A satellite-ground ranging method suitable for multi-satellite TT&C scenarios

Abstract

The application relates to a satellite-ground ranging method suitable for a multi-satellite measurement and control situation, and relates to a satellite-ground ranging method. The application aims to solve the problem that a physical layer of advanced on-orbit system system service data stream and pseudo code data stream cannot be compatible in a multi-satellite measurement and control scene. The process is as follows: at a transmitting end: a downlink telemetry uplink remote control signal is directly sequence spread through a CA code at the transmitting end I path, so as to realize transmission of measurement and control information between a satellite and the ground; a pseudo code ranging sequence is directly sequence spread through the CA code at the transmitting end Q path, so as to realize a ranging function between the satellite and the ground; at a receiving end: 1, transmitting signals of different satellites are separated, and a pseudo code phase and a Doppler frequency shift are obtained; 2, a carrier tracking loop and a pseudo code tracking loop are realized to stably work; 3, I path coherent integration output is carried out to output continuous bits; Q path coherent integration output is carried out to output continuous bits, transmission time is solved, and then actual satellite-ground distance is obtained. The application is used in the field of space technology.

Description

Technical Field

[0001] This invention relates to satellite-to-ground ranging methods and to the field of aerospace technology. Background Technology

[0002] The integrated space-ground information network, with satellite constellation systems as a key component, is a crucial network infrastructure supporting my country's economic development and national defense informatization, and has become a key development direction for my country's "new infrastructure" initiative. As the aerospace system continues to grow and the number of spacecraft increases, telemetry, tracking, and command (TT&C) technology has become an essential component for the daily performance management of large-scale constellations, ensuring network robustness, and enhancing service capabilities.

[0003] Telemetry, tracking, and command (TT&C) mainly refers to the tracking, telemetry, and remote control of spacecraft, including acquiring spacecraft motion and orbital information, obtaining their operational status, and performing necessary command control. Since its emergence in the 1940s, space TT&C systems have undergone three stages: separate TT&C, unified carrier TT&C, and spread spectrum TT&C. Spread spectrum TT&C systems can unify multiple functions such as telemetry and remote control, ranging and TT&C, data communication, and broadband image transmission, as well as unify multi-station and multi-target measurements. Its essence lies in utilizing the correlation of spread spectrum sequences to achieve a TT&C communication system based on CDMA or MC-CDMA. Its advantages include:

[0004] 1. Due to the strong autocorrelation of pseudo-random codes, a series of satellites sharing the same carrier frequency will not experience severe co-channel interference, and can be used as an identifier for different satellite signals.

[0005] 2. Widening the bandwidth means that the signal-to-noise ratio of the received signal does not need to be very high, and provides a certain spreading gain according to Shannon's theorem.

[0006] 3. At the receiver end, the chip phase of the pseudo-random code provides the necessary ranging signal.

[0007] However, in multi-satellite telemetry and control scenarios, the physical layer of the Advanced Orbiting System (AOS) system's business data stream and pseudocode data stream are incompatible. Summary of the Invention

[0008] The purpose of this invention is to solve the problem of incompatibility between the physical layer of advanced on-orbit system business data streams and pseudocode data streams in multi-satellite telemetry and control scenarios, and to propose a satellite-to-ground ranging method suitable for multi-satellite telemetry and control scenarios.

[0009] The specific process of a satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios is as follows:

[0010] The processing procedure at the transmitting end is as follows:

[0011] The I channel of the transmitting end is directly spread by the CA code to the downlink telemetry and uplink remote control signal to realize the transmission of the measurement and control text between the satellite and the earth;

[0012] The Q channel of the transmitting end is directly spread by the CA code to the pseudo code ranging sequence to realize the ranging function between the satellite and the earth;

[0013] The CA code is used to distinguish different satellite signals;

[0014] The I channel and the Q channel are not homologous and have different transmission rates;

[0015] The I channel and the Q channel are modulated on the same frequency carrier, but the phase difference of the two carriers is kept at 90 degrees, which is orthogonal and convenient for the receiver to distinguish;

[0016] The digital signal output by the radio frequency board DA of the transmitting end is shown in formula (1),

[0017]

