JPH0341382A - Code tracking method of gps receiver - Google Patents

Abstract

PURPOSE:To enable a calculation processing time and errors to be reduced by guantizing the phase of a pseudo-noise code by a controller and setting the pseudo-noise code with the quantized phase to a pseudo-noise code generator. CONSTITUTION:A measured value is estimated from the value of a quantization error generated in setting the code phase of a pseudo-noise code, the correlation characteristic curve of a demodulator and the amplitude value of a detection result when no quantization error is present. Thus, the quantization error generated in setting the code phase of the pseudo-noise code is removed and an increase in a measurement error is suppressed by further filtering measured results of a plurality of times. Further, the same detection circuit is used in a phase difference detection between advance and delay phases and the phase of the pseudo-noise code is changed over in time series to detect a phase difference, simplifying the circuit of the demodulator. A phase difference between a satellite signal and the pseudo-noise code estimated in a receiver is obtained from a measurement including the quantization error by estimating a measured value obtained when no quantization error is present for measured results obtained at different times.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a code tracking method for a GPS receiver that measures a position by using radio waves from a global positioning satellite system.

Conventional technology 3 F/ Conventionally, in the code tracking method of a GPS receiver,
In order to simplify the circuit that generates the pseudo-noise signal used, the set phase is quantized to a larger value, the phase difference is measured, and a finer phase is estimated by pattern matching.

For example, the configuration described in Japanese Patent No. 15182/1982, filed by the present applicant, is known. The configuration will be briefly explained below using FIGS. 5 to 7.

In Fig. 5, 2 is an antenna that receives radio waves from satellite 1, 3 is an amplifier that amplifies this received signal, 4 is a local oscillator that converts the frequency of this output signal, 5 is a mixer that converts the frequency, and 6 is an intermediate bandpass filter that selects the frequency signal;
7 is an intermediate frequency amplifier; 8 is a control unit that controls the receiver; 9
1 is a demodulation unit that outputs a detection signal to this control unit; 10 is a pseudo-noise code generator that outputs pseudo-noise specific to the satellite; and 11 is a carrier wave for demodulating the two-phase phase modulation signal sent from the satellite. It is a numerically controlled oscillator that reproduces. FIG. 6 is a block diagram illustrating the pseudo noise generator 10 of FIG. 5 in more detail. 10-1 is a shift register that inputs an 8.184 MHz clock signal and generates a 1.023 MHz φ0-φ7 clock, and 10-2 is a 1m5e
A counter 10-3 presets the upper 10 bits of the code phase value quantized at 1/1023 m5ec at a rate of 1/1023 m5ec at a rate of once per c, and counts the above-mentioned Φ7. ROM that outputs a unique pseudo-noise code, 10-4 is a latch that adjusts the output timing of this ROM, 10-5 is 1/8 from the control section
The selector 10-6 selects two clocks from the 8-phase clock of the shift register based on the lower 3 bits of the phase quantized by 184 m5ec. 10-7 is a latch that latches the pseudo-noise code at the center phase of the pseudo-noise code, and 10-8 is a latch that latches the pseudo-noise code at the center phase of the pseudo-noise code using this selected clock.
This is a latch that launches the pseudo-noise code with a phase delay of two chips.

The operation of the above configuration will be explained below.

In FIG. 5, an omnidirectional antenna 2 receives radio waves from a satellite 15, and a mixer 5 converts the frequency of the output signal from an amplifier 3. After this signal is band-limited by a bandpass filter 6, it is amplified by an intermediate amplifier 7.

This output signal is demodulated for each satellite in the demodulation section 9 and output to the control section 8 . The pseudo-noise code output from the pseudo-noise generator 10 is output to the demodulator 9, and the received signal is despread. In order to receive satellite data, the output of a numerically controlled oscillator that reproduces a carrier wave is supplied to the demodulator 9. Further, the demodulator 9 detects the difference between the phase of the pseudo code generated by the pseudo noise code generator 10 and the pseudo noise code of the satellite signal, and the controller 8 tracks the code of the satellite signal. Then, the control section 8 calculates the position of the receiving antenna 2 based on the data obtained from the demodulation section 9, and does not output it to the outside.

