Distributed satellite system phase error calibration method based on pseudorandom sequence
By adopting a phase error calibration method for distributed satellite systems based on pseudo-random sequences in satellite communication systems, the measurement deviation problem caused by equipment delay is solved, and efficient phase error calibration and improved accuracy of satellite synchronous transmission is achieved.
Patent Information
- Application Number
- CN202510234070.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-28
- Publication Date
- 2025-06-03
AI Technical Summary
In satellite communication, measurement deviations caused by equipment delay are difficult to be efficiently calibrated, affecting the accuracy and coordination capabilities of satellite synchronous transmission.
The phase error calibration method of distributed satellite system based on pseudo-random sequence is adopted, and no additional equipment is required. By measuring the cable length and device delay, the downlink transmission delay of each forwarding satellite is calculated, and the phase of the transmitted signal is adjusted to achieve phase consistency of the signal.
The measurement deviation caused by the delay of efficient calibration equipment is realized, the accuracy and coordination capabilities of satellite synchronous transmission are improved, and the adaptability is strong.
Smart Images
Figure CN120090686A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of wireless communication, and particularly relates to a phase error calibration method for a distributed satellite system based on a pseudo-random sequence. Background Art
[0002] Satellite communication can achieve global coverage, without relying on ground infrastructure, and provide real-time and reliable data transmission services. Especially when ground communication facilities are underdeveloped or affected by natural disasters, it becomes an important means to connect remote areas with the outside world. In addition, its disaster resistance, mobility, multi-user services, and enhanced security make satellite synchronous transmission play an indispensable role in many fields such as financial transactions, emergency communications, and navigation systems. In the field of satellite communication, since signals need to travel over vast spatial distances, it is particularly important to ensure the accuracy of information transmission, and the necessity of time synchronization is particularly prominent in this environment. For applications that require precise time synchronization such as GPS, and large-scale data transmission such as meteorological observations, satellite synchronous transmission provides precise timestamps, ensuring the integrity and timeliness of data. However, with the modern society's demand for high-speed and efficient communication, satellite synchronous transmission requires higher precision. When measuring the distance between a satellite and a ground gateway station and clock synchronization, a better method is needed to calibrate the measurement results to ensure the consistency of the phase of data transmitted by the satellite during synchronous transmission.
[0003] The inter-satellite link adopts a Time-Division Duplexing (TDD) system. The ranging method uses Symmetric Double-Sided Two-Way Ranging (SDS-TWR), and its performance depends on the measurement accuracy, which is affected by many factors such as device delay, ionospheric delay, frequency deviation, and relative motion between satellites. Here, the device delay that significantly reduces the measurement accuracy is focused on. The traditional calibration method is to establish a calibration self-closed loop. However, it is difficult to establish a calibration self-closed loop in a TDD link. To overcome these problems, a new type of error calibration method has been studied, which does not require additional equipment and can efficiently calibrate the measurement deviation caused by device delay in distance measurement and clock difference measurement. According to the distance, the downlink delay of satellite transmission can be obtained, and thus the phase can be calibrated to achieve satellite formation synchronous transmission. Summary of the Invention
[0004] To solve the above problems, the present invention discloses a phase error calibration method for a distributed satellite system based on a pseudo-random sequence. This method studies a new type of error calibration method that does not require additional equipment and can efficiently calibrate the measurement deviation caused by equipment delay in range measurement and clock difference measurement. According to the calibrated distance between the satellite and the gateway station, each relay satellite calculates the time delay during the downlink transmission of its respective link and sends the time delay information to the transmitting satellite. The transmitting satellite adjusts the phase of the signals transmitted on each link according to the downlink time delays of different links, so that the signals arriving at the gateway station via different downlink links are in phase, thereby realizing synchronous signal transmission in the satellite formation system and improving the collaborative ability of satellite synchronous transmission.
[0005] The technical solution adopted by the present invention is as follows:
[0006] The present invention provides a phase error calibration method for a distributed satellite system based on a pseudo-random sequence, including the following steps:
[0007] Step 1: First, model the SDS-TWR ranging process to obtain the expressions of range measurement error and clock measurement error caused by equipment.
