CN104215979A - Large frequency shift GNSS signal capture method based on segmented correlative combination and FFT computation - Google Patents

Large frequency shift GNSS signal capture method based on segmented correlative combination and FFT computation Download PDF

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Publication number
CN104215979A
CN104215979A CN201310206933.1A CN201310206933A CN104215979A CN 104215979 A CN104215979 A CN 104215979A CN 201310206933 A CN201310206933 A CN 201310206933A CN 104215979 A CN104215979 A CN 104215979A
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large frequency
value
correlative
gnss signal
frequency deviation
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张延东
朱柏承
孟凡琛
甘哲
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Peking University
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Peking University
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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
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
    • 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
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

The invention discloses a large frequency shift GNSS signal capture method based on the segmented correlative combination and FFT computation. By means of the segmented correlative combination and FFT computation, the parallel search of carrier frequency can be performed during code phase serial search, the large frequency shift GNSS signal capturing time is shortened greatly, and the signal-noise ratio loss is small. Particularly, the method includes firstly dividing received signals into a plurality of segments, performing the correlative computation on the segments and local pseudo codes to acquire a plurality of correlative values, performing the FFT computation after correlative value sequence zero padding, and judging the maximum value after the computation result modulus; if the value is higher than a judgment threshold, judging the code phase as the acquired code phase and the frequency point corresponded to the value as the captured carrier frequency; if the value is smaller than the judgment threshold, adjusting the local code phase to continue the process until the time-frequency two-dimensional search of the large frequency shift GNSS signals is completed.

