Communications with spectrum sharing in 5g networks via drone-mounted base stations

The fifth generation wireless network is designed to accommodate enormous traffic demands for the next decade and to satisfy varying quality of service for different users. Drone-mounted base stations (DBSs) characterized by high mobility and low cost intrinsic attributes can be deployed to enhance the network capacity. In-band full-duplex (IBFD) is a promising technology for future wireless communications that can potentially enhance the spectrum efficiency and the throughput capacity. Therefore, the following issues have been identified and investigated in this dissertation in order to achieve high spectrum efficiency and high user quality of service. First, the problem of deploying DBSs is studied. Deploying more DBSs may increase the total throughput of the network but at the expense of the operation cost. The droNe-mounted bAse station PlacEment (NAPE) problem with consideration of IBFD communications and DBS backhaul is then formulated. The objective is to minimize the number of deployed DBSs while maximizing the total throughput of the network by incorporating IBFD-enabled communications for both access links and backhaul links via DBSs as relay nodes. A heuristic algorithm is proposed to solve the NAPE problem, and its performance is evaluated via extensive simulations. Second, the 3-D DBS placement problem is investigated as the communication efficiency is greatly affected by the positions of DBSs. Then, the DBS placement with IBFD communications (DSP-IBFD) problem for downlink communications is formulated, and two heuristic algorithms are proposed to solve the DSP-IBFD problem based on different DBS placement strategies. The performance of the proposed algorithms are demonstrated via extensive simulations. Third, the potential benefits of jointly optimizing the radio resource assignment and 3-D DBS placement are explored, upon which the Drone-mounted Base Station Placement with IBFD communications (DBSP-IBFD) problem is formulated. Since the DBSP-IBFD problem is NP-hard, it is then decomposed into two sub-problems: the joint bandwidth, power allocation and UE association problem and the DBS placement problem. A 1/2(1-/2^{l}})-approximation algorithm is proposed to solve the DBSP-IBFD problem based on the solutions to the two sub-problems, where l is the number of simulation runs. Simulation results demonstrate that the throughput of the proposed approximation algorithm is superior to benchmark algorithms. Fourth, the uplink communications is studied as the mobile users need to transmit and receive data to and from base stations. The Backhaul-aware Uplink communications in a full-duplex DBS-aided HetNet (BUD) problem is investigated with the objective to maximize the total throughput of the network while minimizing the number of deployed DBSs. Since the BUD problem is NP-hard, it is then decomposed into three sub-problems: the joint UE association, power and bandwidth assignment problem, the DBS placement problem and the problem of determining the number of DBSs to be deployed. The AA-BUD algorithm is proposed to solve the BUD problem with guaranteed performance based on the solutions to the three sub-problems, and its performance is demonstrated via extensive simulations. The future work comprises two parts. First, a DBS can be used to provide both communications and computing services to users. Thus, how to minimize the average latency of all users in a DBS-aided mobile edge computing network requires further investigation. Second, the short flying time of a drone limits the deployment and the performance of DBSs. Free space optics (FSO) can be utilized as the backhaul link and the energizer to provision both communication and energy to a DBS. How to optimize the charging efficiency while maximizing the total throughput of the network requires further investigation

Trajectory optimization and resource allocation for UAV base stations under in-band backhaul constraint

The application of unmanned aerial vehicles (UAVs) to emerging communication systems has attracted a lot of research interests due to the advantages of UAVs, such as high mobility, flexible deployment, and cost-effectiveness. The UAV-carried base stations (UAV-BS) can provide on-demand service to users in temporary or emergency events. However, how to optimize the communication performance of a UAV-BS with a limited-bandwidth wireless backhaul is still a challenge. This paper focuses on improving the spectrum efficiency of a UAV-BS while guaranteeing user fairness under in-band backhaul constraint. We propose to maximize the minimum user rate among all the users served by the UAV-BS by jointly optimizing the allocation of bandwidth and transmit power, as well as the trajectory of the UAV-BS. As the formulated problem is non-convex, we propose an efficient algorithm to solve it suboptimally based on the alternating optimization and successive convex optimization methods. Computer simulation results show that the proposed algorithm achieves a significantly higher minimum user rate than the benchmark schemes

Space-Air-Ground Integrated 6G Wireless Communication Networks: A Review of Antenna Technologies and Application Scenarios

A review of technological solutions and advances in the framework of a Vertical Heterogeneous Network (VHetNet) integrating satellite, airborne and terrestrial networks is presented. The disruptive features and challenges offered by a fruitful cooperation among these segments within a ubiquitous and seamless wireless connectivity are described. The available technologies and the key research directions for achieving global wireless coverage by considering all these layers are thoroughly discussed. Emphasis is placed on the available antenna systems in satellite, airborne and ground layers by highlighting strengths and weakness and by providing some interesting trends in research. A summary of the most suitable applicative scenarios for future 6G wireless communications are finally illustrated

Exploiting UAV as NOMA based relay for coverage extension

Unmanned aerial vehicles (UAVs) aided communication has acquired research interest in many civilian and military applications. The use of UAV as base stations and as aerial relays to improve coverage of existing cellular networks is prevalent in current literature. Along with this, a few studies have proposed the use of non-orthogonal multiple access (NOMA) in UAV communications. In this paper, we propose a network where a ground user and an aerial UAV relay is accessed using NOMA, where the UAV acts as decode-and-forward (DF) relay to extend the coverage of source. The performance of the proposed model is shown by evaluating outage behaviour for different transmit power and fading environments with Monte Carlo simulations. System throughput of proposed network appears to be better than orthogonal multiple access (OMA) based equivalent network. The results show that with an adequate height of the UAV NOMA based relay, quality of service (QoS) of cell edge user is satisfactory

A review of relay network on UAVS for enhanced connectivity

One of the best evolution in technology breakthroughs is the Unmanned Aerial Vehicle (UAV). This aerial system is able to perform the mission in an agile environment and can reach the hard areas to perform the tasks autonomously. UAVs can be used in post-disaster situations to estimate damages, to monitor and to respond to the victims. The Ground Control Station can also provide emergency messages and ad-hoc communication to the Mobile Users of the disaster-stricken community using this network. A wireless network can also extend its communication range using UAV as a relay. Major requirements from such networks are robustness, scalability, energy efficiency and reliability. In general, UAVs are easy to deploy, have Line of Sight options and are flexible in nature. However, their 3D mobility, energy constraints, and deployment environment introduce many challenges. This paper provides a discussion of basic UAV based multi-hop relay network architecture and analyses their benefits, applications, and tradeoffs. Key design considerations and challenges are investigated finding fundamental issues and potential research directions to exploit them. Finally, analytical tools and frameworks for performance optimizations are presented

HAPS for 6G Networks: Potential Use Cases, Open Challenges, and Possible Solutions

High altitude platform station (HAPS), which is deployed in the stratosphere at an altitude of 20-50 kilometres, has attracted much attention in recent years due to their large footprint, line-of-sight links, and fixed position relative to the Earth. Compared with existing network infrastructure, HAPS has a much larger coverage area than terrestrial base stations and is much closer than satellites to the ground users. Besides small-cells and macro-cells, a HAPS can offer one mega-cell, which can complement legacy networks in 6G and beyond wireless systems. This paper explores potential use cases and discusses relevant open challenges of integrating HAPS into legacy networks, while also suggesting some solutions to these challenges. The cumulative density functions of spectral efficiency of the integrated network and cell-edge users are studied and compared with terrestrial network. The results show the capacity gains achieved by the integrated network are beneficial to cell-edge users. Furthermore, the advantages of a HAPS for backhauling aerial base stations are demonstrated by the simulation results