Method for Detecting False Lock of Downlink Signal of Deep Space Probe

Abstract

The present invention discloses a method for detecting mislocking of downlink signals of a deep space probe, which specifically includes the following steps: Step 1, calculate the transmission delay t of the downlink signal of the probe sy , before the time of T0 + t sy , if the ground locks the downlink signal, mislocking of the downlink signal is considered; otherwise, go to Step 2; Step 2, check the locking situation of the telemetry subcarrier. If the carrier is locked and the locking time of the subcarrier is less than the telemetry transmission time τ of 4 frames, it is preliminarily determined that the downlink signal is correctly locked; otherwise, the possibility of carrier signal mislocking is considered, and go to Step 3; Step 3, compare the difference between the measured and theoretical Doppler values. If the absolute value of this difference is greater than the limit value K f , mislocking of the signal is considered; otherwise, go to Step 4; Step 4, compare the difference between the actual signal-to-noise ratio and the theoretical signal-to-noise ratio of the downlink signal. If the absolute value of this difference is greater than the limit value K M , mislocking of the signal is considered; otherwise, return to the first step to re-enter the detection process. Using the present invention can effectively detect whether the deep space TT&C system mislocks the downlink signal of the probe.

Description

Technical Field

[0001] The present invention belongs to the technical field of deep space measurement and control in aerospace, and relates to a method for detecting mislocking of downlink signals of deep space detectors. Background Technique

[0002] With the development of China's aerospace industry, the number of deep space measurement and control missions has increased year by year. From Chang'e-1 to Chang'e-5 and Mars missions, the measurement and control distance has become farther and farther, and the working mode has become more and more complex. For example, the Chang'e-5 mission includes an orbiter, a lander, a returner, etc., and the working frequency points and modes of each target are different. The Mars mission is even more complex. It takes 7 months to fly to Mars, and the farthest distance reaches 400 million kilometers. There are also planned deep space exploration missions such as asteroid exploration and manned lunar landing in the future, and the detection distance will be even farther.

[0003] In long-distance deep space exploration activities, the signal-to-noise ratio of the downlink signal of the detector will be as low as 20 dBHz, and the signal is extremely weak. Under this level condition, external signals can easily interfere with the reception of the satellite downlink signal, resulting in the ground measurement and control equipment mislocking external signals. To improve the reliability of the ground measurement and control equipment to receive and lock the satellite downlink signal, it is necessary to quickly detect and judge whether the detector is mislocked, so as to provide a basis for corresponding handling. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for detecting mislocking of downlink signals of deep space detectors, which can effectively detect whether the deep space measurement and control system mislocks the downlink signals of the detectors.

[0005] The technical solution adopted by the present invention is a method for detecting mislocking of downlink signals of deep space detectors, which specifically includes the following steps:

[0006] Step 1, calculate the transmission delay of the downlink signal of the detector , before time, if the ground locks the downlink signal, then consider the downlink signal mislocked; otherwise, go to Step 2;

[0007] Step 2, check the locking situation of the telemetry subcarrier. After the carrier is locked, if the subcarrier locking time is less than the telemetry transmission time of 4 frames , then initially judge that the downlink signal is correctly locked; otherwise, consider the possibility of carrier signal mislocking and go to Step 3;

[0008] Step 3, compare the difference between the measured Doppler and the theoretical value. If the absolute value of this difference is greater than the limit value , then consider signal mislocking, otherwise go to Step 4;

[0009] Step 4, compare the difference between the actual signal-to-noise ratio and the theoretical signal-to-noise ratio of the downlink signal. If the absolute value of this difference is greater than the limit value , then consider signal mislocking, otherwise return to the first step and re-enter the detection process.

[0010] The features of the present invention also lie in:

[0011] In step 1, the following formula (1) is used to calculate the transmission delay of the detector's downlink signal reaching the ground :

[0012] (1);

[0013] Wherein, is the theoretical predicted position coordinate of the detector, is the position coordinate of the ground measurement and control equipment, is the speed of light.

[0014] In step 2, the following formula (2) is used to calculate the telemetry transmission time of 4 frames

[0015] (2);

[0016] Wherein, represents the length of the detector's downlink telemetry frame, is the telemetry code rate.

[0017] In step 3, when the detector does not lock the uplink signal and only sends the downlink signal, calculate the one-way Doppler of the detector; when the detector locks the uplink signal and coherently forwards it to the ground, calculate the two-way Doppler of the detector:

[0018] The one-way Doppler of the detector is calculated using the following formula (3):

[0019] (3);

[0020] Wherein, represents the frequency of the downlink signal transmitted by the aircraft, is the theoretical predicted speed of the detector;

[0021] The two-way Doppler of the detector is calculated using the following formula (4):

[0022] (4);

[0023] Wherein, represents the frequency of the uplink signal transmitted by the ground measurement and control equipment, is the theoretical predicted speed of the detector, is the forwarding ratio;

[0024] Read through the ground measurement and control equipment to calculate the actual Doppler value of the detector's downlink signal , calculate the absolute value of the difference between the actual Doppler and the theoretical Doppler through the following formula (5) :

[0025] (5);

[0026] If is greater than the limit value , then consider signal mislocking, otherwise go to step 4.

