CN202362461U - GPS signal capturing device based on FPGA - Google Patents
GPS signal capturing device based on FPGA Download PDFInfo
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- CN202362461U CN202362461U CN2011203789567U CN201120378956U CN202362461U CN 202362461 U CN202362461 U CN 202362461U CN 2011203789567 U CN2011203789567 U CN 2011203789567U CN 201120378956 U CN201120378956 U CN 201120378956U CN 202362461 U CN202362461 U CN 202362461U
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Abstract
The utility model relates to a GPS signal capturing device based on an FPGA. The GPS signal capturing device includes a clock generating module, a main control module, a GPS signal storage module, a carrier wave oscillator module, a carrier wave stripping module, a pseudo code read module, an average sampling module, an FFT/IFFT module, a threshold decision and initial phase calculation module, and a fine capturing module. The clock generating module is in an output connection with the carrier wave oscillator module. The carrier wave oscillator module is in an output connection with the carrier wave stripping module. The GPS signal storage module is in an input connection with an intermediate frequency signal, and is in a bi-directional connection with the fine capturing module. The GPS signal storage module is in an output connection with the carrier wave stripping module. The carrier wave stripping module is in an output connection with the average sampling module. The average sampling module is in an output connection with an FFT module. The pseudo code read module is in an output connection with the other FFT module. The two FFT modules are in an output connection with an IFFT module. The IFFT module is in an output connection the threshold decision and initial phase calculation module. The threshold decision and initial phase calculation module is in an output connection with the fine capturing module.
Description
Technical field
The invention belongs to reception technique field, gps satellite location, a kind of gps signal acquisition equipment that especially utilizes the FPGA hardware platform to realize based on FPGA.
Background technology
The GPS software receiver carries out base band signal process through software; Compare with traditional ASIC (proprietary hardware chip) hardware receiver; Software receiver has characteristics such as opening, dirigibility and extendability; Need not change under the prerequisite of hardware, the needs through just satisfying different user to the adjustment and the upgrading of software parameter have greatly reduced the required cost of system upgrade.
Field programmable gate array (FPGA) has advantages such as dirigibility and fast processing concurrently, and its inside is made up of the logic array of rule, can develop special chip, makes small product size very little, is easy to carry.FPGA inside has abundant logical resource, and its flexible configuration can carry out parallel processing to multi-channel data, and efficient is high.Because the inconvenience of PC platform is carried, the reasons such as resource-constrained of DSP platform make and have compared clear superiority based on the software receiver of FPGA platform with PC, DSP platform.
The GPS base band signal process mainly comprises catches and follows the tracks of two aspects, and catching is the prerequisite of following the tracks of.At present, the gps signal catching method mainly contains two big main flows, and a kind of is the time domain related algorithm; Another kind is the parallel phase acquisition algorithm of frequency domain, and preceding a kind of method realizes fairly simple, but more consuming time; A kind of method in back is to utilize the related operation of FFT in realizing catching, though relatively save time, realizes FFT with software; Need to handle big data volume, because the restriction of platform is not suitable for handling big data quantity FFT.In order to realize FFT, big data quantity is treated to small data quantity, can cause so again and catch the pseudo-code initial phase very big error is arranged.
Summary of the invention
The utility model provides a kind of gps signal acquisition equipment based on FPGA; Adopt the average sample technology that the parallel phase acquisition algorithm of frequency domain is improved; Completion obtains pseudo-code initial phase scope and initial carrier frequency to the initial acquisition of gps signal, utilizes the time domain related algorithm to do further essence again according to the initial phase scope of pseudo-code and initial carrier frequency and catches; Accurate initial phase and carrier frequency have so just been obtained; Realization is quick to gps signal, catches accurately, for Base-Band Processing at the back comprises that processing such as tracking, positioning calculation provide pseudo-code phase and carrier wave frequency information fast and accurately.Solved existing catching method and circuit system complicacy, capture time length and be unfavorable for that FPGA Platform Implementation, acquisition phase have technical matterss such as error.
