Design of Coded Slotted ALOHA Operated with q-ary Physical-layer Network Coding

We study a physical-layer network coding (PNC) enhanced slotted ALOHA (SA) scheme. At the transmitters, practical q-ary modulation codes (a practical lattice code) and contention resolution diversity SA (CRDSA) protocol are utilized, where active users send replicas of their coded-modulated messages in randomly selected slots. At the receiver, q-ary linear PNC is employed to compute L network-coded messages (or linear message combinations), which can be regarded as a practical embodiment of compute-forward and lattice decoding. Upon collecting a sufficient number of network-coded messages, the receiver carries out generalized matrix inversion to recover a subset of all active users' messages. Numerical results demonstrate dramatically increased throughput performance by as much as 80%, as well as advances in the trade-offs among system load, latency and energy efficiency.