User-Coupling Angle-Domain Adaptive Filtering Based Frequency Synchronization for Massive MIMO Multiuser Uplink

In this paper, we develop a user-coupling angle-domain adaptive filtering (UC-ADAF)-based frequency synchronization method for the uplink of a massive multiple-input multiple-output (MIMO) multiuser network, in the presence of highly overlapping angle-of-arrival (AoA) regions among coexisting users. In order to deal with the extremely severe multiuser interference (MUI) among users with highly overlapping AoA region, we propose to couple them together and perform joint carrier frequency offset (CFO) estimation and data detection. For the coupled users, the UC angle-constraining matrix (UC-ACM) can inherently suppress the interference from non-overlapping users and the UC-ADAF vectors are adaptively optimized to further eliminate the MUI from slightly overlapping users. Moreover, the challenging problem of addressing the severe MUI caused by highly overlapping users is circumvented through joint estimation and detection. The effectiveness of the proposed UC-ADAF approach and its robustness against overlapping degree among coupled users and the total number of mutually overlapping users, as well as its superiority over the existing methods, are demonstrated by numerical results.