WO2014089988A1

WO2014089988A1 - High-sensitivity beidou auxiliary timing device, timing receiver and timing method

Info

Publication number: WO2014089988A1
Application number: PCT/CN2013/081844
Authority: WO
Inventors: 邱剑宁; 王瀚晟
Original assignee: 北京东方联星科技有限公司
Priority date: 2012-12-14
Filing date: 2013-08-20
Publication date: 2014-06-19
Also published as: CN103033828B; CN103033828A

Abstract

Provided are a high-sensitivity BEIDOU auxiliary timing device, timing receiver and timing method. Under a bad signal condition, as though only one satellite is tracked, in case of failing to complete positioning resolving, time synchronization of a BEIDOU system still can be completed depending on cycle time information extracted from a received navigation signal, providing a high-sensitivity timing service. The high-sensitivity BEIDOU auxiliary timing device comprises a frame header searching correlator, a frame header searching threshold judgment module, a cycle time extracting correlator and a cycle time threshold judgment module which are connected sequentially, wherein the output of the frame header searching threshold judgment module is connected to the output of the cycle time threshold judgment module and the input of the frame header searching correlator; and the frame header searching correlator comprises a frame header phase-coherence accumulation module and a frame header non-phase-coherence accumulation module which are connected with each other, and the cycle time extracting correlator comprises a cycle time phase-coherence accumulation module and a cycle time non-phase-coherence accumulation module which are connected with each other.

Description

High-sensitivity Beidou auxiliary timing device and timing receiver and timing method

Technical field

The invention relates to the technical field of satellite navigation timing, in particular to a high-sensitivity Beidou auxiliary timing device and a high-sensitivity Beidou navigation timing receiver and a timing method embedded with the high-sensitivity auxiliary timing device. Background technique

The basic meaning of timing is to provide time information to other devices or systems through standard or customized interfaces and protocols. The initial timing is basically achieved by observing the regular motion of celestial bodies such as the sun and stars, called astronomical timing. The astronomical measurement relies on the Earth's rotation, and the inhomogeneity of the Earth's rotation makes the time (World Time) accuracy of the astronomical method unsatisfactory for all aspects of the social and economic needs of the mid-20th century. A more accurate and stable time standard came into being. This is the "atomic clock." At present, all countries in the world use atomic clocks to generate and maintain standard time. This is the "time base". Then, time signals are sent to users through various means and media, including: short wave, long wave, telephone network, internet, satellite, etc. . This entire process is called a "time-sending system."

The basic method of short-wave timing is to broadcast a time signal (referred to as a time number) by a radio station, and the user receives the time number with the radio receiver, and then performs local time-to-time. Long-wave timing uses long-wave (low-frequency) for time-frequency transmission and calibration. It is a timing method with higher coverage than short-wavelength and more accurate calibration. The network time and telephone time are used to provide the user with a standard time signal by means of user inquiry. Satellite timing can achieve large coverage of the broadcast signal, and it is more accurate than the first two timing methods. According to the satellite's role in the timing of satellites, the satellite timing is divided into active and transitive. The active satellite has a precision clock that broadcasts standard time signals; the relay only forwards standard time signals sent by satellite ground stations from ground time references.

The basic principle of satellite navigation and positioning is to measure the distance between the satellite at the known location and the receiver of the user, and then combine the data of multiple satellites to know the specific location of the receiver. To achieve this, the position of the satellite can be detected in the satellite ephemeris based on the time recorded by the onboard clock, and the distance from the user to the satellite is propagated to the time elapsed by the user by recording the satellite signal, which is multiplied by The speed of light is obtained. Due to satellite orbit error, interference from the atmosphere ionosphere, the synchronization of the star clock with the local clock, etc., this distance is not the real distance between the user and the satellite, but the pseudorange. When the satellite is working normally, the navigation message is continuously transmitted with a pseudo-random code consisting of 1 and 0 binary symbols. The navigation message includes information such as satellite ephemeris, working conditions, clock correction, ionospheric delay correction, and atmospheric refraction correction. The user receives the navigation message, extracts the satellite time and compares it with his own clock to know the distance between the satellite and the user, and then uses the navigation message. The satellite ephemeris data is derived from the location of the satellite when the message is transmitted, and the position and velocity of the user in the geodetic coordinate system.

