CN101907715B - Precise delay implementation method for satellite navigation digital baseband signal - Google Patents
Precise delay implementation method for satellite navigation digital baseband signal Download PDFInfo
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Abstract
The invention relates to a precise delay implementation method for a satellite navigation digital baseband signal. In the method, a pseudo range is decomposed into great number delay and small number delay, wherein the great number delay is realized by the delay of a plurality of entire clock periods; and the small number delay is realized by digital delay processing. The digital delay processing comprises the processes of data interpolation, digital delay filtering and selection. A small number delay signal is subjected to reverse mirror image filtering after the data interpolation and is subjected to anti-aliasing filtering before the selection. Not only the variation range of the pseudo range but also the control accuracy can be ensured by using a great number implementation method and a small number implementation method respectively.
Description
Technical field
The present invention relates to satellite navigation and simulation technical field, the precise delay implementation method of a kind of satellite navigation digital baseband signal of saying so more specifically.
Background technology
The ultimate principle of utilizing satellite to carry out navigator fix is: ground receiver is measured the actual range with respect to four satellites, constitutes a space geometry equation, finds the solution the volume coordinate of receiver position again according to the co-ordinates of satellite in the satellite ephemeris.Distance error is the main source of final positioning error.In the actual location process, exist relative motion between satellite and the receiver, cause distance between satellite and the receiver in continuous variation, because electromagnetic wave is with light velocity propagation, this variable in distance will cause the electromagnetic wave propagation time to change.See from the angle of receiver, receive signal and be one with the satellite clock benchmark be reference, retardation at the signal that constantly changes, it is neither together that different satellite-signals arrive the retardation of receivers.The signal delay that relative motion between satellite and receiver causes, amount of additional delay all can be brought to the propagation of satellite navigation signals in ionosphere and troposphere.
In satellite navigation signal simulator, after the satellite digital baseband signal produced, an important job was exactly to realize this delay of signals.The time delay control of signal generator following three kinds of methods commonly used realize:
(1) simulation time delay control
The know-why of simulation time delay control is based on when a signal passes through a wave filter, will produce certain group delay.The signal that therefore can let signal generator produce is realized time delay control through several analog filters, but in this method analog filter time delay to receive external influences such as comprising temperature very big, precision is not high yet.
(2) NCO time delay control
The NCO delay control method adopts the DDS technology based on sign indicating number NCO (Numerical Controlled Oscillator, digital controlled oscillator).Cycle and the phase place of NCO method through control code NCO simulated pseudorange that Doppler causes, principle that pseudorange rates changes with general Direct Digital frequency synthesis (Direct Digital Frequency Synthesis; DDFS) similar, just output is the sign indicating number clock with square-wave waveform.Sign indicating number DDS need not to search magnitudes table, but the symbol phases accumulator value is compared with setting carry value, and when being worth greater than this, NCO exports high level; Otherwise output low level then is with this clock reference as pseudo-noise code generator.Its major parameter comprises frequency control word, phase control words.There are following three problems in the NCO method:
A. the initial phase control accuracy is limited by the NCO working clock frequency, causes the pseudorange control accuracy to reduce, and the null value uncertainty increases;
The time delay that the B.NCO method realizes is a time averaging result, and it can not realize single pseudo-code or the disconnected precise delay of minor time slice, promptly can not precise real-time reflects the variation of signal time delay;
C. because the phase truncation effect of sign indicating number NCO causes spurious effects, cause the pseudo-code phase shake to worsen, signal quality descends.
(3) digital delay filtering device
Adopt the digital delay filtering utensil to have the precision of delay controlled, can realize the precise delay of single pseudo-code.But signal delay amount in the satellite navigation signal simulator (being pseudorange) variation range is big, and accuracy requirement is high.Requiring like pseudorange in the GPS navigation signal simulator is 26000000.02 meters, and pace of change can reach hundreds of metre per second (m/s)s.The retardation of individual digit delay filter is fixed, and can't adapt to the demand of the rapid variation of satellite navigation signal simulator pseudorange.And design digital delay filter operand is big in real time, can't satisfy the demand of signal real time simulation.
Summary of the invention
To prior art, the invention provides a kind of precise delay method of satellite navigation digital baseband signal.
