JP2003255036A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously detect an IF frequency carrier wave, even in the case the signal intensity of the wave from a satellite is weak. <P>SOLUTION: A signal transmitted from a GPS satellite is received by an antenna 14 and converted into an intermediate frequency (IF) wave by a frequency converter 23, and then a synchronization holding section 25 executes holding of the synchronization of the signal. In the case the signal strength of the wave from the satellite is weak, two channel circuits 91 among a plurality of channel circuits 91 are assigned, and frequencies shifted by a prescribed frequency β upwardly and downwardly, in relation to an expected frequency of the IF carrier wave are set respectively. The frequency of the IF carrier wave is continuously detected by comparing levels of the reception in the two channel circuits 91. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a Global Navigation Satellites System (GNSS).
The present invention relates to a receiving device that receives signals transmitted from a plurality of satellites constituting m) and calculates its own position.

[0002]

2. Description of the Related Art In recent years, Global Navigation Satellites S (GNSS) has been used to measure the position of a moving body on the ground using artificial satellites that orbit the earth.
ystem) is becoming popular. As such a global positioning system, the GPS (Glob
al Positioning System), GLONASS constructed by the former Soviet Union, and GALILEO being constructed mainly by European countries. In the following description, a GPS, which is being widely used in Japan as a global positioning system, will be described, but the same applies to other global positioning systems.

In this GPS system, a signal sent from a GPS satellite is received to calculate its own position G
The PS receiver has a function of receiving signals from at least four or more GPS satellites, calculating the position of itself based on the received signals, and notifying the user of the position. The GPS receiving device demodulates the signal transmitted from each GPS satellite to obtain the orbit information of each GPS satellite, and based on the orbit information and time information of each GPS satellite and the delay time of the received signal,
The self-three-dimensional position is calculated by simultaneous equations.

In the GPS system, at least four GPS satellites are required to obtain a received signal for the following reason. That is, there is an error between the internal time of the clock provided in the GPS receiving device and the time obtained by the atomic clock provided in each GPS satellite, and four unknown parameters of the three-dimensional position and the accurate time, which eliminate the influence of the error, are set. This is because at least four pseudo-ranges from GPS satellites are needed to calculate.

In the GPS system, a GP for consumer use
When using S receiver, GPS satellite (Navstar)
The spread spectrum signal radio wave called the C / A (Clear and Acquisition) code from the L1 band is received and the positioning calculation is performed.

The transmission signal called the C / A code in the L1 band has a transmission signal speed, that is, a chip rate of 1.
Pseudo-random noise with a code length of 023 MHz, such as a so-called Gold code, of 1023.
e; PN) spreading code, the frequency is 1575.42 MHz due to a signal obtained by directly spreading data of 50 bps.
Binary Phase Shift Keying (hereinafter referred to as BPS)
The signal is modulated based on the K modulation method). In this case, since the code length is 1023, the spreading code of the C / A code is 1023 as shown in the first row of FIG.
The chip is repeated for one cycle, that is, one cycle = 1 millisecond (msec).

The spread code of the C / A code differs for each GPS satellite, but which GPS satellite uses which spread code can be detected in advance by the GPS receiver. In addition, the GPS receiving device is capable of grasping from which GPS satellite a signal can be received at that point and at that time by a navigation message described later. Therefore, in the case of three-dimensional positioning, for example, the GPS receiving device can obtain at least four GPs that can be acquired at that point and at that time.
The position of the self is obtained by receiving the radio wave from the S satellite, despreading the spectrum, and performing positioning calculation.

Further, 1 bit of the signal data from the GPS satellite is transmitted in units of 20 cycles of the spread code, that is, in units of 20 milliseconds, as shown in the second row in the figure. That is, the data transmission rate is 50b as described above.
ps. Further, 1023 chips for one cycle of the spread code are inverted when the bit is "1" and "0".

Further, in the signal from the GPS satellite, one word is formed in 30 bits, that is, 600 milliseconds, as shown in the third row in FIG. Furthermore, in the signal from the GPS satellite, one subframe is formed in 10 words, that is, in 6 seconds, as shown in the fourth row in FIG. Then, in the signal from the GPS satellite, as shown in the fifth row in the figure, the preamble that is always the specified bit pattern is always included in the first word of one subframe even when the data is updated. It is inserted and data is transmitted following this preamble.

Furthermore, in the signal from the GPS satellite, 5 subframes, that is, 1 frame is formed in 30 seconds. Then, in the signal from the GPS satellite, the navigation message described above is transmitted in the data unit of this one frame.

The first 3 of the 1 frame of data
Each subframe is information unique to the GPS satellite called Ephemeris information. This ephemeris information includes a parameter for determining the orbit of the GPS satellite and the time at which the signal from the GPS satellite is transmitted.

Since all GPS satellites are equipped with atomic clocks, common time information is used, and the signal transmission time from the GPS satellites contained in the ephemeris information is set to 1 second of the atomic clock. The spread code of the GPS satellite is generated as being synchronized with the atomic clock.

The orbit information included in the ephemeris information is
It is updated every few hours, but until the update is done,
It is the same information. Therefore, the GPS receiving device can accurately use the same orbit information for several hours by holding the orbit information included in the ephemeris information in the memory. The signal transmission time from the GPS satellite is updated every second.

On the other hand, the navigation messages of the remaining two subframes of the data of one frame are information called Almanac information transmitted in common from all GPS satellites. This almanac information requires 25 frames to acquire all the information, and the approximate position information of each GPS satellite and which GP
It is composed of information and the like indicating whether the S satellite can be used. This almanac information is updated every few days,
Until the update is performed, the same information is used. Therefore, the GPS receiving device can accurately use the same information for several days by holding the almanac information in the memory.

In order to receive the above-mentioned data by receiving the signal from the GPS satellite, the GPS receiving device first removes the carrier and then the C / A code used in the GPS satellite to be received. Using the same spreading code, the signal from the GPS satellite is acquired by phase-locking the C / A code with respect to the signal from the GPS satellite.
Performs spectrum despreading. GPS receiver is C / A
When the spectrum despreading is performed in phase synchronization with the code, the bits are detected, and the navigation message including the time information and the like can be acquired based on the signal from the GPS satellite.

The GPS receiving device captures signals from GPS satellites by phase synchronization search of C / A code.
As this phase synchronization search, the self-generated spreading code and G
Detects the correlation with the spread code of the received signal from the PS satellite,
For example, when the correlation value of the correlation detection result is larger than a predetermined value, it is determined that the two are synchronized. When the GPS receiver determines that the synchronization is not achieved, it uses some synchronization method to control the phase of the spreading code generated by itself and synchronize with the spreading code of the received signal. There is.

As described above, the signal from the GPS satellite is a signal obtained by modulating the carrier based on the BPSK modulation method with the signal obtained by spreading the data with the spreading code. Therefore, in order to receive the signal from the GPS satellite, the GPS receiver needs to synchronize not only the spread code but also the carrier and the data, but the spread code and the carrier cannot be synchronized independently.

In addition, the GPS receiver normally uses the carrier frequency of the received signal as an intermediate frequency (Interm) within several MHz.
ediate Frequency; hereinafter referred to as IF. ) To convert the received signal to an IF signal, and the IF signal is used to perform the above-described synchronization detection processing. The carrier in this IF signal (hereinafter, referred to as an IF carrier) is mainly a frequency error component due to Doppler shift according to the moving speed of the GPS satellites and the inside of the GPS receiver when converting the received signal to the IF signal. And the frequency error component of the local oscillator generated in.

Therefore, in the GPS receiver,
Since the IF carrier frequency is unknown due to these frequency error factors, it is necessary to search for that frequency. Also, the synchronization point (synchronization phase) within one cycle of the spreading code
Is unknown because it depends on the positional relationship between the GPS receiving device and the GPS satellites. Therefore, as described above, the GPS receiving device requires some kind of synchronization method.

The conventional GPS receiver uses a synchronization method that combines frequency search for carriers, synchronization acquisition by a sliding correlator, and synchronization holding by a DLL (Delay Locked Loop) and Costas loop. Hereinafter, this synchronization method will be described.

As the clock for driving the spread code generator of the GPS receiver, a clock obtained by dividing the reference frequency oscillator prepared in the GPS receiver is generally used.
A high-precision crystal oscillator is used as the reference frequency oscillator, and the GPS receiving apparatus uses a local oscillation signal used to convert a reception signal from a GPS satellite into an IF signal based on the output of the reference frequency oscillator. To generate.

Here, FIG. 16 shows the processing contents of the frequency search. The GPS receiver performs a phase synchronization search for the spread code when the frequency of the clock signal that drives the spread code generator is a certain frequency f1. That is, the GPS receiving apparatus detects the correlation between the signal received from the GPS satellite and the spread code at each chip phase by sequentially shifting the phase of the spread code by one chip, and detects the peak of the correlation. The phase that can be synchronized is detected by. Further, when the frequency of the clock signal is f1 and there is no synchronized phase in all of the 1023 chip phase searches when the frequency of the clock signal is f1, the GPS receiver changes, for example, the frequency division ratio to the reference frequency oscillator to change the clock frequency. Change the frequency of the signal to another frequency f2,
Similarly, a phase search for 1023 chips is performed. The GPS receiver realizes the frequency search by changing the frequency of the clock signal stepwise and repeating such an operation.

