highly desirable, which require careful planning and design of drone sensing networks. In this paper, we seek to meet this need by using the existing terrestrial radio frequency (RF) networks for passive sensing of drones. To this end we develop an analytical framework that provides the fundamental limits on the network-wide drone detection probability. In particular, we characterize the joint impact of the salient features of the terrestrial RF networks, such as the spatial randomness of the node locations, the directional 3D antenna patterns, and the mixed line of sight/non line of sight (LoS/NLoS) propagation characteristics of the air-to-ground (A2G) channels. Since the strength of the drone signal and the aggregate interference in a sensing network are fundamentally limited by the 3D network geometry and the inherent spatial randomness, we use tools from stochastic geometry to derive the closed-form expressions for the probabilities of detection, false alarm and coverage. This, in turn, demonstrates the impact of the sensor density, beam tilt angle, half power beam width (HPBW) and different degrees of LoS dominance, on the projected detection performance. Our analysis reveals optimal beam tilt angles, and sensor density that maximize the network-wide detection of the drones.}, journal={IEEE OPEN JOURNAL OF THE COMMUNICATIONS SOCIETY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sinha, Priyanka and Guvenc, Ismail and Gursoy, M. Cenk}, year={2021}, pages={2111–2130} } @article{maeng_deshmukh_guvenc_bhuyan_dai_2021, title={Interference Analysis and Mitigation for Aerial IoT Considering 3D Antenna Patterns}, volume={70}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2020.3046121}, DOI={10.1109/TVT.2020.3046121}, abstractNote={Due to dense deployments of Internet of things (IoT) networks, interference management becomes a critical challenge. With the proliferation of aerial IoT devices, such as unmanned aerial vehicles (UAVs), interference characteristics in 3D environments will be different than those in the existing terrestrial IoT networks. In this paper, we consider 3D topology IoT networks with a mixture of aerial and terrestrial links, with low-cost cross-dipole antennas at ground nodes and both omni-directional and cross-dipole antennas at aerial nodes. Considering a massive-access communication scenario, we first derive the statistics of the channel gain at IoT receivers in closed form while taking into account the radiation patterns of both ground and aerial nodes. These are then used to calculate the ergodic achievable rate as a function of the height of the aerial receiver and the cumulative interference. We propose a low-complexity interference mitigation scheme that utilizes 3D antenna radiation pattern with different dipole antenna settings. Our results show that using the proposed scheme, the ergodic achievable rate improves as the height of the aerial receivers increases. In addition, we also show that the ratio between the ground and aerial receivers that maximizes the peak rate increases with the height of the aerial IoT receiver.}, number={1}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Maeng, Sung Joon and Deshmukh, Mrugen A. and Guvenc, Ismail and Bhuyan, Arupjyoti and Dai, Huaiyu}, year={2021}, month={Jan}, pages={490–503} } @article{al-hourani_guvenc_2021, title={On Modeling Satellite-to-Ground Path-Loss in Urban Environments}, volume={25}, ISSN={["1558-2558"]}, url={https://doi.org/10.1109/LCOMM.2020.3037351}, DOI={10.1109/LCOMM.2020.3037351}, abstractNote={We are currently witnessing a leap in provisioning wireless networks using satellites, enabled by the recent reduction in the launching costs and the advent of the Internet-of-Things. Understanding the path-loss between satellites and ground users is vital for the proper planning and design of such networks. This letter presents a systematic framework for modeling satellite-to-ground path-loss in urban environments. The modeling approach is semi-analytic, where the line-of-sight probability is obtained using tractable tools from stochastic geometry, while the shadowing is captured using a Gaussian mixture model that can be trained using measurements collected from global navigation satellite system (GNSS) receivers. The presented modeling framework balances simplicity and accuracy as illustrated with the results of the conducted measurements.}, number={3}, journal={IEEE COMMUNICATIONS LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Al-Hourani, Akram and Guvenc, Ismail}, year={2021}, month={Mar}, pages={696–700} } @article{ding_dai_guvenc_bhuyan_2021, title={Outage Analysis for Cooperative mmWave UAV Communications With Beam Training Overhead}, volume={10}, ISSN={["2162-2345"]}, url={https://doi.org/10.1109/LWC.2021.3098424}, DOI={10.1109/LWC.2021.3098424}, abstractNote={In this letter, we investigate the tradeoff between reliability and beam training overhead in cooperative millimeter wave (mmWave) unmanned aerial vehicle (UAV) communications. In particular, we analyze how outage probability varies with the number of neighboring UAVs being probed as potential relays for relay selection. Unlike existing work, the limited number of UAV beams as well as UAV orientations are explicitly considered in our analysis. We derive the outage probability in closed form and verify our analysis via simulations. The results facilitate us to understand the fundamental limits of cooperative mmWave UAV communications.}, number={10}, journal={IEEE WIRELESS COMMUNICATIONS LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Ding, Haichuan and Dai, Huaiyu and Guvenc, Ismail and Bhuyan, Arupjyoti}, year={2021}, month={Oct}, pages={2249–2253} } @article{yapici_rupasinghe_guvenc_dai_bhuyan_2021, title={Physical Layer Security for NOMA Transmission in mmWave Drone Networks}, volume={70}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2021.3066350}, DOI={10.1109/TVT.2021.3066350}, abstractNote={The non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) transmission enable the unmanned aerial vehicle (UAV) assisted wireless networks to provide broadband connectivity over densely packed urban areas. The presence of malicious receivers, however, compromise the security of the UAV-to-ground communications links, thereby degrading secrecy rates. In this work, we consider a NOMA-based transmission strategy in a mmWave UAV-assisted wireless network, and investigate the respective secrecy-rate performance rigorously. In particular, we propose a protected-zone approach to enhance the secrecy-rate performance by preventing the most vulnerable subregion (outside the user region) from the presence of malicious receivers. The respective secrecy rates are then derived analytically as a function of the particular protected zone, which verifies great secrecy rate improvements through optimizing shape of the protected zone in use. Furthermore, we show that the optimal protected zone shape for mmWave links appears as a compromise between protecting the angle versus distance dimension, which would otherwise form to protect solely the distance dimension for sub-6 GHz links. We also numerically evaluate the impact of transmission power, protected-zone size, and UAV altitude on the secrecy-rate performance improvement for the sake of practical deployments.}, number={4}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yapici, Yavuz and Rupasinghe, Nadisanka and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2021}, month={Apr}, pages={3568–3582} } @article{singh_bhattacherjee_ozturk_guvenc_dai_sichitiu_bhuyan_2021, title={Placement of mmWave Base Stations for Serving Urban Drone Corridors}, DOI={10.1109/VTC2021-Spring51267.2021.9448923}, abstractNote={As the use of unmanned aerial vehicles (UAVs) in various commercial, civil, and military applications increases, it becomes important to study the design of aerial drone corridors that can support multiple simultaneous UAV missions. In this work, we study the placement of base stations (BSs) to serve aerial drone corridors while satisfying specific UAV mission requirements, such as the geometrical waypoints for the UAV to fly through and the minimum data rate to be supported along the mission trajectory. We develop a mathematical model of the drone corridor and propose a brute force algorithm that leverages A* search to meet the quality of service (QoS) requirements of the corridor by choosing the minimal set of BS locations from a pre-determined initial set. Using raytracing simulations, BS placement results are presented for various antenna array sizes in a dense urban region in East Manhattan. It was found that, for the scenario under consideration, a single BS equipped with an 8x8 antenna array is sufficient to satisfy the given QoS requirements of the corridor, while two BSs are required when using 4x4 antenna arrays.}, journal={2021 IEEE 93RD VEHICULAR TECHNOLOGY CONFERENCE (VTC2021-SPRING)}, author={Singh, Simran and Bhattacherjee, Udita and Ozturk, Ender and Guvenc, Ismail and Dai, Huaiyu and Sichitiu, Mihail and Bhuyan, Arupjyoti}, year={2021} } @article{maeng_yapici_guvenc_dai_bhuyan_2021, title={Power Allocation for Fingerprint-Based PHY-Layer Authentication with mmWave UAV Networks}, ISSN={["1550-3607"]}, DOI={10.1109/ICC42927.2021.9500273}, abstractNote={Physical layer security (PLS) techniques can help to protect wireless networks from eavesdropper attacks. In this paper, we consider the authentication technique that uses fingerprint embedding to defend 5G cellular networks with unmanned aerial vehicle (UAV) systems from eavesdroppers and intruders. Since the millimeter wave (mmWave) cellular networks use narrow and directional beams, PLS can take further advantage of the 3D spatial dimension for improving the authentication of UAV users. Considering a multi-user mmWave cellular network, we propose a power allocation technique that jointly takes into account splitting of the transmit power between the precoder and the authentication tag, which manages both the secrecy as well as the achievable rate. Our results show that we can obtain optimal achievable rate with expected secrecy.}, journal={IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC 2021)}, author={Maeng, Sung Joon and Yapici, Yavuz and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2021} } @article{deshmukh_sahin_guvenc_2021, title={RL-Based Waveform Adaptation With Partial Overlapping Tones in HetNets}, volume={25}, ISSN={["1558-2558"]}, url={https://doi.org/10.1109/LCOMM.2021.3088841}, DOI={10.1109/LCOMM.2021.3088841}, abstractNote={Partially-overlapping tones (POT) mitigate the co-channel interference in a wireless network by exploiting the space between adjacent subcarriers through intentional frequency offsets (FOs). In this letter, we use partially-overlapping tones (POT) in a two-tier heterogeneous network, where multiple small cells (SCs) interfere with a macro cell. We propose a multi-agent Q-learning-based approach to obtain transmit power and intentional FOs assigned to SCs for filtered multi-tones with various pulse shapes. We show that the proposed method reduces the total interference and in turn, increases the throughput in the network. We then compare the performance of the proposed approach to the existing schemes and demonstrate its advantage with numerical results.}, number={9}, journal={IEEE COMMUNICATIONS LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Deshmukh, Mrugen and Sahin, Alphan and Guvenc, Ismail}, year={2021}, month={Sep}, pages={3129–3133} } @article{bhuyan_guvenc_dai_sichitiu_singh_rahmati_maeng_2021, title={Secure 5G Network for a Nationwide Drone Corridor}, ISSN={["1095-323X"]}, DOI={10.1109/AERO50100.2021.9438162}, abstractNote={5G can provide the multiplicative capacity gains needed to support a large number of drones/UAS (Unmanned Aircraft Systems). 5G cellular networks with newly available millimeter wave (mmWave) frequency bands can provide wireless communication links for control as well as data traffic for drones and drone swarms. Drones are becoming increasingly important for commercial uses such as delivery and transportation as well as for public safety search and rescue of natural disaster victims, surveillance of remote critical infrastructure, surveys of environmental quality in protected regions, and detection of threats during major public events. This paper presents research findings in the following areas critical to validating the effectiveness of providing required 5G access to the drones with security, reliability, and spectral efficiency: 1) Radio coverage for the drone corridor by adding a separate set of antennas for coverage in the air while the conventional set of antennas continues to provide coverage on the ground. Beam transmission and validation with ray-tracing simulations are covered. 2) Optimization of uplink communication from a swarm of drones with a single mmWave beam by grouping the drones with power allocations for non-orthogonal multiple access (NOMA). 3) Optimization of the network lifetime of a swarm of drones resulting in suitable trajectories in the presence of interference. 4) Methods including precoding that can enhance physical layer security with channel information about the interference source. The paper concludes with plans for future research to provide further scientific basis for the proposed cellular drone network.}, journal={2021 IEEE AEROSPACE CONFERENCE (AEROCONF 2021)}, author={Bhuyan, Arupjyoti and Guvenc, Ismail and Dai, Huaiyu and Sichitiu, Mihail L. and Singh, Simran and Rahmati, Ali and Maeng, Sung Joon}, year={2021} } @article{medaiyese_ezuma_lauf_guvenc_2021, title={Semi-supervised Learning Framework for UAV Detection}, DOI={10.1109/PIMRC50174.2021.9569452}, abstractNote={The use of supervised learning with various sensing techniques such as audio, visual imaging, thermal sensing, RADAR, and radio frequency (RF) have been widely applied in the detection of unmanned aerial vehicles (UAV) in an environment. However, little or no attention has been given to the application of unsupervised or semi-supervised algorithms for UAV detection. In this paper, we propose a semi-supervised technique and architecture for detecting UAVs in an environment by exploiting the RF signals (i.e., fingerprints) between a UAV and its flight-controller communication under wireless inference such as Bluetooth and WiFi. By decomposing the RF signals using a two-level wavelet packet transform, we estimated the second moment statistic (i.e., variance) of the coefficients in each packet as a feature set. We developed a local outlier factor model as the UAV detection algorithm using the coefficient variances of the wavelet packets from WiFi and Bluetooth signals. When detecting the presence of RF-based UAV, we achieved an accuracy of 96.7% and 86% at a signal-to-noise ratio of 30 dB and 18 dB, respectively. The application of this approach is not limited to UAV detection as it can be extended to the detection of rogue RF devices in an environment.