On the Spectral Efficiency Analysis and Optimization for UAV-Relay Massive MIMO Network

Abstract

The complex urban infrastructure or man-made incidents may cause limited connectivity to users (UEs) in a bottleneck area between high rising buildings, or UEs in area with the local base station (BS) malfunctioning due to fire/ electrical issues. To provide the transmissions from the BS to UEs, we propose to adopt UAVs as aerial relays, given that massive MIMO, a mainstream technology for the next generation network, is assumed to be deployed at the BS. In this work, we provide a novel analytical analysis of the proposed UAV relay mMIMO system focusing on the spectral efficiency. Furthermore, the system sum rate maximization problem is also formulated by jointly optimizing the altitude of the UAV and the quality-of-service (QoS) conditions of ground UEs. The problem is naturally hard to solve due to the non-convex constraints and non-concave objective function. To address it, we propose a two-step algorithm based on inner convex approximation. Then numerical results are used to demonstrate the validity of the theoretical analysis and the effectiveness of the proposed approach.