When the GPS receiver detects the frequency of the clock signal that can be synchronized by performing such a frequency search, it finally synchronizes the phase of the spread code with the frequency of the clock signal. This allows
The GPS receiving device can capture the signal from the GPS satellite even if the oscillation frequency of the crystal oscillator is deviated.

However, such a conventional synchronization method is not suitable for high-speed synchronization in principle. In the GPS receiver, if it takes time to synchronize the spread code and the IF carrier, the reaction becomes slow, which causes inconvenience in use. Therefore, in an actual GPS receiver, in order to compensate for this drawback, the number of channels is increased and parallel processing is performed to shorten the time until synchronization acquisition.

On the other hand, a matched filter is used as a method for performing synchronous acquisition of a spread spectrum signal at a high speed instead of the method using the sliding correlation described above. The matched filter can be realized digitally by a so-called transversal filter. Also,
As a matched filter, recent DSP (Digital Si
Fast Fourier Transform (Fast Fourier Transfor
m; hereinafter referred to as FFT. ) Has been used to implement a method for synchronizing spread codes at high speed with a digital matched filter. The latter is based on a long-known method for speeding up correlation calculation.

By using these matched filters, the GPS receiver detects the peak of the correlation when there is a correlation, for example, as shown in FIG. 17 for one cycle of the output waveform. The position of this peak indicates the beginning of the spread code. By detecting this peak, the GPS receiver can capture synchronization, that is, detect the phase of the spread code in the received signal. Also, G
The PS receiver uses, for example, the above-described digital matched filter that uses the FFT, and operates in the frequency domain of the FFT to determine the IF of the spread code and the phase of the spread code.
The carrier frequency can be detected. And GP
The S receiver converts the phase of the spread code into a pseudorange, and when at least four GPS satellites are detected, the G
The position of the PS receiver can be calculated, and the IF
The speed of the GPS receiver can be calculated based on the carrier frequency.

[0027]

By the way, in the GPS receiver, under the condition that the reception level of the signal transmitted from the GPS satellite is low, the synchronization between the reception signal and the spread code is maintained, while the IF is kept. Frequently, carrier synchronization is incomplete. Even in such a case, the phase of the spread code can be detected, so that there is no problem in calculating the position of the GPS receiving device.

However, the IF carrier frequency is G
It is constantly changing due to the influence of the Doppler effect due to the change in the relative position between the PS receiver and the GPS satellite. For this reason, under the above-described condition in which the IF carrier is not held in synchronism, there is a problem that the synchronism of the received signal and the spread code will be incomplete eventually, and the position cannot be calculated. It was

The present invention has been made in view of the above-mentioned conventional circumstances, and when receiving the signals transmitted from a plurality of satellites constituting the global positioning system and calculating its own position, the satellites are used. Even if the received level of the transmitted signal is low, detection of the IF carrier frequency is continued as much as possible, which allows the spread code to be held in synchronization and the position to be calculated. The purpose is to provide a device.

[0030]

A receiving device according to claim 1 of the present invention is a receiving device which receives signals transmitted from a plurality of satellites constituting a global positioning system and calculates its own position. Receiving means for receiving the signal transmitted from the satellite, frequency converting means for converting the frequency of the received signal received by the receiving means into a predetermined intermediate frequency, and intermediate frequency signal obtained by the frequency converting means. The phase and carrier frequency of the spread code in are assigned to a plurality of channels provided independently corresponding to the satellites and set, and the spread code and the carrier are held in synchronization and included in the intermediate frequency signal. If the signal strength from the satellite is below a predetermined strength, the synchronization means for demodulating the message to Channels for maintaining synchronization of the signals from the satellites concerned, and the frequencies higher and lower than the original carrier frequency by a predetermined value are set as initial values for these two channels respectively. Control means for controlling the synchronizing means so as to keep the carrier synchronized with the satellite by newly setting a frequency for reducing the difference between the signal levels output from the two channels. It is characterized by having and.

According to the present invention configured as described above,
Two channels in the synchronization means can be assigned to satellites with reduced received signal strength. Then, these two channels keep the frequency higher and lower than the original carrier frequency of the signal from the satellite by a predetermined value, respectively, and keep the difference between the signal levels respectively output from these two channels. Control to minimize. Therefore, even if there is a satellite with a weak received signal,
The detection of the carrier frequency in the intermediate frequency signal corresponding to this satellite can be continued, and thus the spread code synchronization can be maintained.

Further, in the receiving apparatus according to the present invention, the control means integrates or averages the results obtained by detecting the signal levels output from the two channels a plurality of times, and integrates or averages the respective signal levels. It is desirable to newly set a frequency for reducing the difference between these two channels. As a result, even if the signal level output from each channel fluctuates greatly due to the influence of noise or the like, the detection of the carrier frequency at the intermediate frequency can be reliably continued.

Further, in the receiving device according to the present invention,
The synchronization means includes a synchronization acquisition means for detecting the phase of the spread code in the intermediate frequency signal obtained by the frequency conversion means and a carrier acquisition frequency for the carrier frequency in the intermediate frequency signal, and the synchronization acquisition means. The spread code phase and the carrier frequency are set by assigning them to a plurality of channels provided independently corresponding to the satellites, and the set spread code phase and carrier frequency are set as initial values. It is desirable to include synchronization holding means for holding synchronization between the spread code and the carrier and for demodulating the message included in the intermediate frequency signal. With this, synchronization acquisition for detecting the phase of the spread code in the intermediate frequency signal and detection of the carrier frequency in the intermediate frequency signal,
The synchronization holding of the spread code and the carrier can be performed separately by the synchronization acquisition means and the synchronization holding means.
Therefore, the synchronization acquisition processing can be performed at high speed with a small circuit scale, and the time required to synchronize with the signal from the satellite can be significantly reduced.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described below in detail with reference to the drawings. Below, the Global Positioning System (GNSS: Global)
A case will be described in which the present invention is applied to a receiving device that receives signals transmitted from at least four satellites that make up the Navigation Satellites System) and calculates its own position based on these received signals. In this example, a GPS (Global Positioning System) widely used in Japan is assumed as a global positioning system, and a GPS receiving device will be described as a receiving device compatible with this GPS.

This GPS receiver is for L1 band, C / A
This is to receive a spread spectrum signal radio wave called a (Clear and Acquisition) code as a received signal. As shown in FIG. 1, when demodulating a received received signal, pseudo random noise (Pseudo- rando
(m Noise; PN) sequence spreading code and the spread code in the received signal are synchronized by separating the function and the spread code and carrier wave (hereinafter referred to as carrier) synchronization function is separated. It is configured to speed up the synchronization acquisition based on the circuit scale. However, the present invention is not limited to the application to such a GPS receiving device, and may be applied to a receiving device that receives signals transmitted from a plurality of satellites forming the global positioning system and calculates the position. Of course, it can be widely applied.

As shown in the figure, the GPS receiver 10 is a crystal oscillator (X'tal Oscillator; hereinafter referred to as XO) which generates a transmission signal D1 having a predetermined transmission frequency.
11 and a predetermined oscillation frequency F different from this XO11
Temperature Compensated X'tal Oscillator for Generating Oscillation Signal D2 with _OSC ;
Hereinafter referred to as TCXO. ) 12 and a multiplier / divider 13 for multiplying and / or dividing the oscillation signal D2 supplied from the TCXO 12.

The XO 11 generates an oscillation signal D1 having a predetermined oscillation frequency of, for example, 32.768 kHz. The XO 11 uses the generated oscillation signal D1 for RT described later.
Supply to C (Real Time Clock) 27.

The TCXO12 is different from the XO11 and has a predetermined oscillation frequency F _OSC of, for example, about 18.414 MHz.
Generate an oscillating signal D2. The TCXO 12 supplies the generated oscillation signal D2 to the multiplier / divider 13 and the frequency synthesizer 18 described later.

The multiplier / divider 13 is a CPU (Ce
The oscillation signal D2 supplied from the TCXO 12 is multiplied by a predetermined multiplication rate and / or divided by a predetermined division ratio based on the control signal D3 supplied from the ntral processing unit 26. The multiplication / frequency divider 13 includes a synchronization acquisition unit 24, which will be described later, a synchronization holding unit 25, which will be described later, a CPU 26, a timer 28 which will be described later, and an oscillation signal D3 which has been multiplied and / or divided.
And to a memory 29 described later.

