@article{asokan_ozdemir_guvenc_sichitiu_2024, title={Aerial RF and Throughput Measurements on a Non-Standalone 5G Wireless Network}, ISBN={["979-8-3503-1765-7"]}, ISSN={["2473-070X"]}, DOI={10.1109/DySPAN60163.2024.10632812}, journal={2024 IEEE INTERNATIONAL SYMPOSIUM ON DYNAMIC SPECTRUM ACCESS NETWORKS, DYSPAN 2024}, author={Asokan, Ram and Ozdemir, Ozgur and Guvenc, Ismail and Sichitiu, Mihail L.}, year={2024}, pages={120–123} }
 @article{maeng_raouf_guvenc_ozdemir_sichitiu_dutta_2024, title={Key Observations from Altitude-Dependent Sub-6 GHz Spectrum Measurements at AERPAW}, ISBN={["979-8-3503-1765-7"]}, ISSN={["2473-070X"]}, DOI={10.1109/DySPAN60163.2024.10632856}, journal={2024 IEEE INTERNATIONAL SYMPOSIUM ON DYNAMIC SPECTRUM ACCESS NETWORKS, DYSPAN 2024}, author={Maeng, Sung Joon and Raouf, Amir H. F. and Guvenc, Ismail and Ozdemir, Ozgur and Sichitiu, Mihail L. and Dutta, Rudra}, year={2024}, pages={135–138} }
 @article{maeng_ozdemir_guvenc_sichitiu_2024, title={Kriging-Based 3-D Spectrum Awareness for Radio Dynamic Zones Using Aerial Spectrum Sensors}, volume={24}, ISSN={["1558-1748"]}, url={https://doi.org/10.1109/JSEN.2024.3357430}, DOI={10.1109/JSEN.2024.3357430}, abstractNote={Radio dynamic zones (RDZs) are geographical areas within which dedicated spectrum resources are monitored and controlled to enable the development and testing of new spectrum technologies. Real-time spectrum awareness within an RDZ is critical for preventing interference with nearby incumbent users of the spectrum. In this article, we consider a 3-D RDZ scenario and propose to use unmanned aerial vehicles (UAVs) equipped with spectrum sensors to create and maintain a 3-D radio map of received signal power from different sources within the RDZ. In particular, we introduce a 3-D Kriging interpolation technique that uses realistic 3-D correlation models of the signal power extracted from extensive measurements carried out at the NSF Aerial Experimentation and Research Platform for Advanced Wireless (AERPAW) platform. Using ${C}$ -band signal measurements by a UAV at altitudes between 30 and 110 m, we first develop realistic propagation models on air-to-ground path loss, shadowing, spatial correlation, and semi-variogram, while taking into account the knowledge of antenna radiation patterns and ground reflection. Subsequently, we generate a 3-D radio map of a signal source within the RDZ using the Kriging interpolation and evaluate its sensitivity to the number of measurements used and their spatial distribution. Our results show that the proposed 3-D Kriging interpolation technique provides significantly better radio maps when compared with an approach that assumes perfect knowledge of path loss. Specifically, the root-mean-square error (RMSE) of the signal power prediction achieved by our proposed 3-D Kriging method is notably lower compared to that of the perfect path loss-based prediction, especially when the height difference between measured and the target locations is less than 20 m.}, number={6}, journal={IEEE SENSORS JOURNAL}, author={Maeng, Sung Joon and Ozdemir, Ozgur and Guvenc, Ismail and Sichitiu, Mihail L.}, year={2024}, month={Mar}, pages={9044–9058} }
 @article{maeng_ozdemir_guvenc_sichitiu_dutta_mushi_2023, title={AERIQ: SDR-Based LTE I/Q Measurement and Analysis Framework for Air-to-Ground Propagation Modeling}, ISSN={["1095-323X"]}, DOI={10.1109/AERO55745.2023.10115787}, abstractNote={In this paper, we introduce AERIQ: a software-defined radio (SDR) based I/Q measurement and analysis framework for wireless signals for aerial experimentation. AERIQ is integrated into controllable aerial vehicles, it is flexible, repeatable, and provides raw I/Q samples for post-processing the data to extract various key parameters of interest (KPIs) over a 3D volume. Using SDRs, we collect I/Q data with unmanned aerial vehicles (UAVs) flying at various altitudes in a radio dynamic zone (RDZ) like outdoor environment, from a 4G LTE eNB that we configure to operate at 3.51 GHz. Using the raw I/Q samples, and using Matlab's LTE Toolbox, we provide a step-by-step description for frequency offset