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1. On the Feasibility of High Throughput mmWave Backhaul Networks in Urban Areas

   https://doi.org/10.1109/ICNC47757.2020.9049824  

   Hu, Qiang; Blough, Douglas M. (February 2020, Proceedings of the International Conference on Computing, Networking and Communications)

   In this paper, we investigate the design of high throughput relay-assisted millimeter-wave (mmWave) backhaul networks in urban areas. Different from most related works, we consider the deployment of dedicated simple mmWave relay devices to help enhance the line-of-sight (LoS) connectivity of the backhaul network in urban areas with abundant obstacles. Given a set of (logical) backhaul links between base stations in the network, we propose an algorithm to find high-throughput LoS paths with relays for all logical links by minimizing interference within and between paths. We also propose methods to modify the backhaul topology to increase the probability of finding high-throughput paths using our algorithm. Extensive simulations, based on a 3-D model of a section of downtown Atlanta, demonstrate that high-throughput topologies, with minimal inter-path and intra-path interference, are feasible in most cases. The analyses also yield some insights on the mmWave backhaul network design problem. 

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2. On Enhancing WiGig Communications With A UAV-Mounted RIS System: A Contextual Multi-Armed Bandit Approach

   https://doi.org/10.1109/PIMRC56721.2023.10293924  

   Hashima, Sherief; Mohamed, Ehab Mahmoud; Hatano, Kohei; Takimoto, Eiji; Fouda, Mostafa M; Md_Fadlullah, Zubair (September 2023, IEEE)

   Recently emerging WiGig systems experience limited coverage and signal strength fluctuations due to strict line-of-sight (LoS) connectivity requirements. In this paper, we address these shortcomings of WiGig communication by exploiting two emerging technologies in tandem, namely the reconfigurable intelligent surface (RIS) and unmanned aerial vehicles (UAVs). In ultra-dense traffic sites (referred to as hotspots) where WiGig nodes or User Devices (UDs) experience complex propagation and non-line-of-sight (non-LoS) environment, we envision the deployment of a UAV-mounted RIS system to complement the WiGig base station (WGBS) to deliver services to the UDs. However, commercially available UAVs have limited energy (i.e., constrained flight time). Therefore, the trajectory of our considered UAV needs to be locally estimated to enable it to serve multiple hotspots while minimizing its energy consumption within the WGBS coverage boundaries. Since this tradeoff problem is computationally expensive for the resource-constrained UAV, we argue that sequential learning can be a lightweight yet effective solution to locally solve the problem with a low impact on the available energy on the UAV. We formally formulate this problem as a contextual multi-armed bandit (CMAB) game. Then, we develop the linear randomized upper confidence bound (Lin-RUCB) algorithm to solve the problem effectively. We regard the UAV as the bandit learner, which attempts to maximize its attainable rate (i.e., the reward) by serving distinct hotspots in its trajectory that we treat as the arms of the considered bandit. The context is defined as the hotspots’ locations provided using GPS (global positioning system) service and the reward history of each hotspot. Our proposal accounts for the energy expenditure of the UAV in moving from one hotspot to another within its battery charge lifetime. We evaluate the performance of our proposal via extensive simulations that exhibit the superiority of our proposed. 

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3. UAV Positioning for Improving Coverage-Connectivity Tradeoff in Millimeter-Wave Wireless Channels

   Abdel-Malek, Mai; Ibrahim, Ahmed S.; Mokhtar, Mohamed (July 2017, The second NSF millimeter wave workshop)

   In this work, we utilizie unmanned aerial vehicles (UAVs) to enhance the connectivity of the backhaul of small-cells (SCs) network and achieve better coverage for those user equipment (UE) in deep fade and not attached to any SCs. Deploying UAVs as a backbone for communication systems has gained an increasing prominence, especially in emergency network breakdown as an efficient and reliable alternative to restore the network connectivity. Moreover, to meet the ever increasing demand on high date rate applications, larger bandwidth is needed which is realizable in mm-wave frequencies range from 20 to 60 GHz. In mm-wave frequencies range, transmitted signals suffer from deleterious path loss mainly due to direct path blockages and significant penetrations losses. We exploit the mobility of UAVs and optimize its position to cope with such impairments. To the best of our knowledge, this work is the first to optimize the UAVs’ locations to jointly increase the connectivity between SCs and improve coverage by overcoming mm-wave harmful pathloss. 

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4. UAV-Based in-band Integrated Access and Backhaul for 5G Communications

   Fouda, Abdurrahman; Ibrahim, Ahmed S; Guvenc, Ismail; Ghosh, Monisha (October 2018, IEEE Vehicular Technology Conference (VTC2018-Fall))

   We introduce the concept of using unmanned aerial vehicles (UAVs) as drone base stations for in-band Integrated Access and Backhaul (IB-IAB) scenarios for 5G networks. We first present a system model for forward link transmissions in an IB-IAB multi-tier drone cellular network. We then investigate the key challenges of this scenario and propose a framework that utilizes the flying capabilities of the UAVs as the main degree of freedom to find the optimal precoder design for the backhaul links, user-base station association, UAV 3D hovering locations, and power allocations. We discuss how the proposed algorithm can be utilized to optimize the network performance in both large and small scales. Finally, we use an exhaustive search-based solution to demonstrate the performance gains that can be achieved from the presented algorithm in terms of the received signal to interference plus noise ratio (SINR) and overall network sum-rate. 

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5. Ray Tracing Analysis for UAV-Assisted Integrated Access and Backhaul Millimeter Wave Networks

   https://doi.org/10.1109/WoWMoM.2019.8792969  

   Perez, Alberto; Fouda, Abdurrahman; Ibrahim, Ahmed S. (June 2019, 2019 IEEE 20th International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM))

   The use of Millimeter-wave (mmWave) spectrum in cellular communications has recently attracted growing interest to support the expected massive increase in traffic demands. However, the high path-loss at mmWave frequencies poses severe challenges. In this paper, we analyze the potential coverage gains of using unmanned aerial vehicles (UAVs), as hovering relays, in integrated access and backhaul (IAB) mmWave cellular scenarios. Specifically, we utilize the WinProp software package, which employs ray tracing methodology, to study the propagation characteristics of outdoor mmWave channels at 30 and 60 GHz frequency bands in a Manhattan-like environment. In doing so, we propose the implementation of amplify-and-forward (AF) and decode-and-forward (DF) relaying mechanisms in the WinProp software. We show how the 3D deployment of UAVs can be defined based on the coverage ray tracing maps at access and backhaul links. Furthermore, we propose an adaptive UAV transmission power for the AF relaying. We demonstrate, with the aid of ray tracing simulations, the performance gains of the proposed relaying modes in terms of downlink coverage, and the received signal to interference and noise ratio (SINR). 

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