CN101576612A - Method for estimating carrier-to-noise ratio of GPS signal and GPS receiver - Google Patents

Abstract

The invention discloses a method for estimating the carrier-to-noise ratio of GPS signals and a GPS receiver. The method for estimating the carrier-to-noise ratio of the GPS signal includes: dividing the digital signal into an in-phase component and a quadrature component; correlating the in-phase component and the quadrature component with the local pseudo-random noise code to obtain an in-phase component signal and a quadrature component signal , the local pseudo-random noise code has the same phase as the pseudo-random noise code in the GPS signal; based on the in-phase component signal and the quadrature component signal, estimate a first estimated value and a second estimated value related to the GPS signal; Dividing the first estimated value by the second estimated value to obtain the strength of the GPS signal; and finding the corresponding carrier-to-noise ratio value from a preset lookup table according to the strength of the GPS signal. Based on the estimated strength of the GPS signal, the present invention obtains the carrier-to-noise ratio through a pre-set lookup table, which can reduce hardware resource occupation and computational complexity.

Description

Method for Estimating Carrier-to-Noise Ratio of GPS Signal and GPS Receiver

technical field

The invention relates to a method for processing GPS signals and a GPS receiver, in particular to a method for estimating the carrier-to-noise ratio of GPS signals and a GPS receiver.

Background technique

GPS signals are spread spectrum signals transmitted by GPS satellites at L1 or L2 frequencies. Civilian GPS receivers usually use the L1 frequency (1575.42MHZ). Several signals sent on the L1 carrier are: coarse acquisition code (C/A code), P code and navigation data. Detailed data on satellite orbits are included in the navigation data. The C/A code is a pseudorandom noise code (PRN code), which is mainly used for positioning purposes in civilian receivers. Each satellite has a unique C/A code, and the C/A code is cycled repeatedly. The C/A code is a sequence of 0s and 1s (binary). Each 0 or 1 is considered a "chip". The C/A code is 1023 chips long and is transmitted at a rate of 1.023 megachips per second, ie one cycle of the C/A code lasts 1 millisecond. Those of ordinary skill in the art may consider a "chip" to be a unit of data length or time length. Navigation data is also a sequence of 0s and 1s (binary) and is sent at a rate of 50 bits per second.

In order to achieve positioning, the GPS receiver needs to capture GPS signals from different satellites and demodulate the navigation data of the GPS signals. GPS signals from different satellites have C/A codes with different start times and different Doppler frequency shifts. Therefore, to search for a satellite signal, a GPS receiver usually performs a two-dimensional search, searching for each C/A code with a different start time on each possible frequency. GPS receiver includes antenna, radio frequency front end and baseband signal processing unit. The GPS signal transmitted by the GPS satellite is received by the antenna and sent to the RF front-end. The RF front-end converts the received RF signal into a signal with the desired output frequency, and digitizes the converted signal at a predetermined sampling frequency. The converted and digitized signal is Considered to be an intermediate frequency signal. Then, the intermediate frequency signal is sent to the capture module of the baseband signal processing unit. In the acquisition module, the starting point of the C/A code and the frequency of the carrier are searched through the correlation operation of the intermediate frequency signal, the local C/A code and the local carrier, especially the Doppler frequency shift of the GPS signal. If the search module captures the GPS signal, for example, the frequency error of the carrier is within 1 Hz, and the phase error of the C/A code is 1/2 chip, the tracking module of the baseband signal processing unit enters the tracking state, so that the local C/A code and the local The carrier tracks the changes of the C/A code and the carrier in the GPS signal to obtain accurate C/A code phase shift and Doppler frequency shift. The tracking module includes a carrier tracking loop and a C/A code tracking loop, respectively tracking the carrier and the C/A code in the GPS signal in real time to demodulate the navigation data contained in the GPS signal.

