A high-precision distance measurement method based on spread spectrum system

Abstract

The present invention discloses a high-precision ranging method based on a spread spectrum system, and relates to the field of aerospace measurement and control. The present invention comprises: a ground station sends an uplink measurement signal, which is coherently forwarded by a satellite to form a downlink measurement signal, and the satellite completes the capture and tracking of the carrier pseudo code of the uplink measurement signal during the coherent forwarding process; the ground station receives the downlink measurement signal, and performs carrier pseudo code capture and tracking of the downlink measurement signal; after the ground station stably tracks the carrier pseudo code, the pseudo code phases of the uplink measurement signal and the downlink measurement signal at the same time are obtained, and the difference between the two is used to obtain the satellite-to-ground distance value, and at the same time, the speed value converted from the carrier Doppler frequency value is used to smooth the distance value to obtain a high-precision ranging result. The present invention has the characteristics of stable phase tracking performance, high ranging accuracy, and strong system compatibility.

Description

Technical Field

[0001] The present invention relates to the field of aerospace measurement and control technology, and in particular to a high-precision distance measurement method based on a spread spectrum system. Background Art

[0002] In the field of aerospace measurement and control, commonly used ranging systems include sidetone ranging, pseudo-code ranging, and mixed audio and code ranging. For example, sidetone ranging uses a mechanism in which a 100kHz main sidetone is constantly emitted and multiple levels of secondary sidetones are emitted in rotation. The distance between the satellite and the ground is obtained by measuring the sidetone phase difference between the ground station's transmitter and receiver. The ranging accuracy of this method is determined by the 100kHz main sidetone tracking accuracy, and the achievable ranging accuracy is only on the order of ten meters. The ranging accuracy of other commonly used ranging systems in the prior art is also only on the order of meters or even ten meters, which can no longer meet the increasingly high requirements for satellite orbit determination accuracy.

[0003] In order to further improve the satellite orbit determination accuracy, it is necessary to effectively improve the ranging accuracy of the measurement and control system to achieve centimeter-level ranging accuracy. However, such a ranging method has not yet been disclosed in the prior art. Summary of the invention

[0004] In view of this, the present invention provides a high-precision ranging method based on a spread spectrum system, which can effectively improve the ranging accuracy of the measurement and control system and achieve centimeter-level ranging accuracy.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A high-precision ranging method based on a spread spectrum system comprises the following steps:

[0007] Step 1: The ground station sends an uplink measurement signal, which is coherently forwarded by the satellite to form a downlink measurement signal. The satellite completes the capture and tracking of the carrier pseudo code of the uplink measurement signal during the coherent forwarding process.

[0008] Step 2: The ground station receives the downlink measurement signal and performs carrier pseudo code capture and tracking of the downlink measurement signal;

[0009] Step 3: After the ground station stably tracks the carrier pseudo code, it obtains the pseudo code phase of the uplink measurement signal and the downlink measurement signal at the same time, and the difference between the two is used to obtain the satellite-to-ground distance value. At the same time, the speed value converted from the carrier Doppler frequency value is used to smooth the distance value to reduce the random error of ranging and obtain a high-precision ranging result.

[0010] Furthermore, the specific method of step 2 is:

[0011] Step 201, using a parallel capture method to capture the carrier pseudo code, performing N-segment FFT analysis on the carrier within the Doppler capture range, and dividing the pseudo code into M segments within 1023 chips, thereby simultaneously searching for the maximum value of signal energy in two dimensions of carrier Doppler frequency and pseudo code chip phase, that is, searching for the maximum value at M×N points, and completing the initial capture of carrier Doppler frequency and pseudo code chip phase; N≥1, M=1~9;

[0012] Step 202, adopting a suppressed carrier phase-locked loop to track the carrier phase, and using the Doppler frequency obtained by tracking to assist the pseudo code tracking loop to track the pseudo code phase; the pseudo code phase tracking adopts an advance-lag loop, and achieves stable tracking of the pseudo code phase through narrow correlation operation.

