KR101015890B1 - Signal acquisition method and apparatus of GNSS receiver - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for acquiring a signal of a global navigation satellite system (GNSS) receiver. In order to perform fast signal acquisition for a navigation signal, an input signal rate control technique and a pseudo noise (PRN) Fast Fourier transform (FFT) lookup table (FFT Lookup Table), FFT Doppler Search, Max Serial Search, etc. It features.

The signal acquisition method and apparatus of the satellite navigation system receiver according to the present invention can shorten the signal acquisition time of the GNSS receiver and reduce the fast Fourier transform (FFT) operation. Can be efficiently satisfied.

Global Navigation Satellite System (GNSS), Acquisition,

Description

Signal acquisition method and apparatus of satellite navigation system receiver

The present invention relates to a navigation receiving method and apparatus of a global navigation satellite system (GNSS) receiver, and more particularly, to a method and apparatus for fast signal acquisition for a global navigation satellite system (GNSS) navigation signal.

The present invention is derived from a study conducted as part of the technology development of satellite navigation ground station system and search rescue terminal by the Ministry of Knowledge Economy [2006-S-021-03, Development of satellite navigation ground station system and search rescue terminal].

The Global Navigation Satellite System (GNSS) is a series of systems that locates targets and provides visual information using multiple satellites and terrestrial receivers.

The satellite navigation system is used for navigation, geodetic and surveying of ground, air and sea traffic. The scope of application is expanding in various fields such as earth science, and is applied to national crisis management such as search & rescue and natural disaster response system.

 The world's three largest satellite navigation systems are the Global Positioning System (GPS) in the United States, the Global NAvigation Satellite System (GLONASS) in Russia, and GALILEO in the European Union.

However, GLONASS (GLObal NAvigation Satellite System) is difficult to provide global service due to the lack of the number of satellites to operate, and GALILEO is now in the stage of launching its first test satellite, so it is actually operating the system at this point. GPS only.

China's Beidou satellite and Japan's Quasi-Zenith Satellite System (QZSS) are satellite-based signal reinforcement systems (SBAS) and regional navigation satellites (RNSS). System).

The reason why countries are rushing to develop satellite navigation system (GNSS) is because GNSS is a cutting-edge core technology infrastruc- ture and its ripple effect on the industry is closely related to military and security aspects.

The Global Navigation Satellite System (GNSS) controls space segments and satellites that are usually located in the mid-orbit around the Earth. It consists of subdivisions such as ground control segments that monitor and provide services, and user segments of service users.

The GNSS receiver calculates satellite state (position, velocity, acceleration, etc.) using the initialization process, signal acquisition and tracking process, information extraction process of extracting satellite navigation information from the acquired GNSS signal, and extracted satellite navigation information. The receiver obtains position information and time information through a navigation solution calculation process that calculates corresponding satellite estimates.

Here, the signal acquisition and tracking process is the most basic and important function that the GNSS receiver performs.

In particular, the signal acquisition process, also called initial synchronization, is the first essential process for normal operation of the GNSS receiver, and is a process of finding the carrier frequency and code phase of the GNSS satellite signal.

In order to acquire a signal, a process of searching for a two-dimensional search grid obtained by dividing a range of code phases and carrier frequencies by a predetermined size is performed.

In addition, to improve the performance of the GNSS navigation receiver, it is necessary to quickly search the search grid to reduce the average signal acquisition time.

A method of simultaneously searching multiple search grids for fast signal acquisition has been proposed.

Searching multiple search grids simultaneously includes multiple correlators, matched filters, and fast fourier transforms (FFTs).

Multiple correlators are a method of using multiple correlators for searching multiple code phases simultaneously.

The matched filter is a mathematically equivalent method to the multi-correlator, but it has the advantage of consuming less resources than the multi-correlator by different implementation methods.

Correlators using fast fourier transform (FFT) are equivalent in the frequency domain to multiple correlators or matched filters, and have complex computations but considerably short signal processing time.

The Fast Fourier transform (FFT) method is the fastest among the three signal acquisition methods presented above.

