Group Delay Modeling,Measurement And Calibration Technique For High Accuracy Navigation Receiver

High accuracy navigation receiver is widely distributed and used in the Ground Section, Space Section, Control Section of the Satellite Navigation System, which is important measuring equipment for time synchronization and precise orbit determination in the Satellite Navigation System, and is the foundation to guarantee the quality of the navigation service.In the high accuracy navigation receiver, the correlation peak distortion introduced by the non-ideal channel group delay will bring in ranging error, and has become the major source of the errors that can’t be modeling in the pseudorange measurement. So it is important to do research in the group delay modeling,measurement and calibration technique.The distortion of the signal correlation peak is related to group delay, and most research think that the signal correlation peak will be distorted if group delay within the signal bandwidth is fluctuant, and different group delay fluctuations will lead to different distortions in the signal correlation peak. In fact, there are situation that two group delays with different shape may generate two correlation peaks that have almost the same shape, and the difference of delay estimation can be ignore. Thus, this paper proposes define of the equivalent group delay, this define can simplify the analysis of the effect of the non-ideal group delay on the correlation peak distortion, and instruct the group delay measurement and calibration, when measuring and calibrating the group delay, it is only need to ensure that the group delay after calibration can be equivalent to the ideal group delay.At present, the effect of the non-ideal group delay on the high accuracy measurement is usually analysis by simulation, which has not the universality, and it is also inefficient. This paper do deep research on the inherent principle of the effect of the non-ideal group delay on the distortion of correlation peak, and establish a general group delay analysis model based on Fourier series, in this model, any group delay can be decomposed to a series of cosine group delay and sine group delay with limited orders, and the transfer function that has cosine group delay or sine group delay can be decomposed to the summation of a series of linear phase transfer functions with limited orders, thus the analytic relationship between non-ideal group delay and signal correlation peak distortion is found for the first time. In this model, the decomposed issues that has low frequency is the major factor that influence the signal correlation peak, and the effect of the decomposed issues has high frequency on the signal correlation peak is small, and even can be ignore. This model can be used to analysis the effect of the group delay on the delay estimation, and can instruct the group delay measurement and calibration, it is only need to calibrate the decomposed issues that can distort the correlation peak.This paper proposed a new group delay measurement based on the narrow-band spread spectrum signals, this method solves the problem of the traditional group delay measurement method that can satisfy the high measuring accuracy and high frequency resolution at the same time, and can implement high measuring accuracy with any frequency resolution, and can achieve the measuring accuracy about 0.01 ns. This paper also provide an optimal design for the measuring parameter:the wider the early-late correlation space is, the higher the measuring accuracy is; the more serious of the fluctuation of the group delay is, the lower code rate should be. For the most filters that used in the navigation application, the code rate with 1.023 MHz can be fine. And in simulation of this paper, for the cosine group delay whose fluctuation range is 50 ns and fluctuation period is 10.23 MHz, the narrow-band spread spectrum signals with code rate of 1.023 MHz can fulfill measuring accuracy about 0.01 ns.According to the group delay analysis model based on Fourier series and the define of the equivalent group delay, this paper propose a high accuracy measurement method for the equivalent group delay, this method measures the equivalent group delay by estimating the Fourier coefficient of the group delay. Simulation results indicated that after compensating the group delay with the group delay measured, the shape of the correlation peak and the idea correlation peak is almost the same, and the delay estimation error is less than 0.02 ns, which can be ignored.In the traditional group delay calibration techniques, the analog group delay equalization technique has poor measuring accuracy and it is un-flexible also, the frequency domain calibration technique is very complex because this method should do FFT and IFFT calculation with a large of data, the time domain calibration technique has low calculation complexity, but in the current algorithm, it is difficult to get an analytic express for the calibration filter, whose order is hard to determinate, and it is hard to demonstrate the calibrate performance theoretic also. This paper proposes a group delay calibrate algorithm based on the Fourier series model, whose filter has an analytic express. The algorithm can eliminate the effect of the non-ideal group delay on the delay estimation theoretic, and the implement efficiency is also fine, and can eliminate the effect of the non-ideal group delay with low orders of the filter. An experiment is fulfilled to validate this method, and experiment results indicate that a FIR filter with orders of 13 can eliminate the effect of the IF filter whose group delay fluctuation is about 80 ns on the signal correlation peak distortion and delay estimation bias.