Downlink Cell-Free Fixed Wireless Access: Architectures, Physical Realities, and Research Opportunities

Recently, a new paradigm of wireless access, termed as cell-free massive multiple-input multiple-output (MIMO), has drawn significant research interest. Its primary distinction from conventional MIMO aided cellular networks is the ability to eliminate detrimental inter-cell interference (ICI), or convert ICI, into extra power for intended signal via multi-cell cooperation approach originated network MIMO. However, information-theoretical limit access achieved at expense large configuration overhead and high processing complexity. Because dynamic nature channels, global channel state information (CSI) invoked quickly becomes outdated, leading performance degradation. This article focuses on implementation fixed (FWA), complementary solution fiber-to-the-premise (FTTP) where latter prohibitively expensive. In particular, we discuss centralization architectures characteristics FWA, well their joint implications imperfect CSI performance. Moreover, measurement-based offline simulations show that long coherence time (‘quasi-static’) assumption real-world FWA channels only valid against completely motionless background, and, thus, it should not be used in system design analysis. Finally, present opportunities terms physical infrastructure, data processing, machine learning.