CN102645661B - Method for processing tracking loop signals in GPS (global positioning system) software receiver and device - Google Patents

Abstract

The invention provides a method for processing tracking loop signals in a GPS (global positioning system) software receiver. The method includes quantifying local carriers; and accurately tracking GPS signals on the basis of the quantified local carriers and the received GPS signals. By the aid of the method, most of floating-point operation in a tracking loop is eliminated, the sensitivity of the tracking loop is guaranteed, and the processing performance of the tracking loop is enhanced. In addition, the method is low in complexity and calculation, and is also suitable for real-time application to tracking loops in embedded software receivers.

Description

Track loop signal processing method in GPS software receiver and device

Technical field

The present invention relates to GLONASS (Global Navigation Satellite System) GNS S (Global Navigation Satellite System) software navigation receiver, particularly relate to the track loop of GPS software receiver.

Background technology

Along with Embedded Mobile platform stores and the rapid raising of arithmetic capability, for GPS software receiver portability provides huge development space, but due to the existence of large amount of complex computing in Base-Band Processing, the real time implementation of software receiver is still the ultimate challenge faced at present.Through catching operation obtain the Doppler shift of satellite-signal and the initial value of code phase after, track loop will be entered into, carry out following the tracks of accurately continuously to satellite-signal, demodulate required navigation data, and obtain final position and velocity information by extracting ephemeris, its computation of pseudoranges, satellite position calculation, receiver user position calculation etc.Visible, in GPS software receiver, mainly following two operations consume most time and resource: catch in operation and there is a large amount of related operation, track loop also has intensive numerical operation.For the real time implementation of software receiver, except improving the speed of capturing satellite signal, the processing speed and the efficiency that improve track loop are also very important.

In Embedded GPS software receiver, the computing of tracking phase is the most intensive, and operand is maximum, therefore also becomes maximum link consuming time, and how realizing efficient track loop signal transacting becomes the key point realizing GPS software receiver real time implementation process.The method of the current raising track loop signal transacting performance FLL mainly contained based on square wave digital integrator assists the algorithm filter of phaselocked loop, and phase-locked FLL shares the discriminator algorithm etc. of four-quadrant arctan function unit.These disposal routes require higher for resource and arithmetic capability, and algorithm complex is high and conversion speed slow, are difficult to realize following the tracks of fast.In addition, these methods need to perform on the PC that performance is high, and the embedded device of main flow is all monokaryon at present, and do not support multinuclear or multithreading task, therefore, said method can not be applicable to the applied environment of embedded device well.

Summary of the invention

Therefore, the object of the invention is to the defect overcoming above-mentioned prior art, one track loop signal processing method is fast provided, while the sensitivity of guarantee tracking phase, improve the treatment effeciency of track loop, achieve the real-time follow-up to gps signal.

The object of the invention is to be achieved through the following technical solutions:

On the one hand, the invention provides a kind of for the track loop signal processing method in GPS software receiver, described method comprises:

Step 1, quantizes local carrier;

Step 2, realizes the accurate tracking to gps signal based on the local carrier after quantification and the gps signal received.

In technique scheme, step 1) can comprise the following steps:

Step 11) according to quantification gradation n, carrier function value Y (t) is on average divided into n territory by the function curve of local carrier, wherein n is determined by quantizing bit number;

Step 12) calculate phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region;

Step 13) be mapped to all phase values in each region of described phase place corresponding to this region carrier function codomain in a carrier function value, to obtain the local carrier after quantizing.

In technique scheme, described quantizing bit number can be 4bit, 3bit, 2bit or 1bit, and described quantification gradation n can be 16,8,4,2 or 3.

In technique scheme, step 13) before can also comprise step 1) each territory of carrier function value Y (t) of obtaining and step 2) each region of phase place of obtaining amplifies certain multiple, makes it become the step of integer field respectively.

In technique scheme, step 1) can comprise the following steps:

Step 11 ') with Y (t) higher limit/2, null value and Y (t) lower limit/2 for the function curve of local carrier is divided into multiple different region by Y (t) value by cut-point;

Step 12 ') calculate phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region;

Step 13 ') all phase values in each region of described phase place are mapped to corresponding Y (t) higher limit/2, null value and Y (t) lower limit/2 one of them, to obtain the local carrier after quantizing.

Another aspect, present invention also offers the track loop signal processing apparatus in a kind of GPS software receiver, described device comprises: quantization modules, quantizes local carrier; Tracking module, for the computing carrying out being correlated with based on the local carrier after quantizing and the gps signal that receives to realize the accurate tracking to gps signal.

Wherein, carrier function value Y (t) can be on average divided into n territory according to quantification gradation n by the function curve of local carrier by described quantization modules, and wherein n is determined by quantizing bit number; Calculate the phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region; And the carrier function value be mapped to by all phase values in each region of described phase place in the carrier function codomain corresponding to this region, to obtain the local carrier after quantizing; N can be 16,8,4,2 or 3.

In said apparatus, each territory of carrier function value Y (t) and each region of phase place before phase value function value being mapped, can also be amplified certain multiple, make it become integer field respectively by described quantization modules respectively.

In said apparatus, described quantization modules can with Y (t) higher limit/2, null value and Y (t) lower limit/2 for the function curve of local carrier be divided into multiple different region by Y (t) value by cut-point; Calculate the phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region; And all phase values in each region of described phase place are mapped to corresponding Y (t) higher limit/2, null value and Y (t) lower limit/2 one of them, to obtain the local carrier after quantizing.

Another aspect, present invention also offers the track loop in a kind of GPS software receiver, and described track loop comprises track loop signal processing apparatus as above.