[0013] Furthermore, the specific method of step 202 is:

[0014] The local carrier digital controlled oscillator generates I\Q two-channel carriers, which are multiplied with the downlink measurement signal to complete down-conversion and generate I\Q two-channel zero intermediate frequency signals;

[0015] The local pseudo code generator generates three pseudo codes, namely, an advance branch, a lag branch and an alignment branch; wherein the advance branch is 1 / L0 chip ahead of the pseudo code phase of the alignment branch, and the lag branch is 1 / L0 chip behind the pseudo code phase of the alignment branch;

[0016] The three leading, lagging and aligning branch pseudo codes are respectively multiplied with the carrier I\Q zero intermediate frequency signal to complete despreading, and the leading, lagging and aligning branch despreading signals are output;

[0017] The quasi-branch despread signal enters the carrier loop filtering and phase detection process to complete the stable phase tracking of the carrier phase-locked loop; in the carrier loop filtering process, the loop bandwidth B L Adopting a gradually narrowing strategy, the loop bandwidth B in the nth step Ln is the loop bandwidth B of the previous step L(n-1) Half:

[0018]

[0019] After the carrier phase-locked loop stabilizes tracking, the Doppler frequency fd generated by the local carrier digitally controlled oscillator R体 According to the RF frequency f of the downlink measurement signal R体 With the pseudo code rate f c偈de The proportional relationship between them is converted into pseudo code Doppler frequency fd c偈de , fd c偈de Placed in the local pseudo code generator, the auxiliary pseudo code completes phase tracking; the conversion relationship is as follows:

[0020]

[0021] The despread signals of the leading and lagging branches enter the pseudo-code loop filtering and phase detection process to complete the stable phase tracking of the pseudo-code loop;

[0022] The locking state of the pseudo code delay locking loop is judged by the locking judgment module. When it is judged to be stably locked, the phase difference between the leading branch, the lagging branch and the alignment branch is adjusted to 1 / L. n chips, L n The value gradually decreases according to the following proportional relationship:

[0023] L n =L n-1 ×2, L0=2, n=1,2,3.

[0024] Furthermore, the specific method of step 3 is:

[0025] Step 301: perform distance calculation at the nth 0.5s to obtain a distance value R n , the mth 0.05s in the nth 0.5s obtains a velocity value V n,m ; Differencing the 10 velocity values ​​within the nth 0.5s, we get the acceleration value a n :

[0026]

[0027] Step 302, calculate the intermediate speed in the nth 0.5s as:

[0028]

[0029] Step 303, calculate the middle distance in the nth 0.5s as:

[0030]

[0031] Step 304, calculate the distance after speed smoothing assistance for the nth 0.5s:

[0032]

[0033] Compared with the background technology, the present invention has the following advantages:

[0034] 1. The present invention can effectively improve the ranging accuracy of the system by upgrading the algorithm of the spread spectrum ranging system in the existing measurement and control system, and is fully compatible with the existing measurement and control system without the need for large-scale hardware equipment upgrades.

[0035] 2. The present invention effectively reduces the random error of ranging by adopting the methods of pseudo code narrow correlation, bandwidth adaptation and speed-assisted distance smoothing, and can achieve centimeter-level high-precision ranging. Compared with other ranging systems currently in use, the ranging accuracy is improved by at least 2 orders of magnitude.

[0036] 3. The present invention has the characteristics of stable phase tracking performance, high ranging accuracy and strong system compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 4 is a flow chart of a high-precision distance measurement method in an embodiment of the present invention.

[0038] Figure 2 It is a schematic diagram of the principle of carrier tracking assisted pseudo code tracking and narrow correlation operation in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further explained below in conjunction with the accompanying drawings.

[0040] A high-precision ranging method based on spread spectrum system, such as Figure 1 As shown, the following steps are included:

[0041] Step 1: The ground station sends an uplink measurement signal, which is coherently forwarded by the satellite to form a downlink measurement signal. The satellite completes the capture and tracking of the carrier pseudo code of the uplink measurement signal during the coherent forwarding process.

