Spectral efficiency analysis of massive MIMO system

Abstract

In this paper, we studied the massive multiple-input multiple-output (MIMO) system performance with N antenna users and streams can be multiplexed per each user. The spectral efficiency (SE) of uplink and downlink expressions is derived for any N antenna users and these achievable using estimated channels and per user basis minimum mean squared error successive interference cancellation (MMSE-SIC) detector. This MMSE-SIC analysis shows similar to asymptotic SE of linear MMSE detectors indicating that the SE increases from having multi antenna users can be harvested using linear detectors. We also generalize the power scaling laws for massive MIMO and handling arbitrary N antenna users and show that that one can reduce the multiplication of the pilot power and payload power as 1/M where M is the number of BS antennas, and still notably increase the SE with M before reaching a non-zero asymptotic limit. Simulations show that SE increase with N antenna users, also note that the same improvement can be achieved by serving N times more single-antenna users instead. Thus the additional user antennas are particular useful for SE improvements when there is few active users in the system.