Another aspect, the invention provides a kind of GPS software receiver, and described GPS software receiver comprises above-mentioned track loop.

Compared with prior art, the invention has the advantages that:

In the signal processing of track loop, by local carrier is quantized, so that the trigonometric function operation in track loop signal transacting is mapped as integer arithmetic, eliminate floating-point operations most in tracking loop, while ensureing track loop sensitivity, improve the handling property of track loop.And the method complexity and operand are all lower, be also suitable for be embedded software GPS tracking loop real time implementation application.

Accompanying drawing explanation

Referring to accompanying drawing, embodiments of the present invention is further illustrated, wherein:

Fig. 1 is the 4Bit quantization function regional partition schematic diagram according to the embodiment of the present invention;

Fig. 2 is the 3Bit quantization function regional partition schematic diagram according to the embodiment of the present invention;

Fig. 3 is the 2Bit quantization function regional partition schematic diagram according to the embodiment of the present invention;

Fig. 4 is the 1Bit quantization function regional partition schematic diagram according to the embodiment of the present invention;

Fig. 5 is the 1Bit quantization function regional partition schematic diagram of the optimization according to the embodiment of the present invention;

Fig. 6 is the result schematic diagram of the emulated data process to different length according to the embodiment of the present invention;

Fig. 7 is the result schematic diagram to 6 frame real data process according to the embodiment of the present invention;

Fig. 8 is the tracking results schematic diagram of the local carrier adopting 1Bit to quantize in high s/n ratio environment;

Fig. 9 is the tracking results schematic diagram of the local carrier adopting 1Bit to quantize in low signal-to-noise ratio environment;

Figure 10 is the tracking results schematic diagram of the local carrier adopting the 1Bit through optimizing to quantize according to the preferred embodiment of the invention.

Embodiment

In order to make object of the present invention, technical scheme and advantage are clearly understood, below in conjunction with accompanying drawing, by specific embodiment, the present invention is described in more detail.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.

In order to understand the present invention better, first tracking loop and its signal processing are simply analyzed.GPS, after realizing signal capture, obtains the guestimate to code phase and carrier frequency, then needs the accurate estimation utilized tracking loop to obtain to code phase and carrier frequency, to realize the comparatively meticulous tracking to gps signal.In fact the signal transacting of track loop is exactly for initial value with the rough code phase captured and carrier doppler translation, realize local signal (code phase and local carrier) and the accurate synchronization of gps signal received, thus obtain the carrier frequency of gps signal and the accurate estimation of code phase to extract the navigation message of gps satellite.That is the ultimate principle of tracking loop is actually the frequency of constantly adjustment local oscillator, and the local signal making it produce and the gps signal received match.Tracking loop comprises carrier tracking loop (being called for short carrier wave ring, for accurately estimating the carrier frequency of gps signal) and code tracking loop (for accurately estimating the code phase of gps signal).

For initial alignment, simple analysis is carried out for the operand in carrier loop signal processing below.

In carrier tracking loop, it mainly comprises following calculating process:

The demodulation computing of in-phase end (I road):

$D\left(n\right)\cos \left({\mathrm{\ω}}_{\mathrm{IF}}n\right)\cos ({\mathrm{\ω}}_{\mathrm{IF}}+\mathrm{\φ})=\frac{1}{2}D\left(n\right)\cos \left(\mathrm{\φ}\right)+\frac{1}{2}D\left(n\right)\cos (2{\mathrm{\ω}}_{\mathrm{IF}}n+\mathrm{\φ})---\left(1.1\right)$

The demodulation computing of orthogonal end (Q road):

$D\left(n\right)\cos \left({\mathrm{\ω}}_{\mathrm{IF}}n\right)\sin ({\mathrm{\ω}}_{\mathrm{IF}}+\mathrm{\φ})=\frac{1}{2}D\left(n\right)\sin \left(\mathrm{\φ}\right)+\frac{1}{2}D\left(n\right)\sin (2{\mathrm{\ω}}_{\mathrm{IF}}n+\mathrm{\φ})---\left(1.2\right)$

In-phase end (I road) exports:

$I=\frac{1}{2}D\left(n\right)\cos \left(\mathrm{\φ}\right)---\left(1.3\right)$

Orthogonal end (Q road) exports:

$Q=\frac{1}{2}D\left(n\right)\sin \left(\mathrm{\φ}\right)---\left(1.4\right)$

Finally, phase error:

$\frac{Q}{I}=\frac{\frac{1}{2}D\left(n\right)\sin \left(\mathrm{\φ}\right)}{\frac{1}{2}D\left(n\right)\cos \left(\mathrm{\φ}\right)}=\tan \left(\mathrm{\φ}\right)---\left(1.5\right)$

$\mathrm{\φ}={\tan }^{-1}\left(\frac{Q}{I}\right)$ (the phase demodulation function of carrier wave ring) (1.6)

As can be seen from above-mentioned formula, homophase and orthogonal two-way local carrier signal (cos (ω are concentrated on for calculating main in carrier wave ring _iF+ φ) and sin (ω _iF+ φ)) with receive signal (cos (ω _iFthe computing of multiplication operation n)) and phase demodulation function, wherein remove beyond multiplying and also comprise a large amount of trigonometric function operation, these trigonometric function operations are all floating point arithmetics in specific implementation, and the efficiency of the computing of floating number on embedded device is relatively low.In addition, in track loop, need ceaselessly to adjust phase place and frequency, what guarantee was correct demodulates navigation data.Suppose that RF front-end sampling rate is 5.714MHz (GP2015), so every millisecond of navigation data is sampled as 5714 points, and the data often processing 1 millisecond in carrier tracking loop will circulate 5714 aforesaid operations.