The GPS receiver 10 also includes an antenna 14 for receiving an RF (Radio Frequency) signal transmitted from a GPS satellite, and a low noise amplifier (Low) for amplifying a received RF signal D5 received by the antenna 14. Noise Amplifier; hereinafter referred to as LNA.) 15
And the amplified RF signal D amplified by this LNA 15.
Band pass filter (hereinafter, referred to as BPF) 16 that passes a predetermined frequency band component out of 6
And the amplified RF signal D passed by this BPF 16
7, a frequency synthesizer 18 for generating a local oscillation signal D10 having a predetermined frequency F _LO based on the oscillation signal D2 supplied from the TCXO 12, and a predetermined frequency F _RF amplified by the amplifier 17. A mixer 19 for multiplying the amplified RF signal D8 having the local oscillation signal D10 supplied from the frequency synthesizer 18, and a predetermined frequency F _IF down-converted by being multiplied by the mixer 19.
Intermediate Frequency;
It is called IF. ) An amplifier 20 that amplifies the signal D11, and a low pass filter (hereinafter referred to as LPF) 21 that passes a predetermined frequency band component of the amplified IF signal D12 amplified by the amplifier 20.
The analog-type amplified IF signal D13 passed by the LPF 21 is converted to the digital-type amplified IF signal D14.
Analog / digital converter (Analog / Digit)
al Converter; hereinafter referred to as A / D. ) 22 and.

The antenna 14 is an R in which a carrier with a frequency of 1575.42 MHz transmitted from a satellite (hereinafter, referred to as a GPS satellite) that constitutes GPS is spread.
Receive the F signal. The received RF signal D5 received by the antenna 14 is supplied to the LNA 15.

The LNA 15 amplifies the received RF signal D5 received by the antenna 14. The LNA 15 supplies the amplified amplified RF signal D6 to the BPF 16.

The BPF 16 is a so-called SAW (Surface).
Acoustic wave) filter, and passes a predetermined frequency band component of the amplified RF signal D6 amplified by the LNA 15. The amplified RF signal D7 passed by the BPF 16 is supplied to the amplifier 17.

The amplifier 17 further amplifies the amplified RF signal D7 passed by the BPF 16. Amplifier 17
Is the amplified predetermined frequency F _RF , that is, 157
The amplified RF signal D8 of 5.42 MHz is supplied to the mixer 19.

Under the control of the control signal D9 supplied from the CPU 26, the frequency synthesizer 18 is controlled by the TCX.
A local oscillation signal D10 having a predetermined frequency F _LO is generated based on the oscillation signal D2 supplied from O12. The frequency synthesizer 18 uses the generated local oscillation signal D10.
Is supplied to the mixer 19.

The mixer 19 down-converts the amplified RF signal D8 by multiplying the amplified RF signal D8 having the predetermined frequency F _RF amplified by the amplifier 17 by the local oscillation signal D10 supplied from the frequency synthesizer 18. Then, the IF signal D11 having a predetermined frequency F _IF of, for example, about 1.023 MHz is generated. The IF signal D11 is supplied to the amplifier 20.

The amplifier 20 amplifies the IF signal D11 down-converted by the mixer 19. Amplifier 2
0 supplies the amplified amplified IF signal D12 to the LPF 21. The LPF 21 passes a lower band component than the predetermined frequency of the amplified IF signal D12 amplified by the amplifier 20. The amplified IF signal D13 passed by the LPF 21 is supplied to the A / D 22.

The A / D 22 converts the analog amplified IF signal D13 passed by the LPF 21 into a digital amplified IF signal D14. The amplified IF signal D14 converted by the A / D 22 is supplied to the synchronization acquisition unit 24 and the synchronization holding unit 25 bit by bit.

In the GPS receiver 10, among these units, the LNAs 15, 17, 20 and the BPF1 are included.
6, frequency synthesizer 18, mixer 19, LPF2
1, and the A / D 22 is a reception RF having a high frequency of 1575.42 MHz received by the antenna 14.
To facilitate the digital signal processing of the signal D5,
For example, the frequency conversion unit 23 down-converts to the amplified IF signal D14 having a low frequency F _{IF of} about 1.023 MHz.

Further, the GPS receiver 10 performs synchronous acquisition of the spread code generated by itself and the expanded code in the amplified IF signal D14 supplied from the A / D 22, and synchronous acquisition for detecting the carrier frequency in the amplified IF signal D14. The amplified IF signal D1 supplied from the unit 24 and the A / D 22
4, a synchronization holding unit 25 for holding the synchronization between the spread code and the carrier and demodulating the message, a CPU 26 for collectively controlling each unit to perform various arithmetic processing, and a time based on the oscillation signal D1 supplied from the XO11. RT to measure
C27 and a timer 28 as an internal clock of the CPU 26
RAM (Random Access Memory) and ROM (Read O
nly Memory) and the like.

The synchronization acquisition unit 24, which will be described in detail later, is C
Under the control of the PU 26, based on the multiplied and / or frequency-divided oscillation signal D3 supplied from the frequency multiplier / frequency divider 13, synchronization acquisition of the spread code in the amplified IF signal D14 supplied from the A / D 22 is performed. And the carrier frequency in the amplified IF signal D14 is detected. At this time, the synchronization acquisition unit 24 performs synchronization acquisition with coarse accuracy.
The synchronization acquisition unit 24 supplies the satellite number for identifying the detected GPS satellite, the phase of the spread code, and the carrier frequency to the synchronization holding unit 25 and the CPU 26.

The synchronization holding unit 25, which will be described in detail later, is C
Under the control of the PU 26, based on the multiplied and / or divided oscillation signal D3 supplied from the multiplier / divider 13, the spread code and carrier in the amplified IF signal D14 supplied from the A / D 22 While keeping the synchronization of
The navigation message included in the amplified IF signal D14 is demodulated. At this time, the synchronization holding unit 25, as described later,
The operation is started with the satellite number, the phase of the spread code, and the carrier frequency supplied from the synchronization acquisition unit 24 as initial values. The synchronization holding unit 25 uses the amplification I from a plurality of GPS satellites.
The F signal D14 is held in synchronism in parallel, and the detected spread code phase, carrier frequency, and navigation message are supplied to the CPU 26.

The CPU 26 acquires the phase of the spread code, the carrier frequency, and the navigation message supplied from the synchronization holding unit 25, and based on these various information, the CPU 26 of its own.
Various calculation processes such as a process of calculating the dimensional position and a process of correcting the time information of the GPS receiving apparatus 10 are performed. Further, the CPU 26 inputs / outputs each unit of the GPS receiving apparatus 10 and various peripherals, and input / output with the outside.
ut) controls overall.

The RTC 27 measures time based on the oscillation signal D1 supplied from the XO 11. This RTC2
7 is the time information measured by 27, which is used until the accurate time information of the GPS satellite is obtained, and the CPU 26 which has obtained the accurate time information of the position satellite of the GPS receiving device XO11 It is corrected as appropriate by controlling.

The timer 28 functions as an internal clock of the CPU 26, and is used for generating various timing signals necessary for the operation of each section and for time reference. For example, in the GPS receiving apparatus 10, the synchronization holding unit 25 is synchronized with the phase of the spread code captured by the synchronization capturing unit 24.
The timer 28 refers to the timing for starting the operation of the spreading code generator described later.

The memory 29 is composed of RAM, ROM and the like. In the memory 29, a RAM is used as a work area when various processes are performed by the CPU 26 and the like, when buffering various input data, and when storing intermediate data and calculation result data generated in the calculation process. Also RAM is used. Further, in the memory 29, a ROM is used as a means for storing various programs and fixed data.

In the GPS receiver 10, these synchronization acquisition unit 24, synchronization holding unit 25, CPU 26,
The RTC 27, the timer 28, and the memory 29 are configured as a baseband processing unit.

A GPS receiver 10 having such units
In the above, at least each of the units except the XO 11, the TCXO 12, the antenna 14, the LNA 15, and the BPF 16 can be configured as a demodulation circuit 30 that is formed of one integrated chip.

The GPS receiving apparatus 10 receives RF signals from at least four GPS satellites, converts the RF signals into IF signals by the frequency conversion unit 23, and then acquires synchronization of spread codes by the synchronization acquisition unit 24. Also, the carrier frequency is detected, and the synchronization holding unit 25 holds the synchronization between the spreading code and the carrier and demodulates the navigation message. Then, the GPS receiver 10 detects the phase of the spread code,
CP based on carrier frequency and navigation message
The position and speed of the GPS receiving apparatus 10 are calculated by U26.

Next, the synchronization acquisition unit 24 and the synchronization holding unit 25 in such a GPS receiver 10 will be described in detail. As described above, the GPS receiving device 10 has a configuration in which the synchronization acquisition function and the synchronization holding function are separated into the synchronization acquisition unit 24 and the synchronization holding unit 25. here,
The reason why the functions are separated in this way will also be described.

The synchronization acquisition unit 24, as described above,
The synchronization of the spread code in the signal and the detection of the carrier frequency are performed at high speed. The synchronization acquisition unit 24 uses a matched filter in order to perform synchronization acquisition of the spread code at high speed. Specifically, the synchronization acquisition unit 24 can use a so-called transversal filter 50 as the matched filter, as shown in FIG. 2, for example.

