A method for using beidou second-generation satellite time service

Abstract

The application discloses a method for time service by using Beidou II satellite, and time reference is obtained by using the clock of Beidou II navigation satellite, and standard time is kept, so that the time service function is realized. Since the relative frequency stability of the clock loaded on each Beidou II navigation satellite of the Beidou II satellite navigation system is very high, the clock is used to generate high-precision frequency standard, and the time service is performed by using the Beidou II navigation satellite in the sky, and an atomic clock is not needed to generate and keep the standard time. However, the atomic clock is needed to be used as the time reference to generate and keep the standard time in other traditional time service modes. Therefore, the time service mode realized by using the Beidou II navigation satellite is lower in cost and saves hardware resources compared with other traditional time service modes.

Description

Technical Field

[0001] This invention relates to a timing method using BeiDou-2 satellites, which uses BeiDou-2 satellite signals received by a satellite navigation receiver to obtain a high-precision time reference, and belongs to the field of satellite navigation and timing. Background Technology

[0002] Starting in 2005, my country began developing and constructing the BeiDou-2 satellite navigation system. By the end of 2012, it had basically completed a regional satellite navigation system capable of global expansion, consisting of 5 geostationary orbit (GEO) satellites, 5 inclined geosynchronous orbit (IGSO) satellites, and 4 medium Earth orbit (MEO) satellites. This system provides continuous three-dimensional positioning and velocity measurement capabilities, as well as high-precision time synchronization capabilities for my country and surrounding regions and sea areas. The BeiDou-2 system, with its independent intellectual property rights, uses a clock with very high relative frequency stability to generate high-precision frequency standards. Generally, the relative frequency stability of a navigation satellite clock is (10... -10 ~10 -15 ) / d.

[0003] Modern missile and space tests require precise time synchronization, and most of the equipment involved in these tests needs a standard time signal provided by a time synchronization system. In recent years, with the rapid development of national defense science and technology and the national economy, time synchronization is no longer just a special requirement for missile and space tests; the demands for time synchronization in conventional weapons testing, communications, power, navigation, and even daily life are also increasing. Currently, countries around the world use atomic clocks to generate and maintain standard time, which is the "time reference." Then, the time signal is delivered to users through various means and media, including shortwave, longwave, telephone networks, the Internet, and satellites, thereby achieving time synchronization across different systems. Table 1 below compares the characteristics of various time synchronization methods:

[0004] Table 1 Comparison of characteristics of various time synchronization methods

[0005]

[0006] As can be seen from the table above, navigation satellite time synchronization is superior to other time synchronization methods in terms of both accuracy and stability. It is not limited by time and space, and navigation satellites are a public resource, so no additional time reference is required.

[0007] With the increasing development of modern digital communication technology, navigation and positioning systems for civilian vehicles and ships, as well as digital switches, cross-connect equipment, SDH (Synchronization Digital Hierarchy) transmission systems, CDMA base stations, and BITS (Building Integrated Timing Supply) equipment all require reference clocks and frequency sources. However, it is impractical to equip every device that requires a reference clock with one, as the hardware cost would be too high. Summary of the Invention

[0008] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a time synchronization method using BeiDou-2, which realizes the use of satellite navigation receivers to receive BeiDou-2 satellite signals to obtain a high-precision time reference, greatly reducing costs.

[0009] The technical solution of this invention is:

[0010] A method for time synchronization using BeiDou-2 satellites includes the following steps:

[0011] (1) Obtain the accurate local location coordinates (x, y, z);

[0012] (2) Using the Beidou-2 satellite navigation message received by the satellite navigation receiver, the attribute information of the navigation satellite corresponding to the Beidou-2 satellite navigation message at the current time is parsed out. When the attribute information of at least one Beidou-2 navigation satellite is parsed out, proceed to step (3). The attribute information includes the position, velocity, satellite clock error and satellite clock drift of the Beidou-2 navigation satellite.