For initial alignment, as long as first three frame usually obtaining the navigation message of gps satellite just can be located.The elementary cell of navigation message is the prime frame reaching 1500bit, and its transfer rate is 50bps, and therefore 30s could pass a prime frame.A prime frame comprises 5 subframes (the long 6s of each subframe), and the 1st, 2,3 subframes respectively have 10 code words, and each code word is 30bit; The data bits that therefore can calculate first three subframe is 3 × 6000ms × 5714=102852000 (3 represent 3 subframes, the data length of 6000 milliseconds of expressions subframe), the number of times of tracking loop circular treatment that Here it is.In actual applications, owing to receiving the randomness of navigation signal time, can not ensure just in time to process from the first frame of navigation data, therefore this cycle index is minimum value on knowledge theory, carries out calculated amount analysis for the time being herein with this theoretical minimum value.

Therefore, for the situation of initial alignment, the floating multiplication operation times existed in carrier loop is 102852000 × 2=205704000 (because being mainly included in the multiplication operation of homophase and orthogonal two-way local signal and Received signal strength in carrier wave ring); Trigonometric function operation number of times is similarly 205704000 times (can as can be seen from formula 1.3 and 1.4).In addition, usually for the renewal frequency of phase place be 1ms once, that is phase detector is that 1ms upgrades a secondary data, will process 3 frame data altogether, every frame 6000ms, and the operation times of phase detector intermediate cam function is 18000 times (see formula 1.6).

In code tracking loop, be different from the phase demodulation function that carrier tracking loop adopts the phase demodulation function that it adopts is: that is except the homophase in similar and above-mentioned carrier wave ring is with except orthorhombic phase calculates, the result of the phase detector in code tracking loop be by morning code, instantaneous code, Wan Ma tri-road signal accumulation generate, the process of accumulation is the result that the signal of two-phase three tunnel out of phase is multiplied with the signal contraposition received and then is added respectively.Therefore, the actual calculating comprising three tunnel two-phases in code tracking loop, for first location, its theoretical minimum operation times is that 3 × 6000ms × 5714 × 3 × 2=617112000 time (3 refer to three road signals, 2 refer to homophase and orthorhombic phase), in each computing, wherein comprise a floating add computing and a floating multiplication computing.Same code tracking loop is also 1ms for the update cycle of phase place, is adjusted after processing 1ms data by phase detector result, for code phase discriminator, adopts then in the calculating of phase demodulation function, floating multiplication computing is 8 × 18000=144000 time, floating add computing is 6 × 18000=108000 time, extracting operation is 4 × 18000=72000 time, and so large calculated amount makes on embedded receiver, realize real-time follow-up and becomes very difficult.

Can be found out by above-mentioned analysis, in the process of track loop processing signals, a large amount of computings concentrates in the multiplication operations of trigonometric function operation and two-way local signal and input signal.In order to reduce operand, prior art is all at the enterprising Row sum-equal matrix of the structure of two loops, but requires higher for the resource of equipment and arithmetic capability.

In one embodiment of the invention, a kind of track loop signal processing method for GPS software receiver is provided.The method, thus realizes quantizing local carrier with by judging that corresponding functional value is given in the interval at phase place place by the mapping relations of setting up phase place and carrier function value; Then the computing carrying out based on the local carrier after quantification and the gps signal received being correlated with is to realize the accurate tracking to gps signal.Therefore, the method save intensive trigonometric function operation consume a large amount of time, can realize following the tracks of fast.Preferably, trigonometric function can be mapped as integer, to eliminate most floating-point operation, thus promote the signal transacting efficiency of track loop.

Below with local orthorhombic phase carrier function: for example illustrates the concrete steps of the method.It will be understood by those skilled in the art that the character (i.e. the relation of sine function and cosine function) due to trigonometric function itself, the method is similarly also applicable to local homophase carrier wave.More specifically, the method mainly comprises the following steps:

Step 1) according to quantification gradation n by the function curve of local carrier (such as, the sin cos functions of local carrier, can see Fig. 1-Fig. 5) be on average divided into n territory (also can be called carrier function codomain, also can referred to as function value or codomain) by carrier function value Y (t); Wherein, quantification gradation n can be the detailed description of (can vide infra composition graphs 1-Fig. 5 to step 1) determined according to quantizing bit number (such as, 4Bit, 3Bit, 2bit, 1bit etc.)).

Step 2) calculate phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region (also can be called phase field);

Step 3) set up quantification mapping function, by the carrier function value (also can referred to as functional value) in the carrier function codomain that all phase values in each region of phase place are mapped to corresponding to this region, to obtain the local carrier after quantizing;

Step 4) realize the accurate tracking to gps signal based on the local carrier after quantification and the gps signal received.

Quantize in the method to as if local carrier, namely first local carrier is quantized, local carrier is multiplied by mutually with the gps signal received carries out follow-up operation afterwards, thus in actual operation, reduce intensive trigonometric function operation amount.Should be understood that the symmetry according to sin cos functions, the functional value distribution of half period before only calculating, the functional value distribution of rear half period can draw according to the function distribution reckoning of front half period.

Wherein, in step 1) in quantification gradation n can be 16,8,4 or 2 etc., quantizing process based on described grade also can be called that 4Bit quantizes, 3Bit quantizes, 2Bit quantizes or 1Bit quantizes, the concrete quantizing process hereafter will discussed respectively by reference to the accompanying drawings on each quantification gradation respectively accordingly.In a preferred embodiment, determine the quantification gradation adopted according to the result of catching, if the number of satellite captured fewer (signal intensity is lower), just adopt high-grade quantification, if contrary, then adopt low-grade quantification to improve arithmetic speed.Such as, if the number of satellite captured is 4, then 4bit can be adopted to quantize or 3bit quantification; If the number of satellite captured is greater than 4 but be less than or equal to 6, then 3bit or 2bit can be adopted to quantize; If the number of satellite captured is greater than 6 but be less than or equal to 8, then can quantize with 2bit or 1bit quantification; If the number of satellite captured is more than 8, then 1bit can be adopted to quantize.Above example is only for illustrative purposes, it will be understood by those skilled in the art that according to actual conditions or demand, selects quantification gradation neatly.

