基于π/4-DQPSK码间相关特性的自动频率控制算法与实现

Algorithm and Realization of Automatic Frequency Control Based on Correlation Characteristic of π/4-DQPSK Codes

为了降低传统AFC算法的运算量,扩大追踪范围,基于软件无线电的思想,利用π/4-DQPSK相邻码元间的特殊相位跳变关系,提出一种利用差分解调数据直接计算频率偏移量的频偏估计算法,并实现接收机本振自动频率控制.阐述了π/4-DQPSK差分解调原理,进行了频率偏移量计算的模型推导,对比分析了新算法与传统算法在AWGN信道和TU50多径信道下的性能.经Monte-Carlo仿真结果与实际测试验证,该算法计算简单,频率控制效果好,收敛速度快,运算量小,非常适合在工程中应用.

In order to reduce the computational complexity and expand the tracking scope of the traditional AFC method, a new AFC method for π/4-DQPSK modulation is proposed based on software-defined radio, using the phase correlation between the continuous bits. The method can calculate frequency offset directly from differential demodulated π/4-DQPSK signals to automatically correct receiver local oscillator frequency. The principle of π/4- DQPSK differential demodulation is elaborated. The mathematical model of frequency offset calculation is estab- lished. The performance of the new method and that of the traditional method in AWGN channel and TU50 channel are analyzed and compared. The Monte-Carlo simulation and application test results show that the proposed method is good and fast in convergence and small in computational complexity, and thus suitable for practical application.