}, journal={2021 IEEE 32ND ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC)}, author={Medaiyese, Olusiji O. and Ezuma, Martins and Lauf, Adrian P. and Guvenc, Ismail}, year={2021} } @article{eroglu_anjinappa_guvenc_pala_2021, title={Slow Beam Steering and NOMA for Indoor Multi-User Visible Light Communications}, volume={20}, ISSN={["1558-0660"]}, url={https://doi.org/10.1109/TMC.2019.2960495}, DOI={10.1109/TMC.2019.2960495}, abstractNote={Visible light communication (VLC) is an emerging technology that enables broadband data rates using the visible spectrum. In this paper, considering slow beam steering where VLC beam directions are assumed to be fixed during a transmission frame, we find the steering angles that simultaneously serve multiple users within the frame duration and maximize the data rates. This is achieved by solving a non-convex optimization problem using a grid-based search and majorization-minimization (MM) procedure. Subsequently, we consider multiple steerable beams with a larger number of users in the network and propose an algorithm to cluster users and serve each cluster with a separate beam. We optimize the transmit power of each beam to maximize the data rates. Finally, we propose a non-orthogonal multiple access (NOMA) scheme for the beam steering and user clustering scenario, to further increase the data rates of the users. The simulation results show that the proposed beam steering method can efficiently serve a high number of users, and with power optimization, a sum rate gain up to thirteen times is possible. The simulation results for NOMA suggests an additional 10 Mbps sum rate gain for each NOMA user pair.}, number={4}, journal={IEEE TRANSACTIONS ON MOBILE COMPUTING}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Eroglu, Yusuf Said and Anjinappa, Chethan Kumar and Guvenc, Ismail and Pala, Nezih}, year={2021}, month={Apr}, pages={1627–1641} } @article{du_ozdemir_erden_guvenc_2021, title={Sub-Terahertz and mmWave Penetration Loss Measurements for Indoor Environments}, ISSN={["2164-7038"]}, DOI={10.1109/ICCWorkshops50388.2021.9473898}, abstractNote={Millimeter-wave (mmWave) and terahertz (THz) spectrum can support significantly higher data rates compared to lower frequency bands and hence are being actively considered for 5G wireless networks and beyond. These bands have high free-space path loss (FSPL) in line-of-sight (LOS) propagation due to their shorter wavelength. Moreover, in non-line-of-sight (NLOS) scenario, these two bands suffer higher penetration loss than lower frequency bands which could seriously affect the network coverage. It is therefore critical to study the NLOS penetration loss introduced by different building materials at mmWave and THz bands, to help establish link budgets for an accurate performance analysis in indoor environments. In this work, we measured the penetration loss and the attenuation of several common constructional materials at mmWave (28 and 39 GHz) and sub-THz (120 and 144 GHz) bands. Measurements were conducted using a channel sounder based on NI PXI platforms. Results show that the penetration loss changes extensively based on the frequency and the material properties, ranging from 0.401 dB for ceiling tile at 28 GHz, to 16.608 dB for plywood at 144 GHz. Ceiling tile has the lowest measured attenuation at 28 GHz, while clear glass has the highest attenuation of 27.633 dB/cm at 144 GHz. As expected, the penetration loss and attenuation increased with frequency for all the tested materials.}, journal={2021 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS)}, author={Du, Kairui and Ozdemir, Ozgur and Erden, Fatih and Guvenc, Ismail}, year={2021} } @article{mujumdar_celebi_guvenc_saichitiu_hwang_kang_2021, title={Use of LoRa for UAV Remote ID with Multi-User Interference and Different Spreading Factors}, DOI={10.1109/VTC2021-Spring51267.2021.9448804}, abstractNote={Reliable and long-range wireless communications carry critical importance for remote identification (ID) of unmanned aerial systems (UAS). Federal Aviation Authority (FAA) in the United States has recently released rules that describe how drones can broadcast their ID and location information, without mandating a specific radio access technology. In this paper, we study LoRa as a candidate technology for drone remote ID. We first provide a brief overview of the recent FAA rules on drone remote ID released in December 2020. Subsequently, we provide preliminary results based on ray tracing and MATLAB simulations that evaluate the reliability and range of LoRa for UAS remote ID scenarios. Two different LoRa multi-user interference scenarios are considered: in one scenario, the interferer uses the same spreading factor (SF) as the desired user, while in another scenario, desired and interfering user SFs are different. Our results quantify the performance gains that may be obtained under different interference conditions, using various coding rates and SFs.}, journal={2021 IEEE 93RD VEHICULAR TECHNOLOGY CONFERENCE (VTC2021-SPRING)}, author={Mujumdar, Omkar and Celebi, Haluk and Guvenc, Ismail and Saichitiu, Mihail and Hwang, Sunghyun and Kang, Kyu-Min}, year={2021} } @article{chowdhury_maeng_bulut_guvenc_2020, title={3-D Trajectory Optimization in UAV-Assisted Cellular Networks Considering Antenna Radiation Pattern and Backhaul Constraint}, volume={56}, url={https://doi.org/10.1109/TAES.2020.2981233}, DOI={10.1109/TAES.2020.2981233}, abstractNote={This article explores the effects of 3-D antenna radiation pattern and backhaul constraint on optimal 3-D path planning problem of an unmanned aerial vehicle (UAV), in interference prevalent downlink cellular networks. We consider a cellular-connected UAV that is tasked to travel between two locations within a fixed time, and it can be used to improve the cellular connectivity of ground users by acting as a relay. Since the antenna gain of a cellular base station changes significantly with the UAV altitude, the UAV can improve the signal quality in its backhaul link by changing its height over the course of its mission. This problem is nonconvex, and thus, we explore the dynamic programming technique to solve it. We show that the 3-D optimal paths can introduce significant network performance gain over the trajectories with fixed UAV heights.}, number={5}, journal={IEEE Transactions on Aerospace and Electronic Systems}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Chowdhury, Md Moin Uddin and Maeng, Sung Joon and Bulut, Eyuphan and Guvenc, Ismail}, year={2020}, month={Oct}, pages={3735–3750} } @article{marojevic_guvenc_dutta_sichitiu_floyd_2020, title={Advanced Wireless for Unmanned Aerial Systems: 5G Standardization, Research Challenges, and AERPAW Architecture}, volume={15}, url={https://doi.org/10.1109/MVT.2020.2979494}, DOI={10.1109/MVT.2020.2979494}, abstractNote={The 5G mobile communications systems merge traditionally separate communications and networking systems and services to effectively support a myriad of heterogeneous applications. Researchers and industry working groups are investigating the integration of aerial nodes, shared spectrum techniques, and new network architectures, which are gradually being introduced into standards. This article discusses relevant standardization efforts for the integration of unmanned aerial systems (UASs) into 5G and the requirements for an aerial wireless testbed. We introduce the aerial experimentation and research platform for advanced wireless (AERPAW) and, specifically, its architecture, which is designed for enabling experimental research in controlled yet production-like environments. Sample research projects and trials show the critical R&D needs, broad scope, and impact that such a platform can have on technology evolution, regulation, and standardization as well as future services.}, number={2}, journal={IEEE Vehicular Technology Magazine}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Marojevic, Vuk and Guvenc, Ismail and Dutta, Rudra and Sichitiu, Mihail L. and Floyd, Brian A.}, year={2020}, month={Jun}, pages={22–30} } @article{namuduri_fiebig_hari_matolak_guvenc_maattanen_2020, title={Communication Support for Unmanned Air Transportation}, volume={15}, ISSN={["1556-6080"]}, DOI={10.1109/MVT.2020.2985879}, abstractNote={IEEE VEHICULAR TECHNOLOGY MAGAZINE | JUNE 2020 provides a systematic view of the state of the art for RoC and its deployment challenges. The authors further propose a nonconfigurable distributed antenna unit with a related resource mapping scheme and nonconfigurable air-to-cable to achieve higher throughput and low power consumption for large-scale deployments. The simulation results demonstrate that the proposed RoC meets the 5G KPIs of peak data rate, peak spectrum efficiency, and latency. Author Information Anwer Al-Dulaimi (anwer.al-dulaimi@ exfo.com) is a technical product owner in the Center of Excellence at EXFO Inc., Montréal, Canada. He received his Ph.D. degree in electronic and computer engineering from Brunel University, London, in 2012. His research interests include 5G and beyond networks, cloud computing, and the Internet of Things. He is chair of the IEEE 1932.1 Standard for Licensed/Unlicensed Spectrum Interoperability in Wireless Mobile Network and an IEEE Dis tinguish ed Lecturer. Rose Qingyang Hu (rose.hu @ usu.edu) is a full professor in the Department of Electrical and Computer Engineering at Utah State University, Logan. She received her Ph.D. degree in electrical engineering from the University of Kansas, Lawrence. She is an IEEE Communications Society Distinguished Lecturer (2015–2018) and has been a frequent guest editor for IEEE Communications Magazine, IEEE Wireless Communications Magazine, and IEEE Network Magazine. She is a Senior Member of the IEEE and a member of the Phi Kappa Phi Honor Society. mdas provides analyTics counTers for differenT neTwork componenTs by moniToring load levels and resource sTaTus.}, number={2}, journal={IEEE VEHICULAR TECHNOLOGY MAGAZINE}, author={Namuduri, Kamesh and Fiebig, Uwe-Carsten and Hari, K. V. S. and Matolak, David W. and Guvenc, Ismail and Maattanen, Helka-Liina}, year={2020}, month={Jun}, pages={20–21} } @article{erden_ozdemir_khawaja_guvenc_2020, title={Correction of Channel Sounding Clock Drift and Antenna Rotation Effects for mmWave Angular Profile Measurements}, volume={1}, ISSN={["2637-6431"]}, url={https://doi.org/10.1109/OJAP.2020.2979243}, DOI={10.1109/OJAP.2020.2979243}, abstractNote={Proper characterization of the millimeter-wave (mmWave) propagation channel requires measuring the power angular-delay profile of the channel which includes angle-of-departure and angle-of-arrival of the multipath components (MPCs). In this paper, we first describe in detail our rotating directional antennas-based 28 GHz channel sounder. Then, for this specific sounder class, we describe and address the following two problems in extracting the MPCs from the measurements: 1) For long-distance channel measurements, triggering signal cannot be generated for the TX and the RX using a single clock (SICL). This necessitates the use of separate clocks (SECLs) which introduces a random timing drift between the clocks. 2) As positions of the antennas change during scanning, total distance traveled by the same MPC differs at each measurement. These problems together cause missing some of the MPCs and detecting MPCs that do not exist in reality. We propose an algorithm to correct the clock drift and MPC delay errors due to the rotation of the antennas. We compare the MPCs from the SICL measurement and the corrected SECL measurements using a Hungarian algorithm based MPC matching method. We show that the percentage of the matched MPCs increases from 28.36% to 74.13% after the correction process.}, journal={IEEE OPEN JOURNAL OF ANTENNAS AND PROPAGATION}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Erden, Fatih and Ozdemir, Ozgur and Khawaja, Wahab and Guvenc, Ismail}, year={2020}, pages={71–87} } @article{khawaja_ozdemir_yapici_erden_guvenc_2020, title={Coverage Enhancement for NLOS mmWave Links Using Passive Reflectors}, volume={1}, ISSN={["2644-125X"]}, url={https://doi.org/10.1109/OJCOMS.2020.2969751}, DOI={10.1109/OJCOMS.2020.2969751}, abstractNote={The future 5G networks are expected to use millimeter wave (mmWave) frequency bands to take advantage of the large unused spectrum. However, due to the high path loss at mmWave frequencies, coverage of mmWave signals can get severely reduced, especially for non-line-of-sight (NLOS) scenarios as mmWave signals are severely attenuated when going through obstructions. In this work, we study the use of passive metallic reflectors of different shapes/sizes to improve 28 GHz mmWave signal coverage for both indoor and outdoor NLOS scenarios. We quantify the gains that can be achieved in the link quality with metallic reflectors using measurements, analytical expressions, and ray tracing simulations. In particular, we provide an analytical model for the end-to-end received power in an NLOS scenario using reflectors of different shapes and sizes. For a given size of the flat metallic sheet reflector approaching to the size of the incident beam, we show that the reflected received power for the NLOS link is the same as line-of-sight (LOS) free space received power of the same link distance. Extensive results are provided to study the impact of environmental features and reflector characteristics on NLOS link quality.