Selective fractional incremental relaying protocol in cooperative systems

In cooperative systems, the fractional incremental relaying (FIR) protocol can achieve higher spectral efficiency than the traditional incremental relaying (IRL) protocol by transmitting a fraction of packet, instead of the whole packet, at a time when retransmission is needed. The incremental redundancy (IRD) protocol can also be utilized when retransmission is necessary. Based on the two protocols, a novel protocol termed as selective fractional incremental relaying (SFIR) is presented in this paper. The FIR and the IRD protocols are combined in the SFIR protocol, when retransmission is needed, one of the two protocols is adaptively selected according to the channel conditions. The boundary condition of the SFIR protocol is presented by analyzing and comparing the performance of the FIR and the IRD protocols. Simulation results are also given to prove that the proposed SFIR protocol makes more efficient use of channel freedom degrees than the FIR and the IRD protocols do.