Building blocks of physical-layer network coding

This paper investigates the fundamental building blocks of physical-layer network coding (PNC). Since its conception, PNC has developed into a subfield of network coding investigated by many. Most of the prior work, however, focused on the simplest communication setup in which PNC could be applied, namely the two-way-relay channel (TWRC). Studies of the application of PNC in general networks are relatively few. This paper is an attempt to fill this gap. To do so, we put forth two ideas: 1) For the purpose of scheduling transmissions, a general network can be decomposed into small building blocks of PNC, referred to as the PNC atoms. 2) TWRC is only one of many possible PNC atoms - besides TWRC, we identify eight other PNC atoms. We present formal definitions for the nine PNC atoms. We then formulate the PNC scheduling problem as a linear program based on the decomposition principle stated in 1) above. Two major results of our simulation experiments are as follows. First, under the decomposition framework, the throughput performance of PNC is significantly better than those of the traditional multi-hop scheme and the non-physical-layer network coding scheme - e.g., under heavy traffic volume, PNC can achieve 100% throughput gain relative to the traditional multi-hop scheme. Second, PNC decomposition based on a variety of different PNC atoms yield much better performance than PNC decomposition based on the TWRC atom alone.