To carry out these four kinds of quantification gradations of 4Bit, 3Bit, 2Bit, 1Bit to local carrier, the method is described in more detail below.

1,4Bit quantizes

In step 1) according to quantification gradation n, carrier function value Y (t) is on average divided into n territory by the function curve of local carrier.

4Bit is quantized, quantification gradation n=2 ⁴=16 grades, suppose that the amplitude of local carrier is 1, then the value after local carrier quantification is-1 to 1.According to the symmetry of trigonometric function, first analyze 0 to the mapping relations on π, can being expressed as of local orthorhombic phase carrier wave:

Fig. 1 gives the 4Bit quantization function regional partition schematic diagram according to the embodiment of the present invention.Wherein, the first half of function curve is on average divided into 8 pieces by the value of Y (t) by the number of degrees first quantized according to 4Bit, and the phase place calculated corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region, then the value in each region are mapped as corresponding functional value.According to the symmetry of sin cos functions, the functional value distribution of half period before only calculating, the functional value distribution of rear half period can draw according to the function distribution reckoning of front half period, decreases trigonometric function operation amount like this in actual operation.

Then, in step 2) calculate phase place corresponding to each Y (t) value cut-point, these phase places are divided into multiple different region.

As shown in Figure 1, functional value is distributed between 0 to 1 on 0 to π interval, and orthorhombic phase function is split into multiple phase field: [0, x1], [x1, x2], [x2, x3] ... [x15, x16], be the signal of 1 for amplitude, Y (t) value is split into 8 territories: [0,0.125], [0.125,0.25], [0.25,0.375], [0.375,0.5], [0.5,0.625], [0.625,0.75], [0.75,0.875], [0.875,1].Corresponding phase place starting point is obtained respectively: [0,0.12533], [0.12533 according to the separation of Y (t) codomain, 0.25268.], [0.25268,0.38440], [0.38440,0.52360], [0.52360,0.67513], [0.67513,0.84806], [0.84806,1.06511], [1.06544,1.57080].

Preferably, in execution step 3) set up and quantize before mapping function, can respectively by step 1) and step 2) obtain Y (t) codomain and phase field are amplified certain multiple, it is made to become integer field respectively, thus reduce the number of times of floating-point operation further, to improve the processing speed of track loop.Such as, amplify 10000 times, obtain Y (t) codomain: [0,1250], [1250,2500], [2500,3750], [3750,5000], [5000,6250], [6250,7500], [7500,8750], [8750,10000].Corresponding phase field is: [0,12533], [12533,25268.], [25268,38440], [38440,52360], [52360,67513], [67513,84806], [84806,106511], [106544,157080].

Then, in step 3) set up quantification mapping function, by the carrier function value (also can referred to as functional value) in the carrier function codomain that all phase values in each region of phase place are mapped to corresponding to this region, to obtain the local carrier after quantizing.

Such as, can by phase field [0,12533] all phase values in are all mapped to the intermediate value 625 of carrier function codomain corresponding to this phase field [0,1250], the like, phase field [12533,25268.], [25268,38440], [38440,52360], [52360,67513], [67513,84806], [84806,106511], [106544,157080] can be mapped to the intermediate value 1875,3125,4375,5625,6875,8125,9375 of the carrier function codomain corresponding to it respectively.Those skilled in the art should be understood that the above-mentioned intermediate value being mapped to carrier function codomain is only limit for illustrative purposes instead of to this, also can be mapped to other values in respective function codomain.Thus set up phase place function value and arrive interval 0 on quantification mapping function (see following quantification mapping function S (t)):

$S\left(t\right)=\left\{\begin{array}{cc}625& 0\&le;\mathrm{\&theta;}<12533\\ 1875& 12533\&le;\mathrm{\&theta;}<25268\\ 3125& 25268\&le;\mathrm{\&theta;}<38440\\ 4375& 38440\&le;\mathrm{\&theta;}<52360\\ 5625& 52360\&le;\mathrm{\&theta;}<67513\\ 6875& 67513\&le;\mathrm{\&theta;}<84806\\ 8125& 84806\&le;\mathrm{\&theta;}<106511\\ 9375& 106500\&le;\mathrm{\&theta;}<157080\end{array}\right.$

Corresponding relation according to trigonometric function:

sin(α+π)＝-sinα，sin(α-π)＝-sinα (1.8)

The Function Mapping relation of other intervals (such as π is interval to 2 π) can be obtained, finally obtain the local carrier quadrature component after quantizing.

In like manner, according to the relation of sine function and cosine function:

$\sin (\mathrm{\&alpha;}+\frac{\mathrm{\&pi;}}{2})=\cos \mathrm{\&alpha;},$ $\cos (\mathrm{\&alpha;}+\frac{\mathrm{\&pi;}}{2})=-\sin \mathrm{\&alpha;}---\left(1.9\right)$

The quantification mapping function of local carrier in-phase component can be set up, and obtain the local carrier in-phase component after quantizing.It should be noted that, no matter be quadrature component or in-phase component, they have an initial phase place, might not be zero-based, first to be transformed within the scope of 2 π if phase place is greater than 2 π, then from initial phase, judge it falls within which interval of mapping function, revests corresponding round values.