As the matched filter, the synchronization acquisition section 24 may use a digital matched filter 60 utilizing a fast Fourier transform (hereinafter referred to as FFT) as shown in FIG. 3, for example.

Specifically, the digital matched filter 60, as shown in the figure, has an amplified IF signal D14 obtained by the antenna 14 and the frequency converter 23 described above.
The IF signal corresponding to is sampled by the sampler 61 that samples the input signal at a predetermined sampling frequency based on the oscillation signal D12 generated by the TCXO 12 described above, and then input. The digital matched filter 60 includes a memory 62 that buffers the IF signal sampled by the sampler 61, an FFT processing unit 63 that reads the IF signal buffered by the memory 62 and performs an FFT, and the FF.
A memory 64 for buffering the frequency domain signal obtained by the FFT processing by the T processing unit 63;
A spreading code generator 65 that generates the same spreading code as the spreading code in the RF signal from the S satellite, an FFT processing unit 66 that performs FFT processing on the spreading code generated by the spreading code generator 65, and this FFT. Of the memory 67 that buffers the frequency domain signal obtained by the FFT processing by the processing unit 66, the frequency domain signal buffered in the memory 64 and the frequency domain signal buffered in the memory 67 Multiplier 68 for multiplying the complex conjugate signal of either one by the other
And an inverse FFT (Inversed Fast Fourier Transfor) for the frequency domain signal multiplied by the multiplier 68.
m; hereinafter referred to as IFFT. ) The IFFT processing unit 69 that performs the processing, and the spreading code and the spreading code generator 6 in the RF signal from the GPS satellite based on the autocorrelation function obtained by the IFFT processing unit 69 performing the IFFT processing.
5 has a peak detector 70 for detecting the peak of the correlation with the spreading code.

Such a digital matched filter 6
0 is actually a DSP (Digital Signal Process) for each unit of the FFT processing units 63 and 66, the spreading code generator 65, the multiplier 68, the IFFT processing unit 69, and the peak detector 70.
or) is implemented as software executed by. That is, the synchronization acquisition unit 24 to which the digital matched filter 60 is applied has a sampler 81 corresponding to the above-mentioned sampler 61, a RAM 82 corresponding to the above-mentioned memory 62, and the above-mentioned memory 6 as shown in FIG.
RAM / ROM 83 corresponding to 4, 67 and the above-mentioned F
FT processing units 63, 66, spreading code generator 65, multiplier 6
8, the IFFT processing unit 69, and the DSP 84 that executes the processing of the peak detector 70.

In the example shown in FIG.
An IF signal of 1.023 MHz is sampled by the sampler 81 at 4.096 MHz, and the DSP 84 performs an operation equivalent to that of the digital matched filter 60 to perform synchronous acquisition of the spread code, that is, phase detection of the spread code in the IF signal. It can be performed with a precision of / 4 chip. Further, the synchronization acquisition unit 24 is a RAM
If the capacity of 82 is 16 milliseconds, DSP
By operating the FFT in the frequency domain by 84, with an accuracy of 1/16 kHz (± 1/32 kHz),
The carrier frequency in the IF signal (hereinafter referred to as the IF carrier) can be detected. Synchronization acquisition unit 24
Since the IF signal stored in the RAM 82 includes signals from a plurality of GPS satellites, a plurality of GPS signals are calculated by calculating the correlation with the spread code of each GPS satellite.
Satellites can be detected.

The GPS receiver 10 has the synchronization acquisition unit 2
Based on the phase of the spreading code and the carrier frequency for at least four GPS satellites detected by 4,
The position and speed of the GPS receiver 10 can be calculated.

However, in the GPS receiver 10,
The above-mentioned 1/4 chip as the spread code phase detection accuracy and 1 / 16k as the carrier frequency detection accuracy.
It is difficult to say that the calculation results of the position and speed of the GPS receiving device 10 obtained under Hz have sufficient accuracy. In the GPS receiver 10, in order to improve the accuracy, it is necessary to increase the sampling frequency by the sampler 81 and increase the time length for storing the IF signal. It is assumed that the capacity of the memory will increase and the processing time until the phase and carrier frequency of the spread code are detected will become long. Further, in the GPS receiver 10, if the synchronization acquisition unit 24 does not receive a navigation message from the outside, it is necessary to demodulate the navigation messages from the position satellites of at least four GPS receivers every 20 milliseconds. As such, the DSP 84 must always be extremely fast in detecting synchronization and demodulating navigation messages. These problems bring about an increase in cost and power consumption due to the enormous size of hardware.

Therefore, in the GPS receiver 10,
The synchronization acquisition unit 24 performs synchronization acquisition with coarse accuracy,
The synchronization holding unit 25 holds the synchronization of a plurality of GPS satellites and demodulates the navigation message.

The synchronization acquisition unit 24 supplies the detected GPS satellite number, the phase of the spread code, and the carrier frequency to the synchronization holding unit 25. On the other hand, the synchronization holding unit 25 starts the operation with these various kinds of information supplied from the synchronization capturing unit 24 as initial values. The synchronization holding unit 25, based on the phase of the spread code, uses a DLL (Delay Locked Loop) described later.
Match the start timing of the spreading code generated by the circuit. As the spread code, one corresponding to the GPS satellite number is set. At this time, the GPS receiver 10 is affected by the error of the oscillation frequency of the oscillation signal generated by the oscillator such as Doppler shift and TCXO12, but the spread code is basically repeated at a cycle of 1 millisecond. Therefore, the start timing of the spreading code generated by the DLL circuit may be shifted by an integral multiple of 1 millisecond.

Since the IF carrier frequency includes the error of the oscillator such as the TCXO12 that generates the sampling clock for taking the IF signal into the memory such as the RAM 82 described above, it is assumed that the problem of the resolution described above is eliminated. Is not the exact value, that is, the sum of the carrier frequency and the Doppler shift amount. However, GPS
In the receiving device 10, when the synchronization acquisition unit 24 and the synchronization holding unit 25 are operating with the same oscillator, that is, the clock whose oscillation source is the TCXO 12, both have exactly the same frequency error. There is no problem with the holding unit 25 starting the operation with the IF carrier frequency detected by the synchronization acquisition unit 24 as the initial value.

[0071] synchronization holding unit 25 from performing the synchronization holding of a plurality of GPS satellites in parallel, for example, as shown in FIG. 5, a plurality of independent channels circuit ₉₁ 1, ₉₁ 2,
..., 91 _N. Channel circuits 91 ₁ , 91
₂ , ..., 91 _N are respectively assigned to the individual detection results by the synchronization acquisition unit 24 by the setting of the control register 92. In the following description, a plurality of channel circuits ₉₁ 1, ₉₁ 2, ...
, 91 _N are collectively referred to as a channel circuit 91 unless otherwise specified.

As shown in FIG. 6, the channel circuit 91 is a combination of a Costas loop 101 for IF carrier synchronization and a DLL 102 for spreading code synchronization, which realizes both synchronization acquisition and synchronization retention in a conventional GPS receiver. The circuit is basically configured in the same manner.

The Costas loop 101 includes an amplification I obtained by the antenna 14 and the frequency conversion section 23 described above.
For an IF signal corresponding to the F signal D14, a spread code generator (PN Generator; hereinafter referred to as PNG) described later.
A signal obtained by multiplying the spread code generated by 128 and having a phase of P (Prompt) by the multiplier 103 is input. In addition, the above-mentioned antenna 1 is provided in the DLL 102.
4 and the IF signal corresponding to the amplified IF signal D14 obtained by the frequency conversion unit 23 are input.

In the Costas loop 101, the input signal is separated into the in-phase component (I) and the quadrature component (Q), and the in-phase component signal is NCO (Numeric Controlled).
The sine component of the reproduction carrier generated by the oscillator 104 is multiplied by the multiplier 105, while the cosine component of the reproduction carrier generated by the NCO 104 is multiplied by the multiplier 10 in the signal of the orthogonal component.
Multiplied by 6. In the Costas loop 101, a predetermined frequency band component of the in-phase component signal obtained by the multiplier 105 is passed by the LPF 107, and this signal is detected by the phase detector 110, the binarization circuit 111, and the sum of squares calculation circuit 112. Is supplied to. On the other hand, in the Costas loop 101, the predetermined frequency band component of the quadrature component signal obtained by the multiplier 106 is the LPF.
108 and this signal is passed through the phase detector 110.
And the sum of squares calculation circuit 112. In the Costas loop 101, the phase information detected by the phase detector 110 based on the signals output from the LPFs 107 and 108 is supplied to the NCO 104 via the loop filter 109. Also, Costas Loop 10
In No. 1, the signals output from the LPFs 107 and 108 are supplied to the sum of squares calculation circuit 112, and the sum of squares (I ² calculated by the sum of squares calculation circuit 112 is calculated.
+ Q ² ) is output as the correlation value (P) for the spreading code whose phase is P. Furthermore, Costas Loop 1
In 01, the signal output from the LPF 107 is 2
The information supplied to the binarization circuit 111 and binarized is output as a navigation message.