[0018] Wherein C(t) represents the CA sequence of a specific code number; D(t) is the measurement and control text transmitted by the I channel; Y(t) is the T2B / T4B ranging pseudo code adopted in the CCSDS standard, and the period is 1009740; I P Q P I ω is the carrier angular frequency; t is the time; s(t) is the signal form finally output by the radio frequency board DA;

[0019] In order to ensure that the I channel and the Q channel with different transmission rates have the same signal-to-noise ratio, the power of the I channel and the Q channel should satisfy formula (2);

[0020]

[0021] Wherein R I R Q is the transmission rate of the ranging pseudo code of the Q channel; N0 is the power spectral density of the double-sided white noise; SNR is the signal-to-noise ratio;

[0022] The processing flow of the receiving end is performed according to the following steps:

[0023] Step 1, FFT capture is performed on the intermediate frequency data input into the baseband processing system to realize three-dimensional search of the CA code number, CA code phase and Doppler frequency shift, separate the transmitting signals of different satellites, and obtain the pseudo code phase and Doppler frequency shift of the receiving end at the capturing moment of the transmitting signal;

[0024] The FFT is fast Fourier transform;

[0025] Step 2, track channels of satellites assigned to the relevant peaks greater than a set capture threshold in step 1, realize stable work of carrier tracking loop and pseudo code tracking loop;

[0026] Step 3, when the carrier tracking loop and the pseudo code tracking loop realize stable work, coherently integrate I to output continuous bits;

[0027] When the carrier tracking loop and the pseudo code tracking loop realize stable work, coherently integrate Q to output continuous bits, based on the bits, calculate the transmission time, and bring the transmission time into a two-way one-way ranging formula to obtain the actual distance between the satellite and the ground.

[0028] The beneficial effects of the present application are:

[0029] The present application realizes the compatibility of Advanced Orbiting System (AOS) system service data stream and pseudo code data stream physical layer in a multi-satellite measurement and control scene.

[0030] The present application solves the problem that the existing pseudo code ranging cannot be integrated into the Consultative Committee for Space Data Systems (CCSDS) related standards, and there is no clear solution for multi-satellite measurement and control receivers. Directly use the physical channel layer of the AOS system, that is, modulate the AOS data stream and the ranging pseudo code on the same carrier by using the non-balanced QPSK modulation system, and use the good autocorrelation and cross-correlation characteristics of the CA code to identify different CA codes as different satellites, and through the direct sequence spread spectrum of the CA code with a code length of 1023 to the I channel measurement and control text and the Q channel pseudo code sequence, the receiving end captures through FFT, realizes three-dimensional search of satellite, pseudo code phase and carrier Doppler frequency shift, then realizes tracking of I, Q two-way code phase and carrier frequency shift through the Costas loop and the early-late loop, and calculates the continuous 0, 1 sequence through coherent integration, then the I channel output can be used for bit synchronization and frame synchronization, so as to realize reading of the telemetry data, and the Q channel output is used for CA code phase and composite pseudo code phase decision, so as to obtain the measurement distance between the satellite and the ground.

[0031] The present application includes the following beneficial effects:

[0032] 1. The application realizes the transmission of uplink remote control and downlink remote measurement text and the measurement of satellite-ground distance by non-equilibrium QPSK I, Q two paths respectively carrying measurement and control text and ranging pseudo code, can adjust the power divider of the local oscillator according to the rate of I, Q two paths, so that the demodulation of measurement and control text and the phase judgment of pseudo code keep at a high correct rate. The process of forming and multiplexing of internal data stream of high-level on-orbit system is not involved in principle, so the time delay controllability is high, which is beneficial to improve the ranging accuracy. At the same time, the method of two-way single-pass ranging is adopted, which saves the traditional pseudo code regeneration step, and can eliminate clock difference, and realizes higher ranging accuracy.

