Hybrid Pilot-aided Channel Estimation in Massive MIMO Uplink

This paper concerns with the uplink of multiuser multi-cell massive MIMO systems, and presents a hybrid pilot-aided channel estimation technique, where both time-multiplexed (TM) pilots and time-superimposed (TS) pilots are jointly employed for channel estimation in a frame. We show that the design of hybrid pilots combines the complementary advantages between TM pilots and TS pilots, and thereby, allows for a superior solution compared to conventional pilot schemes. In large-number-of-antennas regime, we asymptotically analyze the closed-form expression of the uplink throughput, and obtain the pilot-design-criteria for using both TM pilots and TS pilots. Numerical analysis and system simulation results show that TM pilot is more effective for the uplink transmission of a relatively large frame-size, while TS pilot has the substantial advantage in frame-based transmission of a limited size. It is obvious that such hybrid scheme can significantly improve the performance of massive MIMO systems.