Satellite-borne TT&C communication machine spread spectrum ranging Doppler compensation method

Abstract

The application provides a kind of spread spectrum ranging Doppler compensation method of spaceborne TT&C communication machine, comprising the following steps: TT&C communication machine is tracked to uplink measurement signal and is demodulated;The Doppler difference value ΔD of current frame and last frame is calculated at the starting position of the nth measurement frame n ;Compensation value DRn is calculated;Pseudo code chip phase P0 is revised;Complete current frame ranging compensation.The beneficial effects of the application are as follows: by subtracting the Doppler frequency value of the current frame and the last frame at the starting position of the measurement frame, and multiplying it with a fixed parameter, the result of multiplication is revised to the pseudo code chip, and the revised result is filled into the downlink measurement frame, thereby eliminating the influence of Doppler dynamic on the ranging value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of satellite-ground ranging, and particularly relates to a spread spectrum ranging Doppler compensation method for a satellite-borne TT&C (Telemetry, Tracking and Command) communication machine. BACKGROUND

[0002] The satellite-borne TT&C communication machine is used for establishing a satellite-ground link in combination with a ground TT&C station to complete satellite-ground remote control, telemetry and ranging and the like.

[0003] Ranging function: pseudo code measurement is performed on an uplink frame to form a downlink measurement frame, and the satellite ranging function is realized in cooperation with the ground station; the conventional index requires that the ranging accuracy is: <=1.5m (standard deviation); the Doppler variation rate is: better than + / -20kHz / s; and the Doppler variation range is: + / -400kHz.

[0004] When the ranging function test is performed on the ground, the distance value obtained by the ground ranging approximately remains stable at a fixed Doppler or no Doppler dynamic, and the maximum variation range is <=1.5m;

[0005] When the ground station sets the uplink ranging signal Doppler variation rate to 20kHz / s and the Doppler variation range to + / -400kHz, the distance value obtained by the ground ranging will change along with the Doppler variation, and the distance variation range can reach 10m at most, which exceeds the index requirement. SUMMARY

[0006] Therefore, the application aims to provide a spread spectrum ranging Doppler compensation method for a satellite-borne TT&C communication machine to solve the problem that the ranging range of the TT&C communication machine does not meet the index requirement due to dynamic Doppler variation.

[0007] To achieve the above object, the technical scheme of the application is as follows:

[0008] A spread spectrum ranging Doppler compensation method for a satellite-borne TT&C communication machine, comprising the following steps:

[0009] S1, the TT&C communication machine tracks and demodulates the uplink measurement signal;

[0010] S2, the Doppler difference value AD between the current frame and the previous frame is calculated at the starting position of the nth measurement frame n ;

[0011] S3, the compensation value DRn is calculated;

[0012] S4, the pseudo code chip phase P0 is corrected to obtain the compensation coefficient K0, and the compensation coefficient K0 is brought into step S3;

[0013] S5, the compensation value DRn calculated in step S3 is used to complete the current frame ranging compensation.

[0014] Further, in step S1, the TT&C communication machine tracks and demodulates the uplink measurement signal, including:

[0015] The TT&C communication machine demodulates one frame of measurement frame every 0.5 seconds to obtain the pseudo code period count, pseudo code count, pseudo code chip phase and average Doppler frequency information.

[0016] Further, in step S2, the Doppler difference ΔD n is calculated, including:

[0017] The formula is as follows:

[0018] ΔD n = D n - D n-1 (n=1, 2, 3...);

[0019] In the formula, ΔD n is the Doppler difference, D n is the current frame Doppler value, and D n-1 is the last frame Doppler value.

[0020] Further, in step S3, the compensation value DRn is calculated, including:

[0021] The formula is as follows:

[0022] DRn=ΔD n ×K0 / 2^M;

[0023] In the formula, DRn is the compensation value, K0 is the compensation coefficient; and the product K0×ΔD n is right shifted by M bits.

