Rethinking Uplink Hybrid Processing: When Is Pure Analog Processing Suggested?

In this correspondence paper, we analytically characterize the benefit of digital processing in uplink massive multiple-input multiple-output (MIMO) with a sub-connected hybrid architecture. By assuming that the number of radio frequency chains is equal to that of users, we characterize achievable rates of both pure analog detection and hybrid detection under the independent identically distributed Rayleigh fading channel model. From the derived expressions, we discover that the analog processing can outperform the hybrid processing using the maximal ratio combining or zero-forcing criterion in cases under some engineering assumptions. Performance comparison of the schemes are presented under tests with various number of users and number of antennas at the base station.