A Two-Step Frequency Offset Estimation Algorithm Using the iNET Preamble in Multipath Fading Channels

In multipath channels, because of the frequency selective fading, the carrier synchronization problem is very complicated. This paper proposes a two-step frequency offset estimation algorithm for SOQPSK-TG equipped with the iNET preamble and operating in multipath fading channels. It begins with improving the structure of the preamble in the case of keeping the frame structure of iNET pilot overhead unchanged. The improved Kay algorithm with large estimation range for coarse estimation is used to ensure the range of frequency offset estimation. And then, in order to improve the accuracy of frequency offset estimation, the L&R algorithm with higher estimation accuracy is used for fine estimation. At the same time, the modified Kay and L&R estimators are derived under the improved preamble structure. Simulations, performed over channel impulse response measured in multipath scenarios encountered in aeronautical telemetry, show the range of the proposed estimation synchronization scheme is two times the range of the classical estimators, and the estimation accuracy can reach the CRB.