Reduced Complexity Techniques and Performance Analysis towards 6G Cell-Free Massive MIMO – CellFree6G

Distributed antenna systems (DAS) are expected to play a fundamental role in next generation wireless systems. In DASs, access points (AP) are distributed over a wide area and connected to a centralized processing unit. They present great potential to enhance spectral and power efficiency compared to traditional cellular systems with centralized base stations (BS). We have analyzed the capacity of DASs, leveraging on a mathematical framework based on Euclidean random matrices. To reap the benefits promised by this analysis, the use of a centralized optimal joint processing is crucial. However, an optimal maximum likelihood detector has an unaffordable complexity for large systems. Interestingly, in centralized massive MIMO systems, the channels between users and BS tend to become jointly orthogonal, allowing low complexity matched filters to attain the same performance as maximum likelihood detectors, asymptotically. In Cell-Free DAS however, more sophisticated receivers are needed.