Blind estimation of multipath delays in OFDM systems

In order to coherently detect the transmitted data symbols, an orthogonal frequency division multiplexing (OFDM) receiver requires reliable identification and equalization of the experienced wireless multipath fading channels. The information of path delays plays an important role in the procedure of identification and equalization. The need for high data rates motivated the search for blind identification and equalization methods because they save bandwidth by avoiding the use of training sequences. In OFDM systems, multipath fading channels introduce interference between adjacent symbols which can be prevented by inserting a cyclic prefix (CP) before each symbol. In this paper, we find that the power of the interference in the CP interval can be estimated by using the circular convolution and based on the variations of the interference power, the time delay of each path can be estimated blindly.