Optimal Power Allocation in Linearly Coded OFDMA Relay Networks

In this paper, a linearly coded (LC) relaying scheme is proposed for multiuser relay network in which a number of users communicate simultaneously with a common destination with the help of one relay node, by using orthogonal frequency division multiple access (OFDMA). The proposed linear coding at the relay node enables exploiting the frequency diversity in the relay-to-destination (R-to-D) link. Moreover, closed-form pairwise error probability (PEP) and asymptotically tight bit error rate (BER) for linearly coded orthogonal frequency division multiplexing (LC-OFDM) system are derived so that an accurate end-to-end (source to destination) BER expression can be obtained. Based on this accurate end-to-end BER expression, optimal power allocation strategy between source nodes and relay node is easily developed by convex optimization when the total transmit power is a constraint. Simulation results show that our optimal power allocation consumes only half the power of equal power allocation in high signal-to-noise ratio (SNR) region.