Least Square Optimization of Pilot Sequence Length for Massive MIMO Systems

Pilot sequence length is a crucial parameter that has a significant impact on massive multiple input multiple output (MIMO) systems. In a massive MIMO radio cell, the base station (BS) estimates the channel from mutually orthogonal uplink pilot sequences to configure a receiver for the uplink and (assuming reciprocity) a precoder for the forward link. Reuse of pilot sequences in adjacent cells results in pilot contamination in massive MIMO systems. Having long pilot sequences would reduce pilot contamination at the expense of spectral efficiency and throughput while too short pilot sequence would affect the orthogonality and channel estimation. In this paper, we propose to optimize the pilot sequence length by applying the least square technique on the uplink channel using total pilot power as the constraint. Numerical results show the feasibility of this approach.