}, journal={IEEE OPEN JOURNAL OF THE COMMUNICATIONS SOCIETY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Khawaja, Wahab and Ozdemir, Ozgur and Yapici, Yavuz and Erden, Fatih and Guvenc, Ismail}, year={2020}, pages={263–281} } @article{ezuma_erden_anjinappa_ozdemir_guvenc_2020, title={Detection and Classification of UAVs Using RF Fingerprints in the Presence of Wi-Fi and Bluetooth Interference}, volume={1}, ISSN={["2644-125X"]}, url={https://doi.org/10.1109/OJCOMS.2019.2955889}, DOI={10.1109/OJCOMS.2019.2955889}, abstractNote={This paper investigates the problem of detection and classification of unmanned aerial vehicles (UAVs) in the presence of wireless interference signals using a passive radio frequency (RF) surveillance system. The system uses a multistage detector to distinguish signals transmitted by a UAV controller from the background noise and interference signals. First, RF signals from any source are detected using a Markov models-based naïve Bayes decision mechanism. When the receiver operates at a signal-to-noise ratio (SNR) of 10 dB, and the threshold, which defines the states of the models, is set at a level 3.5 times the standard deviation of the preprocessed noise data, a detection accuracy of 99.8% with a false alarm rate of 2.8% is achieved. Second, signals from Wi-Fi and Bluetooth emitters, if present, are detected based on the bandwidth and modulation features of the detected RF signal. Once the input signal is identified as a UAV controller signal, it is classified using machine learning (ML) techniques. Fifteen statistical features extracted from the energy transients of the UAV controller signals are fed to neighborhood component analysis (NCA), and the three most significant features are selected. The performance of the NCA and five different ML classifiers are studied for 15 different types of UAV controllers. A classification accuracy of 98.13% is achieved by k-nearest neighbor classifier at 25 dB SNR. Classification performance is also investigated at different SNR levels and for a set of 17 UAV controllers which includes two pairs from the same UAV controller models.}, journal={IEEE OPEN JOURNAL OF THE COMMUNICATIONS SOCIETY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Ezuma, Martins and Erden, Fatih and Anjinappa, Chethan Kumar and Ozdemir, Ozgur and Guvenc, Ismail}, year={2020}, pages={60–76} } @article{turgut_gursoy_guvenc_2020, title={Energy Harvesting in Unmanned Aerial Vehicle Networks With 3D Antenna Radiation Patterns}, volume={4}, url={https://doi.org/10.1109/TGCN.2020.3007588}, DOI={10.1109/TGCN.2020.3007588}, abstractNote={In this paper, an analytical framework is provided to analyze the energy coverage performance of unmanned aerial vehicle (UAV) energy harvesting networks with clustered user equipments (UEs). Locations of UEs are modeled as a Poisson Cluster Process (PCP), and UAVs are assumed to be located at a certain height above the center of user clusters. Hence, user-centric UAV deployments are addressed. Two different models are considered for the line-of-sight (LOS) probability function to compare their effects on the network performance. Moreover, antennas with doughnut-shaped radiation patterns are employed at both UAVs and UEs, and the impact of practical 3D antenna radiation patterns on the network performance is also investigated. Initially, the path loss of each tier is statistically described by deriving the complementary cumulative distribution function and probability density function. Following this, association probabilities with each tier are determined, and energy coverage probability of the UAV network is characterized in terms of key system and network parameters for UAV deployments both at a single height level and more generally at multiple heights. Through numerical results, we have shown that cluster size and UAV height play crucial roles on the energy coverage performance. Furthermore, energy coverage probability is significantly affected by the antenna orientation and number of UAVs in the network.}, number={4}, journal={IEEE Transactions on Green Communications and Networking}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Turgut, Esma and Gursoy, M. Cenk and Guvenc, Ismail}, year={2020}, month={Dec}, pages={1149–1164} } @article{yapici_guvenc_2020, title={Energy- vs Spectral-Efficiency for Energy-Harvesting Hybrid RF/VLC Networks}, ISSN={["1058-6393"]}, DOI={10.1109/IEEECONF51394.2020.9443343}, abstractNote={We consider a hybrid radio frequency (RF) / visible light communications (VLC) scenario where the RF link is empowered by the energy harvested during the VLC transmission. We take into account the power consumption of the access point (AP), which is composed of light emitting diodes (LEDs), while it is communicating with a far user over a two-hop hybrid RF/VLC link. In particular, we consider the energy efficiency of the end-to-end network in enhancing the energy-harvesting performance by choosing the optimal direct current (DC) bias, which is overlooked in the existing literature. To this end, we model the energy consumption of the commercially available LEDs, and formulate a joint energy- and spectral-efficiency optimization problem. The extreme cases of optimizing energy and spectral efficiency individually underscores the importance of optimizing the DC bias for a given joint (multi-objective) optimization problem.}, journal={2020 54TH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS}, author={Yapici, Yavuz and Guvenc, Ismail}, year={2020}, pages={1152–1156} } @article{rahmati_hosseinalipour_yapici_guvenc_dai_bhuyan_2020, title={Energy-Efficient Beamforming and Power Control for Uplink NOMA in mmWave UAV Networks}, ISSN={["2576-6813"]}, DOI={10.1109/GLOBECOM42002.2020.9348114}, abstractNote={The integration of unmanned aerial vehicles (UAVs) into the terrestrial communications networks with a variety of tasks is viewed as a key technology for 5G and beyond. In this work, we consider the uplink millimeter-wave (mmWave) transmission between a set of UAVs and a base station (BS), where the UAVs deploy uplink non-orthogonal multiple access (NOMA) in multiple clusters. Furthermore, the BS also serves its own desired ground user equipment (UE) in the presence of many other ground UEs associated with other cells, which share the same frequency band. Considering the limited energy budget of UAVs, we formulate an energy efficiency (EE) problem, and propose a solution aided by the Dinkelbach's algorithm and successive convex approximation (SCA). Using realistic air-to-ground (A2G) and terrestrial channel models, we assess the performance of the proposed algorithm under various circumstances (maximum transmit power for UAVs, quality-of-service (QoS) constraint for the desired UE, etc.), and identify the best use cases.}, journal={2020 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM)}, author={Rahmati, Ali and Hosseinalipour, Seyyedali and Yapici, Yavuz and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2020} } @article{kumbhar_binol_singh_guvenc_akkaya_2020, title={Heuristic approach for jointly optimising FeICIC and UAV locations in multi-tier LTE-advanced public safety HetNet}, volume={14}, ISSN={["1751-8636"]}, DOI={10.1049/iet-com.2019.1315}, abstractNote={UAV enabled communications and networking can enhance wireless connectivity and support emerging services. However, this would require system-level understanding to modify and extend the existing terrestrial network infrastructure. In this paper, we integrate UAVs both as user equipment and base stations into existing LTE-Advanced heterogeneous network (HetNet) and provide system-level insights of this three-tier LTE-Advanced air-ground HetNet (AG-HetNet). This AG-HetNet leverages cell range expansion (CRE), ICIC, 3D beamforming, and enhanced support for UAVs. Using system-level understanding and through brute-force technique and heuristics algorithms, we evaluate the performance of AG-HetNet in terms of fifth percentile spectral efficiency (5pSE) and coverage probability. We compare 5pSE and coverage probability, when aerial base-stations (UABS) are deployed on a fixed hexagonal grid and when their locations are optimized using genetic algorithm (GA) and elitist harmony search algorithm based on genetic algorithm (eHSGA). Our simulation results show the heuristic algorithms outperform the brute-force technique and achieve better peak values of coverage probability and 5pSE. Simulation results also show that trade-off exists between peak values and computation time when using heuristic algorithms. Furthermore, the three-tier hierarchical structuring of FeICIC provides considerably better 5pSE and coverage probability than eICIC.}, number={20}, journal={IET COMMUNICATIONS}, author={Kumbhar, Abhaykumar and Binol, Hamidullah and Singh, Simran and Guvenc, Ismail and Akkaya, Kemal}, year={2020}, month={Dec}, pages={3585–3598} } @article{maeng_yapici_guvenc_dai_bhuyan_2020, title={Hybrid Precoding for mmWave Massive MIMO With One-Bit DAC}, url={https://doi.org/10.1109/LCOMM.2020.3015674}, DOI={10.1109/LCOMM.2020.3015674}, abstractNote={Hybrid beamforming is key to achieving energy-efficient 5G wireless networks equipped with massive amount of antennas. Low-resolution data converters bring yet another degree of freedom to energy efficiency for the state-of-the-art 5G transceivers. In this work, we consider the design of hybrid precoders for massive multiple-input multiple-output (MIMO) channels in millimeter-wave (mmWave) spectrum along with one-bit digital-to-analog converters (DACs) and finite-quantized phase shifters. In particular, we propose an alternating-optimization-based precoder design which recursively computes the covariance of the quantization distortion, and updates the precoders accordingly. Numerical results verify that the achievable rate improves quickly through iterations that involve updates to the weight matrix, distortion covariance of the quantization, and the respective precoders.}, journal={IEEE Communications Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Maeng, Sung Joon and Yapici, Yavuz and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2020}, month={Dec}, pages={1–1} } @article{yapici_guvenc_dai_2020, title={Low-Resolution Limited-Feedback NOMA for mmWave Communications}, volume={19}, url={https://doi.org/10.1109/TWC.2020.2993212}, DOI={10.1109/TWC.2020.2993212}, abstractNote={The spectrum-efficient millimeter-wave (mmWave) communications has recently attracted much attention as a viable solution to spectrum crunch problem. In this work, we propose a novel non-orthogonal multiple access (NOMA) framework, which makes use of the directional propagation characteristics of mmWave communications so as to improve the spectral efficiency through non-orthogonal signaling. In particular, we consider one-bit quantized angle information as a limited yet effective feedback scheme describing the channel quality of user equipment (UE) in mmWave bands. The UE pairs for NOMA transmission are then established using not only the one-bit distance feedback as a classical approach, but also the one-bit angle feedback. The proposed strategy is therefore referred to as two-bit NOMA. We also propose a novel hybrid strategy, called combined NOMA, for the circumstances with no UE pair through two-bit NOMA. Whenever no UE pair is available through any NOMA strategy, we resort to single user transmission (SUT) with proper UE selection schemes. The hybrid outage sum-rate performance is also analyzed thoroughly with the respective outage and rate expressions. The numerical results verify that the proposed strategy outperforms one-bit NOMA schemes with either angle- or distance-only feedback, and has a very close outage sum-rate performance to that for the optimal full-resolution feedback.}, number={8}, journal={IEEE Transactions on Wireless Communications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yapici, Yavuz and Guvenc, Ismail and Dai, Huaiyu}, year={2020}, month={Aug}, pages={5433–5446} } @article{gentile_molisch_chuang_michelson_bodi_bhardwaj_ozdemir_khawaja_guvenc_cheng_et al._2020, title={Methodology for Benchmarking Radio-Frequency Channel Sounders Through a System Model}, volume={19}, ISSN={["1558-2248"]}, url={https://doi.org/10.1109/TWC.2020.3003617}, DOI={10.1109/TWC.2020.3003617}, abstractNote={Development of a comprehensive channel propagation model for high-fidelity design and deployment of wireless communication networks necessitates an exhaustive measurement campaign in a variety of operating environments and with different configuration settings. As the campaign is time-consuming and expensive, the effort is typically shared by multiple organizations, inevitably with their own channel-sounder architectures and processing methods. Without proper benchmarking, it cannot be discerned whether observed differences in the measurements are actually due to the varying environments or to discrepancies between the channel sounders themselves. The simplest approach for benchmarking is to transport participant channel sounders to a common environment, collect data, and compare results. Because this is rarely feasible, this paper proposes an alternative methodology – which is both practical and reliable – based on a mathematical system model to represent the channel sounder. The model parameters correspond to the hardware features specific to each system, characterized through precision, in situ calibration to ensure accurate representation; to ensure fair comparison, the model is applied to a ground-truth channel response that is identical for all systems. Five worldwide organizations participated in the cross-validation of their systems through the proposed methodology. Channel sounder descriptions, calibration procedures, and processing methods are provided for each organization as well as results and comparisons for 20 ground-truth channel responses.}, number={10}, journal={IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Gentile, Camillo and Molisch, Andreas F. and Chuang, Jack and Michelson, David G. and Bodi, Anuraag and Bhardwaj, Anmol and Ozdemir, Ozgur and Khawaja, Wahab Ali Gulzar and Guvenc, Ismail and Cheng, Zihang and et al.}, year={2020}, month={Oct}, pages={6504–6519} } @article{ruble_guvenc_2020, title={Multilinear Singular Value Decomposition for Millimeter Wave Channel Parameter Estimation}, volume={8}, ISSN={["2169-3536"]}, DOI={10.1109/ACCESS.2020.2988485}, abstractNote={Fifth generation (5G) cellular standards are set to utilize millimeter wave (mmWave) frequencies, which enable data speeds greater than 10 Gbps and sub-centimeter localization accuracy. These capabilities rely on accurate estimates of the channel parameters, which we define as the angle of arrival, angle of departure, and path distance for each path between the transmitter and receiver. Estimating the channel parameters in a computationally efficient manner poses a challenge because it requires estimation of parameters from a high-dimensional measurement – particularly for multi-carrier systems since each subcarrier must be estimated separately. Additionally, channel parameter estimation must be able to handle hybrid beamforming, which uses a combination of digital and analog beamforming to reduce the number of required analog to digital converters. This paper introduces a channel parameter estimation technique based on the multilinear singular value decomposition (MSVD), a Tucker form tensor analog of the singular value decomposition, for massive multiple input multiple output (MIMO) multi-carrier systems with hybrid beamforming. The MSVD tensor estimation approach is more computationally efficient than methods such as the canonical polyadic decomposition (CPD) and the Tucker form of the MSVD enables paths to be extracted based on signal energy. The algorithms performance is compared to the CPD method and shown to closely match the Cramer-Rao bound (CRB) of channel parameter estimates through simulations. Additionally, limitations of channel parameter estimation and communication waveform effects are studied.