[0013] (3) By improving the monitoring method independently through TRAIM, we can monitor each Beidou-2 navigation satellite participating in the time synchronization in real time, eliminate abnormal Beidou-2 navigation satellites, and proceed to step (4).

[0014] (4) Using the position, velocity, clock bias, and clock drift of the BeiDou-2 navigation satellites obtained in step (2), calculate the local clock bias Δt of the satellite navigation receiver according to the following formula:

[0015] (x i -x) 2 +(y i -y) 2 +(z i -z) 2 =(P i -Δt·c-ΔT i ·cD i ) 2

[0016] Where (x, y, z) are the local location coordinates of the receiver obtained in step (1), (x, y, z) i y i z i P represents the position coordinates of the i-th Beidou-2 navigation satellite detected by the satellite navigation receiver; i Let ΔT be the pseudorange of the i-th Beidou-2 navigation satellite, and c be the speed of light; i D is the clock difference of the Beidou-2 navigation satellites; i This refers to the ranging errors generated by the ionosphere and troposphere on the BeiDou-2 navigation satellites.

[0017] Simultaneously, the local clock drift of the satellite navigation receiver is calculated according to the following formula.

[0018]

[0019] in, The velocity of the i-th Beidou-2 navigation satellite detected by the satellite navigation receiver; The clock drift of the i-th Beidou navigation satellite searched by the satellite navigation receiver; Let cosα be the pseudorange variation rate of the i-th navigation satellite searched by the satellite navigation receiver. i cosβ i cosγ i It is the direction cosine of a cuboid formed with the i-th Beidou-2 navigation satellite and the satellite navigation receiver as the endpoints of the diagonal;

[0020] (5) Based on the local clock drift and local clock difference of the satellite navigation receiver obtained in step (4), the satellite timing module completes satellite timing to obtain the local time information, B code time code and second pulse signal of the satellite navigation receiver.

[0021] The steps for the satellite timing module to complete satellite timing in step (5) are as follows:

[0022] (a) Based on the obtained local clock drift and local clock error of the satellite navigation receiver, using the formula Calculate the local time CURR_time of the satellite navigation receiver, and then execute steps (b), (c), and (d) simultaneously; where ZERO_time is the power-on time of the satellite navigation receiver; Δt is the local clock difference of the satellite navigation receiver; CURR_tic is the local clock drift of the satellite navigation receiver; RCO_tic is the duration from the power-on time to the current time; RCO_tic is the duration from the power-on time to the start of calculating the local clock difference.

[0023] (b) Adjust the local time CURR_time of the satellite navigation receiver calculated in step (a) to the nearest whole second to obtain the adjusted local time information of the satellite navigation receiver;

[0024] (c) First, generate a second pulse signal, then calculate the difference between the local time CURR_time of the satellite navigation receiver obtained in step (a) and the whole second. This difference is the compensation delay amount. Finally, use the compensation delay amount to correct the second pulse signal.

[0025] (d) Based on the local time CURR_time of the satellite navigation receiver calculated in step (a), perform B-code encoding to generate B-code time code.

[0026] The advantages of this invention compared to the prior art are:

[0027] (1) This invention uses BeiDou-2 navigation satellites to achieve time synchronization. It utilizes the clocks of BeiDou-2 navigation satellites in the sky to obtain a time reference and maintain standard time. Since each BeiDou-2 navigation satellite is equipped with a clock with very high relative frequency stability to generate a high-precision frequency standard, generally speaking, the relative frequency stability of the BeiDou-2 navigation satellite clock is (10... -10 ~10 -15 Furthermore, this is a free public resource for all users. Using satellite navigation for time synchronization does not require atomic clocks to generate and maintain standard time; while other traditional time synchronization methods require atomic clocks as a time reference to generate and maintain standard time. Therefore, satellite navigation time synchronization is more cost-effective and saves hardware resources compared to other traditional time synchronization methods.

