Modified CMA method and implementation for time-varying OFDM channel estimation

In a typical wireless LAN application exploiting the OFDM technology, the preamble is usually used to acquire the channel state information in front of data payload. However, if the length of the frame is short, the bandwidth efficiency is restricted by the overhead due to the frame. For such an application that the length of the frame is long, we have to take into account the time-varying effect. In this paper, we study a semi-blind channel estimation method for improving bandwidth efficiency. Although the decision feedback method can be used for channel tracking, the well-known error propagation problem can seriously degrade the system performance. In our work, the semi-blind channel tracking method applies a decision error criterion to adaptively change the use of the error control signal between the constant modulus algorithm and the decision feedback in order to avoid the error propagation problem. Simulation results show that the proposed semi-blind channel tracking scheme has better BER performance than the decision feedback method.