CN115685271A - Two-stage rapid signal capture method of time division navigation signal under large Doppler - Google Patents
Two-stage rapid signal capture method of time division navigation signal under large Doppler Download PDFInfo
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Abstract
The application relates to a two-stage rapid signal capturing method of time division navigation signals under large Doppler. The method comprises the following steps: acquiring a digital baseband signal received by a navigation receiver, and sampling the digital baseband signal to obtain a first sampling signal; traversing a first code phase searching range, and performing code phase capturing on a time division pulse sequence corresponding to the first sampling signal to obtain a first pseudo code phase capturing result; after waiting for a preset time interval, sampling the digital baseband signal to obtain a second sampling signal, and obtaining a second code phase search range according to the pre-estimated maximum Doppler of the digital baseband signal; traversing a second code phase searching range, and performing code phase capturing on a time division pulse sequence corresponding to a second sampling signal to obtain a second pseudo code phase capturing result; and obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result. By adopting the method, the time division spread spectrum signal with large Doppler frequency offset can be rapidly captured.
Description
Technical Field
The application relates to the technical field of satellite navigation, in particular to a two-stage rapid signal acquisition method of time division navigation signals under large Doppler.
Background
The Beidou navigation system has the characteristics of global coverage, all-day work and the like, and the Beidou navigation system is widely applied to various industries, including the fields of vehicle and aircraft navigation, personal navigation, bridge monitoring, modern agriculture, precise mapping and the like. In a GPS receiver, acquisition of a signal is a prerequisite for signal tracking and demodulation of navigation data bits. During acquisition, carrier Doppler frequency shift search and C/A code initial phase search need to be completed for each satellite in a GPS constellation at the same time. The Beidou system improves the measurement performance of the system by adding the measurement link of the Ka frequency point. The Ka frequency point signal has high carrier frequency and large Doppler dynamic range, and adopts a time division system signal, namely, a time division pulse control sequence is modulated on the basis of the traditional continuous navigation signal, and the continuous signal is changed into a discontinuous signal. On the other hand, the low-orbit satellite is adopted to broadcast the navigation enhancement signal, so that the performance of the Beidou system can be further improved, but the low-orbit satellite has large dynamic state, so that the Doppler variation range of the enhancement signal is large, and meanwhile, in order to solve the problem of receiving and transmitting isolation of the low-orbit satellite, the enhancement signal can also adopt a time division system, so that the low-orbit navigation enhancement signal received on the ground is also a time division signal with large Doppler.
In the conventional method, to complete signal acquisition, a search needs to be performed in an uncertain region of a pseudo code and a doppler frequency, and for a time division navigation signal with large doppler, the conventional continuous signal acquisition method suffers from large performance loss and needs to overcome the problem of a sharp increase of a search space caused by large doppler. The method using the assistance information can compress the search range during signal acquisition, but needs to know the ephemeris of the satellite and the approximate position of the satellite in advance.
Disclosure of Invention
In view of the foregoing, it is necessary to provide a two-stage fast signal acquisition method for time division navigation signals under large doppler.
A two-stage fast signal acquisition method for time-division navigation signals under large doppler, the method comprising:
acquiring a digital baseband signal received by a navigation receiver, and sampling the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
traversing a preset first code phase searching range, performing code phase capturing on the time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase searching range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result;
after waiting for a preset time interval at an initial sampling point of the first sampling signal, sampling the digital baseband signal to obtain a second sampling signal, and calculating according to a pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range;
traversing the second code phase search range, and performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result;
and obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
In one embodiment, the method further comprises the following steps: the mathematical model of the digital baseband signal is as follows:
wherein,
to navigate the digital baseband signals received by the receiving device,
amplitude of carrier wave，
In order to provide a satellite navigation message,
in order to sample the points of interest,
in order to delay the transmission of the signal,
is the carrier-wave doppler of the signal,w(k) In the case of baseband noise, the noise is,
for the purpose of the spreading codes in the navigation signal,
is a time-division pulse signal, and has a pulse width,
is a symbol of an imaginary unit of a number,
is the radio frequency carrier initial phase.
In one embodiment, the method further comprises the following steps: performing incoherent accumulation on a plurality of coherent integration results obtained after coherent integration is performed on each time division pulse of the first sampling signal and a local spread spectrum code corresponding to the current code phase to obtain an incoherent accumulation result corresponding to the current code phase; the current code phase is in a preset first code phase searching range; and traversing the first code phase searching range to obtain a non-coherent accumulation result corresponding to each code phase in the first code phase searching range, and obtaining a pseudo code phase capturing result in the first code phase searching range according to the magnitude relation between each non-coherent accumulation result and a decision threshold.
