A random access scheme with physical-layer network coding and user identification

A slotted random access scheme is proposed that is based on physical-layer network coding. The scheme uses signature codes that enable the receiver to detect which users are active in each round and which linear combination of packets is received. Feedback enables in each round, one of the users to drop a packet, keeping the queue sizes limited. It is proven that for a broad class of feedback mechanisms the scheme is stable in the sense that the receiver can eventually decode all packets. Numerical results demonstrate that the scheme performs well in terms of the expected queue size, the maximum delay as well as the expected number of retransmissions per packet.