The purpose of the utility model realizes with following technical scheme: a kind of gps signal acquisition equipment based on FPGA; It is characterized in that: build the FPGA hardware platform and combine, total control module, gps signal memory module, carrier oscillator module, carrier wave strip module, pseudo-code read module, average sample module, FFT/IFFT module, threshold judgement and the initial phase computing module of comprise the clock generating module, realizing by state machine and the smart trapping module of correlator realization with GPS receiver radio frequency front-end chip; System clock connects the smart trapping module that clock generating module, two FFT modules, pseudo-code read module, IFFT module, threshold judgement and initial phase computing modules and correlator are realized respectively; The output of clock generating module connects the carrier oscillator module; The output of carrier oscillator module connects the carrier wave strip module; The input of gps signal memory module connects the GPS intermediate-freuqncy signal of radio-frequency front-end and two-way connection of smart trapping module of realizing with correlator; The output of gps signal memory module connects the carrier wave strip module, and the output of carrier wave strip module connects the average sample module, and the output of average sample module connects a FFT module; The output of pseudo-code read module connects another FFT module; The output of two FFT modules connects the IFFT module, and the output of IFFT module connects threshold judgement and initial phase computing module, the smart trapping module that threshold judgement and initial phase computing module output join dependency device are realized.
The advantage of the utility model and showing effect:
1) the initial acquisition process has reduced operand, also is equivalent to save resource.If with 1KHZ is stepping, according to the catch frequency search that will carry out 21 steppings of Doppler shift to a satellite, the operand of search has two FFT computings, an IFFT computing, twice complex multiplication computing each time.The number of data points of average sample aftertreatment reduces, and has so just significantly reduced operand.
What 2) only also can be met tracer request with the initial acquisition module is not pseudo-code initial phase and carrier frequency very accurately.Can obtain pseudo-code initial phase scope according to the geometric ratio relation by the initial phase computing module, the point in the middle of getting also satisfies the requirement of following the tracks of phase place.
3) carrier frequency that can confirm according to pseudo-code initial phase scope and initial acquisition of smart trapping module through shortening frequency step, is carried out essence and is caught and obtain accurate pseudo-code initial phase and carrier frequency.
4) the smart trapping module after the initial acquisition is to select according to the requirement of following the tracks of.If the tracking module velocity ratio is very fast, on tracking time, require just can only not select the initial acquisition process when not being very strict, the time of catching so very soon.
5) speed of initial acquisition is greatly improved, and capture time has shortened a lot.If with the frequency parallel search, the time of catching a star is 1.14ms, if with the frequency serial search, the time of catching a star is 25ms.
Description of drawings
Fig. 1 is the logical relation synoptic diagram of each module of the utility model;
Fig. 2 is the state transition diagram of total control module;
Fig. 3 is the principle framework figure of initial acquisition process;
Fig. 4 is the principle framework figure of smart acquisition procedure;
Fig. 5 is an average sample process synoptic diagram.
Embodiment
Further specify below in conjunction with the technical scheme of accompanying drawing the utility model.
As shown in Figure 1; System clock connects the smart trapping module that clock generating module, two FFT modules, pseudo-code read module, IFFT module, threshold judgement and initial phase computing modules and correlator are realized respectively; The output of clock generating module connects the carrier oscillator module; The output of carrier oscillator module connects the carrier wave strip module, and the input of gps signal memory module connects the GPS intermediate-freuqncy signal of radio-frequency front-end and two-way connection of smart trapping module of realizing with correlator, and the output of gps signal memory module connects the carrier wave strip module; The output of carrier wave strip module connects the average sample module; The output of average sample module connects a FFT module, and the output of pseudo-code read module connects another FFT module, and the output of two FFT modules connects the IFFT module; The output of IFFT module connects threshold judgement and initial phase computing module, the smart trapping module that threshold judgement and initial phase computing module output join dependency device are realized.
