Rapid repositioning method for satellite navigation signal after long-time lock losing

Abstract

After the satellite loses the lock and is recaptured, if the lock losing time is less than the lock losing time threshold and the satellite ephemeris is still in the period of validity, repositioning is carried out by adopting the rapid repositioning method after the satellite navigation signal loses the lock for a long time; the method comprises the following steps: dividing the transmitting time of a satellite signal into a part above bit time and a part below the bit time; when the lock is lost, the launch moment is continuously and recursively deduced locally; after the signals are captured again and bit synchronization is achieved, the pseudo code period counter is used for obtaining the number of pseudo code periods in the bit time; a pseudo code and a carrier wave tracking loop are used to acquire a value in a single pseudo code period at a real emission moment to jointly form a part below bit time of the real emission moment; if a cross-bit phenomenon exists between the transmitting moment recursion value and the transmitting moment real value, correcting a part above the bit time in the transmitting moment recursion value by adopting a part below the bit time of the formed real transmitting moment; and reconstructing a real emission moment, obtaining a relative pseudo-range, and replacing the real pseudo-range with the relative pseudo-range for positioning.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite navigation, and particularly relates to a method for a receiver to quickly participate in positioning after the satellite navigation signal has been unlocked for an extremely long time and then reacquired. Background Art

[0002] In the satellite navigation and positioning process, the receiver has to go through steps such as signal acquisition, carrier tracking, pseudocode tracking, bit synchronization, subframe synchronization, ephemeris information parsing and extraction in sequence to obtain complete pseudorange information and calculate the correct satellite position before completing the positioning. Usually, signal acquisition, carrier / pseudocode tracking, and bit synchronization can be completed within 1 second, and the subframe synchronization takes no less than 6 seconds. When the satellite signal is unlocked and reacquired, since the ephemeris information has been saved and does not need to be parsed again, if the repositioning is carried out according to the conventional process, the time is not less than 7 seconds. However, in many current application scenarios, the repositioning time index is much smaller than the above theoretical value, and the positioning process must be modified to achieve fast positioning. On the other hand, the unlocking maintenance time of many existing methods is usually short, only dozens of seconds. After exceeding the threshold, the conventional positioning process starts again, which takes a long time. How to quickly reposition after an extremely long time of unlocking has become a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for quickly repositioning after a long time of unlocking of a satellite navigation signal, so as to solve the problem of quickly repositioning after the satellite signal has been unlocked for an extremely long time and then reacquired.

[0004] To achieve the above purpose, the present invention provides a method for quickly repositioning after a long time of unlocking of a satellite navigation signal. A unlocking time threshold is set. After the satellite is unlocked and reacquired, if the unlocking time < the unlocking time threshold and the ephemeris of the satellite is still within the valid period, this method is used for repositioning. This method includes: dividing the transmission time of the satellite signal into a part above the bit time and a part below the bit time; when the signal is unlocked, continuously recursively deduce the transmission time locally; when the signal is reacquired and bit synchronization is achieved, use a pseudocode period counter to obtain the number of pseudocode periods within the bit time; use a pseudocode tracking loop and a carrier tracking loop to obtain the value of the real transmission time within a single pseudocode period, and jointly form the part below the bit time of the real transmission time; if there is a phenomenon of crossing bits between the recursively deduced value of the transmission time and the real value of the transmission time, use the part below the bit time of the formed real transmission time to correct the part above the bit time in the recursively deduced value of the transmission time; reconstruct the real transmission time, obtain the relative pseudorange, and use the relative pseudorange to replace the real pseudorange for positioning.

[0005] The above-mentioned method for rapid repositioning after long-term loss of lock of satellite navigation signals, wherein the idea of setting the loss-of-lock time threshold is as follows: after the loss of lock, there is no bit period ambiguity in the recursive value of the satellite signal transmission time, that is, the error between the recursive value of the transmission time and the true value of the transmission time should not exceed half of the single-bit period of the navigation message.

