Throughput maximization through adaptive decode-remodulate-and-forward relaying scheme

This paper deals with the throughput maximization for a new cooperative relaying scheme combined with an adaptive modulation technique. More precisely, we propose a new adaptive Decode-Remodulate-and-Forward (DRF) scheme where the relay decodes and remodulates the received signal with the appropriate modulation scheme before relaying it to the destination. The modulation constellations at the source and relay nodes can be different in order to adapt them to the channels qualities and to maximize the end-to-end throughput. The destination operates a soft-combining, relying on the LLRs (Log Likelihood Ratio) of signals emanating from the source and the relay. Our approach for throughput optimization, applied for DRF scheme in uplink CDMA communications, is carried on while keeping the global multiple-access-interference (MAI) cost constant. This optimization constraint is introduced to ensure throughput maximization with no impairment to the global system performance due to MAI. Simulation results show that the proposed adaptive DRF cooperation protocol provide a significant enhancement, in terms of system throughput, over the direct transmission scheme.