CN107305254B - Method and device for realizing bit synchronization - Google Patents

Method and device for realizing bit synchronization Download PDF

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CN107305254B
CN107305254B CN201610252488.6A CN201610252488A CN107305254B CN 107305254 B CN107305254 B CN 107305254B CN 201610252488 A CN201610252488 A CN 201610252488A CN 107305254 B CN107305254 B CN 107305254B
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data
bit synchronization
correlation operation
signal
noise ratio
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CN107305254A (en
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宋挥师
孙涛
徐雄伟
刘航
赵海龙
刘晓燕
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Datang Semiconductor Design Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/35—Constructional details or hardware or software details of the signal processing chain
    • G01S19/37—Hardware or software details of the signal processing chain

Abstract

A method and device for realizing bit synchronization includes: selecting any adjacent 20 data from the data stream shifted into the shift register as segment data of bit synchronization analysis; performing correlation operation on 20 data in the divided segment data; after absolute value or square processing is carried out on the correlation operation result, the absolute value or square processed correlation operation result of the same candidate position is accumulated to obtain the corresponding signal-to-noise ratio gain of each candidate position; and calculating the difference value between the maximum value and the second maximum value of the signal-to-noise ratio gain corresponding to the candidate position, comparing the calculated difference value with a preset threshold value, and determining bit synchronization. According to the method provided by the embodiment of the invention, bit synchronization processing is carried out after signal-to-noise ratio gain is obtained by carrying out correlation operation on the divided segment data, so that the bit synchronization time is reduced, and the working efficiency of bit synchronization is improved.

Description

Method and device for realizing bit synchronization
Technical Field
The present disclosure relates to positioning technologies, and more particularly, to a method and apparatus for implementing bit synchronization.
Background
After the Global Positioning System (GPS) receiver finishes acquiring and tracking the received signal, it then performs bit synchronization, frame synchronization, demodulation and decoding processes, so as to obtain the signal transmission time and navigation message from the received signal, and finally realize GPS navigation positioning.
The bit synchronization is also called bit synchronization, which is that a receiving channel determines the position of a current received signal at a certain data bit according to a certain algorithm, or determines the starting edge position of the data bit in the received signal. For a 50 bit/second (bps) pilot message modulated on a corresponding carrier, each pilot message corresponds to 20 coarse acquisition (C/a) code periods, thus leading to uncertainty in the bit flip boundary. The position of the bit flip boundary of the modulation message is obtained, namely, the bit synchronization is realized, and the method is the basis for realizing demodulation message, measuring pseudo range and realizing high-sensitivity tracking by utilizing coherent accumulation. The receiver must estimate the position of the bit flip boundary to achieve bit synchronization.
Common bit synchronization algorithms include a histogram method, a Maximum Likelihood (ML) bit synchronization algorithm, and the like; wherein the content of the first and second substances,
the histogram method is a very basic bit synchronization algorithm, and the method counts the sign change of adjacent integral values output by a carrier ring, has 20 candidate positions in total, and considers a position as a bit boundary if the sign change frequency at the position is obviously greater than that at other positions after a period of time statistics. For example, as shown in fig. 1, data bits with a width of 1 millisecond (ms) output by a carrier ring are numbered by 1 to 20, where the first data bit with the number of 1 is arbitrarily selected, and then the data jump situation between two adjacent milliseconds is counted one by one: and if the ith data jumps to the (i + 1) th data, adding 1 to a counter corresponding to the (i + 1) th histogram, otherwise, keeping the counter unchanged. Thus, each time 20ms of data is processed, the histogram method checks to see if the statistics are one of two cases: counter value with one histogram reaching threshold N1(ii) a As shown in fig. 1, the counter in the fourth histogram is largest, that is, in a data stream of a period of time, after counting the data stream according to a period of 20ms, the number of bit transitions from the third ms to the fourth ms is largest, and the value of the counter reaches the threshold value N again1Second, considering the bit synchronization implementation, the bit edge deviation is determined to be 3 ms. Thus the first 4 th to 20 th milliseconds plus 1 st to 3 rd milliseconds belong to one bit, while the 4 th to 20 th milliseconds plus the 1 st to 3 rd milliseconds immediately following it belong to the next bit, and the rest of the data bit partitioning can be analogized; the counter value of at least two histograms reaches or exceeds the threshold value N2: the situation shows that the signal strength is too weak, or the data bit jump contained in the navigation message in the period is too little, the bit synchronization fails, all the counters in all the histograms are cleared, and the statistics of the data jump is started from the beginning. If neither of the above two cases occurs, the receiver continues to check and count the data streams one by one. If the carrier ring appears to be signal-pair before bit synchronization has not been achievedIf the lock is lost, the statistical process also needs to be reset and restarted. The drawback of the histogram method is that as the signal strength becomes weaker, its performance becomes worse and worse, and at lower carrier-to-noise ratios, it takes several tens of seconds to obtain reliable synchronization. This time is too long and far beyond the range that a typical receiver can tolerate.
