A method and system for calculating time delay of a device-to-ground link based on detector time code

Abstract

The link delay between the detector and the ground is an important factor affecting the accuracy of timing, and is mainly obtained through test measurements during the AIT or large system docking test phase. Due to the different software and hardware design architectures of the on-board electronic equipment, some detectors have fuzzy matching problems in the output signal of the measurement of the link delay between the detector and the ground using the existing pulse time recording method for measuring the link delay between the detector and the ground. Based on the principle of device-to-ground timing, the on-board time code in the detector telemetry frame and the GPS time code attached by the ground time source at the moment of receiving the telemetry frame are obtained using the ground baseband equipment. A method and system for calculating the link delay between the detector and the ground based on the detector time code are proposed, which can be used to calculate the order of magnitude of the link delay between the detector and the ground and determine the exact value of the link delay between the detector and the ground in combination with the actual measurement results.

Description

Technical Field

[0001] The present invention relates to a method and system for calculating the link delay of a time code on a detector, which can be used to determine the order of magnitude of the link delay and obtain the accurate value of the link delay in combination with the measurement result. Background Art

[0002] In the third phase of the lunar exploration mission, the probe's computer cannot obtain GPS satellite signals like near-Earth satellites to achieve accurate time synchronization between the probe and the Earth. However, the lunar unmanned automatic sampling and return mission has many key links and irreversible key actions. The lunar power descent, lunar orbit rendezvous and docking, and reentry and return processes have high requirements for time synchronization between the probe and the Earth. In order to ensure the success of the mission, the probe can only be accurately timed on the ground.

[0003] The purpose of ground time calibration is to keep the detector time consistent with the ground time. The onboard computer will continuously calculate and maintain the time code, and broadcast or send the time code to other devices on the detector so that the entire detector has a unified time synchronization relationship.

[0004] The detector data tube computer calculates the time code T on the generator of any telemetry frame group frame moment 器上-轨 After passing through the computer and test equipment, the telemetry frame is transmitted to the ground telemetry demodulation equipment through the space link or coaxial cable. The ground telemetry demodulation equipment down-converts, demodulates and decodes the received telemetry signal, and then obtains the GPS standard time T GPS同步 , and parse and obtain the on-device time code T from the corresponding telemetry frame 器上-轨 . Thus, the time difference ΔT is obtained. 器地 =T GPS同步 -T 器上-轨 .

[0005] It should be noted that the telemetry frame is generated from the time it has experienced the delays of T0, T1, T2, T3, T4 and T5 in the table before it is demodulated by the ground telemetry demodulation equipment to obtain the baseband data and locked to the GPS standard time T GPS同步 , this delay is called the link delay ΔT 链路 (Here we can consider ΔT 链路 =T 0 +T 1 +T 2 +T 3 +T 4 -T 5 ). ΔT 链路It includes the time delay caused by the on-board equipment software / hardware, the space link between the device and the ground, and the ground measurement and control equipment. The data used during on-orbit operation is obtained through the large-system device-ground measurement and control docking test and measured using an oscilloscope. The data used in ground tests is obtained through the AIT stage and measured using pulse time recording equipment.

[0006] In order to accurately calibrate the time and keep the time synchronized, it is necessary to apply the time difference T 校时 =ΔT 器地 -ΔT 链路 Prepare the time calibration instruction and input it to the computer on the digital tube. The time calibration instruction here is relative time calibration. Figure 1 T6 and T7 can be ignored.

[0007] Table 1 Time mark description

[0008]

[0009] The testing principle of the device-to-ground link delay during the detector AIT and large system docking test phases is based on the pulse recording time, and the device-to-ground link delay is measured by measuring the difference between the previous and subsequent times.

[0010] Take the pulse time recording device in electrical performance testing as an example to explain ΔT 链路 Measurement method, ΔT in large system measurement and control docking test 链路 The measurement principle is the same, except that the time difference between the two pulses is calculated on the oscilloscope display screen. The measurement principle is as follows: The computer inserts the time code T of the telemetry frame TM0. 器上-轨 At the same time, the device outputs a time pulse to the outside (the specific output pulse time is related to the software design. If the pulse is not output at the time of inserting the time code, it needs to be compensated during the time calibration process) to the ground pulse time recording device. The pulse time recording device locks the pulse and obtains the GPS standard time T GPS(2) The computer on the simulcast device will have a time code T 器上-轨 The telemetry frame TM0 is transmitted to the ground through the measurement and control equipment on the device. The ground telemetry demodulation equipment demodulates and identifies the first bit of the telemetry frame header before outputting and locking and obtaining the GPS standard time T GPS(1) The link time difference ΔT is obtained. 链路 =T GPS(1) -T GPS(2) After multiple measurements, the link delay ΔT 链路 And take the average as the link inherent delay parameter.

