Outage Analysis of Superposition-Modulation-Aided Network-Coded Cooperation in the Presence of Network Coding Noise

We consider a network, where multiple source–destination (S–D) pairs communicate with the aid of a half-duplex relay node (RN), which adopts decode-and-forward (DF) relaying and superposition modulation (SPM) for combining the signals transmitted by the source nodes (SNs) and then forwards the composite signal to all the destination nodes (DNs). Each DN extracts the signals transmitted by its own SN from the composite signal by subtracting the signals overheard from the unwanted SNs. We derive tight lower bounds for the outage probability for transmission over Rayleigh fading channels and invoke diversity combining (DC) at the DNs, which is validated by simulation for both the symmetric and the asymmetric network configurations. For the high signal-to-noise ratio regime, we derive both an upper bound and a lower bound for the outage performance and analyze the achievable diversity gain. It is revealed that a diversity order of 2 is achieved, regardless of the number of SN–DN pairs in the network. We also highlight the fact that the outage performance is dominated by the quality of the worst overheated link because it contributes most substantially to the network coding (NC) noise. Finally, we use the lower bound for designing a relay selection scheme for the proposed SPM-based network-coded cooperative communication (SPM-NC-CC) system.