Finally, in step 4) carry out computing to realize the accurate tracking to gps signal based on the local carrier after quantizing with the gps signal received.

Such as, the local carrier after obtained quantification is multiplied with the gps signal received, then calculates phase demodulation function of carrier tracking loop and code tracking loop etc.In an embodiment of the present invention, do not limit the concrete track loop treatment step after local carrier quantizes, it can be identical with the processing procedure of existing track loop.In the method, carrier function value due to this locality is exaggerated N and doubly becomes integer, therefore its accumulated value also becomes original N times, as can be seen from the phase demodulation function of two loops, accumulated value amplifies same multiple and does not have any impact to identified result, but after being a cancellation floating-point operation, substantially increase operation efficiency.

2,3Bit quantizes

3Bit is quantized, quantification gradation n=2 ³=8 grades, suppose that the amplitude of local carrier is 1, then the value after local carrier quantification is-1 to 1.Equally according to the symmetry of trigonometric function, first analyze 0 to the mapping relations on π, the formula that can be expressed as (1.7) of local orthorhombic phase carrier wave.

Fig. 2 is the 3Bit quantization function regional partition schematic diagram according to the embodiment of the present invention.As shown in Figure 2, functional value is distributed between 0 to 1 on 0 to π interval, according to the number of degrees that 3Bit quantizes, the first half of function curve is on average divided into 4 pieces by the value of Y (t), then the phase place corresponding to each Y (t) value cut-point is calculated, these phase places are divided into multiple different region, then the value in each region are mapped as corresponding functional value.According to the symmetry of sin cos functions, the same functional value distribution only calculating front half period, the functional value of rear half period and the functional value distribution of in-phase component can draw according to the function distribution reckoning of front half period, decrease trigonometric function operation amount like this in actual operation.

As shown in Figure 2, orthorhombic phase functional value and Y (t) value are split into multiple territory, and Y (t) codomain is divided into: [0,0.25], [0.25,0.5], [0.5,0.75], [0.75,1]; Corresponding phase field is divided into: [0,0.25268], [0.25268,0.52360], [0.52360,0.84806], [0.84806,1.57080].Set up phase place function value arrive interval 0 to quantize similar mode with 4Bit upper mapping function:

$S\left(t\right)=\left\{\begin{array}{cc}125& 0\&le;\mathrm{\&theta;}<25268\\ 375& 25268\&le;\mathrm{\&theta;}<52360\\ 625& 52360\&le;\mathrm{\&theta;}<84806\\ 875& 84806\&le;\mathrm{\&theta;}<157080\end{array}\right.$

So far, the quadrature component of local carrier arrives 0 interval quantization function is set up.Then according to the corresponding relation formula (1.8) of trigonometric function and periodically set up the Function Mapping relation of π to 2 π intervals, the 3Bit of such multicarrier orthogonal component quantizes to complete, and in like manner sets up the quantification mapping function of carrier wave in-phase component according to the relational expression (1.9) of sine function and cosine function.

3,2Bit quantizes

2Bit is quantized, in signal transacting, adopt many quantification techniques, when not being harsh especially for sensitivity requirement, 2Bit quantizes the handling property that effectively can improve software radio, at the RF fore-end of GPS, most quantization levels all have selected 2Bit, and it is little for the impact of sensitivity by analysis, be well suited for business machine uses, what only have the GPS at minority tip to adopt is that 8Bit quantizes progression.

The quantification gradation n=2 that 2Bit quantizes ²=4 grades, suppose that the amplitude of local carrier is 1, then local carrier supposes after quantizing that the amplitude of local carrier is 1, then the value after local carrier quantification is-1 to 1.Equally according to the symmetry of trigonometric function, first analyze 0 to the mapping relations on π, the formula that can be expressed as (1.7) of local orthorhombic phase carrier wave.

Fig. 3 is the 2Bit quantization function regional partition schematic diagram according to the embodiment of the present invention.As shown in Figure 3, functional value is distributed between 0 to 1 on 0 to π interval, according to the number of degrees that 2Bit quantizes, the first half of function curve is on average divided into 2 pieces by the value of Y (t), then the phase place corresponding to each Y (t) value cut-point is calculated, these phase places are divided into several different region, then the value in each region are mapped as corresponding functional value.According to the symmetry of sin cos functions, the same functional value distribution only calculating front half period.

As shown in Figure 3, Y (t) codomain is divided into: [0,0.5], [0.5,1]; Corresponding phase field is divided into: [0,0.52360], [0.52360,1.57080].

Set up phase place function value to arrive interval 0 upper mapping function:

$S\left(t\right)=\left\{\begin{array}{cc}250& 0\&le;\mathrm{\&theta;}<52360\\ 750& 52360\&le;\mathrm{\&theta;}<157080\end{array}\right.$

So far, the quadrature component of local carrier arrives 0 interval quantization function is set up.Then according to the corresponding relation formula (1.8) of trigonometric function and periodically set up the Function Mapping relation of π to 2 π intervals, the 2Bit of such multicarrier orthogonal component quantizes to complete, and in like manner sets up the quantification mapping function of carrier wave in-phase component according to the relational expression (1.9) of sine function and cosine function.

4,1Bit quantizes

Quantizing for 1Bit, is adopt extreme quantification manner in signal transacting, and 1Bit quantizes to mean that the value of signal can only simply be distinguished by two values, and two quantized values significantly will certainly promote operation efficiency, but also will be very serious for the impact of sensitivity.

The quantification gradation n=2 that 1Bit quantizes ¹=2 grades, suppose that the amplitude of local carrier is 1, then local carrier supposes after quantizing that the amplitude of local carrier is 1, then the value after local carrier quantification is-1 to 1.Equally according to the symmetry of trigonometric function, first analyze the mapping relations on 0 to 2 π, the formula that can be expressed as (1.7) of local orthorhombic phase carrier wave.