[0011] The matching of pulses in the current measurement method using pulse recording time equipment or oscilloscope measurement is as follows: Figure 2 As shown, where ΔT 链路n =ΔT链路0 +nT, T is the time taken by the computer to download a frame of telemetry. The output pulse of the telemetry frame TM0 may match any pulse after pulse 1. In some detectors, there is almost no delay inside the computer. According to the time order of magnitude of the delay of the onboard measurement and control equipment, the space link delay, and the ground demodulation equipment delay, the TM0 pulse matches the pulse 1, and the link delay ΔT is obtained by calculating the time difference between the two pulses. 链路 . However, the software design of some detectors’ digital tube computers has telemetry frame buffering, so the TM0 pulse cannot simply match with pulse 1, but may match with pulse 2 or even pulse n. The digital tube computers on the detectors use different hardware architectures and software designs. After the telemetry frame TM0 inserts the time code and outputs the pulse, the internal buffering time of the digital tube computer is different. This creates a problem of pulse measurement signal matching ambiguity. Which pulse output by the ground demodulation equipment should the TM0 pulse match to obtain the true detector-to-ground link delay? Summary of the invention

[0012] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method and system for calculating the device-to-ground link delay of the time code on a detector, and obtain an accurate device-to-ground link delay in combination with a test method based on a pulse measurement signal.

[0013] The technical solution of the present invention is: a method for calculating the time delay of the detector-to-ground link of the time code on the detector, without the need for ground time calibration, and the steps are as follows:

[0014] S1. Build the ground test system and detector, receive telemetry frames, and obtain feature data;

[0015] S2. Calculate the link delay state equations at high bit rate and low bit rate based on the characteristic data;

[0016] S3. Obtain n groups of possible expected values ​​through the device-to-ground link delay state equation in step S2, and obtain the actual device-to-ground link delay using the maximum likelihood principle.

[0017] When receiving each telemetry frame, the ground test system adds the current GPS time code to the telemetry frame.

[0018] The computer on the detector is designed with two telemetry code rates and can switch the telemetry code rates.

[0019] The characteristic data include on-board time code and GPS time code at two telemetry code rates.

[0020] The specific calculation process of the link delay state equation in step S2 is:

[0021] Regardless of whether the detector tube computer works at a high code rate or a low code rate, the actual detector-ground time difference T 校时 are equal, so it follows that:

[0022] T 校时-高 =ΔT 器地-高 -ΔT 链路-高 (1)

[0023] T 校时-低 =ΔT 器地-低 -ΔT 链路-低 (2)

[0024] T 校时-高 =T 校时-低 (3)

[0025] ΔT 器地-高 =T GPS-高 -ΔT 链路-高 (4)

[0026] ΔT 器地-低 =T GPS-低 -ΔT 链路-低 (5)

[0027] ΔT 链路-低 =mΔT 链路-高 (6)

[0028] From (1)(2)(3)(4)(5)(6) we can conclude that:

[0029]

[0030]

[0031] Where, ΔT 链路-高 is the link delay between the detector and the ground when the detector is working at a high bit rate, ΔT 器地-高 is the time difference between the detector and the ground when the detector is working at a high bit rate, T 器上-高 T is the time code of a telemetry frame received by the ground test system when the detector is working at a high code rate. GPS-高 is the corresponding GPS time code; ΔT 链路-低 is the link delay between the detector and the ground when the detector is working at a low bit rate, ΔT 器地-低 T is the time difference between the detector and the ground when the detector is telemetered at a low bit rate. 器上-低 T is the time code of a telemetry frame received by the ground test system when the detector is working at a low bit rate. GPS-低 is the corresponding GPS time code.