estimation/correction, synchronization, cell search, channel estimation, and reference signal received power (RSRP). We provide various representative results for each step, such as RSRP measurements and corresponding analytical approximation at different UAV altitudes, coherence bandwidth and coherence time of the channel at different UAV altitudes and link distances, and kriging based 3D RSRP interpolation. The collected raw data as well as the software developed for obtaining and post-processing such data are provided publicly for potential use by other researchers. AERIQ is also available in emulation and testbed environments for external researchers to access and use as part of the NSF AERPAW platform at NC State University.}, journal={2023 IEEE AEROSPACE CONFERENCE}, author={Maeng, S. J. and Ozdemir, O. and Guvenc, I. and Sichitiu, M. L. and Dutta, R. and Mushi, M.}, year={2023} }
 @article{raouf_maeng_guvenc_ozdemir_sichitiu_2023, title={Cellular Spectrum Occupancy Probability in Urban and Rural Scenarios at Various UAS Altitudes}, ISSN={["2166-9570"]}, DOI={10.1109/PIMRC56721.2023.10293763}, abstractNote={The ever-growing demand for wireless connectivity, coupled with limited spectrum resources, has resulted in spectrum congestion and interference. This research investigates the probability of occupancy in common sub-6 GHz cellular network bands based on measurements conducted in urban and rural environments. Specifically, we analyze the spectrum occupancy of various long-term evolution (LTE), 5th generation (5G) and Citizens Broadband Radio Service (CBRS) bands used in the United States, considering both uplink and downlink transmissions at altitudes up to 180 meters. Additionally, we explore the influence of altitude on the probability of spectrum occupancy in these bands. Our findings reveal that the probability of occupancy is generally higher in the downlink compared to the uplink. Moreover, we observe that line-of-sight (LoS) signals play a critical role in higher altitudes. These results provide insights spectrum utilization in various cellular bands across different altitudes, with implications on interference and spectrum coexistence between terrestrial networks and unmanned aerial systems (UASs) in the future.}, journal={2023 IEEE 34TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, PIMRC}, author={Raouf, Amir Hossein Fahim and Maeng, Sung Joon and Guvenc, Ismail and Ozdemir, Ozgur and Sichitiu, Mihail}, year={2023} }
 @article{gurses_funderburk_kesler_powell_rahman_ozdemir_mushi_sichitiu_guvenc_dutta_et al._2023, title={Demonstration of Joint SDR/UAV Experiment Development in AERPAW}, ISSN={["2155-7578"]}, url={http://dx.doi.org/10.1109/milcom58377.2023.10356351}, DOI={10.1109/MILCOM58377.2023.10356351}, abstractNote={The Aerial Experimentation and Research Platform for Advanced Wireless (AERPAW) is an outdoor testbed providing the experimenters access to programmable radios and programmable vehicles. A key aspect of AERPAW is its experiment development environment. This demo introduces potential users to the main capabilities of AERPAW’s development environment. The demo exercises the main three flexible testbed capabilities, namely the ability of an experimenter to choose a wireless radio setup, a vehicle setup, and to set up traffic. The experiment is then executed live, and the collected data is post-processed and displayed.}, journal={MILCOM 2023 - 2023 IEEE MILITARY COMMUNICATIONS CONFERENCE}, author={Gurses, Anil and Funderburk, Mark and Kesler, John and Powell, Keith and Rahman, Talha F. and Ozdemir, Ozgur and Mushi, Magreth and Sichitiu, Mihail L. and Guvenc, Ismail and Dutta, Rudra and et al.}, year={2023} }