In order to improve the synchronization performance of a receiver at a low carrier-to-noise ratio (C/N0), a maximum likelihood bit synchronization algorithm is adopted, the method accumulates 20 continuous data after each candidate position, after the corresponding bit energy is obtained by envelope calculation, the bit energy is subjected to incoherent accumulation for a period of time, and thus the position with the maximum bit energy in the corresponding 20 positions is the position of a bit boundary. The method improves the signal-to-noise ratio by increasing the number of incoherent accumulations, and can be used under the condition of low signal-to-noise ratio. The specific algorithm is described as follows:
the model of the signal received by the receiver at the k epoch after the local C/A code correlation is assumed to be
rk＝Ack+nk(1)
Wherein c iskFor modulating 20 repetitions of navigation messages, e.g. ck+δ＝ck+1+δ＝…＝ck+19+δ＝bkEach of ckMaintaining a C/A code period; δ is the position of the bit boundary, δ ∈ {0, 1, … 19 }; bkFor modulated navigation messages, bkE { +/-1 }; a is the signal power; n iskIs a mean value of 0 and a variance of
Figure BDA0000971315010000021
An additive white gaussian noise, a likelihood function comprising N received signal vectors can be represented by the product of the likelihood functions of each received signal:
Figure BDA0000971315010000022
to find the bit start edge position, equation (2) needs to be maximized under the parameters δ, a, b; the first term in the formula (2) is independent of other parameters and can be ignoredA little bit; the latter two terms can be considered as 2| A | f (r; delta; b) + N | A | Y2The maximization of the formula (2) is realized by maximizing f (r; delta; b), wherein
Figure BDA0000971315010000031
In the formula (I), the compound is shown in the specification,
Figure BDA0000971315010000032
to round down, K ═ N/20+1, where l denotes the number of milliseconds of the received signal; when b iskAnd
Figure BDA0000971315010000033
when the signs of (2) are equal, equation (3) reaches the maximum value. According to x · sign (x) | x |, the maximization of equation (3) may be equivalent to the maximization of equation (4),
Figure BDA0000971315010000034
thus, the maximum likelihood bit synchronization algorithm can be reduced to the maximum likelihood bit synchronization calculation formula of formula (5),
relative to the histogram algorithm, the maximum likelihood bit synchronization algorithm can achieve good bit synchronization at signal strengths above 20 decibel-hertz (dB-Hz), and it takes only a few seconds. However, the maximum likelihood bit synchronization algorithm usually needs to fix a larger number of incoherent accumulation times to ensure the synchronization performance under low signal-to-noise ratio, for the case of high signal-to-noise ratio, more incoherent accumulation is redundant, and the redundant incoherent accumulation greatly increases the average synchronization time and affects the working efficiency of bit synchronization.
Disclosure of Invention
The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.
Embodiments of the present invention provide a method and an apparatus for implementing bit synchronization, which can reduce a bit synchronization time and improve bit synchronization efficiency.
