JP3226449B2 - GPS signal tracking method for GPS receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GPS (Global Positioning System) for receiving a positioning satellite signal and measuring a position.
m) A method for tracking a satellite signal of a GPS receiver, such as a NAVSTAR satellite operated in the United States or a GLONASS satellite operated in the Russian Federation, which determines a position by comparing a plurality of measured satellite times. Things.

[0002]

2. Description of the Related Art In recent years, GPS receivers have been widely used as position sensors for car navigation systems, navigation devices for ships, and navigation devices for aircraft.

[0003] A conventional satellite signal tracking method for a GPS receiver disclosed in Japanese Patent Application Laid-Open No. 63-15182 will be described below. Fig. 6 shows a conventional GP using the NAVSTAR satellite.
It is a block diagram which shows the structure of S receiver. In FIG. 6, 1 is a GPS satellite, 2 is an antenna for receiving a signal of a GPS satellite having a carrier frequency of 1.57542 GHz, 3 is a filter for filtering a satellite signal, 4 is an amplifier for amplifying a satellite signal, 5
Converts the frequency of the amplified satellite signal to an intermediate frequency signal 1.
571 328 GHz local oscillator, 6 is a mixer for mixing the signal of the local oscillator 5 and the satellite signal, 7 is 4.092 MHz with frequency conversion
A filter for filtering the intermediate frequency signal, an amplifier for amplifying the intermediate frequency signal, a comparator for binarizing the intermediate frequency signal, a latch for sampling the binarized intermediate frequency signal,
Reference numeral 11 denotes a local oscillator for converting the frequency of the intermediate frequency signal into a base band, and reference numeral 12 denotes a mixer for mixing the output of the local oscillator 11.

A pseudo-noise generator 13 generates a pseudo-noise unique to each of a plurality of satellites, and a demodulator 14 mixes a satellite signal and an output of the pseudo-noise generator 13 for each of a plurality of satellites to obtain a correlation. , A demodulator that performs time integration at a fixed cycle, 15 is a switch that switches the output of the demodulator 14 that has been time integrated for each satellite to make it time-sequential, and 16 corrects the Doppler shift of satellite signals and the error of the reference oscillator 22 ,
For a plurality of satellites, a numerically controlled oscillator 17 that tracks the carrier of the satellite signal and sequentially outputs the reproduced carrier, the output 17 of the numerically controlled oscillator 16 sequentially converts the output signal of the demodulator 14 into orthogonal frequency for each satellite. Mixer, 18 is a mixer
A switch for alternately switching the I signal and the Q signal output from 17; 19, an adder for cumulatively adding the output of the mixer 17; 20, a RAM (random access memory) for storing an intermediate result of the cumulative addition; A control unit that controls the pseudo-noise generator 13 and the numerically controlled oscillator 16 so as to track the satellite signal by using the cumulative addition value of the in-phase component and the quadrature component of the satellite signal output from the unit 17, and 22 is a GPS receiver. This is a reference oscillator that determines a reference timing.

[0005] A method of tracking a satellite signal in the GPS receiver configured as described above will be described. First, multiple GPs
The radio wave of the S satellite 1 is received by the antenna 2, and the received signal is amplified by an amplifier 4 except for an unnecessary signal by a filter 3. Further, the frequency is converted by a frequency conversion circuit including the local oscillator 5, the mixer 6, and the filter 7. This filter 7
Is a signal centered at 4.092 MHz. Next, after the intermediate frequency signal is amplified and the amplitude is limited by the amplifier 8, the intermediate frequency signal is converted into a binary signal by the comparator 9. The binarized signal is sampled in the latch 10 by a clock signal of 16.368 MHz output from the reference oscillator 22. Thereafter, the received signal is processed as a discrete value by a logic circuit or an arithmetic circuit or as a digital signal.

Next, a quadrature frequency conversion is performed on the sampled signal by an I signal of 4.092 MHz output from the local oscillator 11 and a Q signal having a 90 ° phase difference. The I and Q signals of the frequency-converted satellite signals are subjected to independent signal processing for each satellite to be received. The pseudo-noise generator 13 outputs pseudo-noise peculiar to each receiving satellite. The pseudo noise unique to the satellite is called a C / A code, which has a code rate of 1.023 Mbps, a code length of 1023 bits,
The cycle is 1 msec. The demodulator 14 mixes the satellite signal and the pseudo noise for each satellite.

The phase of the pseudo noise is quantized in units of 1/16 chip corresponding to 16.368 MHz, which is a clock signal for signal processing, and this quantized phase value is used as a pseudo noise generator 13.
Set to. After the satellite signal and the pseudo noise are mixed by the demodulator 14, the signal is smoothed by time integration to a sampling frequency of several hundred kHz. Numerically controlled oscillator 16 oscillates a reproduced carrier for each satellite and outputs orthogonal I and Q signals. Based on this output, the mixer 17 performs orthogonal frequency conversion on the smoothed signal. In this frequency conversion, since the sampling frequency of the signal is low, a plurality of satellites are processed in a time-division manner. The I signal of the in-phase component and the Q signal of the quadrature component output from the mixer 17 are converted by the switch 18 into time-sequential signals.

The accumulator comprising the adder 19 and the RAM 20 accumulates the I signal and the Q signal output from the mixer 17 for each satellite. The period of addition is defined as 1 msec from the beginning to the end of the C / A code as one section. The control unit 21 receives the cumulative addition result of 1 msec, and controls the numerically controlled oscillator 16 so that the amplitude of the Q signal component, which is the cumulative addition result, is reduced, thereby tracking the carrier of the satellite signal.