Fast Fourier Transform (FFT) can be divided into Parallel Frequency Space Search and Parallel Code Phase Search.

In order for the GNSS receiver to operate in real time, the information that is provided to the tracking process becomes useful when a signal acquisition process must be performed at a short time.

If the signal acquisition process of the GNSS receiver consumes a long time, the information of acquisition is not appropriate to operate the tracking loop process. Therefore, the time difference between the signal acquisition and the current data should be estimated and transmitted to the tracking loop.

However, if the time difference becomes longer, the estimation error increases and the tracking loop does not operate.

Therefore, in order to perform continuous data processing, it is necessary to shorten the processing time of the block data, which is a problem of reducing the amount of software required for signal acquisition.

The technical problem to be achieved by the present invention relates to a method and device for receiving navigation navigation system Global Navigation Satellite System (GNSS), in order to perform a fast signal acquisition for the navigation signal, the input signal rate control (Rate Control), pseudo noise (PRN) Fast Signal Acquisition Using Fast Fourier Transform (FFT Lookup Table), FFT Doppler Search, and Max Serial Search It is to provide a method and apparatus for.

One embodiment of a signal acquisition method of a satellite navigation system receiver according to the present invention for solving the above technical problem, Fast Fourier transform (FFT) code of the pseudo-random noise (PRN) code of the satellite A PRN code storing step of storing a result value obtained by the processing; An input signal adjusting step of adjusting the speed of an input signal based on a chip speed of a pseudo noise (PRN) code of the satellite; Performing an FFT operation on the speed-controlled input signal; An IFTF execution step of performing an inverse fast Fourier transform (IFTF) by multiplying the FFT result of the stored PRN code by the FFT result of the input signal; And a maximum value retrieving step of retrieving a maximum value for each Doppler frequency of an input signal from the IFTF execution result value.

Preferably, the signal acquisition method of the satellite navigation system receiver includes a carrier removing step of multiplying the input signal by a sine wave function to output a baseband signal; And an FFT search step of shifting an FFT result value for the input signal to implement a Doppler frequency change.

Preferably, the chip speed of the pseudo noise (PRN) code in the input signal adjusting step of the signal acquisition method of the satellite navigation system receiver is dependent on the search resolution.

Preferably, the input signal in the input signal adjusting step of the signal acquisition method of the satellite navigation system receiver is a result function of multiplying an intermediate frequency (IF) signal by a sinusoidal wave function.

Preferably, the method further includes performing frequency scaling on the input signal adjusted in the input signal adjusting step of the signal acquisition method of the satellite navigation system receiver.

According to an embodiment of the present invention, there is provided an apparatus for acquiring a signal of a satellite navigation system (GNSS) receiver according to an embodiment of the present invention, wherein a pseudo-random noise (PRN) code of a satellite is fast Fourier transformed (FFT: fast). An FFT storage unit for storing a result obtained by Fourier transform; An input signal controller configured to adjust the speed of an input signal based on a chip speed of a pseudo noise (PRN) code of the satellite; An FFT calculator configured to perform FFT on the speed-controlled input signal; An IFTF operation unit for performing an inverse fast Fourier transform (IFTF) by multiplying the FFT result of the stored PRN code by the FFT result of the input signal; And a maximum value searching unit searching for a maximum value of each Doppler frequency of the input signal in the IFTF calculation result value.

Preferably, the input signal controller of the signal acquisition device of the GNSS receiver adjusts the speed of the input signal based on a chip speed of a pseudo noise (PRN) code of the satellite. ); And a frequency scaling unit for performing frequency scaling on the speed-controlled input signal.

Preferably, the chip speed of the pseudo noise (PRN) code of the input signal controller of the signal acquisition device of the satellite navigation system (GNSS) receiver depends on the search resolution.

Preferably, the signal acquisition device of the satellite navigation system (GNSS) receiver further includes a carrier removing unit for multiplying the input signal by a sinusoidal wave function to output a baseband signal.

Preferably, the signal acquisition device of the satellite navigation system (GNSS) receiver further includes an FFT search unit for shifting the FFT result value for the input signal to implement a Doppler frequency change.