On the other hand, in the DLL 102, the input IF signal is multiplied by the spreading code, which is generated by the PNG 128 and is E (Early), which is ahead of P, and is multiplied by the multiplier 113.
The multiplier 114 multiplies the spreading code, which is L (Late) in which the phase generated by is delayed from P. DL
In L102, the NCO 10 in the Costas loop 101 is applied to the signal obtained by the multiplier 113.
The sine component of 4 is multiplied by the multiplier 115, and the cosine component of the NCO 104 in the Costas loop 101 is also multiplied by the multiplier 116. Then, in the DLL 102, a predetermined frequency band component of the signal of the in-phase component obtained by the multiplier 115 is L
The signal is passed by the PF 117 and is supplied to the sum of squares calculation circuit 119. On the other hand, in DLL 102, a predetermined frequency band component of the orthogonal component signal obtained by multiplier 116 is passed by LPF 118, and this signal is supplied to sum of squares calculation circuit 119. Further, in the DLL 102, the signal obtained by the multiplier 114 is multiplied by the in-phase component signal obtained by the multiplier 103 by the multiplier 120, and the quadrature component signal obtained by the multiplier 103 is obtained. Are multiplied by the multiplier 121. And DLL 102
In, the predetermined frequency band component of the in-phase component signal obtained by the multiplier 120 is passed by the LPF 122, and this signal is supplied to the sum of squares calculation circuit 124. On the other hand, in the DLL 102, a predetermined frequency band component of the quadrature component signal obtained by the multiplier 121 is passed by the LPF 123, and this signal is supplied to the square sum calculation circuit 124.

In DLL 102, the signals output from each of square sum calculation circuits 119 and 124 are supplied to phase detector 125, and the phase information detected by phase detector 125 based on these signals is loop filtered. Is supplied to the NCO 127 via 126, and further N
Each phase E, P, L is generated by the PNG 128 based on the signal having the predetermined frequency generated by the CO 127.
Spreading code is generated and output to each unit.

Here, FIG. 7 shows an example of the spreading code of each phase E, P, L output from the PNG 127. As shown in FIG. 7, the phase is P (Prompt) from the PNG 127.
Spread code and E (Early) whose phase leads P
And a spreading code that is L (Late) whose phase is delayed from P is output. Each of these phases E, P,
The spreading codes of L are the multiplier 113 and the multiplier 10 respectively.
3, input to the multiplier 114.

Further, in the DLL 102, square sum calculation is performed.
Sum of squares calculated by the output circuit 119 (I^Two+ Q^Two)
Is the correlation value (E) for the spreading code whose phase is E
While the sum of squares calculation circuit 124 outputs
Calculated sum of squares (I^Two+ Q ^Two), The phase is set to L
It is output as the correlation value (L) for the spreading code.

As described above, the channel circuit 91 having the same structure as the circuit in which the Costas loop 101 for IF carrier synchronization and the DLL 102 for spreading code synchronization are combined.
In the synchronization holding unit 25 having the
The number of the PS satellite, the phase of the spread code, and the carrier frequency are set as initial values. The setting of this initial value is performed by directly communicating with the synchronization acquisition unit 24 or by the CPU 2 controlling the synchronization acquisition unit 24 and the synchronization holding unit 25.
This is done by going through 6.

The synchronization holding unit 25 as described above synchronizes the spread code with the synchronization as follows. That is, as shown in FIG. 8, the timer is started at the timing when the synchronization acquisition unit 24 acquires the IF signal into the memory such as the RAM 82, and the synchronization acquisition unit 24 performs the phase of the spread code with respect to the IF signal stored in the memory. When h is detected, the synchronization holding unit 25 receives the value of the phase h, and then the DLL 10 is deviated by h from the integer multiple of 1 millisecond by the same timer.
By initiating the spreading code generated by 2,
Match the phase with the spreading code of the received signal. Note that "PN" in the figure indicates a PN sequence code, that is, a spreading code.

Here, in the conventional circuit combining the Costas loop and the DLL, since the phase of the spreading code in the received signal is unknown, the IF carrier frequency generated by the DLL and the cycle of the spreading code are slightly shifted. , In the process of sliding the phase with respect to the spread code of the IF signal, a phase having a significant strength correlation was detected. Therefore, in the conventional circuit, in the case of detecting the phase, in the worst case, the carrier frequency in the range of several kHz and all the phases in the spread code having the code length of 1023 are detected. It took a long time to establish.

On the other hand, in the GPS receiver 10, although the synchronization holding unit 25 has basically the same configuration as the conventional circuit, the phase of the spread code received by the synchronization holding unit 25 and the IF carrier frequency. Since the initial values of and are slightly deviated from the true values, the phases having significant intensity correlation always exist in the vicinity of the initial values even if errors are included. Therefore, like the conventional circuit, the synchronization holding unit 25 first sets the control of the loop filters 109 and 126 in the Costas loop 101 and the DLL 102 in a stopped state, and sets the signals generated by the NCOs 104 and 127 near the initial values. After searching for a correlation with a significant intensity while changing the
The control is switched to control from 09 and 126 respectively. As a result, the synchronization holding unit 25 can establish synchronization of the phase of the spreading code by the DLL 102 and establishment of synchronization of the phase of the carrier by the Costas loop 101 in an extremely short time, and thereafter can keep the synchronization. . In the synchronization holding unit 25, since the initial value of the IF carrier frequency can be set with the accuracy of several tens Hz, the LPF 107, 1
The bandwidths of 08, 117, 118, 122, 123 and the loop filters 109, 126 can be narrowed from the beginning, and synchronization can be established in a state where the S / N (Signal to Noise ratio) is high.

In the GPS receiver 10, the synchronization holding unit 25 is set to, for example, 1.023 MHz × 16 = 16.368.
If the DLL 102 is operated with a clock of MHz and the phase of the spreading code is detected with a time resolution of 1 / 16.368 MHz in the DLL 102, the pseudo distance from the phase of the spreading code to the GPS satellite can be calculated with an accuracy of 1/16 chip. Yes, and the NCO 104 in the Costas loop 101 is 1H
If the control is performed in units of z, the resolution of the IF carrier frequency becomes 1 Hz, and the DLL 102 and the Costas loop 101 can maintain synchronization with these precisions.

As described above, in the GPS receiver 10, when the synchronization holding unit 25 holds the synchronization,
The position of the GPS receiving apparatus 10 can be continuously calculated and output based on the phase of the spread code generated by the DLL 102, and the Costas loop 101 is also available.
The speed of the GPS receiving apparatus 10 can be continuously calculated and output based on the IF carrier frequency obtained by.

As described above, the synchronization holding unit 25 sets the phase of the spread code and the IF carrier frequency passed from the synchronization acquisition unit 24 as initial values, so that significant strength is obtained near these initial values. Search for the phase at which the correlation is obtained. This is because the oscillator of the clock source mounted on the GPS receiver 10, that is, the TCXO 12 has an error with respect to the nominal frequency. GP
In the S receiver 10, when the synchronization acquisition unit 24 is configured by using the digital matched filter 60 using the FFT shown in FIG. 3, the IF signal is stored in the memory and then the DSP processing time Since the detection result is supplied to the synchronization holding unit 24 with a delay, the nominal frequency F of the oscillator is
The error between the _OSC and [Delta] F _OSC, when the DSP processing time is T seconds, the time point when the detection result to the tracking unit 24 is supplied, the error of T × ΔF _OSC / _{F OS C} occurs.
For example, in the GPS receiver 10, if T = 3 seconds and ΔF _OSC / F _OSC is within a range of ± 3 ppm, an error of ± 9 microseconds = about ± 9 chips occurs. As described above, in the GPS receiver 10, the DS
The longer the processing time of P, the larger the error.

In the GPS receiver 10, G
The Doppler shift of the carrier frequency caused by the movement of the PS satellite and the GPS receiver 10 also causes an error. In the GPS receiver 10, assuming that the carrier frequency, that is, 1575.42 MHz is F _RF and the Doppler shift of the received signal is ΔF _D , the period of the spread code due to the Doppler shift, that is, 1 millisecond is approximately (1 -ΔF _D / _{F RF)} becomes doubled, for example,
When the Doppler shift in the range of +5 to -5 kHz occurs, an error of about -9.5 to 9.5 microseconds = about -9.5 to 9.5 chips occurs in 3 seconds.

These two examples are values that are relatively close to reality, and in the GPS receiving apparatus 10, when factors of both the error of the oscillator and the Doppler shift are combined, the error is within a range of about ± 20 chips. Therefore, the correlation may be detected by searching only this range. For example, the synchronization holding unit 25 starts the spreading code generated by the DLL 102 20 phases earlier than the phase of the spreading code supplied from the synchronization acquisition unit 24, and the spreading code at that time is set to the NCO 104 or 127. Set the frequency (1 + 5
/1575.420) If it is set longer than millisecond, the slide for the spread code of the signal from the GPS satellite included in the IF signal will start from the point shifted by +20 chips and spread for an appropriate time. It is possible to search for the presence or absence of correlation while the phases of the codes are sliding.

