Wireless Bidirectional Relaying Using Physical Layer Network Coding With Heterogeneous PSK Modulation

Abstract

In bidirectional relaying using physical layer network coding (PLNC), it is generally assumed that users employ same modulation schemes in the multiple access phase. It may not be desirable for the users to always use the same modulation schemes, particularly when user-relay channels are not equally strong. Such a scheme is called heterogeneous PLNC where users employ different modulation schemes. In this paper, we provide a general analytical framework to find the network coding maps to be used at the relay during the broadcast phase, when the users employ heterogeneous, but symmetric phase-shift keying modulations. The fade state plane is partitioned into regions, where given network coding maps are employed. This partition has been obtained analytically, which is computationally efficient when compared to the computationally intensive approach taken by Zhang et al. which uses brute force computer-based search. Performance results are provided in terms of relay error rate and bit error rate.