Comparative Study of Dynamic TDD with Full-Duplex in Cell-Free Massive MIMO Systems.

In this paper, we present a comparative study of the performance of a dynamic time division duplex (DTDD) enabled cell free massive multiple-input multiple-output (CF-mMIMO) with a full-duplex (FD)CF-mMIMO system. Both DTDD and FD enable a CF-system to serve uplink (UL) and downlink (DL) user equipments (UEs) simultaneously over the same time-frequency resources. However, interference from other access points (APs) affects the performance of both of these duplexing strategies. Additionally, the intra-AP self-interference suppression level has a significant impact on the sum UL-DL spectral efficiency (SE) of an FD CF-system. On the other hand, in DTDD, concurrent UL/DL reception/transmission is facilitated by judiciously apportioning the UL and DL time slots across half-duplex APs based on the localized UL/DL traffic load. Due to this, DTDD obviates the need for intra-AP interference cancelation. Our numerical experiments reveal that the achievable sum SE with DTDD can match, and even outperform, an FD system with similar antenna density. Thus, DTDD is a potential duplexing scheme that can be incorporated in the next generation wireless systems to serve concurrent UL-DL traffic load without the need for implementing complex hardware and algorithms for self-interference cancelation as in FD systems.