 @article{maeng_ozdemir_guvenc_sichitiu_mushi_dutta_2023, title={LTE I/Q Data Set for UAV Propagation Modeling, Communication, and Navigation Research}, volume={61}, ISSN={["1558-1896"]}, DOI={10.1109/MCOM.005.2200784}, abstractNote={Unmanned aerial vehicles (UAVs) have recently been gaining considerable attention due to their vast range of potential applications. To facilitate UAV use cases involving beyond visual line of sight (BVLOS), cellular networks have emerged as ground connectivity points, enabling remote control and payload communication for UAV links. However, the availability of limited datasets obstructs the study of cellular technology coverage for UAV flights at different altitudes and the development of machine learning (ML) techniques for improving UAV communication and navigation. In this article, we introduce raw LTE in-phase and quadrature (I/Q) sample data sets obtained from physical field experiments of the NSF AERPAW experimentation platform. A UAV equipped with a software-defined radio (SDR) was flown at altitudes ranging from 30 m to 110 m, collecting raw I/Q samples from an SDR-based LTE base station operating at 3.51 GHz. We have implemented a standardized metadata format that can be used to replicate the results obtained from the collected datasets. The post-processing of raw I/Q samples is described and representative results are provided. In the end, we give examples of potential uses of the provided dataset, post-processing sample code, and I/Q collection sample experiment code by other ML, wireless, and UAV researchers.}, number={9}, journal={IEEE COMMUNICATIONS MAGAZINE}, author={Maeng, Sung Joon and Ozdemir, Ozgur and Guvenc, Ismail and Sichitiu, Mihail L. and Mushi, Magreth and Dutta, Rudra}, year={2023}, month={Sep}, pages={90–96} }
 @article{ganesh_khawaja_ozdemir_guvenc_nomoto_ide_2023, title={Propagation Measurements and Coverage Analysis for mmWave and Sub-THz Frequency Bands with Transparent Reflectors}, ISSN={["2577-2465"]}, DOI={10.1109/VTC2023-Spring57618.2023.10200244}, abstractNote={The emerging 5G and future 6G technologies are envisioned to provide higher bandwidths and coverage using millimeter wave (mmWave) and sub-Terahertz (THz) frequency bands. The growing demand for higher data rates using these bands can be addressed by overcoming high path loss, especially for non-line-of-sight (NLOS) scenarios. In this work, we investigate the use of passive transparent reflectors to improve signal coverage in an NLOS indoor scenario. Measurements are conducted to characterize the maximum reflectivity property of the transparent reflector using channel sounder equipment from NI. Flat and curved reflectors, each with a size of 16 inches by 16 inches, are used to study coverage improvements with different reflector shapes and orientations. The measurement results using passive metallic reflectors are also compared with the ray-tracing-based simulations, to further corroborate our inferences. The analysis reveals that the transparent reflector outperforms the metal reflector and increases the radio propagation coverage in all three frequencies of interest: 28 GHz, 39 GHz, and 120 GHz. Using transparent reflectors, there is an increase in peak received power that is greater than 5 dB for certain scenarios compared to metallic reflectors when used in flat mode, and greater than 3 dB when used in curved (convex) mode.}, journal={2023 IEEE 97TH VEHICULAR TECHNOLOGY CONFERENCE, VTC2023-SPRING}, author={Ganesh, Ashwini P. and Khawaja, Wahab and Ozdemir, Ozgur and Guvenc, Ismail and Nomoto, Hiroyuki and Ide, Yasuaki}, year={2023} }
 @article{maeng_ozdemir_nandakumar_guvenc_sichitiu_dutta_mushi_2023, title={Spectrum Activity Monitoring and Analysis for Sub-6 GHz Bands Using a Helikite}, ISSN={["2155-2487"]}, DOI={10.1109/COMSNETS56262.2023.10041314}, abstractNote={In this paper, we report sub-6 GHz spectrum measurement results at multiple ground fixed nodes and a helikite flying at altitudes up to 500 feet. Measurements are carried out at the NSF AERPAW platform in Raleigh, NC. We first describe our measurement methodology using software defined radios (SDRs) and explain the details of the measurement environment. Subsequently, we analyze the impact of terrain, measurement altitude, measurement frequency, and the time of the day on spectrum measurements for various different sub-6 GHz bands. In particular, we present spectrum occupancy results from various different LTE bands first in a rural environment, and then in an urban campus environment. Results show that for both environments, measured power at a given spectrum band increases with altitude up to 500 feet. On the other hand, in the urban environment, an abrupt increase in the aggregate received power is observed in all considered bands as the helikite rises above the buildings, when compared with the more gradual increase of the received power in same bands for the rural environment.}, journal={2023 15TH INTERNATIONAL CONFERENCE ON COMMUNICATION SYSTEMS & NETWORKS, COMSNETS}, author={Maeng, S. J. and Ozdemir, O. and Nandakumar, H. N. and Guvenc, I. and Sichitiu, M. L. and Dutta, R. and Mushi, M.}, year={2023} }
