CN102508266A - Filter method for restraining multipath interference and noise - Google Patents

Abstract

The invention discloses a filter method for restraining multipath interference and noise, which assists a code pseudo range by carrier Doppler to restrain multipath and environmental noises. With respect to the fixed filtering windows in the prior art, the filter method provides dynamic regulating filtering windows; the filtering state is entered from a first data; the lengths of the windows are added one by one until the pre-set filtering window lengths are reached. Without any doubt, the method is more flexible and can enter the filtering state rapidly without waiting for the time of a filtering window length. The system is instable at the initial phase of positioning; the positioning point skips greatly; the method can enhance positioning precision at the initial phase and is especially significant to the precise positioning in the situation of serious multipath interference in globe positioning system (GPS) positioning and a city environment with other environmental noises.

Description

A kind of filtered method that suppresses multipath interference and noise

Technical field

The present invention relates to the filtered method in the gps system, especially a kind of filtered method that suppresses multipath interference and noise belongs to the GPS communication technical field.

Background technology

The radiofrequency signal of gps satellite emission is for to be modulated at resulting signal on the carrier wave with C/A sign indicating number and navigation data.Modern general digital GPS receiver comprises radio frequency receiving antenna, low-converter, channel base band signal and data output, accomplish signal reception, catch, bit synchronous, follow the tracks of, separate and be in harmonious proportion positioning calculation etc.Its basic workflow is: gps antenna receives all visible gps satellite signals; And faint electromagnetic wave is converted into weak current; Through pre-low-noise amplifier faint marking current is amplified then, then high-frequency signal is down-converted to the digital baseband channel of sending into each reception behind the digital intermediate frequency signal and handle through the frequency conversion conversion.Processing procedure comprises: at first trapping module is accomplished two-dimensional search through the time delay to all uncertain C/A sign indicating numbers with all uncertain Doppler shifts; Thereby find satellites in view, rough C/A code delay and Doppler shift; After accomplishing bit synchronous the result is input to tracking module; And tracking module is mainly accomplished the tracking of C/A sign indicating number, phase place and Doppler shift, thereby obtains the accurate estimated value of these parameters.It is consistent with the carrier for digital signal frequency that receives to adopt phase place and Doppler frequency shift estimation to duplicate local carrier frequency, and then peels off carrier wave, obtains C/A sign indicating number and navigation data sign indicating number, and this is a carrier tracking loop; The code delay that utilization is estimated obtains advanced code, instantaneous code and hysteresis sign indicating number through the computing of correlator, and then it is consistent with the C/A sign indicating number in the digital signal that receives to duplicate local C/A sign indicating number, and then peels off the C/A sign indicating number, and this is the code tracking loop.Code tracking loop and carrier tracking loop are referred to as track loop.Obtain navigation data after the processing through track loop; The navigation data decoding obtains the ephemeris and the almanac of satellite; Can calculate the position of satellite and the launch time of satellite-signal by them; Can obtain the travel-time of signal from the satellite to the receiver in conjunction with local zone time; Obtain pseudorange after multiply by the light velocity, be referred to as the former of pseudorange rather than distance, rather than arrive the actual distance of receiver from satellite because this has the last deviations of caused distance such as measuring error such as atmosphere time delay, receiver clock error and receiver apart from the inside.So far satellite position and pseudorange have been obtained.At least want the data of 4 satellites, just can the simultaneous solution system of equations obtain the position that receiver belongs to, this is the positioning calculation process.

During actual GPS measures,, cause bearing accuracy to reduce because multipath disturbs and other influence of environmental noise.The generation that multipath disturbs can be explained as follows: the signal that receiver antenna receives comprises the direct signal that obtains after the reflection of the reflecting surface around the receiving antenna through one or many from the direct signal and the direct signal of direction; It is multipath signal; The travel path of multipath signal and direct signal is different; Therefore different amplitude, phase place and time delay are arranged, thereby cause the waveform of composite signal to be distorted.And other neighbourhood noise comprises the measuring error of atmosphere time delay, receiver clock error and receiver etc., thereby influences bearing accuracy, produces positioning error.Wherein the research of multipath inhibition method is carried out from suppressing multipath Antenna Design, the design of loop phase detector and three aspects of Data Post usually; They cut both ways, and perfect multipath suppresses strategy and considers after the design object integrated use to these methods often.In the digital signal processing of receiver internal trace loop, take multiple measure to suppress multipath effect and seem that quite reality is with effective.