[0027] In step 4, calculate the signal-to-noise ratio of the downlink signal received by the ground TT&C equipment from the deep space probe using the following formula (6):

[0028] (6);

[0029] Wherein, is the omnidirectional radiation power of the probe, is the space attenuation, is the influence loss of the planet, is other losses except for the known losses, is the antenna gain of the ground TT&C equipment, is the antenna noise temperature of the ground TT&C equipment when full, is the Boltzmann constant;

[0030] Read the actual signal-to-noise ratio of the downlink signal through the ground TT&C equipment , calculate the absolute value of the difference between the actual signal-to-noise ratio and the theoretical signal-to-noise ratio of the downlink signal

[0031] (7);

[0032] If is greater than the limit value , then consider signal mislocking, otherwise return to the first step and re-enter the detection process.

[0033] The beneficial effect of the present invention is that a method for detecting signal mislocking of the downlink signal of a deep space probe provided by the present invention comprehensively considers the locking situation of the telemetry subcarrier, the difference between the measured and predicted Doppler, and the detection of whether the downlink signal intensity is mislocked. This method has high reliability and is easy to operate, and is suitable for effectively detecting whether the downlink signal of the deep space TT&C system is mislocked. Description of the Drawings

[0034] Figure 1 is a flowchart of the method for detecting signal mislocking of the downlink signal of the deep space probe of the present invention. Specific Embodiments

[0035] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0036] The method for detecting mislocking of the downlink signal of the deep space probe in the present invention is as follows Figure 1 as shown, and specifically includes the following steps:

[0037] Step 1, calculate the transmission delay of the downlink signal of the probe:

[0038] is the time when the downlink signal of the probe is sent. According to the theoretical predicted trajectory, calculate the transmission delay of the downlink signal of the probe reaching the ground .

[0039] (1);

[0040] Among them, is the theoretical predicted position coordinate of the probe, is the position coordinate of the ground TT&C equipment, is the speed of light.

[0041] Before time, if the ground locks the downlink signal, consider the mislocking of the downlink signal; otherwise, go to Step 2.

[0042] Step 2, check the locking situation of the telemetry subcarrier;

[0043] After the carrier is locked, if the subcarrier locking time is less than 4 frames of telemetry transmission time , it is initially judged that the downlink signal is locked correctly; otherwise, consider the possibility of carrier signal mislocking and go to Step 3.

[0044] (2);

[0045] Among them represents the length of the downlink telemetry frame of the probe, is the telemetry code rate.

[0046] Step 3, compare the measured and theoretical Doppler differences

[0047] According to the theoretical predicted trajectory, calculate the theoretical value of the downlink Doppler. The theoretical value of the Doppler is divided into unidirectional Doppler and bidirectional Doppler. When the probe does not lock the uplink signal and only sends the downlink signal, calculate the unidirectional Doppler of the probe; when the probe locks the uplink signal and coherently forwards it to the ground, calculate the bidirectional Doppler of the probe.

[0048] Unidirectional Doppler of the probe:

[0049] (3);

[0050] Among them, represents the frequency of the downlink signal emitted by the aircraft, is the theoretical predicted speed of the probe.

[0051] Detector two-way Doppler:

[0052] (4);

[0053] Wherein represents the uplink signal frequency transmitted by the ground TT&C equipment, is the theoretical predicted speed of the detector, is the transponder ratio.

[0054] Read out the actual Doppler value of the detector's downlink signal through the ground TT&C equipment , calculate the absolute value of the difference between the actual Doppler and the theoretical Doppler

[0055] (5);

[0056] If is greater than a certain limit value ( Specifically determined according to the theoretical prediction accuracy in the actual mission, and the clock frequency deviation of the detector needs to be considered), then signal mislocking is considered. Otherwise, go to step 4.

[0057] Step 4, compare the actual intensity of the downlink signal with the theoretical difference

[0058] For spacecraft in deep space exploration missions, the intensity of their downlink signals has been calibrated. The general calculation method for the signal-to-noise ratio of the downlink signals received by the ground TT&C equipment is:

[0059] (6)

[0060] Wherein is the omnidirectional radiation power of the detector, is the space attenuation, is the influence loss of the planet, is other losses except for the known losses, is the antenna gain of the ground TT&C equipment, is the antenna noise temperature of the ground TT&C equipment, is the Boltzmann constant.

