CN102338878B - Novel multi-path inhibition BOC (Binary Offset Carrier) code tracking method and code tracking ring - Google Patents

Novel multi-path inhibition BOC (Binary Offset Carrier) code tracking method and code tracking ring Download PDF

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CN102338878B
CN102338878B CN 201110201926 CN201110201926A CN102338878B CN 102338878 B CN102338878 B CN 102338878B CN 201110201926 CN201110201926 CN 201110201926 CN 201110201926 A CN201110201926 A CN 201110201926A CN 102338878 B CN102338878 B CN 102338878B
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reference waveform
code
forward direction
boc
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CN102338878A (en
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何春
徐辉
宗竹林
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University of Electronic Science and Technology of China
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Abstract

The invention provides a pseudo-random code phase tracking method and a code tracking ring multi-path inhibition BOC (Binary Offset Carrier) code tracking method, which effectively inhibit multi-path effect according to structural characteristics of a BOC signal. A pseudo-random code generating step, a BOC code generating step, a reference waveform generating step, a relevant waveform constructing step, a mutual correlation step, a phase discrimination function generating step and a phase discrimination step are included. According to the invention, in the correlation waveform constructing step, the constructed forward correlation function and backward correlation function only have one peak value and good linearity is obtained; and a zero crossing point of a phase discrimination curve and a zero crossing point while no multi-path signal is available have no deviation when multi-path effect exists so that the offset of the tracking point is overcome to achieve the accurate distance measuring and positioning purpose.

Description

A kind of multipaths restraint BOC code tracking method and code tracking loop
Technical field
The present invention relates to the communication technology, particularly subcarrier BOC (scale-of-two offset carrier, Binary Offset Carrier) modulation technique.
Background technology
One, BOC sub-carrier modulation:
The frequency range that International Telecommunication Association (ITU) distributes to satellite navigation system (GNSS) use is limited, increasing navigation signal takies this originally with regard to crowded satellite navigation band resource, the increase of synchronous signal power makes between system more and more serious with intrasystem interference.These interference will cause system performance to descend or be unavailable, so the system compatibility of GNSS becomes the major issue of puzzlement Navigation System Development day by day.In order to improve the compatibility of each navigational system, need to improve on signal structure, this has just led the modernization of GNSS signal.Think through long-term research navigation signal is carried out scale-of-two offset carrier (Binary Offset Carrier) modulation, i.e. subcarrier BOC modulation is to solve each navigational system signal spectrum to separate effective measures.The BOC sub-carrier modulation is to modulate on the basis at BPSK, increases by one with the modulated process of scale-of-two subcarrier as modulated signals.That is, the square wave greater than or equal to a pseudorandom chip frequency as subcarrier, with through the spread-spectrum signal of pseudo-random code modulation, subcarrier being modulated that Navsat produces, obtains base band BOC subcarrier modulated signal to the BOC sub-carrier modulation with one; Afterwards, utilize base band BOC subcarrier modulated signal to be modulated to main carrier, form the final intermediate-freuqncy signal that sends.After pseudorandom chip and subcarrier multiplied each other, the frequency spectrum of signal was divided into two parts, so the separation spectrum modulation is again in the BOC modulation.The main thought of BOC modulation is to reduce the BPSK(binary phase shift keying) interference between modulation signal.Because the BPSK modulation signal has a sinc(Singh) frequency spectrum of function shape.Therefore the main spectrum energy of BPSK modulation signal concentrates near carrier frequency.And near signal energy carrier frequency of BOC modulation is low, and two main frequency spectrum main lobes are away from carrier wave.
Usually, being expressed as of receiver base band BOC subcarrier modulated signal S (t) that receive:
S ( t ) = e - j θ 0 · Σ i a i μ p T s ( t - ip T s - t 0 ) · C T s ( t - t 0 )
Wherein:
a iThe expression value is the navigation data of "+1 " or " 1 ", and i is integer;
Figure GDA00003195184000012
For the cycle is nT sThe rect.p. spread symbol; P represents the periodicity of subcarrier in the pseudo-random code cycle;
Figure GDA00003195184000013
Indication cycle is T sSubcarrier;
θ 0And t 0Be respectively phase shift and time shift.
Fig. 1 has provided a BOC sub-carrier modulation example:
Navigation data a iBe { 1 ,-1,1,1 ,-1 ,+1 };
Figure GDA00003195184000021
The frequency expansion sequence that expression utilizes pseudo-random code modulation navigation data to obtain;
Figure GDA00003195184000025
The expression frequency is the subcarrier of 4 times of frequency expansion sequences;
The BOC subcarrier modulated signal that S (t) expression obtains with the frequency expansion sequence modulating subcarrier.
Modulated BOC waveform can be expressed as BOC (pn, n) or BOC (m, n) (wherein p, n, m are positive integer) or BOC(f sc, f c) (f wherein scSubcarrier frequency, f cPseudorandom chip frequency), m=pn=f sc/ f ref, n=f c/ f ref, p=f sc/ f c
Work as f refDuring=1.023MHz, BOC (10,5) vice carrier frequency f sc=10 * 1.023MHz and spreading code code check f c=5 * 1.023MHz.Its power spectrum chart as shown in Figure 2, main lobe is in the both sides of centre frequency.
The autocorrelation function of BOC (pn, n) is shown below:
R x ( &epsiv; ) = ( - 1 ) k + 1 [ 1 p ( - k 2 + 2 pk + k - p ) - ( 4 p - 2 k + 1 ) | &epsiv; | T 0 ] , | &epsiv; | < T c 0 , otherwise
Wherein
Figure GDA00003195184000023
Figure GDA00003195184000024
Expression is greater than the smallest positive integral of x; ε is the auto-correlation mistiming; T c=1/f c, be the chip lengths of a pseudo-random code; p=f sc/ f c, be the ratio of subcarrier frequency and pseudo-random code frequency.
BOC (10,5) related function as shown in Figure 3, BOC (pn, n) signal has a plurality of self correlated peaks.Due to a plurality of relevant peaks being arranged, cause the phase demodulation curve that a plurality of zero crossings are arranged.
Two, the classical EML code tracking loop of the navigation neceiver structure under the BPSK modulation:
The target of code tracking loop is the Phase Tracking (phase place of frequency expansion sequence is namely the phase place of pseudo-random code) of pseudo-random code in keeping to the received signal.Pseudo-random code is used for the bigness scale distance.Receiver obtains the travel-time of navigation data by the phase differential of more known transmit middle pseudo-random sequence and the actual pseudo-random sequence (phase place that code tracking loop traces into) that receives, and then calculates the particular location of receiver.Typical code tracking loop in the GPS receiver is leading-hysteresis code tracking loop structure (EML), as shown in Figure 4.
