Blind channel estimation for hierarchical modulation in OFDM systems

In this paper, we propose a blind channel estimation method for advanced terrestrial digital multimedia broadcasting (AT-DMB) systems which use orthogonal frequency division multiplexing with hierarchical subcarrier modulation. The AT-DMB system adopts hierarchical 16-ary quadrature amplitude modulation to ensure backward-compatibility with the traditional T-DMB systems, which use differential quadrature phase shift keying for subcarrier modulation, and to support higher transmission rate. Due to the hierarchical modulation, the conventional T-DMB signal and the additional signal have different error rate at same signal to noise ratio. The proposed method exploits the reliability difference and weighs the decided symbols according to the reliability of them to improve the accuracy of the channel estimates. Through computer simulations, we verify the proposed method.