Uplink and downlink user pairing in full-duplex multi-user systems: Complexity and algorithms

In this paper, we consider a wireless network with one full-duplex (FD) base station (BS) and a set of half-duplex (HD) user equipments (UEs). In such scenario, in addition to the self-interference, the co-channel interference from uplink UEs to downlink UEs is the main bottleneck for the network performance. To overcome this, we consider the problem of maximizing the minimum fairness rate among all UEs by jointly determining the UE uplink/downlink directions and pairing the UEs over different resource blocks. We first show that the UE pairing problem is NP-hard in general. To develop efficient suboptimal algorithms, we formulate the considered problem as a mixed integer linear program and handle it by the iterative reweighted ℓ_q-norm minimization (IRM) method. In particular, we propose a two-stage IRM algorithm that determines the UE transmission directions in the first stage followed by optimizing the UE pairs in the second stage. Simulation results are presented to show the efficacy of the proposed algorithm over some heuristic methods.