[0032] The specific process of obtaining the real device-to-ground link delay in step S3 is as follows:

[0033] According to the calculated ΔT 链路-高 , ΔT 链路-低 , by taking the average value of n groups of values, we get and If the relationship is a linear multiple, high and low bit rates are no longer distinguished. Instead; According to the analysis of the ground pulse signal matching problem, the link delay ΔT 链路 Measure n possible expected values ​​and ΔT 链路n =ΔT 链路0 +nT, where when n=1, ΔT 链路1 is the first set of expected values, ..., ΔT 链路n is the nth group of expected values; the actual link delay is obtained from the (n+1)th group of values ​​using equation (8):

[0034]

[0035] According to the above formula, there exists a set minimum, then the group of measured values ​​ΔT is considered 链路n is the actual link delay of the current detector.

[0036] A time delay acquisition system for a detector-ground link of a time code, comprising a ground test system, a detector, a time delay state equation establishment module and a time delay state equation calculation module;

[0037] The ground test system and the detector receive the telemetry frames and obtain characteristic data;

[0038] The delay state equation building module calculates the device-to-ground link delay state equation under high bit rate and low bit rate according to the characteristic data;

[0039] The delay state equation calculation module obtains n groups of possible expected values ​​through the delay state equation, and obtains the real device-to-ground link delay using the maximum likelihood principle.

[0040] The ground test system adds the current GPS time code to each telemetry frame when receiving the telemetry frame; the computer on the detector is designed with two telemetry code rates and can switch the telemetry code rates; the characteristic data includes the on-board time code and GPS time code at the two telemetry code rates.

[0041] The specific calculation process of the time-delay state equation is:

[0042] Regardless of whether the detector tube computer works at a high code rate or a low code rate, the actual detector-ground time difference T 校时 are equal, so it follows that:

[0043] T 校时-高 =ΔT 器地-高 -ΔT 链路-高 (1)

[0044] T 校时-低 =ΔT 器地-低 -ΔT 链路-低 (2)

[0045] T 校时-高 =T 校时-低 (3)

[0046] ΔT 器地-高 =T GPS-高 -ΔT 链路-高 (4)

[0047] ΔT 器地-低 =T GPS-低 -ΔT 链路-低 (5)

[0048] ΔT 链路-低 =mΔT 链路-高 (6)

[0049] From (1)(2)(3)(4)(5)(6) we can conclude that:

[0050]

[0051]

[0052] Where, ΔT 链路-高 is the link delay between the detector and the ground when the detector is working at a high bit rate, ΔT 器地-高 is the time difference between the detector and the ground when the detector is working at a high bit rate, T 器上-高 T is the time code of a telemetry frame received by the ground test system when the detector is working at a high code rate. GPS-高 is the corresponding GPS time code; ΔT 链路-低 is the link delay between the detector and the ground when the detector is working at a low bit rate, ΔT 器地-低 T is the time difference between the detector and the ground when the detector is telemetered at a low bit rate. 器上-低 T is the time code of a telemetry frame received by the ground test system when the detector is working at a low bit rate. GPS-低 is the corresponding GPS time code.

[0053] The specific process of obtaining the real device-to-ground link delay is as follows:

[0054] According to the calculated ΔT 链路-高 , ΔT 链路-低 , by taking the average value of n groups of values, we get and If the relationship is a linear multiple, high and low bit rates are no longer distinguished. Instead; According to the analysis of the ground pulse signal matching problem, the link delay ΔT 链路 Measure n possible expected values ​​and ΔT 链路n =ΔT 链路0 +nT, where when n=1, ΔT 链路1 is the first set of expected values, ..., ΔT 链路n is the nth group of expected values; the actual link delay is obtained from the (n+1)th group of values ​​using equation (8):

[0055]

[0056] According to the above formula, there exists a set minimum, then the group of measured values ​​ΔT is considered 链路n is the actual link delay of the current detector.

[0057] The beneficial effects of the present invention are:

[0058] 1) The present invention is based on the analysis of the principle of device-ground time synchronization, and utilizes the high and low telemetry code rate switching of the detector data tube computer to obtain the device time code in the detector telemetry frame received by the ground baseband equipment under the two code rates and the GPS time code attached by the ground time source at the moment of receiving the telemetry frame, and calculates the device-ground link delay through mathematical deduction.

