Analysis of NOMA based UAV assisted short-packet communication system and blocklength minimization for IoT applications

Recently, academia and industry have shown keen interest in achieving ultra-reliable and low latency communication (URLLC) through short-packet communication to meet the strict demands concerning high reliability and latency for 5G and beyond applications. Un-manned aerial vehicle (UAV) has caught attention recently because of its cost, air time, and mobility, whereas, the non-orthogonal multiple access (NOMA) technique has proven effective in dense user network. Hence, a UAV based system with NOMA has been studied in this paper for remote coverage. In this system, devices communicate to the base station (BS) through a UAV relay where direct link from devices to BS is absent. As UAV has direct line of sight (LOS) to the remote devices, hence, all the analysis is done over a Rician fading channel. In this work, a closed-form expression of average block error rate (BLER) has been formulated for the given system model, which is used as performance metric to analyse the system performance. Moreover, exact BLER expression facilitates in optimization with partial channel state information (CSI) only, which reduces the latency and complexity. Furthermore, we derive an asymptotic expression for BLER in high signal to noise (SNR) regime. Also, a blocklength minimization problem is formulated and optimized with reliability constraints. Simulation results are presented to verify analytical work, as well as comparison of the results with orthogonal multiple access scheme are also shown.