We propose non-regenerative multi-way relaying where a half-duplex multi-antenna relay station (RS) assists multiple singleantenna nodes to communicate with each other. The required number of communication phases is equal to the number of the nodes, N. There are only one multiple-access phase, where the nodes transmit simultaneously to the RS, and N − 1 broadcast (BC) phases. Two transmission methods for the BC phases are proposed, namely, multiplexing transmission and analog network coded transmission. The latter is a cooperation method between the RS and the nodes to manage the interference in the network. Assuming that perfect channel state information is available, the RS performs transceive beamforming to the received signals and transmits simultaneously to all nodes in each BC phase. We address the optimum transceive beamforming maximising the sum rate of non-regenerative multi-way relaying. Due to the nonconvexity of the optimization problem, we propose suboptimum but practical signal processing schemes. For multiplexing transmission, we propose suboptimum schemes based on zero forcing, minimising the mean square error, and maximising the signal to noise ratio. For analog network coded transmission, we propose suboptimum schemes based on matched filtering and semidefinite relaxation of maximising the minimum signal to noise ratio. It is shown that analog network coded transmission outperforms multiplexing transmission.

In this paper, we introduce non-regenerative multiway relaying. A half-duplex multi-antenna relay station (RS) assists multiple nodes which want to communicate to each other. Each node has a message and wants to decode the messages from all other nodes. The number of communication phases is equal to the number of nodes, N, such that when N = 2, we have the well known two-way relaying. In the first phase, all nodes transmit simultaneously to the RS and in the following (N-1) phases the RS applies transceive beamforming and transmits to all nodes. The achievable sum rate for asymmetric traffic and symmetric traffic cases are derived for N -phase multi-way relaying. Three low complexity linear transceive beamformers based on Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Maximisation of Signal to Noise Ratio (MSNR) criteria are designed for N -phase multi-way relaying. From sum rate analysis, MMSE outperforms the other beamformers at the expense of using feedback channel to obtain the noise variance of the nodes. If interference cancellation is performed at all nodes, MSNR achieves the highest performance gain.

We consider non-regenerative multi-group multi-way (MGMW) relaying. A half-duplex non-regenerative multiantenna relay station (RS) assists multiple communication groups. In each group, multiple half-duplex nodes exchange messages. In our proposal, the required number of communication phases is equal to the maximum number of nodes among the groups. In the first phase, all nodes transmit simultaneously to the RS. Assuming perfect channel state information is available at the RS, in the following broadcast (BC) phases the RS applies transceive beamforming to its received signal and transmits simultaneously to all nodes. We propose three BC strategies for the BC phases: unicasting, multicasting and hybrid uni/multicasting. For the multicasting strategy, network coding is applied to maintain the same number of communication phases as for the other strategies. We address transceive beamforming maximising the sum rate of non-regenerative MGMW relaying. Due to the high complexity of finding the optimum transceive beamforming maximising the sum rate, we design generalised low complexity transceive beamforming algorithms for all BC strategies: matched filter, zero forcing, minimisation of mean square error and BC-strategy-aware transceive beamforming. It is shown that the sum rate performance of non-regenerative MGMW relaying depends both on the chosen BC strategies and the applied transceive beamforming at the RS.

In non-regenerative two-way relaying, two communicating nodes transmit simultaneously to the Relay Station (RS). The RS processes the received signal and forwards it to both nodes simultaneously. In order to obtain its partner's information, each node performs self-interference cancellation by subtracting its transmitted signal from its received signal. However, in multi-user two-way relaying, the interference at each node is not only the a priori self-interference, but also the interference from the other two-way pairs' nodes. Using Zero Forcing (ZF) transceive beamforming, the RS spends unnecessary energy to cancel the interference that can be cancelled by the nodes. Therefore, we propose to apply pairaware transceive beamforming (PATB) at the RS to cancel only the other-pair interference and let each node cancels its self-interference. Two PATB schemes are proposed, namely, pair-aware (PA) matched filter (PA-MF) and PA semidefinite relaxation of maximising the minimum signal to noise ratio (PA-SDR). From sum rate analysis, PA-SDR outperforms PA-MF, and both outperform non-PA ZF.

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