[0059] 2) The device-to-ground link delay calculation method in this article can be used in the AIT stage or large system docking test. The possible values ​​of several groups of device-to-ground link delays are measured by ground pulse measurement equipment. The accurate device-to-ground link delay value is determined by this method, eliminating the signal matching ambiguity problem in the ground measurement of the device-to-ground link delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a schematic diagram of the detector timing system;

[0061] Figure 2 This is a schematic diagram of the pulse output of the counting tube and demodulation equipment;

[0062] Figure 3 It is a connection diagram of the test system of the present invention;

[0063] Figure 4 The device-to-ground link delay and its average value under high bit rate calculated by the present invention;

[0064] Figure 5 The device-to-ground link delay and its average value at a low bit rate calculated by the present invention. DETAILED DESCRIPTION

[0065] In the third phase of the lunar exploration mission, the probe's computer cannot obtain GPS satellite signals like near-Earth satellites to achieve accurate time synchronization between the probe and the Earth. However, the lunar unmanned automatic sampling and return mission has many key links and irreversible key actions. The lunar power descent, lunar orbit rendezvous and docking, and reentry and return processes have high requirements for time synchronization between the probe and the Earth. In order to ensure the success of the mission, the probe can only be accurately timed on the ground.

[0066] The present invention provides a method for calculating the time delay of the detector-to-ground link of the time code, which does not require ground time calibration, and the steps are as follows:

[0067] S1. Build the ground test system and detector, receive telemetry frames, and obtain feature data;

[0068] S2. Using the mathematical relationship and empirical equations of the detector at high / low bit rates, derive the link delay state equations at high and low bit rates.

[0069] S3. Obtain n groups of possible expected values ​​through the device-to-ground link delay state equation in step S2, and obtain the actual device-to-ground link delay using the maximum likelihood principle.

[0070] When the ground test system receives each telemetry frame, it adds the current GPS time code to the telemetry frame.

[0071] The computer on the detector is designed with two telemetry code rates and can switch the telemetry code rates.

[0072] The characteristic data include on-board time code and GPS time code at two telemetry code rates;

[0073] The specific calculation process of the link delay state equation in step S2 is:

[0074] Regardless of whether the detector tube computer works at a high code rate or a low code rate, the actual detector-ground time difference T 校时 are equal, so it follows that:

[0075] T 校时-高 =ΔT 器地-高 -ΔT 链路-高 (1)

[0076] T 校时-低 =ΔT 器地-低 -Δ 链 T 路-低 (2)

[0077] T 校时-高 =T 校时-低 (3)

[0078] ΔT 器地-高 =T GPS-高 -ΔT 链路-高 (4)

[0079] ΔT 器地-低 =T GPS-低 -ΔT 链路-低 (5)

[0080] ΔT 链路-低 =mΔT 链路-高 (6)

[0081] From (1)(2)(3)(4)(5)(6) we can conclude that:

[0082]

[0083]

[0084] Where, ΔT 链路-高 is the link delay between the detector and the ground when the detector is working at a high bit rate, ΔT 器地-高 is the time difference between the detector and the ground when the detector is working at a high bit rate, T 器上-高 T is the time code of a telemetry frame received by the ground test system when the detector is working at a high code rate. GPS-高 is the corresponding GPS time code;

[0085] ΔT 链路-低 is the link delay between the detector and the ground when the detector is working at a low bit rate, ΔT 器地-低 T is the time difference between the detector and the ground when the detector is telemetered at a low bit rate. 器上-低 T is the time code of a telemetry frame received by the ground test system when the detector is working at a low bit rate. GPS-低 is the corresponding GPS time code;

[0086] Formula (5) is an empirical formula obtained through large system docking test. The high bit rate is n times the low bit rate. The link delay ΔT under the low bit rate is 链路-低 is the link delay ΔT at high speed 链路-高 n times, mainly related to the modulation and demodulation rate. GPS-高 , T 器上-高 , T GPS-低 , T 器上-低 All of them can be obtained through the ground test system, and the values ​​of a period of time before and after the high and low code rates are switched are selected for data processing.

[0087] The specific process of step S3 is:

[0088] Calculate ΔT using formula (6) (7) 链路-高 , ΔT 链路-低 , by averaging multiple sets of values and It is a linear multiple relationship, and the following analysis will no longer distinguish between high and low bit rates. According to the analysis of the ground pulse signal matching problem, the link delay ΔT 链路 The measurement can obtain n possible expected values, and ΔT 链路n =ΔT 链路0 +nT (n=0, 1, 2), use the following equation (8) to determine how to obtain the actual link delay from the (n+1) sets of values.