In one embodiment, the method further comprises the following steps: when the incoherent accumulation result is larger than a decision threshold, successfully acquiring the code phase, and obtaining an acquisition result according to the code phase corresponding to the current local spread spectrum code; and when the incoherent accumulation result is less than or equal to a decision threshold, failing to acquire the code phase, sliding a preset pseudo code phase search interval backwards in the first code phase search range, calculating an incoherent accumulation result corresponding to the slid code phase, iterating the process until each code phase in the first code phase search range is searched, stopping iteration, and outputting an acquisition result in the first code phase search range.
In one embodiment, the method further comprises the following steps: performing non-coherent accumulation on a plurality of coherent integration results obtained by performing coherent integration on each time division pulse of the first sampling signal and the local spread spectrum code corresponding to the current code phase, and obtaining a non-coherent accumulation result corresponding to the current code phase as follows:
wherein,
is a code phase of
The result of the corresponding non-coherent accumulation,
is the phase of the baseband digital signal and,
is a base-band complex signal and is,
is as follows
The position of the starting sampling point of each pulse signal,
for local replication of phase is
The spreading code of (a) is used,
in order to be a short-time correlation length,
the number of pulses corresponding to the first sampling signal.
In one embodiment, the method further comprises the following steps: and calculating according to the pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range as follows:
wherein,
for the second code phase search range,
for the maximum doppler corresponding to the digital baseband signal,
，
is the radio frequency of the signal and,
in order to be at the pseudo-code rate,
which represents a rounding-up operation, is performed,
the time interval is a time interval of,
the interval is searched for the pseudo code phase.
In one embodiment, the method further comprises the following steps: according to the first pseudo code phase capturing result and the second pseudo code phase capturing result, carrier Doppler is obtained as follows:
wherein,
in the form of a carrier wave doppler, the doppler,
is the ratio of the signal radio frequency to the pseudo code rate,
for the second pseudo-code phase acquisition result,
for the first pseudo-code phase acquisition result,
are time intervals.
In one embodiment, the method further comprises the following steps: the second pseudo code phase acquisition result is:
wherein,
for the second pseudo-code phase acquisition result,
is as follows
Get maximum time corresponding
The value of (a) is,
is a code phase of
The result of the corresponding non-coherent accumulation,
for the first pseudo-code phase acquisition result,
for the second code phase search range,
the interval is searched for a pseudo code phase.
In one embodiment, the method further comprises the following steps: the first pseudo code phase acquisition result is:
wherein,
the result is captured for the first pseudo-code phase,
is the phase of the code and is,
is as follows
Taking maximum time to correspond to
The value of (a) is,
is a code phase of
The result of the corresponding non-coherent accumulation,
the interval is searched for the pseudo-code phase,
the number of cells is searched for the pseudo code phase.
In one embodiment, the method further comprises the following steps: and obtaining the carrier Doppler estimation precision according to the time interval and the pseudo code phase search interval as follows:
wherein,
is the accuracy of the estimation of the carrier doppler,
the interval is searched for the pseudo-code phase,
the ratio of the signal radio frequency to the pseudo code rate; adjusting the time interval and the pseudo code phase search interval to adjust an acquisition accuracy of carrier doppler.
A two-stage fast signal acquisition apparatus for time-division navigation signals under large doppler, the apparatus comprising:
the signal acquisition module is used for acquiring a digital baseband signal received by the navigation receiver and sampling the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
the first-stage searching module is used for traversing a preset first code phase searching range, performing code phase capturing on the time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase searching range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result;
the searching range determining module is used for sampling the digital baseband signal after waiting for a preset time interval at an initial sampling point of the first sampling signal to obtain a second sampling signal, and obtaining a second code phase searching range according to the pre-estimated maximum Doppler corresponding to the digital baseband signal;
the second-stage searching module is used for traversing the second code phase searching range and performing code phase capturing on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase capturing result;
and the carrier Doppler estimation module is used for obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:
acquiring a digital baseband signal received by a navigation receiver, and sampling the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
traversing a preset first code phase searching range, performing code phase capturing on the time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase searching range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result;
after waiting for a preset time interval at an initial sampling point of the first sampling signal, sampling the digital baseband signal to obtain a second sampling signal, and calculating according to a pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range;
traversing the second code phase search range, and performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result;
and obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out the steps of:
acquiring a digital baseband signal received by a navigation receiver, and sampling the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
traversing a preset first code phase searching range, performing code phase capturing on the time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase searching range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result;
after waiting for a preset time interval at an initial sampling point of the first sampling signal, sampling the digital baseband signal to obtain a second sampling signal, and calculating according to a pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range;
traversing the second code phase searching range, and performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result;
and obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
The two-stage rapid signal capturing method of the time division navigation signal under the large Doppler realizes the capturing of the Doppler of the signal by performing two times of serial time dimension searching on the received digital baseband signal, and particularly converts two-dimensional time-frequency searching into one-dimensional time searching and one-dimensional frequency estimation, when the one-dimensional time searching is performed, the pseudo code phase is captured twice, the first stage of capturing can perform rapid searching on the code phase of the signal in a larger time range under the condition that the signal has large Doppler frequency offset, the initial capturing of the code phase of the signal is completed, the second stage of capturing is based on the first stage of capturing, the time searching range of the signal can be greatly compressed, a more accurate phase searching result is obtained, after the two-stage pseudo code phase capturing is realized, the carrier Doppler is calculated according to the two-time pseudo code phase capturing results, the searching space of the Doppler of the signal is greatly compressed, and the capturing efficiency of the time division spread spectrum signal under the large Doppler frequency offset is improved.
