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HARQ performance over massive MIMO channels using chase combining and CZA pilot decontamination

Pilot contamination is known to seriously limit the performance of massive MIMO systems due to degradation of channel estimation. Channel Zooming Algorithm (CZA) has been proposed as an efficient iterative algorithm to ensure the mitigation of the pilot contamination effect. This algorithm is able to zoom through iterations on the signal of the strongest user by taking advantage of the difference in space signatures and transmitted data sequences. CZA has been proved to be efficient for pilot contamination in the massive MIMO systems in the case of large number of antennas and long data packets. In this paper, we propose a novel version of CZA that utilizes the benefits of retransmitted packets combining. We consider a truncated Hybrid Automatic Repeat reQuest (HARQ), where the number of retransmissions is limited using Chase combining (CC). We evaluate the Packet Error Rate (PER) performance of the proposed approach for different order modulations as BPSK, QPSK, 16-QAM and 64-QAM. Simulation results show that very good performances can be achieved after very few transmission attempts with our HARQ scheme using CC and CZA, despite possible different contamination during each retransmission.