CN2896304Y - Device for providing estimation to signal-to-noise ratio of spread spectrum signal - Google Patents

Abstract

The utility model discloses a device that estimates SNR of the frequency-expansion signal which comprises: a radio frequency front that samples the frequency-expansion signal and obtains the signal; a Doppler Shift removing module that divides the digital signal into the in-phase component and the orthogonal component; an integral module that respectively implements relevant calculation of the in-phase component and the orthogonal component with the preset local pseudo-random noise (PRN) code in a preset time in order to get an in-phase component output and an orthogonal component output. During the said preset time, the in-phase component and the orthogonal component respectively comprises the data points with preset number; a square summation module that is used to obtain the square of the in-phase component output and the orthogonal component output and sum up the squares in order to get the signal power; a noise power mean value module that utilizes the in-phase component and the orthogonal component to get the noise power mean value; and SNR estimation module that utilized the signal power, the noise power mean value and the preset number to calculate the estimated value of the frequency-expanded signal.

Description

The signal to noise ratio (S/N ratio) of spread-spectrum signal is provided the device of estimation

Technical field

The utility model relates to a kind of device of handling spread-spectrum signal, particularly relates to the device that a kind of signal to noise ratio (S/N ratio) to spread-spectrum signal provides estimation.

Background technology

Because spread spectrum technic has numerous advantages, it is widely used in every field such as communication, electronic countermeasure, navigation and location.Spread spectrum communication is that information data to be transmitted is modulated by Pseudo-Random Noise Code (PRN) at transmitting terminal, realizes transmitting after the spread spectrum again; Receiving end then adopts identical coding to carry out demodulation and relevant treatment, recovers original information data.

Gps signal is by the spread-spectrum signal of gps satellite in L1 or the transmission of L2 frequency.Civilian GPS receiver uses L1 frequency (1575.42MHZ) usually.The several signals that send on the L1 carrier wave are: thick catch code (C/A sign indicating number), P sign indicating number and navigation data.The detailed data of satellite orbit is included in the navigation data.The C/A sign indicating number is a kind of Pseudo-Random Noise Code (a PRN sign indicating number), is mainly used in the location purposes in the commercial receiver.Each satellite all has a unique C/A sign indicating number, and this C/A sign indicating number that circulates repeatedly.The C/A sign indicating number is one 0 and 1 (scale-of-two) sequence.Each 0 or 1 is considered to one " chip ".The C/A sign indicating number has 1023 chips long, and sends with the speed of per second 1.023 million chips, and promptly the one-period of C/A sign indicating number continues 1 millisecond.Those of ordinary skill in the art can think that " chip " is the unit of data length or time span.Each chip also can think to have two states :+1 and-1.Navigation data also is one 0 and 1 (scale-of-two) sequence, and sends with the speed of per second 50 bits.

The GPS receiver comprises antenna, radio-frequency front-end and baseband signal processing unit.The gps signal of gps satellite emission sends radio-frequency front-end to after being received by antenna.Radio-frequency front-end is converted to the signal with desired output frequency with the radiofrequency signal that receives, and with predetermined sampling frequency will change signal digitalized.Then, this digital signal is sent to the trapping module of baseband signal processing unit.At trapping module, search for the Doppler shift of the starting point of C/A sign indicating number and the frequency of carrier wave, particularly gps signal by the related operation that digital signal and local C/A sign indicating number carry out.If search module confirms to capture gps signal, for example the frequency error of carrier wave is in 1Hz, the C/A code phase error is 1/2 chip, the tracking module of baseband signal processing unit then enters tracking mode, make local C/A sign indicating number and local carrier follow the tracks of the C/A sign indicating number in the gps signal and the variation of carrier wave, thereby obtain phase shift of accurate C/A sign indicating number and Doppler shift.Tracking module comprises carrier tracking loop and C/A code tracking loop, respectively carrier wave in the gps signal and C/A sign indicating number is carried out real-time follow-up, thereby demodulates the navigation data that comprises in the gps signal.

