Resource Allocation for Selection-Based Cooperative OFDM Networks

This paper considers resource allocation to achieve max-min fairness in a selection-based orthogonal frequency division multiplexing network wherein source nodes are assisted by fixed decode-and-forward relays. Crucial design questions such as whether to relay, r elay assignment and power allocation form a combinatorial problem with exponential solution complexity. The first set of problems assume perfect source-relay channels and that sources distribute power equally across subcarriers. The solutions based on these simplifications help illustrate our general methodol ogy and also why these solutions provide tight bounds. We then formulate the general problem of transmission strategy selection, relay assignment, and power allocation at the sources and relays considering all communication channels, i.e., imperfect sourcerelay channels. In both sets of problems, transmissions over subcarriers are assumed to be independent. Given the attendant problems of synchronization and the implementation using a FFT/IFFT pair, resource allocation at the subcarrier level appears impractical. We , therefore, consider resource allocation at the level of the entire OFDM block. While optimal resource allocation requires an exhaustive search, we develop tight bounds with lower complexity. Finally, we propose a decentralized block-based relaying scheme. Simulation results using the COST-231 channel model show that this scheme yields close-tooptimal performance while offering many computational benefits.