  To address the coverage and capacity challenges in fifth-generation (5G)
wireless networks, the relay technique has been considered as a promising
solution and recently attracted great attentions from academia. The multiway
relay channel (mRC), which serves as a fundamental building block of a relay
network, defines the family of all possible information-flow patterns between a
relay node and its neighboring nodes. Combined with several new techniques,
such as physical-layer network coding (PLNC), signal and interference
alignments, multi-input multi-output (MIMO), etc., the mRC exhibits superior
capability to assist multiuser information exchange. In this article, we aim to
provide a comprehensive overview on the state-of-the-art of the mRC from the
perspectives of both information-theoretic and communication-theoretic studies.
The key results are summarized and discussed to identify the current research
progress of the mRC. Open problems and research challenges are also discussed
to spur future research towards the mRC.