[0008] Step 2: Measure the cable length; before the satellite is launched, connect the device to be tested with a cable on the ground; use the cable connection method, and after multiple measurements, obtain the round-trip time delay caused by the equipment and calibrate the satellite clock.
[0009] Step 3: The transmitting satellite formation uses the SDS-TWR ranging method to measure and calibrate the distance from each relay satellite to the gateway station, and convert the calibrated distance into transmission time delay.
[0010] Step 4: The relay satellite calculates the downlink transmission time delay of the transmitted signal via different relay satellites. Each relay satellite calculates the time delay during the downlink transmission of its respective link and sends the time delay information to the transmitting satellite. The transmitting satellite adjusts the phase of the signals transmitted on each downlink relay link according to the time delays of different downlink relay links, so that the signals arriving at the gateway station via different downlink relay links are in phase, thereby realizing synchronous data transmission in the satellite formation system.
[0011] Further, in Step 1, the SDS-TWR ranging is modeled. At time t 1 device M sends a local pseudo-random sequence to device S. Device S receives the pseudo-random sequence at time t 2 and calculates the phase difference information ρ 1 between its local phase and the received phase. The phase of the signal received by device S at time t 2 is actually equal to the phase of the pseudo-random sequence sent by M at time t 1 . Then ρ1 The expression is as follows:
[0012]
[0013] Among them, is the local pseudo-random sequence phase of device S at time t 2 moment, is the phase of the pseudo-random sequence of M at time t 1 moment. After device S processes the pseudo-random sequence, it sends the pseudo-random sequence to device M at time t 3 moment, and device M receives it at time t 4 moment to obtain the phase difference ρ 2 ; After device M processes the pseudo-random sequence, it sends the pseudo-random sequence to device S at time t 5 moment, and device M receives it at time t 6 moment to obtain the phase information difference ρ 3 . By analyzing the same as
[0014] above, we can get:
[0015]
[0016] Analyze the expression of ρ 1 and transform it as follows:
[0017]
[0018] The average frequency of the local phase from t 1 to t 2 can be expressed as the product of the normalized average frequency and the standard frequency f. t Msend is the transmission device delay of device M, t MS12 is the propagation path delay, t Sreceive is the reception delay of device S, t airMS12 is the ionospheric delay. The same definitions are given for ρ 2 and ρ 3 .
[0019] For the distance estimate value R sds the expression is as follows:
[0020]
[0021] The clock difference ΔT sds the expression is as follows:
[0022]
[0023] In step 1, further modeling processing is performed on the pseudo-random sequence. Let f M (t) and f S(t) represent the actual frequencies of device M and device S respectively, and the expressions are as follows
[0024]
[0025] where, α M (t) and α S (t) are frequency drift amounts. Taking the expectations of k M (t) and k S (t), we can get:
[0026]
[0027] Taking the distance and clock difference at time t 6 as the true values, then the difference between the measured value and the true value is the error. Let e R and e ΔT represent the distance measurement error and the clock measurement error respectively, and we can obtain:
[0028]
[0029] where, c is the speed of light, t MSdelay and t SMdelay are the one-way device transmission delays from device M to device S and from device S to device M respectively. The expressions are as follows:
[0030]
[0031] It can be seen that the measurement error is mainly composed of the frequency offsets K M and K S , the device sending and receiving delays t MSdelay and t SMdelay , the forwarding delays t Md and t Sd . Here, we mainly study the delays caused by the device:
[0032]
[0033] The device delay is on the order of μs. If the device uses a 40 MHz frequency oscillator, the order of magnitude of K M and K S is one in a million, so the product of the two is on the order of picoseconds and can be ignored. Therefore, simplifying the above formula gives:
[0034]
[0035] Measure the cable length in step 2. Connect the devices with the reference cable l b , and take the average of multiple measurements as the distance measurement expectation E[R lb . Then connect the cable l 1and l b Connection, multiple measurements are averaged as the expected value of distance measurement E[R l1+lb ], for l 2 Do the same process to get E[R l2+lb ]. The error caused by the connector is in the order of picoseconds and can be ignored. Then the lengths of the two cables to be tested can be obtained:
[0036]