Further, the phase output from the pseudo noise generator 13 is moved at intervals of 1 msec, and the change in the amplitude of the I signal component, which is the cumulative addition result, is examined. From this change, the pseudo noise of the pseudo noise generator 13 and the satellite are compared. The pseudo noise of the satellite signal is tracked by measuring the phase difference between the signal and the pseudo noise. Further, the control unit 21 uses the BPSK modulation (Binary Phase Shift) from the satellite based on the sign of the I signal component that is the cumulative addition result.
t Keying) to receive 50bps data. Then, by measuring the phase of the pseudo noise and the timing of the 50 bps data, the time at which the satellite emitted the radio wave is obtained. Further, the control unit 21 uses the orbit information and time information received for a plurality of satellites and the measured time to generate G
The position of the antenna of the PS receiver is obtained by calculation and output to the outside.

FIG. 7 is a block diagram showing a configuration of a pseudo noise generator in a conventional GPS receiver. In FIG. 7, reference numeral 13a denotes an internal clock that ticks a reference time in the GPS receiver.
3b is a time comparison for obtaining the start timing of the pseudo noise by comparing the internal time and the phase output by the control unit 21 for each of the plurality of satellites, 13c starts outputting the first longest code sequence by this start timing, Then the clock signal
A first code generator that outputs the next code every 16 codes, 13d is a second code generator that sequentially outputs a second longest code sequence similarly to the first code generator 13c, and 13e is specified by the control unit 21 13f is a code number conversion table for outputting two phase selection signals determined by the number of the pseudo noise to be performed, 13f is a phase selection for selecting a signal from the output of the second code generator by these two phase selection signals, 13g Are two arithmetic elements for calculating the logical sum of the selected two signals and the output of the first code generator.

The operation of the pseudo noise generator 13 configured as described above will be described below. Internal clock 13a is G
The time indicated by the satellite signal is measured by comparing the pseudo-noise generated based on the time with the pseudo-noise of the satellite signal. The time comparison 13b determines the phase of the pseudo noise with respect to the internal clock 13a by obtaining the start timing of the pseudo noise. The start timing of the pseudo noise is approximately 1 msec, and the phase of the generated pseudo noise is changed once every 1 msec.

The first code generator 13c and the second code generator 13d
It consists of a 10-bit shift register and a logical operation element.
Further, the second code generator 13d outputs signals having 10 kinds of phases whose phases are shifted from each other by 16 clock signals in parallel from each of the 10-bit shift registers.

The pseudo noise generator 13 outputs 1 or 0 at the timing of a clock signal of 16.368 MHz output from the reference oscillator 22.
Is output. Accordingly, the phase of the code output from the pseudo noise generator 13 is the smallest step when the clock signal of 16.368 MHz is used. That is, the pseudo noise generator 13 has 1/16
Set the value of the phase quantized in chip units. The reference of this phase is an internal clock determined by counting the clock signal in the control unit of the GPS receiver.

FIG. 8A shows a change in the correlation value with the satellite signal when the phase of the pseudo noise output from the demodulator is changed.
FIG. 8 (b) sets the quantized phase in the pseudo noise generator,
FIG. 4 is a diagram schematically illustrating a change in a correlation value obtained by a demodulator. FIG. 8 shows a change in a correlation value with a satellite signal due to a phase change of pseudo noise generated by a GPS receiver.
The phase change of the pseudo noise generated in the receiver, the vertical axis is the correlation value between the satellite signal and the code generated in the GPS receiver, and is shown as an absolute value. The phase of the code is a relative change and no reference is provided.

FIG. 8A shows a correlation value between the pseudo noise output from the pseudo noise generator 13 and the satellite signal when the phase of the pseudo noise is changed.
This is the output of the demodulator 14. The correlation value becomes maximum when the pseudo noise output from the pseudo noise generator 13 and the pseudo noise of the satellite signal have the same phase. The amplitude decreases in the range of one chip before and after the phase difference between the two, and when the phase difference exceeds one chip, the amplitude becomes substantially zero. However, one chip is a time interval corresponding to one bit of the pseudo noise.

Now, it is assumed that the internal clock and the time stamped by the satellite signal have a certain phase relationship. A phase quantized in units of 1/16 chip is set in the pseudo noise generator 13. FIG.
(b) shows the phase before the quantization on the horizontal axis, and when the quantized phase is set in the pseudo noise generator 13, the demodulator 14
5 schematically shows the change in the correlation value obtained in (1). Also,
The unit of quantization is 1/16 chip. If the phase relationship between the internal clock and the satellite signal that the GPS receiver ticks is changed,
The shape of (b) changes, but the step shape is the same.
If there is an error due to the quantization, the measurement error of the phase of the satellite signal, that is, the satellite time, increases. Therefore, the phase before and after about 1/2 chip with respect to the satellite signal is set in the pseudo noise generator 13, and the result of non-quantization observation is calculated using the portion rounded up or down during quantization. The quantization error is removed by the prediction method.

[0017]

If the frequency of the reference oscillator is determined so as not to be in a relationship between the code rate of the pseudo noise and the integer ratio, and the period of the cumulative addition is not related to the period of the pseudo noise of 1 msec, the quantization is improved. By setting the obtained phase value in the pseudo noise generator, the output phase of the pseudo noise generator fluctuates by the amount of quantization, but this fluctuation is a fast change, and the pseudo noise is tracked. It can be removed by a filter. Therefore, although the measurement result is less disturbed, the frequency of the reference oscillator and the code rate of the pseudo noise are not an integer ratio, so that the control timing of the GPS receiver and the frequency conversion of the satellite signal are complicated. For this reason, many GPS receivers use the frequency of the reference oscillator as the relationship between the code rate of the pseudo noise and the integer ratio.

