Time Domain Channel Estimation for OFDM-Based Amplify-and-Forward Cooperative Networks

Consider the scene that in a street environment, there is no direct channel between the source node and the destination node because of distance or obstacles, and it needs some relay nodes to do the cooperative communications. In this paper, we propose a time domain channel estimation method for an OFDM-based amplify-and-forward (AF) cooperative network. Different from the traditional frequency domain channel estimation, utilizing the special comb-type pilots and a simple transformation to the pilot subcarriers at each relay node, we do the time domain correlation processing to estimate the equivalent channel impulse response (CIR) from the source node to the destination node via each relay node. Based on this method, in order to reduce the effects of the equivalent noises from each relay node and the destination node, we propose two kinds of channel estimation methods, which are the time domain linear minimum mean square error (LMMSE) channel estimation and its simplified expression. Also, the corresponding Cramér-Rao bound (CRB) is derived. Simulation results show that our proposed methods have good MSE (Mean Square Error) performance. Compared with direct time domain channel estimation method, the simplified time domain LMMSE channel estimation is closer to the CRB.