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

TL;DR

This paper proposes non-orthogonal uplink pilot designs for massive MIMO cellular networks, enhancing spectral efficiency and user rates by locally orthogonal codes and interference mitigation strategies.

Contribution

It introduces a novel class of pilot codes that are locally orthogonal within cells and low in cross-cell interference, improving downlink spectral efficiency.

Findings

User-rate CDF improves with proposed codes

Simulation shows enhanced cell throughput

Interference mitigation benefits performance

Abstract

Cellular networks of massive MIMO base-stations employing TDD/OFDM and relying on uplink training for both downlink and uplink transmission are viewed as an attractive candidate for 5G deployments, as they promise high area spectral and energy efficiencies with relatively simple low-latency operation. We investigate the use of non-orthogonal uplink pilot designs as a means for improving the area spectral efficiency in the downlink of such massive MIMO cellular networks. 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 estimates 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 simulation-based analysis shows, such cellular operation based on the proposed codes yields user-rate CDF improvement with respect to conventional operation, which can be exploited to improve cell and/or cell-throughput performance.