Description

A kind ofly to be correlated with in conjunction with the large frequency deviation GNSS signal catching method of FFT computing based on segmentation
Technical field
The invention belongs to GPS (Global Position System) receiver spread-spectrum signal process field, to be a kind ofly specifically correlated with in conjunction with the carrier frequency capturing method of FFT computing based on segmentation.
Background technology
GLONASS (Global Navigation Satellite System) (Global Navigation Satellite System, GNSS) can be user provides successional Position, Velocity and Time information, can meet navigation, locate, test the speed, the many services requirement such as time service and rescue.The current whole world mainly contains four large satellite navigational system: the gps system of the U.S., Muscovite GLONASS system, the Galileo system in Europe and the dipper system of China.These systems all in the mode of CDMA or frequency division multiple access to the round-the-clock broadcast satellite signals of Global Subscriber.
As shown in Figure 1, it is the basis of various spread-spectrum signal Code acquisition scheme to the Acquisition Scheme basic structure of GNSS spread-spectrum signal code.The basic procedure of signal capture is: base-band spread-spectrum signal C (t) obtains detection limit with S (t) through, integration relevant to local code, a square summation, detection limit is adjudicated, if detection limit exceedes detection threshold, think and catch, otherwise adjust local spreading code phase place, carry out the detection of next phase place.
When receiver runs at a relatively high speed, can there is larger Doppler carrier frequency shift (FS) in above-mentioned baseband signal, now needs the reference carrier frequency of search larger in signal capture process.When adopting traditional carrier frequency serial search strategy, the signal capture time is longer.Therefore, be necessary to find one Doppler frequency offset estimation method fast, to realize the accurate estimation to large frequency offset signal carrier frequency.
Summary of the invention
The object of the invention is the weak point overcome in above-mentioned background, provide a kind of and be correlated with in conjunction with the large frequency deviation GNSS signal catching method of FFT computing based on segmentation.
The method is relevant in conjunction with FFT computing by segmentation, and can complete the parallel search of carrier frequency while code phase serial search, highly shortened the capture time of large frequency deviation GNSS signal, and snr loss is less, its theory diagram as shown in Figure 2.The present invention mainly comprises following step:
The first step: digital signal samples.
Received signal strength is after Digital Down Convert, and obtaining baseband signal (containing Doppler frequency deviation) is:
r ( k ) = D ( k ) PN ( k ) e j ( 2 π f d k T s - θ )
Wherein D (k) is binary modulated information, and PN (k) is spread spectrum code sequence, f dfor Doppler frequency deviation, T sfor the spread-spectrum code chip cycle, θ is carrier phase.
Second step: be that Received signal strength and the local pseudo-code of M chip is divided into R subsegment respectively by length, every segment length P=M/R, then corresponding subsegment being carried out relevant accumulating operation respectively, when temporarily not considering binary modulated informational influence, obtaining correlation:
C ( i ) = Σ k = ( i - 1 ) * P + 1 i * P PN ( k ) PN ( k + Δ ) e j ( 2 π f d k T s - θ )
= Σ k = ( i - 1 ) * P + 1 i * P R ( Δ ) e j ( 2 π f d k T s - θ )
= R ( Δ ) · e j [ ( 2 π f d ( i - 1 ) * P + 1 ) T s - θ ] 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s )
Wherein i=1, the autocorrelation function that 2,3...R, R (Δ) are spreading code, Δ is the phase differential of Received signal strength and local spreading code.
3rd step: carry out FFT computing by after sequence of correlation values zero padding.
To carry out the FFT computing of S point after R relevant value complement S-R individual 0, obtaining S FFT output valve is:
Z c ( m ) + j * Z s ( m ) = Σ i = 1 S C ( i ) e - j 2 π S im = Σ i = 1 R C ( i ) e - j 2 π S im
= Σ i = 1 R R ( Δ ) · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · e j { 2 π f d [ ( i - 1 ) P + 1 ] T s - 2 π S im - θ }
= R ( Δ ) · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S )
= R ( Δ ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S )
4th step: to FFT computing Output rusults delivery.
To FFT output valve delivery, obtain Acquisition Detection amount:
Z ( m ) = | Z 2 c ( m ) + Z 2 s ( m ) | = | R ( Δ ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S ) | 2
= | R ( Δ ) · sin ( π f d P T s ) sin ( π f d T s ) · sin [ πR ( f d P T s - m S ) ] sin [ π ( f d P T s - m S ) ] | 2
= R ( Δ ) 2 · | sin ( M R π f d T s ) sin ( π f d T s ) | 2 · | sin [ πR ( f d M R T s - m S ) ] sin [ π ( f d M R T s - m S ) ] | 2
5th step: maximum modulus value is adjudicated.
When Received signal strength spreading code phase place and local spreading code phase place are not synchronous, R (Δ) ≈ 0, maximum modulus value is no more than threshold value, at this moment needs adjustment local code phase place, continues to perform step 2 to step 5.
When Received signal strength spreading code phase place and local spreading code phase place basic synchronization, R (Δ) ≈ 1, Acquisition Detection amount is as follows:
Z ( m ) = | sin ( M R π f d T s ) sin ( π f d T s ) | 2 · | sin [ πR ( f d M R T s - m S ) ] sin [ π ( f d M R T s - m S ) ] | 2
Wherein, Section 1 is the snr loss that in integration section, frequency deviation causes, only relevant with input Doppler frequency difference, has nothing to do with m value; Section 2 size changes with m value, when time, corresponding this value is reached maximum (wherein [] represents floor operation), now Acquisition Detection amount Z (m) ≈ M 2, the Doppler frequency deviation estimated value that acquisition procedure obtains
When during for non-integer, can not exclusively cause certain snr loss because of phase compensation.Use this method to carry out in signal capture process, signal to noise ratio (S/N ratio) total losses is with inputting the change of Doppler frequency deviation value as shown in Figure 3.
Accompanying drawing explanation
Fig. 1 is code acquisition basic structure block diagram;
Fig. 2 is that segmentation of the present invention is relevant in conjunction with FFT computing signal capture theory diagram;
Fig. 3 is that segmentation of the present invention is correlated with in conjunction with snr loss in FFT computing signal capture process with the change curve of carrier doppler frequency deviation size;
Fig. 4 is that segmentation of the present invention is relevant in conjunction with FFT computing signal capture correlation distribution plan;
Embodiment
What the present invention proposed is correlated with in conjunction with the large frequency deviation GNSS signal catching method of FFT computing based on segmentation, is that example is described as follows with gps signal.
This method Frequency Estimation scope is f d max = ± 1 / T s 2 ( M / R ) , Frequency estimation accuracy is f d 0 = 2 f d max S , The size of Nonlinear Transformation in Frequency Offset Estimation scope according to demand and estimated accuracy determination segment length M/R and FFT count S.
The first step: digital signal samples.
Receive gps signal after Digital Down Convert, obtaining baseband signal (containing Doppler frequency deviation) is:
r ( k ) = D ( k ) PN ( k ) e j ( 2 π f d k T s - θ )
Wherein D (k) is GPS text modulation intelligence; PN (k) is gps satellite spread spectrum code sequence; f dfor Doppler frequency deviation, size is 40KHz; T sfor the spread-spectrum code chip cycle, size is θ is carrier phase.
Second step: the Received signal strength of length M=1023 chip and local pseudo-code are divided into R=93 subsegment respectively, every segment length P=M/R=11, then corresponding subsegment being carried out relevant accumulating operation respectively, when temporarily not considering binary modulated informational influence, obtaining correlation:
C ( i ) = Σ k = ( i - 1 ) * P + 1 i * P PN ( k ) PN ( k + Δ ) e j ( 2 π f d k T s - θ )
= Σ k = ( i - 1 ) * P + 1 i * P R ( Δ ) e j ( 2 π f d k T s - θ )
= R ( Δ ) · e j [ ( 2 π f d ( i - 1 ) * P + 1 ) T s - θ ] 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s )
The autocorrelation function that wherein i=1,2,3..., 93, R (Δ) are spreading code, Δ is the phase differential of Received signal strength and local spreading code.
3rd step: carry out FFT computing by after sequence of correlation values zero padding.
To carry out the FFT computing of S=512 point after R=93 relevant value complement S-R=512-93=419 individual 0, obtaining S=512 FFT output valve is:
Z c ( m ) + j * Z s ( m ) = Σ i = 1 S C ( i ) e - j 2 π S im = Σ i = 1 R C ( i ) e - j 2 π S im
= Σ i = 1 R R ( Δ ) · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · e j { 2 π f d [ ( i - 1 ) P + 1 ] T s - 2 π S im - θ }
= R ( Δ ) · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S )
= R ( Δ ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S )
4th step: to FFT computing Output rusults delivery.
To FFT output valve delivery, obtain Acquisition Detection amount:
Z ( m ) = | Z 2 c ( m ) + Z 2 s ( m ) | = | R ( Δ ) · e j [ 2 π f d ( 1 - p ) T s - θ ] · 1 - e j ( 2 π f d P T s ) 1 - e j ( 2 π f d T s ) · 1 - e j 2 πR ( f d P T s - m S ) 1 - e j 2 π ( f d P T s - m S ) | 2
= | R ( Δ ) · sin ( π f d P T s ) sin ( π f d T s ) · sin [ πR ( f d P T s - m S ) ] sin [ π ( f d P T s - m S ) ] | 2
= R ( Δ ) 2 · | sin ( M R π f d T s ) sin ( π f d T s ) | 2 · | sin [ πR ( f d M R T s - m S ) ] sin [ π ( f d M R T s - m S ) ] | 2
5th step: maximum modulus value is adjudicated.
When Received signal strength spreading code phase place and local spreading code phase place are not synchronous, R (Δ) ≈ 0, maximum modulus value is no more than threshold value, at this moment needs adjustment local code phase place, continues to perform step 2 to step 5.
When Received signal strength spreading code phase place and local spreading code phase place basic synchronization, R (Δ) ≈ 1, Acquisition Detection amount is as follows:
Z ( m ) = | sin ( M R π f d T s ) sin ( π f d T s ) | 2 · | sin [ πR ( f d M R T s - m S ) ] sin [ π ( f d M R T s - m S ) ] | 2
= | sin ( 1023 93 × π × ( 40 × 10 3 ) × ( 1 1.023 × 10 - 6 ) ) sin ( π × ( 40 × 10 3 ) × ( 1 1.023 × 10 - 6 ) ) | 2 ×
| sin [ π × 93 × ( ( 40 × 10 3 ) × 1023 93 × ( 1 1.023 × 10 - 6 ) - m 512 ) ] sin [ π × ( ( 40 × 10 3 ) × 1023 93 × ( 1 1.023 × 10 - 6 ) - m 512 ) ] | 2
When π × 93 × ( ( 40 × 10 3 ) × 1023 93 × ( 1 1.023 × 10 - 6 ) - m 512 ) = 0 Time, this gets maximal value, and now corresponding m value size is doppler frequency deviation estimated value is f d = mR SM T s = 39.961 KHz , Estimated frequency error is 40Hz.