[0042] Step 2: The ground station receives the downlink measurement signal and performs carrier pseudo code capture and tracking of the downlink measurement signal;

[0043] Step 3: After the ground station stably tracks the carrier pseudo code, it obtains the pseudo code phase of the uplink measurement signal and the downlink measurement signal at the same time, and the difference between the two is used to obtain the satellite-to-ground distance value. At the same time, the speed value converted from the carrier Doppler frequency value is used to smooth the distance value to reduce the random error of ranging and obtain a high-precision ranging result.

[0044] The specific method of step 2 is as follows:

[0045] Step 201, the carrier pseudo code is captured in parallel, the carrier is subjected to N-segment FFT analysis within the Doppler capture range, the pseudo code is divided into M segments within 1023 code bits, and the maximum signal energy search is performed in two dimensions, the carrier Doppler frequency and the pseudo code chip phase, to complete the initial capture of the carrier Doppler frequency and the pseudo code chip phase.

[0046] Step 202: Carrier phase tracking is performed by using a suppressed carrier phase-locked loop, and the Doppler frequency obtained by tracking is used to assist a pseudo-code tracking loop to complete phase tracking. Pseudo-code phase tracking is performed by using an advance-lag loop, and stable tracking of the pseudo-code phase is achieved through narrow correlation operation.

[0047] like Figure 2 As shown, the specific method of step 202 is as follows:

[0048] The local carrier NCO generates two carriers, I and Q, which are multiplied with the downlink measurement signal to complete the down-conversion, and multiplied with the pseudo code generated by the alignment branch in the pseudo code loop to achieve despreading. Then, the data is decelerated and filtered through n-point integration cleaning, and finally enters the loop filtering and phase detection process to complete the stable closed loop of the phase-locked loop. In the loop filtering process, the loop bandwidth B L A gradual reduction strategy is adopted to ensure that the carrier is locked within a smaller bandwidth and the tracking error is smaller. L The reduction strategy is as follows:

[0049]

[0050] The Doppler frequency fd generated by the local carrier NCO RF According to the RF frequency f of the downlink measurement signal RF With the pseudo code rate f code The proportional relationship between them is converted into pseudo code Doppler frequency fd code , this value is placed in the local pseudo code generator in the pseudo code tracking loop to assist the pseudo code in completing phase tracking. The conversion relationship is shown in the following formula:

[0051]

[0052] The local pseudo code generator generates three pseudo codes, namely the leading branch, the lagging branch and the aligning branch. The leading branch is 1 / L0 chip ahead of the pseudo code phase of the aligning branch, and the lagging branch is 1 / L0 chip behind the pseudo code phase of the aligning branch. Under this condition, the three pseudo codes are multiplied with the down-converted signal of channel I in the carrier tracking loop to complete despreading, and then the data is decelerated and filtered through m-point integral cleaning, and finally enters the loop filtering and phase detection process to complete the stable closed loop of the pseudo code loop.

[0053] The lock judgment module judges the lock state of the pseudo code delay lock loop. When it is determined to be stably locked, the phase difference between the leading branch, the lagging branch and the alignment branch is adjusted to 1 / L n chips, L n The value is gradually reduced according to a certain proportional relationship to achieve pseudo code narrow correlation operation and pseudo code phase stable tracking. n The changing relationship is shown as follows:

[0054] L n =L n-1 ×2, L0=2, n=1,2,3

[0055] Step 3 specifically includes the following steps:

[0056] Step 301: The nth 0.5s distance is solved to obtain a distance value R n , a speed value V is obtained every 0.05s in the nth 0.5s nm ; The 10 speed values ​​within the nth 0.5s are differentiated to obtain the acceleration value a n , the difference process is shown in the following formula:

[0057]

[0058] Step 302, the intermediate speed in the nth 0.5s is:

[0059]

[0060] Step 303, the middle distance in the nth 0.5s is:

[0061]

[0062] Step 304: the distance after speed smoothing in the nth 0.5s is:

[0063]

[0064] In summary, the present invention has the characteristics of stable phase tracking performance, high ranging accuracy, and strong system compatibility. It can achieve centimeter-level ranging accuracy. Compared with other ranging systems currently in use, the ranging accuracy is improved by at least 2 orders of magnitude.