Intermediate-freuqncy signal input receiver from transmitting terminal, receiver multiplies each other the local carrier that intermediate-freuqncy signal and local oscillator send, and with local carrier 90-degree rotation phase place after carrier multiplication, recover I, Q two-way baseband signal (for the code tracking loop of BPSK modulation, the BPSK modulation does not have the sub-carrier modulation process, directly obtain the final intermediate-freuqncy signal that sends with frequency expansion sequence modulation main carrier, the baseband signal here refers to frequency expansion sequence).I, Q two-way frequency expansion sequence input to code tracking loop.Code tracking loop comprises the PRN(pseudo-random code) code generator, multiplier, integration zero clearing device, code loop phase detector.The PRN code generator is for generation of 3 road local codes.This three road local code is respectively (E), instant (P) and (L) code that lags behind in advance, and the intersymbol between them is apart from being usually
Figure GDA00003195184000031
Chip lengths.The baseband signal of I branch road multiplies each other with three road local codes respectively through multiplier, then inputs to corresponding integration zero clearing device and carry out the integration zero clearing, obtains the correlated results of the baseband signal of local code and input.Integration zero clearing device also is correlator or cumulative zero clearing device.The correlated results I of the baseband signal of local advanced code and input E, the correlated results I of the baseband signal of local lag code and input LEntering a yard ring Discr. compares.The Q branch road is identical with the I branch road in the processing procedure of code tracking loop.As shown in Fig. 5 (a): the correlation of the code that lags behind is greater than the correlation of advanced code, and the local code phase place need reduce, and namely the code sequence need postpone; Otherwise the correlation of the code that lags behind is less than the correlation of advanced code, and the local code phase place need increase, and the code sequence need shift to an earlier date; As the correlation of the code that lags behind equates with the correlation of advanced code, yard sequence without any need for adjustment, as shown in Fig. 5 (b).If code phase needs to adjust, code ring Discr. is just given the time of the generation of the code sequence that the PRN code generator feeds back to adjust feedback.
That is, the effect of code tracking loop is to adjust the phase place of local output pseudo-random code by the Output rusults of code loop phase detector, makes the phase place of output pseudo-random code consistent with the phase place of the spreading code that receives.Thereby reach the Phase Tracking to the spreading code that receives.
Afterwards, the instant correlated results I on I road and Q road L, Q LProduce the phase error of local carrier after incoming carrier loop phase detector, the phase place to local oscillator after the carrier loop wave filter overcomes noise is adjusted.Adjustment to the phase place of local oscillator is not that the present invention is concerned about, in this article, supposes the tracking carrier wave that carrier tracking loop is stable, and namely carrier track is without skew.
Suppose the code tracking loop of carrier phase locking, if code ring Discr. uses dot product (DP) phase demodulation, it is output as:
DP=I P(I E-I L)
In advance, the chip-spaced of lag correlation device (early, late correlator) is d, I POutput for instant correlator.
Three, the multipath effect of navigation signal
Satellite to the signal of receiver through reflection, scattering, diffraction after, the signal that arrives receiver contains the multipath composition, is called multipath signal.Multipath signal changes with the difference of environment, do not have correlativity on time and space, the positioning error that causes can not be by such as the DGPS(differential Global Positioning System) differential technique eliminate, so the range error that multipath causes is the GNSS(GLONASS (Global Navigation Satellite System)) main source of positioning error.Multipath composition in the signal that the user receives can destroy the direct projection path signal from Navsat, cause that a yard multipath causes range error, cause that the carrier wave multipath is phase error, cause Doppler error and signal degradation, especially obvious in the city high building towers environment and indoor environment, this badly influences the continuity of navigation and the accuracy of location.Theoretically, the positioning error that multipath brings under the modern modulation signal of GNSS is limited at the chip range T of actual propagation cIn, i.e. 1/f cScope in.BOC (10,5) with GPS is example, and actual bit rate is that speed is the thick ranging code in the C/A(spreading code of 1.023M) 5 times of code.The multipaths restraint ability of C/A coded signal own is more than 300m like this, and the multipaths restraint ability of BOC (10,5) signal itself is more than 60m, and to BOC (1,1) signal, the multipaths restraint ability is still more than 300m.The frequency f of subcarrier in the modern modulation signal of GNSS scOn the not impact of multipaths restraint ability.As seen the modern modulation signal of GNSS is because the range error that multipath brings still exists.
The signal model r (t) of receiver end is expressed as:
r(t)=S(t)+αe S(t-δ)
Wherein, S (t) is direct projection footpath signal, and α is the second footpath signal be the second footpath signal with respect to relative amplitude, the θ of direct projection footpath signal S (t) is that the second footpath signal is with respect to the chip delay of direct projection footpath signal S (t) with respect to relative phase, the δ of direct projection footpath signal S (t); The second footpath signal is road signal the strongest in multipath signal, perhaps the summation of all multipath signals.
When having multipath signal, early relevant I EWith late relevant I LBe expressed as:
I E=R(ε-d/2)+α·R(ε-d/2-δ)cosθ
I L=R(ε+d/2)+α·R(ε+d/2-δ)cosθ
Wherein, ε is poor with the correlation time of the frequency expansion sequence that receives for the local pseudo-random sequence that produces, d is the code distance (chip-spaced) between morning, slow correlator, δ is the second footpath signal with respect to the delay of direct projection footpath signal, θ is the second footpath signal with respect to the phase differential of direct projection footpath signal, and α is the second footpath signal with respect to the relative amplitude of direct projection footpath signal.
According to EML dot product phase-demodulating principle, when the correlation of the code that lags behind equates with the correlation of advanced code, yard sequence without any need for adjustment:
DP=I P(I E-I L)=0, I E=I L, have:
R(ε-d/2)+α·R(ε-d/2-δ)cosθ=R(ε+d/2)+α·R(ε+d/2-δ)cosθ
Phase detector output DP is the zero crossing that 0 o'clock corresponding ε is the phase demodulation curve.In the situation that without any noise, multipath and interference, ε=0 is the zero crossing that in code tracking loop, the code generator modulation produces the random code phase place.As shown in Figure 6, when the code tracking loop of EML structure uses the dot product phase detector, when being applied to the reception of BPSK modulation signal, ε=0 is without the zero crossing of the ideal signal phase demodulation curve of multipath, and in take this zero crossing as code tracking loop, code generator is modulated the keyed end that produces the random code phase place, wherein intersymbol is apart from the time interval that refers between morning, slow correlator, and Tc represents pseudorandom chip width.