The clock generating module produces the sampling rate clock according to system clock; The gps signal memory module is stored the GPS intermediate-freuqncy signal that radio-frequency front-end comes according to the sampling rate clock; The carrier oscillator module is according to sampling rate clock generating carrier wave, and the carrier wave strip module connects carrier oscillator module and gps signal memory module, carrier wave SIN value and COS value and GPS intermediate-freuqncy signal multiplied each other the GPS intermediate-freuqncy signal is peeled off carrier wave; The average sample module connects the carrier wave strip module; Carrier wave is peeled off data afterwards average sampling, the data after the average sample are sent into the FFT module and are carried out the FFT computing, and the pseudo-code read module reads the pseudo-code that prestores according to system clock; And the pseudo-code that reads is sent into the FFT module carry out the FFT computing, two FFT modules are carried out the FFT computing to data after the average sample and pseudo-code respectively simultaneously according to system clock; Data after two FFT computings multiply each other and send into the IFFT module then and carry out the IFFT computing; Threshold judgement is connected the IFFT module with the initial phase computing module; Data according to after the IFFT computing are carried out threshold judgement, obtain initial phase scope and initial carrier frequency; The smart trapping module that correlator is realized connects threshold judgement and initial phase computing module, obtains accurate pseudo-code initial phase and carrier frequency according to initial phase scope and initial carrier frequency, controls whole flow process by the total control module that state machine is realized.Because what acquisition equipment was handled is the GPS intermediate frequency data that comes from the radio-frequency front-end system collection; The chip rate of pseudo-code is 1.023MHZ; The whole sign indicating number cycle comprises 1023 code elements, and a pseudo-code cycle is 1ms, because the pseudo-code code length is 1ms; Catch operation so need the data of 1ms to accomplish at least, the data of employing 1ms are accomplished and are caught.Sampling clock is 5.714MHZ.A pseudo-code cycle 1ms just has 5714 discrete sampled datas.The average sample rate is the sampling rate of 1.024MHZ, is equivalent to be sampled as 1024 parts to 5714 point data, then the data in each part is done on average, is 1024 points after the sampling.Counting of each cycle decided by 5.714MHZ and two clocks of 1.024MHZ.As shown in Figure 5.
The utility model is to the intermediate frequency acquired signal from GPS receiver radio frequency front end; At first adopt the average sample method that the intermediate frequency acquired signal is carried out down-sampling, the energy of the point in each sampling period is averaged, the sample data of the data that obtain after average after as down-sampling; Counting after the average sample satisfied basic 2FFT computing; Sampling rate decides thus, accomplishes the initial acquisition to gps signal, obtains pseudo-code initial phase scope and initial carrier frequency; Then, according to the initial phase scope and the initial carrier frequency of pseudo-code, utilize the time domain related algorithm to do further essence again and catch, obtain accurate pseudo-code initial phase and carrier frequency, realization is quick to gps signal, catches accurately.And smart catching is can be optional according to requiring of following the tracks of.This can be selected through revising control module.Total control module is to be realized by the state machine of Mealy type, the control total system, and one has 8 states; Reset respectively, wait for beginning to write intermediate-freuqncy signal, wait intermediate-freuqncy signal RAM to be written full; Produce beginning initial acquisition signal, wait for that an initial acquisition finishes, the wait essence is caught end; The carrier wave stepping adds one, defends asterisk and adds one.The state transition diagram of total control module is as shown in Figure 2.
Fig. 3 provides the process of initial acquisition: at first the GPS intermediate-freuqncy signal and the local carrier that receive are multiplied each other, obtain I and Q component, average sampling then; Data after handling are FFT handle, local pseudo-code is carried out FFT handle and conjugation, above-mentioned two resulting results of FFT are carried out complex multiplication; And homophase and the quadrature two paths of signals that obtains carried out IFFT, and the result of IFFT is asked mould, mould is the intermediate-freuqncy signal and the local correlation that produces signal of input; Find out top and time peak in the correlation, and compare, if greater than thresholding with predefined threshold value; Show that then signal is captured to, obtain preliminary pseudo-code initial phase and carrier frequency, otherwise; Show not capture signal that the adjustment local carrier frequency repeats said process; If do not capture satellite yet after having searched for the Doppler shift scope of setting, then asterisk is defended in adjustment, continues search.