[0024] Further, in step S4, the pseudo code chip phase P0 is corrected, including:

[0025] The formula is as follows:

[0026] P0=R0 / C×RC×2^16×2^M;

[0027] In the formula, P0 is the corrected pseudo code chip phase, R0 is the corrected distance value, C, RC and M are all determined numbers, and the formula of R0 is as follows:

[0028] R0=ΔD n / 2^N×fs×Acc×0.00045;

[0029] In the formula, ΔD n is the Doppler difference, N is the bit width, fs is the sampling frequency, and Acc is the accuracy;

[0030] P0 is first expanded by 2^M times, that is, P0=ΔDn / 2^N x fs x Acc x 0.00045 / C x RC x 2^16 x 2^M;

[0031] Further, the formula for defining the compensation coefficient K0 is as follows:

[0032] K0=1 / 2^N x fs x Acc x 0.00045 / C x RC x 2^16 x 2^M;

[0033] In the formula, N is bit width, fs is sampling frequency, and Acc is accuracy; K0 is constant by N, fs, Acc, C, RC and M being all determined numbers.

[0034] Further, in step S5, the current frame ranging compensation is completed, including:

[0035] The modified pseudo code phase formula is as follows:

[0036] ;

[0037] The modified pseudo code phase is filled into the downlink measurement frame to complete the current frame ranging value correction.

[0038] Further, the FPGA does not support decimal operation, and the method of first expanding 2^M times, then multiplying and then dividing by 2^M is adopted for approximate calculation, the multiplication and division are both realized by shifting, and the value of M ensures that the P0 value after being expanded by 2^M times is greater than or equal to 31.

[0039] Further, when the pseudo code chip phase is insufficient, the high bit , is borrowed, and the overflow carry is added to the high bit , .

[0040] Compared with the prior art, the satellite-borne TT&C communication machine spread spectrum ranging Doppler compensation method has the following advantages:

[0041] Under the non-coherent measurement, TT&C data transmission integrated system and the like, the ground measurement equipment can effectively compensate the ranging result when the uplink measurement signal has Doppler dynamics. The difference between the current frame and the previous frame Doppler frequency value is obtained at the starting position of the measurement frame, and is multiplied by a fixed parameter, the multiplication result is modified to the pseudo code chip, and the modified result is filled into the downlink measurement frame, so that the influence of the Doppler dynamics on the ranging value is eliminated. The present application has the advantages of simple structure, easy implementation and no need to store a large amount of waveforms. The present application can be well applied to the satellite-borne TT&C equipment, and the ranging value solving accuracy under Doppler dynamics can be improved by using the present application. BRIEF DESCRIPTION OF DRAWINGS

[0042] The accompanying drawings, which form a part of the disclosure, are included to provide a further understanding of the application, illustrate the preferred embodiments of the application and assist in explaining the application. In the drawings:

[0043] Figure 1 Distance value diagram without Doppler for the embodiment of the application;

[0044] Figure 2 Original Doppler diagram for the embodiment of the application;

[0045] Figure 3 Original distance value diagram for the embodiment of the application;

[0046] Figure 4 ΔDpl(n) waveform curve diagram for the embodiment of the application;

[0047] Figure 5 Corrected distance value diagram for the embodiment of the application;

[0048] Figure 6 FPGA program distance compensation flowchart diagram for the embodiment of the application. DETAILED DESCRIPTION

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0050] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" and the like are only for the purpose of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0051] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integral connection, it can be mechanical connection, or electrical connection, it can be direct connection, or indirect connection through intermediate medium, or internal connection of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0052] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0053] As Figures 1 to 6 shown, a spread spectrum ranging Doppler compensation method for a spaceborne TT&C communication machine, comprising the following steps:

[0054] S1, the TT&C communication machine tracks and demodulates the uplink measurement signal;

[0055] S2, at the starting position of the nth measurement frame, the Doppler difference AD between the current frame and the previous frame is calculated n ;

[0056] S3, the compensation value DRn is calculated;

[0057] S4, the pseudo code chip phase P0 is corrected to obtain the compensation coefficient K0, and the compensation coefficient K0 is brought into step S3;

[0058] S5, the current frame ranging compensation is completed based on the compensation value DRn calculated in step S3.

