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This paper studies the resource allocation for Orthogonal Frequency-Division Multiple-Access (OFDMA) relay network with multiple source nodes, multiple relay nodes, and a single destination node. First, the optimal source/relay/subchannel allocation problem is formulated as a binary integer programming problem with the objective of minimizing overall transmission power under the constraints on the Bit-Error-Rate (BER) and data rate. However, the optimal solution to the optimization problem is computationally complex to obtain and may be unfair. Assuming knowledge of the instantaneous channel gains for all links in the entire network, an iterative three-step sub-optimal fair resource allocation algorithm with low complexity is proposed.