Next, the pseudo noise generator 10 will be explained using FIG. 6. The pseudo noise generator 10 receives 1/8184 from the control unit 8.
The phase data of the 13-bit pseudo-noise code quantized by m5ec is received. Based on the lower three bits of this data, the data selector selects two clocks from the clocks φ0 to φ7 having eight types of phases. Then, the latch 10-6 latches the pseudo-noise code at a phase V2 chips ahead of the phase center of the pseudo-noise code of the selected satellite signal. Latch 10-7 then launches the pseudo-noise code at the center phase of the pseudo-noise code of the satellite signal. Latch 10-8 launches the pseudo-noise code at a phase 172 chips behind the phase center of the pseudo-noise code of the satellite signal. The top 10 pins of phase data are preset in a preset counter at a cycle of 1 m5ec. Then, the pseudo noise codes written in the ROM are sequentially read out at timings corresponding to the 10-bit phase data. As mentioned above, the phase of the pseudo noise code is approximately 120n
Set with coarseness of sec. Next, FIG. 7 shows a detailed configuration of the demodulator 9. In FIG. 7, a detection circuit 9-1 detects a phase difference between carrier waves, and a detection circuit 9 receives data.
-2 and two detection circuits 9- that measure the phase of the code.
3.9-4. Next, in order to improve the accuracy of position measurement, the control unit 8 calculates a phase error based on the output amplitude of the demodulation unit 9 and the response characteristic curve of the demodulation unit 9.
Positioning is performed by comparing the error predicted by quantum conversion and determining the difference between the code phase of the satellite signal and the pseudo-noise code phase predicted by the receiver.

Problems to be Solved by the Invention However, in the conventional code tracking method of a GPS receiver, the phase difference of pseudo-noise codes is calculated for each measurement, which requires a large amount of calculation processing. Additionally, if there is a lot of noise in the received signal, there is a possibility that positioning errors may occur due to nonlinear effects. In addition, in order to simplify the circuit of the demodulator, the same detection circuit is used to detect the phase difference between leading and lagging phases, and when detecting the phase difference by switching the phase of the pseudo-noise code in time series, the measurement time Since the quantization error of the pseudo noise code differs depending on the method, there is a problem that errors are likely to occur in position measurement.

The present invention aims to reduce the calculation processing time and minimize errors, which are the above-mentioned problems.

Means for Solving the Problems In order to achieve the above object, the technical solution of the present invention is as follows:
First, the measured value when there is no quantization error is estimated from the value of the quantization error in the code phase setting of the pseudo-noise code, the correlation characteristic curve of the demodulator, and the amplitude value of the detection result. . Second, in addition to estimating the measured value when there is no quantization error, the same detection circuit is used to compare the code phase difference between leading and lagging pseudo-noise codes, and the code phase of the pseudo-noise code is The phase difference is detected by switching in time series.

The present invention first estimates the measured value when there is no quantization error from the value of the quantization error in the code phase setting of the pseudo-noise code, the correlation characteristic curve of the demodulator, and the amplitude value of the detection result. , the quantization error in the code phase setting of the pseudo-noise code is removed, and the results of multiple measurements are further filtered to reduce the noise component and suppress the increase in positioning error. Furthermore, the same detection circuit is used to detect the phase difference between leading and lagging phases, and the phase of the pseudo-noise code is switched in time series to detect the phase difference, thereby simplifying the circuit of the demodulator 91\-/. By estimating the measurement value without quantization error rather than the measurement with quantization error, the method eliminates the difference in quantization error that varies depending on the measurement time, and calculates the satellite signal for measurement results at different times. The phase difference between the pseudo noise code code predicted by the receiver and the pseudo noise code code predicted by the receiver is determined.

Embodiment A first embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a characteristic diagram showing the response characteristics of the demodulator in the circuit configuration of the GPS receiver in the first embodiment of the present invention. The present invention is based on the conventional example shown in FIGS. 5 to 7.
A circuit configuration similar to that of the PS receiver is used, and a description thereof will be omitted here, and only the parts specific to the present invention will be explained.

First, in order to improve the position measurement accuracy, the phase setting error due to quantization and the response characteristics of the demodulator 9 are used.
Estimate the measurement result obtained when setting a phase without quantization error from the output amplitude of .

FIG. 1 is a response characteristic curve of the demodulating section 9 for 10 degrees to explain a specific method of this estimation. The horizontal axis is the phase difference τ between the received signal and the pseudo noise code generated at the receiver, and the vertical axis is the predicted correlation result. Regarding the phase difference between the satellite signal and the pseudo-noise code of the receiver, let K and K be the correlation results in positive and negative V2 chips including quantization error, and let Δτ be the phase quantization error. However, a is the signal strength, f(
τ) is the correlation response of the demodulator 9 to the phase difference τ of the pseudo-noise code, and g() is the amplitude response of the demodulator 9. Then, K is estimated to be the correlation result obtained when there is no quantization error. -g[a-f (0,5+Δτ+ε))K = g f with the error of the predicted value as ε
There is a relationship of a−f (−0,5+Δτ+ε)). Therefore, g (k) = a−f (0,5+Δτ+ε)g′−
(k) = a−f (−0,5+Δτ1ε)K =
a-f (Q, 5+ε) medium g(K) fF(△T) + fF (x]x-o”
1K =a −f (0,5+ε) Medium g(k)fF(△r) +fF (x)l'x w
Q He 111 ・\ However, it becomes. As tracking becomes considerably more accurate, ε becomes smaller.