Yet in practice, this keyed end obviously is subjected to multi-path influence, when ε is non-vanishing, and I E=I L(phase detector output DP is 0).In practice, with the unknown number ε of iterative equation, ε has multiple roots.Select Min| ε | be keyed end.Min| ε | be the code range error (length represents that yard range error can poorly according to correlation time multiply by the light velocity and obtain, and correlation time, difference was the code range error of time representation) of time representation.
Without multipath ideally, use the code tracking loop of the EML structure of dot product phase detector to be applied to BOC(1,1) the phase demodulation curve of signal as shown in Figure 7, DP=I P(I E-I L)=0 o'clock, I when ε is zero E=I LIn practice, be subjected to the impact of multipath signal, I when ε is non-vanishing E=I L(the zero crossing skew refers in the situation that how through impact in the zero crossing skew, the zero crossing of the zero crossing of phase demodulation curve with without multipath signal the time compared, skew appears), again because BOC (pn, n) signal has a plurality of relevant peaks, the phase demodulation curve has a plurality of zero crossings, cause the Min| ε that tries to achieve | can not reflect real code range error, the wrong choice keyed end, thus in impact to the received signal, the phase place of pseudo-random code is accurately followed the tracks of.
Multipath can represent with an error envelope usually on the impact of code tracking precision, suppose that the second footpath signal is constant with respect to the relative amplitude α of direct projection footpath signal, when the second footpath signal during with respect to the phase differential θ of direct projection footpath signal=0 ° and θ=180 °, the temporal pseudo range measurement error ε that multipath causes reaches respectively minimum and maximum value, can get multipath error enveloping curve or multipath error envelope (multipath error envelope, MEE).As shown in Figure 8, the code tracking loop of EML structure is applied to the multipath error enveloping curve that bpsk signal receives, and in figure, lower enveloping curve represents that phase differential θ is π, and coenvelope phase differential θ is 0.As shown in Figure 9, for BOC(1,1) when signal used EML constructive code tracking loop to carry out code tracking, the multipath error enveloping curve was in some scope of multidiameter, and multipath error is compared BPSK and is had some improvement, and is T as working as the intersymbol distance cThe time, when multidiameter was near 250m, pseudorange error reduced.But use the BOC(1 of EML constructive code tracking loop, 1) signal compares bpsk signal, and its multipath error scope does not improve.
At present, in order to overcome multi-path influence, the reference code of this locality that code generator is produced changes other some waveforms (rather than pseudo-random code) into, by some ancillary techniques, select local reference waveform to construct expectation phase demodulation curve, all be called a yard coherent reference waveform technology (CCRW technology).But so far, the BOC modulation signal also do not occur being applicable to, can construct the code tracking loop of the good phase demodulation curve of phase characteristic.The phase demodulation curve of current code tracking loop structure all the zero crossing deviation from origin can occur, phase demodulation curve linear bad, and the phase demodulation curve has the problems such as a plurality of zero crossings, causes can't avoiding tracking error when reception, is difficult to accurate location.
Summary of the invention
Technical matters to be solved by this invention is, a kind of design feature according to the BOC signal is provided, and effectively suppresses pseudo-random code phases tracking and the code tracking loop of multi-path influence.
The present invention solves the problems of the technologies described above the technical scheme that adopts to be, a kind of multipaths restraint BOC code tracking method is characterized in that, comprises the following steps:
The pseudorandom number generation step: code tracking loop generates pseudo-random code according to identified result in this locality;
The BOC code generates step: according to the pseudorandom number generation BOC code of this locality generation;
Reference waveform generates step: code tracking loop generates pseudo-random code and BOC code according to this locality, generates forward direction reference waveform, backward reference waveform, instant reference waveform;
Described forward direction reference waveform is, width is the bipolarity waveform code F (t) of L, and before being created in the pseudorandom chip that this locality of practical function produces, the end point of forward direction reference waveform is alignd with the starting point of the pseudorandom chip of local generation; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first-1, is+1 afterwards, and when the pseudorandom chip of practical function is-1, the forward direction reference waveform is first+1, is-1 afterwards;
Described backward reference waveform is, width is the bipolarity waveform code B (t) of L, and after being created in the pseudorandom chip that this locality of practical function produces, the end point of the local pseudorandom chip that produces is alignd with the starting point of backward reference waveform; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first+1, is-1 afterwards; When the pseudorandom chip of practical function is-1, the forward direction reference waveform is first-1, is+1 afterwards;
Described instant reference waveform is that width is T pThe rectangle square wave, the center-aligned of the center of instant reference waveform and the BOC chip of this locality of practical function generation; When the BOC of practical function chip was-1, the amplitude of instant reference waveform was-1; When the BOC of practical function chip was+1, the amplitude of P (t) was+1.
Waveform correlation constitution step: utilize the forward direction reference waveform to construct forward direction waveform correlation F c(t); Utilize backward reference waveform to construct backward waveform correlation B c(t);
The simple crosscorrelation step: code tracking loop receives the base band BOC subcarrier modulated signal of input, base band BOC subcarrier modulated signal is carried out simple crosscorrelation with forward direction waveform correlation, backward waveform correlation, instant reference waveform respectively obtain forward direction related function, backward related function, instant related function;
The phase demodulation function generates step: forward direction related function and instant related function are multiplied each other, obtain forward direction phase demodulation function; Backward related function and instant related function are multiplied each other, obtain backward phase demodulation function;
The phase demodulation step: forward direction phase demodulation functional value greater than 0 and backward phase demodulation functional value equal at 0 o'clock, identified result is for postponing the phase place of local pseudo-random code; Forward direction phase demodulation functional value less than 0 and backward phase demodulation functional value equal at 0 o'clock, identified result is the phase place that shifts to an earlier date local pseudo-random code.
Concrete, in described phase demodulation step, forward direction phase demodulation functional value is postponed the phase place of local reference waveform divided by the retardation that the gain of phase detector obtains; The lead that backward phase demodulation functional value is obtained divided by the gain of phase detector shifts to an earlier date the phase place of local reference waveform.
Concrete, in described waveform correlation constitution step, utilize the forward direction reference waveform to construct forward direction waveform correlation F c(t),
Figure GDA00003195184000071
Wherein, F (t) is the forward direction reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency;
Utilize backward reference waveform to construct backward waveform correlation B c(t), Wherein, B (t) is the forward direction reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency.