Preferably, the FFT search unit of the signal acquisition device of the GNSS receiver determines a shift value of the FFT result for the input signal based on the Doppler search number; A Doppler shift shifting an FFT result according to the determined FFT shift value; And an adjusting unit that performs frequency scaling of the shifted FFT result.

Preferably, the FFT storage unit of the signal acquisition device of the GNSS receiver includes an oversampling unit for repeatedly sampling the satellite PRN code based on a search resolution; And a memory configured to store a result of performing an FFT operation on the PRN code of the satellite.

One embodiment of a signal acquisition method of a satellite navigation system receiver according to the present invention for solving the above technical problem, Fast Fourier transform (FFT) code of the pseudo-random noise (PRN) code of the satellite A PRN code storing step of storing a result value obtained by the processing; Performing an FFT operation after adjusting the speed of the input signal based on the chip speed of the pseudo noise code; And a correlation checking step of obtaining a correlation value between the FFT result value of the PRN code and the FFT result of the input signal.

 Preferably, the correlation value of the signal acquisition method of the satellite navigation system receiver is obtained by performing an inverse fast Fourier transform (IFTF) by multiplying the FFT result of the PRN code by the FFT result of the input signal. It features.

Preferably, the Doppler frequency change of the input signal in the correlation checking step of the signal acquisition method of the satellite navigation system receiver is obtained by shifting the FFT result of the input signal.

As described above, the signal acquisition method and apparatus of the satellite navigation system according to the present invention provide an implementation method using an FFT to obtain a navigation signal within a short time in the signal acquisition of the GNSS navigation receiver.

The signal acquisition time of the GNSS receiver can be shortened through the signal acquisition method and apparatus of the satellite navigation system according to the present invention.

In addition, by reducing the FFT operation, the hardware resources and specifications constituting the receiver can be efficiently satisfied.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings that can be easily implemented by those skilled in the art.

Global Navigation Satellite System (GNSS) receivers started in the first analog form and are now the mainstream receivers using digital hardware.

A general GNSS receiver using digital hardware converts a GNSS signal received from an antenna into an intermediate frequency (IF) signal to perform A / D conversion to perform reverse spread from an RF (Radio Frequency) front-end part and an IF signal. It consists of a digital processor and a microprocessor that controls the receiver's operation and performs navigation.

With the development of the semiconductor industry, hardware-based GNSS receivers are increasingly developing into smaller, lower power, lower cost structures.

Recently, in order to make up for the shortcomings of hardware-based GNSS receivers, studies on software-based GNSS receivers (SGR) technologies that process both the RF front-end and the RF front-end by software have been actively conducted.

Software GNSS receivers aim to configure receivers in simplified hardware by eliminating portions of hardware that can be processed by software from existing hardware receivers.

That is, the software GNSS receiver A / D converts the GNSS signal converted to the intermediate frequency through the RF front-end, and then processes the software using software implemented in the processor without going through a hardware correlator.

Software GNSS receiver can shorten the system development time because the algorithm developed through simulation can be applied directly to the receiver, and the change of algorithm can be applied immediately without modification of hardware. It can be done easily.

In addition, even when combined with other systems, the combination algorithm can be implemented using only the raw A / D converted values of the two systems and the combination of more powerful and stable forms can be achieved.

1 shows a general structure of a software-based GNSS receiver.

The software-based GNSS receiver consists of an RF front-end 110 and a processor 120.

The GNSS signal is converted to an intermediate frequency through an amplification and a down conversion in the RF front-end 110, and is discretized into a digital intermediate frequency (IF) signal through an A / D converter and input to a digital signal processor.

The processor 120 performs the functions of signal acquisition and tracking, navigation data extraction, and position calculation of the receiver using the discrete IF signals obtained from the RF front-end.

FIG. 2 is a diagram illustrating the performance of signal acquisition and tracking, navigation data extraction, and position calculation of a receiver using discrete IF signals obtained from the RF front-end of a GNSS receiver.