The C/A code tracking loop usually adopts an early-late phase-locked loop (early-late loop), which includes a C/A code generator, an integrating module, a phase detector and a filter. The C/A code generator generates two signals with a predetermined phase difference based on the C/A code phase shift output by the capture module, i.e. an early (early) and a late (late) C/A code, and the predetermined phase difference can be set to a chip. The early and late C/A codes and the input intermediate frequency signal complete the correlation operation in the integral module and then output two signals. The two signals are processed by the phase detector and filter to generate a control signal to adjust the C/A code. The local C/A code generated by the generator keeps the phase of the local C/A code in phase with the phase of the C/A code in the received GPS signal. At this time, the local C/A code is instant (prompt) C/A code. This instant C/A code is provided to the carrier tracking loop. The carrier tracking loop includes a carrier oscillator, an integrating block, a phase detector and a filter. The carrier oscillator generates a local carrier based on the Doppler frequency shift output by the acquisition module, and the local carrier, the instant C/A code and the input intermediate frequency signal are integrated in the integration module. The output of the integration module is processed by a phase detector and a filter to generate a control signal to adjust the carrier oscillator to generate a local carrier synchronized with the carrier in the GPS signal.

Due to various interferences, the radio frequency signal received from the antenna includes useful signal and noise. The useful signal is the GPS signal sent from the GPS satellite to the receiver to help the receiver complete positioning and other functions. Carrier-to-noise ratio (CN0) is a standard format required by the National Marine Electronics Association (NMEA) for GPS receiver output. The carrier-to-noise ratio is an expression of signal strength, which refers to the ratio of the carrier power to the noise power within the noise bandwidth per hertz (Hz), and is generally expressed in decibel-hertz (dB-Hz). When the carrier-to-noise ratio is high, it means that the GPS signal is strong. Conversely, when the carrier-to-noise ratio is low, it means that the GPS signal is weak.

FIG. 1 shows a conventional block diagram 100 for providing an estimate of the carrier-to-noise ratio of a GPS signal. The GPS receiver converts the received GPS signal into a signal having a desired output frequency, and digitizes the converted signal at a predetermined sampling frequency. The converted and digitized signal is considered an intermediate frequency signal. The local carrier output by the local carrier generator 104 is used to convert the intermediate frequency signal to the baseband in the Doppler frequency shift removal module 102 to obtain the in-phase component I and the quadrature component Q. The local carrier generator 104 outputs two local quadrature carrier signals: a sine signal and a cosine signal. One of the two carrier signals (also known as the first local reference signal) is generated by the carrier NCO 106. Another carrier signal (also known as the second local reference signal) is obtained by shifting the phase of the first local reference signal. The phase shifting operation is performed by the π/2 phase shifting module 108 . The in-phase component I and the quadrature component Q are respectively integrated with the local C/A code output by the code generator 110 for a predetermined time length K in the first integration module 112 to obtain the integrated in-phase and quadrature signal components I (P), Q(P), where the phase of the local C/A code is the same as that of the C/A code in the intermediate frequency signal. The first integration module 112 is the integration module in the tracking loop. The local C/A code is a local immediate (Prompt) C/A code output by a C/A code generator in an early-late phase-locked loop (early-late loop). In the first square summation module 114, the signal components of the in-phase and quadrature paths output by the first integration module 112 are respectively squared, and the squared values are added to obtain the signal power C.

In the noise power calculation module, the noise power N is calculated based on the in-phase component I and the quadrature component Q. The noise power calculation module includes a second integration module 116 and a second square summation module 118 . The in-phase component I and the quadrature component Q are integrated for a predetermined time length K in the second integration module 116 to obtain integrated in-phase and quadrature signal components. In the second square summation module 118, the signal components of the in-phase and quadrature paths output by the second integration module 116 are respectively squared, and the squared values are added to obtain the noise power N. The integration time K of the first integration module 112 and the second integration module 116 can be dynamically set according to the application environment. When there is navigation bit assistance, the value of the integration time K can be greater than 20 milliseconds. When there is no navigation bit assistance, the maximum value of the integration time K is 20 milliseconds.