[0006] The above-mentioned method for rapid repositioning after long-term loss of lock of satellite navigation signals, wherein the receiver is only blocked from signals when it is moving on the ground surface. Under this constraint condition, within the same time, the situation where the distance change between the satellite and the receiver is the largest occurs when: at the time of loss of lock, the satellite is exactly on the horizon of the receiver's field of view and is moving towards the zenith, and at the time of reacquisition, the receiver moves along the intersection line of the satellite orbit plane and the earth's surface towards the satellite ascending node. At this time, the calculation method of the loss-of-lock time threshold is as follows:

[0007]

[0008] Wherein, d0 is the distance between the satellite and the receiver at the time of loss of lock; R e is the radius of the earth; R s is the satellite orbit altitude; d1 is the distance between the satellite and the receiver at the time of reacquisition; θ is the angle between the line connecting the receiver to the earth's center and the line connecting the satellite to the earth's center; v u is the maximum moving speed of the receiver; T d is the loss-of-lock time threshold; ω s is the angular velocity of the satellite moving around the earth when the satellite orbit is simplified to a circle; T b is the length of a single-bit period of the navigation message; c is the speed of light; δ is the receiver clock drift.

[0009] The above-mentioned method for rapid repositioning after long-term loss of lock of satellite navigation signals, wherein when the signal loses lock, record the transmission time t sr of the satellite when it participated in positioning for the last time, and continuously recursively calculate the transmission time using the receiver crystal oscillator: during the signal loss-of-lock period, every time the crystal oscillator count value reaches the positioning solution period T, reset it to 0 and continue counting. At the same time, make t sr = t sr + T to maintain the recursive calculation of the transmission time.

[0010] The above-mentioned method for rapid repositioning after long-term loss of lock of satellite navigation signals, wherein to judge the bit synchronization situation of the satellite after loss-of-lock reacquisition, for GPS satellites, detect the rising edge of the cumulative value of adjacent two milliseconds (ms); for Beidou MEO / IGSO satellites, detect the matching situation between the cumulative value of every 20 ms and the NH code; use the histogram method. When there is a cumulative flip or NH code match, the count at this histogram is incremented by 1. The upper limit of the synchronization detection accumulation is set to 18, and the lower limit is set to 1; when the count of a single histogram exceeds the upper limit and the counts of other histograms are all less than the lower limit, it is determined that the bit is synchronized, otherwise it is non-synchronized.

[0011] The above method for rapid relocalization after long - term loss of lock of satellite navigation signals, wherein a pseudo - code period counter ca is set in the pseudo - code tracking loop of the receiver, with a range of 0 to 19, and a +1 operation is performed after tracking for a complete pseudo - code period. The value of ca represents the number of whole weeks of the pseudo - code received by the tracked satellite at the current bit time; when bit synchronization is achieved, the value of ca is initialized and marked as valid.

[0012] The above method for rapid relocalization after long - term loss of lock of satellite navigation signals, wherein for a satellite recaptured after loss of lock, when bit synchronization is achieved but frame synchronization has not been reached, the following part of the bit time of the true transmission time of the satellite is obtained: where p is the pseudo - code phase after carrier smoothing obtained from the carrier tracking loop, and T c is the number of chips in a complete pseudo - code period.

[0013] The above method for rapid relocalization after long - term loss of lock of satellite navigation signals, wherein the above - bit - time part of the recursive value of the transmission time of the satellite recaptured after loss of lock is obtained: where floor is the floor operation, t sr is the recursive value of the transmission time, and T b is the length of a single - bit period of the navigation message; the following part of the bit time of the recursive value of the transmission time of the satellite is obtained: If there is a cross - bit phenomenon between the following part of the bit time of the recursive value of the transmission time and the following part of the bit time of the true value of the transmission time, the above - bit - time part of the recursive value of the transmission time is corrected as follows:

[0014]

[0015] The above method for rapid relocalization after long - term loss of lock of satellite navigation signals, wherein the true transmission time of the satellite recaptured after loss of lock is reconstructed:

[0016] The above method for rapid relocalization after long - term loss of lock of satellite navigation signals, wherein the following relative pseudo - range positioning equations are solved to complete the positioning:

[0017]

[0018] where ρ i is the relative pseudo - range of the i - th satellite; c is the speed of light; M i is the sum of the group delay, transmission clock error, ionospheric delay, tropospheric delay, satellite position residual, ionospheric and tropospheric model residual, residual after correction of the transmission clock error, and receiver internal noise of the i - th satellite; is the satellite coordinate at the transmission time of the i - th satellite; (x u , y u , zu ) is the local coordinate to be solved; is the launch time of the i-th satellite, obtained by reconstruction, where i = 1, 2, …, n, and n is the total number of satellites, is the integer part of the launch time of the i-th satellite, is the fractional part of the launch time of the i-th satellite; taking the satellite that first obtains the accurate launch time as the reference, if the integer part of the launch time of other satellites and the integer part of the launch time of the reference satellite have a difference of 1 s, add or subtract 1 s from the fractional part of the launch time of other satellites accordingly to eliminate the cross-second existing between the launch times of different satellites and make

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] (1) The present invention realizes fast positioning after the signal is out of lock for a long time. The out-of-lock time is greater than half an hour, far exceeding the usual dozens of seconds of the existing methods;

[0021] (2) The present invention uses relative pseudorange instead of true pseudorange for positioning, can ignore the maintenance of the reception time, and reduces the pseudorange calculation complexity after reacquisition;

[0022] (3) The present invention omits the frame synchronization link through the recursion, correction, and reconstruction of the launch time, and can usually be positioned within 1 s, greatly shortening the positioning time required. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The method for fast repositioning of satellite navigation signals after long-term out-of-lock of the present invention is given by the following embodiments and drawings.

[0024] Figure 1 is a schematic diagram of the out-of-lock time threshold calculation principle in the present invention.

[0025] Figure 2 is a flowchart of the method for fast repositioning of satellite navigation signals after long-term out-of-lock of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The following will further describe in detail Figures 1 to 2 the method for fast repositioning of satellite navigation signals after long-term out-of-lock of the present invention.

[0027] Set the out-of-lock time threshold. After out-of-lock reacquisition, check the signal out-of-lock time. If the out-of-lock time < the out-of-lock time threshold and the ephemeris of this satellite (referring to the satellite that reacquires the target after out-of-lock) is still within the valid period, then use this method for repositioning; otherwise, process according to the conventional positioning process.

[0028] The idea of setting the out-of-lock time threshold is as follows: after the out-of-lock occurs, there is no bit period ambiguity in the recursive value of the satellite signal transmission time, that is, the error between the recursive value of the transmission time and the true value of the transmission time should not exceed half of the single-bit period of the navigation message.

[0029] The error between the recursive value of the transmission time and the true value of the transmission time is caused by three aspects: 1) the satellite's movement around the earth; 2) the receiver's own movement; the above two movements together cause the distance between the satellite and the receiver to change, and a corresponding difference is generated between the recursive value and the true value; 3) the drift of the receiver's crystal oscillator causes the recursive value to drift.

[0030] According to the above idea, the receiver will only be blocked from the signal when it is moving on the ground surface. Under this constraint condition, within the same time, the situation where the distance between the satellite and the receiver changes the most occurs when: at the time of out-of-lock, the satellite is exactly on the horizon of the receiver's field of view and moving towards the zenith, and at the time of reacquisition, the receiver moves along the intersection line of the satellite orbit plane and the earth's surface towards the satellite's ascending node, as Figure 1 , and at this time, the calculation method of the out-of-lock time threshold is:

[0031]

[0032] where, d0 is the distance between the satellite and the receiver at the time of out-of-lock; R e is the radius of the earth; R s is the satellite orbit altitude; d1 is the distance between the satellite and the receiver at the time of reacquisition; θ is the angle between the line connecting the receiver to the earth's center and the line connecting the satellite to the earth's center; v u is the maximum movement speed of the receiver; T d is the out-of-lock time threshold; ω s is the angular velocity of the satellite moving around the earth when the satellite orbit is simplified to a circle; T b is the length of a single-bit period of the navigation message (i.e., 20 ms); c is the speed of light; δ is the receiver clock drift.