}, journal={IEEE ACCESS}, author={Ruble, Macey and Guvenc, Ismail}, year={2020}, pages={75592–75606} } @article{khawaja_ozdemir_erden_ozturk_guvenc_2020, title={Multiple ray received power modelling for mmWave indoor and outdoor scenarios}, volume={14}, ISSN={["1751-8733"]}, url={https://doi.org/10.1049/iet-map.2020.0046}, DOI={10.1049/iet-map.2020.0046}, abstractNote={IET Microwaves, Antennas & PropagationVolume 14, Issue 14 p. 1825-1836 Research ArticleFree Access Multiple ray received power modelling for mmWave indoor and outdoor scenarios Wahab Khawaja, Corresponding Author Wahab Khawaja wahab.ali@must.edu.pk Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USA Mirpur University of Science and Technology, Mirpur, AJK, PakistanSearch for more papers by this authorOzgur Ozdemir, Ozgur Ozdemir Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorFatih Erden, Fatih Erden orcid.org/0000-0002-1708-3063 Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorEnder Ozturk, Ender Ozturk orcid.org/0000-0002-6390-8089 Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorIsmail Guvenc, Ismail Guvenc Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this author Wahab Khawaja, Corresponding Author Wahab Khawaja wahab.ali@must.edu.pk Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USA Mirpur University of Science and Technology, Mirpur, AJK, PakistanSearch for more papers by this authorOzgur Ozdemir, Ozgur Ozdemir Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorFatih Erden, Fatih Erden orcid.org/0000-0002-1708-3063 Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorEnder Ozturk, Ender Ozturk orcid.org/0000-0002-6390-8089 Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this authorIsmail Guvenc, Ismail Guvenc Department of Electrical and Computer Engineering, North Carolina State University, 890 Oval Dr, Raleigh, NC, 27606 USASearch for more papers by this author First published: 22 October 2020 https://doi.org/10.1049/iet-map.2020.0046Citations: 2AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Millimetre-wave (mmWave) frequency bands are expected to be used for future fifth generation networks due to the availability of a large unused spectrum. However, the attenuation at mmWave frequencies is high. To resolve this issue, the utilisation of high gain antennas and beamforming mechanisms are widely investigated in the literature. In this work, the authors considered mmWave end-to-end propagation modelled by individual ray sources and explored the effects of the number of rays in the model and radiation patterns of the deployed antennas on the received power. It is shown that taking the dominant two rays is sufficient to model the channel for outdoor open areas as opposed to the indoor corridor which needs five dominant rays to have a good fit for the measurement and simulation results. It is observed that the radiation pattern of the antenna affects the slope of the path loss. Multi-path components increase the received power, thus, for indoor corridor scenarios, path loss according to the link distance is smaller for lower gain antennas due to increased reception of reflected components. For an outdoor open area, the slope of the path loss is found to be very close to that of the free space. 1 Introduction There has been a significant increase in the number of smart communication devices and high data rate applications in the last decade. This trend is expected to grow rapidly in the future [[1]]. However, the available spectrum at the sub-6 GHz band is limited. Higher frequency bands (e.g. millimetre-wave (mmWave) bands) are not heavily utilised, thus, offer larger bandwidths for wireless communication systems. Therefore, research efforts have been concentrated on exploring higher frequencies as an alternative to the sub-6 GHz band. The opening of the mmWave spectrum for mobile usage by FCC [[2]] has given a boost to the current research studies to best utilise these bands. However, mmWave communication suffers from its inherent high free space attenuation as well as high penetration losses. In this work, we used measurements, analytical ray modelling and ray-tracing simulations to model line-of-sight (LoS) characteristics of a mmWave communication channel in a corridor type indoor and open space outdoor environments at 28 GHz frequency band. We analytically calculated received signal properties using the dominant five-ray and two-ray received power models based on first-order reflections for the indoor corridor and outdoor open area, respectively. To compare with our analytical results, measurements were conducted at North Carolina State University using a PXI-based channel sounder platform from National Instruments, and two sets of directional horn antennas with gains 17 and 23 dBi at 28 GHz. The test setup used indoor and outdoor are shown in Figs. 1 and 2, respectively. Fig. 1Open in figure viewerPowerPoint Indoor corridor propagation setup at the basement of Engineering Building II, North Carolina State University Fig. 2Open in figure viewerPowerPoint Outdoor measurement setup at the top floor of a multi-storey car park, Centennial Campus, North Carolina State University The rest of the paper is organised as follows. Readers will find a comprehensive literature review as well as a summary of our contributions in Section 2. Section 3 includes details on received power modelling for indoor and outdoor environments. Section 4 covers experimental and ray-tracing simulations setup. In Section 5, the number of rays and percentage power sum of dominant five rays with a total power of rays is provided. In Section 6, results of measurements, simulations, and calculations for received power are given. In Section 7, a detailed discussion is presented for five-ray and two-ray models. Section 8 provides Ricean K-factor analysis and the paper ends with concluding remarks in Section 9. 2 Literature review and contributions Various approaches have been proposed in the literature to overcome the high attenuation problem at mmWave frequencies [[3], [4]]. A common method is to increase the gain or directivity of the antennas [[5], [6]]. The high directivity is obtained either by beamforming or deploying directional antennas (e.g. horn antennas). In addition to antenna type, material characteristics of the objects in the environment also play an important role in figuring the propagation statistics [[7], [8]]. One way of modelling propagation statistics is by using ray tracing. In the literature, different types of indoor geometries either in LoS or non-LoS (NLoS) scenarios for a wide variety of frequency bands are investigated using ray tracing software [[9]-[12]]. In this work, we modelled the end-to-end propagation as individual ray sources. For the indoor environment, five rays are used in calculations. One is the LoS and four are the reflected rays from two walls, ceiling, and ground. Each ray source contributes to the resulting received power. Contributions of the reflected rays are found to increase with the link distance. This is because when transmitter and receiver antennas are close, reflected fields are rejected by the receiver antenna because of its directional pattern. Together with high Fresnel reflection coefficient values along with the link, we observe an increase in the received power compared to free space, i.e. the slope of the path loss is smaller than that of the free space for indoor. For outdoor open area, two-ray model is found to be sufficient to model the received power and because of the absence of three first-order reflections, no obvious difference between path loss slopes have been detected. The analytical modelling results based on ray sources are compared with measurement and ray-tracing simulation results. We also made a comparative analysis of the measurements with five-ray and two-ray analytical models and ray-tracing simulations with five rays are provided for the indoor environment. The comparative analysis is carried out using z-test of the path loss model parameters. The z-test values indicate that the two-ray model does not provide a close match to the measurement path loss for the indoor corridor. On the other hand, the five-ray model provides a close fit to the measurement data. The ratio of power sum of dominant five rays to power sum of total rays obtained from measurements are also provided in this work. The percentage is greater than 90% for all the scenarios, which indicates that five rays are sufficient for modelling. The Ricean K-factor is also provided to study the contribution of LoS ray and diffuse rays over the link for two different gain antennas. Table 1 shows the related work in the literature, where ray tracing is used. Comparison of the available literature with our work highlights the following distinctions of our work: Propagation modelling based on dominant rays at 28 GHz is considered in our work. Table 1. Related work in the literature on mmWave channel modelling using ray tracing Literature Number of rays Frequency Maximum distance Reported channel statistics [[13]] 2 sub-6 GHz and mmWave 10 km Received power, two-ray model, break point distance based on first Fresnel zone [[14]] 1, 2, 5, 20 100 MHz, 1800 MHz, 2400 MHz 10 km Path loss, two-ray model, effect of first Fresnel zone on path loss exponent [[15]] 2 1.5 GHz 1 km Two-ray model, path loss exponent for vertically and horizontally polarised signals [[16]] 3 3.6 GHz, 10.6 GHz 100 m Path loss, three ray model for UWB propagation [[17]] 3 1900 MHz 400 m Three ray propagation model for PCS and -cellular services [[18]] 62 0.06 THz-1 THz 6 m Distance and frequency selective characteristics, coherence bandwidth, channel capacity, and temporal broadening analysis [[19]] 9 60 GHz 60 m LOS, 25 m NLOS Received power, indoor corridor power distribution comparison with Rayleigh and Rician [[20]] 2, 4, 5 2.4 GHz 50 m Received power analysis in open and closed corridors [[21]] 2, multiple rays 94 GHz 6 m Path loss, multipath analysis [[22]] 2, 4 94 'GHz 1.5 m Received power, multipath analysis for radars [[23]] 2, 4, 6, 10 2.4 GHz 10 m Path loss This study 2, 5 28 GHz 40 m indoor, 100 m outdoor Received power, path loss, the effect of antenna gain, adequacy analysis on number of rays using z-test and Ricean K-factor Five dominant rays were found to be adequate for the indoor corridor propagation modelling whereas, two dominant rays were found to adequately model the open area outdoors. The antenna gain of each individual ray is modelled based on its geometric position from the radiation pattern of the antenna provided in the datasheet. The resolvable distance of the rays compared to the LoS as a function of the link distance is also provided. Smaller than this resolvable distance, the rays will be superimposed coherently with the LoS component. A polarisation-dependent reflection coefficient for different materials is used at 28 GHz. A z-test is also performed for comparison of parameters of two-ray and five-ray path loss models obtained analytically, through ray-tracing simulations and measurements. A commonly occurring scenario for future fifth generation (5G) deployments is closely positioned transmitter and receivers at indoor corridors. This commonly occurring scenario in a typical indoor corridor environment is studied. There are other works in the literature in which five, even more, first-order reflections are taken into account [[18]-[27]]. We only considered rays experiencing the first-order reflection. This is because most of the received power comes from the LoS signal and the first-order reflections. For the purpose of illustration, consider that we have a second-order reflected ray with the same reflection coefficient as the first-order reflected ray, . Then the power contribution of the second-order reflected ray will be times the first order reflected ray. Generally, for common non-metallic surfaces such as walls and ground, hence, the power coming from second-order reflected ray will be smaller than the first-order reflected ray. In addition, rays that we consider as second-order reflections have to undergo longer paths than the first-order reflections as the geometry of a corridor obliges. Let the distance travelled by a first-order reflected ray from the transmitter to the receiver be , and additional distance travelled due to the second reflection. Then, the power of the second-order reflected ray will be smaller than the first-order reflected ray by a factor of due to free space path loss. Overall, the received power due to the second-order reflections will be significantly smaller compared to the first-order reflections and the contribution of the second-order reflections to the total received power will be small. Consequently, third and higher-order reflections will also have small contributions, thus negligible. The difference between first-order and second-order reflections in a similar setup is shown in a previous work, [[3]], as well. Moreover, considering higher-order reflections increases the complexity of the model unnecessarily compared to their contribution to the received power. Therefore, our model based on LoS and first-order reflections provides a robust and simple way to calculate received power in corridors and similar shaped indoor environments. Similarly, for outdoor open area two-ray model is sufficient to model the received power. 