@article{maeng_chowdhury_guvenc_bhuyan_dai_2023, title={Base Station Antenna Uptilt Optimization for Cellular-Connected Drone Corridors}, volume={59}, ISSN={["1557-9603"]}, url={https://doi.org/10.1109/TAES.2023.3237994}, DOI={10.1109/TAES.2023.3237994}, abstractNote={Reliable wireless coverage in drone corridors is critical to enable a connected, safe, and secure airspace. To support beyond-visual-line-of-sight operations of aerial vehicles in a drone corridor, cellular base stations (BSs) can serve as a convenient infrastructure as they are widely deployed to provide seamless wireless coverage. However, antennas in the existing cellular networks are downtilted to optimally serve their ground users, which results in coverage holes at higher altitudes when they are used to serve drones. In this article, we consider the use of additional uptilted antennas at each cellular BS and optimize the uptilt angle to maximize the wireless coverage probability across a given drone corridor. Through numerical results, we characterize the optimal value of the antenna uptilt angle for a given antenna pattern as well as the minimum/maximum altitudes of the drone corridor.}, number={4}, journal={IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS}, author={Maeng, Sung Joon and Chowdhury, Md Moin Uddin and Guvenc, Ismail and Bhuyan, Arupjyoti and Dai, Huaiyu}, year={2023}, month={Aug}, pages={4729–4737} }
 @article{ozturk_anjinappa_erden_chowdhury_guvenc_dai_bhuyan_2023, title={Channel Rank Improvement in Urban Drone Corridors Using Passive Intelligent Reflectors}, ISSN={["1095-323X"]}, DOI={10.1109/AERO55745.2023.10115741}, abstractNote={Multiple-input multiple-output (MIMO) techniques can help in scaling the achievable air-to-ground (A2G) channel capacity while communicating with drones. However, spatial multiplexing with drones suffers from rank-deficient channels due to the unobstructed line-of-sight (LoS), especially in millimeter-wave (mmWave) frequencies that use narrow beams. One possible solution is utilizing low-cost and low-complexity metamaterial-based intelligent reflecting surfaces (IRS) to enrich the multi path environment, taking into account that the drones are restricted to flying only within well-defined drone corridors. A hurdle with this solution is placing the IRSs optimally. In this study, we propose an approach for IRS placement with a goal to improve the spatial multiplexing gains, and hence, to maximize the average channel capacity in a predefined drone corridor. Our results at 6 GHz, 28 GHz, and 60 GHz show that the proposed approach increases the average rates for all frequency bands for a given drone corridor when compared with the environment with no IRSs present, and IRS-aided channels perform close to each other at sub-6 and mmWave bands.}, journal={2023 IEEE AEROSPACE CONFERENCE}, author={Ozturk, Ender and Anjinappa, Chethan K. and Erden, Fatih and Chowdhury, Md Moin Uddin and Guvenc, Ismail and Dai, Huaiyu and Bhuyan, Arupjyoti}, year={2023} }
 @article{chowdhury_sinha_mahler_guvenc_2023, title={Mobility State Detection of Cellular-Connected UAVs Based on Handover Count Statistics}, volume={4}, ISSN={["2644-1330"]}, url={https://doi.org/10.1109/OJVT.2023.3296138}, DOI={10.1109/OJVT.2023.3296138}, abstractNote={Estimating the speed of aerial user equipment (UE) is critically important to provide reliable mobility management for cellular-connected unmanned aerial vehicles (UAVs) since this can enhance the quality of service. The 3GPP standard uses the number of handovers made by a UE during a predefined time period to estimate the speed and the mobility state efficiently. In this article, we introduce an approximation to the probability mass function of handover count (HOC) as a function of a cellular-connected UAV's height and velocity, HOC measurement time window, and different ground base station (GBS) densities. Afterward, we derive the Cramer-Rao lower bound (CRLB) for the speed estimate of a UAV and also provide a simple biased estimator for its speed based on the GBS density and HOC measurement period. We show that for a low handover parameter, the biased estimator turns into a minimum variance unbiased estimator (MVUE). Using this estimator, we study the problem of detecting the mobility state of a UAV as low, medium, or high mobility as per the 3GPP specifications. Using our proposed MVUE, we also characterize the accuracy improvement in speed estimation and mobility state detection as the GBS density and the HOC measurement window increase.}, journal={IEEE OPEN JOURNAL OF VEHICULAR TECHNOLOGY}, author={Chowdhury, Md Moin Uddin and Sinha, Priyanka and Mahler, Kim and Guvenc, Ismail}, year={2023}, pages={490–504} }
