JP2000171543A - High-precision satellite navigation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a high-precision positioning operation without using any complicated apparatus as a satellite navigation apparatus by selecting the delay time characteristic of a surface acoustic wave(SAW) filter is such a way that an influence which is given to the positioning operation of the navigation apparatus due to ripples having a frequency group delay characteristic caused by multiple reflection or spatial propagation by the SAE filter is removed by a signal processing circuit which performs a synchronous detection. SOLUTION: This high-precision satellite navigation apparatus is provided with a signal processing part in which a satellite signal passed through an SAW filter is synchronously detected in a PN code for back diffusion. In this case, the SAW filter is constituted in such a way that the delay time between an input and an output is set to be longer than the time in which a prescribed chip portion is added to one chip portion in the PN code so that the influence of a group delay characteristic generated by its spatial propagation signal and its multiple reflection signal does not affect the control of the phase-locked loop of the signal processing part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite navigation system for receiving a signal of a satellite navigation system and measuring a position.

[0002]

2. Description of the Related Art In a conventional satellite navigation device, a satellite signal modulated by a PN (pseudo noise) code in a satellite and spread spectrum is received by an antenna unit, and the frequency is converted to a frequency that can be processed by a frequency conversion unit. Then, the converted signal is A / D converted. This digitized signal is sent to a signal processing unit, and under the control of software, is synchronously detected by a despread PN code, data is demodulated, and the satellite navigation system signal transmission time is derived from the demodulated data. At the same time, the reception time of the satellite navigation system signal required for measuring the distance between the satellite and the receiver is obtained using the clock time inside the satellite navigation device, and the time difference is obtained.

The signal reception time of this satellite navigation system is:
Since the received signal is obtained at the timing of synchronous detection in the satellite navigation system, the delay time inside the receiver until the data received by the antenna unit is synchronously detected is common to all satellite signals in each satellite navigation system. There must be. However, since the normal satellite navigation system is subject to the Doppler effect due to the relative speed of the satellite and the satellite navigation device, the signal frequency of the satellite navigation system that reaches the frequency conversion circuit of the receiver differs, so the frequency group delay of the frequency conversion circuit It is necessary to keep the characteristics constant.

[0004] When the signal frequency is different for each satellite as in the GLONSSSS system, the transmission frequency of each satellite is higher than the above Doppler frequency.
This means that the group delay characteristics must be kept constant over the entire band of a wide range of signal frequencies. Assuming that the frequency conversion circuit has a different delay time for each satellite signal, a positioning error corresponding to the difference is included, which causes deterioration of the positioning accuracy.

On the other hand, in the frequency converter, a signal selection circuit such as a band-pass filter for removing unnecessary waves is generally used in order to secure S / N and anti-jam performance.
It is difficult to keep the group delay characteristic of the entire signal band constant while securing the S / N and anti-jamming wave performance. To make the group delay characteristic constant, the frequency group delay characteristic must be reduced even if the cutoff characteristic is sacrificed. You must use a type of filter that can be constant. In this case, as described above, there is a high possibility that the S / N and the anti-jamming performance will be reduced, which causes a practical problem.

To solve such a problem, it is conceivable to use a SAW (surface acoustic wave) filter as a filter having a steep cut-off characteristic and a flat group delay characteristic. , Multiple reflections between IDTs (inter digital transducers) arranged in the input and output sections inside,
A signal that spatially propagates between the input and output terminals of the AW filter is superimposed as an unnecessary component on the original output signal of the SAW filter and synthesized. As a result, even when a SAW filter having a constant group delay characteristic over the entire signal band is used, the frequency group delay characteristic within the signal band has a ripple of about several tens of nanoseconds due to an unnecessary component. Become.

[0007]

Conventionally, in a satellite navigation system, in order to remove the influence of the frequency group delay characteristic due to the band limiting filter in the frequency converter, the frequency group delay characteristic is measured in advance. A method of performing positioning with few errors by storing it in a memory in the receiver and correcting the measurement result of the reception time based on the stored frequency group delay characteristic is adopted. In this case, if the ambient temperature changes, the position of the ripple in the group delay characteristic also changes due to the temperature characteristics of the band limiting filter such as the SAW filter. Therefore, it is necessary to keep the temperature of the receiver constant by using a constant temperature device using an oven or the like, which has disadvantages that the size of the receiver is enlarged and power consumption is increased.

