A relay system where two users are served by one Base Station (BS) and one Relay Station (RS) is focused on. A scheme based on Superposition Coding (SC) for Decode-and-Forward (DF) half-duplex relaying is proposed. Thanks to its design and power allocation ratios derived analytically, the proposed scheme is able to serve both users simultaneously, while attaining the same sum rate as the optimal benchmark scheme that exclusively allocates the best user. Simulation results show considerable fairness improvement over a large range of SNRs. © 2011 IEEE.