Space-time physical-layer network coding: Harnessing interference in multi-way communication

In this paper, a space-time physical-layer network coding method is proposed in fully-connected multi-way relay networks. The proposed method includes two essential steps: side-information learning; and space-time relay transmission. In the phase of side-information learning, sets of users are scheduled to transmit messages over networks and the remaining users and relays overhear the transmitted messages to learn the interference patterns. In the phase of space-time relay transmission, multiple relays cooperatively transmit linear combinations of received messages in the previous phase using space-time precoding so that all users simultaneously harness their side-information in decoding. With this transmission technique, it is shown that the sum of degrees of freedom of the network is improved compared to existing interference management methods. Our key finding is that efficiently exploiting both transmitted and overheard messages as side-information brings substantial performance gains to fully-connected multi-way relay networks.