CN110045398A - A Code Phase Zero-Crossing Deviation Suppression Method Based on Optimal Correlation Spacing - Google Patents

Abstract

The present invention provides a code phase zero-crossing deviation suppression method based on an optimal correlation interval, which effectively suppresses the code phase zero-crossing deviation of the early-delayed code-phase discriminator by designing the optimal correlation interval of the early-delayed code-phase discriminator, wherein Under the condition of known spreading code rate f _c and baseband signal sampling frequency f _s , the designed optimal correlation interval D is: The above-mentioned method for suppressing the deviation of code phase zero-crossing point based on the optimal correlation interval can be applied to satellite navigation signal receivers or other types of spread spectrum receivers. In the whole implementation process of the present invention, only the correlation interval of the code phase discriminator is changed. The present invention is simple to implement, has a small amount of computation, and is very convenient to implement, and can be directly used in traditional satellite navigation signal receivers or other types of expansion devices. in the pseudocode tracking loop in the frequency receiver.

Description

A Code Phase Zero-Crossing Deviation Suppression Method Based on Optimal Correlation Spacing

technical field

The invention belongs to the technical field of navigation, and in particular relates to a code phase zero-crossing point deviation method based on an optimal correlation interval, which can be used in satellite navigation signal receivers or other types of spread spectrum receivers.

Background technique

In time synchronization systems such as satellite navigation, the code phase of the spread spectrum signal is an important observation, which can provide users with high-precision and unambiguous time-difference observations. If the side lobes are not ignored, the spread spectrum signal is theoretically infinite bandwidth. When sampling an infinite bandwidth signal with a finite sampling rate, the resulting digital signal is distorted. Therefore, when estimating the code phase of a finitely sampled digital spread spectrum signal, in addition to thermal noise, there will also be a distortion error, which cannot be ignored in high-precision applications.

In the Early Minus Later (E-L) code phase discriminator, the zero-crossing deviation refers to the code phase estimation error caused by sampling distortion. There are two types of zero-crossing deviation, one is the insufficient code phase resolution of the digital signal correlation curve; the other is the asymmetry of the digital signal autocorrelation curve. The time domain resolution of a digital signal is determined by the sampling rate. For digital spread spectrum signals, the initial code phase information can be distributed at different sampling times and resolved in the correlation domain. Therefore, the code phase resolution in the correlation domain of the digital spread spectrum signal is much larger than the time domain phase resolution. Non-equivalent sampling is to improve the resolution of the digital spread spectrum code signal in the correlation domain by designing the sampling frequency of the non-integer multiple spread spectrum code rate, so as to effectively suppress the zero-crossing deviation caused by the resolution. However, unequal sampling does not eliminate the asymmetry of the autocorrelation curve, and therefore, does not eliminate the zero-crossing bias caused by the asymmetry. Some researchers have proposed a method for optimal sampling of spread spectrum signals, but this design requires too much sampling frequency and spread spectrum code rate, which is not conducive to engineering implementation.

SUMMARY OF THE INVENTION

Aiming at the defects of the prior art, the present invention provides a method for suppressing the zero-crossing deviation of the code phase based on the optimal correlation interval, aiming at suppressing the zero-crossing deviation of the early delayed digital code phase discriminator.

For realizing the technical purpose of the present invention, the following technical solutions are adopted:

A code phase zero-crossing deviation suppression method based on the optimal correlation interval, which can effectively suppress the code phase zero-crossing deviation of the early-delayed code-phase discriminator by designing the optimal correlation interval of the early-delayed code-phase discriminator. Under the conditions of spreading code rate f _c and baseband signal sampling frequency f _s , the optimal correlation interval D designed is:

An early-delay code phase discriminator, which adopts the above optimal correlation interval-based code phase zero-crossing deviation suppression method to suppress the code phase zero-crossing deviation of the early deceleration code phase discriminator. Specifically, the code phase zero-crossing point deviation of the early-delayed code-phase discriminator is effectively suppressed by designing the optimal correlation interval of the early-delayed code-phase discriminator, where at the known spreading code rate _fc and baseband signal sampling frequency _fs Under the condition of , the optimal correlation interval D designed is:

The above-mentioned method for suppressing the deviation of code phase zero-crossing point based on the optimal correlation interval can be applied to satellite navigation signal receivers or other types of spread spectrum receivers. That is, a satellite navigation signal receiver, comprising an early-delayed code phase discriminator, and the code phase of the early-delayed code-phase discriminator is suppressed by the optimal correlation interval-based code phase zero-crossing deviation suppression method as claimed in claim 1 Zero-crossing deviation. Specifically, the code phase zero-crossing point deviation of the early-delayed code-phase discriminator is effectively suppressed by designing the optimal correlation interval of the early-delayed code-phase discriminator, where at the known spreading code rate _fc and baseband signal sampling frequency _fs Under the condition of , the optimal correlation interval D designed is:

The beneficial effects of the present invention are:

By designing the optimal correlation interval of the early-delay code phase discriminator, the zero-crossing deviation of the code phase can be effectively suppressed. In addition, in the entire implementation process of the present invention, only the correlation interval of the code phase discriminator is changed, and complex operations such as matrix inversion and eigendecomposition are not involved. Therefore, the present invention is simple to implement, has a small amount of computation, and is also very convenient to implement. It is directly used in the pseudo code tracking loop in traditional satellite navigation signal receivers or other types of spread spectrum receivers.

Description of drawings

Fig. 1 is a schematic diagram of time domain sampling of early-late code signal;

Fig. 2 is the schematic diagram of the resolution of code phase and zero-crossing point deviation;

Fig. 3 is the code phase discrimination curve corresponding to different correlator intervals;

Fig. 4 is the code phase zero-crossing point deviation corresponding to different correlator intervals;

Figure 5 is a curve of the standard deviation of the zero-crossing deviation of the code phase as a function of the correlator interval.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

In time synchronization systems such as satellite navigation, the code phase of the spread spectrum signal is an important observation, which can provide users with high-precision and unambiguous time-difference observations. However, in a digital code phase discriminator, the finitely sampled baseband signal distorts the correlation peaks, resulting in code phase zero-crossing deviations. The invention proposes a code phase zero-crossing point deviation suppression method based on the optimal correlation interval, which can effectively suppress the code phase zero-crossing point deviation caused by the asymmetry of the correlation peak by designing the optimal correlation interval of the early-delayed code phase discriminator. . The simulation results show that the digital code phase discriminator based on the optimal correlation interval can suppress the zero-crossing deviation within the range of the correlation peak code phase resolution.

Specifically, the present invention provides a code phase zero-crossing deviation suppression method based on an optimal correlation interval, which effectively suppresses the code phase zero-crossing point of the early decrementing code phase discriminator by designing the optimal correlation interval of the early decrementing code phase discriminator. deviation, in which the optimal correlation interval D is designed under the condition of known spreading code rate f _c and baseband signal sampling frequency f _s :

The above-mentioned method for suppressing the code phase zero-crossing deviation based on the optimal correlation interval can be applied to satellite navigation signal receivers or other types of spread spectrum receivers, that is, pseudo codes of satellite navigation signal receivers or other types of spread spectrum receivers. in the tracking loop.

The design idea of the optimal correlation interval D of the early-delay code phase discriminator is as follows:

The first step is to establish the zero-crossing deviation analysis model of the spread spectrum signal.

When the early-delay code phase discriminator samples the received signal in a non-equivalent manner, there are differences in the sampling positions of different spreading code symbols. For different spreading code symbols with the same theoretical width, the actual number of sampling points may also be different. In the early-late code-phase discriminator, the initial phase of the received signal is estimated by the matched correlation of the local signal and the received signal. The time domain resolution of the initial phase of the signal depends on the sampling interval in the time domain, but its resolution in the correlation domain is affected by both the spreading code rate and the sampling frequency. Since the phase information of different sampling points can be synthesized, usually, the resolution of the initial phase of the signal in the correlation domain is higher than that in the time domain.

