Performance analysis and code design of distributed space-time trellis codes for the detection-and-forward systems

In this paper, we analyze the performance of a detection-and-forward (DF) relay system in slow and quasi-slow Rayleigh fading channels. In the first part of the paper, we assume perfect decoding at the relay. While in the second part, the relay node no longer decodes the signal from the source but demodulates it. We analyze the performance of this relay system by taking into consideration the imperfect demodulations made by the relay. We propose a detection metric to address the effect of demodulation errors. The upper bounds of the pairwise error probability (PEP) are derived for both cases in slow and quasi-slow Rayleigh fading channels, and the design criteria for the distributed space-time trellis codes (DSTTCs) are formulated accordingly. Based on the proposed design criteria, the new QPSK DSTTCs are constructed. Simulation has shown that the codes we designed based on the performance analysis can improve the system performance.