Therefore, even if K ``g (k)・F(△τ) K f−g (k )・F(△τ), it will not lead to a tracking error. This calculation is performed in the control unit 8 in FIG. 5.F(△τ ), F(△τ) and g
(k) is a function determined by the characteristics of the receiver, and is calculated by predetermining a table for Δτ and k in a storage device such as a ROM, and reading it out from the table.

Although obtained in this way, K changes slowly over time compared to △τ, and the time is calculated using numerical calculations of 1s
After sufficiently removing noise using a tracking filter with a time constant of c,
The codes are compared with each other at a cycle of 00 m5ec to determine the code phase error, and the code phase is corrected.

According to the above processing method, the measured value when there is no quantization error is estimated from the value of the quantization error in the phase setting of the pseudo-noise code, the correlation characteristics of the demodulator, and the amplitude value of the detection result. By doing this, it is possible to remove the quantization error in the phase setting of the pseudo-noise code, and further filter the results of multiple measurements to reduce the noise component, suppress the increase in positioning error, and simplify the pseudo-noise code generator. can be realized through easy processing.

Furthermore, by storing the correlation characteristics of the demodulator in a table in a storage device and searching the table, it is possible to perform simple processing such as two multiplications and additions and subtractions for one phase measurement.

A second embodiment of the present invention will be described below with reference to FIG. FIG. 2 is a characteristic diagram showing the response characteristics of the D13 Hoehno tuning section in the circuit configuration receiver of the GPS receiver in the second embodiment of the present invention. The configuration of the receiver is the same as that of the prior art example, so the explanation will be omitted.

In this embodiment, the correlation characteristic of the demodulator 9 in FIG. 5 is linear. Using the phase setting error due to quantization and the response characteristics of the demodulator 9, the demodulator in Figure 2 shows the procedure for estimating the measurement result obtained when a phase with no quantization error is set than the output amplitude of the demodulator 9. This will be explained using the response characteristic curve No. 9. The horizontal axis is the phase difference τ between the received signal and the pseudo-noise code generated at the receiver, and the vertical axis is the predicted correlation result.

Regarding the phase difference between the satellite signal and the pseudo-noise code, let K be the correlation result in positive and negative V2 chips including quantization error, and Δτ be the quantization error of -1 phase. . However, A is the signal strength and the response f of the demodulator 9 to the phase difference τ of the pseudo-noise code code.
(τ). Then, estimate K and − of the correlation results obtained when there is no quantization error. The error of the predicted value is ε
Then K = A-f (0,5+ε) K = A-f (-[15+ε) To 14K = A-f (0,5+Δτ+ε) K = A-f
There is a relationship of (-0,5+Δτ+ε). Therefore, assuming that ε is sufficiently small, there is a relationship as follows. This calculation is performed in the control section 8 shown in FIG. F (Δτ) and F (Δτ) are functions determined by the characteristics of the receiver, and are calculated by preparing a table for Δτ in a storage device such as a ROM in advance and reading the table.

The time change obtained in this way is slower than that of △τ, and after sufficiently removing noise using a tracking filter with a time constant of 1 sec based on numerical calculations, 200
The codes are compared with each other at a period of m5ec to determine the code phase error, and the code phase is corrected.

15 to -7 As mentioned above, by making the demodulator 9 have linear characteristics,
Table searches can be cut in half, processing time can be shortened, and the number of tables can also be reduced.

A third embodiment of the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 is a configuration diagram showing the configuration of a demodulator in the circuit configuration of the GPS receiver according to the present invention. In FIG. 3, 51.5-2.5-3.5-4 are mixers, and 9-1.9-2 are detection circuits. The rest of the configuration of the GPS receiver is the same as that of the prior art example. The operation of the above configuration will be explained below. In FIG. 3, a detection circuit 9-5 for detecting the phase of a carrier wave and a detection circuit 9-6 for measuring the phase difference of codes and receiving data are used as the detection circuits. Detection circuit 9-5
detects the phase difference with the received signal using the orthogonal signal of the regenerated carrier wave generated by the numerically controlled oscillator 11. On the other hand, the detection circuit 9-6 measures the phase difference of the code and receives the data in a time-division manner using the timing shown in FIG. 4 in units of 1 m5ec. (a) in Figure 4 shows the time-sharing processing,
This is the phase difference between the code being tracked by the receiver and the code supplied to the detection circuit 96. However, as in the previous embodiment, the code phase is the quantization error △τ.