As described above, conventionally, the correlation detection is performed by using the DLL and the Costas loop within the range of 1023 chips and the IF carrier frequency while changing within the range of the error of the oscillator and the Doppler shift amount. In contrast to what was done, in the GPS receiver 10, the carrier frequency of the initial value has only a slight error,
Since the range for detecting the correlation is only a few tenths,
The time required for establishing synchronization by the synchronization holding unit 25 can be made extremely short.

As described above, the GPS receiving apparatus 10 is configured by separating the synchronization acquisition function and the synchronization holding function, so that the synchronization acquisition unit 24 spreads the signal from the GPS satellites included in the IF signal. The phase of the code and the IF carrier frequency can be detected at high speed, and the synchronization holding unit 25 can quickly shift to the synchronization holding operation based on the detection result. However, the GPS receiver 10
In the case where the processing sequence is increased to detect a weak GPS satellite signal included in the IF signal, or when the synchronization acquisition unit 24 is operated with a low-speed clock in order to suppress power consumption. Is the synchronization acquisition unit 24
Processing time becomes longer, and accordingly, the range to be searched by the synchronization holding unit 25 until the synchronization is established becomes wider, which is not preferable.

Generally, in the GPS receiver, a common crystal oscillator is used as a source oscillator for generating a clock for signal processing in the local converter in the frequency converter and in the baseband processor. Similarly to the above, as shown in FIG. 1, the local oscillator in the frequency conversion unit 23 and the source oscillator of the operation clock of the synchronization acquisition unit 24 and the synchronization holding unit 25 are connected to the TCXO.
Common to 12. The synchronization holding unit 25 then detects the IF carrier frequency and TCX detected by the synchronization acquisition unit 24.
The difference from the intermediate frequency F _{IF of} 1.023 MHz based on the nominal value of O12 is ΔF _IF, and 1575.42
If the carrier frequency of the signal from the GPS satellite, which is MHz, is F _RF , the time required for the synchronization acquisition processing after the synchronization acquisition unit 24 captures the IF signal in the memory is T seconds, and the phase of the spread code is h, As shown in FIG. 9, the phase h of the spread code is h + Δh (Δh = −T × ΔF _IF / Δ _RF ).
Correct as follows. For example, ΔF _IF = + 3 kHz, T
= 10 seconds, Δh = -19 microseconds = about -1
It has 9 chips. By performing such a correction, the synchronization holding unit 25 can correct the phase shift of the spread code caused by the error of the oscillation frequency due to the TCXO 12 and the Doppler shift extremely accurately, and the synchronization acquisition unit 24.
Even if it takes several tens of seconds to perform the synchronization acquisition process by, the synchronization can be established by the search in the range of about 1 chip.

The reason why such a correction is possible is as follows.

In the GPS receiver 10, the frequency change
The conversion unit 23 recognizes a known key of the signal from the GPS satellite.
Carrier frequency F_RFKnown intermediate frequency F_IFStrange
In order to convert, the nominal oscillation frequency F_OSCTCXO12
Based on the frequency synthesizer 18
Wave number F_LO= N × F_OSC(N is a constant number, N >> 1)
Generate, F_IF= F_RF-F_LOSo that This
Here, the signal from the GPS satellite actually received is
Frequency F_IFAgainst the oscillation frequency of TCXO12
Error ΔF caused by error and Doppler shift_IFBut
It has been added. That is, the GPS receiver 10
In addition, the Doppler shift amount is ΔF_DAnd TCXO1
The error from the nominal oscillation frequency due to 2 is ΔF_OSCTo
When, F_IF+ ΔF_IF= F_RF+ ΔF_D-F_LO= F_RF+
ΔF_D-Nx (F_{OS C}+ ΔF_OSC) Becomes Therefore, in the GPS receiver 10,
The IF carrier frequency detected by the synchronization acquisition unit 24 is F_IF+ ΔF_IF, ΔF_IF= ΔF_D−N × ΔF_OSC Becomes What is important here is that the synchronization acquisition unit 24 detects
Can be ΔF_IFAnd only ΔF_D, Δ
F_OSCIs unknown at the initial acquisition stage
That is.

Here, the spreading code of TCXO12
The timer operates at the nominal oscillation frequency for 1 millisecond, which is one cycle length.
If it does, the error ΔF_OSCTo be real
In case of 1 millisecond x F_OSC/ (F_OSC+ Δ
F_OSC) ≈ (1-ΔF_OSC/ F_{O SC}) Milliseconds
It On the other hand, one cycle length of the spread code in the received signal is
Doppler shift amount ΔF_D1 ms × F_RF/
(F_RF+ ΔF_D) ≈ (1-ΔF _D/ F_RF) With milliseconds
Become. Therefore, one cycle of the spread code in the received signal
Counted by length and nominal oscillation frequency by TCXO12
The ratio to 1 millisecond is (1-ΔF_D/ F_RF) / (1-ΔF_OSC/
F_OSC) ≈1-ΔF_D/ F_{R F}+ ΔF_OSC/ F
_OSC Becomes Furthermore, if the right side of this equation is transformed, 1-ΔF_IF/ F_RF+ (ΔF_OSC/ F_OSC) ×
(F_IF/ (N × F_{OS C})) ≈ 1-ΔF_IF/ F_RF Becomes Thus, in the GPS receiver 10,
Δ which is an unknown parameter to the synchronization acquisition unit 24
F_D, ΔF_OSCA fairly good approximation without
You can

As a result, in the GPS receiving apparatus 10, the synchronization acquisition processing is performed from the time when the synchronization acquisition unit 24 acquires the IF signal into the memory, and the detected phase h of the spread code is supplied to the synchronization holding unit 25. If it takes T seconds to reach, the phase of the spread code detected by the synchronization acquisition unit 24 during this T seconds is shifted by −T × ΔF _IF / F _RF . Therefore, as shown in FIG. 9, the synchronization holding unit 25 uses the DLL 102 by h + Δh obtained by adding the correction value Δh = −T × ΔF _IF / F _{R F} to the phase h of the spread code supplied from the synchronization acquisition unit 24. By adjusting the start timing of the spreading code to be generated, it is possible to correct the phase shift of the spreading code that has occurred during the synchronization acquisition processing time, and it is possible to detect the correlation within the range of about 1 chip. Synchronization can be established in a very short time. In the GPS receiver 10,
For example, the correction value may be calculated by the CPU 26, the calculation result may be supplied to the synchronization holding unit 25, the phase may be corrected by the synchronization holding unit 25, and then the synchronization acquisition process by the synchronization acquisition unit 24 may be started.

The information necessary for such a method of correcting the phase of the spread code is only the IF carrier frequency detected by the synchronization acquisition unit 24. In the GPS receiver 10, the error of the oscillation frequency due to the TCXO 12 is also Doppler. The shift amount is also unnecessary as information. Also, GPS
In the receiving apparatus 10, even if the local oscillation frequency F _LO is set so that F _IF = F _RO −F _LO does not depend on the IF carrier frequency, it is only necessary to change the sign of ΔF _IF. .

In addition, the GPS receiving apparatus 10 detects the G phase when the synchronization acquisition unit 24 detects the phase of the spread code and the IF carrier frequency of the signal from the GPS satellite based on the IF signal.
The signal strength can also be detected from the signal from the PS satellite and the magnitude of the correlation value with respect to the spread code of a predetermined GPS satellite. At this time, in the GPS receiving apparatus 10, when establishing synchronization by the synchronization holding unit 25, when there is an untrue correlation in the vicinity of the phase of the spread code supplied from the synchronization acquisition unit 24, that is, especially the signal strength. Has a strong GPS
If the signals from the satellites have a partial correlation where the phases are out of phase even if they are the same GPS satellite, or if there is a similar correlation between different GPS satellites, the synchronization holding unit 25 makes an error. May be synchronized with a non-true correlation.

Therefore, in the GPS receiver 10,
When the synchronization acquisition unit 24 has accurately detected the maximum correlation, the synchronization holding unit 25 is supplied with information indicating the signal strength in addition to the phase of the spread code and the IF carrier frequency. As a result, in the GPS receiving apparatus 10, if the level of the correlation detected by the synchronization holding unit 25 is so different that it cannot be regarded as equivalent to the signal strength supplied from the synchronization acquisition unit 24, it is regarded as a false correlation. By making a determination and moving to another phase search, the probability of false synchronization with false correlation can be reduced.

In the GPS receiver 10, the LPF 107 in the Costas loop 101 of the synchronization holding unit 25,
108 and loop filter 109, and DLL 102
In the LPFs 117, 118, 122, 123 and the loop filter 126, the sensitivity is improved because the S / N is improved by narrowing the band, but the response becomes slow. Therefore, in the GPS receiving device 10, the followability to a rapid change in the position of the GPS receiving device 10 deteriorates in the synchronization establishment and the subsequent synchronization holding. Therefore,
In the GPS receiver 10, it is better to emphasize followability when the received signal is strong and to improve the sensitivity when the received signal is weak. The synchronization holding unit 25 sets the bands of these filters to
It can be set in the initial stage of the synchronization holding operation according to the signal strength supplied from the synchronization acquisition unit 24.