The C/A code tracking loop adopts the phaselocked loop (early-late ring) that shift to an earlier date-lags usually, and it comprises C/A sign indicating number generator, integration module, phase detector and wave filter.C/A sign indicating number generator produces two signals with predetermined phase difference based on the C/A sign indicating number phase shift of trapping module output, promptly shifts to an earlier date (early) and (late) C/A sign indicating number that lags, and the predetermined phase difference can be set to a chip.In advance and the intermediate-freuqncy signal of lag C/A sign indicating number and input export two paths of signals after in integration module, finishing related operation, this two paths of signals is through the processing of phase detector and wave filter, produce a control signal and regulate the local C/A sign indicating number that C/A sign indicating number generator produces, C/A code phase in the gps signal that makes the phase place of local C/A sign indicating number and receive keeps homophase, and the local C/A sign indicating number of this moment is instant (prompt) C/A sign indicating number.This instant C/A sign indicating number offers carrier tracking loop.Carrier tracking loop comprises carrier oscillator, integration module, phase detector and wave filter.Carrier oscillator produces a local carrier based on the Doppler shift of trapping module output, and the intermediate-freuqncy signal of this local carrier, instant C/A sign indicating number and input is carried out integration in integration module.The output of integration module produces a control signal and regulates carrier oscillator through the processing of phase detector and wave filter, with the local carrier of carrier synchronization in generation and the gps signal.

The parameter setting of existing C/A code tracking loop and carrier tracking loop is fixed, and parameter mainly comprises integral time and filtering bandwidth, that is to say, it all is constant in the tracing process that integral time and filtering bandwidth carry out gps signal in track loop.Yet because various interference, the radiofrequency signal that receives from antenna comprises useful signal and noise.Useful signal is from the gps signal of gps satellite to the receiver transmission, finishes functions such as location to help receiver.The intensity of signal defines with signal to noise ratio (snr), and signal to noise ratio (S/N ratio) is meant the power of the power of useful signal divided by noise, is unit with decibel generally.When signal to noise ratio (S/N ratio) was higher, the expression gps signal was stronger, this moment receiver should be positioned at outdoor and environment that the open degree of sky is preferable under, the rate of change of Doppler shift and Doppler shift is bigger.Otherwise when signal to noise ratio (S/N ratio) was low, the expression gps signal was faint, and this moment, receiver should be to be positioned under the environment of indoor or other signal shieldings, and the rate of change of Doppler shift and Doppler shift is less.Because the difference of signal intensity if track loop when gps signal is followed the tracks of, adopts same bandwidth and integral time all the time, when signal is strong, might cause loop adjustment speed slow excessively, can not follow the tracks of the variation of gps signal, causes the loop losing lock; In addition, when signal is more weak, can causes the loop filtering weak effect, can't follow the tracks of feeble signal.Therefore, the signal to noise ratio (S/N ratio) of the gps signal that need receive receiver is estimated, based on the estimated value of signal to noise ratio (S/N ratio), adjusts the parameter of track loop.

The utility model content

The device that the purpose of this utility model is to provide a kind of signal to noise ratio (S/N ratio) of the spread-spectrum signal that receiver is received to estimate is to determine the initial parameter of track loop.

The device that another purpose of the present utility model is to provide a kind of signal to noise ratio (S/N ratio) of the spread-spectrum signal that receiver is received to estimate realizing the real-time switching of track loop parameter, thereby makes track loop follow the tracks of spread-spectrum signal effectively.

For achieving the above object, the utility model provides a kind of device that the signal to noise ratio (S/N ratio) of spread-spectrum signal is estimated.This device comprises radio-frequency front-end, Doppler shift removal module, integration module, square summation module, peak value searching module, the module of averaging and SNR estimation module.Radio-frequency front-end is converted to digital signal with the spread-spectrum signal that receives.Doppler shift is removed module digital signal is divided into in-phase component and quadrature component.Integration module is carried out related operation with local Pseudo-Random Noise Code respectively with in-phase component and quadrature component, obtains the in-phase component output and the quadrature component output of predetermined quantity.Each corresponding in-phase component output and quadrature component output are asked respectively square for square summation module and with the square value addition, the signal that obtains predetermined quantity is exported the result.The peak value searching module is search peak from the signal output result of predetermined quantity, and peak value output result is a signal power.The module of averaging is averaged to non-peak value output result, obtains the noise power average.The SNR estimation module is utilized signal power and noise power average, calculates the estimated value of the signal to noise ratio (S/N ratio) of spread-spectrum signal.

