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1. An FSO-based Drone Assisted Mobile Access Network for Emergency Communications

   https://doi.org/10.1109/TNSE.2019.2942266  

   Wu, Di; Sun, Xiang; Ansari, Nirwan (September 2019, IEEE Transactions on Network Science and Engineering)

   Deploying drone-mounted base stations (DBSs) can quickly recover the communications of the mobile users (MUs) in a disaster struck area. That is, the DBSs can act as relay nodes to transmit data from remote working base stations to the MUs. Since the DBSs could be deployed very close to the MUs, the access link data rates between the DBSs and the MUs are well provisioned. However, the DBSs may be far away from the remote working base stations, and thus the backhaul link data rate between a DBS and the remote working base station could be throttled. Free Space Optics (FSO), which has been demonstrated to provision high speed point-to-point wireless communications, can be leveraged to improve the capacity of the backhaul link. Since FSO requires line-of-sight between a DBS and a remote working macro base station, DBSs have to carefully deployed. In this paper, we design a QoS aware drone base station placement and mobile user association strategy (RESCUE) to jointly optimize the DBS deployment, MU association, and bandwidth allocation such that the number of the served MUs in the disaster struck area could be maximized. The performance of RESCUE is validated via extensive simulations. 

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2. Backhaul-Aware Uplink Communications in Full-Duplex DBS-Aided HetNets

   https://doi.org/10.1109/GLOBECOM38437.2019.9013471  

   Zhang, Liang; Ansari, Nirwan (December 2019, 2019 IEEE Global Communications Conference (GLOBECOM))

   Drone-mounted base stations (DBSs) are promising solutions to provide ubiquitous connections to users and support many applications in the fifth generation of mobile networks while full duplex communications has the potential to improve the spectrum efficiency. In this paper, we have investigated the backhaul-aware uplink communications in a full-duplex DBS-aided HetNet (BUD) problem with the objective to maximize the total throughput of the network, and this problem is decomposed into two sub-problems: the DBS Placement problem (including the vertical position and horizontal position) and the joint UE association, power and bandwidth assignment (Joint-UPB) problem. Since the BUD problem is NP- hard, we propose approximation algorithms to solve the sub-problems and another, named the AA-BUD algorithm, to solve the BUD problem with guaranteed performance. The performance of the AA- BUD algorithm has been demonstrated via extensive simulations, and results show that the AA-BUD algorithm is superior to two benchmark algorithms. 

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3. Joint Link-level and Network-level Reconfiguration for mmWave Backhaul Survivability in Urban Environments

   https://doi.org/10.1145/3345768.3355913  

   Liu, Yuchen; Hu, Qiang; Blough, Douglas M. (January 2019, Proceedings of the 22nd International ACM Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems)

   mmWave communication has been recognized as a highly promising technology for 5G wireless backhaul, which is capable of providing multi-gigabit per second transmission rates. However, in urban wireless backhaul environments, unforeseen events can cause short-term blockages or node failures and, therefore, network survivability is extremely important. In this paper, we investigate a novel relay-assisted mmWave backhaul network architecture, where a number of small-cell BSs and relays are deployed, e.g. on the lampposts of urban streets. Relays are used to provide multi-hop line-of-sight paths between small-cell BSs, which form logical links of the network. In this scenario, the interconnected logical links make up a mesh network, which offers opportunities for both link-level and network-level reconfiguration. We propose two joint link-network level reconfiguration schemes for recovery after exceptional events. One prioritizes relay path (link-level) reconfiguration and uses alternate network-level paths only if necessary. The other splits traffic on both reconfigured links and backup paths to improve network throughput. Simulation results demonstrate that the proposed schemes significantly outperform purely link-level and purely network-level reconfiguration schemes. The proposed approaches are shown to not only maintain high network throughput but to also provide robust blockage/fault tolerance across a range of scenarios for urban mmWave backhaul networks. 

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4. A Multi-Layer Multi-Timescale Network Utility Maximization Framework for the SDN-Based LayBack Architecture Enabling Wireless Backhaul Resource Sharing

   https://doi.org/10.3390/electronics8090937  

   Wang, Mu; Karakoc, Nurullah; Ferrari, Lorenzo; Shantharama, Prateek; Thyagaturu, Akhilesh S.; Reisslein, Martin; Scaglione, Anna (September 2019, Electronics)

   With the emergence of small cell networks and fifth-generation (5G) wireless networks, the backhaul becomes increasingly complex. This study addresses the problem of how a central SDN orchestrator can flexibly share the total backhaul capacity of the various wireless operators among their gateways and radio nodes (e.g., LTE enhanced Node Bs or Wi-Fi access points). In order to address this backhaul resource allocation problem, we introduce a novel backhaul optimization methodology in the context of the recently proposed LayBack SDN backhaul architecture. In particular, we explore the decomposition of the central optimization problem into a layered dual decomposition model that matches the architectural layers of the LayBack backhaul architecture. In order to promote scalability and responsiveness, we employ different timescales, i.e., fast timescales at the radio nodes and slower timescales in the higher LayBack layers that are closer to the central SDN orchestrator. We numerically evaluate the scalable layered optimization for a specific case of the LayBack backhaul architecture with four layers, namely a radio node (eNB) layer, a gateway layer, an operator layer, and central coordination in an SDN orchestrator layer. The coordinated sharing of the total backhaul capacity among multiple operators lowers the queue lengths compared to the conventional backhaul without sharing among operators. 

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5. Terahertz Wireless Communications: Co-Sharing for Terrestrial and Satellite Systems Above 100 GHz

   Yunchou Xing, Theodore S. (October 2021, IEEE communications letters)

   Abstract—This letter demonstrates how spectrum up to 1 THz will support mobile communications beyond 5G in the coming decades. Results of rooftop surrogate satellite/tower base station measurements at 140 GHz show the natural isolation between terrestrial networks and surrogate satellite systems, as well as between terrestrial mobile users and co-channel fixed backhaul links. These first-of-their-kind measurements and accompanying analysis show that by keeping the energy radiated by terrestrial emitters on the horizon (e.g., elevation angles g.t. 15 deg), there will not likely be interference in the same or adjacent bands between passive satellite sensors and terrestrial terminals, or between mobile links and terrestrial backhaul links at frequencies above 100 GHz. Index Terms—Mmwave, terahertz, spectrum sharing and coexistence, satellite, OOBE, interference mitigation. 

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