Power Optimization and ARSs Selection in Uplink Cell-Free Multi-ARSs Communication Systems

Cell-Free (CF) is one of the techniques that play a crucial role in the evolution of current 5th Generation (5G) technology to satisfy the needs of emerging communication applications. In this paper, we analyze the uplink CF system utilizing multiple aerial relay stations (ARSs), where ARSs are defined as unmanned aerial vehicles functioning as relay stations. ARSs are designed with multiple antennas that concurrently serve a specific number of terrestrial users in a given area. In terms of signal processing, the system uses the time division duplex (TDD) protocol for communication and the minimum mean squared error (MMSE) method for channel estimation. We determine the uplink user throughput expression by applying the matched filtering (MF) technique and optimize pilot/data transmission power to enhance system quality using the successive convex approximation (SCA) method and the linear problem (LP), respectively. Additionally, we propose an ARS selection strategy based on the large-scale fading factor to reduce system load, computational complexity, and energy consumption for ARSs. The results indicate that addressing the power optimization problem improves user throughput. Furthermore, the findings also reveal that when a certain number of ARSs are selected, the ARS selection method outperforms the CF (no selection) technique in terms of the user throughput. Accordingly, we discover the best number of ARSs for the proposed system.