The utility model also provides a kind of device that the signal to noise ratio (S/N ratio) of spread-spectrum signal is estimated.This device comprises radio-frequency front-end, Doppler shift removal module, integration module, square summation module, noise power average module and SNR estimation module.Radio-frequency front-end is sampled to spread-spectrum signal and is obtained digital signal.The orthogonal transformation module is divided into in-phase component and quadrature component with digital signal.Integration module is carried out related operation in the length with predefined local Pseudo-Random Noise Code respectively at the fixed time with in-phase component and quadrature component, obtains in-phase component output and quadrature component output.In described schedule time length, in-phase component and quadrature component comprise the data point of predetermined quantity respectively.Square summation module is exported in-phase component output and quadrature component and is asked respectively square and with the square value addition, obtain signal power.Noise power average module is utilized in-phase component and quadrature component, obtains the noise power average.The SNR estimation module is utilized signal power, noise power average and described predetermined quantity, calculates the estimated value of the signal to noise ratio (S/N ratio) of spread-spectrum signal.

Compared with prior art, the utility model is simple and reliable to the estimation unit of the signal to noise ratio (S/N ratio) of spread-spectrum signal, has reduced hardware implementation complexity and chip power-consumption.In addition, can utilize the estimated value of signal to noise ratio (S/N ratio) to adjust the parameter of track loop in real time, make track loop follow the tracks of spread-spectrum signal under the varying environment effectively.

Description of drawings

Other characteristic of the present utility model and advantage will be in following detailed descriptions and are more obvious in conjunction with illustrated explanation, and wherein same numbers is represented similar elements, and wherein:

Fig. 1 is the utility model receiver carries out SNR estimation to the spread-spectrum signal that receives at acquisition phase a block scheme.

Fig. 2 is the utility model receiver carries out SNR estimation to the spread-spectrum signal that receives at tracking phase a block scheme.

Embodiment

Receiver receives the gps signal of gps satellite emission, and to its catch, tracking and demodulation.The purpose that gps signal is followed the tracks of is to adjust the frequency and the phase place of the local signal that receiver produces, and make itself and gps signal synchronous, thereby realization is to the demodulation of gps signal.Carrier tracking loop and C/A code tracking loop are used for following the tracks of carrier wave and the C/A sign indicating number in the gps signal respectively.The parameter of track loop, for example, integral time and filtering bandwidth, the signal to noise ratio (S/N ratio) size of the gps signal that need receive according to receiver is provided with different values, to follow the tracks of gps signal effectively.After confirming to capture gps signal, begin to start track loop, so that gps signal is followed the tracks of.Before starting track loop, need carry out SNR estimation to the gps signal that acquisition phase captures, according to this SNR estimation value, the parameter of initialization track loop.Enter tracking phase, the signal to noise ratio (S/N ratio) of the gps signal that estimation in real time receives according to each SNR estimation value constantly, is provided with different track loop parameters.To describe receiver below respectively and provide estimation approach to the signal to noise ratio (S/N ratio) of the gps signal that receives at acquisition phase and tracking phase.

Fig. 1 is the utility model receiver 100 carries out SNR estimation to the spread-spectrum signal that receives at acquisition phase a block scheme.Spread-spectrum signal is gps satellite gps signal based on the emission of C/A sign indicating number on the carrier wave of L1 frequency (1575.42MHz).The gps signal of gps satellite emission is received by antenna 110.The signal r (t) that receives from antenna 110 comprises gps signal and noise signal.Received signal can be expressed as:

In the following formula, P is the power of received signal; τ is gps signal time delay of 100 from the satellite transmits to the receiver; C (t) is the C/A chip, and bit rate is f _CAD (t) refers to the navigation bit of 50Hz; ω _cBe carrier frequency, ω _c=2 π * 1575.42MHz; ω _dIt is Doppler shift;  is the carrier wave initial phase; N (t) is the zero-mean white Gaussian noise.

The signal r (t) that receives from antenna 110 transforms to intermediate frequency through the low-converter (not shown) of radio-frequency front-end 120, supposes that intermediate frequency is f _IF, pass through analog/digital (A/D) sampling module (not shown) again to the intermediate frequency signals sampling, obtain digital intermediate frequency signal r _IF(n).Suppose that sample frequency is f _S, then the sampling number K of each chip is f _S/ f _CADigital signal r _IF(n) expression-form is:

Here, n is the discretize time; τ _IFPropagation delay time for discretize; ω _IFBe the intermediate frequency carrier frequency, ω _IF=2 π * f _IFMHz.

