一种高动态弱GNSS信号跟踪解调算法研究与实现

在某些高动态弱信号场景中，载波相位难以锁定。为实现对高动态弱全球导航卫星系统(GNSS)信号的跟踪，考虑锁频环较锁相环更为鲁棒，提出了一种基于锁频环(FLL)+差分解调的算法，实现对GNSS信号的跟踪和解调。该算法采用二阶FLL实现对卫星信号的频率进行跟踪，差分解调算法实现对比特数据的解调。工程应用上，算法采用现场可编程门阵列和数字信号处理器(FPGA+DSP)的架构实现，在FPGA中实现信号的跟踪信号的前处理，在DSP中实现跟踪环路算法、位同步和差分解调。本文在Matlab平台中实现算法的仿真，通过模拟器平台和对天接收真实的GNSS信号对算法进行验证。仿真结果与实验结果表明，该算法在高动态弱信号条件下能实现对卫星信号的稳定跟踪和数据的解调，克服了锁相环难以锁定导致数据无法解调的难题，最终实现GNSS信号在该条件下的位置、速度和时间(PVT)解算。

Research and implementation of tracking demodulation algorithm for high dynamic and weak GNSS signal

In some high dynamic weak signal scenarios, the carrier phase is difficult to lock. In order to track the high dynamic weak Global Navigation Satellite System(GNSS) signal, considering that the Frequency Locked Loop(FLL) is more robust than the Phase-Locked Loop(PLL), an algorithm based on FLL+differential demodulation is proposed to track and demodulate the GNSS signal. The algorithm uses the second-order FLL to track the frequency of satellite signal, and the differential demodulation algorithm is employed to demodulate bit data. In engineering application, the algorithm adopts the architecture of Field Programmable Gate Array+Digital Signal Processing(FPGA+DSP), realizes the pre-processing of signal tracking signal in FPGA, and realizes the tracking loop algorithm, bit synchronization and differential modulation in DSP. The simulation of the algorithm is performed in Matlab platform, and the algorithm is verified by receiving the real GNSS signal from the simulator platform and the sky. The simulation and experimental results show that the algorithm can realize the stable tracking of satellite signal and data demodulation under the condition of high dynamic and weak signal, and overcome the problem that the data cannot be demodulated due to the difficulty of PLL locking, finally realize the Position Velocity and Time(PVT) solution of GNSS signal under this condition.