The first filter 120 and the second filter 122 are used to filter the calculated signal power C and noise power N to obtain relatively stable signal power C and noise power N. The first and second filters 120, 122 may be low pass filters. Utilize following formula (a) to calculate the carrier-to-noise ratio CN0 of GPS signal in the carrier-to-noise ratio estimation module 124:

CN0＝[10*lg10(C/N-1)+10*lgK]dB-Hz (a)

Among them, C and N are the above-mentioned signal power and noise power respectively, and K is the integration time for calculating signal power C and noise power N.

Using the following formula (b), the sensitivity (Sensitivity) of the GPS receiver can be obtained based on the carrier-to-noise ratio CN0:

Sensitivity＝CN0-174(dBm) (b)

As can be seen from the above description, the traditional method for calculating the GPS signal carrier-to-noise ratio needs to additionally set a noise power calculation module to calculate the noise power, and then, in the carrier-to-noise ratio estimation module 124 based on the signal power and the noise power, the above formula ( a) Calculate the carrier-to-noise ratio. Therefore, this traditional carrier-to-noise ratio estimation method not only has a complicated calculation process but also consumes a lot of hardware resources.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for estimating the carrier-to-noise ratio of GPS signals and a GPS receiver, which can reduce hardware resources and computational complexity.

In order to solve the above technical problems, the present invention provides a method for estimating the carrier-to-noise ratio of the GPS signal. The GPS signal is converted into a digital signal. The method includes: using a preset local reference signal, the digital signal is divided into an in-phase component and a positive The quadrature component; the in-phase component and the quadrature component are respectively correlated with the local pseudo-random noise code to obtain an in-phase component signal and a quadrature component signal. The phase of the local pseudo-random noise code and the pseudo-random noise code in the GPS signal The same; based on the in-phase component signal and the quadrature component signal, estimate a first estimated value and a second estimated value related to the GPS signal; divide the first estimated value by the second estimated value to obtain the strength of the GPS signal; And according to the strength of the GPS signal, find the corresponding carrier-to-noise ratio value from the preset look-up table.

The invention also provides a GPS receiver for estimating the carrier-to-noise ratio of the GPS signal, and the GPS receiver converts the GPS signal into a digital signal. The GPS receiver includes a Doppler frequency shift removal module, an integration module, a signal strength estimation module and a conversion module. The Doppler frequency shift removal module divides the digital signal into an in-phase component and a quadrature component; the integration module performs a correlation operation on the in-phase component and the quadrature component with the local pseudo-random noise code to obtain an in-phase component signal and a quadrature component signal, The local pseudorandom noise code is in the same phase as the pseudorandom noise code in the GPS signal. The signal strength estimation module estimates a first estimated value and a second estimated value related to the GPS signal according to the in-phase component signal and the quadrature component signal output by the integrating module, and based on the first estimated value and the second estimated value, calculates The strength of the GPS signal. The conversion module finds the corresponding carrier-to-noise ratio value from the preset look-up table based on the strength of the GPS signal.

Compared with the prior art, the present invention obtains the carrier-to-noise ratio of the GPS signal through a pre-set lookup table based on the estimated strength of the GPS signal, which can reduce hardware resource occupation and computational complexity.

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments, so as to make the characteristics and advantages of the present invention more obvious.

Description of drawings

Figure 1 is a conventional block diagram for providing an estimate of the carrier-to-noise ratio of a GPS signal.

Figure 2 is a block diagram of the present invention providing an estimate of the carrier-to-noise ratio of a GPS signal.

FIG. 3 is a block diagram of the signal strength estimation module in FIG. 2 estimating the strength of GPS signals in one embodiment.

FIG. 4 is a simulation curve diagram of the corresponding relationship between GPS signal strength and sensitivity estimated in FIG. 3 .