Drawings
FIG. 1 is a flow chart illustrating a two-stage fast signal acquisition method for time-division navigation signals under large Doppler in one embodiment;
FIG. 2 is a schematic diagram of an embodiment of a time-division spread-spectrum signal;
FIG. 3 is a diagram illustrating correlation peak results for a first search and a second search, under an embodiment;
FIG. 4 is a block diagram of a two-stage fast signal acquisition device for time-division navigation signals under large Doppler in one embodiment;
FIG. 5 is a diagram of the internal structure of a computer device in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
In one embodiment, as shown in fig. 1, a two-stage fast signal acquisition method for time-division navigation signals under large doppler is provided, which includes the following steps:
The GPS signal is a spread spectrum signal that has been subjected to direct sequence spread spectrum modulation and carrier modulation. For spread spectrum systems, acquisition means that the phase difference between the local reference code and the receiving code is less than one symbol width, the clock frequencies of the receiving and transmitting codes are basically consistent, and simultaneously, the carriers are mutually aligned to realize the synchronization of the input signal and the local signal. The coarse synchronization process of the pseudo code phase and the carrier frequency in the GPS system is pseudo code capturing, an effective pseudo code capturing method is the core of research of a high dynamic GPS receiver, and the performance of the system is improved by shortening the capturing time. When capturing the signal of the transmitting end, the receiver can confirm the successful capturing only after the pseudo code phase and the carrier Doppler frequency which are locally reproduced by the receiver are matched with the received signal, thereby realizing the bit synchronization of the received and transmitted signal. In the present invention, the digital baseband signal includes a time division spread spectrum signal with a large doppler frequency offset, the first sampling signal includes a multi-segment time division pulse signal, as shown in the schematic structural diagram of the time division spread spectrum signal shown in fig. 2, compared with the traditional acquisition of the spread spectrum signal, the time division spread spectrum signal adds a time division pulse sequence, which is a discontinuous signal,
for the pulse period, the time-divided pulse sequence being of pulse width
Has signal pulses therein
There is no signal in time, so when the time division pulse sequence is subjected to code phase acquisition, the time division pulse sequence is multiplied by a PN code (pseudo random code), and a signal in the presence of a signal pulse can be processed.
And 104, traversing a preset first code phase search range, performing code phase capturing on the time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase search range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result.
The first code phase search range is a preset signal capture time range, the duration of a part of time division spread spectrum signals with signals is short, and the Doppler tolerance range is large, so that only a pseudo code phase can be captured in a capture link, code phase capture is carried out on a time division pulse sequence corresponding to a first sampling signal to serve as first-stage search, a first pseudo code phase capture result is obtained through the first-stage search, pseudo code Doppler is obtained through two pseudo code phase capture results, carrier Doppler is further obtained, and rapid capture of the signals can be still maintained under the condition that a search space is greatly reduced.
And 106, after waiting for a preset time interval at the initial sampling point of the first sampling signal, sampling the digital baseband signal to obtain a second sampling signal, and calculating according to the maximum Doppler corresponding to the digital baseband signal estimated in advance to obtain a second code phase search range.
The principle of Doppler acquisition is to have a time interval of
The received signal is captured twice, the pseudo code Doppler is calculated according to the code phase capture difference of the two times, then the pseudo code Doppler is converted to the carrier Doppler, the carrier Doppler is estimated by utilizing the difference result of the two code phase captures, the second code phase search range is calculated according to the maximum Doppler corresponding to the estimated digital baseband signal, and compared with the first-stage search, the search range of the second-stage search is greatly reduced.
