Frequency Synchronization for Uplink Massive MIMO with Adaptive MUI Suppression in Angle-domain

TL;DR

This paper introduces an adaptive angle-domain filtering method for frequency synchronization in uplink massive MIMO systems, effectively suppressing multiuser interference even with overlapping AoA regions and imperfect knowledge.

Contribution

The paper proposes a novel ADAF-based frequency synchronization technique with two-stage MUI suppression applicable to overlapping users, enhancing robustness and reducing complexity.

Findings

Effective suppression of MUI from overlapping users.

Robustness to imperfect AoA knowledge.

Superior performance over existing methods.

Abstract

In this paper, we develop a novel angle-domain adaptive filtering (ADAF)-based frequency synchronization method for the uplink of a massive multiple-input multiple-output (MIMO) multiuser network, which is applicable for users with either separate or overlapped angle-of-arrival (AoA) regions. For each user, we first introduce the angle-constraining matrix (ACM), which consists of a set of selected match-filter (MF) beamformers pointing to the AoAs of the interested user. Then, the adaptive beamformer can be acquired by appropriately designing the ADAF vectors. Such beamformer can achieve two-stage adaptive multiuser interference (MUI) suppression, i.e., inherently suppressing the MUI from non-overlapping users by ACM in the first stage and substantially mitigating the MUI from adjacent overlapping users by ADAF vector in the second stage. For both separate and mutually overlapping users, the carrier frequency offset (CFO) estimation and subsequent data detection can be performed independently for each user, which significantly reduces computational complexity. Moreover, ADAF is rather robust to imperfect AoA knowledge and side cluster of scatterers, making itself promising for multiuser uplink transmission. We also analyze the performance of CFO estimation and obtain an approximated closed-form expression of mean-squared error (MSE). The effectiveness of the proposed method and its superiority over the existing methods are demonstrated by numerical results.