The signal acquisition module 210 detects the presence or absence of a GNSS signal in the discrete IF signal and provides information of the corresponding signal to the signal tracking module 220 to enable continuous signal tracking.

The signal tracking module 220 tracks the code delay and Doppler frequency of the received GNSS signal through the carrier and code tracking loops and generates raw measurements for the navigation calculation.

As the carrier tracking loop, a technique such as a phase locked loop (PLL) or a frequency locked loop (FLL) assisted PLL is used, and a delay lock loop (DLL) is generally used as the code tracking loop.

The navigation message processing module 240 decodes the navigation message of the received GNSS signal and extracts navigation data for correcting satellite orbit information and time and delay errors.

The navigation module 230 calculates the position of the GNSS satellite from satellite orbit information (Ephemeris), and calculates the position and velocity of the receiver using measurements such as pseudo range and pseudo range change rate.

3 is a diagram illustrating a signal acquisition method using an FFT.

 The signal acquisition module 210 of FIG. 2 performs a function of detecting a received GNSS signal through a two-dimensional search of a code delay and a Doppler frequency.

In the signal search, the signal acquisition module sets a search interval at a predetermined interval, and sequentially moves the search interval to determine whether to acquire a signal by checking a correlation between a corresponding Doppler frequency and a code.

The search range of the Doppler frequency is set differently according to the purpose and range of the receiver.

In general, a software-based GPS receiver uses a parallel search method using fast fourier transform (FFT) -inverse FFT (IFFT) as shown in FIG.

The FFT-IFFT-based signal acquisition technique defines the cyclic correlation function of the frequency domain corresponding to the two-dimensional search space and processes parallelized code at once. It has the advantages of high-speed signal acquisition and software design.

4 is a view showing a signal acquisition result for the GPS satellite (PRN18) detected using the FFT-IFFT technique.

5 is a diagram illustrating a structure of a signal acquisition unit of a GNSS receiver according to the present invention.

The signal acquisition of the GNSS receiver according to the present invention is operated by the parallel code search method of the FFT method.

The signal acquisition unit of the GNSS receiver according to the present invention includes a carrier removing unit 501, an input signal adjusting unit 502, an FFT operator 503, an FFT Doppler searcher 504, an FFT storage unit 505, and an IFFT operator 506. ) And a maximum value retrieval unit 507.

The carrier removing unit 501 serves to drop the signal to the baseband by multiplying the SIN and COS carriers with respect to the digitized input sample input through the ADC (A / D converter) of the RF front-end (110 of FIG. 1). To perform.

The input signal controller 502 adjusts the speed of the input sample according to PRN (Pseudo-Random Noise) code chip rate in order to perform an FFT operation having a resolution within 500 MHz.

The chip speed of PRN (Pseudo-Random Noise) code depends on the search resolution.

The FFT calculator 503 performs an FFT operation on the rate-controlled input sample.

The FFT Doppler search unit 504 changes the Doppler frequency with respect to the result of the FFT calculator.

The Doppler frequency change in the signal acquisition of the GNSS receiver according to the present invention is not performed by the carrier removing unit 501, but is performed on the result of the FFT operation.

The FFT storage unit 505 improves the operation speed by storing the FFT result for PRN (Pseudo-Random Noise) code in memory in advance.

The IFFT operator 506 multiplies the result of the FFT Doppler searcher 504 by the result of the FFT storage 504 to perform an inverse fast Fourier transform (IFFT) operation.

The maximum value retrieval unit 507 retrieves a maximum value for each Doppler frequency.

6 is a diagram illustrating a detailed structure of an input signal controller of FIG. 5.

When the GNSS receiver is initialized, the external controller 611 calculates the chip rate according to the required FFT size and search resolution of PRN (Pseudo-Random Noise) code according to the type of the GNSS signal.

The chip search resolution of the PRN code is typically 0.5.

The rate controller 612 performs a function of changing the speed of samples input through the carrier removing unit to the chip rate of a pseudo-random noise (PRN) code.

The scaling unit 613 scales input sample values accumulated at a changed speed for efficient FFT operation.

