Novel Bounds for Semi-Blind Multiple-Access in Massive MIMO

We consider the standard Multi-User Multiple-Input-Multiple-Output (MU-MIMO) system, where only K active users, unknown in advance, out of N, wish to convey their messages to a single receiver. We derive two necessary lower bounds on the number of antennas (degrees of freedom) on both the receiver and transmitter sides, where the first holds for any MU-MIMO system and the second holds for any energy detection-based MU-MIMO. Then, we revisit techniques with identical scaling laws, such as compressive sensing and group testing, and discuss when the optimal antenna scaling laws for the MU-MIMO problem can be obtained. We also numerically evaluate the presented bounds and compare them against recent achievability results from the last ISIT.