Physical network coding for asymmetric data rate transmission via improved nesting QAM constellations

A novel rectangular QAM nesting method for physical network coding is proposed for the broadcast phase in two-way relay networks, by which the asymmetric data rate transmission is achieved with a higher order modulation constellation carrying the higher data rate information while the lower data rate information carried by a sub-constellation nested in the higher order constellation. The novel nesting idea is implemented by two successive steps. Firstly the sub-constellations are constructed via Ungerboeck´s set Partitioning (UP). Then we attempt to maximize the minimum distance between the signal points in each sub-constellation through changing the position of some signal points in a simple but effective way. And thereby, the optimized physical network coding is produced with improved BER performance and higher throughput. The results are clearly demonstrated by both theoretical analysis and simulation results.