Outage performance of UAV-assisted AF relaying with hardware impairments

The use of unmanned aerial vehicle (UAV) as aerial relay, i.e. UAV-assisted relaying, has the advantages of easy deployment, agility, and mobility compared to the traditional ground relaying. In this paper, our goal is to acquire the universal outage probability (OP) analytical expression for multi-rotor UAV-assisted AF relaying with transceiver hardware impairments (HIs) while considering a practical large-scale fading. Contrary to the existing works on the UAV-assisted relaying, where the OP was derived by assuming a specific small-scale fading, we make a more general assumption of arbitrary small-scale fading and thereafter apply an integral region shape-based approximate method (IRS-AM) to deduce a closed-form OP expression with adjustable error in a more common way. The derivation process is free of the concrete model of the small-scale fading while the final OP expression has a concise and intuitive form, which is determined by the cumulative distribution function (CDF) of the small-scale fading in both two links. Based on the derived results, we demonstrate the ceiling effect caused by HIs on the multi-rotor UAV-assisted AF relaying and obtain the end-to-end signal-to-noise-and-distortion ratio (SNDR) bound, which depends on the aggregate HIs levels and determines whether the considered relay network is always in outage or not. Computer simulations validate our studies and reveal the influence of HIs on the OP and the optimal UAV altitude. (C) 2021 Elsevier B.V. All rights reserved.