[0033] 2. The method can adopt different length of direct spread sequence according to the measurement and control demand of different constellation scale and actual bandwidth, the application takes CA code as an example, there are 37 kinds of commonly used CA code, the length is 1023, that is, the small satellite constellation of not more than 37 satellites can be identified by CA code. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The baseband data processing block diagram of the measurement and control transponder for Zynq platform is shown, PS is processing system (Processing System), and PL is programmable logic (Progarmmable Logic);

[0035] Figure 2 The generation diagram of ranging pseudo code sequence T2B / T4B in CCSDS standard is shown, C1, C2, C3, C4, C5 and C6 are sub-codes, and combining logic is combining logic;

[0036] Figure 3 The tracking loop flow chart is shown, E is the advance pseudo code, P is the intermediate pseudo code, and L is the lag pseudo code;

[0037] Figure 4 The schematic diagram of two-way single-pass pseudo code ranging is shown, CA_X is CA code number, CA_Phase is CA code phase, and flag is stable tracking state flag;

[0038] Figure 5 The flow chart of Q path pseudo code phase solution of the receiving end is shown;

[0039] Figure 6 The first correlator output result of each sub-code changes with the input pseudo code phase diagram. DETAILED DESCRIPTION

[0040] Embodiment one: the specific process of the star-ground ranging method suitable for multi-satellite measurement and control situation is:

[0041] The implementation platform of the baseband part of the measurement and control machine relies on the Zynq development board of Xilinx, the PL end is FPGA, and the PS end is ARM core, which realizes complex data operation and control process. The specific processing block diagram is shown in Figure 1

[0042] The processing flow at the transmitting end is carried out in the following steps:

[0043] At the transmitting end, the I path passes through the CA code to perform direct sequence spread spectrum on the downlink telemetry uplink remote control signal, so as to realize the transmission of measurement and control text between the satellite and the ground.

[0044] At the transmitting end, the Q path passes through the CA code to perform direct sequence spread spectrum on the pseudo-code ranging sequence, such as the T2B / T4B sequence in the CCSDS standard as shown in Figure 2

[0045] The CA code is used to distinguish different satellite signals.

[0046] The two-way data of the I path and the Q path are not homologous and have different transmission rates; the information transmitted by the I path and the information transmitted by the Q path come from different data sources.

[0047] Although the I and Q paths are modulated on the same frequency carrier, the phase difference of the two carriers is kept at 90 degrees, which is orthogonal, facilitating the differentiation of the receiver.

[0048] The digital signal output by the transmitting end radio frequency board DA is shown in formula (1),

[0049]

[0050] Where C(t) represents a specific code CA sequence; D(t) is the measurement and control text transmitted by the I path; Y(t) is the T2B / T4B ranging pseudo-code adopted in the CCSDS standard, with a period of 1009740; P I is the I path output power; P Q is the Q path output power; ω is the carrier angular frequency; t is the time; s(t) is the signal form finally output by the radio frequency board DA;

[0051] For the spread spectrum measurement and control system, different carrier frequency bands mainly reflect the different frequency points after the uplink and downlink mixing at the radio frequency end, and there is no difference for the baseband processing.

[0052] Unlike traditional QPSK, in order to ensure that the I and Q paths with different transmission rates have the same signal-to-noise ratio, the power of the I and Q paths should satisfy formula (2), and the power allocation ratio of the two channels is generally between -10bB and 10dB under normal circumstances.

[0053] ​​

[0054] wherein R I is the transmission rate of the I-channel telemetry message; R Q is the transmission rate of the Q-channel ranging pseudo-code; N0 is the power spectral density of the bilateral white noise; and SNR is the signal-to-noise ratio;

[0055] The processing flow at the receiving end is performed in the following steps:

[0056] Step 1: FFT capture is performed on the intermediate frequency data input into the baseband processing system. The specific form of the intermediate frequency data is related to the AD sampling frequency and accuracy of the radio frequency front end of the superheterodyne receiver. Three-dimensional search is implemented on the CA code number, CA code phase and Doppler frequency shift. If the searched intermediate frequency data contains the spread spectrum telemetry data and ranging information through a specific CA code number, the correlation integral of the intermediate frequency data at a specific frequency point and pseudo-code phase will have a clear peak value, so that the transmission signals of different satellites are separated, and the pseudo-code phase and Doppler frequency shift of the receiving end at the capture time of the transmission signals (transmission signals of different satellites) are obtained.

[0057] The FFT is a fast Fourier transform.

[0058] Step 2: A tracking channel is allocated to the satellite with a correlation peak greater than a set capture threshold in step 1, so as to realize stable operation of the carrier tracking loop and the pseudo-code tracking loop. Since the PL part of the Zynq platform processes data in parallel, real-time tracking of the telemetry signals of multiple satellites can be realized through multiple multiplexing of the tracking circuit. The specific flowchart of tracking is shown in FIG. 6. The core is a 6-way correlator. The I-channel / Q-channel intermediate orthogonal correlator is used for carrier loop tracking, and the I-channel / Q-channel respective leading / lagging orthogonal correlator is used for code loop tracking. Figure 4

[0059] Step 3: When the carrier tracking loop and the pseudo-code tracking loop realize stable operation, coherent integration is performed on the I-channel to output continuous bits.