[0028] (2) This invention is highly versatile and is not limited by external environment and geographical location. The navigation satellite timing method only relies on the already built Beidou-2 satellite navigation system. No matter how harsh the external terrain, climate and other conditions are, it can realize global, all-weather, real-time timing function without being limited by time and space. Other timing methods such as shortwave, longwave, telephone network and Internet require other material conditions to cooperate and have limited coverage. They are limited by time and space to a certain extent when used.

[0029] (3) The time accuracy and frequency stability obtained by the present invention are relatively high. Existing time synchronization technologies generally send the time reference signal to the user through shortwave, longwave, telephone network, Internet and other means. The time accuracy and frequency stability depend on the properties of the atomic clock that generates the time reference and are affected by the propagation path. Therefore, their time accuracy and frequency stability are very limited. Navigation satellite time synchronization, on the other hand, places the device using the technology of the present invention directly where the time reference is needed. Although it uses the clock of the navigation satellite and the navigation signal also needs to propagate in the atmosphere, the clock of the navigation satellite generally uses rubidium clock, cesium clock or even hydrogen clock. Moreover, the time synchronization method of the present invention has made corresponding corrections to the clock error, clock drift and atmospheric propagation delay of the satellite clock, ensuring the accuracy and stability of the time synchronization.

[0030] (4) This invention has a wide range of applications. It is based on the Beidou-2 satellite navigation system designed by my country and does not rely on the already built US GPS and Russian GLONASS satellite navigation systems. There is no need to worry about the satellite system being controlled by other countries and becoming unusable at critical moments. Therefore, it can be applied to the field of military operations and key areas related to national livelihoods such as communications and electricity. Attached Figure Description

[0031] Figure 1 This is a flowchart of the method of the present invention;

[0032] Figure 2 This is a schematic diagram of the satellite timing module of the present invention;

[0033] Figure 3 This refers to the local clock bias corresponding to the BeiDou-2 navigation satellite obtained using the method of this invention. Detailed Implementation

[0034] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0035] This invention provides a timing method using BeiDou-2 satellites. In this invention, BeiDou-2 satellites are received by a receiver or receiver equipped with a BeiDou-2 satellite receiver (described as a "satellite navigation receiver" in this invention). After receiving the BeiDou-2 satellite signal, the satellite navigation receiver performs relevant processing to obtain demodulated digital information that can be processed by the navigation and timing section. Finally, the navigation and timing section performs relevant processing to obtain timing information.

[0036] like Figure 1 As shown, the method steps of the present invention are as follows:

[0037] (1) First, obtain the coordinates of the receiver or the local location. You can use a measurement-type positioning receiver to obtain the coordinates of the receiver's location. If the satellite navigation receiver that receives Beidou-2 satellites has a positioning function, you can first locate the location and obtain the coordinates of the receiver before starting the timing function.

[0038] (2) Using the Beidou-2 satellite navigation message received by the satellite navigation receiver, the attribute information of the navigation satellite corresponding to the Beidou-2 satellite navigation message at the current time is parsed out. When the attribute information of at least one Beidou-2 navigation satellite is parsed out, proceed to step (3).

[0039] Satellite navigation receivers can search for visible BeiDou-2 navigation satellites in the sky and demodulate the satellite navigation messages through the receiver channel. Based on the BeiDou-2 satellite navigation messages received by the satellite navigation receiver, and according to the navigation message format specified in the published BeiDou-2 navigation satellite related data, the satellite navigation receiver parses the current time attribute information of the BeiDou-2 navigation satellite corresponding to the satellite navigation message. When the satellite navigation receiver parses the attribute information of at least one BeiDou-2 navigation satellite, it proceeds to step (3). The attribute information of the BeiDou-2 navigation satellite includes the position (X, Y, Z), velocity Vx, Vy and Vz, satellite clock difference and satellite clock drift of the BeiDou-2 navigation satellite.

