A rate adaptive physical layer network coding scheme: Joint network coding and modulation

The physical layer network coding (PNC) technique exploits the broadcast nature of wireless channels to obtain additional transmission efficiency gains. In this paper, the authors first find and prove that: if we rotate the modulation constellations of multiple sources by proper angles, the points of the equivalent superpositioned constellation at the receiver would cluster into clouds, with each cloud center corresponding to a different sum of the source symbols. Utilizing this nature, this paper proposes a novel PNC scheme which is able to adapt the throughput and symbol error probability according to channel conditions, referred to as joint network coding and modulation (JNCM). The theoretical analysis and simulation results prove that JNCM achieves lower SER than complex field network coding, better throughput than PNC schemes over finite field and finally achieves a joint optimization of efficiency and reliability.