FIG. 5 is a lookup table corresponding to the estimated GPS signal strength and carrier-to-noise ratio in FIG. 3 .

Detailed ways

FIG. 2 is a block diagram 200 of the present invention for providing an estimate of the carrier-to-noise ratio of a GPS signal. The GPS receiver converts the received GPS signal into a signal having a desired output frequency, and digitizes the converted signal at a predetermined sampling frequency. The converted and digitized signal is considered an intermediate frequency signal. The local carrier output by the local carrier generator 204 is used to convert the intermediate frequency signal to the baseband in the Doppler frequency shift removal module 202 to obtain the in-phase component I and the quadrature component Q. The local carrier generator 204 outputs two local quadrature carrier signals: a sine signal and a cosine signal. One of the two carrier signals (also known as the first local reference signal) is generated by the carrier NCO 206. Another carrier signal (also known as the second local reference signal) is obtained by phase shifting the first local reference signal, and the phase shifting operation is performed by the π/2 phase shifting module 208 . The in-phase component I and the quadrature component Q are respectively correlated with the local C/A code output by the code generator 210 in the integration module 212 within a predetermined time length to complete the integration of the in-phase component I and the quadrature component Q, thereby The in-phase component signal I(P) and the quadrature component signal Q(P) are obtained, where the phase of the local C/A code is the same as that of the C/A code in the intermediate frequency signal. In one embodiment of the present invention, the local C/A code is the local instant (Prompt) C/A code output by the C/A code generator in the early-late phase-locked loop (early-late ring), and the integration module 212 is an integral module in the tracking loop.

The signal strength estimation module 300 estimates the strength of the GPS signal based on the in-phase component signal I(P) and the quadrature component signal Q(P). In an embodiment of the present invention, a specific implementation block diagram of estimating the strength of the GPS signal by the signal strength estimation module 300 is shown in FIG. 3 . The signal strength estimation module 300 estimates the strength of the GPS signal based on the following formula (1).

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the above formula, M is the integration time of the in-phase component signal and the quadrature component signal, SL is the first estimated value related to the GPS signal, and NL is the second estimated value related to the GPS signal.

Referring to FIG. 3, in the first integration unit 302, an integration operation is performed on the in-phase component signal I(P) and the quadrature component signal Q(P) within a predetermined time length M, respectively. Next, in the square summation unit 304, the integral of the in-phase component signal and the integral of the quadrature component signal output by the first integration unit 302 are respectively squared, and the square values are added to obtain the first estimate related to the GPS signal Value SL.

In the square unit 306, square operations are performed on the in-phase component signal I(P) and the quadrature component signal Q(P) respectively. Next, in the second integration unit 308 , an integration operation is performed for a predetermined time length M on the square of the in-phase component signal and the square of the quadrature component signal output from the square unit 306 . Then, in the summation unit 310, the two integration results output by the second integration unit 310 are added to obtain the second estimated value NL related to the GPS signal.

The present invention is not limited to using the above formula (1) to estimate the first estimated value SL and the second estimated value NL related to the GPS signal. In other embodiments of the present invention, the signal strength estimation module 300 may also use the following formula (2) or (3) to estimate the first estimated value SL and the second estimated value NL related to the GPS signal.

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; |</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span>\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The first estimated value SL and the second estimated value NL have a non-linear relationship. Both the first estimated value and the second estimated value include the influence of the signal and the influence of the noise.

The value of the integration time M in the above formulas (1), (2) and (3) can be flexibly set according to the signal strength. When the signal is strong, the value of the integration time M is small; when the signal is weak, the value of the integration time M is large. For example, when there is navigation bit assistance, the integration time M can be dynamically set according to the application environment, so that the value of M is greater than 20 milliseconds. When there is no navigation bit assistance, the maximum value of the integration time M is 20 milliseconds.