In the Data Post method after following the tracks of, coming the auxiliary code pseudorange with carrier doppler is a relatively effective method, and simple to operate, need not take ample resources, does not also change loop architectures, thereby is popular in recent years.But existing carrier doppler auxiliary code pseudorange method adopts fixedly filter window length N, just can get into filter state so must wait for the N time.

Summary of the invention

The present invention is directed to the fixedly defective of filter window length N of existing carrier doppler auxiliary code pseudorange method, proposed a kind of filtered method that suppresses multipath interference and noise.

The technical scheme that the present invention takes is: a kind of filtered method that suppresses multipath interference and noise, and the carrier doppler that obtains later with Base-Band Processing is the basis with a sign indicating number pseudorange, adopts carrier doppler to come the auxiliary code pseudorange; Accurate sign indicating number pseudorange after obtaining smoothly; It is characterized in that: the wave filter that dynamic adjustment filter window length is set substitutes the fixedly wave filter of filter window length, begins promptly to get into filter state from first pseudorange collected and carrier doppler data, and filter window length is from initial one; And behind smooth value of per second output after this; Filter window length added one successively when the implementation pseudorange was level and smooth, and after reaching predefined filter window length N, filter window length remains unchanged; Under each filter window length; Carry out the computation process of three steps, obtain the final pseudorange smooth value in this moment, the computation process of three steps is following:

1) obtain after the sign indicating number pseudorange and carrier doppler of a filter window length n, at first the priori estimates of the sign indicating number pseudorange after the filtering that calculates the corresponding moment of the following formula of process:

i＝0，1，2...n

$\stackrel{\‾}{\mathrm{\ρ}}\left(t_0\right)=\frac{1}{n}\underset{i=0}{\overset{n}{\mathrm{\Σ}}}\widehat{\mathrm{\ρ}}\left(t_0\right)$

2) then; The priori estimates of the individual sign indicating number pseudorange after treatment of the n that utilizes filter window length n to comprise in second; Obtain the sign indicating number pseudorange average of this section n within time second after average, and with its process as the start time of this n time second the sign indicating number pseudorange value after average:

3) at last the sign indicating number pseudorange value after average and the carrier doppler of this n in the time calculate the smooth value of yard pseudorange in this moment according to the process of the start time of top formula:

Wherein filter window length be different from the existing method always with the fixed value Calculation Method, expression as follows:

$n=\left\{\begin{array}{ccc}t& \mathrm{when}& t<N\\ N& \mathrm{when}& t\&GreaterEqual;N_s\end{array}\right.$

In the above formula, n is variable smooth window length, and unit is a time second; N is predefined fixedly filter window length; T is a time point;

Be the corresponding wavelength of transmission frequency; Δ f _RDoppler measurement amount for the receiver generation;

Be the pseudorange of Doppler after level and smooth;

For the pseudorange of start time is estimated; ρ (t _i) be original pseudo range measurement amount;

Be time period t _oTo t _iLast initial time t _oSign indicating number pseudorange estimator;

For on receiver A, for j satellite, at the sign indicating number pseudorange of moment t.

The present invention has following advantage and is showing effect:

1) this method is dynamically to adjust the auxiliary correlator method that suppresses multipath of carrier wave of filter window length, in the time, is not to wait pending data merely at the N that begins; But filter window length adds one successively; Until reaching pre-set filter window length N, after this filter window length remains unchanged, and makes it can get into filter state faster; Raising is resolved bearing accuracy in the pseudorange precision of first N in the time thereby improve.With respect to traditional filter window length fixed method, this method is more flexible, can get into filter state fast, and just can get into filter state after needn't waiting for time of a filter window length.The starting stage of location; System is unsettled; Anchor point is beated bigger, bigger deviation possibly occur, and initial just assisting with more accurate carrier doppler is not that very accurate sign indicating number pseudorange has very big meaning comparatively speaking in the location so; This method just can improve bearing accuracy in the starting stage, and especially there is great role the location for being implemented in the urban environment that GPS location exists situation that serious multipath disturbs and other neighbourhood noises accurately.