In the GPS receiving apparatus 10, as a method of supplying the GPS satellite number, the phase of the spread code, the IF carrier frequency, and the signal strength detected by the synchronization acquisition unit 24 to the synchronization holding unit 25, the After determining the format, interrupt method, etc., the synchronization acquisition unit 24
There is a method of directly delivering from the synchronization holding unit 25 to the synchronization holding unit 25, but by controlling the synchronization capturing unit 24 and the synchronization holding unit 25 by the CPU 26 to deliver various information,
It becomes easy to correct the phase of the spread code described above and to set various synchronization procedures according to the situation of the synchronization acquisition unit 24 and the synchronization holding unit 25 described below.

By the way, under the condition that the reception level of the signal transmitted from the GPS satellite is low, the synchronization of the reception signal and the spread code is maintained in the DLL 102, while the synchronization of the IF carrier is lost in the Costas loop 101. It is conceivable that a state of being broken will occur. Even in such a case, if the IF carrier frequency immediately before the synchronization of the IF carrier is lost is CP
By holding the U29 in the memory 29 or the like, it is possible to continue holding the spread code synchronization in the DLL 102 for a while. However, the IF carrier frequency is constantly changing due to the influence of the Doppler effect due to the change in the relative position between the GPS receiving device 10 and the GPS satellites. Therefore, under the above-described situation in which the IF carrier is not held synchronously, the spread code synchronous holding is eventually lost, and the position calculation may become impossible.

Therefore, the GPS receiving apparatus 10 operates as follows to continue detecting the IF carrier frequency even if there is a GPS satellite with a low reception level, thereby synchronizing the spread code. It is possible to continue holding.

In the GPS receiver 10, the synchronization holding unit 25
Square sum calculation circuit 11 in each channel circuit 91 in
The CPU 29 monitors the signal level of the output signal (correlation value (P) for the spread code whose phase is P) from the signal No. 2 and outputs this signal level when the signal level falls below a preset value. It is determined that the signal strength from the satellite assigned to the channel circuit 91 corresponding to the signal is lower than the predetermined strength. In this case, in the GPS receiving apparatus 10, the synchronization holding operation for the signal from the satellite whose signal strength is weakened is changed from the normal operation of holding the synchronization by one channel circuit 91 to two operations as described below. The channel circuit 91 switches to an operation for holding synchronization. However, for other satellites for which sufficient signal strength is obtained, the normal operation of maintaining synchronization using one channel circuit 91 for each satellite is continued.

The CPU 29 uses the square sum calculation circuit 11
It may be possible to judge whether or not the signal strength from the satellite is lower than a predetermined strength by directly comparing the signal level of the output signal from 2 with a predetermined value set in advance. It is desirable that the signal level is detected a plurality of times or for a predetermined time, integrated or averaged, and the above-mentioned determination is made based on the integrated or averaged signal level, in consideration of the fact that the signal level greatly varies due to the influence of the above.

Further, in the GPS receiving apparatus 10, when the synchronization of the spread code is held by the synchronization holding unit 25, the IF carrier frequency and the reception level are irrespective of whether the synchronization of the IF carrier is held or not. Fig. 10 between
There is a relationship as shown in. That is, the reception level is maximum when the IF carrier frequency is completely unique to the received signal, and is minimum at a frequency that is deviated from the IF carrier frequency by a predetermined frequency (denoted by α in the figure). . The value of the half width α depends on the circuit configuration of the GPS receiver 10 and the correlation time, but when the channel circuit 91 is configured to support high sensitivity,
It is about 25 Hz.

In the following, the operation in the case where the two channel circuits 91 hold the synchronism with respect to the satellite whose received signal has weakened will be described with reference to the flowchart shown in FIG.

When the operation for holding the synchronization by the two channel circuits 91 is started, the CPU 29 controls the control register 92 of the synchronization holding unit 25 in step S60 shown in FIG. Two channel circuits 91 for maintaining synchronization of
Secure. Further, in step S60, the CPU 2
9 sets an expected IF carrier frequency F that is expected to be the original IF carrier frequency. The predicted carrier frequency F is, for example, the IF temporarily stored in the memory 29 or the like when the synchronization holding unit 25 is normally operating.
The IF carrier frequency immediately before the carrier synchronization is lost may be set, or the IF carrier frequency calculated by the CPU 29 based on the ephemeris information may be set.

Next, in step S61, the CPU 29
Sets a frequency higher and a frequency lower than the expected IF carrier frequency F by a predetermined frequency β for each of the two channel circuits 91 secured in step S60.

In the following description, the channel circuit 91 in which the frequency higher than the expected IF carrier frequency F by the frequency β is set is referred to as a first channel circuit C1, and only the frequency β is higher than the expected IF carrier frequency F. The channel circuit 91 in which the low frequency is set is referred to as the second channel circuit C2.

Further, in step S61, when setting the frequencies for the first and second channel circuits C1 and C2, the CPU 29 sets the first and second channel circuits C1 and C2 via the control register 92. Control of each channel circuit
This is done by setting the frequency in the CO 104.

As the frequency β, a value smaller than the half-value width α of the IF carrier frequency may be appropriately selected. However, if the value of the frequency β is too small, the sensitivity to changes in the IF carrier frequency becomes too high, and if the value of the frequency β is too large (too close to the half-value width α), a sufficient reception level cannot be obtained. . Specifically, for example, IF
When the half-value width α of the carrier frequency is 25 Hz, it is appropriate to select a value of about 10 Hz as the frequency β.

Next, in step S62, the CPU 2
Reference numeral 9 is a reception level L obtained by calculating the correlation of signals in the first and second channel circuits C1 and C2.
1 and L2 are detected. This reception level is
It is an output signal (correlation value (P) for a spread code whose phase is P) from the sum of squares calculation circuit 112 in the first and second channel circuits C1 and C2.

Here, the first and second channel circuits C
When the IF carrier frequency of the received signal from the GPS satellite assigned to C1 and C2 and the expected IF carrier frequency F completely match, as shown in FIG. One reception level L1, L2
Are equal. In addition, the IF of the received signal from the GPS satellite
When the carrier frequency is higher than the expected IF carrier frequency F, as shown in FIG. 13, the reception level obtained from the second channel circuit C2 is compared with the reception level L1 obtained from the first channel circuit C1. L2 becomes a low value. Further, when the IF carrier frequency of the received signal from the GPS satellite is lower than the expected IF carrier frequency F, as shown in FIG. 14, the first channel circuit C1
The reception level L2 obtained from the second channel circuit C2 is higher than the reception level L1 obtained from

That is, the GPS receiving apparatus 10 compares the two reception levels L1 and L2 to determine whether the first and second channel circuits C1 and C1 are the same.
It is possible to detect the deviation of the IF carrier frequency of the received signal from the GPS satellite with respect to the IF carrier frequency F set in C2.

Therefore, as shown in FIG. 11, the CPU 29 sets the two reception levels L1 and L in step S62.
After detecting 2, step S63 and step S64
In, the magnitudes of the two reception levels L1 and L2 are compared.

Then, when the reception level L1 shows a higher value, the CPU 29 newly sets a frequency higher than the current predicted IF carrier frequency F by a predetermined value as the predicted IF carrier frequency F (step S65). . Then, using this new expected IF carrier frequency F, step S
The processing after 61 is performed. As a result, as shown by the arrow A in FIG. 13, the expected IF carrier frequency F is corrected so as to approach the IF carrier frequency in the reception signal from the satellite, and the reception level L1 decreases and the reception level L decreases.
2 will be increased.

When the reception level L1 shows a lower value, the CPU 29 newly sets the frequency lower than the current predicted IF carrier frequency F by a predetermined value as the predicted IF carrier frequency F (step S66). . Then, using this new expected IF carrier frequency F, step S6
The processing from 1 onward is performed. As a result, as shown by the arrow B in FIG. 14, the expected IF carrier frequency F is corrected so as to approach the IF carrier frequency in the received signal from the satellite, the reception level L1 increases, and the reception level L2 increases.
Will be reduced.

Incidentally, steps S65 and S66.
In step S61, the correction amount for setting a new frequency with respect to the expected IF carrier frequency may be appropriately selected within a range not exceeding twice the frequency β that is adjusted with respect to the expected IF carrier frequency. However, if the correction amount is too large or too small, the predicted I
The time required until the difference between the F carrier frequency and the actual IF carrier frequency converges becomes long. The optimum value to be selected as the correction amount depends on the circuit configuration and the like in the GPS receiving apparatus 10, but in the case of this example, for example, about 1 Hz may be set.

When the reception level L1 and the reception level L2 are substantially equal to each other and the difference between the two is within a predetermined range, the expected IF carrier frequency F becomes the IF carrier frequency of the reception signal from the satellite. On the other hand, assuming that they substantially match, the expected IF carrier frequency F is not corrected, and the process is returned to step S61 or step S62 and the series of processes described above is repeated.

