Multipair DF relaying with network-assisted full-duplex cell-free massive MIMO

We consider a multipair decode-and-forward network-assisted full-duplex (NAFD) cell-free massive multiple-input multiple-output relaying system, where access points (APs) with a downlink (DL) mode serve destination nodes and those with an uplink (UL) mode serve source nodes, at the same time. Aiming at maximizing the sum of the spectral efficiency (SE) of all the transmission pairs, we formulate a mixed-integer nonconvex optimization problem to jointly design the AP mode assignment, power control, and large-scale fading decoding coefficients. This problem is subject to minimum per-pair SE requirements, per-AP power control, and per-source-node power constraints. By employing the successive convex approximation technique, we propose an algorithm to obtain a stationary solution to the formulated problem. Numerical results show that the NAFD approach can increase 90%-likely per-pair SE of the considered system by up to 63% compared with those of the traditional half-duplex and heuristic baseline schemes, respectively.