Next Generation Distributed Radio Access Networks With FSO Fronthauling

In this work, we address a novel framework for next-generation distributed radio access. In contrast with existing studies, where all remote radio heads (RRHs) in a distributed network are directly connected to a central unit (CU), an alternative architecture for advanced flexibility is proposed. In our setup, only one of the RRHs, namely the
$primary$
RRH, communicates directly with the CU, while the connectivity between the rest RRHs, namely
$secondary$
RRHs, and the CU is achieved through the primary RRH via free-space optical links. Assuming that users exploit non-orthogonal multiple access (NOMA) for their transmissions, we introduce two successive interference cancellation (SIC) cooperation schemes, depending on the one-directional or bidirectional communication between the RRHs, as well as, a four-step centralized algorithm for efficient user-RRH association and decoding order operations is proposed. The feasibility of the suggested schemes is adequately demonstrated by deriving analytical expressions for users’ outage probabilities and providing valuable insights into the high signal-to-noise ratio regime. Furthermore, the performance of the proposed system under various weather conditions is investigated via simulation and analytical results. The comparison with a benchmark scheme, where all RRHs are directly connected to the CU and cooperate with each other via ideal links, is provided and it is revealed that although the performance of the proposed system model is weather dependent, in most of the practical cases it achieves similar performance with the ideal benchmark.