However, as shown in FIG. 6 of the conventional example, in a GPS receiver in which the relationship between the two is an integer ratio,
Assuming that the code rate of the pseudo noise included in the satellite signal being received and the frequency ratio of the reference oscillator become very close to an integer, the phase output by the pseudo noise generator occasionally changes by the code clock signal width. . Such a fluctuation component is a low frequency component and cannot be removed by a filter that tracks pseudo noise. If the quantization is 1/16 chip, the fluctuation amount is about 9 m in distance, and the positioning accuracy is deteriorated.

In the above-mentioned conventional configuration, when the accuracy of the reference oscillator is reduced and an inexpensive oscillator is used, if the ratio between the frequency of the reference oscillator and the code rate of the satellite signal deviates greatly from an integer, a correlation value is obtained. Since the phase difference greatly changes between the satellite signal and the pseudo noise of the GPS receiver within the 1-msec period of the cumulative addition, there has been a problem that the time measurement accuracy is deteriorated. Assuming that the error of the reference oscillator 22 is 100 ppm, the deviation of the C / A code after 1 msec elapses is about 1/10 chip, and the distance becomes as large as about 30 m.

Further, it is conceivable to reduce the fluctuation by reducing the quantization unit. However, increasing the sampling frequency increases the operating frequency of the circuit and the power consumption is almost proportional to the operating frequency. There was a problem that it increased.

The present invention solves the above-mentioned problems of the prior art, and suppresses an increase in power consumption by a simple circuit configuration. A GPS receiver capable of accurately measuring the position even with an inexpensive reference oscillator is provided. It is an object to provide a satellite signal tracking method.

[0022]

To achieve the above object, a satellite signal tracking method for a GPS receiver according to the present invention comprises a modulation signal generator and a modulation circuit for modulating a phase set in a pseudo noise generator. The modulation of the phase by the modulation signal generator is a phase change in a range substantially corresponding to the period of the clock signal at which the pseudo noise generator generates the pseudo noise, and the change of the modulation signal is compared with the pseudo noise of the satellite signal. The period of the time shorter than the tracking time constant or a substantially random number, and the phase of the pseudo noise generator output by the control unit is
After modulation by the modulation circuit at the output of the modulation signal generator, the pseudo noise generator quantizes the amount corresponding to the period of the clock signal that generates the pseudo noise as a unit, and sets it as a phase value in the pseudo noise generator. By measuring the correlation between the output signal of the pseudo-noise generator and the satellite signal, and controlling the phase of the pseudo-noise generator so that the correlation value is maximized, tracking the pseudo-noise of the satellite signal. I do.

Also, the modulation signal generator for modulating the phase set in the pseudo noise generator can synchronize the timing of changing the output of the modulation signal with each of the received satellite signals,
Further, the period of the signal generated by the modulation signal generator is determined so as not to have a relationship between the period of the pseudo noise of the satellite signal and the integer ratio.

The pseudo-noise generator has a first state in which the phase of the pseudo-noise generator is changed in synchronization with a period of the pseudo-noise or a period of an integral multiple thereof, and a period that is shorter than the period of the pseudo-noise. Or a means for switching to a second state in which the phase is changed at any time, and a unit corresponding to a period of a clock signal in which the pseudo noise generator generates the pseudo noise is provided as a unit.
The control unit quantizes the phase of the pseudo noise output for each receiving satellite, sets the pseudo noise generator, and sets the code rate of the pseudo noise included in the satellite signal for each receiving satellite,
Find the ratio to the frequency of the oscillator. A criterion for determining whether or not this ratio is close to an integer is determined. In a state close to an integer, the first state is not quantized by using a portion rounded up or down when quantizing the phase of the pseudo noise. Excluding the quantization error by the method of predicting the observation result of the case,
In a state not close to an integer, a second state is characterized in that the pseudo noise of the satellite signal is tracked by controlling the phase of the numerically controlled oscillator.

According to this method, even when the frequency of the reference oscillator and the code rate of the pseudo noise of the satellite signal are close to the integer ratio, the phase of the pseudo noise is modulated and quantized and set in the pseudo noise generator. To prevent fluctuations due to quantization from occurring. Alternatively, accurate positioning without fluctuation due to quantization can be performed by removing a quantization error by a method of predicting an observation result when quantization is not performed by using a portion rounded up or down by quantization. Furthermore, an inexpensive GPS using an inexpensive reference oscillator
Even in a receiver, even if the frequency of the reference oscillator and the code rate of the pseudo noise of the satellite signal deviate from the integer ratio, the phase of the pseudo noise generator can be changed in a short period of time. If the set cycle is long, a phase change that occurs during the period of changing the phase of the pseudo noise generator, which is a problem, becomes small, so that the position can be measured accurately.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of the GPS receiver according to Embodiment 1 of the present invention. In the following drawings, the same reference numerals are given to those having the same functions and effects as described with reference to FIG. In FIG. 1, 1 is a GPS satellite, 2 is an antenna, 3, 7 is a filter, 4, 8 is an amplifier, 5, 11 is a local oscillator, 6, 12, and
17 is a mixer, 9 is a comparator, 10 is a latch, 14 is a demodulator, 1
5 and 18 are switches, 16 is a numerically controlled oscillator, 19 is an adder, 2
0 is a RAM, 21 is a control unit, 22 is a reference oscillator, 30 is a modulation signal generator, and 31 is a pseudo noise generator. Embodiment 1
6 is different from the conventional example in that a modulation signal generator 30 for generating an 8-bit modulation signal is provided, and the configuration of the pseudo noise generator 13 shown in FIG. This is that a pseudo noise generator 31 provided with a means for modulating the phase value of a signal to be set in the modulator 13 with the modulation signal is used.

