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Interference Cancellation at the Relay for Multi-User Wireless Cooperative Networks

We study multi-user transmission and detection schemes for a multi-access relay network (MARN) with linear constraints at all nodes. In a $(J, J_a, R_a, M)$ MARN, $J$ sources, each equipped with $J_a$ antennas, communicate to one $M$-antenna destination through one $R_a$-antenna relay. A new protocol called IC-Relay-TDMA is proposed which takes two phases. During the first phase, symbols of different sources are transmitted concurrently to the relay. At the relay, interference cancellation (IC) techniques, previously proposed for systems with direct transmission, are applied to decouple the information of different sources without decoding. During the second phase, symbols of different sources are forwarded to the destination in a time division multi-access (TDMA) fashion. At the destination, the maximum-likelihood (ML) decoding is performed source-by-source. The protocol of IC-Relay-TDMA requires the number of relay antennas no less than the number of sources, i.e., $R_a\ge J$. Through outage analysis, the achievable diversity gain of the proposed scheme is shown to be $\min\{J_a(R_a-J+1),R_aM\}$. When {\small$M\le J_a\left(1-\frac{J-1}{R_a}\right)$}, the proposed scheme achieves the maximum interference-free (int-free) diversity gain $R_aM$. Since concurrent transmission is allowed during the first phase, compared to full TDMA transmission, the proposed scheme achieves the same diversity, but with a higher symbol rate.