Two-Dimensional Superposition Modulation and Power Allocation for Cooperative Wireless Communication System

Superposition modulation provides an alternative approach to transmit a node´s own data packets along with its neighbor´s relay packets in the same time- slot and frequency, which can improve spectral efficiency of cooperative wireless communication system. We propose a design criterion for two- dimensional superposition modulation based cooperative transmission where two users cooperate to transmit their data to a base station. We investigate M-PSK superposition modulation based cooperative scenario for Rayleigh fading channels and thoroughly derive the average symbol error rate (SER) of such system with decode-and-forward relaying. Furthermore, we introduce a design parameter called power allocation ratio, i.e., ratio of transmit power for relay data to total power, which can be adaptively changed within the derived limit. We also derive SER expressions in terms of the power allocation ratio and demonstrate its effect on average SER. Based on analytical results and computer based simulations, we show that the proposed scheme provides reduced SER and increased goodput compared to existing schemes in practical scenarios.