Characterization of IDF and SDF Relaying Protocols in SSK Modulation Systems

In this paper, the performance of space shift keying (SSK) modulation is investigated in a cooperative communication system, using incremental decode-and-forward (IDF) and selective decode-and-forward (SDF) relays. The IDF and SDF relays use instantaneous signal-to-noise ratio (SNR) to verify the quality of received signal, which is not applicable to SSK modulation. In addition to instantaneous SNR, channel coefficients play the main role in the performance of SSK modulation. Moreover, in this modulation scheme, the active channel coefficient is unknown. In this paper, instead of instantaneous SNR, a new reliable criterion is introduced to be used in the IDF or SDF protocols for SSK modulation. This criterion is based on the Euclidean distances between active channel coefficient and other inactive channel coefficients. The analytical expressions are derived to calculate the average bit error rate (ABER) and the power consumptions in a cooperative system, over Rayleigh fading channels, for both IDF and SDF relaying protocols. There is good agreement between the Monte Carlo simulated and analytical results. These results show that this Euclidean distance-based criterion, in IDF or SDF relaying protocols, improves cooperative diversity gain and the ABER performance significantly.