The maximum FFT size that can be calculated when performing FFT operation through real hardware is generally 65536 = 2 ^ 16, and this value is exceeded when the sampling rate of the input sample is high.

By adjusting the speed of the input sample through the input signal controller 502, the GNSS receiver according to the present invention can perform the FFT on the input sample according to the PRN code chip resolution when performing the FFT operation on several GNSS signals. have.

FIG. 7 illustrates a detailed structure of the FFT Doppler search unit in FIG. 5.

When the GNSS receiver is initialized, the external controller 721 determines the FFT size determined according to the type of the GNSS signal, and calculates the number of possible Doppler searches based on the determined FFT size.

The Doppler Bin Shift Controller 723 determines the shift value of the FFT based on the calculated Doppler search number.

The Doppler shift 724 performs the FFT shift by the FFT shift value determined by the Doppler Bin Shift Controller 723.

The scaling unit 722 performs scaling in advance in order to satisfy the number of bits required for the IFFT operation when the sample values of which the Doppler frequency is changed are moved.

The structure of the carrier removing unit 501 of FIG. 5 is simplified through the scaling unit.

The carrier elimination unit does not operate several times while changing the Doppler frequency, and performs the FFT operation in one operation at the fundamental frequency, thereby saving time by the Doppler search number * FFT operation time.

FIG. 8 is a diagram illustrating a detailed structure of the FFT storage unit in FIG. 5.

When the GNSS receiver is initialized, the oversampling unit (Oversamplig, 832) receives the chip resolution through the external controller 831, and repeatedly oversamples the PRN codes of all satellites according to the chip resolution.

The scaling unit 834 scales the result of performing the FFT operation 833 on the PRN codes of all the satellites according to the FFT scaling of the input signal.

The memory 835 stores 835 a result of performing an FFT operation on the PRN code of the satellite.

Through the FFT storage unit in the present invention, the GNSS receiver can reduce the operating time of the receiver by directly importing from the memory without performing the FFT operation on the PRN code separately.

By multiplying the result of the FFT Doppler searcher (504 of FIG. 5) with the result of the FFT storage unit (505 of FIG. 5) and performing an IFFT operation, a correlation value of possible code phases for one Doppler frequency can be obtained.

9 is a flowchart illustrating a maximum value search in the maximum value search unit of FIG. 5.

Correlation values obtained by performing the IFFT (506 in FIG. 5) operation exist for all Doppler frequencies.

In addition, the correlation values obtained by performing the IFFT operation (506 of FIG. 5) are increased exponentially when the Coherent and NonCoherent functions or the Secondary Code functions are performed.

An increase in correlation results in an increase in memory space to store it.

Therefore, in order to effectively utilize the memory space, the GNSS receiver according to the present invention uses a method of obtaining and updating a maximum value for each Doppler frequency instead of obtaining a maximum value after obtaining a correlation value for all frequencies.

10 is a flowchart illustrating a signal acquisition method of the satellite navigation system according to the present invention.

The result obtained by fast Fourier transform (FFT) of the pseudo-random noise (PRN) code of the satellite is stored in advance in the FFT storage unit (S1010).

The speed of the input signal is adjusted based on the chip speed of the pseudo noise (PRN) code of the satellite (S1020).

The FFT calculator performs an FFT on the speed adjusted input signal (S1030).

The IFFT operator performs an IFFT by multiplying the FFT result of the stored PRN code by the FFT result of the input signal (S1040).

The maximum value for each Doppler frequency of the input signal is retrieved from the IFFT execution result value (S1050).

So far I looked at the center of the preferred embodiment for the present invention.

Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 shows a general structure of a software-based GNSS receiver.

FIG. 2 is a diagram illustrating the performance of signal acquisition and tracking, navigation data extraction, and position calculation of a receiver using discrete IF signals obtained from the RF front-end of a GNSS receiver.

3 is a diagram illustrating a signal acquisition method using an FFT.

4 is a view showing a signal acquisition result for the GPS satellite (PRN18) detected using the FFT-IFFT technique.

5 is a diagram illustrating a structure of a signal acquisition unit of a GNSS receiver according to the present invention.