3 Received power modelling based on dominant rays for indoor corridor and outdoor open area In this section, we will first discuss antenna radiation pattern effects on propagation. Later, a received power calculation model based on dominant LoS signal and reflected rays in the indoor corridor (five-ray model) is presented. Two-ray model as a special case of the five-ray model is used for outdoor open area. 3.1 Antenna radiation pattern and propagation effects The antenna radiation pattern plays an important role in modelling the propagation characteristics of directional mmWave links. In the model, we used two directional horn antenna sets which have different gains and respective half-power beamwidths (HPBWs) in the azimuth and elevation planes. We represent the 3D antenna gain as a surface area extended on a sphere at a distance d with a given solid angle . The surface area A subtended by the antenna gain at a distance d from the source is , where the solid angle is given as: (1) where is the radiated power from the antenna in spherical coordinates as a function of distance d, elevation, and azimuth angles of and , respectively. is the maximum radiated power. The propagation from the transmitting antenna is modelled as a spherical wavefront. The majority of the radiated power is concentrated over the area covered by the solid angle represented by and , where these two angles represent the antenna HPBWs in the elevation and azimuth planes, respectively. Moreover, if and are small, we can approximate the area extended by and in space as at a fixed distance in the far-field region. The rays lying in this region will have significantly higher gain compared to the rays lying outside this area. 3.2 Ray resolution along the link distance The propagation from the antenna can be considered either as a wavefront propagation or decomposed as ray-based propagation [[28], [29]]. In the case of ray-based propagation, rays are considered to be originating from the transmitting antenna in all directions, where only the rays that interact with physical objects in the environment are taken into account. This is the basic principle of the ray tracing as well. In the case of a rectangular corridor, there are five dominant rays that interact with the surroundings. These rays are LOS, rays reflected from the left and right walls, floor, and ceiling. Theoretically, these rays are distinguishable at every point along the receiver route. The distinguishing characteristics of the individual rays depend on the (i) antenna characteristics at the transmitter and receiver; (ii) the geometry of propagation setup; and (iii) geometry of the environment. Our channel sounder setup can resolve any two rays at a spatial distance represented as , whereas the theoretical ray resolution can resolve rays at any distance. Consider the case of two-ray modelling for a given height of the transmitter and receiver represented as and , respectively (Fig. 3). When the link distance d between the transmitter and receiver is increased such that the difference between the paths travelled by any two rays is smaller than , those rays cannot be resolved, thus can be measured as a superposition. The relevant inequality is as follows: (2) Fig. 3Open in figure viewerPowerPoint Propagation of LoS and GRC from transmitter antenna towards receiver antenna when their heights ( and ) are the same Similarly, for the indoor corridor, the rays reflected from the ground, ceiling, and walls may not be resolvable depending on the link distance d. Fig. 4 shows the difference in path distances of the rays reflected from the ground, ceiling, and walls with respect to the LoS ray. In Fig. 4, the reflected rays are considered to be independent of each other. According to Fig. 4, the ray from the ceiling is the first to get unresolved at 3.1 m compared to ground reflected ray, which gets unresolved at 7 m. The rays from the two walls are not resolvable after 5 m. This indicates that the path of the reflected ray from the ceiling is the smallest compared to the paths of the remaining three rays. Fig. 4Open in figure viewerPowerPoint Difference of ray lengths with the LoS, plotted as a function of link distance 3.3 Received power modelling for indoor corridor The received signal is given by , where represents the transmitted signal, is the impulse response of the channel and is the convolution operation. In case that received and transmitted signals are known, channel impulse response (CIR) could be obtained by applying deconvolution. In this work, we considered the CIR in the indoor corridor (similar to rectangular waveguide). The reason for selecting a corridor is because the future 5G base stations (BSs)/access points (APs) are expected to be deployed in corridors of common building structures (e.g. buildings containing offices or classrooms). The major occupancy in these environments is in the rooms adjacent to the common corridor. Therefore, the BSs/APs are preferred in the corridor to provide optimum coverage to the adjoining rooms and in the corridor itself. Moreover, the indoor corridor can be considered to be a large rectangular room, or a square room (if considered in small portions). Therefore, propagation in this area can help to understand the propagation in other similar environments. The indoor corridor propagation layout is shown in Fig. 5. Based on the 3D geometry shown in Fig. 5, five dominant rays are considered. The characteristics of these rays depend on the antenna radiation pattern at the transmitter and receiver in both azimuth and elevation planes, height of the transmitter and receiver, and distance of the transmitter from the walls, ceiling, and floor for a given receiver position. The height of the transmitter and receiver are kept the same throughout the experiments. The five dominant rays are given as follows: one is the LoS and the other four are the reflected rays from the ground, ceiling, and two walls. Fig. 5Open in figure viewerPowerPoint Layout of the indoor corridor propagation environment As the distance of the receiver increases from the transmitter moving in a straight line received power coming from reflected rays increase as well. Due to the geometry of the test setup, as the link distance increases, reflected rays gets closer to the boresight of the received antenna, thus, captured with a higher gain. As a result of this, the difference between power value calculated taking only free space path loss into account and the five-ray received power increases in favour of the five-ray model. The contribution of the reflected rays to the overall received power is also dependent on the Fresnel reflection coefficients. Reflected rays of more than first-order have a significantly smaller contribution to the received power compared to first-order reflections. Therefore, in our model, we can safely ignore their contributions. Let represent the received LoS component given as: (3) where is the gain of the antenna for the transmitter at elevation and azimuth angles of and , respectively. Similarly, is the gain of the antenna for the receiver at elevation and azimuth angles of and , respectively, represents the delay of the LoS component given by , where c is the speed of the light and d is the distance of the LoS component, represents the phase of the LoS component, represents the dot product between the polarisation unit vectors of the electric field at the transmitter and receiver, respectively. The gain of the antenna for the LoS ray in the azimuth and elevation planes at the transmitter and receiver are given as follows [[30]]: (4) where and represent the direction of departure (DoD) in the elevation and azimuth planes, respectively. Similarly, the direction of arrival (DoA) in the elevation and azimuth planes are given as and . can be expressed as follows: (5) where is the antenna gain and is the relative phase of the component of a ray. If both the transmitter and receiver are aligned to their boresight, then the total gain given in (4) is maximised. Similar to the LoS component, the four dominant received rays reflected from the environment, with the ray index , is expressed as: (6) The reflection coefficient also called Fresnel reflection coefficient for the relative permittivity of the ground material is given as: (7) where the value of Y depends on the polarisation and are given for vertical and horizontal polarisation as follows: (8) If the link distance , then and the gain of the reflected ray approaches to the LoS component gain and the Fresnel reflection coefficient, . Let E represent the average over time, and represent the total received power, then , the coherent addition of the LoS and the reflected rays for , is given as: (9) Equation (9) can be rewritten for d values such that the reflected rays can be resolvable (see Section 3.2, Fig. 4) from each other: (10) From (3), (6), if , and where is the transmitted power. Moreover, for the LoS component, the XPD (cross polarisation discrimination) factor is negligible for vertical–vertical (VV) and horizontal–horizontal (HH) antenna orientations. Similarly, for the reflected rays, the diffuse scattering is small due to smooth reflecting surfaces leading to small XPDs. Therefore, the dot product of the polarisation vectors can be taken as 1 for the LoS and reflected rays. Therefore, the total received power from (9) can be written as follows: (11) where for . Additionally, if the heights of the antennas are not the same and/or not aligned to the boresight, we have additional attenuation due to smaller antenna gain. This attenuation will decrease with the increase in distance between the transmitter and the receiver. Considering the th individual reflected ray at a given link distance, we can write the received power as follows: (12) From (12), it can be observed that the received power of the th reflected ray approaches to the LoS ray at distance when (i) the antenna gains at the transmitter and receiver side are equal to the boresight antenna gains, and (ii) the reflection coefficient is 1. 3.4 Received power modelling for outdoor open area The outdoor open area is selected to study the mmWave propagation with two dominant rays, i.e. LOS and ground reflected component (GRC) with negligible contribution from the surroundings. Therefore, a simple propagation model that only considers two multipath components can accurately characterise the signal propagation. The outdoor open area scenario can be often encountered in parking lots, recreational parks, and highways, among others. The two-ray model can also be considered as a special case of the five-ray model. The two-ray model is used for received power modelling in outdoor open area assuming that antenna heights are significantly high. The contribution of any other rays from far off scatterers is small for the open area and is ignored. In the two-ray modelling, the received power is dependent on the LoS and GRC. Therefore, the total received power is given as follows: (13) where is the phase difference between the LoS and the GRC signals. 3.5 Polarisation effects on the received power The polarisation of electric fields should be taken into account. There are two co-polarised configurations based on antenna orientation used in the measurements, namely VV and HH. The difference in VV and HH antenna orientations is subject to the antenna radiation pattern in the azimuth and elevation planes. However, even though the whole patterns are different in two orthogonal planes, as the HPBWs are the same for both horn antenna sets, no significant difference in the antenna radiation patterns has been observed due to antenna orientation. Cross polarisation of vertical–horizontal (VH) is also introduced to study the XPD factor in the indoor corridor. Considering the channel stationary, we can obtain the XPD factor between the transmitter and receiver as follows: (14) where , and are the received powers for VV, VH and HH antenna orientations, respectively, and E denotes the expected value. A major use of XPD factor is that it helps to study the interaction of the antennas of different beamwidths with the surroundings when cross-polarisation is not negligible. 3.6 Path loss modelling The path loss obtained from the received power measured at different distances from the transmitter are given as follows: (15) An alpha–beta model for the path loss modelling [[31]] is given as: (16) where is the y-intercept in dB, is the slope and X is a random variable and , where expressed in dB is the variance of X. A least square regression is used to fit a regression line (best fit) to the data. 4 Experimental and ray-tracing simulations setup In this section, an indoor and outdoor experimental setup, as well as the ray-tracing simulation setup, are discussed. 4.1 Indoor and outdoor measurement setup Indoor corridor measurements were carried out at the basement of the Engineering Building II, North Carolina State University, shown in Fig. 1. The walls in the corridor are three-layered drywall, the ceiling is Armstrong type ceiling and the ground is a concrete grinded surface. The measurements were carried out using NI mmWave transceiver system operating at 28 GHz. The description of the NI mmWave transceiver system is provided in [[32]]. Two horn antenna sets with gains 17 and 23 dBi were used in the measurements. The HPBWs of 17 dBi antennas are and in the E- and H-planes, respectively. The HPBWs for the 23 dBi antennas in the E- and H-planes are and , respectively. The height of the transmitter and receiver from the ground was fixed to 1.44 m, whereas, the distance of the transmitter and receiver from the ceiling was 0.9 m. The distance from either of the walls to the antennas was 1.24 m. The transmitter was kept at a fixed position, whereas the receiver was moved in a straight line away from the transmitter at constant intervals of 0.3 m starting from 1.9 to 39.7 m. Laser alignment is used between the transmitter and the receiver at every step. The outdoor measurements were carried out at the top floor of a multi-storey car park at North Carolina State University shown in Fig. 2. Similar to the indoor corridor measurements, the transmitter was kept at a fixed place, and the receiver was moved in steps of 5 m beginning from 4.6 to 100 m. The height of the transmitter and receiver was 1.09 m. For both indoor and outdoor measurements, the transmit power has been set to 0 dBm. 4.2 Ray tracing and analytical simulation setup Ray-tracing simulations were carried out using Wireless InSite® software [[33]]. The environment model is shown in Fig. 6. The indoor corridor and the outdoor open area were modelled similar to the real environment with as many details as we could. For the indoor setup, four different material types are used for walls, floor, ceiling, and doors in the ray-tracing simulation environment. The material used for the floor is concrete, whereas, for the ceiling and walls, Armstrong ceiling and drywalls are used, respectively. The relative permittivity of the concrete floor at 28 GHz is 5.31, while it is 3 f}, number={14}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, publisher={Institution of Engineering and Technology (IET)}, author={Khawaja, Wahab and Ozdemir, Ozgur and Erden, Fatih and Ozturk, Ender and Guvenc, Ismail}, year={2020}, month={Nov}, pages={1825–1836} } @article{anjinappa_gurbuz_yapici_guvenc_2020, title={Off-Grid Aware Channel and Covariance Estimation in mmWave Networks}, volume={68}, url={https://doi.org/10.1109/TCOMM.2020.2980829}, DOI={10.1109/TCOMM.2020.2980829}, abstractNote={The spectrum scarcity at sub-6 GHz spectrum has made millimeter-wave (mmWave) frequency band a key component of the next-generation wireless networks. While mmWave spectrum offers extremely large transmission bandwidths to accommodate ever-increasing data rates, unique characteristics of this new spectrum need special consideration to achieve the promised network throughput. In this work, we consider the off-grid targets (basis mismatch) problem for mmWave communications. The off-grid effect naturally appears in compressed sensing (CS) techniques adopting a discretization approach for representing the angular domain. This approach yields a finite set of discrete angle points, which are an approximation to the continuous angular space, and hence degrade the accuracy of related parameter estimation. In order to cope with the off-grid effect, we present a novel parameter-perturbation framework to efficiently estimate the channel and the covariance for mmWave networks. The proposed algorithms employ a smart perturbation mechanism in conjunction with a low-complexity greedy framework of simultaneous orthogonal matching pursuit (SOMP), and jointly solve for the off-grid parameters and weights. Numerical results show a significant performance improvement through our novel framework as a result of handling the off-grid effects, which is totally ignored in the conventional sparse mmWave channel or covariance estimation algorithms.