Digital signal r _IF(n) then be transferred into Doppler shift and remove module 140.Remove in the module 140 at Doppler shift, utilize the local carrier of local carrier oscillator 150 outputs that base band is arrived in digital signal conversion, obtain in-phase component I _BB(n) and quadrature component Q _BB(n).In one embodiment, local carrier oscillator 150 comprises a carrier clock generator (not shown) and pi/2 phase shift module (not shown).Local carrier oscillator l50 produces two quadrature carrier signals: a sinusoidal signal and a cosine signal.One of them carrier signal of two carrier signals (claiming first local carrier again) is produced by the carrier clock generator.Another carrier signal (claiming second local carrier again) obtains by the phase shift to first local carrier.The phase shift operation is carried out by the pi/2 phase shift module.In-phase component I _BB(n) and quadrature component Q _BB(n) can be expressed as:

$\left\{\begin{array}{c}{I}_{\mathrm{BB}}\left(n\right)\sqrt{P}c(n-{\mathrm{\τ}}_{\mathrm{IF}})d(n-{\mathrm{\τ}}_{\mathrm{IF}})\cos (\mathrm{\Δ\ωn}+\mathrm{\φ})+n_i\left(n\right)\\ Q_{\mathrm{BB}}\left(n\right)=\sqrt{P}c(n-{\mathrm{\τ}}_{\mathrm{IF}})d(n-{\mathrm{\τ}}_{\mathrm{IF}})\sin (\mathrm{\Δ\ωn}+\mathrm{\φ})+n_q\left(n\right)\end{array}\right.---\left(3\right)$

In the following formula, Δ ω is a residual frequency departure; φ is the carrier wave initial phase; n _i(n), n _q(n) be respectively the zero-mean white Gaussian noise of homophase and quadrature component, its variance is σ ², and n _i(n), n _q(n) be mutual uncorrelated random variables.For simplifying the analysis, suppose Δ ω=0.

In integration module 160, in-phase component I _BB(n) and quadrature component Q _BB(n) carry out related operation in the length (claiming the predetermined integral time again) at the fixed time with the local C/A sign indicating number of PRN sign indicating number generator 180 generations respectively, finish in-phase component I _BB(n) and quadrature component Q _BB(n) integration.Integration module 160 comprises several parallel correlators, and the quantity of establishing parallel correlator is L.Suppose that the sign indicating number offset spacers between the parallel correlator is 1/2 chip, i.e. K/2 sampling.Because a C/A sign indicating number cycle comprises 1023 chips, therefore, the C/A code phase search of finishing the whole cycle needs 2046 correlations computings, promptly needs 2046 parallel correlators.In this case, the quantity L of parallel correlator is 2046.Each correlator is based on in-phase component I _BB(n) and quadrature component Q _BB(n) carry out related operation with local C/A sign indicating number, obtain in-phase component output and quadrature component output.2046 parallel correlators are carried out identical computing, and difference is just imported the phase place difference of the local C/A sign indicating number of each correlator.In the present embodiment, integration module 160 produces 2046 in-phase component outputs and quadrature component output.The in-phase component output I of l correlator _C(l) and quadrature component output Q _C(l) can be expressed as:

$\left\{\begin{array}{c}{I}_C\left(l\right)=s_i\left(l\right)+{\tilde{n}}_i\left(l\right)\\ Q_C\left(l\right)=s_q\left(l\right)+{\tilde{n}}_q\left(l\right)\end{array}\right.---\left(4\right)$

Wherein, l=0,1,2......L-1; s _i(l) and s _q(l) for through the homophase that obtains behind the related operation and the component of signal of quadrature two-way, With For through the homophase that obtains behind the related operation and the noise component of quadrature two-way.

Component of signal s _i(l) and s _q(l) can be expressed as:

$\left\{\begin{array}{c}{s}_i\left(l\right)=\underset{n=1}{\overset{N}{\mathrm{\Σ}}}\sqrt{P}d(n-{\mathrm{\τ}}_{\mathrm{IF}})c(n-{\mathrm{\τ}}_{\mathrm{IF}})c_{\mathrm{local}}(n-{\mathrm{\τ}}_l)\cos \left(\mathrm{\φ}\right)\\ s_q\left(l\right)=\underset{n=1}{\overset{N}{\mathrm{\Σ}}}\sqrt{P}d(n-{\mathrm{\τ}}_{\mathrm{IF}})c(n-{\mathrm{\τ}}_{\mathrm{IF}})c_{\mathrm{local}}(n-{\mathrm{\τ}}_l)\sin \left(\mathrm{\φ}\right)\end{array}\right.---\left(5\right)$

Here, N is the sampling number of the intermediate-freuqncy signal in the described predetermined integral time, also can think, and in described predetermined integral in the time, in-phase component I _BB(n) and quadrature component Q _BB(n) comprise N data point respectively; c _Local(n-τ _l) be the local C/A sign indicating number of corresponding l correlator; τ _lLocal C/A code delay for corresponding l correlator.