The detailed step of initial acquisition process is:
1. to the input data x (n) of 1ms, SIN () and the COS () component with carrier wave multiplies each other earlier, obtains I and Q component, peels off carrier wave, and the SF average sample of using 1.024MHZ is then calculated its FFT to 1024 points, will import data conversion to frequency domain X (k);
2. for the pseudo-code of 1023 code elements, the SF with 5.714MHZ is sampled as 5714 points earlier, and then average sample calculates its FFT to 1024 points, transforms to frequency domain Y (k);
3. get the complex conjugate of Y (k), output becomes Y* (k);
4. X (k) and Y* (k) carry out pointwise and multiply each other, and the result is Z (k);
5. Z (k) is got the FFT inverse transformation, transforms to time domain z (n), ask absolute value | z (n) |.Absolute value | z (n) | be exactly input signal and the local correlation that produces signal, have 1024;
6. ask | z (n) | in the maximal value and second maximal value, top that is respectively correlation and time peak, thresholding is the ratio on top and time peak, is set to 2.5.Differentiate whether reach threshold value, if do not reach the adjustment carrier frequency, get back to the first step, until can capture till the signal, if still do not capture satellite behind the one-period, then asterisk is defended in adjustment, continues search.If reached threshold value, find out peaked position, calculate its corresponding scope in 5714 point data, it is exactly the initial range of pseudo-code, if peak-peak is produced by frequency component fi, it is exactly the initial carrier frequency of input signal.
7. when capturing a star, according to the requirement of control module, can the initial range of pseudo-code and initial carrier frequency be passed to smart trapping module and do further and catch, confirm accurate value.Also can be directly the intermediate value and the initial carrier frequency of the initial range of pseudo-code be passed to tracking, carry out the tracking of gps signal.
Fig. 4 provides smart acquisition procedure: the GPS intermediate-freuqncy signal that receives is at first multiplied each other with local pseudo-code; Carrier wave with this locality multiplies each other then; Obtain I and Q component, integration is asked quadratic sum then, intermediate-freuqncy signal that obtains importing and the local correlation that produces signal; The pseudo-code phase of this process is to be confirmed by the pseudo-code initial phase scope that initial acquisition obtains, and local carrier is that the carrier frequency that obtained by initial acquisition and the frequency steps of this process come in to confirm.
The detailed step of smart acquisition procedure is:
1. to the input data x (n) of 1ms, elder generation and local pseudo-code multiply each other, the initial range decision that the phase place of pseudo-code is obtained by initial acquisition;
2. result after multiplying each other and carrier wave SIN () and COS () component multiply each other, and obtain I and Q component;
3. I and Q component are done integration respectively and ask quadratic sum;
4. with I and Q rood to the quadratic sum addition obtain correlation;
5. correlation and predetermined thresholding are compared, threshold value is set to 2.5, if surpassed threshold value, is representing and is confirming accurate code phase and carrier parameter, and parameter is passed to tracking, gets into tracing process; If do not surpass threshold value, then according to the initial range slip code phase of pseudo-code, the adjustment carrier wave repeats aforesaid operations, proceeds to catch.
Embodiment:
1) platform: that the fpga core chip adopts is the EP3C40Q240C8 of cyclone III series.
2) development environment: ModelSim and Quartus; The software language that adopts is Verilog; Development process is with the quick smart capture systems functional simulation of ModelSim tool implementation gps signal, with Quartus the software of realizing is carried out comprehensively, and then carries out sequential emulation with the ModelSim instrument; Emulation downloads software on the FPGA hardware platform after all accomplishing, and has so just accomplished the quick smart capture systems of gps signal.
3) the clock generating module of 5.714MHZ: the clock on the hardware platform is 40MHZ, adopts 7 frequency divisions to produce the clock of 5.714MHZ.
4) gps signal memory module: gps signal has been quantified as 2, and quantized value is ± 1 and ± 3, adopts the two-port RAM of 5714*2 to store, and realizes the read-write control to RAM with the state machine of a Mealy type.