[0033] For the method for rapid repositioning after long-term out-of-lock of satellite navigation signals in the present invention, the transmission time of the satellite signal is divided into a part above the bit time and a part below the bit time; when the signal is out-of-lock, the transmission time is continuously recursively calculated locally; when the signal is reacquired and bit synchronization is achieved, the number of pseudo-code periods within the bit time is obtained by using a pseudo-code period counter; the value of the true transmission time within a single pseudo-code period is obtained by using a pseudo-code tracking loop and a carrier tracking loop, and together they form the part below the bit time of the true transmission time; if there is a cross-bit phenomenon between the recursive value of the transmission time and the true value of the transmission time, the part above the bit time in the recursive value of the transmission time is corrected by using the part below the bit time of the formed true transmission time; the true transmission time is reconstructed; after the relative pseudo-range is obtained, positioning is performed.

[0034] The present invention uses relative pseudorange instead of true pseudorange to participate in the positioning solution. After the signal is lost, there is no need to pay attention to the maintenance accuracy of the local reception time. Only by reconstructing the transmission time of the satellite signal can the relative pseudorange be obtained, reducing the complexity of pseudorange calculation after reacquisition.

[0035] In the conventional positioning process, the pseudorange of each satellite can be expressed as:

[0036]

[0037] where t R is the satellite signal reception time; t s is the satellite signal transmission time; (x u , y u , z u ) is the local coordinate to be solved (i.e., the receiver coordinate to be solved); (x s , y s , z s ) is the satellite coordinate at the satellite signal transmission time; T G is the group delay; δt s is the transmission clock error; δt R is the receiving clock error to be solved; T iono and T trno are the ionospheric delay and tropospheric delay respectively; n r is the sum of the satellite position residual, the residual after correcting the transmission clock error, the residual of the ionospheric and tropospheric models, and the receiver internal noise.

[0038] From the pseudorange formula (i.e., formula (2)), the positioning equation set can be expressed as:

[0039]

[0040] where, is the satellite signal transmission time of the i-th satellite, i = 1, 2,..., n, and n is the total number of satellites; is the satellite coordinate at the satellite signal transmission time of the i-th satellite; M i is the sum of the group delay T G , the transmission clock error δt s , the ionospheric delay T iono , the tropospheric delay T trno and n r ; the right side of the positioning equation set is the actual distance between each satellite and the receiver. Although it contains unknowns (x u , y u , z u ), the specific value is uniquely determined; the left side and M i are both known terms; substituting tR Together with δt R regarded as an unknown as a whole, even if t R or δt R is changed, the actual reception time t r = t R - δt R is still uniquely determined.

[0041] Taking seconds as the unit, the transmission time of each satellite is divided into an integer part and a decimal part:

[0042]

[0043] Among them, is the integer part of the transmission time of the i-th satellite; is the decimal part of the transmission time of the i-th satellite.

[0044] Taking the satellite that first obtains the accurate transmission time as the reference, if the integer part of the transmission time of other satellites differs from the integer part of the transmission time of the reference satellite by 1 s, it means that the transmission times of these two satellites exactly cross a second. Add or subtract 1 s from the decimal part of the transmission time of other satellites accordingly to eliminate the possible second crossing between the transmission times of different satellites and make Ignoring the reception time, directly making

[0045]

[0046] Formula (5) is defined as the relative pseudorange positioning equation set. As shown in formula (5), the relative pseudorange ρ of each satellite i no longer contains the reception time t R , and the relative pseudorange value only depends on the transmission time of this satellite After obtaining

[0047] the equations can be solved to complete the positioning calculation.