 @article{sheen_yang_feng_chowdhury_2021, title={A Deep Learning Based Modeling of Reconfigurable Intelligent Surface Assisted Wireless Communications for Phase Shift Configuration}, volume={2}, url={https://doi.org/10.1109/OJCOMS.2021.3050119}, DOI={10.1109/OJCOMS.2021.3050119}, abstractNote={Reconfigurable Intelligent Surface (RIS) has emerged as a promising technology in wireless networks to achieve high spectrum and energy efficiency. RIS typically comprises a large number of low-cost nearly passive elements that can smartly interact with the impinging electromagnetic waves for performance enhancement. However, optimally configuring massive number of RIS elements remains a challenge. In this article, we present a machine learning (ML) based modeling approach that learns the interactions between the phase shifts of the RIS elements and receiver (Rx) location attributes and uses them to predict the achievable rate directly without using channel state information (CSI) or received pilots. Once learned, our model can be used to predict optimal RIS configuration for any new receiver locations in the same wireless network. We leverage deep learning (DL) techniques to build our model and study its performance and robustness. Simulation results demonstrate that the proposed DL model can recommend near-optimal RIS configurations for test receiver locations which achieved close to an upper bound performance that assumes perfect channel knowledge. Our DL model was trained using less than 2% of the total receiver locations. This promising result represents great potential in developing a practical solution for the optimal phase shifts of RIS elements without requesting CSI from the wireless network infrastructure.}, journal={IEEE Open Journal of the Communications Society}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Sheen, Baoling and Yang, Jin and Feng, Xianglong and Chowdhury, Md Moin Uddin}, year={2021}, pages={262–272} }
 @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{prasad_chowdhury_qi_2021, title={CHANNEL RECONSTRUCTION WITH LIMITED FEEDBACK IN INTELLIGENT SURFACE AIDED COMMUNICATIONS}, ISSN={["2577-2465"]}, DOI={10.1109/VTC2021-FALL52928.2021.9625462}, abstractNote={Intelligent reflecting surface (IRS) has been promoted as a leading candidate technology for enhancing coverage as well as spectral and energy efficiencies in future wireless communication networks. An IRS comprises of a multitude of low-cost antenna elements that can be programmed to influence impinging electromagnetic waves in a desirable manner. However, performance enhancements are conditional upon availability of accurate channel estimates, which are especially hard to obtain for a passive IRS that lacks baseband processing capability. In this work, we propose novel channel reconstruction formulations for IRS-assisted communications where the IRS panel has only passive elements and the intended receiver provides just signal strength feedback reports. Our formulations simultaneously exploit low rank property and sparse beam-space representation of the unknown effective channel, and can accommodate subspace side-information whenever available. We design efficient proximal distance based algorithms to reconstruct the effective channel and demonstrate their superior performance via results generated using the open-source SimRIS platform.}, journal={2021 IEEE 94TH VEHICULAR TECHNOLOGY CONFERENCE (VTC2021-FALL)}, author={Prasad, Narayan and Chowdhury, Md Moin Uddin and Qi, Xiao Feng}, year={2021} }
 @article{prasad_chowdhury_qi_2021, title={Channel Reconstruction in Intelligent Surface aided Communications}, ISSN={["2155-2487"]}, DOI={10.1109/COMSNETS51098.2021.9352837}, abstractNote={Intelligent reflecting surface (IRS) has recently emerged as a promising candidate technology for enhancing capacity, coverage, and energy efficiency in future wireless communication systems. An IRS comprises of many low-cost antenna elements that can be programmed to impact and direct impinging electromagnetic waves in a beneficial manner. However, performance enhancements are subject to availability of accurate channel estimates, which are especially hard to obtain for an IRS with all passive elements. In this work, we propose novel channel reconstruction schemes which do not require any active elements on the IRS panel. Our novel formulation combines low-rank matrix completion with subspace side information and also exploits sparsity. It can account for non-ideal IRS elements and leads to an implementable algorithm. This algorithm in turn yields a reconstructed effective channel vector, and as a byproduct, an optimized IRS pattern that is well suited for facilitating data transmission. Furthermore, we propose an algorithm for subspace estimation and also provide a recipe for designing IRS pattern vectors that can be gainfully used during the training phase. Results generated using the opensource SimRIS tool demonstrate substantial spectral efficiency gains with a significantly reduced pilot overhead.}, journal={2021 INTERNATIONAL CONFERENCE ON COMMUNICATION SYSTEMS & NETWORKS (COMSNETS)}, author={Prasad, Narayan and Chowdhury, Md Moin Uddin and Qi, Xiao Feng}, year={2021}, pages={531–539} }
 @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} }