[0059] The specific embodiments of the present application are as follows:

[0060] In the non-coherent ranging system, the spaceborne device (generally a TT&C communication machine) fills the sampled uplink measurement frame phase information into the downlink measurement frame for transmission, and the ground device receives and extracts the uplink measurement frame sampling information in the downlink measurement frame, and combines the sampling information and the measured pseudo-range value to calculate the distance value containing the zero value of the spaceborne device.

[0061] The main content of the downlink measurement frame provided by the satellite is: pseudo code phase information and received Doppler information; the frequency of the measurement frame is 2Hz, i.e. two frames per second, and the average period of the received Doppler frequency is 0.5 seconds.

[0062] When measuring the ranging performance of the on-board equipment, in addition to testing the performance under static conditions (without Doppler frequency offset or with fixed Doppler frequency offset), the performance under dynamic conditions (Doppler sweep) also needs to be tested. The downlink signal transmitted by the on-board equipment has no Doppler frequency offset, so when the uplink signal increases the Doppler dynamic, the code rate of the uplink signal will superimpose the corresponding Doppler dynamic, and in this case, the ground still demodulates at a fixed code rate, which will cause the ranging value to jitter. In the case of fixed ground equipment, the on-board equipment needs to compensate for the influence of the Doppler dynamic.

[0063] The ranging calculation formula of the ground station is simplified as follows:

[0064] ;

[0065] Wherein:

[0066] , is the acquisition of the pseudo code phase at the transmitting end;

[0067] , is the acquisition of the pseudo code phase at the receiving end;

[0068] , C = 299792458 m / s, the pseudo code chip phase accuracy is 16 bits, wherein, is the distance, is the pseudo code rate, is the speed of light, is the pseudo code period count at the transmitting end, is the pseudo code period count at the receiving end, is the pseudo code chip count at the transmitting end, is the pseudo code chip count at the receiving end, is the pseudo code chip phase at the transmitting end, is the pseudo code chip phase at the receiving end, and the corresponding distance value is calculated according to the table 1 as shown below.

[0069] Table 1

[0070]

[0071] When the ground station sends a signal without Doppler information, after receiving and forwarding by the satellite, the distance value demodulated by the ground station will not have obvious fluctuations, and the variance is within 1.5 meters, as shown in Figure 1 .

[0072] When the ground station sends a signal containing Doppler frequency, the Doppler demodulated by the on-board equipment is Dpl(n), n = 0, 1, 2... (n is a sampling point, and each sampling point is spaced 0.5 seconds), as shown in Figure 2 are three different speed original Doppler curves demodulated by the on-board equipment.

[0073] As Figure 3 shown, the ranging value rang(n) calculated by the ground station through satellite receiving and forwarding, n = 1, 2, 3... (n is a sampling point, and each sampling point is spaced 0.5 seconds) ; Figure 3 corresponding to three kinds of ranging value curves when the Doppler change rate is 5KHz / s, 10KHz / s and 20KHz / s; as can be seen from the figure, the distance value demodulated by the ground station will change with the Doppler change, showing a periodic change, and the change range is proportional to the Doppler change rate.

[0074] The reason why the ranging fluctuates after adding Doppler in the transmitted signal is that the Doppler frequency is superimposed on the carrier frequency and code frequency of the signal, the frequency changes, and then the ranging phase changes, if the Doppler is not compensated, it will cause a large deviation in the accuracy of the ranging value.

[0075] The distance value and the phase change are proportional, if it is a fixed Doppler, it will not cause the fluctuation of the distance value, only the changing Doppler will cause the periodic fluctuation of the code phase, so the difference of the obtained Doppler frequency is obtained, ΔDpl(n) = Dpl(n+1)-Dpl(n) (n = 1, 2, 3...), Figure 4 corresponding to three kinds of curves when the Doppler change rate is 5KHz / s, 10KHz / s and 20KHz / s.

