Performance Analysis of Short-Packet Communications in Multi-RIS-based Uplink Systems

Recently, reconfigure intelligent surfaces (RISs) have emerged as one of the most promising and breakthrough technologies for enhancing energy efficiency, spectral efficiency, and coverage by altering the propagation environment while short-packet communications is considered as a key enabler to providing critical applications. In this paper, we study short-packet communications in multi-RIS-based uplink transmission systems over a Rayleigh fading channel. We consider two typical techniques that are maximal-ratio-combining and selection-combining at the base station (BS), where the optimal RIS is selected from a distributed RIS set. In order to evaluate the performance of the investigated uplink system, the closed form and asymptotic for average block error rate (BLER) have been derived under the effects of two phase-shift scenarios, namely random phase-shift (RPS) and optimal phase-shift (OPS) respectively, at RISs. Numerical simulations demonstrate that enlarging the number of distributed RISs with more passive elements helps the system to overcome the disadvantages of both RPS and OPS scenarios and consequently, the BS can reduce the number of antennas while still achieving the desired BLER. Finally, obtained results of Monte-Carlo simulation are provided in order to verify the theoretical analysis accuracy.