[0060] When the carrier tracking loop and the pseudo-code tracking loop realize stable operation, coherent integration is performed on the Q-channel to output continuous bits. Based on the bits, the transmission time is solved, and the actual distance between the satellite and the ground is obtained by bringing the transmission time into the two-way one-way ranging formula.

[0061] Specific implementation method two: The difference between this implementation method and the specific implementation method one is that: in step 2, a tracking channel is allocated to the satellite with a correlation peak greater than a set capture threshold, so as to realize stable operation of the carrier tracking loop and the pseudo-code tracking loop. Since the PL part of the Zynq platform processes data in parallel, real-time tracking of the telemetry signals of multiple satellites can be realized through multiple multiplexing of the tracking circuit. The specific flowchart of tracking is shown in FIG. 6. The core is a 6-way correlator. The I-channel / Q-channel intermediate orthogonal correlator is used for carrier loop tracking, and the I-channel / Q-channel respective leading / lagging orthogonal correlator is used for code loop tracking. Figure 3 ​The core is a 6-path correlator, in which an I / Q middle orthogonal correlator is used for carrier loop tracking, and I / Q leading / lagging orthogonal correlators are used for code loop tracking; the specific process is as follows:

[0062] Figure 3 In the middle,

[0063] The intermediate frequency data are multiplied with two carrier waves generated by a carrier generator according to the captured Doppler shift; the two multiplied data streams are multiplied with three pseudo-codes generated by a pseudo-code generator according to the captured pseudo-code phase, to obtain six signal paths;

[0064] The six signal paths are integrated in a set integration time,

[0065] The carrier loop discriminator uses an I or Q middle orthogonal correlator for carrier loop tracking;

[0066] The pseudo-code loop discriminator uses an I leading orthogonal correlator, an I lagging orthogonal correlator, a Q leading orthogonal correlator, and a Q lagging orthogonal correlator for pseudo-code loop tracking;

[0067] The carrier loop filter feeds back the result output by the carrier loop discriminator to a carrier voltage-controlled oscillator for adjustment;

[0068] The pseudo-code loop filter feeds back the result output by the pseudo-code loop discriminator to a pseudo-code generator for adjustment;

[0069] The capture threshold is set to 3 times the average of the correlation values of each point in the capture range.

[0070] The other steps and parameters are the same as in the first embodiment.

[0071] The third embodiment is different from the first or second embodiment in that: in step 3, when the carrier tracking loop and the pseudo-code tracking loop achieve stable operation, the I path is coherently integrated to output continuous bits;

[0072] When the carrier tracking loop and the pseudo-code tracking loop achieve stable operation, the Q path is coherently integrated to output continuous bits, and the transmission time is calculated based on the bits, and the actual distance between the satellite and the ground is obtained by inputting the transmission time into the two-way one-way ranging formula;

[0073] The specific process is as follows:

[0074] Step 3.1, the I path is coherently integrated to output continuous bits; the specific process is as follows:

[0075] Step 3.1a, bit synchronization;

[0076] Step 3.1b, frame synchronization is performed after bit synchronization is completed based on step 3.1a;

[0077] Step 3.2, the Q channel is coherently integrated to output a continuous bit, and the transmission time is calculated based on the bit, and the actual distance between the satellite and the ground is obtained by inputting the transmission time into the two-way one-way ranging formula.

[0078] The other steps and parameters are the same as those in embodiment one or two.

[0079] Embodiment four: the difference between the embodiment and one of embodiments one to three is that the step 3.1a is bit synchronization, and the specific process is as follows:

[0080] It is assumed that the transmission rate of the I channel measurement and control message is 1 kbps, the spreading factor is 2046, and the chip rate after spreading is 2.046 Mbps;

[0081] When the carrier tracking loop and the pseudo-code tracking loop are stably working, the integration time interval is selected according to the transmission rate of the I channel measurement and control message;

[0082] Taking 0.1 ms as the integration time interval, ten integrations (1 ms / 0.1 ms = 10) can be performed in the transmission time of one measurement and control message bit, which are recorded as time points 1, 2, …, 10. A counter is allocated to each time point (a total of 10 counters), and the initial value of each counter is 0.