Noise component With Expression formula be:

$\left\{\begin{array}{c}{\tilde{n}}_i\left(l\right)=\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{n}_i\left(n\right)c_{\mathrm{local}}(n-{\mathrm{\τ}}_l)\\ {\tilde{n}}_q\left(l\right)=\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{n}_q\left(n\right)c_{\mathrm{local}}(n-{\mathrm{\τ}}_l)\end{array}\right.---\left(6\right)$

When the phase place of local C/A sign indicating number is identical with C/A code phase in the gps signal that receives,, can obtain component of signal s according to formula (5) _i(l) and s _q(l) be:

$\left\{\begin{array}{c}{s}_i\left(l\right)=N\sqrt{P}\cos \left(\mathrm{\φ}\right)\\ s_q\left(l\right)=N\sqrt{P}\sin \left(\mathrm{\φ}\right)\end{array}\right.---\left(7\right)$

Otherwise, s _i(l) and s _q(l) value is very little, can be approximated to be zero.

Because

With Be incoherent zero-mean white Gaussian noise, so its variance is N σ ²

In order to eliminate the influence of carrier residual frequency deviation and initial phase, in square summation module 190, in-phase component output that each correlator in the integration module 160 is produced and quadrature component output are asked respectively square, and with the square value addition, obtain 2046 signals and export results.The signal output of corresponding l correlator is S as a result _Acq(l) expression formula is:

$S_{\mathrm{acq}}\left(l\right)=I_C^2\left(l\right)+Q_C^2\left(l\right)---\left(8\right)$

Wherein, l=0,1,2......2045.

Then, peak value searching module 192 is searched in 2046 signal output results of square summation module 190 outputs, therefrom finds peak value output result, and this peak value output result is exactly signal power S _Acq(l ₀).S _Acq(l ₀) be corresponding l ₀The signal output result that in-phase component output that individual correlator produces and quadrature component output obtain; L wherein ₀The phase place of the local C/A sign indicating number of individual correlator is identical with C/A code phase in the received signal, therefore can obtain:

Work as l=l ₀The time, have:

$I_C\left(l_0\right)~(N\sqrt{P}\cos \left(\mathrm{\φ}\right),N{\mathrm{\σ}}^2),Q_C\left(l_0\right)~(N\sqrt{P}\sin \left(\mathrm{\φ}\right),N{\mathrm{\σ}}^2)---\left(9\right)$

As l ≠ l ₀The time, have:

I _c(l)～(0，Nσ ²)，Q _C(l)～(0，Nσ ²) (10)

As l ≠ l ₀The time, corresponding signal output is S as a result _Acq(l) be noise power.Because noise is a stochastic variable, therefore need average to noise power.The module of averaging 194 is used for carrying out this function, and its non-peak value output result that peak value searching module 192 is judged averages, and obtains noise power average E[S _Acq(l)].

Because

$E\left[I_C^2\left(l\right)\right]=N{\mathrm{\σ}}^2---\left(11\right)$

$E\left[Q_C^2\left(l\right)\right]=N{\mathrm{\σ}}^2---\left(12\right)$

So

E[S _acq(l)]＝2Nσ ² (13)

Signal power S _Acq(l ₀) comprise available signal power and noise power.Because noise is a stochastic variable, utilizes signal power average E[S _Acq(l ₀)] represent signal power.

Because

$E\left[I_C^2\left(l_0\right)\right]=N^{2}P{\cos }^2\left(\mathrm{\φ}\right)+N{\mathrm{\σ}}^2---\left(14\right)$

$E\left[Q_C^2\left(l_0\right)\right]=N^{2}P{\sin }^2\left(\mathrm{\φ}\right)+N{\mathrm{\σ}}^2---\left(15\right)$

So

E[S _acq(l ₀)]＝N ²P+2Nσ ² (16)

SNR estimation module 196 is calculated the SNR estimation value SNR of received signal according to signal power and noise power average _ACQSignal power S _Acq(l ₀) deduct noise power average E[S _Acq(l)], obtain available signal power.The estimated value of signal to noise ratio (S/N ratio) is that available signal power is divided by the noise power average.