The operation of the GPS receiver using the NAVSTAR satellite configured as described above will be described below. Here, radio waves of a plurality of GPS satellites 1 are transmitted to an antenna 2
, And is amplified by the amplifier 4 except for unnecessary signals by the filter 3. Further, the intermediate frequency signal frequency-converted by the frequency conversion circuit including the local oscillator 5, the mixer 6 and the filter 7 is amplified and amplitude-limited by the amplifier 8, and is converted into a binary signal by the comparator 9. The binarized signal is sampled in the latch 10 by the clock signal of the reference oscillator 22. Next, the I signal output from the local oscillator 11 and 90
直交 The sampled signal is subjected to orthogonal frequency conversion by the Q signal having a different phase. The I and Q signals of the frequency-converted satellite signals are subjected to independent signal processing for each satellite to be received. The pseudo-noise generator 31 outputs a pseudo-noise peculiar to each receiving satellite. The demodulator 14 mixes the satellite signal and the pseudo noise for each satellite.

The above operation is the same as that of the conventional example. In this conventional example, the pseudo noise generator 31 is used in units of 1/16 chip corresponding to 16.368 MHz which is a signal processing clock signal.
Is quantized to a 14-bit phase value. In the first embodiment, a 22-bit discrete value quantized with 1/256 fineness is set in the pseudo noise generator 31.

After the satellite signal and the pseudo noise are mixed by the demodulator 14, the signal is smoothed by time integration to a sampling frequency of several hundred kHz. The numerically controlled oscillator 16 oscillates a reproduced carrier signal for each satellite and outputs orthogonal I and Q signals. Based on this output, the mixer 17 performs orthogonal frequency conversion on the smoothed signal. Since the sampling frequency of the signal is low, this frequency conversion is performed on a plurality of satellites in a time division manner. The I signal of the in-phase component and the Q signal of the quadrature component output from the mixer 17 are converted by the switch 18 into time-sequential signals.

The accumulator comprising the adder 19 and the RAM 20 accumulates the I signal and the Q signal output from the mixer 17 for each satellite. The addition period is 1 msec from the beginning to the end of the C / A code. The control unit 21
The cumulative addition result of msec is received, and the cumulative addition result Q
The carrier of the satellite signal is tracked by controlling the numerically controlled oscillator 16 so that the amplitude of the signal component is reduced.

In the conventional example, the phase output from the pseudo noise generator 31 is changed at intervals of 1 msec. However, the pseudo noise generator 31 according to the first embodiment changes the phase once every 58 clocks. . However, the satellite signal and the pseudo noise generator 31
Is evaluated by dividing the time into 1 msec. A change in the amplitude of the I signal component of the cumulative addition result, which is the correlation value, is examined. From this change, the phase difference between the pseudo noise of the pseudo noise generator 31 and the pseudo noise of the satellite signal is measured. Follow.

In measuring the phase difference, the phase of the pseudo noise generator 31 is set to about 1/2 chip with respect to the satellite signal, and the phase of the pseudo noise is controlled so that the correlation value becomes equal. No special consideration is required for the quantization error when setting the phase in the pseudo noise generator 31. Further control unit 21
Receives 50 bps data transmitted by BPSK modulation from the satellite based on the sign of the I signal component as the result of the cumulative addition.
Then, by measuring the phase of the pseudo noise and the timing of the 50 bps data, the time at which the satellite emitted the radio wave is obtained. Further, the control unit 21 uses the orbit information and time information received from a plurality of satellites and the measured time to perform GP
The position of the antenna 2 of the S receiver is obtained by calculation and output to the outside.

FIG. 2 is a block diagram showing a configuration of the pseudo noise generator of the GPS receiver according to the first embodiment. FIG.
, 31a is an internal clock that ticks a reference time in the GPS receiver, 31b is a pseudo-noise start timing and an update timing by comparing a phase output from an adder described later and a time of the internal clock 31a for each of a plurality of satellites. , A first code generator that outputs a first longest code sequence according to the start timing and update timing of the time comparison 31b, and 31d a second longest code sequence similar to the first code generator 31c. The output second code generator 31e receives the number of the pseudo noise designated by the control unit 21, and receives the number determined by the number.
A code number conversion table for outputting the two phase selection signals, 31f is a phase selection for selecting the output of the second code generator 31d based on the two phase selection signals, and 31g is a signal for selecting the two signals and the first signal.
Two arithmetic elements 31h for calculating the logical sum of the outputs of the code generator 31c correspond to the 8-bit signal output from the modulation signal generator 30 and the respective satellites output from the control unit 21 shown in FIG. This is an adder for adding a 22-bit phase.