[0037] In step 2, the device error is measured using the RF cable l 1 and l 2 Connect the devices under test M and S, and use an additional shielded twisted pair cable l p Connect the device. Device M at t send By l 1 Send a measurement signal and pass it through p Send a single pulse signal, device S at t meas-recv Time and t pulse The signal is received at the moment. meas-recv Time and t pulse Phase difference information at time Written as follows:
[0038]
[0039] Then device S performs the same operation on device M. Device M performs the same operation on device M at t′. meas-recv Time and t′ pulse The measurement signal and pulse signal are received at the same time. Similarly, the phase difference between the two times is obtained. Written as follows:
[0040]
[0041] Subtract the two phase differences and measure them multiple times to get the average value as the expectation and simplify it:
[0042]
[0043] According to the distance estimate, the average value of the distance values measured multiple times is taken as the expectation and simplified to obtain:
[0044]
[0045] Combining the two equations, we get the transmission and reception delay between devices:
[0046]
[0047] Substituting it into the device error expression, we can get the error caused by the device's transmit and receive delay on the measurement.
[0048] In the calibration process described in step 3, it can be expressed as:
[0049]
[0050] Among them, the measurement result is expressed as E[R sds [k]], k ∈ [1, 2, 3, 4], the device delay is expressed as t delay [i][j], i, j ∈ [0, 1, 2, 3, 4, 5], i represents the sender, and j represents the receiver. Device 0 represents the gateway station, devices 1, 2, 3, and 4 represent four relay satellites, and device 5 represents the sending satellite in the center of the formation.
[0051] In the phase adjustment process of step 4, first, the relay satellites calculate the downlink delays of their respective links and send them to the sending satellite. The sending satellite converts the delays of different downlink relay links into phase changes of the signals, and adjusts the phase of the transmitted signal according to the phase changes of the four downlink relay links, thereby ensuring that the signals on the four downlink relay links arrive at the gateway station with the same phase, enabling the satellites to synchronously transmit data. The expression of the downlink delay is as follows:
[0052] Among them, R fix is the fixed distance between the relay satellite and the sending satellite, and t process is the processing time of the relay satellite for the signal.
[0053] Compared with the existing technologies, the beneficial effects achieved by the present invention are:
[0054] 1. The present invention provides a new error calibration method, which does not require additional equipment. Only by connecting the device under test with a cable and performing multiple measurements can the device error be obtained, and the operation is simple.
[0055] 2. The device error will change with temperature. The error caused by the device can be measured at different temperatures. In practice, different error calibration values can be adopted according to the current ambient temperature, and the method has strong adaptability.
[0056] 3. It can efficiently calibrate the measurement deviation caused by device delay in distance measurement and clock difference measurement, improve the accuracy of the system distance measurement, and enhance the overall performance of the system.
[0057] 4. According to the calibrated distance between the satellite gateway station, the relay satellites calculate the downlink transmission delays of each satellite in the satellite formation. Finally, the sending satellite adjusts the phases of the transmission signals on different downlink relay links, so that the signals passing through different downlink relay links arrive at the gateway station with the same phase, improving the collaborative ability of satellite synchronous transmission. Description of the Drawings
[0058] Figure 1 Schematic diagram of the satellite formation synchronous transmission communication system in the present invention;
[0059] Figure 2 Flowchart of a phase error calibration method for a distributed satellite system based on pseudo-random sequences provided by the present invention. Detailed implementation manners
[0060] The present invention will be further clarified below in conjunction with the accompanying drawings and specific implementation manners. It should be understood that the following specific implementation manners are only used to illustrate the present invention and not to limit the scope of the present invention. It should be noted that the terms "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the accompanying drawings, and the terms "inner" and "outer" respectively refer to the directions towards or away from the geometric center of a specific component.