And step 108, traversing the second code phase search range, and performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result.
And performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal as a second-stage search, and obtaining a second pseudo code phase acquisition result through the second-stage search. The second-level searching method is the same as the first-level searching method, but the searching range of the second-level searching is reduced, and the searching precision is improved.
And step 110, obtaining carrier Doppler according to the first pseudo code phase capturing result and the second pseudo code phase capturing result.
In a general acquisition method, because of many units for signal searching, the corresponding signal acquisition time is also long, which is not allowed in some receivers with high real-time requirement. The two-stage capturing algorithm provided by the invention can capture the pseudo code phase twice, converts two-dimensional time-frequency search into one-dimensional time search and one-dimensional frequency estimation, and greatly improves the efficiency of the algorithm.
In the two-stage fast signal capturing method for time division navigation signals under large Doppler, the signal Doppler is captured by performing two-time serial time dimension search on received digital baseband signals, specifically, two-dimensional time-frequency search is converted into one-dimensional time search and one-dimensional frequency estimation, when one-dimensional time search is performed, a pseudo code phase is captured twice, the first-stage capture can perform fast search on the code phase of the signal in a larger time range under the condition that the signal has large Doppler frequency offset, initial capture of the code phase of the signal is completed, the second-stage capture is based on the first-stage capture, the time search range of the signal can be greatly compressed, a more accurate phase search result is obtained, after two-time pseudo code phase capture is performed, carrier Doppler is calculated according to the two-time pseudo code phase capture results, the Doppler search space of the signal is greatly compressed, and the capturing efficiency of the time division spread spectrum signal under large Doppler frequency offset is improved.
In one embodiment, the mathematical model of the digital baseband signal is:
wherein,
for digital baseband signals received at the navigation receiver device,
is the amplitude of the carrier wave and,
in order to provide a satellite navigation message,
in order to sample the points of interest,
in order to delay the transmission of the signal,
is the carrier-wave doppler of the signal,w(k) In the case of baseband noise, the noise is,
for the purpose of the spreading codes in the navigation signal,
in order to time-division pulse signals,
is a symbol of an imaginary unit of a number,
is the radio frequency carrier initial phase. In this embodiment, the signal acquisition process can be described as using a known spreading code sequence and time division pulse sequence of the navigation signal to receive the received signal
In the course of a sequence
And
two parameters are estimated. Compared with the traditional capture of spread spectrum signals, the time division spread spectrum signals are added with time division pulse sequences, so that the capture of the signals by the time division pulse sequences is also needed in the capture process.
In one embodiment, traversing a preset first code phase search range, and performing code phase acquisition on a time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase acquisition result in the first code phase search range includes: performing incoherent accumulation on a plurality of coherent integration results obtained by performing coherent integration on each time division pulse of the first sampling signal and a local spread spectrum code corresponding to the current code phase to obtain an incoherent accumulation result corresponding to the current code phase; the current code phase is in a preset first code phase searching range; traversing the first code phase searching range to obtain a non-coherent accumulation result corresponding to each code phase in the first code phase searching range, and obtaining a pseudo code phase capturing result in the first code phase searching range according to the magnitude relation between each non-coherent accumulation result and a judgment threshold; performing incoherent accumulation on a plurality of coherent integration results obtained by coherently integrating each time division pulse of the first sampling signal and the local spreading code corresponding to the current code phase, wherein obtaining the incoherent accumulation result corresponding to the current code phase comprises: performing incoherent accumulation on a plurality of coherent integration results obtained by performing coherent integration on each time division pulse of the first sampling signal and the local spread spectrum code corresponding to the current code phase, wherein the incoherent accumulation result corresponding to the current code phase is obtained by:
wherein,
is a code phase of
Corresponding non-coherent accumulation result，
Is the phase of the baseband digital signal and,
is a base-band complex signal and is,
is as follows
The position of the initial sampling point of each pulse signal,
for local replication of phase is
The spreading code of (a) is used,
in order to be a short-time correlation length,
the number of pulses corresponding to the first sampling signal.
In this embodiment, in the first level search, a selection is made
The signal is captured in a time-division manner,
the duration of the segment time signal is
，
And
from time-hopping pulse patterns
Determine that
Segment time division signal and
performing short-time correlation and post-accumulation operation to obtain
Corresponding non-coherent accumulation result
Short time correlation and pulse width
Remain in agreement, i.e.
