Outage analysis of superposition modulation aided network coded cooperation in the presence of network coding noise

We consider a network, where multiple sourcedestination pairs communicate with the aid of a half-duplex relay node (RN), which adopts decode-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 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 upperbound as well as a lower-bound for the outage performance and analyse 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 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.<br/

Power allocation and group assignment for reducing network coding noise in multi-unicast wireless systems

In this paper, we consider physical-layer network coding (PNC) in a multi-unicast wireless cooperative network with a single relay. We aim to deal with the NC noise, i.e., an additional noise term due to applying NC, with the objective of improving the network data rate. Our approaches are based on relay power-allocation and group-allocation techniques. To this end, we provide a mathematical framework for the achievable information rate of the system with the notion of power assignment at the relay. Based on this framework, we present a novel power-allocation scheme to maximize the total information rate among all the source-destination communication sessions in the network. Further, we provide a closed-form solution for the two-unicast case. Simulation results show that the proposed relay power allocation can significantly help alleviate the adverse effects of NC noise. Next, we propose a group-allocation scheme to assign sessions to different groups for performing PNC at the relay. We combine power allocation and group allocation to further improve performance. The formulated joint optimization problem is NP-hard. Therefore, a suboptimal heuristic algorithm is proposed and implemented at the relay to solve this problem. From the simulation results, the proposed joint group assignment and power-allocation scheme achieves up to 64% overall data rate gain for the multi-unicast system compared with a single-group system with no relay power assignment. This observation shows that PNC can be efficiently harnessed in a multi-unicast cooperative network by exploiting proposed approaches