Make S _ACQ=S _Acq(l ₀); S _{ACQ_n}=E[S _Acq(l)], l ≠ l wherein ₀SNR estimation module 197 is calculated the SNR estimation value SNR of received signal based on signal power and noise power average by following formula _ACQ:

${\mathrm{SNR}}_{\mathrm{ACQ}}=\frac{S_{\mathrm{ACQ}}-S_{\mathrm{ACQ}\_n}}{S_{\mathrm{ACQ}\_n}}---\left(17\right)$

At acquisition phase, in order to guarantee certain detection probability and false-alarm probability, homophase and quadrature component are generally adopted long integral time, make the peak value of peak value searching module 192 outputs all be much higher than other noise signals, promptly the component of signal that obtains this moment will be better than noise signal greatly, so the SNR estimation that the formula of utilization (17) obtains will be very accurate, generally do not need to carry out Filtering Processing.Initialization module 198 utilizes the SNR estimation value of acquisition phase to come the parameter of initialization track loop.In one embodiment, receiver 100 comprises a data library module, and what a look-up table is this database module set in advance.In look-up table, corresponding different SNR estimation scope is provided with the track loop parameter of different numerical value.When signal to noise ratio (S/N ratio) was high, receiver should be to be positioned at opening, in order to tackle sufficiently high dynamic stress, the rate of change that is Doppler shift and Doppler shift is bigger, should reduce the dynamic range of track loop, thereby bigger loop bandwidth is set, adopt short integral time.When signal to noise ratio (S/N ratio) was low, receiver should be to be positioned at indoor or partly to block the area, and the rate of change of Doppler shift and Doppler shift is less, should increase the dynamic range of track loop, thereby less loop bandwidth is set, and adopted long integral time simultaneously.SNR estimation value SNR according to acquisition phase _ACQ, initialization module 198 is selected one group of corresponding parameters with it in look-up table, as the initial parameter of track loop.

Fig. 2 is the utility model receiver carries out SNR estimation to the gps signal that receives at tracking phase a block scheme.Because the SNR estimation of tracking phase is carried out in real time, if continue to utilize the signal-to-noise ratio estimation algorithm of above-mentioned acquisition phase, because search time is long, operand is big, will increase the power consumption of chip.In addition, consider that the dynamic stress of tracing process is bigger,,, will make that algorithm performance descends greatly if continue to utilize the signal-to-noise ratio estimation algorithm of above-mentioned acquisition phase so integral time can not be oversize.Therefore, provide a kind of signal to noise ratio (S/N ratio) that is different from the acquisition phase to received signal to carry out estimation approach at tracking phase.Please refer to Fig. 2, in receiver 200, the gps signal that utilizes radio-frequency front-end 120 that antenna 110 is received is converted to digital intermediate frequency signal r _IF(n), its expression formula is with the formula (2) of above-mentioned acquisition phase.Remove in the module 140 at Doppler shift, the local carrier that utilizes 150 outputs of local carrier oscillator is with digital signal r _IF(n) transform to base band, obtain in-phase component I _BB(n) and quadrature component Q _BB(n), its expression formula is with the formula (3) of above-mentioned acquisition phase.In integration module 260, with in-phase component I _BB(n) and quadrature component Q _BB(n) carry out related operation in the length (claiming the predetermined integral time again) at the fixed time with a local C/A sign indicating number of PRN sign indicating number generator 270 generations respectively, finish in-phase component I _BB(n) and quadrature component Q _BB(n) integration, thus an in-phase component output I (P) and quadrature component output Q (P) obtained.The phase place of the C/A sign indicating number in the phase place of described local C/A sign indicating number and the gps signal that receives is identical.In one embodiment, local C/A sign indicating number is local instant (Prompt) C/A sign indicating number by the output of the C/A sign indicating number generator in the phaselocked loop that shift to an earlier date-lags (early-late ring).In-phase component output I (P) and quadrature component output Q (P) that integration module 260 produces can be expressed as:

$\left\{\begin{array}{c}I\left(P\right)=s_i\left(P\right)+{\tilde{n}}_i\left(P\right)\\ Q\left(P\right)=s_q\left(P\right)+{\tilde{n}}_q\left(p\right)\end{array}\right.---\left(18\right)$

Wherein, s _i(P) and s _q(P) for through the homophase that obtains behind the related operation and the component of signal of quadrature two-way, expression formula is with the formula (7) of above-mentioned acquisition phase, as mentioned above, N in the formula (7) is the sampling number of the intermediate-freuqncy signal in the described predetermined integral time, just, in described predetermined integral in the time, in-phase component I _BB(n) and quadrature component Q _BB(n) comprise N data point respectively;

With

For through the homophase that obtains behind the related operation and the noise component of quadrature two-way, variance is N σ ²I (P), Q (P) has the I with acquisition phase _C(l ₀), Q _C(l ₀) similar distribution, for simplicity's sake, repeat no more here.