[0061] This embodiment proposes a phase error calibration method for a distributed satellite system based on pseudo-random sequences. This method studies a new type of error calibration method that does not require additional equipment and can efficiently calibrate the measurement deviation caused by equipment delay in distance measurement and clock difference measurement. According to the calibrated distance between the satellite gateway station, the downlink transmission delay of the signal sent by the central satellite of the satellite formation via different relay satellites is calculated. Finally, the phases of the signals sent on different downlink relay links are calibrated so that the signals arriving at the gateway station via different downlink relay links are in phase, improving the coordination ability of satellite synchronous transmission. Here, a specific example is used to describe the technical solution proposed in this embodiment in detail and completely.
[0062] As Figure 1 shown, the satellite formation synchronous transmission system includes a satellite formation and a gateway station. The satellite formation consists of 5 satellites. The satellite in the center of the formation is the transmitting satellite, and the 4 surrounding satellites are relay satellites. The transmitting satellite does not communicate directly with the gateway station and needs to synchronously transmit the same signal to the gateway station through the relay satellites.
[0063] This method first models the SDS-TWR ranging process to obtain the expressions of distance measurement error and clock measurement error caused by equipment. Then the cable length is measured. Before the satellite is launched, the device to be tested is connected with a cable on the ground. Using the cable connection method, after multiple measurements, the error caused by the equipment is obtained and the satellite clock is calibrated; then the transmitting satellite forms a formation. During the flight, the SDS-TWR ranging method is used to measure the distance from each transmitting satellite to the gateway station and calibrate it. The relay satellites calculate the downlink transmission delay of the transmitted signal via different relay satellites; the relay satellites upload the experimental data to the transmitting satellite, thereby adjusting the phases of the data transmitted on different links so that the data transmitted by all satellites is in phase, realizing the synchronous transmission of data by the satellite formation, and thus completing the design of the solution.
[0064] As Figure 2 shown, the detailed steps are as follows:
[0065] (1) Model the SDS-TWR ranging process. Among them, there are two transmission devices M and S. The devices measure the distance and clock difference by sending pseudo-random sequences to each other. At time t 1 , device M sends its local pseudo-random sequence to device S. Device S receives the pseudo-random sequence at time t 2 and calculates the phase difference information ρ 1 between its local phase and the received phase. The phase of the received signal at device S at time t 2 is actually equal to the phase of the pseudo-random sequence sent by M at time t 1 . Then the expression of ρ 1 is as follows:
[0066]
[0067] Among them, is the local pseudo-random sequence phase of device S at time t 2 , is the phase of M's pseudo-random sequence at time t 1 . After device S processes the pseudo-random sequence, it sends the pseudo-random sequence to device M at time t 3 . Device M receives it at time t 4 and obtains the phase difference ρ 2 ; after device M processes the pseudo-random sequence, it sends the pseudo-random sequence to device S at time t 5 . Device S receives it at time t 6 and obtains the phase information difference ρ 3 . Analyzing in the same way, we can get:
[0068]
[0069] Analyze the expression of ρ 1 and transform it as follows:
[0070]
[0071] Among them, represents the local phase change of device S, represents the phase difference between the two devices at the same time. The average frequency of the local phase from t 1 to t 2 can be expressed as the product of the normalized average frequency and the standard frequency f. Analyze t 2 - t 1 :
[0072] t2 -t 1 = t Msend +t MS12 +t Sreceive +t airMS12 (5)
[0073] where t Msend is the transmission device delay of device M, t MS12 is the propagation path delay, t Sreceive is the receiving delay of device S, t airMS12 is the ionospheric delay. Then ρ 1 The expression is rewritten as follows:
[0074]
[0075] Similarly, we can write
[0076]
[0077] Assume that the distance between the two devices remains unchanged during a complete measurement cycle, that is, the following equation is satisfied:
[0078] t MS12 = t SM34 = t MS56 = t MSR (9)
[0079] Then we can obtain that for the distance estimate value R sds The expression is as follows:
[0080]
[0081] where c is the speed of light, t MSdelay and t SMdelay are the one-way device transmission delays from device M to device S and from device S to device M respectively. The expressions are as follows:
[0082]
[0083] The clock difference ΔT sds The expression is as follows:
[0084]
[0085] After the end of a round of measurement, device S achieves clock synchronization with device M according to ΔT sds .
