In this paper

we propose a new adaptive dual mode semi-blind channel estimator based on iterative soft information processing.A new reliability measure function is constructed to calculate the reliability factor of the reconstructed signal from the decoder and soft mapping.An option is made adaptively between the decision directed mode and blind estimation mode by comparing the reliability factor with a specified threshold.The estimated channel frequency response can improve the performance of the iterative receiver.Simulation results show that the proposed algorithm combines the two algorithms’ advantages and limits the conventional DD mode’s error propagation.It can track the time-varying channel efficiently without scattered pilots and achieve good system performance.