Fig. 4 is the 1Bit quantization function regional partition schematic diagram according to the embodiment of the present invention.As shown in Figure 4, functional value is distributed between-1 to 1 on 0 to 2 π intervals, according to the number of degrees that 1Bit quantizes, function curve is divided into [-1 by the value of Y (t), 0], [0,1], corresponding phase field is divided into: [0,3.14159], [3.14159,6.28319].The intermediate value of each codomain of Y (t) is: 0.5 and-0.5 (that is, Y (t) higher limit/2 and Y (t) lower limit/2, suppose that Y (t) higher limit and lower limit are respectively 1 ,-1 in this embodiment).

Set up the mapping function in π interval, phase place function Zhi district 0 to 2:

$S\left(t\right)=\left\{\begin{array}{cc}1& 0\&le;\mathrm{\&theta;}<314159\\ -1& 314159\&le;\mathrm{\&theta;}<628319\end{array}\right.$

Wherein, phase field becomes integer field after being exaggerated 100000 times, and the value 1 and-1 of S (t) is that the intermediate value 0.5 and-0.5 of each codomain is amplified 2 times of round valuess obtained, and quantizes for above-mentioned 1Bit, its loss of significance is too large, will certainly have influence on tracking sensitivity.

In yet another embodiment of the present invention, on the basis that above-mentioned 1Bit quantizes, add one-level and quantize, make quantization level become 3, i.e. quantification gradation n=3.Fig. 5 gives the schematic diagram of the 1Bit quantization function regional partition after according to the optimization of the embodiment of the present invention.As shown in Figure 5, Y (t) value that 1Bit quantizes is decided to be :-0.5,0,0.5 (i.e. Y (t) higher limit/2, null value and Y (t) lower limit/2), then segments between phase region corresponding for the functional value of quantification.Phase field is divided into [0,0.52360], [0.52360,1.04720], [1.04720,2.09440], [2.09440,5.75959], [5.75959,6.28319]

Set up the mapping function in 0 to 2 π intervals:

$S\left(t\right)=\left\{\begin{array}{cc}0& 0\&le;\mathrm{\&theta;}<52360\\ 1& 52360\&le;\mathrm{\&theta;}<104720\\ 0& 104720\&le;\mathrm{\&theta;}<209440\\ -1& 209440\&le;\mathrm{\&theta;}<575959\\ 0& 575959\&le;\mathrm{\&theta;}<628319\end{array}\right.$

Below to when adopting the local carrier after quantizing to carry out signal transacting in track loop, the operand for initial alignment is analyzed.

(1). theoretical analysis

First analyze the operand that 4Bit quantizes, arrive for 0 on interval, phase place has been divided into 8 territories, and all will judge before each assignment that phase place is this moment interval at which, think that phase place is stochastic distribution at this, average search number of times is secondary, each search all will compare the bound of phase field, be equivalent to integer arithmetic, its number of times 4.5 × 2=9 time, will carry out the calculating of three tunnel out of phase signals of two-phase in accumulation, operation times is 6 times, and wherein each accumulation computing comprises two integers and takes advantage of (local quantization carrier wave is multiplied by input signal and is multiplied with code) and an integer to add computing, floating-point operation in phase demodulation function is also all converted in order to integer arithmetic, arrives for 0 quantized value outside interval is then calculated by the symmetry of trigonometric function and special function relation, increases a phase transition process, i.e. twice integer plus and minus calculation (wherein comprising a phase field to compare).

3Bit is quantized, arrives 0 on interval, phase place has been divided into 4 territories, and all will judge before each assignment that phase place is this moment interval at which, think that phase place is stochastic distribution equally, average search number of times is secondary, each search all will compare the bound of phase field, be equivalent to integer arithmetic, its number of times 2.5 × 2=5 time, will carry out the calculating of three tunnel out of phase signals of two-phase in accumulation, operation times is 6 times, and wherein each accumulation computing comprises two integers and takes advantage of (local quantization carrier wave is multiplied by input signal and is multiplied with code) and an integer to add computing, floating-point operation in phase demodulation function is also all converted in order to integer arithmetic, arrives for 0 quantized value outside interval is then calculated by the symmetry of trigonometric function and special function relation, increases a phase transition process, i.e. twice integer plus and minus calculation (comprising a phase field to compare).

2Bit is quantized, arrives 0 on interval, phase place has been divided into 2 territories, and all will judge before each assignment that phase place is this moment interval at which, think that phase place is stochastic distribution equally, average search number of times is secondary, each search all will compare the bound of phase field, be equivalent to integer arithmetic, its number of times 1.5 × 2=3 time, the calculating of three tunnel out of phase signals of two-phase will be carried out in accumulation, operation times is 6 times, and wherein each accumulation computing comprises two integers and takes advantage of (local quantization carrier wave is multiplied by input signal and is multiplied with code) and an integer to add computing, and the floating-point operation in phase demodulation function is also all converted in order to integer arithmetic.Arrive for 0 equally quantized value outside interval is then calculated by the symmetry of trigonometric function and special function relation, increases a phase transition process, i.e. twice integer plus and minus calculation (comprising a phase field to compare).

It is more special to quantize for 1Bit, and on 0 to 2 π intervals, phase place has been divided into 2 territories, and all will judge before each assignment that phase place is this moment interval at which, think that phase place is stochastic distribution equally, average search number of times is secondary, each search all will compare the bound of phase field, be equivalent to integer arithmetic, its number of times 1.5 × 2=3 time, the calculating of three tunnel out of phase signals of two-phase will be carried out in accumulation, operation times is 6 times, wherein each accumulation computing comprises two 1 integers and takes advantage of that (carrier wave is 1 or-1 after quantizing here, therefore do not need to do multiplication) and an integer add computing, floating-point operation in phase demodulation function is also all converted in order to integer arithmetic, because 1Bit quantizes to demarcate for the phase place in 0 to 2 π intervals, therefore do not need conversion.

