Signal-Aligned Network Coding in Interference Channels with Limited Receiver Cooperation

Abstract

In this paper, we propose the ideas of signal-aligned network coding (SNC). We present the ideas in two-user time-varying interference channels with limited receiver cooperation. We assume that the receivers are connected to a central processor via wired cooperation links with individual limited capacities. Our SNC scheme determines the precoding matrices of the transmitters so that the transmitted signals are aligned at the receivers. The aligned signals are then decoded into linear combinations of messages by physical-layer network coding strategy. The key idea of our scheme is to ensure that independent linear combinations of messages, also known as network-coded messages, can be decoded at the receivers. Hence the central processor can recover the original messages of the transmitters by solving the linearly independent equations. We prove that our SNC scheme achieves full degrees of freedom (DoF) by utilizing signal alignment and physical-layer network coding. Simulation results show the DoF achieved by our SNC scheme almost doubles that by the orthogonal transmission scheme in two-user time-varying interference channels with limited receiver cooperation. The performance improvement of our SNC scheme mainly comes from efficient utilization of the signal subspaces for conveying independent linear combinations of messages to the central processor.