}, number={6}, journal={IEEE Transactions on Communications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Anjinappa, Chethan Kumar and Gurbuz, Ali Cafer and Yapici, Yavuz and Guvenc, Ismail}, year={2020}, month={Jun}, pages={3908–3921} } @article{chapnevis_guvenc_bulut_2020, title={Traffic Shifting based Resource Optimization in Aggregated IoT Communication}, ISSN={["0742-1303"]}, DOI={10.1109/LCN48667.2020.9314781}, abstractNote={Aggregated Internet of Things (IoT) communication aims to use core network resources efficiently by providing cellular access to a group of IoT devices over the same subscriber identity. Leveraging the low data rates and long data sending intervals of IoT devices, several of the IoT devices in the same serving area of the core network are grouped together and take turns to send their data to their servers without causing overlaps in their communication. In this paper, we take this approach further and benefiting from the flexibility in data sending schedules, we aim to increase savings in cellular resources by shifting (delaying or performing earlier) the regular traffic patterns of IoT devices slightly. To this end, we consider two different traffic shifting models, namely, consistent and inconsistent shifting. We first solve the optimal aggregation of IoT devices under each model by using Integer Linear Programming (ILP). In order to avoid the high complexity of ILP solution, we then develop a heuristic based solution that runs in polynomial time. Through simulations, we show that heuristic based solution provides close to optimal results in various scenarios and shifting based aggregated communication offers more resource optimization (i.e., smaller number of bearers needed to connect all IoT devices) than the aggregated communication with no shifting.}, journal={PROCEEDINGS OF THE 2020 IEEE 45TH CONFERENCE ON LOCAL COMPUTER NETWORKS (LCN 2020)}, author={Chapnevis, Amirahmad and Guvenc, Ismail and Bulut, Eyuphan}, year={2020}, pages={233–243} } @article{khawaja_ozdemir_erden_guvenc_matolak_2020, title={Ultra-Wideband Air-to-Ground Propagation Channel Characterization in an Open Area}, volume={56}, ISSN={["1557-9603"]}, url={https://doi.org/10.1109/TAES.2020.3003104}, DOI={10.1109/TAES.2020.3003104}, abstractNote={This article studies the air-to-ground ultra-wideband channel through propagation measurements between 3.1 to 4.8 GHz using unmanned-aerial-vehicles (UAVs). Different line-of-sight (LOS) and obstructed-LOS scenarios and two antenna orientations were used in the experiments. Multipath channel statistics for different propagation scenarios were obtained, and the Saleh–Valenzuela model was found to provide a good fit for the statistical channel model. An analytical path loss model based on antenna gains in the elevation plane is provided for unobstructed UAV hovering and moving (in a circular path) propagation scenarios.}, number={6}, journal={IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Khawaja, Wahab and Ozdemir, Ozgur and Erden, Fatih and Guvenc, Ismail and Matolak, David W.}, year={2020}, month={Dec}, pages={4533–4555} } @article{cui_briso-rodriguez_guan_guvenc_zhong_2020, title={Wideband Air-to-Ground Channel Characterization for Multiple Propagation Environments}, volume={19}, url={https://doi.org/10.1109/LAWP.2020.3012889}, DOI={10.1109/LAWP.2020.3012889}, abstractNote={Air-to-ground (AG) communications have attracted much attention for future advanced wireless communications. Unmanned aerial vehicle, as a critical enabler in AG communications, can be operated in various environments, such as over-water, hilly, and built-up environments. A better understanding of radio channels in various scenarios can immensely facilitate the deployment and design of wireless systems. Thus, in this letter, wideband characterizations of AG channels are performed based on the multienvironment channel measurements, where the center frequency is set to 6.5 GHz with the bandwidth of 500 MHz, which provides high delay resolution to capture significant multipath. Two key channel parameters, Rician K-factor and root-mean-square (rms) delay spread, are used as metrics to characterize AG channels. The positive Rician K-factor indicates the line-of-sight (LOS)-dominated characteristic of the AG channel. The discrepancy of the rms delay spread shows the obvious influence of multipaths from building on channel delay characteristics.}, number={9}, journal={IEEE Antennas and Wireless Propagation Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Cui, Zhuangzhuang and Briso-Rodriguez, Cesar and Guan, Ke and Guvenc, Ismail and Zhong, Zhangdui}, year={2020}, month={Sep}, pages={1634–1638} } @article{khawaja_guvenc_matolak_fiebig_schneckenburger_2019, title={A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles}, volume={21}, url={https://doi.org/10.1109/COMST.2019.2915069}, DOI={10.1109/COMST.2019.2915069}, abstractNote={In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, wide availability, and relative ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail, relative to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios.}, number={3}, journal={IEEE Communications Surveys & Tutorials}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Khawaja, Wahab and Guvenc, Ismail and Matolak, David W. and Fiebig, Uwe-Carsten and Schneckenburger, Nicolas}, year={2019}, pages={2361–2391} } @article{rupasinghe_yapici_guvenc_ghosh_kakishima_2019, title={Angle Feedback for NOMA Transmission in mmWave Drone Networks}, volume={13}, url={https://doi.org/10.1109/JSTSP.2019.2905226}, DOI={10.1109/JSTSP.2019.2905226}, abstractNote={In this paper, we consider an unmanned aerial vehicle (UAV) based wireless network using non-orthogonal multiple access (NOMA) transmission in millimeter-wave frequencies to deliver broadband data in a spectrally efficient fashion at hotspot scenarios. The necessity for the NOMA transmitter to gather information on user channel quality becomes a major drawback in practical deployments. We therefore consider various limited feedback schemes for NOMA transmission, to relieve the complexity of tracking and feeding back the full channel state information (CSI) of the users. In particular, through beamforming we allow NOMA to exploit the space domain, and hence, the user angle emerges as a promising (yet novel) limited feedback scheme. We show that as the user region for NOMA transmission gets wider, the users become more distinctive at the transmitter side with respect to their angles, making user angle feedback a better alternative than distance feedback in such scenarios. We rigorously derive and analyze the outage sum rate performance for NOMA transmission considering various user ordering strategies involving full CSI, angle, and distance feedback schemes. Our analytical results for NOMA outage sum rates using those feedback schemes match closely with simulations, and provide useful insights on properly choosing a limited feedback scheme for different deployment geometries and operating configurations.}, number={3}, journal={IEEE Journal of Selected Topics in Signal Processing}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Rupasinghe, Nadisanka and Yapici, Yavuz and Guvenc, Ismail and Ghosh, Monisha and Kakishima, Yuichi}, year={2019}, month={Jun}, pages={628–643} } @article{bai_guvenc_yu_zhang_2019, title={Guest Editorial Special Issue on Unmanned Aerial Vehicles Over Internet of Things}, volume={6}, ISSN={["2327-4662"]}, DOI={10.1109/JIOT.2019.2908444}, abstractNote={In the last few years, unmanned aerial vehicles (UAVs) have developed rapidly and the applications of UAVs have been expanded in wide areas, including photography, cargo delivery, inspection, and communications. Conventionally, UAVs are controlled and operated by a ground station using specific radio transmission modules, where the line-of-sight signal transmission is preferred and the operation range is limited, especially in urban areas. Using the Internet of Things (IoT) technologies, a UAV can be regarded as a terminal device connected in the ubiquitous network, where many other UAVs are communicated, navigated, controlled, and surveilled in real time and beyond line-of-sight.}, number={2}, journal={IEEE INTERNET OF THINGS JOURNAL}, author={Bai, Lin and Guvenc, Ismail and Yu, Quan and Zhang, Wei}, year={2019}, month={Apr}, pages={1636–1639} } @article{zeng_debbah_gesbert_guvenc_jin_xu_2019, title={INTEGRATING UAVS INTO 5G AND BEYOND}, volume={26}, ISSN={["1558-0687"]}, DOI={10.1109/MWC.2019.8641419}, abstractNote={The articles in this special issue examines the integration of unmanned aerial system (UAVs) into fifth generation mobile cellular communications (5G) and beyond. The past few years have witnessed a tremendous increase in the use of UAVs in civilian and commercial applications, such as for aerial photography, precision agriculture, traffi c control, video streaming, package delivery, and communication relaying. In June 2016, the U.S. Federal Aviation Administration (FAA) released the operational rules for routine commercial use of small unmanned aircraft systems (UAS), which is anticipated to further spur the growth of the global UAV industry in the coming years. To unlock the full potential of UAVs to enable large-scale usage, it is imperative to develop innovative wireless communication technologies, not only for supporting the critical control and non-payload communications (CNPC) to ensure the safe operation of all UAVs, but also for enabling the high-capacity payload data transmissions for various rate-demanding applications. Integrating UAVs into fi fth generation (5G) (and beyond) cellular systems is a promising technology to achieve the above goals.}, number={1}, journal={IEEE WIRELESS COMMUNICATIONS}, author={Zeng, Yong and Debbah, Merouane and Gesbert, David and Guvenc, Ismail and Jin, Shi and Xu, Jie}, year={2019}, month={Feb}, pages={10–11} } @article{eroglu_yapici_guvenc_2019, title={Impact of Random Receiver Orientation on Visible Light Communications Channel}, volume={67}, ISSN={["1558-0857"]}, url={https://doi.org/10.1109/TCOMM.2018.2879093}, DOI={10.1109/TCOMM.2018.2879093}, abstractNote={Visible light communications (VLC) has been studied thoroughly in recent years as an alternative or complementary technology to radio frequency communications. The reliability of VLC channels highly depends on the availability and alignment of line of sight links. In this paper, we study the effect of random receiver orientation for mobile users over VLC downlink channels, which affects the existence and quality of line of sight links. Based on the statistics of the receiver location and relative orientation with respect to the transmitter LED, we develop an analytical framework to characterize the statistical distribution of VLC downlink channels, which is then utilized to obtain the outage probability and the bit error rate. Our analysis is generalized for arbitrary distributions of relative orientation and location for a single transmitter, and extended to multiple transmitter case for some certain scenarios. Extensive Monte Carlo simulations show a perfect match between the analytical and the simulation data in terms of both the statistical channel distribution and the resulting bit error rate. Our results also characterize the channel attenuation due to random receiver orientation and location for various scenarios of interest.}, number={2}, journal={IEEE TRANSACTIONS ON COMMUNICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Eroglu, Yusuf Said and Yapici, Yavuz and Guvenc, Ismail}, year={2019}, month={Feb}, pages={1313–1325} } @article{fouda_ibrahim_guvenc_ghosh_2019, title={Interference Management in UAV-Assisted Integrated Access and Backhaul Cellular Networks}, volume={7}, ISSN={["2169-3536"]}, DOI={10.1109/ACCESS.2019.2927176}, abstractNote={An integrated access and backhaul (IAB) network architecture can enable flexible and fast deployment of the next-generation cellular networks. However, mutual interference between access and backhaul links, small inter-site distance, and spatial dynamics of user distribution pose major challenges in the practical deployment of the IAB networks. To tackle these problems, we leverage the flying capabilities of unmanned aerial vehicles (UAVs) as hovering IAB-nodes and propose an interference management algorithm to maximize the overall sum rate of the IAB network. In particular, we jointly optimize the user and base station associations, the downlink power allocations for access and backhaul transmissions, and the spatial configurations of the UAVs. We consider two spatial configuration modes of the UAVs, distributed UAVs and drone antenna array (DAA), and show how they are intertwined with the spatial distribution of ground users. Our numerical results show that the proposed algorithm achieves an average of $2.9\times $ and $6.7\times $ gains in the received downlink signal-to-interference-plus-noise ratio (SINR) and overall network sum rate, respectively. Finally, the numerical results reveal that UAVs can not only be used for coverage improvement but also for capacity boosting in the IAB cellular networks.