1Bit for the employing 3 grades of quantification manners improved quantizes, and on 0 to 2 π intervals, phase place has been divided into 5 territories, and all will judge before each assignment that phase place is this moment interval at which, think that phase place is stochastic distribution equally, average search number of times is secondary, each search all will compare the bound of phase field, is equivalent to integer arithmetic, its number of times 3 × 2=6 time, the calculating of three tunnel out of phase signals of two-phase will be carried out in accumulation, operation times is 6 times because carrier wave is quantified as-1,1,0 this three number, on duty for-1 or 1 time only determine that symbol can be used as multiplying, on duty when being 0, because this time cumulative value is exactly 0, so original accumulation result is constant, directly do not do computing.Floating-point operation in phase demodulation function is also all converted in order to integer arithmetic, because 1Bit quantizes to demarcate for the phase place in 0 to 2 π intervals, does not also need conversion.

Visible, by adopting the track loop signal processing method of the embodiment of the present invention, to quantize local carrier, and trigonometric function operation is mapped as integer arithmetic, eliminate floating-point operations most in tracking loop, drastically reduce the area the operand of track loop, improve the handling property of track loop.

(2). experimental analysis

Inventor has also carried out following experiment to further illustrate method of the present invention to the lifting of the signal transacting performance of track loop and the impact on track loop sensitivity.Have employed two kinds of data in an experiment: emulated data and receive data on the spot.In the signal that GPS receives on the spot, its signal to noise ratio (S/N ratio) cannot be measured accurately, therefore the analysis for sensitivity causes difficulty, and simulate signal can be the signal to noise ratio (S/N ratio) of the mode control signal adding noise by people, in addition also can control signal parameter, such as select specific PRN, specific C/A code phase and the parameter such as IF-FRE and Doppler shift, for sensitivity analysis provides favourable support.Experimentation and result as follows:

(2.1) to the lifting of track loop signal transacting performance

First, use emulated data, to contrasting the operation efficiency that local carrier carries out the tracking algorithm of the track loop signal processing method of above-mentioned quantification and the original local carrier of existing employing according to the embodiment of the present invention.Inside emulated data, each value of navigation signal is all random, therefore the emulated data produced is each not identical, experiment porch adopts 1GHz ARMCortex-A8 processor, operating system is the S5PV210 development board of embedded Ubuntu-Linux, inside save as 256M byte, 100 experiments are repeated for often kind of method, result is averaging and obtains net result to facilitate contrast.When Fig. 6 sets forth emulated data (3 frame data and 6 frame data) of process different length, track loop signal processing time local carrier quantized according to the embodiment of the present invention and the contrast schematic diagram in existing track loop processing time.As can be seen from Figure 6, in an embodiment of the present invention, owing to quantizing local carrier, flops is decreased, so to the lifting of the efficiency of track loop very obvious, can realize following the tracks of fast.It is only the performance boost that 4Bit quantizes can reach 50%, 3Bit quantization algorithm is approximately 3 times for the lifting of tracking performance, 2Bit quantization algorithm is approximately 4 times for the performance boost of track loop, and 1Bit is quantized, because its quantization amplitude is maximum, therefore its performance boost is most effective, in initial alignment, the consuming time of tracking loop is reduced within 20 seconds from two points of halfs, nearly 8 times of performance boost, for improve 1Bit quantization method--3 grades of quantifications, its properties prompt also reaches more than 7 times.

Fig. 7 is the result that the True Data using Back Long View area, Beijing to gather on the spot carries out testing.Because the randomness of time of reception, probably miss the frame head of the first frame, in order to ensure to process 5 frame data, receiving and processing the data of 6 frames, adopt embedded S5PV210 development board platform to repeat 100 experiments to average equally.The result of the experiment shown in Fig. 7 demonstrates the result utilizing emulated data to draw as shown in Figure 6 further.As can be seen from Figure 7, for the data of same length, compared with existing track loop method, the track loop signal processing method of the embodiment of the present invention significantly enhances the processing speed of data, can realize following the tracks of fast.

For real time implementation requirement and say, the processing time of system should be less than the time span of the data stream of process, such guarantee processes data at the end of data stream or before terminating, for software GPS receiver, complete initial alignment and need process 3 subframes, the time span of each subframe is 6 seconds, therefore theoretical minimum needs the process data of 18 seconds, (in fact can than more than 18 seconds, because the beginning of reception starting point not necessarily the first frame), 1Bit in the embodiment of the present invention is quantized and 3 grades of quantifications, their processing speed is all within 14 seconds, therefore the processing capability in real time of GPS software receiver can be met.

(2.2) on the impact of track loop sensitivity

Experiment below for carrier wave quantization method of the present invention on the impact of track loop sensitivity.If the impact that carrier wave quantizes for sensitivity is very large, so performance boost is also nonsensical greatly again, and therefore, under most important Water demand, quantification at different levels is for the impact of tracking results.Consider that True Data cannot the factor of Measurement accuracy signal to noise ratio (S/N ratio), this experiment adopts emulated data to carry out, and first generate the emulated data of a large amount of different signal to noise ratio (S/N ratio), signal length is 600 milliseconds, No. PRN of setting satellite is 1 to 12, and sensitivity is from SNR=-35dB to SNR=-10dB.Inventors performed in a large amount of tracking tests and find, 4Bit, 3Bit quantize for sensitivity substantially without affect, under high s/n ratio, the tracking results of the local carrier adopting original local carrier, 4Bit and 3Bit to quantize is more clear, the result that its tracking results is followed original local carrier to follow the tracks of and obtained is substantially the same, and 2Bit and 1Bit quantizes to have a certain impact for sensitivity, especially 1Bit quantizes, but still can judge navigation data.