In square summation module 280, in-phase component output I (P) that integration module 260 is produced and quadrature component are exported Q (P) and are asked respectively square, and with the square value addition, obtain signal power S _TRK, its formula is as follows:

S _TRK＝I ²(P)+Q ²(P) (19)

According to the analysis of top acquisition phase, can obtain the average E[S of signal power _TRK]:

E[S _TRK]＝N ²P+2Nσ ² (20)

Because for gps signal, received signal is submerged among the noise, and according to the regulation of GPS received signal minimum level, even at opening, noise power is also big about 100 times than signal power, so for in-phase component I _BB(n) and quadrature component Q _BB(n), noise accounts for major part, thereby can be regarded as the white Gaussian noise sequence of approximate zero average, i.e. in-phase component I _BB(n) and quadrature component Q _BB(n) variance is σ ²Therefore, to in-phase component I _BB(n) and quadrature component Q _BB(n) square summation can obtain noise power S _{TRK_n}, its formula is as follows:

$S_{\mathrm{TRK}\_n}=I_{\mathrm{BB}}^2\left(n\right)+Q_{\mathrm{BB}}^2\left(n\right)---\left(21\right)$

Because noise is a stochastic variable, need obtain the noise power average.In noise power average module 290, based on in-phase component I _BB(n) and quadrature component Q _BB(n), can obtain noise power average E[S _{TRK_n}], its formula is:

$E\left[S_{\mathrm{TRK}\_n}\right]=E\left[I_{\mathrm{BB}}^2\left(n\right)\right]+E\left[Q_{\mathrm{BB}}^2\left(n\right)\right]---\left(22\right)$

As previously mentioned, in integration module 260, to in-phase component I _BB(n) and quadrature component Q _BB(n) carry out integral operation in the length at the fixed time, in this schedule time length, in-phase component I _RR(n) and quadrature component Q _BB(n) data point that comprises is N.Therefore, noise power average E[S _{TRK_n}] be the average (variance) of N each data point in the data point.

Noise power average module 290 comprises square module 291, average module 293 and summation module 295.Square 291 couples of in-phase component I of module _BB(n) and quadrature component Q _BB(n) each data point is asked respectively square, obtains the square value of N in-phase component data point and the square value of quadrature component data point.Average module 293 is averaged to the square value of N in-phase component data point and the square value of quadrature component data point respectively, obtains the average E[of the square value of in-phase component data point _BB ²And the average E[I of the square value of quadrature component data point (n)] _BB ²(n)].Summation module 295 obtains noise power average E[S to the average addition of the square value of the average of the square value of in-phase component data point and quadrature component data point _{TRK_n}].

Because

$E\left[I_{\mathrm{BB}}^2\left(n\right)\right]={\mathrm{\σ}}^2---\left(23\right)$

$E\left[Q_{\mathrm{BB}}^2\left(n\right)\right]={\mathrm{\σ}}^2---\left(24\right)$

So

E[S _{TRK_n}]＝2σ ² (25)

SNR estimation module 296 is calculated the SNR estimation value SNR of received signal according to the sampling number of the intermediate-freuqncy signal in signal power, noise power average and the described schedule time length _TRKThe noise power average multiply by the sampling number N of the intermediate-freuqncy signal in the described schedule time length, obtains the noise power average in the described schedule time length.Signal power S _TRKDeduct the noise power average in the described schedule time length, obtain available signal power.The estimated value of signal to noise ratio (S/N ratio) is that available signal power is divided by the noise power average in the described schedule time length.SNR estimation module 296 is calculated the SNR estimation value SNR of received signal by following formula _TRK:

${\mathrm{SNR}}_{\mathrm{TRK}}=\frac{S_{\mathrm{TRK}}-\mathrm{NE}\left[S_{\mathrm{TRK}-n}\right]}{\mathrm{NE}\left[S_{\mathrm{TRK}\_n}\right]}---\left(26\right)$

The SNR estimation of the signal that tracking phase is received is carried out aforesaid simplification, has the following advantages: the first, and at the noise component place, not to in-phase component I _BB(n) and quadrature component Q _BB(n) do integral operation, therefore, the quantization bit at noise component place is less, thereby can reduce hardware implementation complexity and chip power-consumption greatly, reaches the purpose of real-time estimated snr; The second, at the component of signal place, made full use of local instant (Prompt) C/A sign indicating number of the sign indicating number generator output in the phaselocked loop that shift to an earlier date-lags (early-late ring), reached multiplexing purpose, help reducing the hardware implementation complexity.