，
Is the signal sampling rate. When in use
（
A preset decision threshold), the code phase is successfully captured, the corresponding local spread spectrum code phase is the captured result, otherwise, the search is continued until the end or the related result exceeds the thresholdTh。
In one embodiment, the step of obtaining the pseudo code phase acquisition result in the first code phase search range according to the magnitude relationship between each non-coherent accumulation result and the decision threshold includes: when the incoherent accumulation result is greater than the judgment threshold, successfully acquiring the code phase, and obtaining an acquisition result according to the code phase corresponding to the current local spread spectrum code; when the incoherent accumulation result is less than or equal to the decision threshold, the code phase acquisition fails, a preset pseudo code phase search interval slides backwards in a first code phase search range, the incoherent accumulation result corresponding to the code phase after sliding is calculated, the process is iterated until each code phase in the first code phase search range is searched, the iteration is stopped, and the acquisition result in the first code phase search range is output; the first pseudo code phase acquisition result is:
wherein,
for the first pseudo-code phase acquisition result,
in order to be able to determine the code phase,
is as follows
Get maximum time corresponding
The value of (a) is set to (b),
is a code phase of
The result of the corresponding non-coherent accumulation,
the interval is searched for the pseudo-code phase,
the number of cells is searched for the pseudo code phase. In this embodiment, the pseudo code phase capturing result of the signal can be obtained by traversing all the possibilities of the pseudo code initial phases and taking the phase corresponding to the maximum value of all the search results.
In one embodiment, the second pseudo-code phase acquisition result is:
wherein,
for the second pseudo-code phase acquisition result,
is as follows
Get maximum time corresponding
The value of (a) is set to (b),
is a code phase of
The result of the corresponding non-coherent accumulation,
for the first pseudo-code phase acquisition result,
for the second code phase search range,
searching an interval for a pseudo code phase; obtaining a second code phase search by maximum Doppler calculation corresponding to the pre-estimated digital baseband signalThe cable range includes: and calculating according to the maximum Doppler corresponding to the pre-estimated digital baseband signal to obtain a second code phase search range as follows:
wherein,
for the second code phase search range,
for the maximum doppler corresponding to the digital baseband signal,
，
is the radio frequency of the signal and,
in order to be at the pseudo-code rate,
which represents a rounding-up operation on the upper part,
in the form of a time interval,
the interval is searched for a pseudo code phase. In this embodiment, the second code phase search range includes
A code phase.
In one embodiment, obtaining carrier doppler based on the first and second pseudo-code phase acquisition results comprises: according to the first pseudo code phase capturing result and the second pseudo code phase capturing result, carrier Doppler is obtained as follows:
wherein,
in the form of a carrier wave doppler, the doppler,
is the ratio of the signal radio frequency to the pseudo code rate,
the result is captured for the second pseudo-code phase,
for the first pseudo-code phase acquisition result,
are time intervals.
In one embodiment, the method further comprises: the estimation precision of the carrier Doppler obtained according to the time interval and the pseudo code phase search interval is as follows:
wherein,
is the accuracy of the estimation of the carrier doppler,
the interval is searched for the pseudo-code phase,
is the ratio of the radio frequency of the signal to the rate of the pseudo code; adjusting time intervals and pseudo code phase search intervals to adjust acquisition accuracy of carrier doppler. In the embodiment, the estimation of carrier Doppler is realized by using the difference result of two times of code phase acquisition, and the carrier Doppler is prolonged
Or reduce
All can improve the capture precision of the signal carrier frequency
、
A code piece,
The accuracy of the carrier frequency estimation is 620Hz.
In a specific embodiment, the present invention provides a two-stage capturing algorithm for a large doppler time division signal, which comprises the following specific steps, as shown in the following table, first obtaining a digital baseband signal to be captured, sampling the digital baseband signal, then performing a first stage search on a first sampled signal, where the total number of code phases searched in a first code phase search range is
Judging whether the time search is finished or not by the pseudo code phase, if so, acquiring carrier Doppler, and if not, acquiring successfully, otherwise, acquiring unsuccessfully; if the time search of the first-stage search is not finished, sliding the pseudo code phase search interval of the local signal backwards, carrying out short-time correlation accumulation operation on the first sampling signal, the local spread spectrum code and the time-hopping pulse pattern to obtain a correlation value corresponding to each pseudo code phase, comparing the correlation value with a threshold, if the correlation value is larger than the threshold, recording the phase at the moment, otherwise, judging whether the time search is finished again, outputting a first pseudo code phase capture result according to the maximum captured phase, and waiting for the acquisition
And sampling the digital baseband signal after time to obtain a second sampling signal, calculating a second code phase search range in the first code phase search range according to the pre-estimated maximum Doppler, performing second-stage search on the second sampling signal in the second code phase search range to obtain a second pseudo code phase acquisition result, and finally calculating to obtain carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result to finish signal acquisition.