For an ideal infinitely sampled spread spectrum signal, the correlation curve between the local signal and the received signal is a smooth, symmetrical triangle. The lead correlator and the lag correlator are two sampling points symmetrical about zero phase on the correlation peak, when the center value of the correlation peak (that is, the phase difference between the local spread spectrum code signal and the spread spectrum code signal received by the navigation receiver) deviates from zero When the phase is changed, the related values of lead and lag also deviate. The early-late code phase discriminator uses the linear relationship between the code phase deviation and the difference between the lead and lag correlation values to estimate the phase difference.

However, for digital signals, the correlation curve between the local signal and the received signal is not a smooth and symmetrical triangle. As shown in Figure 3, when zooming in on the details of the correlation peak, it can be found that the correlation peak changes in a sawtooth shape, has a certain code phase resolution d _r , and can be expressed as:

d _r =1/LCM(f _s ,f _c )

Among them, LCM(a,b) means to solve the least common multiple of a and b, that is, LCM(f _s , f _c ) means to solve the least common multiple of f _c and f _s .

The second step is to define the average sampling points of the rectangular reference waveform.

The method of Code Correlation Reference Waveform (CCRW) is used to analyze the zero-crossing deviation of the early-delay code phase discriminator. Assume that the local initial code phase of the leading correlator is The local initial code phase of the lag correlator is in, Represents the local initial code phase of the punctual correlator and represents the local time of the receiver; 2d ₀ represents the correlation interval of the early decrementing code phase discriminator. If the lead code and the delay code are directly differentiated in the time domain, a rectangular reference waveform can be obtained, and the gate width of the rectangular reference waveform is D (D=2d ₀ ) (ie, the correlation interval of the early-delay code phase discriminator). Now define the average number of sampling points of the rectangular reference waveform as c _s , and it can be expressed as:

c _s =Df _s /f _c

The third step is to design the optimal correlation interval of the early-delay code-phase discriminator.

According to the symmetry principle of the reference code waveform, when the average number of sampling points c _s of the rectangular reference waveform is an even number, the optimal zero-crossing point deviation suppression capability can be obtained. Therefore, a method for designing the optimal gate width (ie, the optimal correlation interval D) of the early-delay code phase discriminator is proposed below.

Under the condition that the spreading code rate f _c and the baseband signal sampling frequency f _s have been set, that is, under the condition that the spreading code rate f _c and the baseband signal sampling frequency f _s are known, the correlation with the optimal zero-crossing deviation suppression performance is designed The interval D is:

Figure 1 shows the time-domain sampling diagram of the spread spectrum signal early-late code and its rectangular reference waveform. In the figure, the initial phase is The pseudo-random code sequence is sampled, the symbol width of the spreading code is t _c (=1/f _c , f _c is the spreading code rate), and the sampling interval of the digital signal is t _s (=1/f _s , f _s is the baseband signal sampling frequency). Assume that the local initial code phase of the leading correlator is The local initial code phase of the lag correlator is where D (=2d ₀ ) represents the correlation interval of the early-late code phase discriminator. If the lead code and the lag code are directly made difference in the time domain, a rectangular reference waveform can be obtained, and the gate width of the rectangular wave is D. Now define the average number of sampling points of the rectangular reference waveform as c _s .

FIG. 2 is a schematic diagram of the resolution and zero-crossing deviation of the code phase. For an ideal infinitely sampled spread spectrum signal, the autocorrelation curve is a smooth symmetrical triangle. The lead and lag correlators are respectively two sampling points on the correlation peak that are symmetrical about the zero phase. When the center value of the correlation peak (that is, the phase difference between the local signal and the received signal) deviates from the zero phase, the lead and lag correlation values will also be If deviation occurs, the early-late code phase discriminator uses the linear relationship between the code phase deviation and the correlation value deviation to estimate the phase difference. However, for digital signals, the correlation curve is not a smooth, symmetrical triangle. When zooming in on the details of the correlation peak, it can be found that the correlation peak changes in a sawtooth shape, with a certain code phase resolution d _r

