一种新的卫星移动通信频率偏移估计算法

A New Frequency Offset Estimation Algorithm in Satellite Mobile Communication

频率偏移估计是卫星移动通信的一个重要问题。本文针对已有频偏估计算法在π／4-CQPSK调制后频偏估计不精确的问题进行分析，提出了一种新的时域特殊字频偏估计算法。该算法结合π／4-CQPSK调制的符号位置相关特性，通过“先粗略后精细”的频偏估计流程，基于同步点的相位均值计算粗频偏，修正后再利用π／4-CQPSK调制下各特殊字段的表达式计算精细频偏，两频偏之和为频偏估计值。结果表明该算法仿真结果与频谱仪FSQ26结果差值不超过1Hz，不确定度为0．5774．Hz。该算法可以应用于卫星移动通信系统EVM测量，并能够精确估计频偏。

Frequency offset estimation is an important problem in satellite mobile communication. The present frequency offset estimation algorithm is inaccurate after π/4-CQPSK modulation. This paper puts forward a new frequency offset estimation algorithm based on special fields in time domain. By considering the symbol position correlation of π/4- CQPSK modulation, this algorithm calculates the frequency offset by the procedure of ＂roush first and then fine＇. The rough frequency offset is calculated based on the phase mean of the synchronization point. After modification, the fine frequency offset is figured out with each special field expression under π/4-CQpSK modulation. The sum of the above two frequen- cy offsets is the estimation value of the frequency offset. It shows that the difference be- tween the simulation result of this algorithm and the value measured by FSQ26 spectrum analyzer is less than 1 Hz with the uncertainty of 0. 5774 Hz. The algorithm can be applied in EVM measurement of satellite mobile communication system, and figures out precise frequency offset.