Performance Analysis of Spatial Modulation Aided UAV Communication Systems in Cooperative Relay Networks

In this paper, by introducing the spatial modulation (SM) scheme into the unmanned aerial vehicle (UAV) relaying system, an SM-aided UAV (SM-UAV) cooperative relay network is presented. The performance of the SM-UAV relay network is investigated over $\text{Nakagami}-m$ fading channels, where the UAV remains stationary over a given area. According to the performance analysis, using the amplify-and-forward (AF) protocol, the effective signal-to-noise ratio (SNR) and the corresponding probability density function and moment generating function are, respectively, derived. With these results, the average bit error rate (BER) is further deduced, and resultant approximate closed-form expression is achieved. Based on the approximate BER, we derive the asymptotic BER to characterize the error performance of the system at high SNR. With this asymptotic BER, the diversity gain of the system is derived, and the resulting diversity order is attained. Simulation results illustrate the effectiveness of the performance analysis. Namely, approximate BER has the value close to the simulated one, and asymptotic BER can match the corresponding simulation well at high SNR. Thus, the BER performance of the system can be effectively assessed in theory, and conventional simulation will be avoided. Besides, the impacts of the antenna number, modulation order, fading parameter, and UAV position on the system performance are also analyzed. The results indicate that the BER performance is increased with the increases of Nakagami parameter $m$ and/or receive antenna and/or the decrease of modulation order.