The embodiment of the invention provides a method for realizing bit synchronization, which comprises the following steps:
selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
carrying out correlation operation on the divided segment data;
after absolute value or square processing is carried out on the correlation operation result, the absolute value or square processed correlation operation result of the same candidate position in the segmented data is accumulated to obtain the signal-to-noise ratio gain corresponding to each candidate position;
and calculating the difference value between the maximum value of the signal-to-noise ratio gain and the second maximum value of the signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference value and a preset threshold value.
Optionally, the segmented data is:
Rk＝(r20(k-1)+1，…，r20k) K is the data bit length;
wherein r isk＝Ack+nk；
C is mentionedkFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is signal power; n iskIs a mean of 0 and a variance ofWhite gaussian noise.
Optionally, the performing the correlation operation includes:
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix;
the probability matrix is used for representing the possible positions of the data demodulated from the segmented data, wherein the data has hopping.
Optionally, the preset probability matrix includes:
and
Figure BDA0000971315010000043
it should be noted that the segment data RkWhen the preset probability matrix T is determined, the method of the embodiment of the invention performs correlation operation, including: carrying out RkAnd T.
Optionally, the determining the bit synchronization includes:
if the calculated difference value is larger than the preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge to finish bit synchronization;
if the calculated difference is less than or equal to the preset threshold and the number of times of the accumulation calculation of the correlation operation result is less than the preset number threshold, dividing 20 adjacent data from the data stream shifted into the shift register as the segmented data of the bit synchronization analysis, and continuing the bit synchronization processing according to the divided segmented data;
and if the difference is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation result is greater than or equal to the preset times threshold value, determining that bit synchronization fails.
On the other hand, an embodiment of the present invention further provides a device for implementing bit synchronization, including: the device comprises a dividing unit, a correlation operation unit, an accumulation unit and a determination unit; wherein the content of the first and second substances,
the dividing unit is used for selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
the correlation operation unit is used for performing correlation operation on the divided segment data;
the accumulation unit is used for accumulating the absolute value of the same candidate position in the segmented data or the correlation operation result of the square processing after the absolute value or the square processing is carried out on the correlation operation result to obtain the signal-to-noise ratio gain corresponding to each candidate position;
the determining unit is used for calculating the difference value between the maximum value of the signal-to-noise ratio gain and the second maximum value of the signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference value and a preset threshold value.
Optionally, the segmented data is:
Rk＝(r20(k-1)+1，…，r20k) K is the data bit length;
wherein r isk＝Ack+nk；
C is mentionedkFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is signal power; n iskIs a mean of 0 and a variance of
Figure BDA0000971315010000051
White gaussian noise.
Optionally, the correlation operation unit is specifically configured to,
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix;
the probability matrix is used for representing the possible positions of the data demodulated from the segmented data, wherein the data has hopping.
Optionally, the preset probability matrix includes:
Figure BDA0000971315010000061
and
Figure BDA0000971315010000062
optionally, the determining unit is specifically configured to,
calculating the difference value between the maximum value of signal-to-noise ratio gain and the second maximum value of signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions;
if the calculated difference value is larger than the preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge to finish bit synchronization;
if the calculated difference is less than or equal to the preset threshold and the number of times of the accumulation calculation of the correlation operation result is less than the preset number threshold, dividing 20 adjacent data from the data stream shifted into the shift register as the segmented data of the bit synchronization analysis, and continuing the bit synchronization processing according to the divided segmented data;
and if the difference is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation result is greater than or equal to the preset times threshold value, determining that bit synchronization fails.
Compared with the related art, the technical scheme of the application comprises the following steps: selecting any adjacent 20 data from the data stream shifted into the shift register as segment data of bit synchronization analysis; performing correlation operation on 20 data in the divided segment data; after absolute value or square processing is carried out on the correlation operation result, the absolute value or square processed correlation operation result of the same candidate position is accumulated to obtain the corresponding signal-to-noise ratio gain of each candidate position; and calculating the difference value between the maximum value and the second maximum value of the signal-to-noise ratio gain corresponding to the candidate position, comparing the calculated difference value with a preset threshold value, and determining bit synchronization. According to the method provided by the embodiment of the invention, bit synchronization processing is carried out after signal-to-noise ratio gain is obtained by carrying out correlation operation on the divided segment data, so that the bit synchronization time is reduced, and the working efficiency of bit synchronization is improved.