The satellite part of the navigation system is used to continuously transmit navigation messages. The satellite navigation message contains system time, clock correction parameters, ionospheric delay model parameters, satellite ephemeris and satellite health status information, etc., in order to provide users with time and location. Result data such as coordinates and velocity, and related information for navigation satellite signal processing. However, since the time difference between the clock used by the user receiver and the satellite onboard clock is called the clock difference, in addition to the user's three-dimensional coordinates x, y, z, the time difference between the satellite and the receiver is introduced as Unknown, then solve the 4 unknowns with 4 equations. Therefore, if you want to know the location of the receiver, you must receive at least 4 satellite signals. By using the time difference A between the calculated local receiver clock and the satellite navigation system, the time between the satellite navigation receiver local clock and the atomic clock-based navigation system can be synchronized. Therefore, each satellite navigation receiver in the state of successful positioning resolution is a high-precision clock.

At present, satellite navigation timing application has developed into a global high-tech industry, and with the increasing maturity of the Beidou satellite navigation system, the timing application based on this system has also received more and more attention. Beidou satellite navigation system is a global satellite positioning and communication system developed by China. It is the third mature satellite navigation system after the United States' Global Positioning System (GPS) and Russia's GLONASS. It can be used around the world all day and all day. It provides high-precision, high-reliability positioning, navigation, and timing services for all types of users, and has short message communication capabilities. As of May 2012, 12 satellites in orbit, have initially provided regional navigation, positioning and timing capabilities. The Beidou satellite navigation system will have a global coverage capability by 2020. With the development of China's Beidou satellite system and the expansion of coverage, the clock inside the mobile terminal can be strongly assisted by the Beidou satellite signal. However, since a large number of mobile terminal users are currently living in an urban environment, the mobile terminal may not be able to ensure continuous tracking of the satellite in a severely occluded environment. The signal of any satellite may be intermittent, so that reception cannot be guaranteed. Complete 4 satellite signals. In the case of weak satellite signal strength and occlusion, higher requirements are placed on the sensitivity of the timing service of the Beidou satellite navigation system. Summary of the invention

The invention discloses a high-sensitivity Beidou auxiliary timing device and a high-sensitivity Beidou navigation timing receiver and a timing method embedded with the high-sensitivity auxiliary timing device, which can track even one under the condition of bad signal occlusion and attenuation. Satellites, in the case of incomplete positioning of position, speed and time, rely on the intra-week information extracted from the received navigation signals to still synchronize the time of the Beidou system and provide high-sensitivity timing services. The technical solution of the present invention is:

A high-sensitivity Beidou auxiliary timing device, comprising: a frame header search correlator and a frame header connected in sequence The search threshold decision module, the intra-week time extraction correlator, and the intra-week time threshold decision module, the output end of the frame header search threshold decision module and the output end of the intra-week time threshold decision module are further connected with the input end of the frame header search correlator The frame header search correlator includes an interconnected frame header coherent accumulation module and a frame header non-coherent accumulation module, which intercepts the received baseband signal segment S^n+m) and the local recurring signal S^m Performing the coherent accumulation and then performing the non-coherent accumulation, and calculating and comparing the obtained non-coherent accumulated values through the frame header search threshold decision module to determine the position of the subframe header of the Beidou navigation message data frame; The intra-week extraction correlator includes an interconnected intra-week coherent accumulation module and a non-coherent accumulation module within the week, and after receiving the determined frame head position signal, a segment of the baseband signal S^ at a fixed position will be intercepted. m) and a local reproduced signal S _n (m) to perform non-coherent integration longer coherent integration, noncoherent threshold value decision module obtained by comparing the calculated and the door weeks, extracting navigation Weeks when text information outputting 1PPS second pulse signal, complete synchronization Beidou system time. A low-cost, high-sensitivity Beidou navigation timing receiver, comprising: a radio frequency module connected to an antenna, a signal acquisition module, a signal tracking module, and the high-sensitivity auxiliary timing device, wherein the radio frequency module is respectively connected to the signal acquisition module And an input end of the signal tracking module, the output end of the signal capture module is connected to the input end of the signal tracking module, and the output end of the signal tracking module is connected to the high-sensitivity auxiliary timing device; when the signal capture module captures only one or less In the case of four satellite signals, the high-sensitivity auxiliary timing device extracts the intra-week information of the navigation message from the received satellite signal, and outputs a 1PPS second pulse signal to complete the synchronization of the Beidou system time. A standard high-sensitivity Beidou navigation timing receiver, comprising: an RF module connected to an antenna, a signal acquisition module, a signal tracking module, a positioning timing module, and the high-sensitivity auxiliary timing device and a timing mode selection module, The RF module is respectively connected to the input end of the signal capture module and the signal tracking module, and the output end of the signal capture module is connected to the input end of the signal tracking module, and the output end of the signal tracking module is respectively connected to the positioning timing module and the high sensitivity auxiliary timing The output end of the device, the positioning timing module and the high-sensitivity auxiliary timing device are respectively connected with the timing mode selection module; when the signal capturing module captures four or more satellite signals, the positioning timing module completes the positioning solution, and the timing module selects the module. Outputting the positioning result and the 1PPS second pulse signal; when the signal acquisition module captures only one or less than four satellite signals, the high-sensitivity auxiliary timing device extracts the intra-week information of the navigation message from the received satellite signal, Output 1PPS seconds pulse Signal, complete synchronization Beidou system time. A timing method based on the high-sensitivity auxiliary timing device, characterized in that it comprises the following steps:

1) On the basis of completing the acquisition and tracking of the Beidou satellite signal, the PR code phase and Doppler frequency information are obtained according to at least one of the captured and tracked Beidou satellite signals; intercepting the received baseband signal segment S^ n+m), with this The ground reproduction signal S^m) performs a dot product operation, performs coherent accumulation, and takes the dot product operation result as an absolute value to perform non-coherent accumulation, the non-coherent accumulation value

Search for the location of the non-coherent accumulation maximum value, and find the position of the sub-frame header of the Beidou navigation telegram data frame; where L is the length of the frame header and n is the starting position of the search.

2) According to the position of the intra-week field determined by the position of the frame header, a piece of baseband signal S^m) at a fixed position is intercepted, and the local reproduction signal S _n (m) is first coherently accumulated and then non-coherently accumulated. Non-coherent accumulated value

Searching for the non-coherent accumulation maximum value, extracting the intra-week time information of the navigation message, and obtaining the Beidou system time; wherein, L represents the number of bits occupied by the time in the storage week, and Sn corresponds to the nth possible intra-week time series.

In the step 2), for the first extraction without prior knowledge of time, the non-coherent accumulated value corresponding to all possible binary sequences S _n (m) is obtained, and the non-coherent accumulation maximum value is searched, and the first week is completed. Extraction of time; for non-first extraction that obtains prior knowledge, first estimate the search range of non-coherent accumulated values, and find all possible binary sequences S _n (m) within the search range of estimated non-coherent accumulated values The corresponding non-coherent accumulation value is searched for the non-coherent accumulation maximum value, and the extraction during the week is completed. In the step 1), the non-coherent accumulated value is calculated as follows: Acc

In the step 1), the non-coherent accumulation value is a final statistic obtained by secondly accumulating the non-coherent accumulated values corresponding to the plurality of subframes, A _CC 2/3⁄4 W = A _CC ^+ + P _{s /} is the subframe length or period. In the step 2), the non-coherent accumulated value is calculated by the following formula: A _CC («) _:

In the step 2), the non-coherent accumulation value is a final statistic obtained by secondly accumulating the non-coherent accumulated values corresponding to the plurality of subframes, Acc2/3⁄4 («;) _:

Technical effects of the present invention:

The invention provides a high-sensitivity Beidou auxiliary timing device. The signal acquisition channel can capture only one or less than four navigation satellites. Under the condition of poor signal occlusion or attenuation, even if only one satellite is tracked, it cannot be completed. position, In the case of speed and time positioning solution, the time of the Beidou system can be synchronized by the information of the week extracted from the received navigation signal, and the satellite signal that can adapt to the standard timing method cannot be normally attenuated and visible. Provides high-sensitivity timing services in harsh signal environments such as insufficient satellites.

The timing method for the high-sensitivity Beidou auxiliary timing device of the present invention is transmitted according to the structure of the data frame according to the navigation message. The data frame is composed of a plurality of subframes, and the beginning portion of each subframe is a frame header of a fixed pattern, and subsequent data is included. Including the characteristics of the information during the week, on the basis of completing the capture and tracking of the Beidou satellite signal, according to at least one Beidou satellite signal captured and tracked, the frame head position is first searched, and after the frame head position is determined, When the Beidou week can be extracted, the 1PPS second pulse signal is output to complete the synchronization of the Beidou system time. There is no need to perform a PVT solution, and the advantage of extracting only the method during the week is that the computational load is greatly reduced compared to the standard PVT solution.

