Seek and Decode: Random Access with Physical-Layer Network Coding and Multiuser Detection

We present a novel scheme for Slotted ALOHA random access systems (RAS) that combines physical-layer network coding (PLNC) with multiuser detection (MUD). PLNC and MUD are applied jointly at the physical (PHY) layer in order to extract any linear combination of messages experiencing a collision within a slot. The set of combinations extracted from a whole frame is then processed by the receiver to recover the original packets. A simple pre-coding stage at the transmitting terminals allows the receiver to further decrease the packet loss rate. We present results for the decoding at the PHY layer as well as several performance measures at frame level, namely throughput, packet loss rate and energy efficiency. The results we present are promising and suggest that a cross layer approach leveraging on the joint use of PLNC and MUD can significantly improve the performance of RA systems in the presence of slow fading