Multiplexing and Diversity Gains in Noncoherent Massive MIMO Systems

We consider a noncoherent uplink and downlink with a large antenna array at the base station. The modulation used is ON-OFF keying, with symbol-by-symbol single-user detection. A ray tracing propagation model is assumed with knowledge at the base station and transmitters of only the ray arrival angles and amplitudes. We identify the sources of performance degradation, quantify notions of diversity gain (related to the detection error performance) and multiplexing gain (related to the number of users simultaneously supported), and present numerical results to demonstrate these gains. Our results indicate that in this noncoherent system, increasing the number of antenna elements can support multiple users, with a vanishing probability of detection error, as long as the number of users is below a certain threshold which increases with the number of antennas. This contrasts with the fact that in a rich scattering propagation environment, uncoded noncoherent systems performing symbol-by-symbol detection cannot support more than one user with a vanishing probability of error.