PiPNC: Piggybacking Physical Layer Network Coding for multihop wireless networks

This paper proposes a new relaying technique, Piggybacking Physical Layer Network Coding (PiPNC), which is most favorable in the scenario that two source nodes exchange data with the help of a relay, and the relay also needs to exchange data with one source node. PiPNC arranges transmissions in two stages, a multiple access (MA) stage and a broadcast (BC) stage, which compose one transmission cycle. In the MA stage, one of the source nodes (with a better channel quality to the relay) can piggyback the symbol targeting to the relay on the symbol targeting to the other source node. In the BC stage, the relay can piggyback the symbol targeting to the source node (with a better channel) on the broadcast symbol. In this way, two bidirectional information interchanges are achieved in one transmission cycle. Designs and optimizations of two PiPNC schemes are presented, and extensive simulations have been conducted to evaluate the system performance and identify the optimal location of the relay.