[0076] It can be found that the changed Doppler and the ranging value change rule are completely consistent, so only the ΔDpl(n) is used to correct the ranging value, and the stable distance value can be restored.

[0077] The corrected distance value is defined as:

[0078] COR_rang(n) = rang(n)-K×ΔDpl(n);

[0079] Wherein, K is about 0.00045 through calculation;

[0080] The ranging waveforms after correction under three different Doppler rates are shown in Figure 5 .

[0081] As can be seen, the accuracy of the ranging value after correction is greatly improved, and there is no obvious change trend, and the standard deviation is within 1.5 meters.

[0082] The corresponding distance value correction process is shown in Figure 6 , and the satellite-borne measurement and control communication machine spread spectrum Doppler compensation FPGA correction method is as follows:

[0083] 1. The on-board product completes the tracking demodulation of the uplink measurement signal, and the on-board device demodulates 1 frame of measurement frame every 0.5 seconds to obtain the information such as pseudo code period count, pseudo code count, pseudo code chip phase and average Doppler frequency; wherein the ranging Doppler bit width N bit (N can be 10~32, etc.), the accuracy is Acc Hz (Acc can be 0.1, 0.01, 0.001, etc.).

[0084] 2. The current frame Doppler value and the last period Doppler difference value are calculated at the starting position of the nth measurement frame, and the formula is as follows:

[0085] ΔD n =D n -D n-1 (n=1,2,3...)).

[0086] 3. ΔD n multiplied by the compensation coefficient K0 to obtain the P0 value expanded by 2^M times, that is, ΔD n ×K0=P0×2^M, the meaning of P0 is to calculate the compensation coefficient K0, and the calculation process of K0 is as follows:

[0087] The distance value to be corrected is as follows:

[0088] R0=ΔD n / 2^N×fs×Acc×0.00045;

[0089] fs is the FPGA sampling frequency (for example, commonly used 110MHz);

[0090] Since R0 is generally within ±10 meters;

[0091] The corresponding corrected pseudo code chip phase P0=R0 / C×RC×2^16=ΔD n / 2^N×fs×Acc×0.00045 / C×RC×2^16;

[0092] Since the FPGA does not support decimal operation, it is approximated by first expanding 2^M times, then dividing by 2^M after multiplication, and both multiplication and division can be realized by shifting; the selected M ensures that the P0 value expanded by 2^M times is greater than or equal to 31;

[0093] P0=R0 / C×RC×2^16×2^M; that is, P0=ΔD n / 2^N×fs×Acc×0.00045 / C×RC×2^16×2^M;

[0094] Then K0=1 / 2^N×fs×Acc×0.00045 / C×RC×2^16×2^M can be defined;

[0095] Since N, fs, Acc, C, RC, and M are all fixed numbers, we can know that K0 is a constant.

[0096] In one embodiment, N is 30 bits, fs is 110 MHz, Acc is 0.01 Hz, C is 299792458 m / s, RC is 3.069 Mbps, and M is 17, then K0 is approximately 40.53.

[0097] 4. Calculate the compensation value DRn

[0098] DRn=ΔD n ×K0 / 2^M;

[0099] Equivalent K0×ΔD n The product is shifted right by M bits (the high bit is complemented by the sign bit).

[0100] 5. Complete downlink measurement frame phase correction

[0101] Corrected pseudo code phase:

[0102] ;

[0103] It should be noted that when the pseudo code chip phase is insufficient, it is necessary to start from the high position 、 Borrow, overflow carry to high bit 、 ; Then the corrected pseudo code phase Fill it into the downlink measurement frame to complete the ranging value correction of the current frame.

[0104] In a preferred embodiment of the present invention, in the downlink measurement frame Cycle count, 2-bit width, corresponding to phase weight 1023, value 0~3; Transmitter pseudo-code chip count, 10-bit width, corresponding to phase weight 1, value 0~1022; The pseudo-code chip phase of the transmitter is 16 bits wide, corresponding to a phase weight of 1 / 2^16, with a value of 0 to 65535).