The operation of the pseudo noise generator 31 configured as described above will be described below. Internal clock 31a is G
The time indicated by the satellite signal is measured by comparing the pseudo-noise generated based on the time with the pseudo-noise of the satellite signal. Time comparison 31b
Generates a start timing of the pseudo noise and an update timing for updating the pseudo noise. These are substantially periodic, the former being about 1 msec and the latter about 0.998 μsec. Then, upon receiving the start timing, the first code generator 31c and the second code generator 31d initialize the inside in synchronization with the clock input. Also, every time the update timing is received, the pseudo noise is updated by one chip in synchronization with the clock input. The control section 21 outputs the phase of the pseudo noise as 22-bit data, and the value is updated once every 58 clocks. The output of the modulation signal generator 30 is also changed once every 58 clocks. The output of the modulation signal generator 30 returns to the original state after 256 updates, during which all the values from 0 to 255 are output once at random. The 8 bits output from the modulation signal generator 30 are added to the adder 31 by combining the lower 22 bits with the phase 22 bits output from the controller 21.
Add by h. Then, the upper 14 bits of the addition output are output to the time comparison 31b. Time comparison 31b is entered
The start timing is obtained by comparing the 14 bits with the output of the internal clock 31a.

Further, only the lower 4 bits of the input output of the internal clock 31a and the output 14 bits of the adder 31h are compared to determine the update timing. The first code generator 31c and the second
The code generator 31d includes a 10-bit shift register and a logical operation element. Further, the second code generator 31d outputs signals having 10 kinds of phases whose phases are shifted from each other by the update timing in parallel from each of the 10-bit shift registers. The phase of the pseudo noise is from 0 to 3FEFFF in hexadecimal notation, and the adder 31h returns to 0 when the phase exceeds this.

The pseudo noise generator 31 outputs 1 or 0 at the timing of the clock signal of 16.368 MHz output from the reference oscillator 22.
Is output. Therefore, the phase of the code output from the pseudo noise generator 31 is the minimum step of the clock signal of 16.368 MHz. That is, 1/16 is used for the time comparison 31b.
Set the value of the phase quantized in chip units. But,
In the first embodiment, the clock signal is inputted with a phase of 8 bits less than the minimum step, and is shifted up by one step of the clock signal with a probability corresponding to the magnitude of the lower 8 bits. Therefore, the phase reflects the lower bits in terms of the long-term average. Such a concept does not hold when the phase of the pseudo noise of the satellite signal and the phase of the pseudo noise of the pseudo noise generator 31 coincide with each other, but the phase difference such as when the phase is advanced or delayed by about 1/2 chip. , The correlation result holds in a phase in which the correlation result changes linearly, and tracking of the pseudo noise can be performed with high accuracy.

Further, the output signal of the modulation signal generator 30 is 0.
It changes at a cycle of about 9 msec, and is about 10 msec even in consideration of interference with the cycle of the pseudo noise. Since the tracking time constant of the pseudo noise is set to several seconds to several tens of seconds, such a component does not affect the measurement. The control unit 21 sets the phase before and after the phase of the pseudo noise generator 31 that tracks the satellite signal, corresponding to 1/2 chip, so that the correlation values of the satellite signals in the two phases are equal. , The pseudo noise of the satellite signal is tracked.

As described above, according to the first embodiment, there are various periods between the phase corresponding to the quantization unit for quantizing the phase of the pseudo noise and having a period that is not an integer ratio with the code rate of the pseudo noise. After adding a modulated signal having a substantially uniform distribution of phase values to the pseudo noise phase set in the pseudo noise generator 31, the phase corresponding to one clock signal of the pseudo noise generator 31 is used as a unit. And the phase of the pseudo noise generator 31 can be equivalently controlled with a finer precision than one clock, and the frequency of the reference oscillator 22 and the code rate of the pseudo noise of the satellite signal can be controlled. Is close to an integer ratio, there is no fluctuation in the measurement result, and the position can be measured with high accuracy. Also, the number of components to be added is small, so that the increase in the circuit scale is small.

Further, by using the inexpensive reference oscillator 22, which is a problem of the conventional example, even when the frequency of the reference oscillator 22 and the code rate of the pseudo noise of the satellite signal are considerably deviated from the integer ratio, the pseudo reference can be obtained. To provide a GPS receiver that is inexpensive and has high positioning accuracy, for example, the cycle for changing the phase of the noise generator 31 is about 3.5 μsec, and the phase change that occurs during the period for changing the phase of the pseudo noise generator 31 is small. Can be.

FIG. 3 shows a GP according to the second embodiment of the present invention.
It is a block diagram which shows the structure of the pseudo-noise generator of S receiver. FIG. 3 is substantially the same as FIG. 2 described in the first embodiment, except that the configuration is such that a signal is output to modulation signal generator 30 when time comparison 31b outputs five update timings. ing. In the first embodiment, the modulation signal generator 30 outputs a common signal to a plurality of satellites. In the second embodiment, a modulation signal is output individually for a plurality of satellites.

The operation of the second embodiment configured as described above will be described below. Here, the operation is roughly the same as in the first embodiment, and only the differences will be described. In the first embodiment shown in FIG.
Although the modulation signal generator 30 changes its output once every 58 clocks, in the second embodiment, the time comparison 31
Each time b outputs the update timing five times, it outputs a signal to the modulation signal generator 30, and the modulation signal generator 30 receives this signal and updates the 8-bit modulation signal. The output of the modulation signal generator 30 returns to its original state after 256 updates, during which the
Outputs all values from to 255.