The invention also provides a high-sensitivity Beidou navigation timing receiver embedded with the above-mentioned high-sensitivity Beidou auxiliary timing device, which comprises a low-cost high-sensitivity Beidou navigation timing receiver and a standard high-sensitivity Beidou navigation timing receiver. The low-cost high-sensitivity Beidou navigation timing receiver includes an RF module connected to the antenna, a signal acquisition module, a signal tracking module, and the high-sensitivity auxiliary timing device, and the advantage is that the signal acquisition channel can capture only one or less than four Navigation satellites, without PVT solution, as long as not all satellite signals are blocked, the timing service will not be interrupted, and the satellite signal will still provide a relatively accurate time during the week, which makes the satellite navigation receiver The clock can still be considered as a precise reference time when it cannot be located. The standard high-sensitivity Beidou navigation timing receiver includes an RF module connected to the antenna, a signal acquisition module, a signal tracking module, a positioning timing module, and the high-sensitivity auxiliary timing device and the timing mode selection module, which have the advantages of being able to provide PVT-based Based on the standard timing method of solving, it also has the function of providing high-sensitivity timing service. In the harsh signal environment where the satellite signal is seriously attenuated and the number of visible satellites is insufficient, the standard timing method can not work normally, and the Beidou system time can still be obtained. , providing time service. DRAWINGS

FIG. 1 is a schematic structural view of a high-sensitivity Beidou auxiliary timing device according to the present invention.

2 is a schematic structural view of a low-cost, high-sensitivity Beidou navigation timing receiver according to the present invention.

FIG. 3 is a schematic structural view of a standard high sensitivity Beidou navigation timing receiver according to the present invention.

4 is a flow chart of a timing method based on a high sensitivity Beidou assisted timing device according to the present invention.

Figure 5 shows the Beidou navigation message structure. detailed description

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. As shown in FIG. 1, a high-sensitivity Beidou auxiliary timing device includes a frame header search correlator connected in sequence, a frame header search threshold decision module, a time-of-week extraction correlator, and a intra-week time threshold decision module, and a frame header search. The output of the threshold decision module and the output of the intra-week time threshold decision module are also connected to the input of the frame header search correlator; the frame header search correlator includes interconnected frame header coherent accumulation modules and frame header non-coherent accumulation Module, the input end of the frame header coherent accumulation module intercepts the received baseband signal segment S^n+m) and the local recurring signal S^m), first performs coherent accumulation and then performs non-coherent accumulation, and the obtained The non-coherent accumulated value input frame header search threshold decision module determines whether the position of the subframe header of the Beidou navigation message is found by the calculation and comparison of the frame header search threshold decision module. If the frame header is not found, the above process is repeated. Find the frame header, and extract the correlator when the frame header position signal is input to the week; the intra-week extraction correlator includes the interconnected intra-week coherent accumulation module and the intra-week non-phase The parameter accumulation module, after receiving the determined frame head position signal, extracts a piece of the baseband signal S^m) and the local reproduction signal S _n (m) at the intercepted fixed position into the week, and extracts the correlator, first Coherent accumulation and non-coherent accumulation, the obtained non-coherent accumulated value is calculated and compared by the intra-week threshold decision module, the information of the week of the navigation message is extracted, and the 1PPS second pulse signal is output to complete the time of the Beidou system. Synchronization. Among them, r in S^n+m) means received, that is, the meaning of the received signal, and 1 in S^m) means local, that is, the meaning of the local signal.