[0083] If the sign of the integration result at the current time point changes relative to the previous time point, the result of the counter corresponding to the current time point is increased by 1.

[0084] After integrating for a period of time (an integer multiple of 1 ms, because the period of one bit is 1 ms, and each counter corresponds to a time point of 0.1 ms, but 1 ms will only have one bit transition, and only one counter result will become 1, so multiple 1 ms need to be integrated, because the transition time point can be 1.1 ms, 2.1 ms, 3.1 ms, or 1.2 ms, 2.2 ms, 3.2 ms, etc. The counter corresponds to 0.1 ms, 0.2 ms, and 0.3 ms transition), whether bit synchronization is achieved is judged according to the maximum value of the counters corresponding to the 10 time points.

[0085] The other steps and parameters are the same as those in one of embodiments one to three.

[0086] Embodiment five: the difference between the embodiment and one of embodiments one to four is that whether bit synchronization is achieved is judged according to the maximum value of the counters corresponding to the 10 time points after integrating for a period of time, and the specific process is as follows:

[0087] If only one counter value exceeds the preset threshold, the bit transition time is determined as the time corresponding to the counter with the maximum count value;

[0088] If multiple counter values exceed the preset threshold, the multiple counters are reset (counters are set to 0), and step 3.1a is repeated;

[0089] The multiple is greater than or equal to 2 and less than or equal to 10.

[0090] The other steps and parameters are the same as those in the first to fourth embodiments.

[0091] The sixth embodiment is different from the first to fifth embodiments in that the step 3.1b, frame synchronization, has the following specific process:

[0092] The telemetry / telecontrol frame header preamble and the result of bit-by-bit XOR of the preamble are detected to realize extraction of specific frame content.

[0093] Since QPSK demodulation causes phase ambiguity, the result of bit-by-bit XOR of the frame header specific preamble is detected.

[0094] The other steps and parameters are the same as those in the first to fifth embodiments.

[0095] The seventh embodiment is different from the first to sixth embodiments in that the step 3.2, coherent integration output of the Q channel for a certain number of bits, based on which the transmission time is calculated, and the actual distance between the satellite and the ground station is obtained by inputting the transmission time into the two-way one-way ranging formula; the specific process is as follows:

[0096] The two-way measurement step in the traditional method, in which the on-board receiver needs to demodulate the uplink signal and generate a ranging regenerated pseudo-code modulated into the downlink signal, is omitted.

[0097] Based on the Q channel data (Q channel data is 0 and 1 bits), the transmission time T1 and T2 expressions are as follows:

[0098] T1 = t t1 + τ + Δt + t r1 (3)

[0099] T2 = t t2 + τ - Δt + t r2 (4)

[0100] Wherein, τ is the transmission time between the satellite antenna and the ground receiver antenna, t t1 is the satellite transmission device delay, Δt is the clock difference existing in the satellite and the ground receiver, t r1 is the satellite receiving device delay, t t2t is the time delay of the ground transmitting device r2 T1 is the time delay of the ground receiving device; T2 is the propagation time from the satellite to the ground; T3 is the propagation time from the ground to the satellite;

[0101] Equations (3) and (4) are only in the form of representation, and are unknown, and the clock difference on the right side of the equation is an unknown term;

[0102] The transmission times T1 and T2 are as shown in Figure 4 ;

[0103] Based on equations (3) and (4), the distance between the satellite and the ground is:

[0104] d = c x τ = 0.5c x [(T1 + T2) - (t t1 +t t2 ) - (t r1 +t r2 )] (5)

[0105] Wherein, c is the speed of light;

[0106] Since the transmission and receiving processing time delays t t1 , t t2 , t r1 , t r2 of the satellite and the ground receiver can be measured on the ground, that is, they can be regarded as known quantities, so the pseudo-code ranging accuracy can be effectively improved.

[0107] The other steps and parameters are the same as one of the first to sixth embodiments.

