Pilot Decontamination in TDD Multicell Massive MIMO Systems With Infinite Number of BS Antennas

The performance of time division duplex (TDD) multiple-input multiple-output (M-MIMO) systems is mainly limited by the pilot contamination, which is a negative effect of reusing uplink pilot sequences in the neighboring cells. A pilot decontamination scheme for TDD multicell M-MIMO systems with an infinite number of base station (BS) antennas is proposed in this paper. The proposed scheme uses Zadoff-Chu (ZC) sequences as uplink pilot sequences and implements distinct orthogonal variable spreading factor (OVSF) code rows at each BS. The set of uplink pilot sequences at each BS is multiplied element-wise with the BS-specific OVSF code row to make uplink pilot sequences orthogonal across the network. Then, a mobile station randomly selects one of these multiplied ZCs from a given set and transmits it on the random access channel at the commencement of coherence interval. The performance of the uplink and downlink rates of the proposed scheme is compared with those of the time-shifted pilot scheme for an infinite number of BS antennas. The simulation results authenticate the validity of the proposed scheme.