Network Coded Distributed Spatial Modulation for Relay Networks

Distributed spatial modulation (DSM) is a cooperative diversity protocol for a wireless network, whereby communication from a source to a destination is aided by multiple intermediate relays. The main advantage of the DSM protocol is that it provides distributed diversity to the source's transmission, while simultaneously allowing the relays to efficiently transmit their own data to the destination. In this paper, network coding is combined with DSM in order to increase the data rate of the source-to-destination link while maintaining the same diversity order of 2 for this data. Two methods of detection are proposed for implementation at the destination node: an error-aware maximum likelihood (ML) demodulator which is robust to demodulation errors at the relays, and a low-complexity suboptimal demodulator which assumes correct demodulation at the relays. The system bit error rate (BER) performance is measured under two different relay geometries. Simulation results show that for the same overall system throughput, the proposed network coded DSM protocol can increase the source-to-destination data rate by approximately 33.3% compared to the conventional DSM system, while still guaranteeing a similar BER as for DSM for both of the considered channel geometries.