Selective Decode-and-Forward Relaying Scheme for Multi-Hop Diversity Transmission Systems

A selective decode-and-forward relaying protocol for serial multi-hop diversity schemes, which adapts transmissions at the source and relays based on the instantaneous received signal-to-noise ratio at each relay, is developed and analyzed. Based on the proposed selective protocol, if the received signal- to-noise ratio at each relay exceeds a certain threshold, that relay combines, decodes, and re-encodes its received signals and then re-transmits. Otherwise, the source repeats its signal. It is shown that employing the proposed method significantly improves the system performance by achieving diversity order equal to the number of hops while maintaining the same maximum normalized spectral efficiency compared to a multi-hop transmission system employing a fixed decode-and-forward relaying scheme. An exact closed-form expression for calculating the outage probability of a serial multi-hop diversity scheme employing fixed decode-and-forward relaying strategy is also obtained. A rigorous mathematical analysis showing that the serial multi-hop diversity scheme offers no diversity gain is given.