Link adaptation algorithm for distributed coded transmissions in relay-aided OFDMA systems

We propose a link adaptation algorithm for cooperative transmissions in an OFDMA-based wireless system. The algorithm aims at maximizing the spectral efficiency of a relay-aided communication link, while satisfying the block error rate constraints at both the relay and the destination nodes. The optimal solution would be to perform an exhaustive search over a high-dimensional space determined by all possible combinations of modulations, code rates and information block lengths on the individual links; clearly, such an approach has an intractable complexity. Our solution is to use a link performance prediction method and a trellis diagram representation such that the resulting algorithm outputs a link configuration that conveys as many as possible information bits and also fulfills the block error rate constraints. The proposed link adaptation algorithm has linear complexity with the number of available resource blocks, but still provides a very good performance, as shown by simulation results.