[0040] (3) Improve the monitoring method through TRAIM (Time Receipt Autonomous Integrity Monitoring), monitor each Beidou-2 navigation satellite participating in time synchronization in real time, remove abnormal Beidou-2 navigation satellites, and proceed to step (4).

[0041] Since satellite navigation receivers can search for multiple visible BeiDou-2 navigation satellites in open areas, in position-keeping mode, there is usually more than one satellite participating in the timing function. In order to ensure timing accuracy, it is necessary to use the TRAIM autonomous integrity monitoring method to perform real-time autonomous integrity monitoring on each BeiDou-2 navigation satellite searched by the satellite navigation receiver and remove abnormal BeiDou-2 navigation satellites. This ensures the effectiveness and reliability of the positioning and timing results, and then proceeds to step (4).

[0042] (4) Based on the position, velocity, clock bias, and clock drift of the BeiDou-2 navigation satellites obtained in step (2), calculate the local clock bias of the satellite navigation receiver using the formula, such as... Figure 3 As shown, the local clock difference value is obtained using the BeiDou-2 navigation satellites of the BeiDou-2 navigation system.

[0043] In this invention, satellite timing is based on the ranging principle. Generally speaking, the receiver can provide the pseudorange and pseudorange change rate of the searched Beidou-2 satellite.

[0044] The fundamental observation equation of the distance measurement method:

[0045] P = ρ + c·(Δt + ΔT) + ΔD iono +ΔD trop (1)

[0046] In the formula: P is the measurement pseudorange, ρ is the geometric distance from the satellite to the receiver (in meters), c is the speed of light (in meters per second), Δt is the receiver clock error, ΔT is the satellite clock error (in seconds), and ΔD... iono For ionospheric delay, ΔD trop For tropospheric delay, the unit is meters.

[0047] Therefore, by measuring the propagation delay of the satellite signal to the receiver and multiplying it by the signal propagation speed, the distance from the satellite to the user terminal can be calculated. In actual measurements, the satellite clock error can be calculated from the navigation message and is a known quantity. For now, we can assume that the satellite clock error is zero, so the time deviation depends only on the receiver's clock error.

[0048] Assuming the receiver's local position coordinates are (x, y, z), and the position coordinates of the BeiDou-2 navigation satellites detected by the satellite navigation receiver are (x, y, z), then... i y i z i The ranging error caused by receiver clock bias is Δt·c, and the ranging error caused by satellite clock bias is ΔT. i c, the ranging error D caused by the ionosphere and troposphere to the BeiDou-2 navigation satellite. i The distance (pseudorange) to different BeiDou-2 navigation satellites measured by the receiver is P. i The local clock error Δt of the satellite navigation receiver can then be calculated using the following formula:

[0049] (x i -x) 2 +(y i -y) 2 +(z i -z) 2 =(P i -Δt·c-ΔT i ·cD i ) 2 (2)

[0050] In formula (2), the ranging error D of the i-th satellite caused by the ionosphere and troposphere is... i The position coordinates (x, y) of the i-th Beidou-2 navigation satellite found by the satellite navigation receiveri y i z i The ranging error caused by satellite clock bias is ΔT. i • c can be obtained from the satellite's message. The pseudorange is obtained by multiplying the time delay between the pseudo-random sequence of the Beidou-2 satellite received by the navigation receiver and the matching pseudo-random sequence generated by the receiver by the signal propagation speed (speed of light). In step (1), the local position coordinates of the navigation receiver are given as (x, y, z), so there is only one unknown in equation (2): the receiver clock error Δt. The navigation receiver only needs to receive one of the Beidou-2 satellites to solve for the receiver clock error, which prepares for further calculation of the receiver's time.

[0051] Since the speed of the satellite navigation receiver is 0, the local clock drift of the satellite navigation receiver can be calculated using the following formula.

