Robust Transceiver Design for Full-Duplex Decode-and-Forward Relay-Assisted MIMO Systems

Abstract

Robust transceiver design against unresolvable system uncertainties is of crucial importance for reliable communication. For instance, full-duplex communication suffers from such uncertainties when canceling the self-interference, since some residual self-interference (RSI) remains uncanceled due to imperfect channel knowledge. We consider a MIMO multihop system, where the source, the relay and the destination are equipped with multiple antennas. The considered decode-andforward (DF) hybrid relay can operate in either half-duplex or full-duplex mode, and the mode changes adaptively depending on the RSI strength. We investigate a robust transceiver design problem, which maximizes the throughput rate of the worstcase RSI under the self-interference channel uncertainty bound constraint. The yielded problem turns out to be a non-convex optimization problem, where the non-convex objective is optimized over the cone of semidefinite matrices. Without loss of generality, we simplify the problem to the optimization over multiple scalar parameters using majorization theory. Furthermore, we propose an efficient algorithm to obtain a local optimal solution iteratively. Eventually, we obtain insights on the optimal antenna allocation at the relay input-frontend and output-frontend, for relay reception and transmission, respectively. Interestingly, given a number of antennas at the relay, the robustness improves if more antennas are allocated to reception than to transmission.is shown to be optimal when there are a massive number of antennas at the relay [25], [26].Further, exploiting multiple antennas at the source and destination can provide the opportunity for improving the communication throughput rate. In a MIMO multi-hop system, the authors in [27] investigate a amplify-and-forward (AF) relay, where the precoder at the relay and the decoder at the destination are jointly optimized for maximizing the sourcedestination throughput rate. Moreover, the authors in [28] study the power allocation problem in two-hop decode-andforward (DF) MIMO FD relaying. These works mainly assume a single stream transmission, which is not always optimal. The authors in [29] consider a MIMO decode-and-forward (DF) relaying scheme with energy harvesting demands at the relay fulfilled by the source. Assuming FD multi-pair communication with multi-antenna transceivers, the authors in [30] study the weighted sum-rate maximization, where they rendered the problem to the weighted mean squared error (MSE) minimization for obtaining low-complex algorithm. These works mainly assume the availability of the SI channel for optimal MIMO pre-and post-processing tasks, where the RSI is simply treated as noise with estimated statistical moments. However, these estimates can not be guaranteed to be valid for all applications and scenarios. Hence, the study of a robust design becomes crucially important.Robust transceiver design against the worst-case RSI channel helps find the threshold for switching between HD and FD operating modes in hybrid relay systems. Th...