Wireless transmission with cooperation on demand for slow and fast fading environments

Mobile users with single antennas can still take advantage of spatial diversity through repetition based cooperative transmission. In this paper, we consider a scheme in which the relay chooses to cooperate only if the source-destination channel is of an unacceptable quality. In our study, we consider a regenerative relay in which the decision to cooperate is based on a signal-to-noise ratio (SNR) threshold and consider the effect of the possible erroneously detected and transmitted data at the relay. We derive an expression for the end-to-end bit-error rate (BER) of binary phase-shift keying (BPSK) modulation and look at the optimal strategy to minimize this end-to-end BER at the destination for high SNR. Some selected performance results show that computer simulations based results coincide with our analytical results.