Beamforming and resource allocation in relay networks

Abstract

Relay can extend the coverage of a network and help signal transmission in shadow areas in wireless communications. The beamforming design and resource allocation schemes are investigated in various relay networks.

First, we consider the full-duplex (FD) two-way amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network with imperfect cancelation of loopback self-interference (SI) and propose joint design of relay and receive beamforming for minimizing the mean square error under a relay transmit power constraint. Due to loopback channel estimation error and limited dynamic range of transceiver, the loopback SI cannot be completely canceled. The relay beamforming matrix should be updated every time slot because the residual SI in the previous time slot is amplified by the current beamforming matrix and added to the received signals from the two sources in the current time slot. We derive the relay beamforming and receive beamforming matrices in closed-form based on minimum mean square error (MMSE). We also propose beamforming design using only the channels of the latest time slots, not from the first time slot. Based on numerical results, we also identify when FD is beneficial and propose selection between FD and half-duplex according to signal-to-noise ratio and interference-to-noise ratio.

Second, we consider a multi-hop AF MIMO relay network. In the multi-hop AF relay networks, the performance deteriorates as the number of hops increases because the effect of noise is enhanced. The forward-and-backward-channel state information (CSI) based beamforming and the all-CSI based beamforming schemes are designed at each node based on the MMSE criterion. In addition, we apply the all-CSI based beamforming scheme to multi-hop nondistributed and distributed AF relay networks.

Third, we consider a two-way decode-and-forward relay network and propose resource allocation schemes. To maximize the achievable sum rate, we propose the power allocation and time allocation schemes.