Due to the influence of noise, the first estimated value SL and the second estimated value NL related to the GPS signal estimated by the signal strength estimation module 300 have some jitter, and are filtered and smoothed by the first filter 312 and the second filter 314 respectively , to obtain relatively stable first estimated value and second estimated value.

The ratio SNR_Level of the first estimated value SL to the second estimated value NL is a value that has a nonlinear relationship with the signal-to-noise ratio, and the larger the ratio, the greater the signal-to-noise ratio. Therefore, in the estimation module 316, the first estimated value SL is divided by the second estimated value NL to obtain a ratio between the first estimated value SL and the second estimated value NL, which can indirectly reflect the strength of the current GPS signal.

FIG. 4 is a simulation graph 400 of the relationship between GPS signal strength SNR_Level and sensitivity estimated in FIG. 3 , where the horizontal axis is sensitivity in decibel milliseconds (dBm), and the vertical axis is GPS signal strength SNR_Level. It can be seen from Fig. 4 that the GPS signal strength estimated according to the above formula (1) has a nonlinear relationship with the sensitivity of the GPS receiver, and the stronger the GPS signal, the higher the sensitivity. Those skilled in the art can understand that the GPS signal strength estimated according to the above formula (2) or (3) has a nonlinear relationship with the sensitivity of the GPS receiver, and the stronger the GPS signal, the higher the sensitivity. The difference is that the values corresponding to the strength and sensitivity of the GPS signal at a certain point on the graph are different from those in FIG. 4 .

According to the graph in Fig. 4, corresponding to different GPS signal strength SNR_Level, a corresponding sensitivity can be obtained. However, there is a certain relationship between the sensitivity and the carrier-to-noise ratio CN0 , as shown in the formula (b) in the background technology section, the carrier-to-noise ratio CN0 can be obtained by adding the value 174 to the sensitivity. That is to say, there is a one-to-one correspondence between the carrier-to-noise ratio and the GPS signal strength. The carrier-to-noise ratio has a nonlinear relationship with the GPS signal strength, and the stronger the GPS signal, the greater the carrier-to-noise ratio. FIG. 5 is a lookup table 500 corresponding to the estimated GPS signal strength and carrier-to-noise ratio in FIG. 3 . In the lookup table, corresponding to different GPS signal strengths, there are different carrier-to-noise ratios. Those of ordinary skill in the art can also understand that if the GPS signal strength is estimated according to the above formula (2) or (3), the corresponding relationship between the estimated GPS signal strength and the carrier-to-noise ratio will change, that is, as shown in Figure 5 The value in the lookup table changes accordingly.

Referring to FIG. 2 again, the conversion module 320 finds the corresponding carrier-to-noise ratio value according to the preset look-up table shown in FIG. carrier-to-noise ratio.

The present invention estimates the strength of the GPS signal based on the in-phase component signal I(P) and the quadrature component signal Q(P) generated in the tracking loop, and then uses a preset lookup table to obtain the carrier-to-noise ratio of the GPS signal, which can Reduce hardware occupation and reduce computational complexity.

Finally, it should be noted that the above embodiments are only used to illustrate the present invention without limitation, although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the present invention can be modified or equivalently replaced , without departing from the spirit and scope of the present invention, all of which should be included in the scope of the claims of the present invention.

Claims (10)

