Power Control in UAV-Supported Ultra Dense Networks: Communications, Caching, and Energy Transfer

By means of network densification, ultra dense networks (UDNs) can efficiently broaden the network coverage and enhance the system throughput. In parallel, unmanned aerial vehicles (UAVs) communications and networking have attracted increasing attention recently due to their high agility and numerous applications. In this article, we present a vision of UAV-supported UDNs. Firstly, we present four representative scenarios to show the broad applications of UAV-supported UDNs in communications, caching and energy transfer. Then, we highlight the efficient power control in UAV-supported UDNs by discussing the main design considerations and methods in a comprehensive manner. Furthermore, we demonstrate the performance superiority of UAV-supported UDNs via case study simulations, compared to traditional fixed infrastructure based networks. In addition, we discuss the dominating technical challenges and open issues ahead. INTRODUCTION The quick development of the mobile Internet and Internet of Things (IoT) brings critical challenges to the design of mobile wireless networks mainly for providing ultra high data rate and very low time delay. According to a recent ITU report [1], the wireless data traffic will be 10,000 times in 2030 compared to that in 2010. Ultra dense network (UDN) is a favorable technique to accomplish the requirements for explosive data traffic [2]. Thanks to the flexible deployment and low transmit power, deploying massive smallcell base stations (SBSs) can efficiently broaden the network coverage and enhance the overall throughpu [3]. Most of existing studies on UDNs have focused on improving the performance of terrestrial heterogeneous cellular networks by addressing various issues, such as, the coexistence of WiFi and heterogeneous smallcell networks [4], user association and resource allocation [5], and energy/spectral efficient frequency reuse in heterogeneous ultra dense scenarios [6], [7], to name just a few. In parallel, unmanned aerial vehicles (UAVs) communications and networking have attracted increasing attention recently due to their high agility and numerous applications. Introducing UAVs into UDNs can achieve significant gains by fully exploiting their potentials [8]. UAVs can be rapidly deployed to serve the wireless users without being Haichao Wang, Guoru Ding (corresponding author), Jin Chen, Jinlong Wang, and Le Wang are with PLA University of Science and Technology; Guoru Ding is also with Southeast University; Feifei Gao is with Tsinghua University December 15, 2017 DRAFT ar X iv :1 71 2. 05 00 4v 1 [ cs .N I] 2 9 N ov 2 01 7 2 hampered by geographical constraints compared to traditional terrestrial infrastructure. For example, they can act as flying base stations (BSs) to enhance wireless coverage and boost throughput at hotspots such as campuses and sport stadiums, or in the region where the cellular infrastructure is unavailable. They can also act as flying/mobile relays at these areas where the communications appear among separated users without reliable direct communication links. In addition, UAVs can achieve effective relocation in response to the users’ mobility. By dynamically adjusting the locations of UAVs, one can establish almost line-of-sight (LOS) communication links in most scenarios, thereby significantly improving the system performance. To exploit the potential merits, this article presents a vision of UAV-supported UDNs and investigates the power control problem in UAV-supported UDNs. Firstly, we present four representative scenarios to show the broad applications of UAV-supported UDNs in communications, caching and energy transfer. Then, we highlight the efficient power control in UAV-supported UDNs by discussing the main design considerations and methods in a comprehensive manner. Furthermore, we demonstrate the performance superiority of UAV-supported UDNs via case study simulations, compared to traditional fixed infrastructure based networks. In addition, we discuss the dominating technical challenges and open issues ahead. UAV-SUPPORTED UDNS In contrast to the conventional terrestrial infrastructure with fixed location, UAVs have unparalleled advantages due to their inherent mobility. UDNs will usher in major developments and changes with UAV supporting. Figure. 1 shows four representative scenarios with UAV supporting. • UAV as flying BSs: UAVs acting as flying BSs provide connectivity for the users in overloaded cells or the cases without infrastructure for wireless access, such as the regions where the cellular infrastructure has been damaged due to natural disasters. • UAV as mobile relays: UAVs as mobile relays can cooperate to forward the information among ground stations with limited backhauls or the separated nodes with negligible direct links. • UAV as motorial energy sources: UAVs can carry an energy source or even act as an energy source to charge the wireless nodes for prolonging the network lifetime. Typical applications include wireless sensor networks and IoT where wire charging is unavailable. • UAV as aerial caches: UAVs can be employed as caches to effectively deliver the contents by tracking the corresponding destinations. One typical application is delay-tolerant surveillance in agriculture, soil, and ocean. There are many types of UAVs that can be used in the application scenarios above. In this article, we mainly consider medium and large UAVs with greater load capacity and flight duration. UAV-Supported BS The spatial utilization of limited spectrum can be greatly improved by deploying UDNs, enabling more users to be served simultaneously. Even so, the traffic may be still overloaded in some hotspots at certain time (e.g., sport stadiums, attendees of festivals, or campuses). To offload the wireless data traffic of user equipments from macrocells or smallcells, UAVs can act as flying BSs to rapidly provide wireless access for ground users [9], [10]. December 15, 2017 DRAFT