Subcarrier allocation, power allocation, and partner selection algorithms are examined for amplify-and-forward cooperative multicarrier systems. Consider a network that consists of multiple cooperative pairs employing a two-phase cooperation scheme where the users first transmit their own messages on each of their subcarriers in Phase I and either retransmit their own messages or relay the messages of their partners in Phase II, i.e., the cooperative phase. In general, subcarrier allocation and partner selection problems are known to be intractable for systems with large number of users and subcarriers. In this work, we propose a mathematically tractable approach to address these issues and show its effectiveness compared to existing algorithms. Specifically, we consider a relaxed problem formulation, where each subcarrier is able to retransmit or relay for all other subcarriers in Phase II over orthogonal channels, and derive the optimal power allocation for this scenario. Efficient subcarrier allocation policies can then be derived based on the power allocation result and a sufficient condition is obtained to determine when cooperation is helpful among two users. A partner selection algorithm is then devised based on the sufficient condition. Given the subcarrier allocation scheme, the optimal power allocation among subcarriers in the cooperative phase can be shown to be a convex optimization problem and, thus, can be solved efficiently using standard convex optimization tools. The efficacy of the proposed algorithms is demonstrated through numerical simulations.
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