Network Coded Distributed Spatial Modulation for Relay Networks

Abstract

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.

Distributed Spatial Modulation Aided NOMA

“…Using the equation (13) in (15), and considering the assigned energy for each symbol according to the NOMA principle, the probability of error for the weaker symbol is given by…”

“…This is possible since the relaying process operates by using the index of the activated (transmitting) relay [11], [12]. Targeting an increased source-to-destination data rate, a network coded version of DSM was introduced in [13] which increases the source data rate by 33% compared to DSM. Other research considers a virtual full-duplex DSM (VFD-DSM) system which is able to transmit a new source symbol in every time slot [14], [15].…”

Virtual Full-Duplex Distributed Spatial Modulation: A New Protocol for Cooperative Diversity

“…The initialization for the backward metrics is given by (12), as shown at the top of the next page and the recursion operates as follows:…”

“…Here the termination of the frame with a zero symbol facilitates the initialization of the backward recursion via (12). Also, log-domain metric computation is recommended for implementation of this algorithm, as for the standard BCJR algorithm of [25]; in such an implementation, all metrics are replaced by their real logarithms, multiplication is replaced by addition, and addition is replaced by the well-known Jacobian logarithm (max * ) [34], defined by max * {x, y} = log(e x + e y )…”

“…The principle of SM was extended to the scenario of half-duplex cooperative networks in [7]- [12]. In particular, a distributed spatial modulation (DSM) protocol was proposed in [10], [11]; here, the relay which becomes active in the seond (cooperative) phase of communication is that which corresponds to the source symbol transmitted in the first (broadcast) phase.…”