Figure 3 is a code phase discrimination curve corresponding to different correlator intervals. The code phase zero-crossing point deviation is actually the zero-crossing point deviation of the code phase discrimination curve. Taking the early-delay code phase discriminator as an example, several correlator intervals of different widths are simulated. In the experiment, the sampling frequency f _s of the baseband spread spectrum signal is set to 100MHz, the spread spectrum code rate f _c is 10.23MHz, the spread spectrum code period is 10230 chips, the spread spectrum code sequence selects the 1 number of the BD B3I signal, and the correlation integration time is 1ms . According to the optimal correlation interval formula, the minimum correlation interval D0 at this time is 0.2046 chips. The following four groups of correlation intervals D0, 0.5D0, 0.25D0 and 0.125D0 are simulated. As shown in Figure 3, only the code phase discriminator whose correlation interval is D0 has the smallest zero-crossing point deviation. In fact, when the correlation interval is an integer multiple of D0 and does not exceed one chip width, the zero-crossing deviation can be minimized.

Fig. 4 is the variation curve of the deviation of the zero-crossing point of the code phase corresponding to different correlator intervals. In addition to being affected by the sampling frequency f _s , the spreading code rate f _c and the correlation interval D, the code phase zero-crossing point deviation dz is also related to the initial code phase 0 of the spread spectrum signal. In fact, the zero-crossing deviation dz varies with the initial code phase period, and the variation period is equal to the time domain resolution ts of the spread spectrum signal. The above four groups of correlation intervals are still simulated below, and only the initial code phase is traversed by using the same simulation conditions. The value interval of the initial phase is the resolution dr of the correlation curve, that is, 10-4 chips; the value range of the initial phase is 0 to 0.3 chips, that is, about three cycles. As shown in Figure 4, when the correlator interval D is D0, the zero-crossing deviation fluctuates within the range of the code phase resolution dr (=10-4 chips); and for other correlation intervals, the zero-crossing deviation The fluctuation range is much larger than the code phase resolution.

Figure 5 is a curve of the standard deviation of the zero-crossing deviation of the code phase as a function of the correlator interval. The variance of the zero-crossing deviation is another indicator to measure the performance of the zero-crossing deviation. It refers to the variance of the zero-crossing deviation corresponding to different spreading code sequences. After standardizing the variance of the zero-crossing deviation, it can also be called the zero-crossing deviation. standard deviation. Since the spread spectrum code sequence is highly random, the standard deviation of the zero-crossing deviation can eliminate the influence of the initial code phase and reflect the general influence of the zero-crossing deviation on the measurement of the code phase. Especially for long-period spread spectrum code sequences, the zero-crossing point deviations at different times are different, and the influence on the code phase accuracy can be approximated as Gaussian white noise. The simulation results show that when the correlation interval is set to be optimal, the standard deviation of the zero-crossing deviation is the smallest; and the farther the correlation interval is from the optimal correlation interval, the greater the standard deviation of the zero-crossing deviation. In fact, if the initial phase of the spread spectrum signal is fixed, the zero-crossing deviations of different spread spectrum sequences are the same.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. a code phase zero-crossing deviation suppression method based on an optimal correlation interval, it is characterized in that: effectively suppress the code phase zero-crossing point of the early-delayed code-phase discriminator by designing the optimal correlation interval of the early-delayed code-phase discriminator deviation, in which the optimal correlation interval D is designed under the condition of known spreading code rate f _c and baseband signal sampling frequency f _s : 2. An early-delay code phase discriminator, characterized in that: adopt the code phase zero-crossing deviation suppression method based on optimal correlation interval as claimed in claim 1 to suppress the code phase zero-crossing point of the early-delay code phase discriminator deviation. 3. A satellite navigation signal receiver, comprising an early decrement code phase discriminator, characterized in that: effectively suppress the code phase overshoot of the early decrement code phase discriminator by designing the optimal correlation interval of the early decrement code phase discriminator. Zero point deviation, in which the optimal correlation interval D is designed under the condition of known spreading code rate f _c and baseband signal sampling frequency f _s :