6 is a diagram illustrating a detailed structure of an input signal controller of FIG. 5.

FIG. 7 illustrates a detailed structure of the FFT Doppler search unit in FIG. 5.

FIG. 8 is a diagram illustrating a detailed structure of the FFT storage unit in FIG. 5.

9 is a flowchart illustrating a maximum value search in the maximum value search unit of FIG. 5.

10 is a flowchart illustrating a signal acquisition method of the satellite navigation system according to the present invention.

Claims (15)

A PRN code storing step of storing a result obtained by fast Fourier transform (FFT) of a pseudo-random noise (PRN) code of a satellite; An input signal adjusting step of adjusting the speed of an input signal based on a chip speed of a pseudo noise (PRN) code of the satellite; Performing an FFT operation on the speed-controlled input signal; An IFFT execution step of performing an inverse fast Fourier transform (IFFT) by multiplying an FFT result of the stored PRN code by an FFT result of the input signal; And And a maximum value retrieval step of retrieving a maximum value of each Doppler frequency of an input signal from the IFFT execution result value. The method of claim 1, Removing a carrier by multiplying the input signal by a sinusoidal function and outputting a baseband signal; And And a FFT search step of shifting an FFT result value for the input signal to implement a Doppler frequency change. The method of claim 1, The chip speed of the pseudo noise (PRN) code in the step of adjusting the input signal is a signal acquisition method of a satellite navigation system (GNSS) receiver, characterized in that it depends on the search resolution. The method of claim 1, The input signal in the input signal control step is a signal acquisition method of a satellite navigation system (GNSS) receiver, characterized in that the result of multiplying an intermediate frequency (IF) signal by a sinusoidal function. The method of claim 1, And performing frequency scaling on the input signal of which the speed is adjusted in the input signal adjusting step. An FFT storage unit for storing a result obtained by fast Fourier transform (FFT) of a pseudo-random noise (PRN) code of a satellite; An input signal controller configured to adjust a speed of an input signal based on a chip speed of the pseudo noise (PRN) code; An FFT calculator configured to perform FFT on the speed-controlled input signal; An IFFT operation unit performing an inverse fast Fourier transform (IFFT) by multiplying an FFT result of the pseudo noise (PRN) code by an FFT result of the input signal; And And a maximum value searcher for searching for a maximum value of each Doppler frequency of an input signal in the IFFT calculation result value. The method of claim 6, wherein the input signal adjusting unit A rate controller for adjusting the speed of the input signal based on a chip speed of the pseudo noise (PRN) code; And And a frequency scaling unit configured to perform frequency scaling on the speed-controlled input signal. 2. The method of claim 6, And a chip speed of the pseudo noise (PRN) code of the input signal controller is changed according to a search resolution. The method of claim 6, And a carrier removal unit for multiplying the input signal by a sinusoidal function and outputting the baseband signal as a baseband signal. The method of claim 6, And a FFT searcher for shifting the FFT result of the input signal to implement a Doppler frequency change. The method of claim 10, The FFT search unit A Doppler movement control unit determining a shift value of an FFT result for the input signal based on a Doppler search number; A Doppler shift shifting an FFT result according to the determined FFT shift value; And And an adjusting unit configured to perform frequency scaling of the shifted FFT result value. The method of claim 6, The FFT storage unit An oversampling unit for repeatedly sampling the pseudo noise (PRN) code based on a search resolution; And a memory storing a result value of performing an FFT operation on the pseudo noise (PRN) code. A PRN code storing step of storing a result obtained by fast Fourier transform (FFT) of a pseudo-random noise (PRN) code of a satellite; Performing an FFT operation after adjusting the speed of the input signal based on the chip speed of the pseudo noise code; And And a correlation test step of obtaining a correlation value based on the FFT result value of the PRN code and the FFT result of the input signal. The method of claim 13, The correlation value is obtained by performing an inverse fast Fourier transform (IFFT) by multiplying the FFT result of the PRN code by the FFT result of the input signal. The method of claim 13, The Doppler frequency change of the input signal in the correlation checking step is obtained by shifting the FFT result value of the input signal.

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