[0089]

[0090] According to formula (8), there exists a set minimum, then the group of measured values ​​ΔT is considered 链路n is the real instrument-to-ground link delay of the current detector. This calculation method eliminates the signal matching ambiguity problem existing in the ground measurement of the instrument-to-ground link delay and obtains the accurate instrument-to-ground link delay.

[0091] In order to ensure the link delay estimation method of this device, a ground verification system is designed to verify the feasibility and correctness of the ground measurement signal measurement solution. The schematic diagram of the ground verification system for measurement and control data transmission is shown in the figure. Figure 3 As shown:

[0092] The main equipment of the measurement and control digital transmission ground test system includes: integrated baseband equipment, RF channel equipment (including frequency converter, test cable, etc.), video channel equipment (including telemetry matcher, etc.), general test instruments and test computers, etc.

[0093] The test system adopts a two-level network structure based on LAN. The integrated baseband equipment and various test instruments are uniformly connected in the measurement and control data transmission local area network, and data exchange is carried out through the network. After receiving the telemetry data from the integrated baseband equipment, the telemetry data transmission front-end computer sends the telemetry data to the master control and other ground equipment that needs telemetry according to the master control communication protocol. The GPS time source provides the time code for the integrated baseband equipment to complete the time calibration of the instrument and the ground.

[0094] The specific implementation is as follows:

[0095] 1) The integrated baseband equipment is capable of receiving the time code in the computer telemetry frame of the detector;

[0096] 2) The GPS time source provides timing for the integrated baseband device, ensuring that the integrated baseband device can obtain the corresponding GPS time code after receiving each telemetry frame;

[0097] 3) Set the coding mode, frame length and code rate in the integrated baseband equipment. The high code rate of the computer telemetry on the detector is 2048bps, the low code rate is 1024bps, and the coding mode is RS+convolutional code; the high code rate of the telemetry code rate is twice the low code rate, that is, m=2;

[0098] 4) constructing a ground test system, and using the data acquisition process described in steps S1, S2, and S3, acquiring characteristic data of the onboard time code and the GPS time code at two telemetry code rates;

[0099] 5) Using the device-to-ground link delay state equation described in step S5, calculate the Table 2 shows the n groups of a priori measured results obtained by using the ground pulse recording equipment introduced in the technical background.

[0100] Table 2 Possible values ​​measured by ground pulse recording equipment

[0101]

[0102] 6) Through the device-to-ground link delay state equation in step S6, n groups of possible expected values ​​can be obtained, and the maximum likelihood principle is used to determine how to obtain the actual device-to-ground link delay from the n groups of values. According to formulas (6) and (7), 161 groups of device-to-ground link delays ΔT under high code rates are calculated: 链路-高 and the link delay ΔT at low bit rate 链路-低 , and find the mean value of the link delay between the device and the ground The link delays at high and low bit rates calculated from 161 sets of sample data and their average values ​​are plotted into a curve. Figure 4 and Figure 5 shown.

[0103] Formula (8) is used to process the n groups of measured results in Table 2, and the measured result 1 satisfies It can be determined that the measured result 1 in Table 2 is the actual device-to-ground link delay, that is, the device-to-ground link delay at high bit rate is 2392ms, and the device-to-ground link delay at high bit rate is 4784ms.