TABLE 1 two-stage acquisition algorithm for large Doppler time division signals
In a specific embodiment, as shown in fig. 3, a schematic diagram of a correlation peak result of a first-stage search and a second-stage search is provided, as can be seen from fig. 3, a range of the second-stage search is greatly reduced compared with a range of the first-stage search, and by capturing two stages of code phases, doppler frequency offset of a signal can be directly calculated without searching doppler of the signal, which means that the method of the present invention can greatly simplify complexity of capturing a time-division navigation signal with large doppler frequency offset.
It should be understood that, although the steps in the flowchart of fig. 1 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a portion of the steps in fig. 1 may include multiple sub-steps or multiple stages that are not necessarily performed at the same time, but may be performed at different times, and the order of performance of the sub-steps or stages is not necessarily sequential, but may be performed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.
In one embodiment, as shown in fig. 4, there is provided a two-stage fast signal acquisition apparatus for time-division navigation signals under large doppler, comprising: a signal acquisition module 402, a first stage search module 404, a search range determination module 406, a second stage search module 408, and a carrier doppler estimation module 410, wherein:
a signal obtaining module 402, configured to obtain a digital baseband signal received by the navigation receiver, and sample the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
the first-stage searching module 404 is configured to traverse a preset first code phase searching range, perform code phase acquisition on a time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase acquisition result within the first code phase searching range, and obtain a first pseudo code phase acquisition result according to a maximum value of the pseudo code phase acquisition result;
a search range determining module 406, configured to sample the digital baseband signal after waiting for a preset time interval at an initial sampling point of the first sampling signal to obtain a second sampling signal, and obtain a second code phase search range according to a pre-estimated maximum doppler corresponding to the digital baseband signal;
the second-stage searching module 408 is configured to traverse a second code phase searching range, and perform code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result;
and a carrier doppler estimation module 410, configured to obtain carrier doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
In one embodiment, the signal acquisition module 402 is further configured to mathematically model the digital baseband signal as:
wherein,
receiving digits for navigationThe baseband signal is then used to generate a baseband signal,
is the amplitude of the carrier wave and,
in order to provide a satellite navigation message,
in order to sample the points of interest,
in order to delay the transmission of the signal,
is the carrier-wave doppler of the signal,w(k) In the case of baseband noise, the noise is,
for the purpose of the spreading codes in the navigation signal,
in order to time-division pulse signals,
is a symbol of an imaginary unit of numbers,
is the radio frequency carrier initial phase.
In one embodiment, the first-stage search module 404 is further configured to perform non-coherent accumulation on a plurality of coherent integration results obtained after performing coherent integration on each time division pulse of the first sampling signal and the local spreading code corresponding to the current code phase to obtain a non-coherent accumulation result corresponding to the current code phase; the current code phase is in a preset first code phase searching range; and traversing the first code phase searching range to obtain a non-coherent accumulation result corresponding to each code phase in the first code phase searching range, and obtaining a pseudo code phase capturing result in the first code phase searching range according to the magnitude relation between each non-coherent accumulation result and the decision threshold.
In one embodiment, the first-stage searching module 404 is further configured to, when the incoherent accumulation result is greater than the decision threshold, successfully acquire the code phase, and obtain an acquisition result according to the code phase corresponding to the current local spreading code; and when the incoherent accumulation result is less than or equal to the judgment threshold, failing to acquire the code phase, sliding a preset pseudo code phase search interval backwards in the first code phase search range, calculating the incoherent accumulation result corresponding to the slid code phase, iterating the process until each code phase in the first code phase search range is searched, stopping iteration, and outputting the acquisition result in the first code phase search range.
In one embodiment, the first-stage search module 404 is further configured to perform non-coherent accumulation on a plurality of coherent integration results obtained after performing coherent integration on each time division pulse of the first sampling signal and the local spreading code corresponding to the current code phase, and obtain a non-coherent accumulation result corresponding to the current code phase as:
wherein,
is a code phase of
The result of the corresponding non-coherent accumulation,
is the phase of the baseband digital signal and,
is a base-band complex signal and is,
is as follows
The position of the initial sampling point of each pulse signal,
for local replication of phase is
The spreading code of (a) is used,
in order to be a short-time correlation length,
the number of pulses corresponding to the first sampling signal.