Therefore, as in the first embodiment, the position can be measured with high accuracy even when the frequency of the reference oscillator 22 and the code rate of the pseudo noise of the satellite signal are close to the integer ratio.
The output signal of the modulation signal generator 30 changes at a cycle of about 1.3 msec, and has a cycle of about 5 msec even when interference with the cycle of the pseudo noise is taken into consideration. Since the tracking time constant of the pseudo noise is several seconds to several tens of seconds, such a component does not affect the measurement. Even when the frequency of the reference oscillator 22 and the code rate of the pseudo noise of the satellite signal deviate considerably from the integer ratio,
The period of changing the phase of the pseudo noise generator 31 is about 4.9 μsec, the phase change occurring during the period of changing the phase of the pseudo noise generator 31 is small, and the position can be measured with high accuracy.
A highly accurate and inexpensive GPS receiver can be provided.

Further, in the first embodiment, the interference component between the satellite signal and the modulation signal changes the state of the interference due to the Doppler shift of the satellite signal and the frequency change of the reference oscillator 22. In No. 2, since the satellite signal and the modulation signal can maintain a fixed relationship, measurement can be always performed in a stable state.

As described above, in addition to being inexpensive and having high positioning accuracy, a modulated signal corresponding to each satellite is generated which maintains a fixed relation to the satellite signal, and this signal is set in the pseudo noise generator 31. After adding to the phase of the pseudo noise to be performed, the phase is quantized in units of a phase corresponding to one clock signal of the pseudo noise generator 31 and set to the pseudo noise generator 31, so that the Doppler shift of the satellite signal and the reference oscillator 22 A GPS receiver having stable performance with little change in performance due to frequency change can be provided.

FIG. 4 shows a GP according to the third embodiment of the present invention.
It is a block diagram which shows the structure of S receiver. In FIG. 4, 1 is a GPS satellite, 2 is an antenna, 3 and 7 are filters, 4 and 8 are amplifiers, 5 and 11 are local oscillators, 6, 12, and 17
Is a mixer, 9 is a comparator, 10 is a latch, 14 is a demodulator, 15,
Reference numeral 18 denotes a switch, 16 denotes a numerically controlled oscillator, 19 denotes an adder, 20 denotes a RAM, 21 denotes a control unit, 22 denotes a reference oscillator, and 32 denotes a pseudo noise generator. The configuration of the third embodiment is the same as the conventional example of FIG. 6, but differs from the conventional example in the operation of the pseudo noise generator 32.

The operation of the GPS receiver configured as described above will be described below. The outline of the operation is the same as that of the first or second embodiment, but the method in which the control unit 21 controls the phase of the pseudo noise generator 32 is different. In the third embodiment, the ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise included in the satellite signal has an almost integer relationship. A pseudo-noise generator 32 is used to match the integer value with an accuracy exceeding 2 ppm or not.
The method of controlling the phase is changed.

FIG. 5 is a block diagram showing a configuration of the pseudo noise generator of the GPS receiver according to the third embodiment. FIG.
, 32a is an internal clock that ticks a reference time in the GPS receiver, 32b is a control unit 21 for each of a plurality of satellites.
32c is a time comparison for comparing the phase output from the internal time with the internal time to determine the start timing and the update timing of the pseudo noise.
A first code generator that starts output of a first longest code sequence at a start timing output by the time comparison 32b and outputs a next code at each update timing output by a switch described later. 32d is a first code generator. The second code generator 32e sequentially outputs the second longest code sequence similarly to 32c, and the control unit 2
A code number conversion table for inputting a pseudo noise number designated by 1 and outputting two phase selection signals determined by this number, 32f
Is a phase selection for selecting an output signal of the second code generator 32d based on two phase selection signals output from the code number conversion table 32e, and 32g is a logical sum of the selected two signals and an output of the first code generator 32c. 32i is a counter that outputs an update timing obtained by dividing the clock signal by 1/16 for each satellite, and 32j is a switch that selects one of the time comparison 32b and the update timing output by the counter 32i. It is.

In the receiving satellite, the ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise included in the satellite signal is
A case where the precision does not exceed 2 ppm for an integer value will be described. At this time, the switch 32j selects the update timing output from the counter 32i. Therefore, the operation of the pseudo noise generator 32 is the same as in the conventional example, and the time comparison 32b determines the phase of the pseudo noise with respect to the internal clock 32a and outputs the start timing of the pseudo noise. The time comparison 32b also outputs the update timing but is not used by the switch 32j. The start timing of the pseudo noise is approximately 1 msec, and the phase of the generated pseudo noise is changed once every 1 msec.
The first code generator 32c and the second code generator 32d start outputting the longest code sequence at this start timing, and then output the next code every 16 clock signals which is the update timing of the counter 32i. Further, the counter 32i is initialized at the start timing.

The first code generator 32c and the second code generator 32d
The second code generator 32d is composed of a 10-bit shift register and a logical operation element. The second code generator 32d outputs signals having 10 kinds of phases, each of which is shifted by 16 clock signals, in parallel from each of the 10-bit shift registers. Output. Phase selection 32f
Selects two satellites determined by the receiving satellite. Arithmetic element
32g calculates the logical sum of the selected two signals and the output of the first code generator 32c and outputs the result as pseudo noise. The control unit 21 sets the phase of the pseudo-noise generator 32 to a phase of about 1/2 chip with respect to the satellite signal, but this set value is a discrete value and is a signal processing clock of 16.368 MHz. It is a value quantized in units of 1/16 chip at the timing.

Further, using the portion rounded up or down by the quantization, an observation result in the case where the quantization is not performed is predicted by using a correlation characteristic of the demodulator 14 as shown in FIG. Exclusion error is excluded. The control unit 21 further measures the correlation between the predicted value and the phase of the pseudo-noise generator 32 tracking the satellite signal as a phase around 1/2 chip, so that the correlation values of the two become equal. The satellite signal is tracked by controlling the phase of the pseudo-noise generator 32.

