Iterative time domain estimation of rapidly changing channel for OFDM systems in a cognitive radio context

Rapidly changing channels typically occurs in high speed situations where Doppler phenomena, related to the terminal´s high speed, affects the use of OFDM systems by producing a loss of orthogonality between different carriers. Thus, the channel estimation and equalisation become a challenging problem especially when the number of pilot carriers is limited. In this paper we make use of the cognitive abilities provided by cognitive radio systems in order to propose an iterative Time Domain Linear Minimum Mean Square Error (TD-LMMSE) estimation algorithm for rapidly changing channels in OFDM system. The TD-LMMSE emulates the effect of a sliding window, and iteratively remove the interference caused by the data field. Simulation results, showing a significant gain in terms of MSE and Bit Error Rate (BER) compared to other state of the art algorithms are reported over a wide Signal-to-Noise Ratio (SNR) range.