In one embodiment, the search range determining module 406 is further configured to obtain a second code phase search range according to the pre-estimated maximum doppler corresponding to the digital baseband signal, where the second code phase search range is:
wherein,
for the second code phase search range,
for a pre-estimated maximum doppler corresponding to the digital baseband signal,
，
is the radio frequency of the signal and,
in order to be at the pseudo-code rate,
which represents a rounding-up operation on the upper part,
the time interval is a time interval of,
the interval is searched for the pseudo code phase.
In one embodiment, the carrier doppler estimation module 410 is further configured to obtain, according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result, carrier doppler as:
wherein,
is a carrier wave doppler (doppler) wave,
the ratio of the signal rf frequency to the pseudo code rate,
for the second pseudo-code phase acquisition result,
the result is captured for the first pseudo-code phase,
are time intervals.
In one embodiment, the second stage search module 408 is further configured to obtain the second pseudo-code phase acquisition result as:
wherein,
for the second pseudo-code phase acquisition result,
is that when
Get maximum time corresponding
The value of (a) is,
is a code phase of
The result of the corresponding non-coherent accumulation,
for the first pseudo-code phase acquisition result,
for the second code phase search range,
the interval is searched for a pseudo code phase.
In one embodiment, the first stage search module 404 is further configured to obtain the following result:
wherein,
the result is captured for the first pseudo-code phase,
is the phase of the code and is,
is that when
Taking maximum time to correspond to
The value of (a) is set to (b),
is a code phase of
The result of the corresponding non-coherent accumulation,
the interval is searched for the pseudo-code phase,
the number of cells is searched for the pseudo code phase.
In one embodiment, the estimation accuracy for carrier doppler obtained from the time interval and the pseudo-code phase search interval is:
wherein,
for the accuracy of the estimation of the carrier doppler,
the interval is searched for the pseudo-code phase,
is the ratio of the radio frequency of the signal to the rate of the pseudo code; adjusting time intervals and pseudo code phase search intervals to adjust carrier dopplerThe capture accuracy of (2).
For specific limitations of the two-stage fast signal capturing apparatus for time division navigation signals under large doppler, reference may be made to the above limitations of the two-stage fast signal capturing method for time division navigation signals under large doppler, which are not described herein again. All or part of each module in the two-stage rapid signal acquisition device for the time division navigation signal under the large Doppler can be realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.
In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 5. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operating system and the computer program to run on the non-volatile storage medium. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to realize a two-stage fast signal acquisition method of time division navigation signals under large Doppler. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.
Those skilled in the art will appreciate that the architecture shown in fig. 5 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.
In an embodiment, a computer device is provided, comprising a memory storing a computer program and a processor implementing the steps of the method in the above embodiments when the processor executes the computer program.
In an embodiment, a computer-readable storage medium is provided, on which a computer program is stored, which computer program, when being executed by a processor, carries out the steps of the method in the above-mentioned embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include non-volatile and/or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically Programmable ROM (EPROM), electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data Rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), rambus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).
All possible combinations of the technical features in the above embodiments may not be described for the sake of brevity, but should be considered as being within the scope of the present disclosure as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not to be understood as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent application shall be subject to the appended claims.
Claims (10)
1. A two-stage fast signal acquisition method for time division navigation signals under large Doppler is characterized by comprising the following steps:
acquiring a digital baseband signal received by a navigation receiver, and sampling the digital baseband signal to obtain a first sampling signal; the digital baseband signal comprises a time division spread spectrum signal with large Doppler frequency offset;
traversing a preset first code phase searching range, performing code phase capturing on a time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase capturing result in the first code phase searching range, and obtaining a first pseudo code phase capturing result according to the maximum value of the pseudo code phase capturing result;
after waiting for a preset time interval at an initial sampling point of the first sampling signal, sampling the digital baseband signal to obtain a second sampling signal, and calculating according to a pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range;
traversing the second code phase search range, and performing code phase acquisition on the time division pulse sequence corresponding to the second sampling signal to obtain a corresponding second pseudo code phase acquisition result;
and obtaining carrier Doppler according to the first pseudo code phase acquisition result and the second pseudo code phase acquisition result.
2. The method of claim 1, wherein the mathematical model of the digital baseband signal is:
wherein,
to navigate the digital baseband signals received by the receiving device,
is the amplitude of the carrier wave and,
in order to provide a satellite navigation message,
in order to sample the points of interest,
in order to delay the transmission of the signal,
is the carrier-wave doppler of the signal,w(k) In the case of baseband noise, the noise is,
for the purpose of the spreading codes in the navigation signal,
in order to time-division pulse signals,
is a symbol of an imaginary unit of a number,
is the radio frequency carrier initial phase.