}, journal={IEEE ACCESS}, author={Fouda, Abdurrahman and Ibrahim, Ahmed S. and Guvenc, Ismail and Ghosh, Monisha}, year={2019}, pages={104553–104566} } @article{ozdemir_anjinappa_hamila_al-dhahir_guvenc_2019, title={Joint Frame Synchronization and Channel Estimation: Sparse Recovery Approach and USRP Implementation}, volume={7}, ISSN={["2169-3536"]}, DOI={10.1109/ACCESS.2019.2905761}, abstractNote={Correlation-based techniques used for frame synchronization can suffer significant performance degradation over multi-path frequency-selective channels. In this paper, we propose a joint frame synchronization and channel estimation (JFSCE) framework as a remedy to this problem. This framework, however, increases the size of the resulting combined channel vector which should capture both the channel impulse response vector and the frame boundary offset and, therefore, its estimation becomes more challenging. On the other hand, because the combined channel vector is sparse, sparse channel estimation methods can be applied. We propose several JFSCE methods using popular sparse signal recovery algorithms which exploit the sparsity of the combined channel vector. Subsequently, the sparse channel vector estimate is used to design a sparse equalizer. Our simulation results and experimental measurements using software defined radios show that in some scenarios our proposed method improves the overall system performance significantly, in terms of the mean square error between the transmitted and the equalized symbols compared to the conventional method.}, journal={IEEE ACCESS}, author={Ozdemir, Ozgur and Anjinappa, Chethan Kumar and Hamila, Ridha and Al-Dhahir, Naofal and Guvenc, Ismail}, year={2019}, pages={39041–39053} } @article{yapici_guvenc_2019, title={NOMA for VLC Downlink Transmission With Random Receiver Orientation}, volume={67}, url={https://doi.org/10.1109/TCOMM.2019.2914195}, DOI={10.1109/TCOMM.2019.2914195}, abstractNote={Visible light communications (VLC) is an emerging technology with a promise of viable solution to spectrum crunch problem in conventional radio-frequency (RF) bands. In this paper, we consider a downlink multiuser VLC network where users randomly change their location and vertical orientation. In order to increase the spectral efficiency, we consider the non-orthogonal multiple access (NOMA) transmission to serve multiple users simultaneously. In particular, we propose individual and group-based user ordering techniques for NOMA with various user feedback schemes. In order to reduce the computational complexity and link overhead, feedback on the channel quality is proposed to be computed using a mean value of the vertical angle (instead of the exact instantaneous value), as well as the distance information. In addition, a two-bit feedback scheme is proposed for the group-based user scheduling, which relies on both the distance and the vertical angle, and differs from the conventional one-bit feedback of the distance only. The outage probability and sum-rate expressions are derived analytically, which show a very good match with the simulation data. Numerical results verify that the practical feedback scheme with the mean vertical angle achieves a near-optimal sum-rate performance, and the two-bit feedback significantly outperforms the one-bit feedback.}, number={8}, journal={IEEE Transactions on Communications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yapici, Yavuz and Guvenc, Ismail}, year={2019}, month={Aug}, pages={5558–5573} } @article{rupasinghe_yapici_guvenc_kakishima_2019, title={Non-Orthogonal Multiple Access for mmWave Drone Networks With Limited Feedback}, volume={67}, ISSN={["1558-0857"]}, url={https://doi.org/10.1109/TCOMM.2018.2867465}, DOI={10.1109/TCOMM.2018.2867465}, abstractNote={Unmanned aerial vehicle (UAV) base stations (BSs) can be a promising solution to provide connectivity and quality-of-service guarantees during temporary events and after disasters. In this paper, we consider a scenario where UAV-BSs are serving a large number of mobile users in a hot spot area (e.g., in a stadium). We introduce non-orthogonal multiple-access (NOMA) transmission at UAV-BSs to serve more users simultaneously considering user distances as the available feedback for a user ordering during NOMA formulation. With millimeter-wave transmission and multi-antenna techniques, we assume that UAV-BS generates directional beams and multiple users are served simultaneously within the same beam. However, due to the limitations of physical vertical beamwidth of the UAV-BS beam, it may not be possible to cover the entire user region at UAV altitudes of practical relevance. During such situations, a beam scanning approach is proposed to maximize the achievable sum rates. We develop a comprehensive framework over which outage probabilities and respective sum rates are derived rigorously and we investigate the optimal operational altitude of UAV-BS to maximize the sum rates using our analytical framework. Our analysis shows that NOMA with distance feedback can provide better outage sum rates than orthogonal multiple access.}, number={1}, journal={IEEE TRANSACTIONS ON COMMUNICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Rupasinghe, Nadisanka and Yapici, Yavuz and Guvenc, Ismail and Kakishima, Yuichi}, year={2019}, month={Jan}, pages={762–777} } @article{bulut_guvenc_akkaya_2019, title={Privacy Preserving Distributed Matching for Device-to-Device IoT Communications}, DOI={10.1145/3317549.3326309}, abstractNote={Device-to-device (D2D) communication enables machine-type devices (MTD) in Internet-of-Things (IoT) network communicate directly with each other and offload the cellular network. However, it may introduce interference as they share the same spectrum with the other devices that are directly connected to the base station. In this study, we look at the problem of assigning D2D communicating IoT pairs to the IoT devices that are directly connected to the base station such that the overall system throughput is not only maximized but also a stable matching is obtained. Different than previous work, we study many-to-one matching and propose a distributed privacy preserving stable matching process for efficient resource allocation without releasing location information.}, journal={PROCEEDINGS OF THE 2019 CONFERENCE ON SECURITY AND PRIVACY IN WIRELESS AND MOBILE NETWORKS (WISEC '19)}, author={Bulut, Eyuphan and Guvenc, Ismail and Akkaya, Kemal}, year={2019}, pages={316–317} } @article{yapici_guvenc_kakishima_2018, title={A MAP-Based Layered Detection Algorithm and Outage Analysis Over MIMO Channels}, volume={17}, url={https://doi.org/10.1109/TWC.2018.2821687}, DOI={10.1109/TWC.2018.2821687}, abstractNote={Efficient symbol detection algorithms carry critical importance for achieving the spatial multiplexing gains promised by multi-input multi-output (MIMO) systems. In this paper, we consider a maximum a posteriori probability (MAP)-based symbol detection algorithm, called M-BLAST, over uncoded quasi-static MIMO channels. Relying on the successive interference cancellation (SIC) receiver, the M-BLAST algorithm offers a superior error performance over its predecessor V-BLAST with a signal-to-noise ratio (SNR) gain of as large as 2 dB under various settings of recent interest. Performance analysis of the M-BLAST algorithm is very complicated since the proposed detection order depends on the decision errors dynamically, which makes an already complex analysis of the conventional ordered SIC receivers even more difficult. To this end, a rigorous analytical framework is proposed to analyze the outage behavior of the M-BLAST algorithm over binary complex alphabets and two transmitting antennas, which has a potential to be generalized to multiple transmitting antennas and multidimensional constellation sets. The numerical results show a very good match between the analytical and simulation data under various SNR values and modulation alphabets.}, number={7}, journal={IEEE Transactions on Wireless Communications}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Yapici, Yavuz and Guvenc, Ismail and Kakishima, Yuichi}, year={2018}, month={Jul}, pages={4256–4269} } @article{mushfique_palathingal_eroglu_yuksel_guvenc_pala_2018, title={A Software-Defined Multi-Element VLC Architecture}, volume={56}, ISSN={["1558-1896"]}, DOI={10.1109/mcom.2018.1700306}, abstractNote={In the modern era of radio frequency (RF) spectrum crunch, visible light communication (VLC) is a recent and promising alternative technology that operates at the visible light spectrum. Thanks to its unlicensed and large bandwidth, VLC can deliver high throughput, better energy efficiency, and low cost data communications. In this article, a hybrid RF/VLC architecture is considered that can simultaneously provide light- ing and communication coverage across a room. Considered architecture involves a novel multi-element hemispherical bulb design, which can transmit multiple data streams over light emitting diode (LED) modules. Simulations considering various VLC transmitter configurations and topologies show that good link quality and high spatial reuse can be maintained in typical indoor communication scenarios.}, number={2}, journal={IEEE COMMUNICATIONS MAGAZINE}, author={Mushfique, Sifat Ibne and Palathingal, Prabath and Eroglu, Yusuf Said and Yuksel, Murat and Guvenc, Ismail and Pala, Nezih}, year={2018}, month={Feb}, pages={196–203} } @article{parvez_rahmati_guvenc_sarwat_dai_2018, title={A Survey on Low Latency Towards 5G: RAN, Core Network and Caching Solutions}, volume={20}, ISSN={["1553-877X"]}, url={https://doi.org/10.1109/COMST.2018.2841349}, DOI={10.1109/COMST.2018.2841349}, abstractNote={The fifth generation (5G) wireless network technology is to be standardized by 2020, where main goals are to improve capacity, reliability, and energy efficiency, while reducing latency and massively increasing connection density. An integral part of 5G is the capability to transmit touch perception type real-time communication empowered by applicable robotics and haptics equipment at the network edge. In this regard, we need drastic changes in network architecture including core and radio access network (RAN) for achieving end-to-end latency on the order of 1 ms. In this paper, we present a detailed survey on the emerging technologies to achieve low latency communications considering three different solution domains: 1) RAN; 2) core network; and 3) caching. We also present a general overview of major 5G cellular network elements such as software defined network, network function virtualization, caching, and mobile edge computing capable of meeting latency and other 5G requirements.}, number={4}, journal={IEEE COMMUNICATIONS SURVEYS AND TUTORIALS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Parvez, Imtiaz and Rahmati, Ali and Guvenc, Ismail and Sarwat, Arif I. and Dai, Huaiyu}, year={2018}, pages={3098–3130} } @article{koohifar_guvenc_sichitiu_2018, title={Autonomous Tracking of Intermittent RF Source Using a UAV Swarm}, volume={6}, ISSN={["2169-3536"]}, url={http://dx.doi.org/10.1109/access.2018.2810599}, DOI={10.1109/access.2018.2810599}, abstractNote={The localization of a radio-frequency transmitter with intermittent transmissions is considered via a group of unmanned aerial vehicles (UAVs) equipped with omnidirectional received signal strength sensors. This group embarks on an autonomous patrol to localize and track the target with a specified accuracy, as quickly as possible. The challenge can be decomposed into two stages: 1) estimation of the target position given previous measurements (localization) and 2) planning the future trajectory of the tracking UAVs to get lower expected localization error given current estimation (path planning). For each stage, we compare two algorithms in terms of performance and computational load. For the localization stage, we compare a detection-based extended Kalman filter (EKF) and a recursive Bayesian estimator. For the path planning stage, we compare a steepest descent posterior Cramer–Rao lower bound path planning and a bioinspired heuristic path planning. Our results show that the steepest descent path planning outperforms the bioinspired path planning by an order of magnitude, and recursive Bayesian estimator narrowly outperforms detection-based EKF.}, journal={IEEE ACCESS}, author={Koohifar, Farshad and Guvenc, Ismail and Sichitiu, Mihail L.}, year={2018}, pages={15884–15897} } @article{iscar_guvenc_dikmese_rupasinghe_2018, title={Efficient Noise Variance Estimation Under Pilot Contamination for Massive MIMO Systems}, volume={67}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2017.2766226}, DOI={10.1109/tvt.2017.2766226}, abstractNote={Massive multiple input multiple output (MIMO) is expected to be one of the enabling technologies for fifth-generation cellular networks. One of the major challenges in massive MIMO systems is the accurate joint estimation of the channel and noise variance, which significantly affects the performance of wireless communications in practical scenarios. In this paper, we first derive a novel maximum likelihood estimator for the noise variance at the receiver of massive MIMO systems considering practical impairments such as pilot contamination. Then, this estimate is used to compute the minimum mean square error estimate of the channel. In order to measure the performance of the proposed noise variance estimator, we derive the corresponding Cramér–Rao lower bound (CRLB). Simulation results show that the estimator is efficient in certain scenarios, outperforming existing approaches in the literature. Furthermore, we develop the estimator and the CRLB for equal and different noise variance at the receive antennas. Although the proposed estimator is valid for all antenna array sizes, its use is particularly effective for massive MIMO systems.}, number={4}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Iscar, Jorge and Guvenc, Ismail and Dikmese, Sener and Rupasinghe, Nadisanka}, year={2018}, month={Apr}, pages={2982–2996} } @article{kumbhar_guvenc_singh_tuncer_2018, title={Exploiting LTE-advanced HetNets and FeICIC for UAV-assisted public safety Communications}, volume={6}, journal={IEEE Access}, author={Kumbhar, A. and Guvenc, I. and Singh, S. and Tuncer, A.