Can Dynamic TDD Enabled Half-Duplex Cell-Free Massive MIMO Outperform Full-Duplex Cellular Massive MIMO?

We consider a dynamic time division duplex (DTDD) enabled cell-free massive multiple-input multiple-output (CF-mMIMO) system, where each half-duplex (HD) access point (AP) is scheduled to operate in the uplink (UL) or downlink (DL) mode based on data demands of user equipments (UEs), with goal maximizing sum UL-DL spectral efficiency (SE). develop new, low complexity, greedy algorithm for combinatorial AP scheduling problem, an optimality guarantee theoretically established via showing that lower bound SE sub-modular. also pilot sequence reuse among UEs limit channel estimation overhead. In CF systems, all APs estimate from every UE, making allocation problem different cellular case. novel iteratively minimizes maximum contamination across UEs. compare performance our solutions, both and simulations, against full (FD) multi-cell mMIMO system. Our results show that, due joint processing signals at central unit, CF-mMIMO HD AP-scheduling significantly outperforms FD-mMIMO terms 90% likely SE. Thus, DTDD promising alternative FD-mMIMO, without cost hardware self-interference suppression.