In this paper, we propose transmit power adaptation scheme for downlink multiple relay orthogonal frequency division multiplexing (MR-OFDM) system to maximize total data rate with fixed bit error rate (BER) and sum power constraint. At first, by allocating the same transmit power at each subcarrier, the proposed scheme only has to select the best subcarriers to each relay station (RS) for both base station to RS link and RS to mobile station link. For efficient subcarrier allocation, the proposed scheme employs an iterative method utilizing Hungarian algorithm. In numerical results, data rate of MR-OFDM based on the proposed scheme is compared to that of the single relay OFDM (SR-OFDM) which does not obtain multiple relay diversity gain. It is also shown that the performance loss of the proposed scheme is negligible compared to the optimal scheme, while its computational complexity is reduced considerably.
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