[0048] Judge the bit synchronization of the satellite after loss of lock and reacquisition. For GPS satellites, detect the flip edge of the cumulative value of adjacent two milliseconds (ms); for Beidou MEO / IGSO satellites, detect the matching situation between the cumulative value every 20 ms and the NH code. Specifically, use the histogram method. When there is a cumulative flip or NH code match, the count at this histogram is incremented by 1. The upper limit of the synchronization detection accumulation is set to 18, and the lower limit is set to 1. When the count of a single histogram exceeds the upper limit and the counts of other histograms are all less than the lower limit, it is determined that bit synchronization is achieved; otherwise, it is asynchronous.

[0049] Set a pseudo-code period counter ca in the pseudo-code tracking loop of the receiver, with a range of 0 to 19. After tracking a complete pseudo-code period, perform a +1 operation. The value of ca represents the number of full weeks of the pseudo-code received by the tracked satellite in the current bit time. When bit synchronization is achieved, initialize the ca value and mark it as valid.

[0050] When the signal loses lock, record the transmission time t of the satellite at the last time it participated in positioning sr , and use the receiver crystal oscillator to continuously recursively calculate the transmission time: During the signal loss period, every time the crystal oscillator count value reaches the positioning solution period T, reset it to 0 and continue counting. At the same time, make t sr = t sr + T, to maintain the recursive calculation of the transmission time. t sr is the recursively calculated value of the transmission time.

[0051] For a satellite that loses lock and then reacquires, after bit synchronization but before frame synchronization is achieved, obtain the part below the bit time of the true transmission time of this satellite: Among them, p is the pseudo-code phase after carrier smoothing obtained from the carrier tracking loop, and T c is the number of chips in a complete pseudo-code period;

[0052] Obtain the part above the bit time of the recursively calculated value of the transmission time of this satellite: Among them, floor is the floor operation;

[0053] Obtain the part below the bit time of the recursively calculated value of the transmission time of this satellite:

[0054] If there is a cross-bit phenomenon between the part below the bit time of the recursively calculated value of the transmission time and the part below the bit time of the true value of the transmission time, then correct the part above the bit time of the recursively calculated value of the transmission time. Specifically as follows:

[0055]

[0056] Reconstruct the true transmission time of this satellite:

[0057] Using the reconstructed true emission time, perform positioning calculation according to formula (5).

[0058] For Beidou GEO satellites, since their frame synchronization time is much less than that of other types of satellites, this method is not required and the conventional positioning process can be directly adopted. The present invention is applicable to GPS satellites, Beidou MEO satellites, and Beidou IGSO satellites.

[0059] Example:

[0060] Taking Beidou MEO satellites as an example, first determine the time threshold for signal loss of lock:

[0061] Let the satellite orbital altitude be R s be approximately 21528 km, and the radius of the earth be R e be approximately 6371 km. According to formula (1), we have:

[0062] d0 = 27161822 m;

[0063]

[0064] Assume the maximum receiver movement speed v u is 100 m / s. The Beidou MEO satellite orbits the earth at a speed of about one circle in 12 hours, that is, ω s = 0.00833333° / s, θ = (76.79949569 - 0.00923266T d )°;

[0065] The receiver clock drift δ usually does not exceed 0.5 ppm. Substitute the speed of light c = 299794258 m / s and the navigation message bit period T b = 0.02 s into the equations of formula (1). After rearrangement, an equation with T d as the variable is obtained:

[0066] 22470T d 2 + 7244336620T d

[0067] + 355489058000000cos(76.79949569 - 0.00923266T d )

[0068] - 235049875445596 = 0

[0069] This equation has no analytical solution. The bisection method is used to solve it. Let the closed interval accuracy be 2 s. Finally, T d = 2621 s;

[0070] Assume that the current receiver is blocked and a loss of lock occurs. Taking a certain Beidou MEO satellite as an example, the time of loss of lock is 432422.524581327 s, and the recurrence value t of the transmission time is initialized with this value. sr , if the sampling period of the receiver observation is 0.1 s, then make t sr = t sr + 0.1 each time of sampling to maintain the recurrence of the transmission time of this satellite;

