Schulz, Leonard PaulLeonard PaulSchulzSchappmann, ChristianChristianSchappmannBauch, GerhardGerhardBauch2024-10-252024-10-25202419th International Symposium on Wireless Communication Systems, ISWCS 2024https://hdl.handle.net/11420/48979Cell-free massive multiple-input multiple-output (MIMO) is a promising technology for future wireless communication systems, where a large number of access points (APs) serve the user equipments (UEs) in the network coherently. Different ways of operating the system are possible, ranging from a fully centralized approach, where all signal processing is performed at a central processing unit (CPU), to a fully distributed approach, where most of the signal processing is performed at the APs. This paper proposes new heuristics to select the large-scale fading decoding (LSFD) weights in a fully distributed cell-free massive MIMO system. Due to the analytical intractability of the system, we rely on extensive Monte-Carlo simulations to evaluate their performance compared to the other operation levels. Importantly, we consider a scalable setup, where the APs are grouped into user-centric clusters. Our results show that a fully distributed system, which locally computes the LSFD weights in each AP using our heuristics, is able to approach the performance of a partially distributed system, where the LSFD weights are selected optimally in a centralized manner, especially for deployments with multiple antennas per AP. Moreover, when considering scalability, the proposed improved fully distributed system achieves substantial gains in terms of spectral efficiency over small-cell systems. Hence, even though fully centralized cell-free systems still achieve the best performance, distributed systems are a viable alternative that can be more practical to implement.enhttp://rightsstatements.org/vocab/InC/1.0/cell-free massive MIMOuplinklarge-scale fading decodingfully distributed operationAP cooperationComputer Science, Information and General Works::004: Computer SciencesTechnology::621: Applied PhysicsNatural Sciences and Mathematics::519: Applied Mathematics, ProbabilitiesConference Paper10.15480/882.1327410.1109/ISWCS61526.2024.1063907010.15480/882.13274Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting / republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to server or lists, or reuse of any copyrighted component of this work in other works.Conference Paper