Claims

1. A method for calculating the time delay of the detector-to-ground link of the time code, without ground time calibration, characterized in that Here are the steps: S1. Build the ground test system and detector, receive telemetry frames, and obtain feature data; S2. Calculate the link delay state equations at high bit rate and low bit rate based on the characteristic data; S3, obtaining n groups of possible expected values ​​through the device-to-ground link delay state equation in step S2, and obtaining the actual device-to-ground link delay using the maximum likelihood principle; The characteristic data include on-board time code and GPS time code at two telemetry code rates; The specific calculation process of the link delay state equation in step S2 is: Regardless of whether the detector tube computer works at a high code rate or a low code rate, the actual detector-ground time difference T 校时 are equal, so we can conclude that: T 校时-高 =ΔT 器地-高 -ΔT 链路-高 (1) T 校时-低 =ΔT 器地-低 -ΔT 链路-低 (2) T 校时-高 =T 校时-低 (3) ΔT 器地-高 =T GPS-高 -ΔT 链路-高 (4) ΔT 器地-低 =T GPS-低 -ΔT 链路-低 (5) ΔT 链路-低 =mΔT 链路-高 (6) From (1)(2)(3)(4)(5)(6) we can conclude that: Where, ΔT 链路-高 is the link delay between the detector and the ground when the detector is working at a high bit rate, ΔT 器地-高 is the time difference between the detector and the ground when the detector is working at a high bit rate, T 器上-高 T is the time code of a telemetry frame received by the ground test system when the detector is working at a high code rate. GPS-高 is the corresponding GPS time code; ΔT 链路-低 is the link delay between the detector and the ground when the detector is working at a low bit rate, ΔT 器地-低 T is the time difference between the detector and the ground when the detector is telemetered at a low bit rate. 器上-低 T is the time code of a telemetry frame received by the ground test system when the detector is working at a low bit rate. GPS-低 is the corresponding GPS time code; The specific process of obtaining the real device-to-ground link delay in step S3 is as follows: According to the calculated ΔT 链路-高 , ΔT 链路-低 , by taking the average value of n groups of values, we get and If the relationship is a linear multiple, high and low bit rates are no longer distinguished. Instead; According to the analysis of the ground pulse signal matching problem, the link delay ΔT 链路 Measure n possible expected values ​​and ΔT 链路n =ΔT 链路0 +nT, where when n=1, ΔT 链路1 is the first set of expected values, ..., ΔT 链路n is the nth group of expected values; the actual link delay is obtained from the (n+1)th group of values ​​using equation (8): According to the above formula, there exists a set minimum, then the group of measured values ​​ΔT is considered 链路n is the actual link delay of the current detector.

2. A time delay acquisition system for the detector-ground link of the time code, characterized in that: It includes a ground test system, a detector, a time-delay state equation establishment module and a time-delay state equation calculation module; The ground test system and the detector receive the telemetry frames and obtain characteristic data; The delay state equation building module calculates the device-to-ground link delay state equation under high bit rate and low bit rate according to the characteristic data; The delay state equation calculation module obtains n groups of possible expected values ​​through the delay state equation, and obtains the real device-to-ground link delay using the maximum likelihood principle; The ground test system adds the current GPS time code to each telemetry frame when receiving the telemetry frame; the computer on the detector is designed with two telemetry code rates and can switch the telemetry code rate; the characteristic data includes the on-device time code and GPS time code at the two telemetry code rates; The specific calculation process of the time-delay state equation is: Regardless of whether the detector tube computer works at a high code rate or a low code rate, the actual detector-ground time difference T 校时 are equal, so it follows that: T 校时-高 =ΔT 器地-高 -ΔT 链路-高 (1) T 校时-低 =ΔT 器地-低 -ΔT 链路-低 (2) T 校时-高 =T 校时-低 (3) ΔT 器地-高 =T GPS-高 -ΔT 链路-高 (4) ΔT 器地-低 =T GPS-低 -ΔT 链路-低 (5) ΔT 链路-低 =mΔT 链路-高 (6) From (1)(2)(3)(4)(5)(6) we can conclude that: Where, ΔT 链路-高 is the link delay between the detector and the ground when the detector is working at a high bit rate, ΔT 器地-高 is the time difference between the detector and the ground when the detector is working at a high bit rate, T 器上-高 T is the time code of a telemetry frame received by the ground test system when the detector is working at a high code rate. GPS-高 is the corresponding GPS time code; ΔT 链路-低 is the link delay between the detector and the ground when the detector is working at a low bit rate, ΔT 器地-低 T is the time difference between the detector and the ground when the detector is telemetered at a low bit rate. 器上-低 T is the time code of a telemetry frame received by the ground test system when the detector is working at a low bit rate. GPS-低 is the corresponding GPS time code; The specific process of obtaining the real device-to-ground link delay is as follows: According to the calculated ΔT 链路-高 , ΔT 链路-低 , by taking the average value of n groups of values, we get and If the relationship is a linear multiple, high and low bit rates are no longer distinguished. Instead; According to the analysis of the ground pulse signal matching problem, the link delay ΔT 链路 Measure n possible expected values ​​and ΔT 链路n =ΔT 链路0 +nT, where when n=1, ΔT 链路1 is the first set of expected values, ..., ΔT 链路n is the nth group of expected values; the actual link delay is obtained from the (n+1)th group of values ​​using equation (8): According to the above formula, there exists a set The minimum value is considered to be the group of measured values ​​ΔT 链路n is the actual link delay of the current detector.

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