A Very-Low Pilot Scheme for mmWave Hybrid Massive MIMO-OFDM Systems

To reduce the large training overhead required by a millimeter-wave (mmWave) massive MIMO system, this letter proposes a pilot placement scheme and the corresponding receiver technique for multi-user uplink channel estimation and data detection over frequency-selective fading channels when OFDM is employed. Specifically, a small group of subcarriers transmit a small segment of pilots followed by data payloads; and all other subcarriers transmit data payloads only. To recover all channels and payload data, the basic idea is that for pilot subcarriers, a semi-blind method is employed for channel estimation and data detection based on low-rank matrix completion; while for the non-pilot subcarriers, the sparsity of mmWave channels in the delay-domain is exploited, based on which the channel estimation can be solved using the compressed-sensing (CS) technique. Simulation results show that significant performance gains can be achieved by our proposed scheme with very low pilot overhead.