# MIMO Relaying UAVs Operating in Public Safety Scenarios
## 1 Introduction
[PERSON] also suggests a shortest-path-routing algorithm to define the minimum number of connections required to minimize the outage probability and the number of hops to support all users. D2D communication is a feature included in next-generation telecommunication systems because it provides extended coverage, energy efficiency, reduced backhaul demands, low latency with reduced transmission delays, and is considered a key method for achieving green communications. IEEE 802.11a, the wireless local area network, Infrared, and  
Figure 1: Relaying UAV scenario. near field communications implement D2D communication. All these applications operate on an unlicensed spectrum and they are limited by device proximity [18]. Relay-assisted D2D communication is a promising technology that can be deployed in future wireless communications that may improve its spectrum efficiency and coverage area on a licensed spectrum [17]. [PERSON] and [PERSON] present studies where all device members share the same frequency band in the network. However, to prevent mutual interference, the base station (BS) reserves a dedicated radio resource for D2D communication and proposes both a centralized and a distributed scheduling algorithm [19]. [PERSON] et al. [20] consider that interference cancelation combined with a power optimization algorithm minimizes the intracell and intercell interference in HetNets. [PERSON] et al. [21] research the transmission rate through cooperation. According to the author, next-generation devices will have information regarding neighboring conditions, and the wireless channel and position information will be essential to establish cooperation schemes. [PERSON] et al. [22] integrate mobile with D2D communication networks, which is used to deliver delay-tolerant packets using store-carry-forward techniques. A UAV extends proximity services as a D2D device while being used as a surveillance tool ensuring safety and efficient connections between cars as reported by [5]. In [PERSON] et al. 's experiment [23], UAVs assist D2D users while flying under a mission (i.e., deliver a packet, monitoring traffic, etc.) The author states, it is possible to upload messages when the drone approaches the users and sends the messages to the core when the drone is near a base station. The experiment considers UAV selection, time allocation of data loading and offloading, as well as channel access competition. In [17], D2D is applied to extend coverage through multihopping techniques where a partial coverage user connects to an out-of-coverage user in such a way that the relaying links are optimized. The management control of UAVs can be integrated using software-defined networks (SDN), container-based network function virtualization (NFV), or fog computing architectures where each drone sends information regarding battery status and location to provide replacement if it is necessary and, at the same time, avoid physical collision with other drones in the network improving scalability and efficiency [24]. This paper shows how speed affects overall transmission using multiantenna relaying drones in public safety emergencies. Our scenario implements a circular trajectory and estimates the sum of the data rates delivered to users in a network using MIMO sidelinks. In this section, we review the evolution of sidelink implementation from Release 12 to Release 17, the procedure to establish sidelinks communication, and MIMO basic concepts. The system model is introduced in Section 2, followed by the results in Section 3, and the conclusion and some topics for future work are presented in Sections 4 and 5, respectively.