Coordinated Pilot Design for Massive MIMO

Abstract

Pilot contamination is a main limiting factor in multi-cell massive multiple-input multiple-output (MIMO) systems due to the non-orthogonality of pilot sequences which can seriously impair the channel measurement. Recent work has suggested coordinating pilot sequence design across multiple cells by choosing the sequences to minimize the channel estimation error. This paper further investigates this approach using a new optimization framework. Specifically, we reformulate the weighted minimum mean-squared error (MMSE) measure as a sum-of-functions-of-matrix-ratio program that can be efficiently solved via a matrix fractional programming approach. The proposed algorithm provides fast convergence to a stationary-point solution of the MMSE problem. Simulations demonstrate the advantage of the proposed method over alternative approaches in enhancing channel estimation accuracy.