Concrete, in described simple crosscorrelation step, base band BOC subcarrier modulated signal and forward direction waveform correlation are carried out simple crosscorrelation obtain forward direction related function α (ε):
Figure GDA00003195184000073
L is the width of forward direction reference waveform, and ε is that correlation time is poor;
Base band BOC subcarrier modulated signal and backward waveform correlation are carried out simple crosscorrelation obtain backward related function β (ε):
&beta; ( &epsiv; ) = | &epsiv; + L 2 | - L 2 , - L &le; &epsiv; &le; 0 , L is the width of backward reference waveform, and ε is that correlation time is poor;
With the cross correlation function R of base band BOC subcarrier modulated signal with the local instant reference waveform that produces XP(ε) be:
R XP ( &epsiv; ) = &Sigma; i = - p i = p &Sigma; i ( - 1 ) i &gamma; ( &epsiv; + i T c 2 p ) ;
Wherein, &gamma; ( &epsiv; ) = 2 p T p T c , | &epsiv; | &le; L 2 2 p T p / T c L / 2 - T c / ( 4 p ) ( | &epsiv; | - T c 4 p ) , L 2 &le; | &epsiv; | &le; T c 4 p ;
ε is that correlation time is poor, and p is the BOC code frequency and the ratio of pseudo-random code frequency, T cBe the width of a pseudorandom chip, T pBe the width of instant reference waveform, L is the width of forward direction reference waveform or backward reference waveform.
The forward direction related function α (ε) that the present invention constructs, backward related function β (ε) only have a peak value and have good linearity, in the situation that there is multi-path influence, the zero crossing of the zero crossing of phase demodulation curve with without multipath signal the time is without departing from, thereby overcome the skew of trace point, reach the purpose of precision ranging and location.
For realizing that above-mentioned Phase Tracking method proposes a kind of code tracking loop, it is characterized in that, comprise pseudo-noise code generator, BOC code generator, reference waveform generator, cross correlation process module, phase demodulation function generation module, code ring phase detector;
Described pseudo-noise code generator is used for, and receives identified result, and generates pseudo-random code according to identified result in this locality;
The BOC code generator is used for, according to the pseudorandom number generation BOC code of this locality generation;
Described reference waveform generator is used for, and generates pseudo-random code and BOC code according to this locality, generates forward direction reference waveform, backward reference waveform, instant reference waveform; The forward direction reference waveform that generates is, width is the bipolarity waveform code F (t) of L, and before being created in the pseudorandom chip that this locality of practical function produces, the end point of forward direction reference waveform is alignd with the starting point of the pseudorandom chip of local generation; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first-1, is+1 afterwards, and when the pseudorandom chip of practical function is-1, the forward direction reference waveform is first+1, is-1 afterwards; The backward reference waveform that generates is, width is the bipolarity waveform code B (t) of L, and after being created in the pseudorandom chip that this locality of practical function produces, the end point of the local pseudorandom chip that produces is alignd with the starting point of backward reference waveform; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first+1, is-1 afterwards; When the pseudorandom chip of practical function is-1, the forward direction reference waveform is first-1, is+1 afterwards; The instant reference waveform that generates is that width is T pThe rectangle square wave, the center-aligned of the center of instant reference waveform and the BOC chip of this locality of practical function generation; When the BOC of practical function chip was-1, the amplitude of instant reference waveform was-1; When the BOC of practical function chip was+1, the amplitude of P (t) was+1; Recycling forward direction reference waveform is constructed forward direction waveform correlation F c(t); Utilize backward reference waveform to construct backward waveform correlation B c(t);
Described cross correlation process module is used for, receive the base band BOC subcarrier modulated signal of input, base band BOC subcarrier modulated signal is carried out simple crosscorrelation with forward direction waveform correlation, backward waveform correlation, instant reference waveform respectively obtain forward direction related function, backward related function, instant related function;
Described phase demodulation function generation module is used for, and forward direction related function and instant related function are multiplied each other, and obtains forward direction phase demodulation function; Backward related function and instant related function are multiplied each other, obtain backward phase demodulation function;
Described code ring phase detector is used for, forward direction phase demodulation functional value greater than 0 and backward phase demodulation functional value equal at 0 o'clock, the identified result of output is for postponing the phase place of local pseudo-random code; Forward direction phase demodulation functional value LittleIn 0 and backward phase demodulation functional value equal at 0 o'clock, output identified result be the phase place that shifts to an earlier date local pseudo-random code.
Concrete, described cross correlation process module comprises multiplier, integration zero clearing device; The forward direction waveform correlation of reference waveform generator, backward waveform correlation, instant reference waveform output terminal are connected with the input end of one of corresponding multiplier respectively, and another input end of each multiplier connects the base band BOC subcarrier modulated signal of input.
Concrete, described phase demodulation generation module comprises multiplier, integration zero clearing device; The output terminal of the output terminal of the integration zero clearing device of output forward direction related function, the integration zero clearing device of the instant related function of output connects respectively with two input ends of same multiplier and is connected, the output terminal of this multiplier is connected with corresponding integration zero clearing device, and the output terminal of this integration zero clearing device is connected with an input end of code ring phase detector; The output terminal of integration zero clearing device of exporting output terminal, the instant related function of output of the integration zero clearing device of backward related function connects respectively with two input ends of same multiplier and is connected, and the output terminal of this integration zero clearing device is connected with another input end of code ring phase detector.
The invention has the beneficial effects as follows, according to BOC(pn, n) design feature of modern modulation signal, based on the real-time correlation properties that receive signal and designed local reference waveform, can overcome the BOC(pn that suppresses multipath signal, n) the code multipaths restraint method impact of signal, can overcome the impact of multipath signal, in the situation that there is multi-path influence, the zero crossing of the zero crossing of phase demodulation curve with without multipath signal the time is without departing from, only have a relevant peaks during on-off delay, guarantee that trace point is not offset, reach the purpose of precision ranging and location.