}, year={2018} } @article{binol_guvenc_bulut_akkaya_2018, title={Hybrid evolutionary search method for complex function optimisation problems}, volume={54}, ISSN={["1350-911X"]}, DOI={10.1049/el.2018.6506}, abstractNote={In this Letter, harmony search (HS) technique hybridised with genetic algorithm (GA) is proposed. This technique mainly takes HS direction estimation mechanism and genetic operators in GA, which significantly increase the convergence of the HS algorithm. Specifically, the authors propose to incorporate main operators of GA into the HS algorithm to avoid some inherent drawbacks of the HS. For example, crossover is incorporated into HS to deal with low accuracy problem, while mutation is incorporated to escape from the local optimum solutions. In addition, elitism is introduced into the HS, to precipitate the performance and prevent the loss of favourable individuals found during the search process. The authors compare the performance of the GA, HS, and other popular HS variants on several benchmark functions. Numerical results show that the proposed hybridisation exhibits a superior performance in comparison to other algorithms.}, number={24}, journal={ELECTRONICS LETTERS}, author={Binol, H. and Guvenc, I. and Bulut, E. and Akkaya, K.}, year={2018}, month={Nov}, pages={1377–1378} } @article{rupasinghe_yapici_iscar_guvenc_2018, title={Impact of Angular Spread in Moderately Large MIMO Systems Under Pilot Contamination}, volume={67}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2018.2866799}, DOI={10.1109/TVT.2018.2866799}, abstractNote={Pilot contamination is known to be one of the main bottlenecks for massive multi-input multioutput (MIMO) networks. For moderately large antenna arrays (of importance to recent/emerging deployments) and correlated MIMO, pilot contamination may not be the dominant limiting factor in certain scenarios. To the best of our knowledge, a rigorous characterization of the achievable rates and their explicit dependence on the angular spread (AS) is not available in the existing literature for moderately large antenna array regime. In this paper, considering eigen-beamforming (EBF) precoding, we derive an exact analytical expression for achievable rates in multicell MIMO systems under pilot contamination, and characterize the relation between the AS, array size, and respective user rates. Our analytical and simulation results reveal that the achievable rates for both the EBF and the regularized zero-forcing precoders follow a nonmonotonic behavior for increasing AS when the antenna array size is moderate. We argue that knowledge of this nonmonotonic behavior can be exploited to develop effective user-cell pairing techniques.}, number={11}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Rupasinghe, Nadisanka and Yapici, Yavuz and Iscar, Jorge and Guvenc, Ismail}, year={2018}, month={Nov}, pages={10631–10644} } @article{merwaday_yuksel_quint_güvenç_saad_kapucu_2018, title={Incentivizing spectrum sharing via subsidy regulations for future wireless networks}, volume={135}, ISSN={1389-1286}, url={http://dx.doi.org/10.1016/J.COMNET.2018.02.011}, DOI={10.1016/J.COMNET.2018.02.011}, abstractNote={Traditional regulatory methods for spectrum licensing have been recently identified as one of the causes for under-utilization of the valuable radio spectrum. Governmental regulatory agencies such as the Federal Communications Commission (FCC) are seeking ways to remove stringent regulatory barriers and facilitate broader access to the spectrum resources. The goal of such new FCC-backed efforts is to allow for an improved and ubiquitous sharing of the precious radio spectrum between commercial service providers. In this paper, an interdisciplinary framework for spectrum management is proposed in which the government, using its regulatory power, can motivate spectrum sharing among the service providers in order to gain a net social benefit. In this framework, a noncooperative game is used to analyze how to foster more sharing of the radio spectrum via the use of regulatory power. The providers are incentivized with subsidized spectrum bands from the regulators. In return, the providers will be asked to provide coverage to the users that are not subscribed to them so as to maintain their subsidy incentives from the government. In a simplification of the model, the providers’ perfect equilibrium strategies are found numerically, and the existence of perfect equilibrium for the government’s strategy is discussed. Our numerical results using real base station locations from two cellular providers show that through subsidization, the government can provide small service providers a fair chance to compete with the large providers, thereby avoiding monopolization in the market.}, journal={Computer Networks}, publisher={Elsevier BV}, author={Merwaday, Arvind and Yuksel, Murat and Quint, Thomas and Güvenç, Ismail and Saad, Walid and Kapucu, Naim}, year={2018}, month={Apr}, pages={132–146} } @article{eroglu_guvenc_sahin_yapici_pala_yuksel_2018, title={Multi-Element VLC Networks: LED Assignment, Power Control, and Optimum Combining}, volume={36}, ISSN={["1558-0008"]}, DOI={10.1109/jsac.2017.2774378}, abstractNote={Visible light communications (VLCs) are a promising technology to address the spectrum crunch problem in radio frequency networks. A major advantage of VLC networks is that they can use the existing lighting infrastructure in indoor environments, which may have large number of LEDs for illumination. While LEDs used for lighting typically have limited bandwidth, presence of many LEDs can be exploited for indoor VLC networks, to serve each user by multiple LEDs for improving link quality and throughput. In this paper, LEDs are grouped and assigned to the users based on received signal strength from each LED, for which different solutions are proposed to achieve maximum throughput, proportional fairness, and quality of service. Additionally, power optimization of LEDs for a given assignment is investigated, and the Jacobian and Hessian matrices of the corresponding optimization problem are derived. Moreover, for multi-element receivers with LED grouping at the transmitter, an improved optimal combining method is proposed. This method suppresses interference caused by simultaneous data transfer of LEDs and improves the overall signal-to-interference-plus-noise-ratio by 2–5 dB. Lastly, an efficient calculation of channel response is presented to simulate multipath VLC channel with low computational complexity.}, number={1}, journal={IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS}, author={Eroglu, Yusuf Said and Guvenc, Ismail and Sahin, Alphan and Yapici, Yavuz and Pala, Nezih and Yuksel, Murat}, year={2018}, month={Jan}, pages={121–135} } @article{ciftler_dikmese_guvenc_akkaya_kadri_2018, title={Occupancy Counting With Burst and Intermittent Signals in Smart Buildings}, volume={5}, ISSN={["2327-4662"]}, DOI={10.1109/jiot.2017.2756689}, abstractNote={Zone-level occupancy counting is a critical technology for smart buildings and can be used for applications, such as building energy management, surveillance, and public safety. Existing occupancy counting techniques typically require installation of large number of occupancy monitoring sensors inside a building and an established wireless network. In this paper, in order to achieve occupancy counting, we consider the use of Wi-Fi probe requests that are continuously transmitted from Wi-Fi enabled smart devices for discovering nearby access points. To this end, Wi-Fi Pineapple equipment are used for passively capturing ambient probe requests from Wi-Fi devices, such as smart phones and tablets, where no connectivity to a Wi-Fi network is required. This information is then used to localize users within coarsely defined occupancy zones, and subsequently to obtain occupancy count within each zone at different time scales. An interacting multimodel (IMM) Kalman filter technique is developed to improve occupancy counting accuracy. Our numerical results using Wi-Fi data collected at a university building show that the use of Wi-Fi probe requests in conjunction with IMM-based Kalman filters can be a viable solution for zone-level occupancy monitoring in smart buildings.}, number={2}, journal={IEEE INTERNET OF THINGS JOURNAL}, author={Ciftler, Bekir Sait and Dikmese, Sener and Guvenc, Ismail and Akkaya, Kemal and Kadri, Abdullah}, year={2018}, month={Apr}, pages={724–735} } @article{khawaja_guvenc_chowdhury_2018, title={UWB channel measurements and modelling for hurricanes}, volume={12}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2018.0003}, abstractNote={Maintaining communications during major hurricanes is critically important for public safety operations by first responders. This requires accurate knowledge of the propagation channel during hurricane conditions. In this work, the authors have carried out ultra-wideband (UWB) channel measurements during hurricane conditions ranging from Category-1 to Category-4, generated at the wall of wind facility of Florida International University. Time-domain P410 radios are used for channel measurements. From the empirical data analysis in time domain, they developed an UWB statistical broadband channel model for hurricanes. In particular, they characterise the effects of rain and wind speed on large-scale and small-scale UWB propagation parameters considering both line-of-sight (LOS) and non-LOS (NLOS) links. Their experimental results show that number of multipath components reduce considerably with wind driven rain (WDR) and with link obstruction (NLOS scenario). Several remarks are also provided that can help explain the behaviour of UWB propagation characteristics under WDR.}, number={10}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Khawaja, Wahab and Guvenc, Ismail and Chowdhury, Arindam}, year={2018}, month={Aug}, pages={1691–1699} } @article{ruble_guvenc_2018, title={Wireless localization for mmWave networks in urban environments}, journal={EURASIP Journal on Advances in Signal Processing}, author={Ruble, M. and Guvenc, I.}, year={2018} } @article{kumbhar_koohifar_guvenc_mueller_2017, title={A Survey on Legacy and Emerging Technologies for Public Safety Communications}, volume={19}, ISSN={["1553-877X"]}, url={https://doi.org/10.1109/COMST.2016.2612223}, DOI={10.1109/comst.2016.2612223}, abstractNote={Effective emergency and natural disaster management depend on the efficient mission-critical voice and data communication between first responders and victims. Land mobile radio system (LMRS) is a legacy narrowband technology used for critical voice communications with limited use for data applications. Recently, long term evolution (LTE) emerged as a broadband communication technology that has a potential to transform the capabilities of public safety technologies by providing broadband, ubiquitous, and mission-critical voice and data support. For example, in the United States, FirstNet is building a nationwide coast-to-coast public safety network based on LTE broadband technology. This paper presents a comparative survey of legacy and the LTE-based public safety networks, and discusses the LMRS-LTE convergence as well as mission-critical push-to-talk over LTE. A simulation study of LMRS and LTE band class 14 technologies is provided using the NS-3 open source tool. An experimental study of APCO-25 and LTE band class 14 is also conducted using software-defined radio to enhance the understanding of the public safety systems. Finally, emerging technologies that may have strong potential for use in public safety networks are reviewed.}, number={1}, journal={IEEE COMMUNICATIONS SURVEYS AND TUTORIALS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Kumbhar, Abhaykumar and Koohifar, Farshad and Guvenc, Ismail and Mueller, Bruce}, year={2017}, pages={97–124} } @article{vasudeva_simsek_lopez-perez_guvenc_2017, title={Analysis of Handover Failures in Heterogeneous Networks With Fading}, volume={66}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2016.2640310}, DOI={10.1109/tvt.2016.2640310}, abstractNote={The handover process is one of the most critical functions in a cellular network and is in charge of maintaining seamless connectivity of user equipments across multiple cells. The handover process is driven by signal measurements from the neighboring base stations (BSs), and it is adversely affected by the time and frequency selectivity of the radio propagation channel. In this paper, we introduce a new model for analyzing handover performance in heterogeneous networks (HetNets) as a function of vehicular user velocity, cell size, and mobility management parameters. In order to investigate the impact of shadowing and fading on handover performance, we extract relevant statistics obtained from a Third-Generation Partnership Project (3GPP)-compliant HetNet simulator, and subsequently, we integrate these statistics into our analytical model to analyze both handover failure and ping-pong probabilities under fluctuating channel conditions. Computer simulations validate the analytical findings, which show that fading can significantly degrade the handover performance in HetNets with vehicular users.}, number={7}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Vasudeva, Karthik and Simsek, Meryem and Lopez-Perez, David and Guvenc, Ismail}, year={2017}, month={Jul}, pages={6060–6074} } @article{arani_mehbodniya_omidi_adachi_saad_guvenc_2017, title={Distributed Learning for Energy-Efficient Resource Management in Self-Organizing Heterogeneous Networks}, volume={66}, ISSN={["1939-9359"]}, DOI={10.1109/tvt.2017.2696974}, abstractNote={In heterogeneous networks, a dense deployment of base stations (BSs) leads to increased total energy consumption, and, consequently, increased cochannel interference (CCI). In this paper, to deal with this problem, self-organizing mechanisms are proposed, for joint channel and power allocation procedures, which are performed in a fully distributed manner. A dynamic channel allocation mechanism is proposed, in which the problem is modeled as a noncooperative game, and a no-regret learning algorithm is applied for solving the game. In order to improve the accuracy and reduce the effect of shadowing, we propose another channel allocation algorithm executed at each user equipment (UE). In this algorithm, each UE reports the channel with minimum CCI to its associated BS. Then, the BS selects its channel based on these received reports. To combat the energy consumption problem, BSs choose their transmission power by employing an