As another method, a reference signal for correction is generated in a receiver, and a frequency group delay characteristic in a frequency conversion section based on a signal frequency of a satellite navigation device is sequentially obtained using the reference signal. There is also a method that enables positioning with less error by correcting the measurement result based on the obtained frequency group delay characteristics.However, even if this method is used, the circuit configuration of the receiver becomes complicated, and the receiver is enlarged. There was a disadvantage.

The present invention provides a combination of the characteristics of a SAW filter having a steep cutoff characteristic and a flat group delay characteristic, and the characteristics of a signal processing circuit used in a satellite navigation system and performing synchronous detection. It was made with attention,
An object of the present invention is to select a SAW filter characteristic so that a ripple in a frequency group delay characteristic caused by multiple reflection or spatial propagation by a SAW filter on positioning of a satellite navigation device can be removed by a synchronous detection circuit of a signal processing circuit. Accordingly, it is an object of the present invention to provide a satellite navigation device capable of performing high-accuracy positioning without using a complicated device.

[0010]

According to a first aspect of the present invention, there is provided a high-accuracy satellite navigation device comprising: a surface acoustic wave filter provided in a frequency conversion circuit for converting a frequency of a satellite signal modulated by a spread spectrum PN code; A signal processing unit for synchronously detecting the satellite signal having passed through the surface acoustic wave filter with a despreading PN code, wherein the signal processing unit performs a phase shift of a predetermined chip of the despreading PN code from the despreading PN code. , And a phase locked loop using a rate code delayed from the despreading PN code by the predetermined chip phase of the PN code, and the surface acoustic wave filter comprises a surface acoustic wave filter. The influence of the group delay characteristic generated by the spatial propagation signal and the multiple reflection signal of the filter does not affect the control of the phase locked loop of the signal processing unit. The delay time between input and output, constructed by setting PN code 1 longer than the time obtained by adding the predetermined chips in chips, characterized in that.

According to this structure, the filter has a sharp cutoff characteristic and a flat group delay characteristic.
An AW filter is adopted, and the characteristics of this SAW filter and
Skillfully combines the characteristics of synchronous detection circuits used in satellite navigation equipment, and performs signal processing to perform synchronous detection on the effect of frequency group delay characteristic ripples caused by multiple reflection or spatial propagation by SAW filters on positioning of satellite navigation equipment. By selecting the delay time characteristic of the SAW filter so that it can be removed by a circuit, highly accurate positioning can be performed without using any complicated device for the satellite navigation device.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a block diagram of a high-accuracy satellite navigation apparatus according to the present invention. In the figure, a satellite signal (RF signal) received by the antenna unit is spectrum-spread by a satellite using a PN code. The RF signal, that is, the satellite signal, received by the antenna unit is amplified by the RF amplifier 1 and band-limited by the RF band-pass filter 3, and hereinafter the first mixer 4, the first IF amplifier 5, the first IF SAW filter 6, and the second mixer 7. Using the second IF low-pass filter 8, convert the frequency to a low frequency that can be processed by the signal processing unit 10, digitize the frequency-converted satellite signal by the A / D converter 9, and supply it to the signal processing unit 10. . The synthesizer circuit 2 supplies necessary frequency signals to the first mixer 4, the second mixer 7, and the signal processing unit 10, respectively.

In the carrier comparator 11 of the signal processing unit 10,
The digitized satellite signal from the A / D converter 9 is compared with the carrier signal generated by the carrier generator 13, and the output of the comparison result is output to the code comparator 1.
Feed to 2. The code comparator 12 compares the output from the carrier comparator 11 with the despreading PN code generated by the code generator 14 (the same PN code as the spreading PN code used in a specific satellite). This despreading P
The phase of the N code is controlled by a control device (not shown) so as to match the phase of the PN code for spreading a satellite signal from a specific satellite. The navigation data from a specific satellite is output from the integrator 15 in a state where these two phases match. In addition, the distance between a specific satellite and the present satellite navigation device is determined from the phase shift amount of the despreading PN code generated by the code generator 14 so that these two phases match.

