Channel estimation and symbol detection for AF relay system based on combined pilot

Obtaining the channel state information (CSI) of the cascaded (S-R-D) and the single-hop (R-D) channel is the key to achieve the cooperative diversity gain in a three-node amplify-and-forward (AF) cooperative relay system. To acquire the single-hop link CSI, a novel channel estimation scheme based on a combined pilot is proposed in this paper, which is a combination of a frequency division multiplexing (FM) pilot and a superimposed pilot (SP). The FM pilot was used in the source node. A low-power relay pilot sequence was superimposed on the information sequence received at the relay node. Then, the single-hop (R-D) channel estimation in frequency domain was completed by the superimposed pilot at the destination node. The data-dependent iterative interference cancellation (DDIIR) scheme was employed to improve the performance of the single-hop link channel estimation at the receiver. Compared with the existing estimation approaches, the estimation of the single-hop channel and cascade channel by the novel method proposed in this paper is relatively independent. Furthermore, this new procedure effectively improves the flexibility of the system and eliminates the error rate platform at high SNR. The simulation results confirmed the effectiveness of the new method.