5) digital controlled oscillator module: adopt the DDS algorithm, by 5.714MHZ clock generating carrier wave, amount is turned to 2, quantized value is ± 1 and ± 2.
6) carrier wave strip module: carry out gps signal and carrier multiplication, the result is ± 1, ± 2, ± 3 and ± 6.
7) pseudo-code read module: the pseudo-code of 32 satellites is produced with the Matlab instrument; In the ROM of pre-stored to a 32*1024*2; The flow process that produces is that 1023 pseudo-code is sampled 5714 points with the 5.714MHZ sampling rate earlier, and using 1.024MHZ sampling rate average sample again is 1024 points.Directly in ROM, read pseudo-code in the time of usefulness.
8) average sample module: with the 1.024MHZ sampling rate data of peeling off behind the carrier wave at 5714 are carried out down-sampling, be equivalent to be sampled as 1024 parts to 5714 point data, the energy of the point in each sampling period is averaged.The data that obtain after average are as a sample data.
9) FFT/IFFT module: produce the FFT IP kernel with Quartus and calculate FFT/IFFT, employing be 1024 FFT/IFFT.
10) threshold judgement and initial phase computing module: obtain correlation by/ result that IFFT draws; Calculate top and time peak in the correlation; Then top and the ratio and the thresholding on time peak are adjudicated; Surpass this satellite of threshold value explanation and capture, the position at place, top is exactly an initial phase, obtains the initial phase scope under a proportional relationship.Tell this satellite of total control module to capture simultaneously.
11) the smart trapping module of correlator realization: earlier with gps signal and carrier multiplication; Multiply each other with pseudo-code, the pseudo-code of this moment is produced by pseudo-code generator, carries out integration then again; Just obtained correlation; Accomplish correlator function, carry out decision threshold then, obtain accurate pseudo-code initial phase and carrier frequency.
12) total control module: be to be realized by the state machine of Mealy type, one has 8 states, resets respectively; Wait begins to write intermediate-freuqncy signal, waits intermediate-freuqncy signal RAM to be written full, produces beginning initial acquisition signal; Wait for that an initial acquisition finishes; The wait essence is caught end, and the carrier wave stepping adds one, defends asterisk and adds one.
Claims (1)
1. gps signal acquisition equipment based on FPGA; It is characterized in that: build the FPGA hardware platform and combine, total control module, gps signal memory module, carrier oscillator module, carrier wave strip module, pseudo-code read module, average sample module, FFT/IFFT module, threshold judgement and the initial phase computing module of comprise the clock generating module, realizing by state machine and the smart trapping module of correlator realization with GPS receiver radio frequency front-end chip; System clock connects the smart trapping module that clock generating module, two FFT modules, pseudo-code read module, IFFT module, threshold judgement and initial phase computing modules and correlator are realized respectively; The output of clock generating module connects the carrier oscillator module; The output of carrier oscillator module connects the carrier wave strip module; The input of gps signal memory module connects the GPS intermediate-freuqncy signal of radio-frequency front-end and two-way connection of smart trapping module of realizing with correlator, and the output of gps signal memory module connects the carrier wave strip module, and the output of carrier wave strip module connects the average sample module; The output of average sample module connects a FFT module; The output of pseudo-code read module connects another FFT module, and the output of two FFT modules connects the IFFT module, and the output of IFFT module connects threshold judgement and initial phase computing module; The smart trapping module that threshold judgement and initial phase computing module output join dependency device are realized, wherein:
1) platform: that the fpga core chip adopts is the EP3C40Q240C8 of cyclone III series;