[0065] The present invention can be used in existing aerospace measurement and control systems. There is no need to modify hardware equipment on a large scale. The system's ranging accuracy can be effectively improved by simply upgrading the algorithm to meet centimeter-level ranging accuracy requirements.

Claims

1. A high-precision ranging method based on a spread spectrum system, characterized in that: The following steps are involved: Step 1: The ground station sends an uplink measurement signal, which is coherently forwarded by the satellite to form a downlink measurement signal. The satellite completes the capture and tracking of the carrier pseudo code of the uplink measurement signal during the coherent forwarding process. Step 2: The ground station receives the downlink measurement signal and performs carrier pseudo code capture and tracking of the downlink measurement signal; the specific method is: Step 201, using a parallel capture method to capture the carrier pseudo code, performing N-segment FFT analysis on the carrier within the Doppler capture range, and dividing the pseudo code into M segments within 1023 chips, thereby simultaneously searching for the maximum value of signal energy in two dimensions of carrier Doppler frequency and pseudo code chip phase, that is, searching for the maximum value at M×N points, and completing the initial capture of carrier Doppler frequency and pseudo code chip phase; N≥1, M=1~9; Step 202, a suppressed carrier phase-locked loop is used to track the carrier phase, and the Doppler frequency obtained by tracking is used to assist the pseudo code tracking loop to track the pseudo code phase; the pseudo code phase tracking adopts an advance-lag loop, and a narrow correlation operation is used to achieve stable tracking of the pseudo code phase; the specific process is as follows: The local carrier digital controlled oscillator generates I\Q two-channel carriers, which are multiplied with the downlink measurement signal to complete down-conversion and generate I\Q two-channel zero intermediate frequency signals; The local pseudo code generator generates three pseudo codes, namely, an advance branch, a lag branch and an alignment branch; wherein the advance branch is 1 / L0 chip ahead of the pseudo code phase of the alignment branch, and the lag branch is 1 / L0 chip behind the pseudo code phase of the alignment branch; The three leading, lagging and aligning branch pseudo codes are respectively multiplied with the carrier I\Q zero intermediate frequency signal to complete despreading, and the leading, lagging and aligning branch despreading signals are output; The quasi-branch despread signal enters the carrier loop filtering and phase detection process to complete the stable phase tracking of the carrier phase-locked loop; in the carrier loop filtering process, the loop bandwidth B L Adopting a gradually narrowing strategy, the loop bandwidth B in the nth step Ln is the loop bandwidth B of the previous step L(n-1) Half: After the carrier phase-locked loop stabilizes tracking, the Doppler frequency fd generated by the local carrier digitally controlled oscillator RF According to the RF frequency f of the downlink measurement signal RF With the pseudo code rate f code The proportional relationship between them is converted into pseudo code Doppler frequency fd code , fd code Placed in the local pseudo code generator, the auxiliary pseudo code completes phase tracking; the conversion relationship is as follows: The despread signals of the leading and lagging branches enter the pseudo-code loop filtering and phase detection process to complete the stable phase tracking of the pseudo-code loop; The locking state of the pseudo code delay locking loop is judged by the locking judgment module. When it is judged to be stably locked, the phase difference between the leading branch, the lagging branch and the alignment branch is adjusted to 1 / L. n chips, L n The value gradually decreases according to the following proportional relationship: L n =L n-1 ×2, L0, 2, n, 1, 2, 3; Step 3: After the ground station stably tracks the carrier pseudo code, it obtains the pseudo code phases of the uplink measurement signal and the downlink measurement signal at the same time, and makes a difference between the two to obtain the satellite-to-ground distance value. At the same time, the speed value converted from the carrier Doppler frequency value is used to smooth the distance value to reduce the random error of ranging and obtain a high-precision ranging result. The specific method is as follows: Step 301: perform distance calculation at the nth 0.5s to obtain a distance value R n , the mth 0.05s in the nth 0.5s obtains a velocity value V n,m ; Differencing the 10 velocity values ​​within the nth 0.5s, we get the acceleration value a n : Step 302, calculate the intermediate speed in the nth 0.5s as: Step 303, calculate the middle distance in the nth 0.5s as: Step 304, calculate the distance after speed smoothing assistance for the nth 0.5s:

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