[0108] The eighth embodiment is different from one of the first to seventh embodiments in that the specific value calculation process of the transmission times T1 and T2 is:

[0109] A. When the carrier tracking loop and the pseudo-code tracking loop are stably working, the number K of bits to be read backward from the Q sequence currently received by the receiver is calculated according to the estimated signal-to-noise of the radio frequency front end, the co-directional coefficient of the ranging composite pseudo-code, the non-co-directional coefficient, and the desired false rejection rate;

[0110]

[0111] Wherein Q is the right tail function of the standard normal distribution, P e is the desired in-phase decision false rejection rate, E c is the average energy of a single chip, and ζ is the co-directional coefficient of the ranging sequence and λ is the correlation factor of the sequence;

[0112] B. The transmission time is calculated through the T2BT4B ranging code in the CCSDS protocol;

[0113] The ranging composite pseudo code used in CCSDS protocol is generated by cyclic shift of six sub-codes with prime number of periods, the sub-code periods are 2, 7, 11, 15, 19, 23, and the total period is 1009470, the specific calculation process is shown in Figure 5 The specific process is as follows:

[0114] Firstly, the sub-code C1 sequence is detected, and the detected sub-code C1 is used as a sampling clock to sample the K Q-bit sequences, and the sampled data is detected by 75 correlators to obtain the phase M Ci of the sub-codes C2-C6 (for example, the period of the sub-code C2 is 7, and 7 correlators are needed, if a correlation peak appears in the first correlator, it is considered that the phase of the sub-code C2 is 1, and if a correlation peak appears in the second correlator, it is considered that the phase of the sub-code C2 is 2);

[0115] The sampled data is a local composite pseudo code, which is composed of C1-C6, and the period of C2+C3+…+C6 is equal to 75, so 75 correlators are needed for detection;

[0116] When the satellite-ground distance does not exceed the maximum ambiguity distance of the composite pseudo code (for T2B / T4B ranging pseudo code, assuming a transmission rate of 1kbps, the unambiguous distance is 3x10 11 m, which can meet most of the measurement and control requirements), the composite pseudo code phase has a unique solution, as shown in Figure 6 The output results of the first correlators of the sub-codes change with the input pseudo code phase, and different input phases of the composite pseudo code correspond to different values of the sub-code phase. In combination with the CA code phase of the satellite in the acquisition process, the transmission time is further accurately determined. When the satellite-ground distance exceeds the maximum ambiguity distance of the composite pseudo code, it is not within the application range of the ranging pseudo code;

[0117] The final composite pseudo code phase can be written as:

[0118]

[0119] Wherein, λ i is the code length of the i-th sub-code, is the number of the i-th sub-code, and M T4B / T2B is the ranging composite pseudo code phase;

[0120] The ground obtains the propagation time T1 of the satellite to the ground by sending the ranging composite pseudo code phase M T4B / T2B to the satellite;

[0121] The satellite obtains the propagation time T2 of the ground to the satellite by transmitting the ranging composite pseudo code phase M T4B / T2B to the ground, and transmits it to the ground through the I signal in the next frame;

[0122] The final propagation time between satellite and ground T j The propagation time T is obtained by the following formula i The actual distance between satellite and ground is calculated by the following formula (5) with the propagation time T

[0123]

[0124] Wherein, M T4B / T2B is the phase of the ranging composite code, f T4B / T2B is the transmission rate of the ranging code, M CA is the phase of the CA code, f CA is the transmission rate of the CA code; * is the multiplication sign; j = 1, 2.

[0125] Wherein, the values of the parameters are shown in the following table:

[0126]

[0127]

[0128] The other steps and parameters are the same as one of the first to seventh embodiments.

[0129] The present application can also have other various embodiments, and those skilled in the art can make various corresponding changes and modifications according to the present application without departing from the spirit and essence of the present application, but these corresponding changes and modifications should all belong to the protection scope of the claims attached to the present application.