As shown in FIG. 2, the basic composition, structure, and signal flow of the low-cost, high-sensitivity Beidou navigation timing receiver incorporating the above-described high-sensitivity Beidou auxiliary timing device are described. The utility model comprises an RF module connected to an antenna, a signal capture module, a signal tracking module and the high-sensitivity auxiliary timing device, wherein the RF module is respectively connected to an input end of the signal capture module and the signal tracking module, and an output end of the signal capture module is connected to the signal tracking module. The input end of the signal tracking module is connected to the high-sensitivity auxiliary timing device; wherein, the antenna is mainly responsible for receiving the signal; the RF module is responsible for down-converting the signal, and the current digital receiver further includes A/D conversion, It is the basis of all back-end processing, and the quality of its signal directly affects the performance of the receiver. The signal acquisition module and signal tracking module are the baseband signal processing part of the receiver, which is mainly responsible for signal acquisition, tracking and locking, including various originals. Output of data and measurement data; when the signal acquisition module captures only one or less than four satellite signals, the high-sensitivity auxiliary timing device extracts the intra-week information of the navigation message from the received satellite signal, and outputs 1PPS Second pulse signal, complete to the north Synchronize system time.

In a low cost implementation, a lower quality clock source can be used. The disadvantage is that it may extend the time required to complete the satellite signal acquisition task. If the initial positioning time of the navigation satellite-assisted clock system, that is, the TTFF indicator is not high, a low-cost clock scheme can be considered. From the point of view of the week, the signal capture channel can capture only one (or less than four) navigation satellites, because PVT resolution is not necessary, and there is no need to capture signals from multiple satellites. Therefore, the advantage of merely extracting the design highlights during the week is the greatly reduced computational load compared to the standard PVT solution.

As shown in FIG. 3, the basic composition, structure, and signal flow of a standard high-sensitivity Beidou navigation timing receiver incorporating the above-described high-sensitivity Beidou auxiliary timing device are described. The radio frequency module, the signal acquisition module, the signal tracking module, the positioning and timing module, and the high-sensitivity auxiliary timing device and the timing mode selection module are connected to the antenna, and the radio frequency module is connected to the antenna. The frequency module is respectively connected to the input end of the signal capturing module and the signal tracking module, the output end of the signal capturing module is connected to the input end of the signal tracking module, and the output end of the signal tracking module is respectively connected to the positioning timing module and the high sensitivity auxiliary timing device, and positioning The timing of the timing module and the high-sensitivity auxiliary timing device are respectively connected to the timing mode selection module; when the signal acquisition module captures four or more satellite signals, the positioning and timing module completes the positioning solution, and the timing module selects the module to output the positioning result. And 1PPS signal; when the signal acquisition module only captures one or less than four satellite signals, the high-sensitivity auxiliary timing device extracts the intra-week information of the navigation message from the received satellite signal, and outputs a 1PPS second pulse signal. , complete the synchronization of the Beidou system time. A timing method based on the high sensitivity auxiliary timing device includes the following steps:

1) On the basis of completing the acquisition and tracking of the Beidou satellite signal, according to at least one Beidou satellite signal captured and tracked, the PRN code phase and Doppler frequency information are obtained; and the received baseband signal segment S^ is intercepted. n+m:), performing a dot product operation with the local reproduction signal S^m), performing coherent accumulation, and taking the dot product operation result as an absolute value to perform non-coherent accumulation, the non-coherent accumulation value SXn + njS m);

2) According to the position of the intra-week field determined by the position of the frame header, a piece of baseband signal S (m:) at a fixed position intercepted, and the local reproduction signal S _n m) are first coherently accumulated and then non-coherent Accumulation, the non-coherent accumulation value

Searching for the non-coherent accumulation maximum value, extracting the intra-week time information of the navigation message, and obtaining the Beidou system time, wherein L represents the number of bits occupied by the time in the storage week, and Sn corresponds to the nth possible intra-week time series.

In step 2), for the first extraction without prior knowledge of time, the non-coherent accumulated value corresponding to all possible binary sequences S _n (m) is obtained, and the non-coherent accumulation maximum value is searched, and the first week is completed. Extraction of time; for non-first extraction that obtains prior knowledge, first estimate the search range of non-coherent accumulated values, and find all possible binary sequences S _n (m) within the search range of estimated non-coherent accumulated values The corresponding non-coherent accumulation value is searched for the non-coherent accumulation maximum value, and the extraction during the week is completed.