Description of drawings
Fig. 1 is a BOC sub-carrier modulation example;
Fig. 2 is the power spectrum chart figure of BOC (10,5);
Fig. 3 is BOC (10,5) related function schematic diagram;
Fig. 4 is the EML structural representation of the typical code tracking loop in the GPS receiver;
Fig. 5 is the schematic diagram that compares according to the correlation of the correlation of the code that lags behind and advanced code in the phase place adjustment;
Fig. 6 is in the situation that without the phase demodulation curve synoptic diagram of multipath phase detector output;
Fig. 7 is in the situation that without multipath, uses the code tracking loop of the EML structure of dot product phase detector to be applied to BOC(1,1) the phase demodulation curve of signal;
Fig. 8 is that the code tracking loop of EML structure is applied to the multipath error enveloping curve that bpsk signal receives;
Multipath error enveloping curve when Fig. 9 is for BOC(1,1) signal uses EML constructive code tracking loop to carry out code tracking;
Figure 10 is the mutual relationship of reference waveform signal in the embodiment time domain;
Figure 11 be forward direction reference waveform and BOC code cross correlation function with and component function;
Figure 12 be backward reference waveform and BOC code cross correlation function with and component function;
Figure 13 be instant reference waveform and BOC code cross correlation function with and component function;
Figure 14 is the present embodiment code tracking loop structure;
Figure 15 is the phase demodulation curve that has adopted the phase detector of the inventive method to construct in the ideal case;
Figure 16 is the phase demodulation curve that has adopted the phase detector of the inventive method to construct when multi-path influence is arranged;
Figure 17 is that GT scheme and multipath error envelope of the present invention compare schematic diagram;
Figure 18 is GT scheme and multipath error envelope of the present invention partial enlarged drawing relatively.
Embodiment
The present embodiment is take BOC(2n, n) be example, the local BOC code frequency that produces is 2 with the ratio of pseudo-random code frequency.
In time domain, the mutual relationship of reference waveform signal as shown in figure 10.
In figure
Figure GDA00003195184000091
Refer to the local pseudo-random sequence that produces,
Figure GDA00003195184000092
The local BOC(2 that produces, 1) code,
Figure GDA00003195184000093
Be respectively the local forward direction reference waveform that produces, backward reference waveform and instant reference waveform, these five signals synchronously produce in receiver, wherein
Figure GDA00003195184000101
Be the output of yard phase demodulation just/secondary postpone (retardation or lead).
The forward direction reference waveform is, width is the bipolarity waveform code F (t) of L, and before being created in the pseudorandom chip that this locality of practical function produces, the end point of forward direction reference waveform is alignd with the starting point of the pseudorandom chip of local generation; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first-1, is+1 afterwards, and when the pseudorandom chip of practical function is-1, the forward direction reference waveform is first+1, is-1 afterwards;
Backward reference waveform is, width is the bipolarity waveform code B (t) of L, and after being created in the pseudorandom chip that this locality of practical function produces, the end point of the local pseudorandom chip that produces is alignd with the starting point of backward reference waveform; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first+1, is-1 afterwards; When the pseudorandom chip of practical function is-1, the forward direction reference waveform is first-1, is+1 afterwards;
Instant reference waveform is that width is T pThe rectangle square wave, the center-aligned of the center of instant reference waveform and the BOC chip of this locality of practical function generation; When the BOC of practical function chip was-1, the amplitude of instant reference waveform was-1; When the BOC of practical function chip was+1, the amplitude of P (t) was 1.
Three kinds of cross correlation property with reference to signal and BOC (pn, n) signal:
(1) the cross correlation function R of forward direction structure reference waveform and BOC code XFc(ε) and characteristic:
R XF ( &epsiv; ) = &Sigma; i = 0 2 p ( - 1 ) i &alpha; ( &epsiv; - i T c 2 p ) , 0 &le; &epsiv; < T c 0 , &epsiv; < 0
Wherein, ε is that correlation time is poor, and p is the ratio of subcarrier frequency and pseudo-random code frequency, T cIt is the width of a pseudorandom chip;
&alpha; ( &epsiv; ) = L 2 - | &epsiv; - L 2 | , 0 &le; &epsiv; &le; L
L is the width of forward direction reference waveform, and ε is that correlation time is poor;
Be 0.2T when the forward direction reference waveform is long c, T cIt is the width of a pseudorandom chip; α (ε) and R XF(ε) as shown in figure 11, the cross correlation function R of forward direction reference waveform and BOC code XF(ε) a plurality of relevant peaks are arranged.R XF(ε) can be formed by α (ε) linear combination, otherwise α (ε) also can be by R XF(ε) linear displacement with it combines, that is:
R XF ( &epsiv; ) + R XF ( &epsiv; - T c 2 p ) = &alpha; ( &epsiv; ) ,
Thus, forward direction related function F of structure on the basis of forward direction reference waveform c(t):
F C ( t ) = F ( t ) + F ( t - T c 2 p )
The forward direction waveform correlation F that constructs c(t) with the cross correlation function of the local BOC code that produces For:
R X F C ( &epsiv; ) = &alpha; ( &epsiv; )
As seen, forward direction related function
Figure GDA00003195184000114
Only have a peak value, and good linearity is arranged.
(2) backward structure reference waveform and BOC code is relevant Function and characteristic:
R XB ( &epsiv; ) = &Sigma; i = 0 2 p ( - 1 ) i &beta; ( &epsiv; + i T c 2 p ) , - T c &le; &epsiv; &le; 0 0 , &epsiv; > 0
Wherein, ε is that correlation time is poor, and p is the ratio of subcarrier frequency and pseudo-random code frequency, T cIt is the width of a pseudorandom chip;
&beta; ( &epsiv; ) = | &epsiv; + L 2 | - L 2 , - L &le; &epsiv; &le; 0
Wherein, ε is that correlation time is poor, and L is the width of backward reference waveform;
Be 0.2T when backward reference waveform is long c, β (ε) and R XB(ε) as shown in figure 12: the cross correlation function R of visible backward reference waveform and BOC code XB(ε) a plurality of relevant peaks are arranged.R XB(ε) can be formed by β (ε) linear combination, otherwise β (ε) also can be by R XB(ε) linear displacement with it combines, that is:
R XB ( &epsiv; ) + R XB ( &epsiv; + T c 2 p ) = &beta; ( &epsiv; )
Thus, rear on the basis of reference waveform after one of structure to related function B c(t):
B c ( t ) = B ( t ) + B ( t + T c 2 p ) ;
The backward waveform correlation B that constructs c(t) and the related function of BOC code be
Figure GDA000031951840001110
R X B C ( &epsiv; ) = &beta; ( &epsiv; ) .
The backward reference waveform of this structure and the related function of BOC code Only have a peak value, and good linearity is arranged.
