Blind channel estimation using cooperative subcarriers for OFDM systems

This work introduces a novel blind channel estimation technique for orthogonal frequency division multiplexing (OFDM) systems over time- varying mobile channels. The proposed estimator exploits the channel correlation over consecutive OFDM symbols to estimate the channel parameters blindly. In the new estimator, particular subcarriers are modulated using M-ary phase shift keying (MPSK), and subcarriers with the same indices in the consecutive OFDM symbol are modulated using M-ary amplitude shift keying (MASK), replacing the pilots in pilot-aided systems. Consequently, all subcarriers are data-bearing, which leads to spectral efficiency improvement. The proposed estimator uses the feature that MPSK and MASK modulated symbols have sufficient channel state information (CSI) that enable them to cooperate in order to detect the MPSK symbols coherently and blindly. Then, the CSI at the corresponding MPSK symbols can be acquired in a decision-directed (DD) fashion. The performance of the proposed estimator is evaluated in terms of symbol error rate (SER) and mean-squared error (MSE), where an exact analytical formula is obtained for the SER of binary phase shift keying (BPSK) symbols in mobile radio channels with various time-varying rates. The obtained results show that the proposed estimator produces accurate channel estimates as compared to pilot-aided and state-of-the-art systems without additional complexity.