As described above, the GPS receiver 1
At 0, if the signal strength from the satellite is weak enough that it is difficult for the Costas loop 101 in the channel circuit 91 to keep the IF carrier synchronized, two channel circuits 91 are set for this satellite and the expected IF carrier is set. The frequency F can be used to continue to detect the IF carrier frequency. Therefore, even if the IF carrier frequency changes due to the influence of the Doppler effect or the like under this situation, the IF carrier frequency can be reliably detected, and the synchronization holding of the spreading code in the DLL 102 can be continued. .

Therefore, the GPS receiver 10 is in a state where there is no margin in the number of satellites that can be used for position calculation,
For example, it is possible to reliably calculate the position even when the intensity of the received signals from these satellites is reduced in the state where only the signals from the minimum required four satellites are received. Therefore, it is possible to expand the place where position calculation can be performed.

In the GPS receiver 10, when the intensity of the signal from the satellite reaches a sufficient intensity for maintaining carrier synchronization in the Costas loop 101 during the series of processing shown in FIG. In this case, the operation of detecting the IF carrier frequency using the two channel circuits 91 may be stopped, and the synchronization holding for this satellite may be switched to the normal operation again. By this time, I
Since the detection of the F carrier frequency is continued, the time required to capture the carrier synchronization immediately after switching to the normal operation can be significantly reduced.

In the series of processing shown in FIG. 11, the predicted IF is calculated by directly comparing the reception levels L1 and L2 detected by the CPU 29 in step S62.
The carrier frequency F may be corrected, but in practice, the first and second reception levels are considered in consideration of the fact that the reception levels L1 and L2 greatly change instantaneously due to the influence of noise or the like.
Of the reception levels L1 and L2 output from the channel circuits C1 and C2 are integrated or averaged, and a prediction I based on the integrated or averaged reception levels is calculated.
It is desirable to modify the F carrier frequency F.

In the above description, the CPU 29
Is assumed to perform the series of processing shown in FIG. 11 by controlling the synchronization holding unit 25.
The control operation by the PU 29 is realized by the CPU 29 operating in accordance with the processing procedure described in the software program stored in the memory 29, for example. However, in the GPS receiver 10, the CPU 2 described above is used.
The processing corresponding to the control operation by 9 may be realized by a hardware method by various digital circuits or analog circuits.

As described above, it goes without saying that the present invention can be appropriately modified without departing from the spirit thereof.

[0125]

According to the present invention, it is possible to assign two channels in the synchronizing means to a satellite whose received signal strength has decreased. Then, these two channels keep the frequency higher and lower than the original carrier frequency of the signal from the satellite by a predetermined value, respectively, and keep the difference between the signal levels respectively output from these two channels. Control to minimize. For this reason, even if there is a satellite in which the strength of the received signal has decreased, it is possible to continue detection of the carrier frequency in the intermediate frequency signal corresponding to this satellite, and thereby maintain the spread code synchronization. be able to.

Therefore, according to the present invention, the position can be continuously calculated even if the intensity of the received signal from the satellite used for the position calculation is lowered. For this reason, the strength of the received signals from these satellites decreased when the number of satellites that could be used for position calculation was not sufficient, for example, when only the minimum required signals from four satellites were received. Even in such cases, it is possible to reliably calculate the position. Therefore, it is possible to expand the place where position calculation can be performed.

Further, even in a situation where it is difficult to synchronize the carrier in the intermediate frequency signal, the carrier frequency in the intermediate frequency signal can be continuously detected, so that the received signal whose strength has decreased reaches a sufficient strength again. In this case, the time required for carrier synchronization acquisition can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of a GPS receiving device shown as an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a matched filter including a transversal filter that can be applied as a synchronization acquisition unit included in the GPS receiving device.

FIG. 3 is a block diagram illustrating a configuration of a digital matched filter using an FFT that can be applied as a synchronization acquisition unit included in the GPS receiving device.

FIG. 4 is a block diagram illustrating an actual implementation example when the digital matched filter shown in FIG. 3 is applied as a synchronization acquisition unit included in the GPS receiving device.

FIG. 5 is a block diagram illustrating a configuration of a synchronization holding unit included in the GPS receiving device.

FIG. 6 is a block diagram illustrating a configuration of a channel circuit included in a synchronization holding unit included in the GPS receiving device.

FIG. 7 is a spread code generator (P
It is a schematic diagram which shows an example of the spreading code output by NG).

FIG. 8 is a diagram for explaining phase matching of spreading codes in a synchronization holding unit included in the GPS receiving device.

FIG. 9 is a diagram for explaining phase correction of a spread code in a synchronization holding unit included in the GPS receiving device.

FIG. 10 is a schematic diagram showing a relationship between an IF carrier frequency of a reception signal from a satellite and a reception level in a channel circuit in the GPS receiving device.

FIG. 11: In the GPS receiver, two channel circuits are assigned to satellites whose signal strength has decreased and I
It is a flow chart explaining a series of processings when detecting an F carrier frequency.

FIG. 12 is a schematic diagram for explaining reception levels L1 and L2 in two channel circuits detected when the expected IF carrier frequency and the actual IF carrier frequency match in the GPS receiving device. is there.

FIG. 13 is a reception level L of two channel circuits detected in the GPS receiver when the actual IF carrier frequency is higher than the expected IF carrier frequency.
It is a schematic diagram for demonstrating 1 and L2.

FIG. 14 is a reception level L in two channel circuits detected when the actual IF carrier frequency is lower than the expected IF carrier frequency in the GPS receiving device.
It is a schematic diagram for demonstrating 1 and L2.

FIG. 15 is a diagram illustrating a configuration of a signal from a GPS satellite.

FIG. 16 is a diagram for explaining a conventional spreading code and carrier synchronization process, and is a diagram for explaining a frequency search.

FIG. 17 is a diagram illustrating an example of an output waveform showing a temporal change of a correlation value detected by using a digital matched filter.

[Explanation of symbols]

10 GPS receiver, 11 XO, 12 TCXO,
13 multiplier / divider, 14 antenna, 15 LNA,
17, 20 amplifier, 16 BPF, 18 frequency synthesizer, 19 mixer, 68, 103, 105, 10
6,113,114,115,116,120,121
Multipliers 21, 107, 108, 117, 118, 1
22, 123 LPF, 22 A / D, 23 frequency conversion unit, 24 synchronization acquisition unit, 25 synchronization holding unit, 26 C
PU, 27 RTC, 28 timer, 29, 62, 6
4,67 memory, 30 demodulation circuit, 50 matched filter, 60 digital matched filter, 61,8
1 sampler, 63, 66 FFT processing unit, 65, 128
Spread code generator, 69 IFFT processing unit, 70 peak detector 70, 82 RAM, 83 RAM / ROM, 8
4 DSP, 91, 91 ₁ , 91 ₂ , ..., 91 _N
Channel circuit, 92 control register, 10
1 Costas Loop, 102 DLL, 104, 127
NCO, 109, 126 loop filter, 110,
125 phase detector, 111 binarization circuit, 112, 1
19,124 Square sum calculation circuit

Claims (3)

[Claims] 1. A receiving device for receiving the signals transmitted from a plurality of satellites constituting the global positioning system to calculate its own position, and a receiving means for receiving the signals transmitted from the satellites. The frequency conversion means for converting the frequency of the reception signal received by the reception means into a predetermined intermediate frequency, and the phase and carrier frequency of the spread code in the intermediate frequency signal obtained by the frequency conversion means are set in correspondence with the satellite. It is set by assigning to each of a plurality of channels provided independently of each other, the synchronization of the spreading code and the carrier is maintained, and the synchronizing means for demodulating the message included in the intermediate frequency signal, and the signal strength from the satellite If the signal intensity falls below a predetermined level, the synchronization means secures two channels to keep the signals from the satellite in sync. Then, a frequency higher and a frequency lower than the original carrier frequency by a predetermined value are set as initial values for these two channels, and a frequency for reducing the difference between the signal levels output from these two channels is set. And a control means for controlling the synchronizing means so as to hold synchronization of the carrier corresponding to the satellite by newly setting these two channels. 2. The control means respectively integrates or averages the results of detection of the signal levels output from the two channels a plurality of times, and determines the frequencies for reducing the difference between the integrated or averaged signal levels. The receiving apparatus according to claim 1, wherein the two channels are newly set. 3. The synchronization means includes a synchronization acquisition means for detecting a phase of a spread code in the intermediate frequency signal obtained by the frequency conversion means, and a synchronization acquisition means for detecting a carrier frequency in the intermediate frequency signal, The phase of the spreading code and the carrier frequency detected by the synchronization acquisition means are assigned and set to a plurality of channels provided independently corresponding to the satellites, and the set phase and carrier frequency of the spreading code are set. The receiving apparatus according to claim 1, further comprising: a synchronization holding unit that holds the spreading code and the carrier as an initial value and demodulates a message included in the intermediate frequency signal.