But under low signal-to-noise ratio, after adopting 1bit to quantize to local carrier, the tracking results obtained is difficult to judge navigation data.Such as, Fig. 8 shows 1Bit under high s/n ratio (-25dB < SNR <-10dB) and quantizes typical tracking results.Fig. 9 shows 1Bit under low signal-to-noise ratio (SNR=-32dB) and quantizes typical tracking results.In figs. 8 and 9, the first half is tracking results, follow-uply therefrom will extract navigation data, and the latter half is correlated results, to judge acquiring satellite whether success.The signal waveform of as can be seen from Figure 8 following the tracks of out is almost close to square wave, can be 1 or-1 by the gem-pure judgement navigation data of cross zero detecting method, and Fig. 9 is the tracking results that 1Bit quantizes at low signal-to-noise ratio, can find out that its signal waveform exported has been difficult to tell the value of navigation data.

And can the problems referred to above be made up after adopting the 1bit after optimizing in the preferred embodiment of the present invention to quantize.Figure 10 shows and quantize typical tracking results according to the 1Bit after the optimization of the embodiment of the present invention under low signal-to-noise ratio (SNR=-32dB).In Figure 10, the first half is tracking results, follow-uply therefrom will extract navigation data, and the latter half is correlated results, to judge acquiring satellite whether success.Figure 10 be with Fig. 9 in equal signal to noise ratio (S/N ratio) environment adopt 3 grades of 1bit quantized to quantize to local carrier after tracking results, well more a lot of than Fig. 9, the value of navigation data can be gone out accurately respectively, little on sensitivity impact.This is because owing to adding 0 value in adopting 3 grades of 1Bit quantized to quantize, therefore multiplication and the calculation of addition unit can be greatly reduced in processing procedure, its operation efficiency is almost quantized the same with 1Bit, equally also have and quantize higher sensitivity, therefore for realizing real time implementation carrier tracking loop than 1Bit.

In yet another embodiment of the present invention, additionally provide the track loop signal processing apparatus for GPS software receiver, this device comprises quantization modules and tracking module.Wherein this quantization modules quantizes local carrier according to above-mentioned method, thus obtains the local carrier after quantizing.This tracking module realizes the accurate tracking to gps signal based on the local carrier after quantification and the gps signal received.

In yet another embodiment of the present invention, additionally provide the track loop in a kind of GPS software receiver, described track loop comprises track loop signal processing apparatus mentioned above.

In yet another embodiment of the present invention, additionally provide GPS software receiver, this GPS software receiver adopts track loop mentioned above.

In sum, the track loop signal processing method of the embodiment of the present invention, by quantizing local carrier, then carries out computing, to realize the accurate tracking to gps signal according to the local carrier signal after quantification and the gps signal received.Analyze by experiment and can find out and the method reduce a large amount of floating-point operation amounts, improve the efficiency of track loop signal transacting, more enough realizations to gps signal fast and real-time follow-up, and tracking sensitivity not to be had much affect.The method improves the handling property of track loop while ensureing track loop sensitivity, and being very suitable for is the real time implementation application of embedded software GPS tracking loop.

Although the present invention is described by preferred embodiment, but the present invention is not limited to embodiment as described herein, also comprises done various change and change without departing from the present invention.

Claims (6)

1. the track loop signal processing method in GPS software receiver, described method comprises:

Step 1, quantizes local carrier;

Step 2, realizes the accurate tracking to gps signal based on the local carrier after quantification and the gps signal received;

Wherein, described step 1 comprises:

Step 11 ') with Y (t) higher limit/2, null value and Y (t) lower limit/2 for the function curve of local carrier is divided into multiple different territory by Y (t) value by cut-point, wherein Y (t) is local carrier function;

Step 12 ') calculate phase place corresponding to each cut-point, these phase places are divided into multiple different region;

Step 13 ') all phase values in each region of described phase place are mapped to corresponding Y (t) higher limit/2, null value and Y (t) lower limit/2 one of them, to obtain the local carrier after quantizing.

2. method according to claim 1, wherein step 13 ') before also comprise step 11 ') each territory of carrier function Y (t) value of obtaining and step 12 ') each region of phase place of obtaining amplifies certain multiple, makes it become the step of integer field respectively.

3. the track loop signal processing apparatus in GPS software receiver, described device comprises:

Quantization modules, quantizes local carrier;

Tracking module, for the computing carrying out being correlated with based on the local carrier after quantizing and the gps signal that receives to realize the accurate tracking to gps signal;

Wherein said quantization modules with Y (t) higher limit/2, null value and Y (t) lower limit/2 for the function curve of local carrier is divided into multiple different territory by Y (t) value by cut-point; Calculate the phase place corresponding to each cut-point, these phase places are divided into multiple different region; And all phase values in each region of described phase place are mapped to corresponding Y (t) higher limit/2, null value and Y (t) lower limit/2 one of them, to obtain the local carrier after quantizing, wherein Y (t) is local carrier function.

4. device according to claim 3, wherein said quantization modules is before mapping phase value function value, respectively certain multiple is amplified in each territory of carrier function Y (t) value and each region of phase place, make it become integer field respectively.

5. the track loop in GPS software receiver, described track loop comprises the device as described in claim 3 or 4.

6. a GPS software receiver, it comprises track loop as claimed in claim 5.