Signaling Design of Two-Way MIMO Full-Duplex Channel: Optimality Under Imperfect Transmit Front-End Chain

摘要

A node in full-duplex mode can simultaneously transmit and receive in the same frequency band. Therefore, the wireless channel between two full-duplex nodes can be bidirectional, having the potential to double the spectral efficiency when compared to the half-duplex network. Due to the proximity of the transmitters and receivers on a node, the overwhelming self-interference becomes the fundamental challenge in implementing a full-duplex network. The mitigation of the self-interference signal can be managed at each step of the communication network by passive and active cancellation methods. In recent results, the feasibility of the single input single output (SISO) full-duplex communication has been experimentally demonstrated. However, the performance is limited by the residual self-interference which is considered to be induced by the imperfections of the transmit front-end chain.In this work, we design the signaling for a multiple input multiple output (MIMO) full-duplex two-way channel with the transmit imperfections. We evaluate the performance of the channel by using a game-theoretical approach, where we focus on the Pareto boundary of the achievable rate region and Nash equilibia (NE). For a MISO full-duplex two-way channel, we prove that beamforming is an optimal transmission strategy which can achieve any point on the Pareto boundary. Furthermore, we present a closed-form expression for the optimal beamforming weights. In our numerical examples we quantify gains in the achievable rates of the proposed beamforming over the zero-forcing beamforming. For general MIMO full-duplex channel, we prove the existence of NE and present the condition for the uniqueness of NE. We then propose a revised iterative water-filling algorithm which is capable of achieving NE if the full-duplex channel has a unique NE. Through simulations we show the threshold of the signal-to-residual-self-interference ratio below which the full-duplex NE outperforms the half-duplex TDMA.