CN102023291A - GPS (global position system) signal high-speed capturing device and method - Google Patents

Abstract

The invention discloses a GPS (global positioning system) signal high-speed capturing device and method, belonging to the technical field of the satellite positioning and navigation. The matched filtering theory is adopted by a GPS receiver to capture the C/A code to complete related despreading algorithm at high speed in real time, and a sliding correlator is adopted to realize the tracking of the C/A code according to a matched filter. The I and Q baseband signals are synthesized before matched filtering, the influence of phase deviation is eliminated, the problem that I/Q matched filtering is needed to realize direct sequence spread spectrum signal capture by adopting the matched filtering in the prior art is overcome, and a great quantity of hardware resources is saved; and meanwhile, spread spectrum code synchronizing information is ensured to be obtained in a code element cycle, the capturing speed is increased, the production cost of the device is reduced, and simultaneously, the usability of a GPS wireless terminal is enhanced.

Description

A kind of gps signal high-speed capture device and method

Technical field

The present invention relates to satnav and airmanship, relate in particular to a kind of GPS (Global PositioningSystem, GPS) signal high-speed capture device and method.

Background technology

At present, can provide the communication system of accurate satnav and navigation to mainly contain four kinds in the world, be respectively the GALILEO in GPS of USA, Muscovite GLONASS, Europe and the Big Dipper positioning system of China, but being most widely used with GPS of USA still wherein.

The principle of GPS is very simple, GPS receiver in the GPS wireless terminal (or GPS navigation instrument) is decoded to the satellite-signal of being received, obtain carrier signal entrained star chart orbit information that includes satellite and high precision time information, pass through formula: the distance=time * speed, the principle that is aided with four point locations again can have been determined user's position.

But, existing GPS wireless terminal exists from start (catching the search and the calibration process of satellite-signal after the unlatching) consuming time to the location that captures satellite-signal long defective, the location that has is consuming time even reach more than 2 minutes, like this, both increased the power consumption of GPS wireless terminal, make the user lose the patience of wait again, have a strong impact on user's satisfaction.Therefore, how to shorten the location duration consuming time of GPS receiver as far as possible, just become a very necessary research striving direction.

Because in the gps satellite positioning system, the L frequency band carriers signal of two spread spectrums of each satellite transmission is called L1 and L2 signal, these two kinds of signals all adopt direct sequence spread spectrum and BPSK (Binary Phase ShiftKeying, two-phase PSK) modulation system.Wherein, the C/A of L1 signal (Clear andAcquisition or Coarse and Access, thick catch code) sign indicating number component uses for commercial.

The GPS receiver is caught the two kinds of approach that mainly contain of handling to C/A: the sign indicating number in frequency domain is caught and the sign indicating number in time domain is caught.Wherein, the sign indicating number Acquisition Scheme in frequency is transformed to the basis with Fourier (Fourier), determines the phase place of received signal C/A sign indicating number by the conversion of FFT (fast fourier transform) and IFFT (invert fast fourier transformation).Sign indicating number Acquisition Scheme in time domain then is the process that local C/A sign indicating number is aimed at received signal.

Use sign indicating number Acquisition Scheme in the frequency domain can realize to the catching fast of C/A sign indicating number, but the repeatedly conversion of FFT and IFFT of needs, and computing is bigger than complexity and spending of hardware.GPS wireless terminal for routine, finish sign indicating number in time domain catches, adopt sliding correlation detector, to consume calculation resources also less, but need carry out repeatedly the related operation operation, all on a possible Doppler (Doppler) frequency, search for a possible code phase at every turn, the C/A code length is 1023, the Doppler frequency range of GPS is ± 5kHz, because each slip half-chip, the code phase search step is to the maximum 2046 times, can increase half-chip to code phase to each search, perhaps can increase 500Hz to frequency, its result must be the product that capture time is proportional to code phase search step and carrier frequency search step required time, thereby still exists sign indicating number to catch the long deficiency of required time.

Summary of the invention

In view of this, fundamental purpose of the present invention is to provide a kind of gps signal high-speed capture device and method, by adopting new C/A sign indicating number catch mechanism, realize catching fast with lower implementation complexity to the C/A code phase, reduce the booting wait time of GPS wireless terminal, improve user's satisfaction.