2) method of dynamically adjusting the carrier doppler auxiliary code pseudorange of filter window length can get into filter state sooner; In fact; In case collect yard pseudorange and carrier doppler, just can get into filter state, thereby the exact value after the filtering can be provided faster.

3) filtered method of the present invention; Utilized sign indicating number pseudorange and the output valve of carrier doppler after the Base-Band Processing equally, length of window has been made dynamic adjustment, compared with existing wave filter framework; It does not increase extra software and hardware consumption when improving performance.

4) as the time t that gets into positioning calculation during more than or equal to predefined filtering window length N, that

After this each corresponding constantly filter length n is N, filtered is not exerted an influence; And as time t during less than N, this moment, n dynamically adjusted, and n just adds one behind filter value of every output, and beginning filtering suppresses noise, improves bearing accuracy.

Description of drawings

Fig. 1 is a prior art GPS receiver complete machine higher-level system structured flowchart;

Fig. 2 is the active link figure of prior art hyperchannel base band signal process engine;

Fig. 3 is the processing procedure of prior art carrier doppler auxiliary code pseudorange;

Fig. 4 is the processing procedure that the present invention dynamically adjusts the carrier doppler auxiliary code pseudorange of filter window length.

Embodiment

Referring to Fig. 1, be receiver complete machine higher-level system structured flowchart.Wherein comprise: radio-frequency antenna, low noise amplifier, radio-frequency module, benchmark running clock source, base band signal process engine, positioning calculation, man-machine interface, power supply etc.Behind antenna reception gps signal, at first pass through low noise amplifier, reduce noise in the time of amplifying signal, then through the radio frequency module.The radio frequency module is down-converted to the carrier frequency of signal near the intermediate frequency by L1 frequency range (1.575GHz), and reduces out-of-band noise with BPF. and disturb.Frequency scheme according in the receiver design proposal derives local oscillator by reference oscillator through frequency synthesizer.After the optical mixing process, kept carrier doppler and spreading code, through follow-up base band signal process process, carried out the two dimension of spreading code and carrier frequency and catch, followed the tracks of afterwards and go up satellite-signal, therefrom correct, continuous solution accesses navigation message, is used for positioning calculation.Behind the location,,, load cartographic information, carry out navigator fix etc. through man-machine interface through NMEA agreement and upper machine communication.

Referring to Fig. 2, be the active link figure of hyperchannel base band signal process engine, digital medium-frequency signal derives from the radio frequency sampling signal, main process comprise catch, bit synchronous, tracking, synchronizing sub-frame and positioning calculation etc.

During the receiver initialization, C/A is sign indicating number not to align with code stream that receive because local oscillator produces, and simultaneously, carrier frequency also owing to there is the influence of Doppler effect, needs acquisition procedure so, carries out the two dimension of spreading code-carrier frequency and catches.The result who catches generally be local code with the sign indicating number deviation that receives in 0.5 chip, carrier frequency and the carrier frequency that receives differ and are no more than 100Hz.

After capturing signal, then realize bit synchronous.Every bit text cycle is 20ms, so must find bit boundaries; After finding bit boundaries, get into tracking mode, code phase and carrier frequency are further aimed at, and obtain their exact value.After the tracing process, receiver is then accomplished the synchronizing sub-frame process, takes out navigation message.At last, resolve the information such as position, speed of receiver with least square method.

Referring to Fig. 3, be the treatment scheme of existing carrier doppler auxiliary code pseudorange algorithm.Introduction by the front can be known, after baseband portion is finished dealing with, according to the trace information of carrier wave ring, can obtain the measured value of carrier doppler; On the other hand, obtain satellite position and satellite-signal launch time according to navigation message decoding, the two combination obtains pseudorange value.After the data of having collected a N time (the N here is predefined filter window length), in the time, at first according to acquired carrier doppler value and sign indicating number pseudorange value, elder generation is with the sign indicating number pseudorange value of carrier doppler at level and smooth N time point at each N; Next, the value that N value is obtained after average is as the smooth value of the sign indicating number pseudorange of the start time in the time period of this N; The smoothing code pseudorange of last binding time starting point and carrier doppler calculate the smooth value of the sign indicating number pseudorange of N time.The sign indicating number pseudorange that obtains combines satellite position to resolve information such as obtaining more accurate receiver location, speed again.

