一种面向水上应急救援定位设备的北斗信号捕获方法

A Beidou Signal Acquisition Technology for Sea Rescue Positioning Devices

为减小水上应急救援定位设备完成触发报警的耗时,提升设备在无先验信息冷启动情况下的定位效率,提出一种针对北斗三号B2a信号的捕获方法,利用匹配滤波器(Partial Matched Filters,PMF)对信号直接数字下变频,采用单边带捕获方法消除B2a信号自相关函数多峰特性,通过匹配相关结合快速傅里叶变换(Fast Fourier Transform,FFT),将码相位-多普勒频移的二维搜索降为一维的频率并行搜索,减少捕获时间。通过推导PMF长度和FFT点数对捕获性能的影响,分析相关损失与多普勒频移和相关器长度的关系,提出参数选择建议。结果表明:在信噪比-30 dB的情况下,仍可获得明显的最大相关峰,顺利完成对信号的捕获;与传统并行码相位搜索方法相比,该方法降低了对采样率的要求,有效减少硬件资源消耗、缩短捕获时间、提高捕获灵敏度。

A method of acquiring B2 a signal of BDS-3 is developed for accelerating no-prior-information cold starting of rescue positioning devices.Digital down conversion is done through matched filter and single side band acquisition is adopted to deal with the multi-peak characteristics of B2 a signal autocorrelation.The matched filter correlator combined with FFT(Fast Fourier Transform)transforms the 2 D(code phase-doppler shift)search into a single dimension(frequency)parallel search to accelerate the search process.The effect of the length of the matched filter and the number of FFT points on acquisition performance is derived and the relation between processing losses and correlator length for different doppler shift is analyzed.The suggestion about choosing of the parameter is given.Experiments show that correlation peak is high enough to achieve signal acquisition even when s/n ratio goes down to-30 dB.The design can achieve faster acquisition with better sensitivity while requiring lower sampling rate and less hardware resource.