FIG. 2 shows the code comparator 1 of the signal processing unit 10.
2, a code generator 14 and an integrator 15 are shown in more detail.
-2, a code comparator 10 including a code comparator L12-3, a despreading PN code P (P code) having a phase to be synchronized with a specific satellite signal, and a predetermined chip (for example, 0. 5 chips) Despread P with advanced phase
N code E (E code), PN for despreading delayed by a predetermined chip (for example, 0.5 chip) phase from P code
A code generator 14 for generating a code L (L code);
The delay lock loop consists of
Is composed.

In FIG. 1, the RF band-pass filter 3 and the second IF low-pass filter 8 are filters of a type capable of keeping the group delay characteristic of all signal frequency bands constant, and the frequency band is widened to thereby provide a receiver. The internal group delay characteristic is made constant in the entire signal band of the satellite signal. Also, the first I
The FSAW filter 5 has a steep cut-off characteristic and a characteristic that the group delay characteristic becomes flat.

Even if the SAW filter 5 is designed so that the group delay characteristic is constant, as described above, the SAW filter 5 may be re-inputted by multiple reflection between the input part IDT and the output part IDT in the SAW filter. Due to the spatial propagation of the signal between the output terminals, a signal that has advanced by a time T corresponding to the delay time T of the SAW filter 5 with respect to the required signal component, and 2n times the delay time T (n is an integer) A signal delayed by a corresponding time of 2 nT is combined with the output signal of the SAW filter 5.

As a result, even if the SAW filter 5 is designed to keep the group delay characteristic constant, the actual characteristics of the SAW filter 5 are not required. Ripple occurs in the group delay characteristic of the frequency band.

If this SAW filter is simply used, the output signal contains an error based on the ripple of the frequency group delay characteristic. Therefore, the code comparator 12 determines the transmission time of the satellite signal and the time of the clock in the satellite navigation system. The distance between the satellite and the satellite navigation device calculated by calculating the time difference from the time includes an error. In addition, when positioning is performed using the calculated distance, positioning is performed using a measurement value including an error of a distance (time difference) corresponding to the ripple of the frequency group delay characteristic. The obtained position of the satellite navigation system naturally includes an error.

According to the present invention, the output of the SAW filter 5 is premised on the occurrence of ripples in the frequency group delay characteristics, and skillfully combines the characteristics of the SAW filter with the characteristics of the synchronous detection circuit used in the navigation device. , The influence of the ripple of the frequency group delay characteristic caused by the multiple reflection or the spatial propagation by the SAW filter on the positioning of the navigation device,
So that it can be removed by the signal processing circuit that performs synchronous detection,
This is a result of selecting the delay time characteristic of the SAW filter.
Hereinafter, a specific description will be given.

The code comparator 12 in the signal processing unit 10
As shown in FIG. 2, an output of the carrier comparator 11 and an E code whose phase is advanced by a predetermined chip (for example, 0.5 chips) from the P code are input, and the comparison result is output. The code comparator E12-1, the output of the carrier comparator 11, and the P code are input, and the code comparator P12-2 to which the comparison result is output is provided. (For example, 0.
And a code comparator L12-3 to which an L code with a delayed phase (for 5 chips) is input and a comparison result is output.

FIG. 3 is a diagram for explaining synchronization tracking by the code comparator E12-1 and the code comparator L12-3. 3A shows a characteristic diagram of the code comparator E12-1, FIG. 3B shows a characteristic diagram of the code comparator L12-3, and FIG. 3C shows a code diagram of the code comparator E12-1.
11 shows a difference output characteristic obtained by calculating a difference between the output of -1 and the output of the code comparator L12-3.

The code comparator E12-1 and the code comparator L12-3 use the code comparator E12 for synchronization tracking.
Control is performed so that the difference between the output of 12-1 and the output of code comparator L12-3 becomes zero. In a state where this difference is controlled to be zero, the despreading PN code (P code)
Are synchronized with the desired satellite signal. At this time,
Code comparator E12-1 and code comparator L12-3
Operate at point P in FIGS. 3A and 3B, respectively.

