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In relay-aided wireless transmission systems, one of the key issues is how todecide assisting relays and manage the energy resource at the source and eachindividual relay, to maximize a certain objective related to systemperformance. This paper addresses the sum rate maximized resource allocation(RA) problem in a point to point orthogonal frequency division modulation(OFDM) transmission system assisted by multiple decode-and-forward (DF) relays,subject to the individual sum power constraints of the source and the relays.In particular, the transmission at each subcarrier can be in either the directmode without any relay assisting, or the relay-aided mode with one or severalrelays assisting. We propose two RA algorithms which optimize the assignment oftransmission mode and source power for every subcarrier, as well as theassisting relays and the power allocation to them for every {relay-aided}subcarrier. First, it is shown that the considered RA problem has zeroLagrangian duality gap when there is a big number of subcarriers. In this case,a duality based algorithm that finds a globally optimum RA is developed.Second, a coordinate-ascent based iterative algorithm, which finds a suboptimumRA but is always applicable regardless of the duality gap of the RA problem, isdeveloped. The effectiveness of these algorithms has been illustrated bynumerical experiments.

Sum Rate Maximized Resource Allocation in Multiple DF Relays Aided OFDM Transmission