Other aspects will be apparent upon reading and understanding the attached drawings and detailed description.
Drawings
FIG. 1 is an analysis diagram of a related art meso-position synchronous histogram method;
FIG. 2 is a flow chart of a method for implementing bit synchronization according to an embodiment of the present invention;
fig. 3 is a block diagram of an apparatus for implementing bit synchronization according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
Fig. 2 is a flowchart of a method for implementing bit synchronization according to an embodiment of the present invention, as shown in fig. 2, including:
step 200, selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
it should be noted that, in the method according to the embodiment of the present invention, when the segment data is selected and divided, an arbitrary start position may be determined from the data stream shifted into the shift register to select the segment data, and the bit synchronization process according to the embodiment of the present invention is simplified as long as 20 adjacent pieces of data are selected.
Optionally, the segmented data is:
Rk＝(r20(k-1)+1，…，r20k) K is the data bit length;
wherein r isk＝Ack+nk；
ckFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is the signal power; n iskIs a mean of 0 and a variance of
Figure BDA0000971315010000071
White gaussian noise.
Here, r iskThe same processing manner as the bit synchronous histogram method. RkRepresenting 20 contiguous data.
Step 201, performing correlation operation on the divided segment data;
optionally, the performing the correlation operation includes:
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix;
the probability matrix is used for representing the possible positions of the data demodulated by the segmented data.
Optionally, the preset probability matrix includes:
Figure BDA0000971315010000081
and
Figure BDA0000971315010000082
it should be noted that the segment data RkWhen the preset probability matrix T is determined, the method of the embodiment of the invention performs correlation operation, including: carrying out RkAnd T.
The likelihood function for bit sync analysis can be converted to the following equation:
Figure BDA0000971315010000083
in addition, a matrix or a variant of the matrix having the same function as the probability matrix may be applied to the embodiment of the present invention.
Step 202, after absolute value or square processing is performed on the correlation operation result, accumulating the absolute values of the same candidate positions in the segmented data or the correlation operation results of the square processing to obtain the signal-to-noise ratio gain corresponding to each candidate position;
in addition to the absolute value or square processing, the fourth power or the like may be any processing method of removing the sign indicating the positive or negative in the correlation calculation result and comparing the magnitude of the number after the positive or negative sign.
The accumulation process here means non-coherent accumulation, in order to obtain a certain signal-to-noise ratio gain. As the number of accumulations increases, the gain increases accordingly.
Step 203, calculating the difference between the maximum value of the signal-to-noise ratio gain and the second maximum value of the signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference and a preset threshold.
Optionally, in the method according to the embodiment of the present invention, the determining and processing for performing bit synchronization includes:
if the calculated difference value is larger than a preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge, and completing bit synchronization;
if the calculated difference value is less than or equal to the preset threshold value and the accumulated calculation times of the correlation operation results are less than the preset time threshold value, dividing 20 adjacent data from the data stream shifted into the shift register again to serve as segmented data of bit synchronization analysis, and continuing bit synchronization processing according to the divided segmented data;
and if the difference value is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation results are more than or equal to the preset times threshold value, determining that the bit synchronization fails.
It should be noted that, according to the empirical analysis of the inventor, the threshold value of the number of times threshold is generally a value of 200 or less. In addition, the preset threshold may be determined by a person skilled in the art in a simulation manner, and the number of times of the accumulation calculation of the correlation calculation result may be different for different preset thresholds by a conventional technical means of the person skilled in the art. If the preset threshold value is smaller, the corresponding required accumulation times are less; otherwise, if the preset threshold is larger, the number of accumulation times required correspondingly will be larger.