For achieving the above object, technical scheme of the present invention is achieved in that

A kind of global position system GPS signal high-speed capture device, this device comprises the demodulator circuit group, described device also comprises synthetic filtering decision circuit and a plurality of sliding correlation detector tracking circuit; Wherein,

The demodulator circuit group comprises a plurality of demodulator circuits, and described demodulator circuit is used for demodulating I, Q two-way baseband signal from described gps signal;

The synthetic filtering decision circuit is used for described I, Q two-way baseband signal are synthesized one the tunnel, and carries out carrier information and the code phase information that relevant despreading obtains this moment by matched filter and decision device successively, sends into corresponding sliding correlation detector tracking circuit then;

Described sliding correlation detector tracking circuit is used for the code phase that carries gps signal by described synthetic filtering decision circuit output is carried out real-time follow-up.

Wherein, described synthetic filtering decision circuit further comprises I/Q compositor, matched filter, decision device and local C/A code generator; Wherein,

Described I/Q compositor is used for described I, Q two-way baseband signal are synthesized one the tunnel;

Described matched filter is used to select gps satellite signal to be correlated with to separate to extend to catch the C/A sign indicating number, and the phase information of exporting described C/A sign indicating number compares for decision device and described local C/A code generator;

Described decision device is used for the output result of described matched filter is adjudicated, to determine whether acquisition success of described C/A sign indicating number.

Further, described I/Q compositor obtains the amplitude and positive and negative realization of one-channel signal for what adopt cordic algorithm according to amplitude and angle value; Or by adopt I, Q two-way maximal value and minimum value half the absolute value sum and I, Q two-way baseband signal positive and negative obtains the amplitude of one-channel signal and positive and negative mode realizes.

Described matched filter by shift register or RAM directly/rotational latency realizes.

In the described sliding correlation detector tracking circuit, comprise the sliding correlation detector of at least 4 gps signal C/A code phases that are used to follow the tracks of caught.

A kind of method of gps signal high-speed capture, described method comprises:

A, utilize described demodulator circuit group from received gps signal, to demodulate I, Q two-way baseband signal;

B, with described I, Q two-way baseband signal input synthetic filtering decision circuit synthetic a tunnel, and by the despreading of being correlated with of described matched filter, obtain the carrier information and the spreading code phase information of described gps signal, and with described code phase information input sliding correlation detector tracking circuit;

One road sliding correlation detector that do not have in C, the described sliding correlation detector tracking circuit carries out real-time follow-up according to carrier information and phase information that described matched filter obtains to gps signal.

Gps signal acquisition equipment provided by the present invention and method have the following advantages:

The present invention adopts the matched filter aided capture, can finish phase capturing in a C/A sign indicating number cycle (1ms), improves greatly with respect to the sliding correlation detector acquisition speed.Before matched filter, adopt I/Q two-way compositor, thereby saved half matched filter resource, have good practical values.

Description of drawings

Fig. 1 is the principle schematic of gps signal high-speed capture device of the present invention;

Fig. 2 is I/Q compositor structural representation among Fig. 1 of the present invention.

Embodiment

Below in conjunction with accompanying drawing and embodiments of the invention method of the present invention is described in further detail.

Fig. 1 is the principle schematic of gps signal high-speed capture device of the present invention, and as shown in Figure 1, this device comprises that demodulator circuit group, synthetic filtering decision circuit A and several are used to follow the tracks of the sliding correlation detector tracking circuit B of the gps signal of having caught; Wherein,

Here, comprise local carrier maker, two multipliers and first low-pass filter 104 and second low-pass filter 104 ' in each demodulator circuit of described demodulator circuit group.Described local carrier maker is used to produce in-phase branch signal 102 and quadrature branch signal 103.

Synthetic filtering decision circuit A comprises I/Q compositor 105, matched filter 106, decision device 107 and local C/A code generator 108.

Here, described I/Q compositor 105 is used for described I, Q two-way baseband signal after first low-pass filter 104 and second low-pass filter 104 ' are exported respectively synthesized one the tunnel.Described I/Q compositor can have two kinds of methods to realize, adopt CORDIC to obtain the amplitude of one-channel signal and positive and negative according to amplitude and angle value, or adopt I, the absolute value sum of half of Q two-way maximal value and minimum value and I/Q two paths of signals positive and negative obtains the amplitude of one-channel signal and positive and negative.

Described matched filter 106 is used to select gps satellite signal to be correlated with to separate to extend to catch the C/A sign indicating number, and the phase information of exporting described C/A sign indicating number compares for decision device 107 and described local C/A code generator 108; Matched filter is according to selected local C/A sign indicating number, and the input of each sample information all can be exported the result of related operation, realizes the direct matched filtering of gps signal.Matched filter 106 can be realized by/rotational latency direct by shift register or RAM.