2) development environment: ModelSim and Quartus; The software language that adopts is Verilog; Development process is with the quick smart capture systems functional simulation of ModelSim tool implementation gps signal; With Quartus the software of realizing is carried out comprehensively, and then carry out sequential emulation with the ModelSim instrument, emulation downloads software on the FPGA hardware platform after all accomplishing;
3) the clock generating module of 5.714MHZ: the clock on the hardware platform is 40MHZ, adopts 7 frequency divisions to produce the clock of 5.714MHZ;
4) gps signal memory module: gps signal has been quantified as 2, and quantized value is ± 1 and ± 3, adopts the two-port RAM of 5714*2 to store, and realizes the read-write control to RAM with the state machine of a Mealy type;
5) digital controlled oscillator module: adopt the DDS algorithm, by 5.714MHZ clock generating carrier wave, amount is turned to 2, quantized value is ± 1 and ± 2;
The carrier wave strip module: carry out gps signal and carrier multiplication, the result is ± 1, ± 2, ± 3 and ± 6;
7) pseudo-code read module: the pseudo-code of 32 satellites is produced with the Matlab instrument; In the ROM of pre-stored to a 32*1024*2; The flow process that produces is that 1023 pseudo-code is sampled 5714 points with the 5.714MHZ sampling rate earlier, and using 1.024MHZ sampling rate average sample again is 1024 points
Directly in ROM, read pseudo-code in the time of usefulness;
8) average sample module: with the 1.024MHZ sampling rate data of peeling off behind the carrier wave at 5714 are carried out down-sampling, be equivalent to be sampled as 1024 parts to 5714 point data, the energy of the point in each sampling period is averaged,
The data that obtain after average are as a sample data;
9) FFT/IFFT module: produce the FFT IP kernel with Quartus and calculate FFT/IFFT, employing be 1024 FFT/IFFT;
10) threshold judgement and initial phase computing module: obtain correlation by/ result that IFFT draws; Calculate top and time peak in the correlation; Then top and the ratio and the thresholding on time peak are adjudicated; Surpass this satellite of threshold value explanation and capture, the position at place, top is exactly an initial phase, obtains the initial phase scope under a proportional relationship;
Tell this satellite of total control module to capture simultaneously;
11) the smart trapping module of correlator realization: earlier with gps signal and carrier multiplication, multiply each other with pseudo-code, the pseudo-code of this moment is produced by pseudo-code generator again; Carry out integration then; Just obtain correlation, carried out decision threshold then, obtained accurate pseudo-code initial phase and carrier frequency;
12) total control module: realize that by the state machine of Mealy type one has 8 states, reset respectively; Wait begins to write intermediate-freuqncy signal, waits intermediate-freuqncy signal RAM to be written full, produces beginning initial acquisition signal; Wait for that an initial acquisition finishes; The wait essence is caught end, and the carrier wave stepping adds one, defends asterisk and adds one.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106772475A (en) * | 2016-12-23 | 2017-05-31 | 天津七六四通信导航技术有限公司 | A kind of circuit and method that faint GPS navigation signal is captured based on FPGA |
| CN108132906A (en) * | 2017-11-30 | 2018-06-08 | 西安空间无线电技术研究所 | A kind of synchronous serial interface bus receiving terminal Anti-interference Design method |
| CN111398996A (en) * | 2020-03-17 | 2020-07-10 | 广州南方卫星导航仪器有限公司 | Surveying and mapping satellite navigation receiver |
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2011
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106772475A (en) * | 2016-12-23 | 2017-05-31 | 天津七六四通信导航技术有限公司 | A kind of circuit and method that faint GPS navigation signal is captured based on FPGA |
| CN106772475B (en) * | 2016-12-23 | 2023-12-12 | 天津七六四通信导航技术有限公司 | Circuit and method for capturing weak GPS navigation signals based on FPGA |
| CN108132906A (en) * | 2017-11-30 | 2018-06-08 | 西安空间无线电技术研究所 | A kind of synchronous serial interface bus receiving terminal Anti-interference Design method |
| CN108132906B (en) * | 2017-11-30 | 2020-02-14 | 西安空间无线电技术研究所 | Anti-interference design method for synchronous serial port bus receiving end |
| CN111398996A (en) * | 2020-03-17 | 2020-07-10 | 广州南方卫星导航仪器有限公司 | Surveying and mapping satellite navigation receiver |
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