Because when tracking phase signal to noise ratio (S/N ratio) to received signal provides estimation, algorithm has been carried out certain simplification, and because the restriction of integral time, the precision of SNR estimation is not high, need carry out the filtering smoothing processing to the result of SNR estimation, make it can be used as the criterion of real-time adjustment track loop parameter.Wave filter 298 is used for the SNR estimation result of received signal that tracking phase is obtained and carries out Filtering Processing, obtains SNR estimation value accurately.In the present embodiment, wave filter 298 is single order Kalman (Kalman) wave filters.Will be appreciated that, also can adopt other method to come the SNR estimation result is carried out filtering, as average filter, low-pass filtering etc.As previously mentioned, tracking phase is that the signal to noise ratio (S/N ratio) of the spread-spectrum signal that receives is estimated in real time, according to each SNR estimation value constantly, the track loop parameter is set in real time.In an embodiment of the present utility model, according to SNR estimation value accurately, handover module 299 is selected one group of corresponding parameters with it from the look-up table that pre-sets, and the parameter of track loop is switched to this group parameter.

The signal-noise ratio estimation method that persons of ordinary skill in the art may appreciate that the received signal of the utility model tracking phase also is applicable to the SNR estimation of the received signal of acquisition phase.

Here term of Cai Yonging and form of presentation just are used for describing, and should not be limited to these terms and statement.Use these terms and statement and do not mean that the equivalent features of getting rid of any signal and description (or wherein part), will be appreciated that the various modifications that may exist also should be included in the claim scope.Other modifications, variation and replacement also may exist.Accordingly, claim should be considered as covering all these equivalents.

Claims (5)

1. the signal to noise ratio (S/N ratio) to spread-spectrum signal provides the device of estimation, it is characterized in that described device comprises:

Radio-frequency front-end, it is converted to digital signal with the spread-spectrum signal that receives;

Doppler shift is removed module, and it is divided into in-phase component and quadrature component with digital signal;

Integration module is carried out related operation with local Pseudo-Random Noise Code respectively with in-phase component and quadrature component, obtains the in-phase component output and the quadrature component output of predetermined quantity;

Square summation module is used for each corresponding in-phase component output and quadrature component output are asked respectively square and with the square value addition, the signal that obtains predetermined quantity is exported the result;

The peak value searching module, search peak from the signal output result of predetermined quantity, peak value output result is a signal power;

The module of averaging is used for non-peak value output result is averaged, and obtains the noise power average; And

The SNR estimation module is utilized signal power and noise power average, calculates the estimated value of the signal to noise ratio (S/N ratio) of spread-spectrum signal.

2. the signal to noise ratio (S/N ratio) to spread-spectrum signal provides the device of estimation, it is characterized in that described device comprises:

Radio-frequency front-end, it is sampled to spread-spectrum signal and obtains digital signal;

Doppler shift is removed module, and it is divided into in-phase component and quadrature component with digital signal;

Integration module, in-phase component and quadrature component are carried out related operation in the length at the fixed time with predefined local Pseudo-Random Noise Code respectively, obtain in-phase component output and quadrature component output, in described schedule time length, in-phase component and quadrature component comprise the data point of predetermined quantity respectively;

Square summation module is used for in-phase component output and quadrature component exported and asks respectively square and with the square value addition, obtain signal power;

Noise power average module is utilized in-phase component and quadrature component, obtains the noise power average; And

The SNR estimation module is utilized signal power, noise power average and described predetermined quantity, calculates the estimated value of the signal to noise ratio (S/N ratio) of spread-spectrum signal.

3. device according to claim 2 is characterized in that, described noise power average module comprises:

Square module is asked respectively square each data point of in-phase component and quadrature component, obtains the square value of in-phase component data point of predetermined quantity and the square value of quadrature component data point;

The average module is averaged to the square value of the in-phase component data point of predetermined quantity and the square value of quadrature component data point respectively, obtains the average of the square value of the average of square value of in-phase component data point and quadrature component data point; And

Summation module the average addition of the square value of the average of the square value of in-phase component data point and quadrature component data point, obtains described noise power average.

4. device according to claim 2 is characterized in that, comprises that also the estimated value that is used for the signal to noise ratio (S/N ratio) of spread-spectrum signal carries out filter filtering.

5. device according to claim 4 is characterized in that, described wave filter is the single order Kalman filter.

Images