Claims

1. A satellite-to-ground ranging method suitable for multi-satellite telemetry and control scenarios, characterized in that: The specific process of the method is as follows: The processing procedure at the transmitting end is as follows: At the transmitting end, the downlink telemetry and uplink remote control signals are directly spread in sequence using CA code on channel I to realize the transmission of telemetry and control messages between satellite and ground. At the transmitting end, the Q-channel uses CA code to perform direct sequence spread spectrum on the pseudo-code ranging sequence in order to realize the ranging function between satellite and ground. CA codes are used to distinguish between different satellite signals; The two data streams, I and Q, are from different sources and have different transmission rates; Although the I and Q channels are modulated on the same frequency carrier, the phase difference between the two carriers remains 90 degrees, making them orthogonal and easy for the receiver to distinguish. The digital signal output by the DA board of the transmitter is shown in equation (1). Where C(t) represents a specific code number CA sequence; D(t) is the measurement and control message transmitted on channel I; Y(t) is the T2B / T4B ranging pseudocode used in the CCSDS standard, with a period of 1009740; P I P is the output power of channel I; Q ω is the Q-channel output power; ω is the carrier angular frequency; t is time; s(t) is the final signal form of the DA output from the RF board; To ensure that the I and Q paths with different transmission rates have the same signal-to-noise ratio, the power of the I and Q paths should satisfy equation (2); Where R I R is the transmission rate of the I-channel telemetry and control message; Q N0 is the transmission rate of the Q-channel ranging pseudocode; N0 is the power spectral density of the bilateral white noise; SNR is the signal-to-noise ratio. The receiving end's processing flow is as follows: Step 1: Perform FFT acquisition on the intermediate frequency data input to the baseband processing system to achieve three-dimensional search of CA code number, CA code phase, and Doppler frequency shift, separate the transmitted signals of different satellites, and obtain the pseudo code phase and Doppler frequency shift of the received signal at the acquisition time. The FFT is the Fast Fourier Transform; Step 2: Assign tracking channels to satellites with correlation peaks greater than the set acquisition threshold in Step 1 to achieve stable operation of the carrier tracking loop and pseudocode tracking loop; Step 3: After the carrier tracking loop and pseudocode tracking loop have achieved stable operation, perform coherent integration on the I channel and output continuous bits; Once the carrier tracking loop and pseudocode tracking loop are operating stably, coherent integration is performed on the Q-path to output continuous bits. The transmission time is calculated based on these bits, and then the transmission time is substituted into the bidirectional one-way ranging formula to obtain the actual distance between the satellite and the ground.

2. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 1, characterized in that: In step 2, tracking channels are allocated to satellites with correlation peaks exceeding the set acquisition threshold from step 1, thereby achieving stable operation of the carrier tracking loop and pseudocode tracking loop; the specific process is as follows: The intermediate frequency data is multiplied by two carrier waves generated by the carrier generator based on the captured Doppler frequency shift; the two multiplied data streams are then multiplied by three pseudo-codes generated by the pseudo-code generator based on the captured pseudo-code phase, namely lead, intermediate, and lag, to obtain six signals. Integrate the six signals within the set integration time. The carrier loop phase detector uses an I-channel or Q-channel intermediate quadrature correlator for carrier loop tracking; The pseudo-code loop phase detector tracks the pseudo-code loop using an I-channel advance quadrature correlator, an I-channel lag quadrature correlator, a Q-channel advance quadrature correlator, and a Q-channel lag quadrature correlator. The carrier loop filter feeds back the output of the carrier loop phase detector to the carrier voltage-controlled oscillator for adjustment. The pseudo-code loop filter feeds back the output of the pseudo-code loop phase detector to the pseudo-code generator for adjustment. The capture threshold is set to three times the average value of the relevant values ​​at each point within the capture range.

3. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 2, characterized in that: In step 3, after the carrier tracking loop and pseudocode tracking loop achieve stable operation, coherent integration is performed on the I-channel to output continuous bits. After the carrier tracking loop and pseudocode tracking loop achieve stable operation, the Q-path is coherently integrated to output continuous bits. The transmission time is calculated based on the bits, and the transmission time is substituted into the two-way one-way ranging formula to obtain the actual distance between the satellite and the ground. The specific process is as follows: Step 3.1: Perform coherent integration on channel I and output a continuous number of bits; the specific process is as follows: Step 3.1a, Bit synchronization; Step 3.1b: Perform frame synchronization after completing bit synchronization in step 3.1a; Step 3.2: Perform coherent integration on the Q-path to output continuous bits, calculate the transmission time based on the bits, and substitute the transmission time into the two-way one-way ranging formula to obtain the actual distance between the satellite and the ground.

4. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 3, characterized in that: The bit synchronization in step 3.1a is as follows: Assume that the transmission rate of the I-channel telemetry and control message is 1kbps, the spreading factor is 2046, and the chip rate after spreading is 2.046Mbps. When the carrier tracking loop and the pseudocode tracking loop achieve stable operation, the integration time interval is selected according to the transmission rate of the I-channel telemetry and control message; With an integration time interval of 0.1ms, the data can be integrated ten times within the transmission time of one bit of a control message, denoted as time 1, 2...

10. Each time is assigned a counter, and the initial value of each counter is 0. If the sign of the integral result at the current time has changed relative to the previous time, the counter result at the current time is incremented by 1; After integrating for a period of time, the maximum value of the counter corresponding to the 10 time points is used to determine whether bit synchronization has been achieved; The time period is an integer multiple of 1ms.

5. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 4, characterized in that: After a period of integration, the maximum value of the counter corresponding to the 10 time points is used to determine whether bit synchronization has been achieved; the specific process is as follows: If only one counter's value exceeds the preset threshold, then the bit transition time is determined to be the time corresponding to the counter with the maximum count value. If the values ​​of multiple counters exceed the preset threshold, then multiple counters are reset and step 3.1a is repeated. The term "multiple" refers to a number greater than or equal to 2 and less than or equal to 10.

6. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 5, characterized in that: Frame synchronization in step 3.1b; The specific process is as follows: The extraction of specific frame content is achieved by detecting the preamble of the telemetry / remote control frame header and the result of bitwise XOR of the preamble in different telemetry / remote control protocols.

7. The satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 6, characterized in that: In step 3.2, the Q-path is coherently integrated to output continuous bits. The transmission time is calculated based on the bits, and the transmission time is substituted into the two-way one-way ranging formula to obtain the actual distance between the satellite and the ground. The specific process is as follows: Based on the Q-channel data transmission time T1, T2 is expressed as: T1=t t1 +τ+Δt+t r1 (3) T2=t t2 +τ-Δt+t r2 (4) Where τ is the transmission time between the satellite antenna and the ground receiver antenna, t t1 The time delay is Δt, where Δt is the clock difference between the satellite and the ground receiver. r1 For satellite receiving equipment latency, t t2 For the delay of ground transmission equipment, t r2 T1 is the latency of the ground receiving equipment; T2 is the propagation time from the satellite to the ground; T3 is the propagation time from the ground to the satellite. Based on formulas (3) and (4), the distance between the satellite and the ground is: d=c×τ=0.5c×[(T1+T2)-(t t1 +t t2 )-(t r1 +t r2 )] (5) Where c is the speed of light.

8. A satellite-to-ground ranging method applicable to multi-satellite telemetry and control scenarios according to claim 7, characterized in that: The specific calculation process for the input times T1 and T2 is as follows: A. When the carrier tracking loop and pseudocode tracking loop are working stably, calculate the number of bits K that need to be read from the currently received Q-channel sequence of the receiver based on the estimated signal-to-noise ratio of the RF front end, the in-direction coefficient and non-in-direction coefficient of the ranging composite pseudocode, and the desired error rate. Where Q is the right-tail function of the standard normal distribution, and P... e To achieve the desired error rate in in-phase decision, E c ζ is the average energy of a single chip, ζ is the homing coefficient of the ranging sequence, and λ is the correlation factor of the sequence; B. Calculate the transmission time using the T2BT4B ranging code in the CCSDS protocol; The specific process is as follows: First, correlation detection is performed on the subcode C1 sequence. The detected subcode C1 is then used as a sampling clock to sample K Q-way bit sequences. After sampling, the data is passed through 75 correlators to detect the phase of subcodes C2 to C6. The final composite pseudocode phase is written as follows: Where, λ i Let i be the code length of the i-th subcode. M is the number of subcodes used. T4B / T2B The phase of the ranging composite pseudocode; Ground-based satellites transmit ranging composite pseudocode phase M. T4B / T2B To obtain the satellite-to-ground propagation time T1; The satellite transmits a ranging composite pseudocode phase M via ground transmission. T4B / T2B To obtain the propagation time T2 from the ground to the satellite, and transmit it to the ground via I-channel signal in the next frame; Final propagation time T between space and Earth j We obtain it from the following formula: Among them, M T4B / T2B For the phase of the ranging composite pseudocode, f T4B / T2B M represents the transmission rate of the ranging code. CA For CA code phase, f CA The transmission rate of the CA code is represented by *; the multiplication sign is represented by j = 1, 2.

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