[0105] After correction , after correction , after correction The calculation process is as follows:

[0106] if before correction ≥DRn

[0107] {

[0108] After correction =Before correction -DRn;

[0109] corrected = before correction ;

[0110] corrected = before correction ;

[0111] }

[0112] else

[0113] {

[0114] corrected = before correction - DRn+2^16;

[0115] if before correction ≥ 1

[0116] {

[0117] corrected = before correction - 1;

[0118] corrected = before correction ;

[0119] }

[0120] else

[0121] {

[0122] corrected = before correction + 1022;

[0123] if before correction ≥ 1

[0124] {

[0125] corrected = before correction - 1;

[0126] }

[0127] else

[0128] {

[0129] corrected = before correction + 3;

[0130] }

[0131] }

[0132] }

[0133] A specific example is shown in Table 2, assuming the DRn calculated value is 7000;

[0134] Table 2

[0135]

[0136] The application is applicable to the case of carrier Doppler varying in triangular, sinusoidal wave form, and the case of fixed carrier Doppler, and is also applicable to the case of different Doppler variation rates.

[0137] Advantages of the application:

[0138] The application can effectively compensate the ranging result when the ground measuring equipment measures the uplink signal in the presence of Doppler dynamics under the non-coherent measurement, measurement and control data transmission integrated system. The difference between the Doppler frequency values of the current frame and the previous frame is multiplied by a fixed parameter at the starting position of the measurement frame, and the multiplication result is corrected to the pseudo code chip. The corrected result is filled into the downlink measurement frame, thereby eliminating the influence of Doppler dynamics on the ranging value. The application has a simple structure and is easy to implement, and does not need to store a large amount of waveforms. The application can be well applied to the spaceborne measurement and control equipment, and the ranging value solving accuracy under Doppler dynamics can be improved by using the application.

[0139] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A Doppler compensation method for spread spectrum ranging of a satellite-borne measurement and control communication device, characterized by: The following steps are involved: S1, the measurement and control communication machine tracks and demodulates the uplink measurement signal; S2. At the starting position of the nth measurement frame, calculate the Doppler difference ΔD between the current frame and the previous frame n ; S3. Calculate the compensation value DRn, DRn=ΔD n ×K0 / 2^M; S4, correct the pseudo code chip phase to P0, P0=ΔD n / 2^N×fs×Acc×0.00045 / C×RC×2^16×2^M; define the compensation coefficient K0, K0=1 / 2^N×fs×Acc×0.00045 / C×RC×2^16×2^M, And bring the compensation coefficient K0 into step S3; S5, based on the compensation value DRn calculated in step S3, complete the current frame ranging compensation, and change the corrected pseudo code phase Fill it into the downlink measurement frame to complete the current frame ranging value correction. The corrected pseudo code phase formula is as follows: ； Where DRn is the compensation value, K0 is the compensation coefficient; N is the bit width, fs is the sampling frequency, Acc is the accuracy, is the pseudo code rate, is the speed of light, M is a fixed number, is the pseudo code cycle count of the transmitter, is the pseudo code chip count at the transmitting end, is the pseudo code chip phase of the transmitter.

2. The Doppler compensation method for spread spectrum ranging of a satellite-borne measurement and control communication device according to claim 1, characterized in that: In step S1, the measurement and control communication machine tracks and demodulates the uplink measurement signal, including: The measurement and control communication machine demodulates one measurement frame every 0.5 seconds to obtain pseudo code cycle count, pseudo code count, pseudo code chip phase and average Doppler frequency information.

3. The Doppler compensation method for spread spectrum ranging of a satellite-borne measurement and control communication device according to claim 1, characterized in that: In step S2, the Doppler difference ΔD is calculated. n ,include: The formula is as follows: ΔD n =D n -D n-1 (n=1,2,3...); Where ΔD n is the Doppler difference, D n is the Doppler value of the current frame, D n-1 is the Doppler value of the previous frame.

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