Performance analysis of cooperative-diversity wireless systems with adaptive modulation and imperfect channel state information

Cooperative diversity is achieved by utilizing neighboring terminals as relays. These relays can forward copies of the same signal to the destination using independent paths to provide spatial diversity. One of the main challenges of cooperative diversity is the throughput loss due to the extra resources needed for relaying. Adaptive modulation can be used to convert the Signal-to-Noise Ratio (SNR) gain (from the cooperative diversity) to throughput enhancement in order to compensate for the throughput loss. The availability of accurate Channel State Information (CSI) is essential for cooperative-diversity systems. However, perfect CSI is not always available in wireless systems. In this paper, we determine analytically the average throughput and bit error rate (BER) of cooperative-diversity systems with adaptive modulation and imperfect CSI over Rayleigh fading channel. Simulation results are also used for verification. Results show that imperfect CSI slightly lowers the throughput gain of the cooperative-diversity system. However, the cooperative-diversity system with imperfect CSI still outperforms the direct transmission.