Contains. Then, as shown in (b), the correlation result is
Output k and -. Then, k and k are Δτ corresponding to each, and K as shown in (C) as in the previous embodiment.
Calculate and. K+ and k have relatively large temporal changes due to quantization errors, or K and K have large tracking constants of the code tracking filter, so their temporal changes are gradual. K and K are each passed through a filter with a time constant of 1 sec, sampled once every 200 m5 ec, and the code tracking filter is calculated.

Note that K and K may be interpolated not only by filters but also by time and compared at the same time.

Furthermore, a filter that combines three filters with different times using a technique such as a Kalman filter may be used.

As described above, the same detection circuit is used to detect the phase difference between the leading phase and the lagging phase, and the phase of the pseudo-noise code is switched in the time series 17 Hoehno series to detect the phase difference. By estimating the measured value when there is no quantization error, we can eliminate the difference in quantization error that varies depending on the measurement time, and calculate the difference between the satellite signal and the pseudo-noise code predicted by the receiver for the measurement results at different times. By determining the code phase difference between the two, the circuit of the demodulator can be further simplified. Furthermore, since the correlation between leading and lagging phases is measured using the same detection circuit, errors caused by differences in detection characteristics are reduced compared to using separate detectors.

Although the above description has been made as a one-channel receiver to simplify the explanation, it can be made into a multi-channel receiver by providing a plurality of demodulators, pseudo-noise generators, and numerically controlled oscillators.

Effects of the Invention As described above, the effect of the present invention is that the pseudo noise code generator can be simplified through easy processing. By making the demodulation section linear, the search for 18 pages of tables can be cut in half, processing time can be shortened, and the number of tables can also be reduced. By using the same detection circuit to detect the phase difference between leading and lagging phases, the demodulator circuit can be further simplified, and compared to using separate detectors, the difference in detection characteristics can be reduced. There are also fewer errors.

[Brief explanation of drawings]

FIG. 1 is a response characteristic diagram of the demodulating section of a GPS receiver for explaining the first embodiment of the present invention, and FIG. 2 is a response characteristic diagram of the demodulating section of the GPS receiver for explaining the second embodiment of the present invention. The response characteristic diagram, FIG. 3, is a GPS response characteristic diagram for explaining the third embodiment of the present invention.
The configuration diagram of the demodulation section of the receiver, FIG. 4, is also the third embodiment of the present invention.
Processing timing diagrams of the demodulation section of the GPS receiver for explaining the embodiment, FIGS. 5, 6, and 7 are the conventional GP
2A and 2B are a block diagram of a GPS receiver, a block diagram of a pseudo noise generator, and a block diagram of a demodulation circuit, respectively, for explaining the S receiver. 1...Satellite, 2...Antenna, 8...Control unit, 9
... Demodulation section, 10 ... Pseudo noise code generator, 11.
...Numerical control generator 19 stopper.

Claims (4)

[Claims] (1) An antenna that receives satellite radio waves, an amplifier that amplifies the received signal, a pseudo-noise code generator, a numerically controlled oscillator that reproduces the carrier wave, a demodulator that detects the received signal, and a control that controls the receiver. The control section quantizes and sets the phase of the pseudo-noise code in the pseudo-noise code generator, and uses the response characteristics of the demodulation section to calculate the phase error due to this quantization as the output of the demodulation section. From the amplitude, estimate the correlation result obtained when setting a phase without quantization error, calculate the phase difference with the pseudo noise code of the satellite signal,
A code tracking method for a GPS receiver characterized by tracking a noise code. (2) Register the correlation characteristics and amplitude characteristics of the demodulator in a table in the storage device, and use this table to calculate the output amplitude of the demodulator.
2. The code tracking method for a GPS receiver according to claim 1, wherein a correlation result obtained when a phase without a quantization error is set is estimated. (3) The demodulation section has linear characteristics, the correlation characteristics of this demodulation section are registered as a table in the storage device, and the table is used to set the phase without quantization error from the output amplitude of the demodulation section. 2. The code tracking method for a GPS receiver according to claim 1, further comprising the step of estimating a correlation result. (4) Detecting the phase difference between the leading and lagging phases of the pseudo-noise code using the same detection circuit, switching the phase of the pseudo-noise code in time series to detect the phase difference, and detecting the phase difference at different measurement times. 4. The code tracking method for a GPS receiver according to claim 1, wherein the phase difference between the received signal and the pseudo noise code predicted by the receiver is determined among the measurement results.