Improved schemes for tracking residual frequency offset in DVB-T systems

Carrier frequency offset (CFO) synchronization is a crucial issue in the implementation of orthogonal frequency division multiplexing (OFDM) systems. Synchronization is performed in two stages: acquisition and tracking. After a first estimation and correction of the CFO performed in the acquisition stage, there still remains a residual frequency offset (RFO) due to real system conditions. This paper presents two new schemes for RFO tracking affecting a digital video broadcasting (DVB-T) system. Due to the nature of DVB-T, where data transmission is performed continuously, RFO tracking needs to be performed accurately during all the data length in order to correct the ICI and the phase rotation impairment produced by this RFO. Comparisons of the novel algorithms with two previously reported estimators in terms of mean square error (MSE), complexity and speed of convergence are performed. The proposed schemes improve performance and/or speed of convergence compared to the conventional estimators with a reduction of the computational complexity. Furthermore, a combined technique for RFO tracking involving the two new schemes is proposed. This method obtains the best results in terms of accuracy, convergence and complexity.