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Design and Analysis of Hierarchical Physical Layer Network Coding

This paper proposes a new relaying technique, hierarchical physical layer network coding (H-PNC), aimed at increasing the spectrum and energy efficiency in multi-hop wireless networks by supporting two bi-directional traffic flows simultaneously. H-PNC is applicable to the scenario in which two source nodes exchange data with the help of a relay, and the relay also needs to exchange data with one source node in an asymmetric two-way relay channel network, where the channel conditions of two source-relay links are asymmetric. H-PNC arranges transmissions in two stages, the multiple access (MA) stage and the broadcast (BC) stage. In the MA stage, the source node with the better channel to the relay can superimpose the symbol targeting to the relay on the symbol targeting to the other source node. In the BC stage, the relay can superimpose the symbol targeting to the source node with the better channel on the broadcast symbol. Thus, one more bidirectional information exchange is achieved beyond traditional PNC. Designs and optimizations of three H-PNC schemes are presented, and the error performance of QPSK–BPSK H-PNC is derived. Extensive simulations have been conducted to evaluate the system performance. Both theoretical analysis and simulation results demonstrated that H-PNC achieves a substantial performance gain.