[0086] (2) Due to the frequency offset coefficient of the pseudo-random sequence and the device experiment coupling, which jointly cause deviations in distance measurement and clock measurement, further modeling processing of the pseudo-random sequence is required. Let f M (t) and fS (t) represent the actual frequencies of device M and device S respectively, and the expressions are as follows
[0087]
[0088] where α M (t) and α S (t) are the frequency drift amounts. Taking the expectations of k M (t) and k S (t), we can obtain:
[0089]
[0090] Taking the distance and clock difference at time t 6 as the true values, then the difference between the measured value and the true value is the error. Let e R and e ΔT represent the distance measurement error and the clock measurement error respectively, and we can get:
[0091]
[0092] It can be seen that the measurement error is mainly caused by the frequency offsets K M and K S , the transmission and reception delays t MSdelay and t SMdelay , and the forwarding delays t Md and t Sd . Here, we mainly study the delays caused by the devices:
[0093]
[0094] The device delays are in the order of μs. If the device uses a 40 MHz frequency oscillator, the order of magnitude of K M and K S is one in a million, so the product of the two is in the order of picoseconds and can be ignored. Therefore, simplifying the above formula gives
[0095]
[0096] It can be seen that the measurement error caused by the device comes from the transmission and reception delays.
[0097] (3) It is necessary to measure the length of the test cable. Three cables are required, the reference cable l b and two cables to be measured l 1 and l 2 . First, connect the devices with the cable l b , and take the average of multiple measurements as the distance measurement expectation E[R lb . Then, connect the cables l 1 and lb Connect, and take the average of multiple measurements as the expected value E[R l1+lb , and perform the same processing on l 2 to obtain E[R l2+lb . The error caused by the connector is on the order of picoseconds and can be ignored. Then the lengths of the two cables to be measured can be obtained as follows:
[0098]
[0099] (4) Measure the transceiver delay between equipment rooms using the cable connection method. Use RF cables l 1 and l 2 to connect the equipment M and S to be measured, and then use an additional shielded twisted pair l p to connect the equipment. First, equipment M sends a measurement signal through l send at t 1 , and at the same time sends a separate pulse signal through l p . Equipment S receives the signals at times t meas-recv and t pulse respectively. Due to equipment delay, the measurement signal arrives later than the pulse signal, that is, t meas-recv > t pulse . t meas-recv includes the transceiver delay t MSdelay of the one-way link and the delay t 1 of RF cable l l1 . The phase difference information at times t meas-recv and t pulse is written as the following formula: is written as the following formula:
[0100]
[0101] Then equipment S performs the same operation on equipment M. Equipment M receives the measurement signal and the pulse signal at times t' meas-recv and t' pulse respectively. Similarly, the phase difference at these two times is written as the following formula:
[0102]
[0103] Take the difference between the two phase differences, and take the average of multiple measurements as the expectation, and it can be written as:
[0104]
[0105] Then, according to Equation (10), taking the average of the distance values of multiple measurements as the expectation, we can obtain
[0106]
[0107] Simplifying equations (21) and (22) yields:
[0108]
[0109] The combined equations (23) and (24) give the transmission and reception delay between devices:
[0110]
[0111] Substituting into equation (17) we can get the measurement error caused by the device receiving and transmitting delay.
