Uplink Spectral and Energy Efficiency of Cell-Free Massive MIMO With Optimal Uniform Quantization

This paper investigates the performance of limited-fronthaul cell-free massive multiple-input multiple-output (MIMO) taking account fronthaul quantization and imperfect channel acquisition. Three cases are studied, which we refer to as Estimate & Quantize, Quantize Estimate, Decentralized, according where estimation is performed exploited. Maximum-ratio combining (MRC), zero-forcing (ZF), minimum mean-square error (MMSE) receivers considered. The Max algorithm Bussgang decomposition exploited model optimum uniform quantization. Exploiting optimal step size quantizer, analytical expressions for spectral energy efficiencies presented. Finally, an access point (AP) assignment proposed improve decentralized scheme. Numerical results investigate gap between limited perfect cases, demonstrate that exploiting relatively few bits, MIMO closely approaches perfect-fronthaul performance.