As described above, when the output of the code comparator E12-1 and the output of the code comparator L12-3 become equal, the phase of the despread PN code given to the code comparator P12-2. Is the phase of the despread PN code to be obtained. Based on this phase, the reception time of the signal is determined, and positioning is performed.

Therefore, the output of the code comparator E12-1 being compared with the output of the code comparator L12-3
E and L in the characteristic of FIG.
By preventing the error (multiple reflection or spatial propagation) generated by the SAW filter 5 from affecting the characteristics (tilt) between the satellites, the error can be prevented from being mixed into the positioning of the satellite navigation device. Become.

FIG. 4 shows the correlation output of the code comparator P12-2. In this example, FIG. 4A shows the phase of the despread PN code to be obtained at point P in FIG. I have. As is apparent from FIG.
The output by the spatially propagated signal generated by the SAW filter 5 and the output by the multiple reflected signal need not be applied to the points E and L in FIG. FIG. 4B shows a signal obtained by combining a desired signal with a spatially propagated signal and a signal subjected to multiple reflection.
The combined signal as in (b) becomes the actual output signal of the code comparator P.

In FIG. 4, the E code, which is advanced by 0.5 chip as a predetermined chip from the P code, and the L code which is 0.5 chip delayed from the P code by a predetermined chip. For example, by setting the delay time T between input and output of the SAW filter 5 to a time equivalent to 1.5 chips, an error due to multiple reflection or spatial propagation generated in the SAW filter 5 is not affected. This shows an example of preventing errors in the positioning of the satellite navigation system.

In the above description, for a predetermined chip,
Although the case of 0.5 chips is described as an example, the present invention is not limited to this, as is clear from the principle of the present invention. Can be taken.

As described above, according to the present invention, the influence of the ripple of the frequency group delay characteristic caused by the multiple reflection or the spatial propagation by the SAW filter on the positioning of the navigation apparatus can be removed by the signal processing circuit for performing the synchronous detection.
Since the delay time characteristic of the filter is selected, high-accuracy positioning can be performed without using any complicated device in the satellite navigation device.

The above description will be described with reference to a characteristic example of the SAW filter. FIG. 5 is a diagram showing the frequency band-pass characteristics of the SAW filter, where the horizontal axis represents frequency and the vertical axis represents amplitude. The SAW filter having the pass characteristic as shown in FIG.
As shown in the amplitude characteristic diagram, in addition to the originally desired signal, an unnecessary signal spatially propagated between the input and output terminals,
Unnecessary signals output by multiple reflection at the IDT in the W filter are output. Assuming that the delay time in the SAW filter is T, the unnecessary signal appears as a spatially propagating wave separated by a time T before the desired signal, and appears as a multiple reflection after being separated by 2T. As a result, FIG.
As shown in the frequency group delay characteristic, ripples having frequency components of 1 / T and 1 / 2T are added to the group delay characteristic.

If this unnecessary component can be removed by any method as shown in the time-amplitude characteristic diagram of FIG. 8, the group delay characteristic in the signal band becomes the unnecessary component as shown in the group delay characteristic of FIG. Is canceled out, and the group delay characteristic in the signal band can be flattened.

In the present invention, the influence of the ripple of the frequency group delay characteristic caused by the multiple reflection or the spatial propagation by the SAW filter on the positioning of the satellite navigation system can be removed by the signal processing circuit for performing synchronous detection. The time characteristics are selected, and are shown in FIGS.
As described above, the ideal state can be equivalently created without using any complicated device.

FIG. 10 is another configuration diagram of the high-accuracy satellite navigation device according to the present invention, showing the configuration of a common receiver for GPS and GLONASS.

In the figure, the GPS signal and the GLONASS signal input from the RF amplifier 100 are input to the two types of frequency converters in the RF signal band. After the GPS signal is split by the directional coupler 200, the RF amplifier 101, R
F bandpass filter 300, first mixer 400, first I
F amplifier 500, first IFSAW filter 600, second
The signal is input to the signal processing unit via the mixer 700, the second IF low-pass filter 800, and the 1-bit A / D conversion circuit 900.