On the other hand, a large number of simulations show that the difference between the maximum value and the second maximum value of the incoherent accumulation value can be used as a parameter in the bit synchronization processing process, and the difference is monotonically increased along with the carrier-to-noise ratio and the incoherent accumulation times, so that the incoherent accumulation times required under a certain carrier-to-noise ratio can be well estimated by limiting the difference by a preset threshold, and further the self-adaptive bit synchronization is realized.
The method of the embodiment of the invention can obtain good bit synchronization performance no matter under the conditions of high signal-to-noise ratio or low signal-to-noise ratio, and the average estimation time, especially the average estimation time of a strong signal, of the method is greatly reduced, thereby obtaining compromise on bit synchronization success rate and synchronization time.
The method of the embodiment of the invention can adaptively adjust the times of incoherent accumulation by carrying out correlation operation on the divided segmented data to obtain the signal-to-noise ratio gain and then carrying out bit synchronization processing, namely, more times of incoherent accumulation is adopted under the condition of relatively low signal-to-noise ratio, and less times of incoherent accumulation is needed under the condition of relatively high signal-to-noise ratio, thereby reducing the bit synchronization time and improving the working efficiency of bit synchronization.
Fig. 3 is a block diagram of an apparatus for implementing bit synchronization according to an embodiment of the present invention, as shown in fig. 3, including: the device comprises a dividing unit, a correlation operation unit, an accumulation unit and a determination unit; wherein the content of the first and second substances,
the dividing unit is used for selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
optionally, the segmented data is:
Rk＝(r20(k-1)+1，…，r20k) K is the data bit length;
wherein r isk＝Ack+nk；
ckFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is the signal power; n iskIs a mean of 0 and a variance of
Figure BDA0000971315010000091
White gaussian noise.
The correlation operation unit is used for performing correlation operation on the divided segment data;
optionally, the correlation operation unit is specifically configured to,
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix;
the probability matrix is used for representing the possible positions of the data demodulated by the segmented data.
Optionally, the preset probability matrix includes:
Figure BDA0000971315010000101
and
the accumulation unit is used for accumulating the absolute value of the same candidate position in the segmented data or the correlation operation result of the square processing after the absolute value or the square processing is carried out on the correlation operation result to obtain the signal-to-noise ratio gain corresponding to each candidate position;
the determining unit is used for calculating the difference value between the maximum value of the signal-to-noise ratio gain and the second maximum value of the signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference value and a preset threshold value.
Optionally, the determining unit is specifically configured to,
calculating the difference value between the maximum value of signal-to-noise ratio gain and the second maximum value of signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions;
if the calculated difference value is larger than a preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge, and completing bit synchronization;
if the calculated difference value is less than or equal to the preset threshold value and the accumulated calculation times of the correlation operation results are less than the preset time threshold value, dividing 20 adjacent data from the data stream shifted into the shift register again to serve as segmented data of bit synchronization analysis, and continuing bit synchronization processing according to the divided segmented data;
and if the difference value is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation results are more than or equal to the preset times threshold value, determining that the bit synchronization fails.
It will be understood by those skilled in the art that all or part of the steps of the above methods may be implemented by a program instructing associated hardware (e.g., a processor) to perform the steps, and the program may be stored in a computer readable storage medium, such as a read only memory, a magnetic or optical disk, and the like. Alternatively, all or part of the steps of the above embodiments may be implemented using one or more integrated circuits. Accordingly, each module/unit in the above embodiments may be implemented in hardware, for example, by an integrated circuit to implement its corresponding function, or in software, for example, by a processor executing a program/instruction stored in a memory to implement its corresponding function. The present invention is not limited to any specific form of combination of hardware and software. ".