 @article{raouf_maeng_guvenc_ozdemir_sichitiu_2023, title={Spectrum Monitoring and Analysis in Urban and Rural Environments at Different Altitudes}, ISSN={["2577-2465"]}, DOI={10.1109/VTC2023-Spring57618.2023.10200994}, abstractNote={Due to the scarcity of spectrum resources, the emergence of new technologies and ever-increasing number of wireless devices operating in the radio frequency spectrum lead to data congestion and interference. In this work, we study the effect of altitude on sub-6 GHz spectrum measurement results obtained at a Helikite flying over two distinct scenarios; i.e., urban and rural environments. Specifically, we aim at investigating the spectrum occupancy of various long-term evolution (LTE), 5th generation (5G) and citizens broadband radio service (CBRS) bands utilized in the United States for both uplink and downlink at altitudes up to 180 meters. Our results reveal that generally the mean value of the measured power increases as the altitude increases where the line-of-sight links with nearby base stations is more available. SigMF-compliant spectrum measurement datasets used in this paper covering all the bands between 100 MHz to 6 GHz are also provided.}, journal={2023 IEEE 97TH VEHICULAR TECHNOLOGY CONFERENCE, VTC2023-SPRING}, author={Raouf, Amir Hossein Fahim and Maeng, Sung Joon and Guvenc, Ismail and Ozdemir, Ozgur and Sichitiu, Mihail}, year={2023} }
 @article{du_mujumdar_ozdemir_ozturk_guvenc_sichitiu_dai_bhuyan_2022, title={60 GHz Outdoor Propagation Measurements and Analysis Using Facebook Terragraph Radios}, ISSN={["2164-2958"]}, DOI={10.1109/RWS53089.2022.9719957}, abstractNote={The high attenuation of millimeter-wave (mmWave) would significantly reduce the coverage areas, and hence it is critical to study the propagation characteristics of mmWave in multiple deployment scenarios. In this work, we investigated the propagation and scattering behavior of 60 GHz mmWave signals in outdoor environments at a travel distance of 98 m for an aerial link (rooftop to rooftop), and 147 m for a ground link (light-pole to light-pole). Measurements were carried out using Facebook Terragraph (TG) radios. Results include received power, path loss, signal-to-noise ratio (SNR), and root mean square (RMS) delay spread for all beamforming directions supported by the antenna array. Strong line-of-sight (LOS) propagation exists in both links. We also observed rich multipath components (MPCs) due to edge scatterings in the aerial link, while only LOS and ground reflection MPCs in the other link.}, journal={2022 IEEE RADIO AND WIRELESS SYMPOSIUM (RWS)}, author={Du, Kairui and Mujumdar, Omkar and Ozdemir, Ozgur and Ozturk, Ender and Guvenc, Ismail and Sichitiu, Mihail L. and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2022}, pages={156–159} }
 @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{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{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{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{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{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{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{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{sayeed_vouras_gentile_weiss_quimby_cheng_modad_zhang_anjinappa_erden_et al._2020, title={A Framework for Developing Algorithms for Estimating Propagation Parameters from Measurements}, ISSN={["2166-0069"]}, DOI={10.1109/GCWkshps50303.2020.9367404}, abstractNote={A framework is proposed for developing and evaluating algorithms for extracting multipath