Similarly, the GLONASS signal divided by the directional coupler 200 is supplied to the RF amplifier 102, the RF bandpass filter 301, the first mixer 401, the first IF amplifier 501, the first IF SAW filter 601, and the second mixer 70.
1 and further divided into two systems of an upper waveband and a lower waveband, and the second IF SAW filters 602, 603 and the second IF
Amplifiers 502, 503, third mixers 702, 703, third IF low-pass filters 801, 802, 1 bit A /
The signal is transmitted to the signal processing unit via the D conversion circuits 901 and 902.

In the signal processing unit 150, the GPS signal and the GL
The ONASS signal is controlled by software so that the selector circuit 1500 has a multi-channel synchronous detection circuit 15.
01, and performs reception demodulation using the signal of the timing circuit 1502.

The synchronous detection circuit 1501 includes a carrier comparator 11, a code comparator 12, a carrier generator 13,
Includes a code generator 14 and an integrator 15, respectively.
The same operation as described above is performed. In FIG. 10, components denoted by reference numerals 1000 to 1013 generate various frequency signals and timing signals necessary for the GPS and GLONASS shared receivers, and It is for supply.
Since these components themselves are general, their individual descriptions are omitted.

In the configuration of the GPS and GLONASS common receiver, the first IFSAW filter 6
01, GLONASS first IFSAW filter 601,
Since the second IF SAW filters 602 and 603 are set to have a delay time equal to or longer than a predetermined chip as described above, an unnecessary signal can be removed by a code comparator provided in the synchronous detection circuit 1501. Since the group delay characteristic can be substantially flattened, positioning with less error is enabled.

[0039]

According to the structure of the present invention, a SAW filter having a sharp cutoff characteristic and a flat group delay characteristic is employed as a filter. The signal processing circuit that performs synchronous detection can effectively combine the characteristics of the synchronous detection circuit that is used and the effect of the ripple of the frequency group delay characteristic caused by multiple reflection or spatial propagation by the SAW filter on the positioning of the satellite navigation system. By selecting the delay time characteristic of the SAW filter, highly accurate positioning can be performed without using any complicated device for the satellite navigation device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high-accuracy satellite navigation device according to the present invention.

FIG. 2 is a partial detailed diagram of a signal processing unit 10;

FIG. 3 is an explanatory diagram of an operation of the code comparator.

FIG. 4 is a diagram showing a correlation output of a code comparator.

FIG. 5 is a graph showing a pass characteristic of a SAW filter.

FIG. 6 is a time-amplitude characteristic diagram of a SAW filter.

FIG. 7 is a frequency group delay characteristic diagram of a SAW filter.

FIG. 8 is a time-amplitude characteristic diagram of the SAW filter when there is no unnecessary wave.

FIG. 9 is a frequency group delay characteristic diagram of a SAW filter when there is no unnecessary wave.

FIG. 10 is another configuration diagram of the high-accuracy satellite navigation device according to the present invention.

[Explanation of symbols]

 Reference Signs List 3 RF band pass filter 6 First IF SAW filter 8 Second IF low pass filter 9 A / D converter 10 Signal processing unit 11 Carrier comparator 12 Code comparator 13 Carrier generator 14 Code generator 15 Integrator 12-1 Code comparator E 12-2 Code comparator P 12-3 Code comparator L

Claims (1)

[Claims] 1. A surface acoustic wave filter provided in a frequency conversion circuit for frequency-converting a satellite signal modulated by a PN code for spread spectrum, and a PN code for despreading the satellite signal passing through the surface acoustic wave filter. A signal processing unit that performs synchronous detection with the signal. The signal processing unit includes an early code whose phase is advanced by a predetermined chip of the despreading PN code from the despreading PN code, and A phase locked loop is formed by using the rate code of the PN code delayed by the predetermined chip phase, and the surface acoustic wave filter has a group delay characteristic generated by a spatial propagation signal and a multiple reflection signal of the surface acoustic wave filter. The delay time between the input and output is adjusted so that the influence of the PN code 1 does not affect the control of the phase locked loop of the signal processing unit.
A high-accuracy satellite navigation device, wherein the time is set to be longer than a time obtained by adding the predetermined chip to the chip.