[0071] Assume that this satellite is the first satellite to be recaptured by the receiver and quickly achieves bit synchronization. At this time, the recurrence value t sr of its transmission time is 433546.724581327 s, and the duration of the loss of lock can be roughly estimated to be 1124 s, which is less than the threshold of 2621 s. According to Figure 2 's positioning process, without waiting for sub-frame synchronization, directly reconstruct the true transmission time according to the present invention;

[0072] Assume that the integer number of chips ca of the received pseudo-code in a single bit read from the pseudo-code counter is 16, and the pseudo-code phase p after carrier smoothing read from the carrier tracking loop is 3518.425;

[0073] The number of chips T c of a single pseudo-code period of Beidou satellite is 10230. Obtain the following part of the bit of the transmission time of this satellite:

[0074] Obtain the part above the bit of the recurrence value of the transmission time of this satellite:

[0075]

[0076] Obtain the part below the bit of the recurrence value of the transmission time of this satellite:

[0077]

[0078] Check whether there is a cross-bit period between the recurrence value of the transmission time and the true value:

[0079] If there is a cross-bit period, it means that during the loss of lock, there is an opposite movement between the satellite and the receiver. Therefore, is corrected and adjusted forward by 20 ms:

[0080]

[0081] Reconstruct the true transmission time of this satellite:

[0082]

[0083] Determine whether its ephemeris is still within the valid period. If it is invalid, sub-frame synchronization still needs to be waited for to extract the ephemeris. If it is valid, the relative pseudorange can be directly formed according to the process of the present invention for positioning:

[0084] Assume that in the ephemeris of the current stored satellite, the reference time t oe is 432000s, and the effective time is 433546 - 432000 = 1546s. Usually, the valid period of the satellite ephemeris can be taken as 2 hours. Therefore, its ephemeris is still within the valid period, and the relative pseudorange can be directly formed according to the process of the present invention for positioning;

[0085] Based on the satellite's launch time, make the reception time Form the relative pseudorange ρ = c(t R - t s ) = c(433546 - 433546 - 0.716343932);

[0086] When the number of satellites with the true launch time obtained is greater than 4, the positioning result can be calculated using formula (5).

Claims

1. A method for rapid repositioning after a satellite navigation signal is lost for a long time, characterized in that: Set the unlock time threshold. After the satellite is unlocked and recaptured, if the unlock time is less than the unlock time threshold and the satellite ephemeris is still valid, this method is used for repositioning. The method includes: Divide the transmission time of the satellite signal into a part above the bit time and a part below the bit time; When the signal is lost, the transmission time is continuously recursively calculated locally; When the signal is recaptured and bit synchronization is achieved, the pseudo code cycle counter is used to obtain the number of pseudo code cycles in the bit time; the pseudo code tracking loop and the carrier tracking loop are used to obtain the value of the actual transmission time in a single pseudo code cycle, which together constitute the following part of the bit time of the actual transmission time; If there is a cross-bit phenomenon between the recursive value of the emission time and the real value of the emission time, the part below the bit time of the real emission time is used to correct the part above the bit time in the recursive value of the emission time; Reconstruct the real transmission time, obtain the relative pseudorange, and use the relative pseudorange instead of the real pseudorange for positioning.

2. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 1, characterized in that: The idea of ​​setting the unlock time threshold is: after losing lock, there is no bit period ambiguity in the recursive value of the satellite signal transmission time, that is, the error between the recursive value of the transmission time and the true value of the transmission time should not exceed half of a single bit period of the navigation message.

3. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 2, characterized in that: The receiver will be blocked from signal only when it moves on the surface. Under this constraint, the maximum change in distance between the satellite and the receiver within the same time occurs when: when the receiver loses lock, the satellite is just on the horizon of the receiver's field of view and is moving toward the zenith. When recapture occurs, the receiver moves along the intersection of the satellite orbit plane and the earth's surface toward the satellite's ascending node. At this time, the lock-loss time threshold is calculated as: Where d0 is the distance between the satellite and the receiver when the lock is lost; R e is the radius of the Earth; R s is the satellite orbit height; d1 is the distance between the satellite and the receiver during recapture; θ is the angle between the line from the receiver to the center of the earth and the line from the satellite to the center of the earth; v u is the maximum moving speed of the receiver; T d That is the unlocking time threshold; ω s is the angular velocity of the satellite orbiting the earth when the satellite orbit is simplified to a circle; T b is the length of a single bit period of the navigation message; c is the speed of light; δ is the receiver clock drift.

4. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 1, characterized in that: When the signal is lost, record the launch time t when the satellite last participated in positioning sr , and use the receiver crystal oscillator to continuously recursively calculate the transmission time: during the signal loss period, each time the crystal oscillator count value reaches the positioning solution cycle T, it is reset to 0 and continues to count. At the same time, t sr =t sr +T, maintain the recursive launch time.

5. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 1, characterized in that: Determine the bit synchronization of the satellite after loss of lock and recapture. For GPS satellites, detect the flip edge of the accumulated values ​​of two adjacent milliseconds; for Beidou MEO / IGSO satellites, detect the matching of the accumulated value of every 20ms with the NH code; use the histogram method, when the accumulation flips or the NH code matches, the count at this histogram is +1, the upper limit of the synchronization detection accumulation is set to 18, and the lower limit is set to 1; when the count of a single histogram exceeds the upper limit and the counts of other histograms are all less than the lower limit, it is determined to be bit synchronized, otherwise it is asynchronous.

6. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 5, characterized in that: A pseudo code cycle counter ca is set in the receiver pseudo code tracking loop, ranging from 0 to 19. After tracking a complete pseudo code cycle, a +1 operation is performed. The ca value represents the number of pseudo code cycles that the tracked satellite has received in the current bit time. When the bit is synchronized, the ca value is initialized and marked as valid.

7. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 6, characterized in that: For a satellite that is recaptured after being locked, after bit synchronization but before frame synchronization, the following part of the bit time of the actual transmission time of the satellite is obtained: Where p is the carrier-smoothed pseudo code phase obtained from the carrier tracking loop, T c is the number of chips in a complete pseudo code period.

8. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 7, characterized in that: The above part of the bit time to obtain the recursive value of the satellite launch time after losing lock: Among them, floor is the rounding down operation, t sr is the recursive value of the launch time, T b It is the length of a single bit period of the navigation message; The bits for obtaining the recursive value of the satellite launch time are as follows: If there is a cross-bit phenomenon between the part below the bit time of the recursive value at the time of transmission and the part below the bit time of the real value at the time of transmission, the part above the bit time of the recursive value at the time of transmission shall be corrected as follows:

9. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 8, characterized in that: Reconstruct the actual launch time of the satellite after losing lock and reacquiring it:

10. The method for rapid repositioning after a satellite navigation signal is lost for a long time as claimed in claim 9, characterized in that: Solve the following relative pseudorange positioning equations to complete positioning: Among them, ρ i is the relative pseudorange of the ith satellite; c is the speed of light; M i is the sum of the group delay, transmit clock error, ionospheric delay, tropospheric delay, satellite position residual, ionospheric and tropospheric model residuals, transmit clock error corrected residuals and receiver internal noise of the i-th satellite; is the satellite coordinates at the launch time of the i-th satellite; (x u ,y u ,z u ) is the local coordinate to be solved; is the launch time of the i-th satellite, obtained by reconstruction, i = 1, 2, ..., n, n is the total number of satellites, is the integer part of the launch time of the i-th satellite, is the decimal part of the launch time of the i-th satellite; Taking the first satellite that obtains the accurate launch time as the benchmark, if the integer part of the launch time of other satellites The integer part of the launch time of the reference satellite If there is a 1 second difference, add or subtract 1 second from the decimal part of the launch time of other satellites accordingly to eliminate the leap seconds between the launch times of different satellites and make j=2,…,n.

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