Technical scheme of the present invention is: navigation signal simulator at first produces the digital baseband part and the pseudorange of satellite navigation signals.Pseudorange is broken down into big number delay and decimal postpones, and big number postpones to realize through the delay of a plurality of whole clock period that the decimal delay then realizes through digital delay processing.After digital baseband signal produces, carry out number delay greatly earlier, carry out decimal again and postpone, realize that finally given pseudorange postpones.
Digital delay processing comprises data interpolating, digital delay filtering and selection process.The decimal inhibit signal is carried out anti-mirror image filtering behind data interpolating, carry out anti-aliasing filter before selecting.
The parameter of digital delay filtering device is pre-designed, is stored in the storer, reads when system moves to be placed in the internal memory, and direct and digital signal is carried out the time domain multiplication.Designed many groups digital delay filtering device in advance, every group of corresponding retardation of digital delay filtering device and unique address.According to the address of fractional value acquisition delay filter, read the parameter of delay filter again.
Pseudorange is split as big number delay and two parts of decimal delay.Big number postpones to be the integral multiple of clock period, realizes through a plurality of whole clock period, realizes the delay of whole clock period through executive routine.Decimal postpones to be to realize the little several times of clock period through digital delay filtering device group.Signal through after postponing is modulated to the satellite carrier frequency through up-conversion, produces the satellite navigation analog radio-frequency signal.
Each bank of filters all has a unique address, and the retardation scope of the corresponding demarcation in this address is demarcated within the retardation scope when the decimal retardation is positioned at, and then can obtain the wave filter corresponding with this demarcation retardation through the address.
The digital delay processing process is as shown in Figure 2, comprises following process:
Process 1: interpolation
Interior inserting raises sampling rate, is " rising sampling ".Interior implementation method of inserting is in the interval of input sampling data x (n), to insert L-1 zero point (L is an integer), makes that the sampled data in time interval T has been expanded L doubly.The interior result who inserts has produced mirror band in frequency band, thereby must use anti-mirror filter to eliminate mirror band.Anti-mirror image filtering sees to be exactly in addition level and smooth the L-1 that inserts 0 value from the time domain angle, to recover original waveform.Anti-mirror filter h
1(n) be the FIR wave filter that N rank have first kind linear phase, h is promptly arranged
1(n)=h
1(N-n-1), N is a filter order.
Process 2: delay filtering
The signal x of output
1(n) carry out time domain multiplication with selected delay filter, realize postponing;
Process 3: select
It is to select one to the sampled data of input is every for use at a distance from D point (D is an integer) that data are selected, and makes that the sampled data in time interval T is compressed to 1/D, and D is commonly referred to " decimation factor ".
h
2(n) be a frequency overlapped-resistable filter.This is because after data selected, the signals sampling frequency became original 1/D, may produce the frequency band aliasing, so carrying out will using frequency overlapped-resistable filter h before data select
2(n) to original signal x
2(n) carry out filtering.
Each process that digital delay is handled can be by formulate:
Process 1: interpolation
Process 2: delay filtering
Process 3: extract
Making
is τ=mL+p, and comprehensive above-mentioned formula obtains:
Because the Navsat movement velocity is fast, pseudorange changes greatly, and the method that the present invention adopts big number and decimal to realize respectively can guarantee the variation range of pseudorange can guarantee control accuracy again.The complicated calculations that adopts the many groups digital delay filtering device that designs in advance to avoid Design of Filter to need both can guarantee arithmetic speed, can guarantee control accuracy again, and this method has significant application value in precise navigation signal imitation.
Description of drawings
Fig. 1 is a single Navsat analogue signal generating block diagram.
Fig. 2 is the data handling procedure of delay filter.
Fig. 3 is original signal and time-delay back signal graph.
Embodiment
Single Navsat analogue signal generating block diagram is as shown in Figure 1, and the emulation of navigation signal simulator partly produces data such as navigation message, pseudorange and logical time.Quiet Mi Shizhongyuan is that sign indicating number generator and carrier wave generation provide frequency reference, and the sign indicating number generator produces the pseudo-random code of satellite, and satellite navigation message is modulated by this sign indicating number, generation standard digital baseband signal.