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (8)

1. A method for implementing bit synchronization, comprising:
selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
carrying out correlation operation on the divided segment data;
after absolute value or square processing is carried out on the correlation operation result, the absolute value or square processed correlation operation result of the same candidate position in the segmented data is accumulated to obtain the signal-to-noise ratio gain corresponding to each candidate position;
calculating the difference value between the maximum value of signal-to-noise ratio gain and the second maximum value of signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference value and a preset threshold value;
wherein the determining to perform bit synchronization comprises:
when the calculated difference value is larger than the preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge to finish bit synchronization;
the performing the correlation operation includes:
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix; the probability matrix is used for representing the possible positions of the data demodulated from the segmented data, wherein the data has hopping.
2. The method of claim 1, wherein the segmented data is:
Rk＝(r20(k-1)+1,…,r20k) K is the data bit length;
wherein r isk＝Ack+nk；
C is mentionedkFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is signal power; n iskIs a mean of 0 and a variance of
Figure FDA0002192802950000011
White additive gaussian noise.
3. The method of claim 1, wherein the predetermined probability matrix comprises:
Figure FDA0002192802950000021
and
Figure FDA0002192802950000022
4. the method according to any of claims 1-3, wherein said determining the bit synchronization further comprises:
when the calculated difference value is less than or equal to the preset threshold value and the number of times of performing the accumulation calculation of the correlation operation result is less than a preset number threshold value, re-dividing 20 adjacent data from the data stream shifted into the shift register as the segmented data of the bit synchronization analysis, and continuing the bit synchronization processing according to the re-divided segmented data;
and when the difference value is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation result are greater than or equal to the preset times threshold value, determining that bit synchronization fails.
5. An apparatus for implementing bit synchronization, comprising: the device comprises a dividing unit, a correlation operation unit, an accumulation unit and a determination unit; wherein the content of the first and second substances,
the dividing unit is used for selecting any group of 20 adjacent data from the data stream shifted into the shift register as segment data of bit synchronization analysis;
the correlation operation unit is used for performing correlation operation on the divided segment data;
the accumulation unit is used for accumulating the absolute value of the same candidate position in the segmented data or the correlation operation result of the square processing after the absolute value or the square processing is carried out on the correlation operation result to obtain the signal-to-noise ratio gain corresponding to each candidate position;
the determining unit is used for calculating the difference value between the maximum value of the signal-to-noise ratio gain and the second maximum value of the signal-to-noise ratio gain in the signal-to-noise ratio gains corresponding to all the candidate positions, and performing bit synchronization determination processing according to the comparison between the calculated difference value and a preset threshold value;
wherein the determining to perform bit synchronization comprises:
when the calculated difference value is larger than the preset threshold value, determining the position corresponding to the maximum value of the signal-to-noise ratio gain as a bit starting edge to finish bit synchronization;
the performing the correlation operation includes:
performing correlation operation on fixed data bits of 20 different candidate positions in the divided segmented data and a preset probability matrix; the probability matrix is used for representing the possible positions of the data demodulated from the segmented data, wherein the data has hopping.
6. The apparatus of claim 5, wherein the segment data is:
Rk＝(r20(k-1)+1,…,r20k) K is the data bit length;
wherein r isk＝Ack+nk；
C is mentionedkFor modulating 20 repetitions of the navigation message, each ckMaintaining a coarse acquisition C/A code period; a is signal power; n iskIs a mean of 0 and a variance of
Figure FDA0002192802950000031
White additive gaussian noise.
7. The apparatus of claim 6, wherein the predetermined probability matrix comprises:
Figure FDA0002192802950000032
and
Figure FDA0002192802950000033
8. the apparatus according to any of claims 5-7, wherein said determining to perform bit synchronization further comprises:
when the calculated difference value is less than or equal to the preset threshold value and the number of times of performing the accumulation calculation of the correlation operation result is less than a preset number threshold value, re-dividing 20 adjacent data from the data stream shifted into the shift register as the segmented data of the bit synchronization analysis, and continuing the bit synchronization processing according to the re-divided segmented data;
and when the difference value is less than or equal to the preset threshold value and the times of the accumulation calculation of the correlation operation result are greater than or equal to the preset times threshold value, determining that bit synchronization fails.
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