(3) the instant reference waveform R of instant reference waveform and BOC code XP(ε) and characteristic:
R XP ( &epsiv; ) = &Sigma; i = - p i = p &Sigma; i ( - 1 ) i &gamma; ( &epsiv; + i T c 2 p )
Wherein, ε is that correlation time is poor, and p is the ratio of subcarrier frequency and pseudo-random code frequency, T cIt is the width of a pseudorandom chip;
&gamma; ( &epsiv; ) = 2 p T p T c , | &epsiv; | &le; L 2 2 p T p / T c L / 2 - T c / ( 4 p ) ( | &epsiv; | - T c / 4 p ) , L 2 &le; | &epsiv; | &le; T c 4 p
Wherein, ε is that correlation time is poor, T pBe the width of backward reference waveform, p is the ratio of subcarrier frequency and pseudo-random code frequency, T cBe the width of a pseudorandom chip, the forward direction reference waveform of L and the width of backward reference waveform.γ (ε) and R XP(ε) be illustrated in fig. 13 shown below:
Figure GDA00003195184000123
The time, γ (ε) is constant; The cross correlation function R of instant reference waveform and BOC code XP(ε) a plurality of relevant peaks are arranged.R XP(ε) can be formed by γ (ε) linear combination.
Figure GDA00003195184000124
And R XP(ε) be the basis that following structure overcomes the Phase Tracking method of multi-path influence.
Intermediate-freuqncy signal (main carrier after the BOC modulated signal modulation that receives from channel) input receiver from transmitting terminal, receiver multiplies each other the local carrier that intermediate-freuqncy signal and local oscillator send, and with local carrier 90-degree rotation phase place after carrier multiplication, recover I, (baseband signal refers to BOC modulated signal r to Q two-way baseband signal B(t)).I, Q two-way BOC modulated signal two-way frequency expansion sequence input to code tracking loop.Criterion based on optimum linearity phase demodulation curve, and the cross correlation function characteristic between the reference waveform signal of above-mentioned analysis and BOC code, a structure code tracking loop as shown in figure 14, because the processing of I, Q two-way is identical, so Figure 14 only illustrates wherein, and the processing structure of one road signal: I, Q two-way frequency expansion sequence input to code tracking loop.Code tracking loop comprises that pseudo-random generator, BOC code generator, reference waveform generator, cross correlation process module, phase demodulation function generation module, code ring phase detector, cross correlation process module, phase demodulation function generation module include multiplier, integration zero clearing device.
Described pseudo-noise code generator is used for, and receives identified result And generate pseudo-random code according to identified result in this locality;
The BOC code generator is used for, according to the pseudorandom number generation BOC code of this locality generation;
Described reference waveform generator is used for, and generates pseudo-random code and BOC code according to this locality, generates the forward direction reference waveform
Figure GDA00003195184000126
Backward reference waveform
Figure GDA00003195184000127
Instant reference waveform Recycling forward direction reference waveform is constructed the forward direction waveform correlation
Figure GDA00003195184000129
Utilize backward reference waveform to construct backward waveform correlation
Figure GDA000031951840001210
The cross correlation process module is used for, and receives the base band BOC subcarrier modulated signal of input, and base band BOC subcarrier modulated signal is carried out simple crosscorrelation and obtained the forward direction related function with forward direction waveform correlation, backward waveform correlation, instant reference waveform respectively
Figure GDA00003195184000131
Backward related function
Figure GDA00003195184000132
Instant related function R XP(ε);
Phase demodulation function generation module is used for, and forward direction related function and instant related function are multiplied each other, and obtains forward direction phase demodulation function Backward related function and instant related function are multiplied each other, obtain backward phase demodulation function
Figure GDA00003195184000134
Code ring phase detector is used for, forward direction phase demodulation functional value greater than 0 and backward phase demodulation functional value equal at 0 o'clock, the identified result of output is for postponing the phase place of local pseudo-random code; Forward direction phase demodulation functional value LittleIn 0 and backward phase demodulation functional value equal at 0 o'clock, output identified result be the phase place that shifts to an earlier date local pseudo-random code;
Interference-free when guaranteeing that identified result inputs to pseudo-noise code generator, also comprise loop filter, voltage controlled oscillator in code tracking loop, identified result inputs to pseudo-noise code generator by loop filter, voltage controlled oscillator after the signals such as filtering are processed.
The cross correlation process module comprises multiplier, integration zero clearing device; The forward direction waveform correlation of reference waveform generator, backward waveform correlation, instant reference waveform output terminal are connected with the input end of one of corresponding multiplier respectively, and another input end of each multiplier connects the base band BOC subcarrier modulated signal of input.The phase demodulation generation module comprises multiplier, integration zero clearing device; The output terminal of the output terminal of the integration zero clearing device of output forward direction related function, the integration zero clearing device of the instant related function of output connects respectively with two input ends of same multiplier and is connected, the output terminal of this multiplier is connected with corresponding integration zero clearing device, and the output terminal of this integration zero clearing device is connected with an input end of code ring phase detector; The output terminal of integration zero clearing device of exporting output terminal, the instant related function of output of the integration zero clearing device of backward related function connects respectively with two input ends of same multiplier and is connected, and the output terminal of this integration zero clearing device is connected with another input end of code ring phase detector.
The baseband signal r of input B(t) waveform correlation, the reference waveform that produce with this locality respectively
Figure GDA00003195184000136
Multiply each other, wherein.Multiplied result is passed through respectively integration zero clearing unit (to improve snr gain) and is obtained cross correlation results.The forward direction waveform correlation multiplies each other with instant reference waveform and obtains forward direction phase demodulation function d FC(ε), backward waveform correlation multiplies each other with instant reference waveform and obtains backward phase demodulation function d Bc(ε).
d ( &epsiv; ) = d F c ( &epsiv; ) + d B c ( &epsiv; )
d F c ( &epsiv; ) = R X F c ( &epsiv; ) &bull; R XP ( &epsiv; )
d B c ( &epsiv; ) = R X B c ( &epsiv; ) &bull; R XP ( &epsiv; )
Forward direction phase demodulation function d FC(ε) with backward phase demodulation function d BCPhase demodulation curve (ε) as shown in figure 15, the zero crossing of the zero crossing of phase demodulation curve with without multipath signal the time in the ideal case, only has a relevant peaks without departing from during on-off delay.In simulation result, when having multi-path influence, the minimum zero crossing of phase demodulation curve is also without skew, and as shown in figure 16, α is the second footpath signal is the second footpath signal with respect to the relative phase of direct projection footpath signal with respect to relative amplitude, the θ of direct projection footpath signal.The minimum zero crossing of phase demodulation curve has determined the accuracy of following the tracks of, so this kind multipaths restraint method has extraordinary performance.
