Optimal Duplex Mode Selection for D2D-Aided Underlaying Cellular Networks

Both Device-to-device (D2D) and full-duplex (FD) have been widely recognized as spectral efficient techniques in the fifth-generation wireless communications systems. By enabling FD mode in D2D communications, the attainable spectrum efficiency can be (in theory) up to twice as high as that of conventional half-duplex (HD) mode D2D technology, provided that the self-interference signal in the former can be sufficiently suppressed. Considering the fact that FD technology does not always outperform the HD technology in arbitrary channel condition, we will delve into the FD gain as well as its preconditions for acquisition in this paper. In particular, the performance of D2D-aided underlaying cellular networks is investigated by assuming that the D2D users are capable of operating at both HD and FD modes. Under a given user workload, the sum throughput in each DU is shown to be always improved by activating D2D links despite an extra DU-induced interference could be imposed on its co-spectrum cellular users. Numerical results show that the FD-D2D mode exhibits its superiority in terms of sum throughput than the HD-D2D mode in a light-workload scenario even if a non-ideal SI cancellation has been implemented in the former, but the latter pulls back a game in a heavy-workload scenario. Furthermore, to maximize the sum throughput, an appropriate mode-selection scheme (i.e., by choosing either FD or HD mode in the current time-slot for each individual D2D user) should be implemented for sufficiently exploiting the FD gain according to the instantaneous radio frequency environment.