Next, the case where the ratio of the frequency of the reference oscillator 22 to the code speed of the pseudo noise included in the satellite signal exceeds 2 ppm with respect to the integer value will be described. At this time, the switch 32j selects the update timing of the time comparison 32b.
Therefore, the operation of the pseudo noise generator 32 is the same as that of FIG. 2 of the first embodiment, and the time comparison 32b generates a start timing of the pseudo noise and an update timing for updating the pseudo noise.
These are substantially periodic, with the former being about 1 msec and the latter about 0.
998 μsec.

Upon receiving the start timing, the first code generator 32c and the second code generator 32d initialize the inside in synchronization with the clock input. Also, every time the update timing is received via the switch 32j, the pseudo noise is updated by one chip in synchronization with the clock input. The controller 21 outputs the phase of the pseudo noise as 14-bit data, and the value is
Update once every 58 clocks.

The difference from the first embodiment is that no modulation is applied to the phase of the pseudo noise by the modulation signal generator 30 and the adder 31h in FIG. However, since the ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise included in the satellite signal exceeds an accuracy of 2 ppm with respect to an integer value, the phase set in the pseudo noise generator 32 is determined by the quantization unit. The 1/16 chip change occurs at time intervals of 31 msec or less. Since the quantized phase is set in the pseudo-noise generator 32, the timing of the output code has a fluctuation relative to the phase to be set by the period of the clock signal, but since this fluctuation is a fast change, It can be removed by a filter that tracks the pseudo-noise signal of the satellite signal, and the measurement result is less disturbed. In addition, since the ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise is substantially an integer ratio, there is no disadvantage that control timing and satellite signal frequency conversion become complicated.

The ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise included in the satellite signal is such that the number of reference oscillators 22 of the GPS receiver is one, and the local oscillator 5, the local oscillator 11, and the numerically controlled oscillator 16 are the reference oscillators. Since it is based on the output of 22, it can be easily measured in the process of tracking the carrier of the satellite signal.

As described above, the ratio between the frequency of the reference oscillator 22 and the code rate of the pseudo noise included in the satellite signal is substantially an integer relationship. For each satellite being received, the relationship of this ratio is as follows. By changing the method of controlling the phase of the pseudo-noise generator 32 depending on whether it exceeds 2 ppm or not with respect to the integer value, the fluctuation due to the quantization of the phase set in the pseudo-noise generator 32 causes Since the period for changing the phase of the pseudo-noise is not affected by the measurement of the indicated time and is sufficiently faster than the change in the phase, the satellite time can be measured with high accuracy. Therefore, a GPS receiver that is inexpensive and has high positioning accuracy can be provided.

In the above description, the GPS receiver using the NAVSTAR satellite has been described.
The present invention can also be applied to a GPS receiver that measures the position by measuring the phase of another spread spectrum signal such as an SS satellite. Demodulator
14 is provided for each receiving satellite, and the phase of the pseudo noise is changed with time to measure the phase difference with the satellite signal. However, the present invention is not limited to this.
Can be measured at once. Also,
The frequency of the reference oscillator 22, the number of stages of frequency conversion, the intermediate frequency, the sampling period, and the like can also be changed. Furthermore, the modulation signal is an 8-bit signal in which various phase values have a substantially uniform distribution during a phase corresponding to a quantization unit for quantizing the phase of pseudo noise from zero. If it changes sufficiently faster than the tracking time constant of the pseudo noise and does not provide a simple ratio to the period of the pseudo noise, a different signal may be used, and simply use the count value of a counter installed for another purpose. You can also. Although the modulation signal generator 30 is assumed to periodically change in magnitude, it may be an oscillator that generates a random number.

[0057]

As described above, according to the present invention,
Since the frequency of the reference oscillator and the code rate of the pseudo noise of the satellite signal are set to an approximate integer ratio, the control timing and the frequency conversion of the satellite signal are simplified, and the satellite signal is tracked by digital processing. Satellite time can be measured with high accuracy. Furthermore, the quantization error of the pseudo noise phase setting by digital processing is obtained by adding a modulation signal having a period that is not an integer ratio to the period of the pseudo noise to the pseudo noise phase and then quantizing the resulting signal to set the pseudo noise in the pseudo noise generator. Or when the frequency of the reference oscillator and the frequency of the pseudo noise of the satellite signal are close to an integer ratio, the phase of the pseudo noise generator is
The phase is changed at a timing corresponding to the code period of the satellite signal of 1 msec, and the measurement result is corrected by correcting the measurement result using the correlation characteristic of the demodulator by the portion rounded up or down by quantization. In addition, even if the accuracy of the reference frequency is deteriorated by using an inexpensive reference oscillator, the phase of the pseudo noise generator is changed at a high frequency.
Within the time interval in which the phase of the pseudo noise generator is changed, the phase change of the pseudo noise is small and the positioning accuracy is not degraded, so that there is an effect that low cost and high positioning accuracy can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a GPS receiver according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a pseudo noise generator of the GPS receiver according to Embodiment 1 of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a pseudo noise generator of a GPS receiver according to Embodiment 2 of the present invention.

FIG. 4 is a block diagram showing a configuration of a GPS receiver according to Embodiment 3 of the present invention.

FIG. 5 is a block diagram showing a configuration of a pseudo noise generator of a GPS receiver according to Embodiment 3 of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional GPS receiver.