Forward direction phase demodulation function d FC(ε) with backward phase demodulation function d BC(ε) input code ring phase detector carries out phase demodulation output.The phase demodulation process of code ring phase detector is as follows:
1) as the d that is input as of control end FC(ε)〉0 and d BC(ε)=0 o'clock, illustrate that the phase place (phase place of local reference waveform is identical with the phase place of the local pseudo-random code that produces, BOC code) of local reference waveform has shifted to an earlier date than the signal phase of inputting, what need to do this moment is exactly that local code is postponed.Suppose to detect the d of this moment FC(ε)=c 0, the local carrier phase place amount that need to postpone is c 0/ g 0, g 0The gain of phase detector, corresponding to the slope of ideal curve linear segment.
2) work as d BC(ε)<0 and d FC(ε)=0 o'clock, illustrate that the code phase of local reference waveform lags behind the phase place of input signal, what will do this moment is exactly to shift to an earlier date local code.Similarly, be d if the output valve of backward phase detector detected BC(ε)=c 1, the local code phase place that need to shift to an earlier date is c 1/ g 0
Use multipath error envelope (MEE) to carry out the comparison of multipaths restraint performance:
Using in identical system front end filter bandwidht situation, institute's the inventive method can be controlled multipath error at 0.001T c" Nunes, F., Sousa, F., and Leit ~ ao, J.gating functions for multipath mitigation in GNSS BOC signals, IEEE Transactions on Aerospace and electronic systemsvol.43, No.3JULY2007 " (the multipaths restraint based on gate function that is used for GPS (Global Position System) BOC modulated subcarrier signal, abbreviation GT scheme) method that proposes and the multipath error envelope of the inventive method compare, as shown in figure 17.Of the present invention in the advantage aspect multipaths restraint in order more clearly to manifest, Figure 18 is the image after the local amplification of of 17 figure.
In figure, gray line is the multipath error enveloping curve of scheme proposed by the invention, and multipath error is in the scope of 0.001Tc; Black line is the multipath error enveloping curve of GT scheme, and multipath error is at 0.015T cIn.What as seen propose is directed to BOC(pn, n) code tracking loop of signal has good multipaths restraint power.
The present invention is applicable to receiver and is receiving the modern modulation signal BOC(pn of GNSS, n) signal carries out multipaths restraint, this is positioned with important meaning for high precisions such as military activity and emergency reliefs, also being conducive to land station provides ephemeris accurately when adopting GNSS modern face modulation signal, help the improvement of location quality of service in the mobile subscriber in city is in complicated multi-path environment.

Claims (10)

1. a multipaths restraint BOC code tracking method, is characterized in that, comprises the following steps:
The pseudorandom number generation step: code tracking loop generates pseudo-random code according to identified result in this locality;
The BOC code generates step: according to the pseudorandom number generation BOC code of this locality generation;
Reference waveform generates step: code tracking loop generates pseudo-random code and BOC code according to this locality, generates forward direction reference waveform, backward reference waveform, instant reference waveform;
Described forward direction reference waveform is, width is the bipolarity waveform code F (t) of L, and before being created in the pseudorandom chip that this locality of practical function produces, the end point of forward direction reference waveform is alignd with the starting point of the pseudorandom chip of local generation; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first-1, is+1 afterwards, and when the pseudorandom chip of practical function is-1, the forward direction reference waveform is first+1, is-1 afterwards;
Described backward reference waveform is, width is the bipolarity waveform code B (t) of L, and after being created in the pseudorandom chip that this locality of practical function produces, the end point of the local pseudorandom chip that produces is alignd with the starting point of backward reference waveform; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first+1, is-1 afterwards; When the pseudorandom chip of practical function is-1, the forward direction reference waveform is first-1, is+1 afterwards;
Described instant reference waveform is that width is T pThe rectangle square wave, the center-aligned of the center of instant reference waveform and the BOC chip of this locality of practical function generation; When the BOC of practical function chip was-1, the amplitude of instant reference waveform was-1; When the BOC of practical function chip was+1, the amplitude of P (t) was+1;
Waveform correlation constitution step: utilize the forward direction reference waveform to construct forward direction waveform correlation F c(t); Utilize backward reference waveform to construct backward waveform correlation B c(t);
The simple crosscorrelation step: code tracking loop receives the base band BOC subcarrier modulated signal of input, base band BOC subcarrier modulated signal is carried out simple crosscorrelation with forward direction waveform correlation, backward waveform correlation, instant reference waveform respectively obtain forward direction related function, backward related function, instant related function;
The phase demodulation function generates step: forward direction related function and instant related function are multiplied each other, obtain forward direction phase demodulation function; Backward related function and instant related function are multiplied each other, obtain backward phase demodulation function;
The phase demodulation step: forward direction phase demodulation functional value greater than 0 and backward phase demodulation functional value equal at 0 o'clock, identified result is for postponing the phase place of local pseudo-random code; Forward direction phase demodulation functional value less than 0 and backward phase demodulation functional value equal at 0 o'clock, identified result is the phase place that shifts to an earlier date local pseudo-random code.
2. multipaths restraint BOC code tracking method as claimed in claim 1, is characterized in that, in described phase demodulation step, forward direction phase demodulation functional value postponed the phase place of local reference waveform divided by the retardation that the gain of phase detector obtains; The lead that backward phase demodulation functional value is obtained divided by the gain of phase detector shifts to an earlier date the phase place of local reference waveform.
3. multipaths restraint BOC code tracking method as claimed in claim 1 or 2, is characterized in that, in described waveform correlation constitution step, utilizes the forward direction reference waveform to construct forward direction waveform correlation F c(t), Wherein, F (t) is the forward direction reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency, and t represents time variable;
Utilize backward reference waveform to construct backward waveform correlation B c(t),
Figure FDA00003195183900022
Wherein, B (t) is backward reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency.
4. multipaths restraint BOC code tracking method as claimed in claim 1 or 2, is characterized in that, in described simple crosscorrelation step, base band BOC subcarrier modulated signal and forward direction waveform correlation carried out simple crosscorrelation obtain forward direction related function α (ε):
&alpha; ( &epsiv; ) = L 2 - | &epsiv; - L 2 | , 0 &le; &epsiv; &le; L ;
Base band BOC subcarrier modulated signal and backward waveform correlation are carried out simple crosscorrelation obtain backward related function β (ε):
&beta; ( &epsiv; ) = | &epsiv; + L 2 | - L 2 , - L &le; &epsiv; &le; 0 ;
With the cross correlation function R of base band BOC subcarrier modulated signal with the local instant reference waveform that produces XP(ε) be:
R XP ( &epsiv; ) = &Sigma; i = - p i = p &Sigma; i ( - 1 ) i &gamma; ( &epsiv; + i T c 2 p ) ;
Wherein, &gamma; ( &epsiv; ) = 2 p T p T c , | &epsiv; | &le; L 2 2 p T p / T c L / 2 - T c / ( 4 p ) ( | &epsiv; | - T c 4 p ) , L 2 &le; | &epsiv; | &le; T c 4 p ;
ε is that correlation time is poor, and p is the BOC code frequency and the ratio of pseudo-random code frequency, T cBe the width of a pseudorandom chip, T pBe the width of instant reference waveform, L is the width of forward direction reference waveform or backward reference waveform.
