On-the-fly Uplink Training and Pilot Code Design for Massive MIMO Cellular Networks

We investigate non-orthogonal uplink pilot designs for improving the area spectral efficiency in the downlink of TDD reciprocity-based massive MIMO cellular networks. In particular, we develop a class of pilot designs that are locally orthogonal within each cell, while maintaining low inner-product properties between codes in different cells. Using channel estimations provided by observations on these codes, each cell independently serves its locally active users with MU-MIMO transmission that is also designed to mitigate interference to a subset of "strongly interfered" out-of-cell users. As our analysis shows, such cellular operation based on the proposed codes yields improvements (with respect to conventional operation) in user-rate CDFs, cell-throughput and cell-edge throughput performance.