[0052]

[0053] in, Let v be the velocity of the i-th Beidou-2 navigation satellite detected by the satellite navigation receiver. x v y v z (x, y, z) represents the velocity values ​​of the satellite navigation receiver in the three directions, in meters per second. The clock drift of the i-th Beidou navigation satellite searched by the satellite navigation receiver is expressed in meters per second. Cosα is the pseudorange variation rate of the i-th navigation satellite i searched by the satellite navigation receiver, in meters per second; i cosβ i cosγ i Let c be the direction cosine of a cuboid formed by the i-th Beidou-2 navigation satellite and the satellite navigation receiver as the endpoints of its diagonals, and c be the speed of light. It's worth noting that clock drift represents the amount of time the clock drifts within a certain time interval. Since the velocity of the satellite navigation receiver is 0, i.e., v... x =0, v y =0, v z =0, so only information from one Beidou-2 navigation satellite is needed to calculate the local clock drift, that is:

[0054] The x-direction velocity of the i-th Beidou-2 satellite y-direction velocity velocity in the z direction and satellite clock drift The pseudorange variation rate can be obtained from the navigation messages of the BeiDou-2 satellites. The value of cosα is obtained by measuring the Doppler signal received by the navigation receiver. i cosβ i and cosγ i Let the direction cosine be the cuboid formed by the i-th Beidou-2 satellite and the navigation receiver as diagonals. Therefore, the local clock drift of the satellite navigation receiver can be calculated by equation (3).

[0055] The local clock error Δt and local clock drift of the satellite navigation receiver are calculated in position-holding mode. And proceed to step (5);

[0056] (5) Based on the local clock drift and local clock difference of the satellite navigation receiver obtained in step (4), the satellite timing module completes the Beidou-2 satellite timing and obtains the local time information, B code time code and second pulse signal of the satellite navigation receiver.

[0057] like Figure 2 As shown, the satellite timing module performs satellite timing through the following steps:

[0058] The steps for the satellite timing module to complete satellite timing are as follows:

[0059] (a) Based on the obtained local clock drift and local clock error of the satellite navigation receiver, using the formula Calculate the local time CURR_time of the satellite navigation receiver, and then execute steps (b), (c), and (d) simultaneously; where ZERO_time is the power-on time of the satellite navigation receiver; Δt is the local clock difference of the satellite navigation receiver; CURR_tic is the local clock drift of the satellite navigation receiver; RCO_tic is the duration from the power-on time to the current time; RCO_tic is the duration from the power-on time to the start of calculating the local clock difference.

[0060] (b) Adjust the local time CURR_time of the satellite navigation receiver calculated in step (a) to the nearest whole second to obtain the adjusted local time information of the satellite navigation receiver. Generally, the time output by the satellite navigation receiver is not strictly synchronized with the time represented by the BeiDou-2 satellite navigation system at the nearest whole second. Therefore, the current time information CURR_time calculated by the above formula is not a whole second value and needs to be adjusted to the nearest whole second.

[0061] (c) First, a second pulse signal is generated. Then, the difference between the local time CURR_time of the satellite navigation receiver obtained in step (a) and the whole second is calculated. This difference is the compensation delay amount. Finally, the compensation delay amount is used to correct the second pulse signal. The generated second pulse has not been corrected and cannot be aligned with other standard second pulses, and it will drift. Therefore, delay compensation and correction are required for the second pulse to generate a high-precision, high-stability second pulse signal. The compensation delay amount is written into a controller to delay the second pulse signal, thereby achieving the effect of the second pulse and making the second pulse accurate and stable. Due to the delay compensation control and other operations on the second pulse signal, the timing accuracy of the timing receiver is greatly improved, and the phenomenon of left and right drift of the second pulse is eliminated.