1. A method for estimating the GPS signal carrier-to-noise ratio, the GPS signal is converted into a digital signal, it is characterized in that the method comprises: 1) using a preset local reference signal to divide the digital signal into an in-phase component and a quadrature component; 2) Correlate the in-phase component and the quadrature component with the local pseudo-random noise code to obtain an in-phase component signal and a quadrature component signal. The phase of the local pseudo-random noise code is the same as that of the pseudo-random noise code in the GPS signal ; 3) Estimating a first estimated value and a second estimated value related to the GPS signal based on the in-phase component signal and the quadrature component signal; 4) dividing the first estimated value by the second estimated value to obtain the strength of the GPS signal; and 5) Find the corresponding carrier-to-noise ratio value from the preset lookup table according to the strength of the GPS signal. 2. the method for estimating GPS signal carrier-to-noise ratio according to claim 1 is characterized in that, described first estimated value and second estimated value are obtained by following formula: $\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}\right.$ Where SL and NL are the first estimated value and the second estimated value respectively; Ii and Qi are the in-phase component signal and the quadrature component signal respectively; M is the integration time. 3. the method for estimating GPS signal carrier-to-noise ratio according to claim 1, is characterized in that, described first estimated value and second estimated value are obtained by following formula: $\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; |</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span>\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; )</span>\end{array}\right.$ Where SL and NL are the first estimated value and the second estimated value respectively; Ii and Qi are the in-phase component signal and the quadrature component signal respectively; M is the integration time. 4. the method for estimating GPS signal carrier-to-noise ratio according to claim 1, is characterized in that, described first estimated value and second estimated value are obtained by following formula: $\left\{\begin{array}{c}\mathrm{<span\; class="notranslate">\; SL</span>}<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\\ \mathrm{<span\; class="notranslate">\; NL</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\sqrt{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>\end{array}\right.$ Where SL and NL are the first estimated value and the second estimated value respectively; Ii and Qi are the in-phase component signal and the quadrature component signal respectively; M is the integration time. 5. according to the method for the estimated GPS signal carrier-to-noise ratio described in any one of claim 1-4, it is characterized in that, described local pseudo-random noise code is output by the pseudo-random noise code generator in the code tracking loop Local instant pseudorandom noise code. 6. The method for estimating the GPS signal carrier-to-noise ratio according to any one of claims 1-4, characterized in that, before the step of calculating the strength of the GPS signal, it also includes the first estimated value and the A step of performing filtering processing on the second estimated value. 7. A GPS receiver for estimating the carrier-to-noise ratio of the GPS signal, the GPS receiver converts the GPS signal into a digital signal, wherein the GPS receiver includes: a Doppler frequency shift removal module that divides the digital signal into an in-phase component and a quadrature component; Integral module, described in-phase component and quadrature component carry out correlation operation with local pseudo-random noise code respectively, obtain an in-phase component signal and a quadrature component signal, the pseudo-random noise code in this local pseudo-random noise code and GPS signal the same phase; A signal strength estimation module, which estimates a first estimated value and a second estimated value related to the GPS signal according to the in-phase component signal and the quadrature component signal output by the integration module, and based on the first estimated value and the second estimated value 2 Estimated, calculated strength of the GPS signal; and A conversion module, which finds the corresponding carrier-to-noise ratio value from a preset look-up table based on the strength of the GPS signal. 8. the GPS receiver of estimating GPS signal carrier-to-noise ratio according to claim 7, is characterized in that, described signal strength estimation module comprises: a first integration unit, configured to integrate the in-phase component signal and the quadrature component signal within a predetermined time length; a square summation unit, used to square the integrals of the in-phase component signal and the quadrature component signal output by the first integration unit and add the squared values to obtain the first estimated value; A square unit is used to square the in-phase component signal and the quadrature component signal respectively; The second integration unit integrates the square of the in-phase component signal and the quadrature component signal output by the square unit within the predetermined time length; A summation unit, which adds the integrals of the in-phase component signal and the quadrature component signal output by the second integration unit to obtain the second estimated value; and The estimation module calculates the strength of the GPS signal based on the first estimated value and the second estimated value. 9. the GPS receiver of estimating GPS signal carrier-to-noise ratio according to claim 8, is characterized in that, described signal strength estimation module also comprises first filter and second filter, respectively to described first estimated value and performing filtering processing with the second estimated value. 10. The GPS receiver for estimating the carrier-to-noise ratio of GPS signals according to claim 9, wherein the first filter and the second filter are low-pass filters.

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