[0061] Read out the actual signal-to-noise ratio of the downlink signal through the ground TT&C equipment , calculate the absolute value of the difference between the actual signal-to-noise ratio of the downlink signal and the theoretical signal-to-noise ratio

[0062] (7)

[0063] If is greater than a certain limit value ( (Specifically determined according to the theoretical prediction accuracy in the actual task), signal mislocking is considered. Otherwise, return to the first step and re-enter the detection process.

[0064] Embodiment

[0065] In a certain deep space exploration mission, the detector sent a downlink signal at 06:59:00 as planned. First, enter Step 1 to calculate the transmission delay which is about 835 s. The ground TT&C equipment was theoretically expected to receive the detector's downlink signal at 07:12:55, but the actual ground reception time was 07:06:12, earlier than the scheduled time. Signal mislocking was considered possible. For further confirmation, transfer to Step 2; the ground TT&C equipment had carrier lock, but the telemetry subcarrier was not locked for a long time (exceeding the 4-frame telemetry transmission time). Signal mislocking was considered possible and transferred to Step 3; the difference between the measured and predicted Doppler values was 20 kHz, greater than the limit value of 2 kHz. Signal mislocking was considered possible. For further confirmation, transfer to Step 4; the difference between the actual and theoretical intensities of the downlink signal was 9 dB, greater than the limit value of 5 dB. Signal mislocking was considered possible. Based on the above steps, it was determined that the detector's downlink signal was mislocked. The ground TT&C equipment promptly re-captured the downlink signal, and the carrier and subcarrier were locked normally, and the telemetry data was demodulated normally.

Claims

1. Method for detecting mislocking of downlink signals of deep space detectors, characterized in that: Specifically, it includes the following steps: Step 1, calculate the transmission delay of the detector's downlink signal , before the moment, if the ground locks the downlink signal, consider the mislocking of the downlink signal; Otherwise, go to step 2; In the said step 1, the transmission delay of the detector's downlink signal reaching the ground is calculated using the following formula (1) :[[-END]] （1）； Among them, is the theoretical predicted position coordinate of the detector, is the position coordinate of the ground TT&C equipment, is the speed of light; T0 is the time when the detector's downlink signal is sent; Step 2, check the telemetry subcarrier locking status. After the carrier is locked, if the subcarrier locking time is less than the telemetry transmission time of 4 frames , then preliminarily judge that the downlink signal locking is correct; otherwise, consider the possibility of incorrect carrier signal locking and go to Step 3; In the said step 2, the 4-frame telemetry transmission time is calculated using the following formula (2) （2）； Among them, represents the downlink telemetry frame length of the detector, is the telemetry code rate; Step 3, compare the difference between the measured Doppler value and the theoretical value. If the absolute value of this difference is greater than the limit value , then signal mislocking is considered; otherwise, proceed to Step 4; In step 3, when the detector does not lock the uplink signal and only transmits the downlink signal, calculate the one-way Doppler of the detector; when the detector locks the uplink signal and coherently forwards it to the ground, calculate the two-way Doppler of the detector: The one-way Doppler of the detector is calculated using the following formula (3): （3）； Among them, represents the downlink signal frequency emitted by the aircraft, is the theoretical predicted speed of the detector; The two-way Doppler of the detector is calculated using the following formula (4): （4）； Among them, represents the uplink signal frequency transmitted by the ground measurement and control equipment, is the theoretical predicted speed of the detector, is the transponder ratio; Read and calculate the actual Doppler value of the detector's downlink signal through ground measurement and control equipment , calculate the absolute value of the difference between the actual Doppler and the theoretical Doppler through the following formula (5) :[[]]END]] （5）； If is greater than the limit value , signal mislocking is considered, otherwise proceed to step 4; Step 4: Compare the difference between the actual signal-to-noise ratio and the theoretical signal-to-noise ratio of the downlink signal. If the absolute value of this difference is greater than the limit value , then consider signal mislocking; otherwise, return to the first step and re-enter the detection process. In the said Step 4, the following formula (6) is used to calculate the signal-to-noise ratio of the downlink signal received by the ground TT&C equipment for the deep space probe: （6）； Among them, is the omnidirectional radiation power of the detector, is the space attenuation, is the influence loss of the planet, is other losses except for the known losses, is the antenna gain of the ground TT&C equipment, is the antenna noise temperature of the full-stack TT&C equipment, is the Boltzmann constant; Read out the actual signal-to-noise ratio of the downlink signal through ground measurement and control equipment , and calculate the absolute value of the difference between the actual signal-to-noise ratio and the theoretical signal-to-noise ratio of the downlink signal （7）； If is greater than the limit value , signal mislocking is considered; otherwise, return to the first step and re-enter the detection process.

Images