Referring to Fig. 4, be the treatment scheme of the carrier doppler auxiliary code pseudorange algorithm after optimizing among the present invention.Existing method is the pseudorange smooth value of the start time at first calculating during this period of time according to the initial measurement of pseudorange in one filtering period and carrier doppler in the disposal route of Fig. 3, and combines this value and interior during this period of time carrier doppler to obtain the smooth value of the pseudorange of each interior during this period of time time point.

This method and existing method different are the value for filter window length; When t＜N, n=t; Otherwise n is fixed as N.Wherein t is the time that receiver gets into positioning calculation; N is corresponding each filter window length constantly; N is predefined filter window length.For simplicity, the n does not here add the subscript of corresponding moment point.Carrier doppler and sign indicating number pseudorange value in conjunction with we obtain from base band through a series of computation process, obtain the smooth value of each sign indicating number pseudorange constantly at last.Obviously this method is more flexible, can get into filter state fast, and just can get into filter state after needn't waiting for time of a filter window length.The starting stage of location; System is unsettled; Anchor point is beated bigger; Bigger deviation possibly occur, initial just assist with more accurate carrier doppler is not that yard pseudorange is to have here each of attention of very big meaning to comprise the N time in firm entering positioning calculation stage constantly very accurately comparatively speaking in the location so.

Claims (1)

1. a filtered method that suppresses multipath interference and noise is the basis with a carrier doppler and a sign indicating number pseudorange that obtains after the Base-Band Processing, adopts carrier doppler to come the auxiliary code pseudorange; Accurate sign indicating number pseudorange after obtaining smoothly, it is characterized in that: the wave filter that dynamic adjustment filter window length is set substitutes the fixedly wave filter of filter window length, begins promptly to get into filter state from first pseudorange collected and carrier doppler data; Filter window length is from initial one, and behind smooth value of per second output after this, carry out pseudorange when level and smooth filter window length add one successively; After reaching predefined filter window length N; Filter window length remains unchanged, and under each filter window length, carries out the computation process of three steps; Obtain the final pseudorange smooth value in this moment, the computation process of three steps is following:

1) obtain after the sign indicating number pseudorange and carrier doppler of a filter window length n, at first the priori estimates of the sign indicating number pseudorange after the filtering that calculates the corresponding moment of the following formula of process:

i＝0，1，2...n

2) then; The priori estimates of the individual sign indicating number pseudorange after treatment of the n that utilizes filter window length n to comprise in second; Obtain the sign indicating number pseudorange average of this section n within time second after average, and with its process as the start time of this n time second the sign indicating number pseudorange value after average:

$\stackrel{\&OverBar;}{\mathrm{\&rho;}}\left(t_0\right)=\frac{1}{n}\underset{i=0}{\overset{n}{\mathrm{\&Sigma;}}}\widehat{\mathrm{\&rho;}}\left(t_0\right)$

3) at last the sign indicating number pseudorange value after average and the carrier doppler of this n in the time calculate the smooth value of yard pseudorange in this moment according to the process of the start time of top formula:

Wherein filter window length be different from the existing method always with the fixed value Calculation Method, expression as follows:

$n=\left\{\begin{array}{ccc}t& \mathrm{when}& t<N\\ N& \mathrm{when}& t\&GreaterEqual;N_s\end{array}\right.$

In the above formula, n is variable smooth window length, and unit is a time second; N is predefined fixedly filter window length; T is a time point;

Be the corresponding wavelength of transmission frequency; Δ f _RDoppler measurement amount for the receiver generation;

Be the pseudorange of Doppler after level and smooth;

For the pseudorange of start time is estimated; ρ (t _i) be original pseudo range measurement amount; Be time period t ₀To t _iLast initial time t ₀Sign indicating number pseudorange estimator;

For on receiver A, for j satellite, at the sign indicating number pseudorange of moment t.

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