Cooperative Multiple Access Systems Using Superposition Modulation

In this paper we propose a spectrally efficient cooperative protocol for multiple access systems based on superposition modulation, which allows each user to transmit its own information and relay the data from the other users simultaneously. Analytical results developed in this paper show that the proposed protocol can provide better outage probability and larger diversity order than that of the direct transmission and selection relaying schemes. Moreover, we derive the probability density function of the mutual information of the proposed protocol. Using this density we study the outage and ergodic capacities, which show that the proposed scheme can provide larger ergodic and outage capacities than the existing cooperative schemes.