采样噪声对北斗全球信号测距误差的影响分析

Ranging error analysis of sampling noise performance based on BeiDou global signals

随着北斗卫星导航系统的全球化,基于软件定义无线电的北斗接收机在北斗导航定位中的应用越来越广泛。但是北斗接收机在实时动态差分等高精度测量应用场景下,其基带采样ADC受到采样时钟抖动影响,再叠加固有的量化噪声和热噪声,对北斗信号的扩频测距精度产生不可忽略的影响。本文首先针对北斗公开的B1I、B1C、B2I、B2a和B3I 5种全球信号,描述了ADC采样中时钟抖动、量化噪声和热噪声等采样噪声的数学模型,提出了影响测距的信噪比综合公式,再通过载噪比进而得出测距误差的一般表达式,并给出了高精度测量要求下不同参数选择的工程化定量分析方法,然后针对不同参数对北斗信号测距误差的影响进行了仿真分析,仿真结果表明,在0.6 cm的测距误差目标下,要求时钟抖动不大于45 ps,接收机中心频率不大于80 MHz,带宽不小于25 MHz,量化位数不少于7位,载噪比不小于30 dB。最后,针对北斗B2I信号进行了实测实验,在时钟抖动为35 ps,接收机中心频率61.38 MHz,带宽32 MHz,量化位数12位,载噪比67 dB时,解算的测距误差为0.41 cm,验证了本文方法的有效性。

With the globalization of BeiDou satellite navigation system,BeiDou receivers based on software defined radio(SDR)are used more and more popular in BeiDou navigation and positioning.However,in the high precision measurement applications,such as real time kinematic(RTK)application,the baseband sampling ADC in BeiDou receivers suffers the influence of sampling clock jitter,which is added with the inherent quantization noise and thermal noise,and generates neglectable influence on the ranging error.In this paper,the BeiDou published global signals B1I,B1C,B2I,B2a and B3I are analyzed firstly.Secondly,the math models of the sampling noises including the clock jitter,quantization noise and thermal noise in ADC sampling are described in detail.Thirdly,the synthesized SNR formula is proposed,and the general expression of the ranging error is derived from the carrier-to-noise ratio(C/N0).An engineering quantitative analysis method for selecting different parameters under high accuracy requirement is given.Furthermore,aiming at the influence of different parameters on the BeiDou signal ranging error,simulation analysis was performed.Simulation results show that under the goal of ranging error of 0.6cm,it is required that the sampling clock jitter should not exceed 45 ps,the central frequency of the receiver should not be larger than 80 MHz,the bandwidth should not be less than 25 MHz,the quantization bit length should not be less than 7 bits,and the C/N0 should not be less than 30 dB.Finally,the test experiment on the BeiDou signal B2I was conducted.Under the conditions of the sampling clock jitter of 35 ps,the receiver central frequency of 61.38 MHz,the bandwidth of 32 MHz,the quantization bit length of 12 bits,and the C/N0 of 67 dB,the solved ranging error is 0.41 cm,which verifies the effectiveness of the proposed method.