[0112] (5) By measuring (4) on all devices on the ground, we can obtain the transmission and reception delay between every two satellites and the transmission and reception delay between the forwarding satellite and the gateway, expressed as t delay [i][j], i,j∈[0,1,2,3,4,5]i represents the sender, j represents the receiver. Device 0 represents the gateway, devices 1, 2, 3, 4 represent the four forwarding satellites, and device 5 represents the sending satellite in the center of the formation. The satellites are sent to the sky to form a formation and the clocks are calibrated. The SDS-TWR method is used to measure the distance between the forwarding satellite and the ground gateway. The measurement result is E[R sds [k]], k∈[1,2,3,4]. Calibrate the ranging results:
[0113]
[0114] (6) Calculate the downlink transmission delay. Because of the satellite formation, the distance between the sending satellite and the forwarding satellite remains unchanged. The distance between each forwarding satellite and the gateway station has been obtained from (5). Then the downlink transmission delay can be obtained:
[0115]
[0116] Where R fix is the distance between the forwarding satellite and the sending satellite, t process It is the time it takes for the satellite to process the signal.
[0117] (7) Calibrate the phase and complete synchronous transmission. The forwarding satellite sends the delay information to the transmitting satellite. The transmitting satellite adjusts the phase of the transmission signal of each link according to the delay of different downlink forwarding links to ensure that the signals of the four downlink forwarding links maintain the same phase when they arrive at the gateway. This completes the design of the synchronous transmission scheme.
[0118] To sum up, it can be simplified as follows:
[0119] 1) Model the SDS-TWR ranging process and obtain the distance estimate R sds and clock estimate ΔTsds ;
[0120] 2) Further model the pseudo-random sequence to derive the measurement error caused by the device and
[0121] 3) Use the reference cable l b , measure the lengths of the cables l 1 and l 2 ;
[0122] 4) Adopt the cable connection method, and through multiple measurements, obtain and to obtain t MSdelay and t SMdelay , and then substitute the transceiver delay into the error calculation expression to obtain and
[0123] 5) Calibrate the ranging results to obtain the calibrated distance R sds [k], k ∈ [1, 2, 3, 4];
[0124] 6) Calculate the transmission delay t downlink [k], k ∈ [1, 2, 3, 4];
[0125] 7) The relay satellite calculates the downlink transmission delay of the transmitted signal via different relay satellites; the relay satellite uploads the experimental data to the transmitting satellite. The relay satellite adjusts the phases of the data transmitted on different links accordingly to ensure that the signals on the four links arrive at the gateway station with consistent phases.
[0126] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include the technical solutions composed of any combination of the above technical features.
Claims
1. A distributed satellite system phase error calibration method based on pseudo-random sequence, characterized in that: The following steps are involved: Step 1: First, the SDS-TWR ranging process is modeled to obtain the distance measurement error and clock measurement error expressions caused by the device; Step 2: Measure the cable length; before the satellite is launched, connect the device to be tested with a cable on the ground; The cable connection method is used to obtain the transmission and reception delay caused by the equipment after multiple measurements, and the satellite clock is calibrated; Step 3: Send the satellite formation and use the SDS-TWR ranging method to measure and calibrate the distance from each forwarding satellite to the gateway, and convert the calibrated distance into transmission delay; Step 4: The forwarding satellite calculates the downlink transmission delay of the transmitted signal through different forwarding satellites. Each forwarding satellite calculates the delay in the downlink transmission of its own link and sends the delay information to the transmitting satellite. The transmitting satellite adjusts the phase of the transmission signal of each link according to the delay of different downlink forwarding links, so that the signals through different downlinks maintain the same phase when they arrive at the gateway, thereby realizing the synchronous transmission of signals by the satellite formation system.
2. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: In step 1, SDS-TWR ranging is modeled. At time t1, device M sends a local pseudo-random sequence to device S. Device S receives the pseudo-random sequence at time t2 and calculates the difference information ρ1 between the local phase and the received phase. The phase of the signal received by device S at time t2 is actually equal to the phase of the pseudo-random sequence sent by M at time t1. Then the expression of ρ1 is as follows: in, is the local pseudo-random sequence phase of device S at time t2, is the phase of the pseudo-random sequence of M at time t1; after device S processes the pseudo-random sequence, it sends the pseudo-random sequence to device M at time t3, and device M receives it at time t4, and obtains a phase difference of ρ2; after device M processes the pseudo-random sequence, it sends the pseudo-random sequence to device S at time t5, and device M receives it at time t4, and obtains a phase difference of ρ2. At time t6, the phase information difference ρ3 is obtained; the analysis is the same as above, and we get: Analyze the expression of ρ1 and transform it as follows: The average frequency of the local phase from t1 to t2 is expressed as the normalized average frequency The product of the standard frequency f, t Msend is the sending device delay of device M, t MS12 is the propagation path delay, t Sreceive is the receiving delay of device S, t airMS12 is the ionospheric delay; the same definition is given to ρ2 and ρ3; For distance estimates The expression is as follows: Clock Difference The expression is as follows:
3. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: In step 1, the pseudo-random sequence is further modeled and f M (t) and f S (t) represents the actual frequency of device M and device S respectively, and the expression is as follows Among them, α M (t) and α S (t) is the frequency drift, for k M (t) and k S (t) Taking the expectation, we get: The distance and clock difference at time t6 are taken as the true value, then the difference between the measured value and the true value is the error. Let e R and e △T Denote the distance measurement error and clock measurement error respectively, and we get: Where c is the speed of light, t MSdelay and t SMdelay They are the one-way device transmission delays from device M to device S and from device S to device M, respectively; the expressions are as follows: From the above, we can see that the measurement error is mainly caused by the frequency offset K M and K S , device sending and receiving delay t MSdelay and t SMdelay , forwarding delay t Md and t Sd Composition; delay caused by equipment: The device delay is in the μs order of magnitude. If the device uses a 40MHz frequency oscillator, K M With K S The order of magnitude is one millionth, so the product of the two is in the order of picoseconds, which can be ignored. Therefore, the above formula is simplified to:
4. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: In step 2, measure the cable length using the reference cable l b Connect the devices and take the average of multiple measurements as the expected distance measurement value. Then use the connector to connect cable l1 and reference cable l b Connection, multiple measurements are averaged as the expected value of distance measurement Do the same for cable l2 and get The error caused by the connector is in the order of picoseconds and can be ignored; then the lengths of the two cables to be tested are:
5. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: In step 2, the device error is measured by connecting the devices M and S under test using RF cables l1 and l2, and an additional shielded twisted pair cable l p Connect device; device M at t send A measurement signal is sent via l1 and at the same time via l p Send a single pulse signal, device S at t meas-recv Time and t pulse The signal is received at the time; t meas-recv Time and t pulse Phase difference information at time Written as follows: Then device S performs the same operation on device M. Device M performs the same operation on device M at t′. meas-recv Time and t′ pulse Receive measurement signals and pulse signals at all times; Similarly, the phase difference between these two moments is obtained Written as follows: Subtract the two phase differences and measure them multiple times to get the average value as the expectation and simplify it: According to the distance estimate, the average value of the distance values measured multiple times is taken as the expectation and simplified to obtain: Combining the two equations, we get the transmission and reception delay between devices: Substituting it into the device error expression, we can get the error caused by the device's transmit and receive delay on the measurement.
6. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: The calibration process in step 3 is expressed as: The measurement results are expressed as The device delay is denoted as t delay [i][j], i,j∈[0,1,2,3,4,5], i represents the sender and j represents the receiver; device 0 represents the gateway, devices 1, 2, 3, 4 represent the four forwarding satellites, and device 5 represents the sending satellite in the center of the formation.
7. The distributed satellite system phase error calibration method based on pseudo-random sequence according to claim 1, characterized in that: In the phase adjustment process in step 4, the forwarding satellite first obtains the downlink delay of each link and sends it to the sending satellite. The sending satellite converts the downlink delay of different links into the phase change of the signal, and adjusts the phase of the sent signal according to the phase change of the four links, thereby ensuring that the signals of the four links maintain the same phase when they arrive at the gateway, so that the satellite formation can transmit data synchronously. The downlink delay expression is as follows: Among them, R fix is the fixed distance between the forwarding satellite and the transmitting satellite, t process It is the time it takes for the satellite to process the signal.