5. code tracking loop, is characterized in that, comprises pseudo-noise code generator, BOC code generator, reference waveform generator, cross correlation process module, phase demodulation function generation module, code ring phase detector;
Described pseudo-noise code generator is used for, and receives identified result, and generates pseudo-random code according to identified result in this locality;
The BOC code generator is used for, according to the pseudorandom number generation BOC code of this locality generation;
Described reference waveform generator is used for, and generates pseudo-random code and BOC code according to this locality, generates forward direction reference waveform, backward reference waveform, instant reference waveform; The forward direction reference waveform that generates is, width is the bipolarity waveform code F (t) of L, and before being created in the pseudorandom chip that this locality of practical function produces, the end point of forward direction reference waveform is alignd with the starting point of the pseudorandom chip of local generation; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first-1, is+1 afterwards, and when the pseudorandom chip of practical function is-1, the forward direction reference waveform is first+1, is-1 afterwards; The backward reference waveform that generates is, width is the bipolarity waveform code B (t) of L, and after being created in the pseudorandom chip that this locality of practical function produces, the end point of the local pseudorandom chip that produces is alignd with the starting point of backward reference waveform; When the pseudorandom chip of practical function is+1, the forward direction reference waveform is first+1, is-1 afterwards; When the pseudorandom chip of practical function is-1, the forward direction reference waveform is first-1, is+1 afterwards; The instant reference waveform that generates is that width is T pThe rectangle square wave, the center-aligned of the center of instant reference waveform and the BOC chip of this locality of practical function generation; When the BOC of practical function chip was-1, the amplitude of instant reference waveform was-1; When the BOC of practical function chip was+1, the amplitude of P (t) was+1; Recycling forward direction reference waveform is constructed forward direction waveform correlation F c(t); Utilize backward reference waveform to construct backward waveform correlation B c(t);
Described cross correlation process module is used for, receive the base band BOC subcarrier modulated signal of input, base band BOC subcarrier modulated signal is carried out simple crosscorrelation with forward direction waveform correlation, backward waveform correlation, instant reference waveform respectively obtain forward direction related function, backward related function, instant related function;
Described phase demodulation function generation module is used for, and forward direction related function and instant related function are multiplied each other, and obtains forward direction phase demodulation function; Backward related function and instant related function are multiplied each other, obtain backward phase demodulation function;
Described code ring phase detector is used for, forward direction phase demodulation functional value greater than 0 and backward phase demodulation functional value equal at 0 o'clock, the identified result of output is for postponing the phase place of local pseudo-random code; Forward direction phase demodulation functional value less than 0 and backward phase demodulation functional value equal at 0 o'clock, output identified result be the phase place that shifts to an earlier date local pseudo-random code.
6. code tracking loop as claimed in claim 5, is characterized in that, described cross correlation process module comprises multiplier, integration zero clearing device; The forward direction waveform correlation of reference waveform generator, backward waveform correlation, instant reference waveform output terminal are connected with the input end of one of corresponding multiplier respectively, and another input end of each multiplier connects the base band BOC subcarrier modulated signal of input.
7. code tracking loop as claimed in claim 6, is characterized in that, described phase demodulation generation module comprises multiplier, integration zero clearing device; The output terminal of the output terminal of the integration zero clearing device of output forward direction related function, the integration zero clearing device of the instant related function of output connects respectively with two input ends of same multiplier and is connected, the output terminal of this multiplier is connected with corresponding integration zero clearing device, and the output terminal of this integration zero clearing device is connected with an input end of code ring phase detector; The output terminal of integration zero clearing device of exporting output terminal, the instant related function of output of the integration zero clearing device of backward related function connects respectively with two input ends of same multiplier and is connected, and the output terminal of this integration zero clearing device is connected with another input end of code ring phase detector.
8. code tracking loop as claimed in claim 5, is characterized in that, described code ring phase detector also is used for, and the retardation that forward direction phase demodulation functional value is obtained divided by the gain of phase detector is as the identified result of output; The lead that backward phase demodulation functional value is obtained divided by the gain of phase detector is as the identified result of output.
9. as code tracking loop as described in claim 5 or 8, it is characterized in that, described reference waveform generator is used for, and utilizes the forward direction reference waveform to construct forward direction waveform correlation F c(t),
Figure FDA00003195183900041
Wherein, F (t) is the forward direction reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency, and t represents time variable;
Utilize backward reference waveform to construct backward waveform correlation B c(t),
Figure FDA00003195183900042
Wherein, B (t) is backward reference waveform, T cBe the width of a pseudorandom chip, p is the BOC code frequency and the ratio of pseudo-random code frequency.
10. code tracking loop as claimed in claim 9, is characterized in that, described cross correlation process module is used for, and base band BOC subcarrier modulated signal and forward direction waveform correlation carried out simple crosscorrelation obtain forward direction related function α (ε):
&alpha; ( &epsiv; ) = L 2 - | &epsiv; - L 2 | , 0 &le; &epsiv; &le; L ;
Base band BOC subcarrier modulated signal and backward waveform correlation are carried out simple crosscorrelation obtain backward related function β (ε):
&beta; ( &epsiv; ) = | &epsiv; + L 2 | - L 2 , - L &le; &epsiv; &le; 0 ;
With the cross correlation function R of base band BOC subcarrier modulated signal with the local instant reference waveform that produces XP(ε) be:
R XP ( &epsiv; ) = &Sigma; i = - p i = p &Sigma; i ( - 1 ) i &gamma; ( &epsiv; + i T c 2 p ) ;
Wherein, &gamma; ( &epsiv; ) = 2 p T p T c , | &epsiv; | &le; L 2 2 p T p / T c L / 2 - T c / ( 4 p ) ( | &epsiv; | - T c 4 p ) , L 2 &le; | &epsiv; | &le; T c 4 p ;
Wherein ε is that correlation time is poor; P is the BOC code frequency and the ratio of pseudo-random code frequency, T cBe the width of a pseudorandom chip, T pBe the width of instant reference waveform, L is the width of forward direction reference waveform or backward reference waveform.
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