propagation components (MPCs) from measurements collected by sounders at millimeter-wave (mmW) frequencies. To focus on algorithmic performance, an idealized model is proposed for the spatial frequency response of the propagation environment measured by a sounder. The input to the sounder model is a pre-determined set of MPC parameters that serve as the “ground truth”. A three-dimensional angle-delay (beamspace) representation of the measured spatial frequency response serves as a natural domain for implementing and analyzing MPC extraction algorithms. Metrics for quantifying the error in estimated MPC parameters are introduced. Initial results are presented for a greedy matching pursuit algorithm that performs a least-squares (LS) reconstruction of the MPC path gains within the iterations. The results indicate that the simple greedy-LS algorithm has the ability to extract MPCs over a large dynamic range, and suggest several avenues for further performance improvement through extensions of the greedy-LS algorithm as well as by incorporating features of other algorithms, such as SAGE and RIMAX.}, journal={2020 IEEE GLOBECOM WORKSHOPS (GC WKSHPS)}, author={Sayeed, Akbar and Vouras, Peter and Gentile, Camillo and Weiss, Alec and Quimby, Jeanne and Cheng, Zihang and Modad, Bassel and Zhang, Yuning and Anjinappa, Chethan and Erden, Fatih and et al.}, year={2020} }
 @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{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{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={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.}, 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{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{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{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{kaksi_ozdemir_hamila_al-dhahir_2018, title={A regularization approach to MSE analysis of OFDM under phase noise}, volume={83}, ISSN={["1618-0399"]}, DOI={10.1016/j.aeue.2017.09.005}, abstractNote={Orthogonal frequency division multiplexing (OFDM) is widely used in broadband wireless communications systems because of its high resilience to frequency-selective fading and its low implementation complexity. Phase noise (PN) is one of the major RF impairments in direct-conversion wireless transceivers. In this paper, we analyze the impact of PN on an OFDM transceiver. We derive an exact normalized mean square error (NMSE) expression under receive-side PN and examine asymptotic and special cases. An optimized regularization parameter for an MMSE equalizer design is derived and shown to result in appreciable NMSE reduction.}, journal={AEU-INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATIONS}, author={Kaksi, Omer and Ozdemir, Ozgur and Hamila, Ridha and Al-Dhahir, Naofal}, year={2018}, pages={303–308} }
 @inproceedings{khawaja_ozdemir_guvenc_2017, title={UAV air-to-ground channel characterization for mmWave systems}, DOI={10.1109/vtcfall.2017.8288376}, abstractNote={Communication at mmWave bands carries critical importance for 5G wireless networks. In this paper, we study the characterization of mmWave air-to-ground (AG) channels for unmanned aerial vehicle (UAV) communications. In particular, we use ray tracing simulations using Remcom Wireless InSite software to study the behavior of AG mmWave bands at two different frequencies: 28 GHz and 60 GHz. Received signal strength (RSS) and root mean square delay spread (RMS-DS) of multipath components (MPCs) are analyzed for different UAV heights considering four different environments: urban, suburban, rural, and over sea. It is observed that the RSS mostly follows the two ray propagation model along the UAV flight path for higher altitudes. This two ray propagation model is affected by the presence of high rise scatterers in urban scenario. Moreover, we present details of a universal serial radio peripheral (USRP) based channel sounder that can be used for AG channel measurements for mmWave (60 GHz) UAV communications.}, booktitle={2017 ieee 86th vehicular technology conference (vtc-fall)}, author={Khawaja, W. and Ozdemir, O. and Guvenc, Ismail}, year={2017} }