Finite Precision Implementation of Recursive Algorithms for Uplink Detection in Cell-Free Networks

Cell-free communication where distributed access points (APs) cooperatively serve users is emerging as an important enabler for 6G. This new architecture for communication systems is expected to enhance the quality of service of all the users due to the coherent transmission and reception of multiple spatially separated APs each with a low number of antennas. When scaling to very large cell-free deployments, the communication overhead between APs becomes a bottleneck. In this paper, we study how two recursive algorithms behave under the assumption of limited bandwidth fronthaul links between APs in the uplink signal estimation of a cell-free network with a daisy-chain topology. We analyze the impact of finite precision on the numerical stability of two RLS implementations named QR-RLS and standard RLS (SRLS). Simulation results show that QR-RLS is numerically stable for all simulated quantization precision and scenarios, while SRLS might be stable when carefully initialized. Moreover, SRLS numerical instability becomes worse when the number of users increases.