Described decision device 107 is used for the output result of described matched filter 106 is adjudicated, to determine whether acquisition success of described C/A sign indicating number.

Sliding correlation detector tracking circuit B, the C/A code phase that is used for gps signal has been caught carries out real-time follow-up.It comprises a local C/A code generator and two multipliers and two totalizers.

The course of work of this gps signal high-speed capture device is as follows: gps signal, be the in-phase branch signal 102 that input signal 101 is produced with the local carrier maker respectively) and quadrature branch signal 103 multiply each other, respectively by after a LPF (low-pass filter) 104 and the 2nd LPF (low-pass filter) 104 ' the filtering high fdrequency component, form I, Q two-way baseband signal then.Because local carrier frequency and received signal there are differences, so also there are the difference of carrier wave and phase place in I, Q two-way baseband signal, traditional method is that I, Q two-way baseband signal are passed through the direct despreading of matched filter, will expend the resource of two matched filters like this.Because gps signal adopts the BPSK modulation system, so I, Q two-way baseband signal can be synthesized and can not caused information loss, and can reduce the expense of No. one matched filter again.So adopt among the present invention I/Q compositor 105 that described I, Q two-way baseband signal are synthesized one the tunnel, then by matched filter 106 despreading of being correlated with.

Here, the described matched filter 106 selections wherein C/A sign indicating number of a gps satellite are caught, when in a C/A code length cycle, not finding to have gps signal, then local carrier frequency is increased 500Hz, begin to carry out the capturing carrier step, when whole carrier cycle does not search gps signal, the C/A sign indicating number that then described matched filter 106 is changed a satellite carries out repeat search, so, can be at short as far as possible time IT to gps signal.Finish carrier information and C/A code phase information to be sent to sliding filter after catching when described matched filter 106, sliding filter begins trace demodulation, and matched filter is changed the C/A sign indicating number and continued search simultaneously.Traditional time domain sign indicating number is caught because the slow general multi-channel parallel that adopts of speed, routine has 12 passage sliding correlation detector parallel captures, because matched filter can be finished in a C/A sign indicating number cycle and catch, reduce capture time greatly, therefore the sliding correlation detector number can correspondingly reduce, because the GPS location need lock 4 satellites at least, therefore general needs 4 sliding correlation detectors to get final product.

The output result of described matched filter 106 is sent into decision device 107 to adjudicate, maximal value in decision device 107 is found a C/A sign indicating number cycle greater than default threshold value after, promptly be judged to be acquisition success, carrier information and code phase information that simultaneously will this moment be given sliding correlation detector tracking circuit B and are followed the tracks of.

Fig. 2 is I/Q compositor structural representation among Fig. 1 of the present invention, and as shown in Figure 2, the amplitude of described I/Q compositor is

Because to use when calculating square, square root calculation, implement more complicated, adopt approximate data and CORDIC rotation algorithm to realize that its approximate data formula is as follows among the present invention:

$\mathrm{Amp}\≈\max \left(\right|I|,|Q\left|\right)+\frac{1}{2}\min \left(\right|I|,|Q\left|\right)$

Wherein: Amp is the range value 205 that above-mentioned formula calculates gained; Branch road I, branch road Q are respectively I, Q two-way baseband signal; Max201 is the maximum value signal of the absolute value of the output of first gate I, Q, and min202 is the I of second gate output, the minimum value signal of Q absolute value.

Described I, Q two-way absolute value input signal compare by comparer, if I＞Q, then comparer output 1, maximum value signal max201 gating I road, i.e. absolute value by first gate; The output of described comparer is output as 0 by first reverser 203, controls minimum value signal min202 gating Q road, promptly passes through the absolute value of second gate.Shift unit 204 dwindles 1/2 with min road output valve.Totalizer 205 is with the superimposed range value that obtains of described two paths of signals.

Because the range value of output is no value of symbol, the I/Q compositor also needs to draw the output signal symbol according to the symbol of original signal.When original signal drops on first, during four-quadrant, its be output as on the occasion of; When original signal dropped on second, third quadrant, it was output as negative value.Just, when I road original signal be on the occasion of the time, be output as on the occasion of.When I road original signal is negative value, be output as negative value.Second reverser 206 is oppositely exported a branch of described Amp205 signal, and described Amp205 signal and reverse signal thereof are imported the 3rd gate, controls the positive and negative of the 3rd gate output signal value by I road raw baseband signal as enable signal again.Because baseband signal exists phase ambiguity and phase error, thus this set just wherein one of select, with Q road signal as judgement, even if its result does not influence its final output result fully on the contrary too.This approximate data will be brought the loss of signal about 1dB.But simplified computing, reduced the expense of equipment.