As shown in FIG. 4, it is a flow chart of a timing method based on the high sensitivity Beidou auxiliary timing device of the present invention. On the basis of completing the acquisition and tracking of the Beidou satellite signal, the phase and Doppler frequency information of the PRN code are obtained, then the coherent accumulation and non-coherent accumulation are performed, and the position of the non-coherent accumulation maximum is searched to determine the frame. Head position; after the position of the frame header is determined, That is, when the Beidou week can be extracted, before the time of the week is extracted, it is necessary to first clear whether there is a prior knowledge about the time. If there is no time prior knowledge, the calculation and search of the non-coherent accumulated value of the full combination in the week are performed; If there is time prior knowledge, first estimate the search range of the non-coherent accumulated value, and reduce the amount of calculation as much as possible. In the search range of the estimated non-coherent accumulated value, calculate the non-coherent accumulated value in the week. And search, search for the maximum value of non-coherent accumulation, and complete the extraction during the Beidou navigation message week.

The satellite navigation message contains system time, clock correction parameters, ionospheric delay model parameters, satellite ephemeris and satellite health status information. This is to provide the user with time, position coordinates, speed and other result data, and to use for navigation satellite signal processing related information. The navigation message is also broadcast to the user in the form of a binary code, so it is also called a data code, or D code. The message is transmitted by the structure of the data frame, and the data frame is composed of a plurality of subframes. The beginning of each sub-frame is the frame header of a fixed pattern, and the subsequent data contains the intra-week time, that is, the transmission time of the next sub-frame.

The frame header of the fixed pattern is repeated at the beginning of each subframe. In one implementation, the high sensitivity Beidou assisted timing device continuously searches for each sub-frame and uses non-coherent accumulation to determine the position of the frame header. More specifically, the header of each subframe will be detected with non-coherent accumulation. In one implementation, the non-coherent accumulation will determine the correlation function between the received satellite signal (S^m)) and the local sequence (S^m), such as the frame header.

The received satellite signals are phase-synchronized and coherently accumulated and stored in the form of a bit stream in the receiver baseband signal processing section memory unit, each bit can be represented as a complex number '' ^θ . Where A is an unknown magnitude,

Θ is the unknown phase, D(m) is the telegram sequence. Set a sliding window of width L to intercept the received satellite signal segment S _r (n+m), calculate the absolute value of the dot product (multiplying and summing) of the segment and the local sequence S^m) Non-coherent accumulation value. The specific calculation method is shown in equation (1):

L is the length of the signal segment or target sequence. If the sequence of the message to be detected is ObOOl l l lO, the local target message sequence is a complex sequence:

S _l (m) = [Β, Β -Β -Β -Β -Β,ΒΥ ⁹ ( 2 ) The received satellite signal is also a complex sequence

S _R (m) = [A, A - A - A - A - A, A] e ^w + N ( 3 ) where N is a complex noise sequence. The corresponding elements in each sequence are multiplied (complex multiplication), and then the real and imaginary parts of the product are added separately, and finally the absolute value is obtained. Obviously, when the target sequence matches the input signal sequence intercepted by the sliding window, the non-coherent accumulation takes the maximum value; and the non-coherent accumulation value obtained when the sequence does not match is small. In another implementation, non-coherent accumulation can also be calculated as follows:

The effect of the two calculation methods is similar, but from the perspective of implementation, the second algorithm can avoid the calculation of the larger amount of calculation, and save the hardware/software overhead. Changing the value of the sliding window position /n, calculating and comparing the non-coherent accumulation values can determine the position of the frame header in the received signal. The search range, ie the range of variation of n, depends on the length of the Beidou telegram sub-frame. In one implementation, the non-coherent accumulation value of the subsequence starting at each element in one sub-frame of the received sequence is calculated, and the position at which the maximum value is located is the frame header. Under weak or strong noise conditions, non-coherent detection of only the position of a single frame header may not yield correct results. The solution is to calculate an additional non-coherent accumulation value at a fixed length from the first correlation operation (the sub-frame length M is set up. Figure 5 shows the structure of the navigation message and the relationship between the aforementioned non-coherent accumulated values) Performing a correlation operation on the first subframe to obtain a first non-coherent accumulation value, performing a correlation operation in the second subframe to obtain a second non-coherent accumulation value, and performing a correlation operation on the third subframe to obtain a third non-coherent accumulation value Only three sub-frames are drawn in the figure. In fact, the fourth non-coherent accumulated value, the fifth non-coherent accumulated value can be obtained by the same idea, and so on. Because the frame header will repeatedly appear in subsequent sub-frames. At the same position, the non-coherent accumulated values obtained at the corresponding positions are added to obtain a final detection statistic. The non-coherent accumulated value is obtained by second accumulating the non-coherent accumulated values corresponding to the plurality of sub-frames. The final statistic, A _CC 2/3⁄4 W = A _CC («;) + + P _{s /} is the length or period of the sub-frame. The more non-coherent accumulated values that form the final detection statistic, the more helpful the smoothing Detecting noise in statistics, mentioning Detection sensitivity.