3. The method of claim 1, wherein traversing a preset first code phase search range, and performing code phase acquisition on a time division pulse sequence corresponding to the first sampling signal to obtain a pseudo code phase acquisition result in the first code phase search range comprises:
performing non-coherent accumulation on a plurality of coherent integration results obtained after coherent integration is performed on each time division pulse of the first sampling signal and a local spread spectrum code corresponding to the current code phase to obtain a non-coherent accumulation result corresponding to the current code phase; the current code phase is in a preset first code phase searching range;
and traversing the first code phase searching range to obtain a non-coherent accumulation result corresponding to each code phase in the first code phase searching range, and obtaining a pseudo code phase capturing result in the first code phase searching range according to the magnitude relation between each non-coherent accumulation result and a decision threshold.
4. The method of claim 3, wherein the step of obtaining the pseudo code phase acquisition result in the first code phase search range according to the magnitude relationship between each non-coherent accumulation result and the decision threshold comprises:
when the incoherent accumulation result is larger than a judgment threshold, successfully capturing the code phase, and obtaining a capture result according to the code phase corresponding to the current local spread spectrum code;
and when the incoherent accumulation result is smaller than or equal to the decision threshold, failing to acquire the code phase, sliding a preset pseudo code phase search interval backwards in the first code phase search range, calculating the incoherent accumulation result corresponding to the slid code phase, iterating the process until each code phase in the first code phase search range is searched, stopping iteration, and outputting the acquisition result in the first code phase search range.
5. The method of claim 3, wherein the performing non-coherent accumulation on a plurality of coherent integration results obtained by performing coherent integration on each time division pulse of the first sampling signal and a local spreading code corresponding to a current code phase to obtain a non-coherent accumulation result corresponding to the current code phase comprises:
performing incoherent accumulation on a plurality of coherent integration results obtained by performing coherent integration on each time division pulse of the first sampling signal and the local spread spectrum code corresponding to the current code phase, wherein the incoherent accumulation result corresponding to the current code phase is obtained by:
wherein,
is a code phase of
The result of the corresponding non-coherent accumulation,
is the phase of the baseband digital signal and,
is a base-band complex signal and is,
is as follows
The position of the initial sampling point of each pulse signal,
for local replication of phase is
The spreading code of (a) is used,
is related for a short timeThe length of the first and second support members,
the number of pulses corresponding to the first sampling signal.
6. The method of claim 1, wherein the calculating a second code phase search range according to the pre-estimated maximum doppler corresponding to the digital baseband signal comprises:
calculating according to the pre-estimated maximum Doppler corresponding to the digital baseband signal to obtain a second code phase search range as follows:
wherein,
for the second code phase search range,
for the maximum doppler corresponding to the pre-estimated digital baseband signal,
，
is the radio frequency of the signal and,
in order to be at the pseudo-code rate,
which represents a rounding-up operation on the upper part,
in the form of a time interval,
the interval is searched for a pseudo code phase.
7. The method of claim 1, wherein obtaining carrier doppler based on the first and second pseudo-code phase acquisition results comprises:
according to the first pseudo code phase capturing result and the second pseudo code phase capturing result, carrier Doppler is obtained as follows:
wherein,
is a carrier wave doppler (doppler) wave,
is the ratio of the signal radio frequency to the pseudo code rate,
for the second pseudo-code phase acquisition result,
the result is captured for the first pseudo-code phase,
are time intervals.
8. The method of any of claims 1 or 7, wherein the second pseudo-code phase acquisition result is:
wherein,
for the second pseudo-code phase acquisition result,
is as follows
Get maximum time corresponding
The value of (a) is,
is a code phase of
The result of the corresponding non-coherent accumulation,
for the first pseudo-code phase acquisition result,
for the second code phase search range,
the interval is searched for the pseudo code phase.
9. The method of any of claims 1 or 7, wherein the first pseudo-code phase acquisition result is:
wherein,
for the first pseudo-code phase acquisition result,
in order to be able to determine the code phase,
is as follows
Get maximum time corresponding
The value of (a) is,
is a code phase of
The result of the corresponding non-coherent accumulation,
the interval is searched for the pseudo-code phase,
the number of cells is searched for the pseudo code phase.
10. The method of claim 7, further comprising:
and obtaining the carrier Doppler estimation precision according to the time interval and the pseudo code phase search interval as follows:
wherein,
for the accuracy of the estimation of the carrier doppler,
the interval is searched for the pseudo-code phase,
is the ratio of the radio frequency of the signal to the rate of the pseudo code;
adjusting the time interval and the pseudo code phase search interval to adjust an acquisition accuracy of carrier doppler.
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