Claims (6)

1. be correlated with in conjunction with a large frequency deviation GNSS signal catching method for FFT computing based on segmentation, its feature comprises following five steps:
Steps A: digital signal samples;
Step B: whole chip is divided into R subsegment, and corresponding subsegment is carried out relevant accumulating operation respectively;
Step C: carry out FFT computing by after sequence of correlation values zero padding;
Step D: to FFT computing Output rusults delivery;
Step e: maximum modulus value is adjudicated.
2. large frequency deviation GNSS signal catching method according to claim 1, is characterized in that: the baseband signal extracted in steps A is wherein D (k) is binary modulated information, and PN (k) is spread spectrum code sequence, f dfor Doppler frequency deviation, T sfor the spread-spectrum code chip cycle, θ is carrier phase.
3. large frequency deviation GNSS signal catching method according to claim 1, is characterized in that: be that the baseband signal of M is divided into R section by chip lengths in step B, every segment length is P, and has P=M/R.
4. large frequency deviation GNSS signal catching method according to claim 1, is characterized in that: will carry out the FFT computing of S point after R relevant value complement S-R individual 0 in step C.
5. large frequency deviation GNSS signal catching method according to claim 1, is characterized in that: Output rusults delivery in step D in detection limit, Section 1 and m value have nothing to do, and the second item size changes with m change.
6. large frequency deviation GNSS signal catching method according to claim 1, is characterized in that: the Output rusults and the judging threshold that compare FFT in step e, if be less than threshold value, then re-execute step B.
CN201310206933.1A 2013-05-29 2013-05-29 Large frequency shift GNSS signal capture method based on segmented correlative combination and FFT computation Pending CN104215979A (en)

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Cited By (7)

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CN106896385A (en) * 2015-12-18 2017-06-27 大唐半导体设计有限公司 A kind of device of frequency search and the method for realizing frequency search
CN106980125A (en) * 2016-01-18 2017-07-25 北京信息科技大学 The drop amount of calculation deblurring processing method that XFAST is captured in a kind of satellite navigation
CN107135013A (en) * 2017-05-04 2017-09-05 中国电子科技集团公司第五十四研究所 A kind of Rapid Acquisition for Direct Sequence Spread-Spectrum Signals method
CN109633705A (en) * 2018-12-28 2019-04-16 深圳市力合微电子股份有限公司 A kind of control method based on Beidou Base-Band Processing two dimension multiplex circuit
CN109728827A (en) * 2018-12-13 2019-05-07 航天恒星科技有限公司 A kind of sequence aided capture low signal-to-noise ratio TPC coding/decoding system
CN110927752A (en) * 2019-12-13 2020-03-27 北京无线电计量测试研究所 High-rate satellite bidirectional time comparison signal demodulation method and system
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106896385A (en) * 2015-12-18 2017-06-27 大唐半导体设计有限公司 A kind of device of frequency search and the method for realizing frequency search
CN106980125A (en) * 2016-01-18 2017-07-25 北京信息科技大学 The drop amount of calculation deblurring processing method that XFAST is captured in a kind of satellite navigation
CN107135013A (en) * 2017-05-04 2017-09-05 中国电子科技集团公司第五十四研究所 A kind of Rapid Acquisition for Direct Sequence Spread-Spectrum Signals method
CN107135013B (en) * 2017-05-04 2019-01-25 中国电子科技集团公司第五十四研究所 A kind of Rapid Acquisition for Direct Sequence Spread-Spectrum Signals method
CN109728827A (en) * 2018-12-13 2019-05-07 航天恒星科技有限公司 A kind of sequence aided capture low signal-to-noise ratio TPC coding/decoding system
CN109728827B (en) * 2018-12-13 2022-11-11 航天恒星科技有限公司 Sequence assisted acquisition low signal-to-noise ratio TPC coding and decoding system
CN109633705A (en) * 2018-12-28 2019-04-16 深圳市力合微电子股份有限公司 A kind of control method based on Beidou Base-Band Processing two dimension multiplex circuit
CN110927752A (en) * 2019-12-13 2020-03-27 北京无线电计量测试研究所 High-rate satellite bidirectional time comparison signal demodulation method and system
CN113452406A (en) * 2021-08-31 2021-09-28 北京理工大学 Signal demodulation method, device, equipment and medium with variable transmission rate
CN113452406B (en) * 2021-08-31 2021-11-26 北京理工大学 Signal demodulation method, device, equipment and medium with variable transmission rate

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Application publication date: 20141217