When the bit wide of I, Q two paths of signals greater than 4 the time, its amplitude also can adopt CORDIC rotation algorithm to realize, but can not bring the loss of signal.

Basic digital matched filter is made of input data shift register unit, tap coupling multiplier unit, sum adder unit usually.Its function is described by following formula:

${\mathrm{Sum}}_k=\underset{n=k-N}{\overset{k-1}{\mathrm{\Σ}}}{\mathrm{Din}}_n\×c_{k-n}$

Wherein: N also is a spreading code length for matched filter integration summation length.Sum _kBe k digital matched filter output constantly, Din _nBe the k output of baseband I/Q compositor constantly, c1～cn is local spreading code.

With Din base band output data width be 4, the spread spectrum code length is 1024 to be example, if adopt shift register directly to realize the time-delay storage, then the two-way matched filtering just needs 1024 * 4 * 2=8k storage register, will expend a large amount of addition resources simultaneously.As seen, in conjunction with calculation element of the present invention,, can play the effect of a large amount of hardware resource of in to gps signal high-speed capture saving by above-mentioned computing.

Method provided by the invention is not limited to above-mentioned concrete scheme, and for example, matched filter and sliding filter circuit structure are not limit.The number of satellite decision (GPS needs 4 satnaves at least) that the number of described sliding filter can be followed the tracks of according to actual needs simultaneously is not limited to two shown in the accompanying drawing 1, also is not limited to have only 4.Amplitude in the described I/Q compositor is calculated half the absolute value sum algorithm that can also adopt I of the present invention, Q two-way baseband signal maximal value and minimum value, can also adopt cordic algorithm.

The above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention.

Claims (6)

1. global position system GPS signal high-speed capture device, this device comprises the demodulator circuit group, it is characterized in that, described device also comprises synthetic filtering decision circuit and a plurality of sliding correlation detector tracking circuit; Wherein,

The demodulator circuit group comprises a plurality of demodulator circuits, and described demodulator circuit is used for demodulating I, Q two-way baseband signal from described gps signal;

The synthetic filtering decision circuit is used for described I, Q two-way baseband signal are synthesized one the tunnel, and carries out carrier information and the code phase information that relevant despreading obtains this moment by matched filter and decision device successively, sends into corresponding sliding correlation detector tracking circuit then;

Described sliding correlation detector tracking circuit is used for the code phase that carries gps signal by described synthetic filtering decision circuit output is carried out real-time follow-up.

2. gps signal high-speed capture device according to claim 1 is characterized in that, described synthetic filtering decision circuit further comprises I/Q compositor, matched filter, decision device and local C/A code generator; Wherein,

Described I/Q compositor is used for described I, Q two-way baseband signal are synthesized one the tunnel;

Described matched filter is used to select gps satellite signal to be correlated with to separate to extend to catch the C/A sign indicating number, and the phase information of exporting described C/A sign indicating number compares for decision device and described local C/A code generator;

Described decision device is used for the output result of described matched filter is adjudicated, to determine whether acquisition success of described C/A sign indicating number.

3. gps signal high-speed capture device according to claim 1 and 2 is characterized in that, described I/Q compositor obtains the amplitude and positive and negative realization of one-channel signal for what adopt cordic algorithm according to amplitude and angle value; Or by adopt I, Q two-way maximal value and minimum value half the absolute value sum and I, Q two-way baseband signal positive and negative obtains the amplitude of one-channel signal and positive and negative mode realizes.

4. gps signal high-speed capture device according to claim 1 and 2 is characterized in that, described matched filter by shift register or RAM directly/rotational latency realizes.

5. gps signal high-speed capture device according to claim 1 is characterized in that, in the described sliding correlation detector tracking circuit, comprises the sliding correlation detector of at least 4 gps signal C/A code phases that are used to follow the tracks of caught.

6. the method for a gps signal high-speed capture is characterized in that, described catching method comprises:

A, utilize described demodulator circuit group from received gps signal, to demodulate I, Q two-way baseband signal;

B, with described I, Q two-way baseband signal input synthetic filtering decision circuit synthetic a tunnel, and by the despreading of being correlated with of described matched filter, obtain the carrier information and the spreading code phase information of described gps signal, and with described code phase information input sliding correlation detector tracking circuit;

One road sliding correlation detector that do not have in C, the described sliding correlation detector tracking circuit carries out real-time follow-up according to carrier information and phase information that described matched filter obtains to gps signal.

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