FIG. 7 is a block diagram showing a configuration of a pseudo noise generator in a conventional GPS receiver.

FIG. 8 (a) shows a change in the correlation value with the satellite signal when the phase of the pseudo noise output from the demodulator is changed, and FIG. 8 (b) shows the setting of the quantized phase in the pseudo noise generator. FIG. 4 is a diagram schematically showing a change in a correlation value obtained by a demodulator.

[Explanation of symbols]

1 ... GPS satellite, 2 ... antenna, 3,7 ... filter, 4,8 ... amplifier, 5,11 ... local oscillator, 6,1
2, 17: Mixer, 9: Comparator, 10: Latch, 13: Modulation signal generator, 13a, 31a, 32a: Internal clock, 13b, 31
b, 32b: time comparison, 13c, 31c, 32c: first code generator, 13d, 31d, 32d: second code generator, 13e, 31e, 3
2e: Code number conversion table, 13f, 31f, 32f: Phase selection, 1
3g, 31g, 32g: Arithmetic element, 14: Demodulator, 15, 18, 32
j: switch, 16: numerically controlled oscillator, 19, 31h: adder, 20: RAM, 21: control unit, 22: reference oscillator,
30… Modulation signal generator, 31, 32… Pseudo noise generator,
32i ... Counter.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-52931 (JP, A) JP-A-3-41382 (JP, A) JP-A-6-21914 (JP, A) JP-A-5-21914 260016 (JP, A) JP-A-7-49371 (JP, A) JP-A-7-27845 (JP, A) JP-A-5-164834 (JP, A) JP-A-63-15182 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01S 5/00-5/14 G01C 21/00-21/36 G01C 23/00-25/00 H04B 1/69-1/713 H04B 7 / 14-7/216 H04B 7/22-7/26 H04Q 7/00-7/04

Claims (3)

(57) [Claims] An antenna for receiving a radio wave from a satellite, a high-frequency circuit for amplifying, filtering, and frequency-converting a received signal, a reference oscillator using a GPS receiver as a reference frequency source,
An analog-to-digital converter or a comparator for quantizing the frequency-converted signal, a pseudo-noise generator for generating a satellite-specific code sequence, and a correlator for obtaining a correlation between the output signal of the pseudo-noise generator and the satellite signal. , A numerically controlled oscillator for sequentially outputting a carrier, a frequency converter corresponding to the numerically controlled oscillator, and a control unit for controlling a GPS receiver
In the receiver, a modulation signal generator and a modulation circuit for modulating a phase set in the pseudo noise generator are provided, and the modulation of the phase by the modulation signal generator is performed for a clock signal in which the pseudo noise generator generates pseudo noise. A phase change in a range approximately corresponding to the cycle, wherein the change of the modulated signal is set to a cycle of a shorter time than a tracking time constant for the pseudo noise of the satellite signal, or substantially a random number, After modulating the phase of the pseudo-noise generator output by the control unit with the output of the modulation signal generator by the modulation circuit, the pseudo-noise generator calculates an amount corresponding to the period of a clock signal at which pseudo noise is generated. By quantizing as a unit and setting it as a phase value in the pseudo noise generator, the correlation between the output signal of the pseudo noise generator and the satellite signal is measured, and this correlation value becomes the maximum. Wherein by controlling the pseudo-noise generator phase, the satellite signal tracking method for a GPS receiver, characterized in that tracking the pseudo-noise of the satellite signal to. 2. A modulation signal generator for modulating a phase set in a pseudo noise generator, a timing for changing an output of the modulation signal is synchronized with each of the received satellite signals, and the modulation signal generator further comprises: 2. The satellite signal tracking method for a GPS receiver according to claim 1, wherein the period of the generated signal is determined so as not to have a relationship of an integer ratio with the period of the pseudo noise of the satellite signal. 3. An antenna for receiving a radio wave from a satellite, a high-frequency circuit for amplifying, filtering, and frequency-converting a received signal, a reference oscillator using a GPS receiver as a reference frequency source,
An analog-to-digital converter or a comparator for quantizing the frequency-converted signal, a pseudo-noise generator for generating a satellite-specific code sequence, and a correlator for obtaining a correlation between the output signal of the pseudo-noise generator and the satellite signal. , A numerically controlled oscillator for sequentially outputting a carrier, a frequency converter corresponding to the numerically controlled oscillator, and a control unit for controlling a GPS receiver
In the receiver, a first state in which the pseudo-noise generator changes the phase of the pseudo-noise generator in synchronization with a period of the pseudo-noise or a period of an integral multiple thereof, and a period that is shorter than the period of the pseudo-noise. Or a means for switching to a second state in which the phase is changed at any time, wherein the control unit outputs for each receiving satellite a unit corresponding to a period of a clock signal in which the pseudo noise generator generates pseudo noise. Quantize the phase of the pseudo-noise to be set and set it in the pseudo-noise generator, and calculate the ratio between the code rate of the pseudo-noise included in the satellite signal for each receiving satellite and the frequency of the reference oscillator to an integer. When a criterion for determining whether or not the state is close is determined, and when the phase is close to an integer, the first state is not quantized by using a portion rounded up or down when quantizing the phase of the pseudo noise. Excluding the quantization error by predicting the observation result, and in a state not close to an integer, by controlling the phase of the numerically controlled oscillator based on the output of the reference oscillator as a second state in a state that is not close to an integer, the pseudo satellite signal A satellite signal tracking method for a GPS receiver, characterized by tracking noise.