A MMSE-based joint timing synchronization and channel estimation scheme for two-way amplify-and-forward relay networks

In the two-way relay networks, the receive nodes are difficult to retrieve the mixture of signals transmitted from different terminal nodes with unknown timing offsets and unknown channel information. This paper presents a joint timing synchronization and channel estimation scheme for two-way amplify-and-forward relay networks to solve this problem. Based on a well-designed training sequence arrangement, delayed timing offset and cascaded channel impulse responses (CIR) in different transmit-relay-receive links can be obtained. The proposed approach utilizes three procedures to acquire timing offsets, inter-terminal delay (ITD), and cascaded CIRs at each terminal node. First, a coarse timing offset (CTO) estimation algorithm is applied to find CTO and ITD. Then, the generalized maximum-likelihood estimation algorithm with an observation vector is exploited to obtain relative timing indices and the corresponding cascaded CIR estimates in all transmit-relay-receive links. Finally, the fine time adjustment based on the minimum mean squared error criterion is performed to reacquire timing offsets, revise the ITD estimate, and reconstruct cascaded CIR estimates. From the simulation results, the proposed approach has excellent timing synchronization and channel estimation performance under multipath fading channels with line-of-sight and non-line-of-sight propagation.