[0062] (d) Based on the local time CURR_time of the satellite navigation receiver calculated in step (a), B-code encoding is performed to generate B-code time codes. The specific process for correcting the second pulse signal is as follows: first, the difference between the local time CURR_time of the satellite navigation receiver calculated in step (a) and the whole second is calculated. This difference is the second pulse signal compensation delay amount. When generating the B-code time code, due to the high accuracy and stability of the final second pulse, the time after whole-second adjustment is precisely synchronized with the satellite system time, thus generating a highly accurate B-code time code.

[0063] The undisclosed technologies in this invention are common knowledge to those skilled in the art.

Claims

1. A time synchronization method using BeiDou-2 satellites, characterized in that... The steps are as follows: (1) Obtain the accurate local location coordinates (x, y, z); (2) Using the BeiDou-2 satellite navigation message received by the satellite navigation receiver, the attribute information of the BeiDou-2 satellite corresponding to the BeiDou-2 satellite at the current time is parsed out. When the attribute information of at least one BeiDou-2 satellite is parsed out, proceed to step (3). The attribute information includes the position, velocity, satellite clock difference and satellite clock drift of the BeiDou-2 satellite. (3) By improving the monitoring method independently through TRAIM, we can monitor each Beidou-2 satellite participating in the time synchronization in real time, eliminate abnormal Beidou-2 satellites, and proceed to step (4). (4) Using the position, velocity, clock bias, and clock drift of the BeiDou-2 satellites obtained in step (2), calculate the local clock bias Δt of the satellite navigation receiver according to the following formula: (x i -x) 2 +(y i -y) 2 +(z i -z) 2 =(P i -Δt·c-ΔT i ·c-D i ) 2 Where (x, y, z) are the local location coordinates of the receiver obtained in step (1), (x, y, z) i y i z i P represents the position coordinates of the i-th Beidou-2 satellite detected by the satellite navigation receiver; i Let ΔT be the pseudorange of the i-th Beidou-2 satellite, and c be the speed of light; i D represents the clock bias of the BeiDou-2 satellites. i The ranging error caused by the ionosphere and troposphere to the BeiDou-2 satellite; Simultaneously, the local clock drift of the satellite navigation receiver is calculated according to the following formula. in, The velocity of the i-th Beidou-2 satellite detected by the satellite navigation receiver; The clock drift of the i-th Beidou-2 satellite searched by the satellite navigation receiver; Let cosα be the pseudorange variation rate of the i-th Beidou-2 satellite searched by the satellite navigation receiver. i cosβ i cosγ i It is the direction cosine of a cuboid formed with the i-th Beidou-2 satellite and the satellite navigation receiver as the endpoints of the diagonal; (5) Based on the local clock drift and local clock difference of the satellite navigation receiver obtained in step (4), the satellite timing module completes satellite timing to obtain the local time information, B code time code and second pulse signal of the satellite navigation receiver.

2. The timing method using BeiDou-2 satellites according to claim 1, characterized in that: The steps for the satellite timing module to complete satellite timing in step (5) are as follows: (a) Based on the obtained local clock drift and local clock error of the satellite navigation receiver, using the formula Calculate the local time CURR_time of the satellite navigation receiver, and then execute steps (b), (c), and (d) simultaneously; where ZERO_time is the power-on time of the satellite navigation receiver; Δt is the local clock difference of the satellite navigation receiver; CURR_tic is the local clock drift of the satellite navigation receiver; RCO_tic is the duration from the power-on time to the current time; RCO_tic is the duration from the power-on time to the start of calculating the local clock difference. (b) Adjust the local time CURR_time of the satellite navigation receiver calculated in step (a) to the nearest whole second to obtain the adjusted local time information of the satellite navigation receiver; (c) First, generate a second pulse signal, then calculate the difference between the local time CURR_time of the satellite navigation receiver obtained in step (a) and the whole second. This difference is the compensation delay amount. Finally, use the compensation delay amount to correct the second pulse signal. (d) Based on the local time CURR_time of the satellite navigation receiver calculated in step (a), perform B-code encoding to generate B-code time code.

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