Multiuser Massive MIMO Systems With Time-Offset Pilots and Successive Interference Cancellation

The Khai Nguyen,Tien Hoa Nguyen,Ha H Nguyen

doi:10.1109/access.2019.2940458

Abstract

This paper proposes time-offset pilots for a single-cell multiuser massive multiple-input multiple-output (MIMO) system and studies its performance under the minimum mean-squared error channel estimator and successive interference cancellation. With the proposed time-offset pilots, users are divided into two groups and the uplink pilots from one group are transmitted simultaneously with the uplink data of the other group, which allows the system to accommodate more users for a given number of pilots. Successive interference cancellation is developed to ease the effect of pilot contamination and enhance data detection. Closed-form expressions for lower bounds of the uplink spectral efficiencies in both the training and data phases are derived when the maximum-ratio combining receiver is used at the base station. The power control problem is formulated with the objective of either maximizing the quality of service that can be equally provided to all users, or minimizing the total transmit power. Since the original power control problems are NP-hard, we also propose algorithms based on the bisection method to solve the problems separately in training and data phases. Analysis and numerical results show that the effect of pilot contamination can be mitigated by successive interference cancellation and proper power control.

Highlights

Over the last decade, massive multiple-input multiple-output (MIMO) systems have gained a strong interest as a promising key technology for enabling the and future generations of wireless communications
With hundreds of antennas equipped at each base station (BS), a massive MIMO system allows multiple users to simultaneously operate in the same time-frequency blocks, while co-channel interference can be effectively mitigated as a result of channel hardening and favorable propagation effects [1]–[4]
SIMULATION RESULTS numerical results are given to evaluate the performance of the multiuser massive MIMO system with time-offset pilots in terms of achievable quality of service (QoS) and power consumption

Summary

Introduction

Massive multiple-input multiple-output (MIMO) systems have gained a strong interest as a promising key technology for enabling the and future generations of wireless communications. The associate editor coordinating the review of this manuscript and approving it for publication was Xianfu Lei. The associate editor coordinating the review of this manuscript and approving it for publication was Xianfu Lei As discussed in these papers, in every coherence interval where the wireless channels between BSs and users are approximately constant, the number of symbols spent for channel estimation directly determines the maximum number of pairwise-orthogonal pilot sequences that can be generated for channel estimation. The number of orthogonal pilot sequences could be limited by the small length of the coherence interval, especially when the propagation environment changes quickly. If the number of users served by one BS keeps increasing, pilot sequences must be reused, resulting in the so-called pilot contamination [11]–[13]. With simple linear receivers such as maximum-ratio combining and zero-forcing, the network’s SE becomes saturated, even when the number of antennas goes to infinity [14]–[17]

Methods

Results

Conclusion