The extraction during the week follows a similar approach and is also achieved using non-coherent accumulation. However, the specific steps are different. The reason is that according to the navigation message structure, the position of the frame header is determined by the aforementioned frame header detection, and the position of the field in the week is also clear, so that the sliding window is no longer used but the fixed position is intercepted. A baseband signal. Unlike the frame header, the seconds field is always changed/incremented in the week, and is not repeated in adjacent subframes and is unknown at the beginning.

There is no prior knowledge/first extraction and prior knowledge extraction in the week. For the first extraction, since there is no prior knowledge, all possible binary combinations must be obtained. 8! (!^ corresponds to the non-coherent accumulated value, the maximum value is searched, and the maximum non-coherent accumulated value is considered to appear at the binary combination matching the real time. Timing applications may only care about time-minutes and seconds that are modulo 24 hours, thus reducing the search range. The search range, ie the range of variation of n, depends on the total number of time-coded combinations in the Beidou message week. In the case of weak signals, it can be used. The non-coherent accumulated value re-accumulation method similar to the frame header detection suppresses the noise and increases the detection probability. The non-coherent accumulated value is the final statistic obtained by the second non-coherent accumulated value corresponding to the multiple sub-frames.

:, Acc2nd(n) - . Considering the increment of the field in the adjacent sub-frame week

The characteristic, the local sequence that generates the non-coherent accumulation values from the adjacent weeks participating in the re-accumulation should have a certain correspondence.

Once a satellite has successfully completed the first intra-weekly extraction, the terminal has acquired a priori knowledge of time. The aid of this prior knowledge will greatly reduce the number of binary combinations to be searched, and reduce the amount of work that is extracted during the week for the satellite and other satellites. In the severely occluded environment of the mobile terminal, continuous tracking of the satellite may not be guaranteed, and the signal of any satellite may be intermittent. However, as long as not all satellite signals are blocked, the timing service will not be interrupted because the terminal may alternately extract the intra-week time of different satellites.

Compared with the standard timing method based on PVT solution, the clock error correction frequency of the method is low. The frequency of correction of the standard method depends on the frequency of the PVT solution, usually higher than 1Ηζ, and some Beidou receivers can reach 20Hz or higher. The clock error correction of the method is equal to the transmission frequency of the sub-frame, and the duration of a Beidou signal sub-frame is usually in the second order, so the clock correction frequency of the method is less than 1Ηζ. As the clock drifts over time, the longer the time, the larger the clock drift. The higher the clock correction frequency, the smaller the clock drift of the clock. Therefore, the timing accuracy of this method is lower than the standard timing method based on PVT solution, but it can adapt to the harsh signal environment such as severe attenuation of satellite signals that cannot work normally by standard timing method and insufficient number of visible satellites.

It should be noted that the above-described embodiments may enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. Accordingly, the present invention has been described in detail with reference to the embodiments of the present invention, and those skilled in the art will understand that the invention may be modified or equivalently substituted without departing from the spirit and scope of the invention. The technical solutions and their improvements are all covered by the scope of protection of the patents of the present invention.

Claims

Claim

A high-sensitivity Beidou auxiliary timing device, comprising: a frame header search correlator sequentially connected, a frame header search threshold decision module, an intra-week extraction correlator, and a intra-week time threshold decision module, said frame The output of the header search threshold decision module and the output of the intra-week time threshold decision module are also connected to the input of the frame header search correlator; the frame header search correlator includes interconnected frame header coherent accumulation modules and frame headers The non-coherent accumulation module intercepts the received baseband signal segment Sf(n+m) and the local recurring signal S^m) to perform coherent accumulation and then perform non-coherent accumulation, and the obtained non-coherent accumulated value is passed. The frame header search threshold decision module performs calculation and comparison to determine the location of the subframe header of the Beidou navigation message data frame; the intra-week extraction correlator includes interconnected intra-week coherent accumulation modules and intra-weekly non-period section of the baseband signal Sf (m) in a fixed position coherent integration module, after receiving the frame header to determine the position signal, and taken to a local reproduced signal S _n (m) to be re-coherent integration into When information noncoherent weeks, noncoherent threshold value decision module obtained by comparing the calculated and the door weeks, extracting navigation data, an output pulse signal 1PPS seconds, complete synchronization Beidou system time.