Among Fig. 1 in the frame of broken lines part be the scheme that signal delay produces, be about to pseudorange and be split as big number and postpone and two parts of decimal delay.Big number postpones to be the integral multiple of clock period, realizes through a plurality of whole clock period, realizes the delay of whole clock period through executive routine.Decimal postpones to be to realize the little several times of clock period through digital delay filtering device group.Signal through after postponing is modulated to the satellite carrier frequency through up-conversion, produces the satellite navigation analog radio-frequency signal.
Each bank of filters all has a unique address, and the retardation scope of the corresponding demarcation in this address is demarcated within the retardation scope when the decimal retardation is positioned at, and then can obtain the wave filter corresponding with this demarcation retardation through the address.
The digital delay processing process is as shown in Figure 2, comprises following process:
Process 1: interpolation
Interior inserting raises sampling rate, is " rising sampling ".Interior implementation method of inserting is in the interval of input sampling data x (n), to insert L-1 zero point (L is an integer), makes that the sampled data in time interval T has been expanded L doubly.The interior result who inserts has produced mirror band in frequency band, thereby must use anti-mirror filter to eliminate mirror band.Anti-mirror image filtering sees to be exactly in addition level and smooth the L-1 that inserts 0 value from the time domain angle, to recover original waveform.Anti-mirror filter h
1(n) be the FIR wave filter that N rank have first kind linear phase, h is promptly arranged
1(n)=h
1(N-n-1), N is a filter order.
Process 2: delay filtering
The signal x of output
1(n) carry out time domain multiplication with selected delay filter, realize postponing;
Process 3: select
It is to select one to the sampled data of input is every for use at a distance from D point (D is an integer) that data are selected, and makes that the sampled data in time interval T is compressed to 1/D, and D is commonly referred to " decimation factor ".
h
2(n) be a frequency overlapped-resistable filter.This is because after data selected, the signals sampling frequency became original 1/D, may produce the frequency band aliasing, so carrying out will using frequency overlapped-resistable filter h before data select
2(n) to original signal x
2(n) carry out filtering.
Each process that digital delay is handled can be by formulate:
Process 1: interpolation
Process 2: delay filtering
Process 3: extract
Making
is τ=mL+p, and comprehensive above-mentioned formula obtains:
Waveform before and after the signal delay is as shown in Figure 3, and the top of Fig. 3 is original signal, and the bottom is the signal of delayed processing.The retardation that adopts the different time delay bank of filters to obtain is different.
Claims (1)
1. the precise delay implementation method of a satellite navigation digital baseband signal is characterized in that:
1), pseudorange is broken down into that big number postpones and decimal postpones, big number postpones to realize through the delay of a plurality of whole clock period that decimal postpones then to realize through digital delay processing;
2), digital delay processing comprises data interpolating, digital delay filtering and selection process, the decimal inhibit signal is carried out anti-mirror image filtering behind data interpolating, carry out anti-aliasing filter before selecting;
Interpolation is inserted in adopting, and interior slotting implementation method is in the interval of input sampling data x (n), to insert L-1 zero point, and L is an integer, makes that the sampled data in time interval T has been expanded L doubly;
Delay filtering: the signal x of output
1(n) carry out time domain multiplication with selected delay filter, realize postponing;
It is to select one to the sampled data of input is every for use at a distance from the D point that data are selected, and D is an integer, makes that the sampled data in time interval T is compressed to 1/D;
3), design is in advance organized the digital delay filtering devices, every group of corresponding retardation of digital delay filtering device and unique address more.
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| CN103293534B (en) * | 2013-05-10 | 2014-12-17 | 西安空间无线电技术研究所 | Satellite navigation signal generation zero calibration method |
| CN105607088A (en) * | 2016-02-17 | 2016-05-25 | 湖南北云科技有限公司 | Rapid guiding tracking device for satellite navigation multifrequency receiver signals |
| CN107329152A (en) * | 2017-05-16 | 2017-11-07 | 上海卫星工程研究所 | The method of testing of satellite navigation receiver position error |
| CN109856594B (en) * | 2019-01-31 | 2020-10-13 | 北京电子工程总体研究所 | Multi-path controllable time delay signal generating device for passive positioning of time difference measuring system |
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