2. A low-cost, high-sensitivity Beidou navigation timing receiver, comprising: a radio frequency module connected to an antenna, a signal acquisition module, a signal tracking module, and the high-sensitivity auxiliary timing device, wherein the radio frequency module respectively connects signals An input end of the capture module and the signal tracking module, the output end of the signal capture module is connected to the input end of the signal tracking module, and the output end of the signal tracking module is connected to the high-sensitivity auxiliary timing device; when the signal capture module captures only one or When there are less than four satellite signals, the high-sensitivity auxiliary timing device extracts the intra-week information of the navigation message from the received satellite signals, and outputs a 1PPS second pulse signal to complete synchronization of the Beidou system time.

A standard high-sensitivity Beidou navigation timing receiver, comprising: a radio frequency module connected to an antenna, a signal acquisition module, a signal tracking module, a positioning timing module, and the high-sensitivity auxiliary timing device and a timing mode selection module The RF module is respectively connected to an input end of the signal capture module and the signal tracking module, and an output end of the signal capture module is connected to an input end of the signal tracking module, and an output end of the signal tracking module is respectively connected to the positioning timing module and the high sensitivity The auxiliary timing device, the positioning timing module and the output of the high-sensitivity auxiliary timing device are respectively connected with the timing mode selection module; when the signal capturing module captures four or more satellite signals, the positioning timing module completes the positioning solution, and passes the timing mode. Selecting a module to output a positioning result and a 1PPS second pulse signal; when the signal capturing module captures only one or less than four satellite signals, the high-sensitivity auxiliary timing device extracts the week of the navigation message from the received satellite signal Information, output 1PPS seconds Red signal, complete synchronization Beidou system time.

A timing method based on the high-sensitivity auxiliary timing device, comprising: the following steps: 1) based on capturing and tracking the Beidou satellite signal, according to at least one captured and tracked The Beidou satellite signal obtains the PRN code phase and Doppler frequency information; intercepts the received baseband signal segment Sf(n+m), performs a dot product operation with the local recurring signal S^m), performs coherent accumulation, and then The result of the dot product operation takes an absolute value, and non-coherent accumulation is performed, and the non-coherent accumulated value SXn + njS m);

2) According to the position of the intra-week field determined by the position of the frame header, a piece of baseband signal Sf(m) at a fixed position is intercepted, and the local reproduction signal S _n (m) is first coherently accumulated and then non-coherently accumulated. Non-coherent accumulated value

The timing method based on the high-sensitivity auxiliary timing device according to claim 4, wherein in the step 2), all possible binary sequences are obtained for the first extraction without time prior knowledge. The non-coherent accumulation value corresponding to S _n (m), the non-coherent accumulation maximum value is searched, and the extraction within the first week is completed; for the non-first extraction that obtains the prior knowledge, the search range of the non-coherent accumulation value is estimated first. In the search range of the estimated non-coherent accumulated value, the non-coherent accumulated value corresponding to all possible binary sequences S _n (m) is obtained, and the non-coherent accumulation maximum value is searched for, and the extraction in the week is completed.

The timing method based on the high-sensitivity auxiliary timing device according to claim 4, wherein in the step 1), the non-coherent accumulation value is calculated by the following formula: Acc (^: Y. S n + injS mi .

The method for timing according to the high-sensitivity auxiliary timing device according to claim 4 or 6, wherein in the step 1), the non-coherent accumulation value is a non-phase corresponding to a plurality of subframes. The final statistic obtained by the second accumulation of the accumulated value,

A _CC («) + A _C + _J P _{s /} ), P _{s /} is the subframe length or period.

The timing method based on the high-sensitivity auxiliary timing device according to claim 4, wherein in the step 2), the non-coherent accumulation value is calculated by:

The method for timing according to the high-sensitivity auxiliary timing device according to claim 4 or 8, wherein in the step 2), the non-coherent accumulation value is a non-phase corresponding to a plurality of subframes The final statistic obtained by the second accumulation of the accumulated value, Acc2/3⁄4 («): YS _r {m)S _n {mi +