JP2595721B2 - Code tracking method for GPS receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention utilizes radio waves of the global positioning satellite system,
The present invention relates to a code tracking method for a GPS (GPS) receiver for measuring a position.

2. Description of the Related Art Conventionally, in a code tracking method of a GPS receiver, in order to simplify a circuit for generating a pseudo-noise signal to be used, a phase difference is measured by quantizing a set phase to a larger value, and a finer phase is measured. Was estimated by pattern matching.

For example, a configuration disclosed in Japanese Patent Application Laid-Open No. 63-15182, filed by the applicant of the present invention, is known. The configuration will be briefly described below with reference to FIGS.

In FIG. 5, 2 is an antenna for receiving the radio wave of the satellite 1, 3 is an amplifier for amplifying the received signal, 4 is a local oscillator for converting the frequency of the output signal, 5 is a mixer for converting the frequency, and 6 is an intermediate unit. 7 is an intermediate frequency amplifier, 8 is a control unit for controlling the receiver, 9 is a demodulation unit that outputs a detection signal to this control unit, and 10 is a pseudo-noise that outputs a pseudo-noise code unique to the satellite. The noise code generator 11 is a numerically controlled oscillator for reproducing a carrier wave for demodulating a two-phase modulated signal sent from a satellite. FIG. 6 is a block diagram for explaining the pseudo noise generator 10 of FIG. 5 in more detail. 10-1 inputs a clock signal of 8.184 MHz, and 1.023 MHz
shift register for generating clocks of zφ0 to φ7, 10-
2 is a counter that presets the upper 10 bits of the code phase value quantized at 1/8184 msec at a rate of once every 1 msec, and counts the φ7. 10-3 is a satellite determined by the control unit according to the value of this counter. ROM that outputs pseudo noise code unique to
10-4 is a latch for adjusting the output timing of this ROM, 10
-5 is a selector for selecting two clocks from the 8-phase clock of the shift register according to the lower 3 bits of the phase quantized at 1/8184 msec from the control unit, and 10-6 is a pseudo noise code based on the selected clock. Latches the pseudo-noise code at a phase 1/2 chip ahead of the phase center of
A latch 0-7 latches the pseudo-noise code at the center phase of the pseudo-noise code by the selected clock.
Reference numeral 8 denotes a latch for latching a pseudo noise code with a phase delayed by 1/2 chip.

The operation of the above configuration will be described below. Fifth
In the figure, the radio wave of the satellite 1 is received by the omnidirectional antenna 2 and the output signal of the amplifier 3 is frequency-converted by the mixer 5. After this signal is band-limited by the band-pass filter 6, it is amplified by the intermediate amplifier 7. This output signal is transmitted to the demodulation unit 9
Demodulated for each satellite and output to the control unit 8. The pseudo-noise code output from the pseudo-noise generator 10 is output to the demodulation unit 9 to despread the received signal. The output of the numerically controlled oscillator 11 for reproducing the carrier is supplied to the demodulator 9 for receiving the satellite data. Further, the phase difference between the pseudo noise code of the satellite signal and the phase of the pseudo noise code generated by the pseudo noise code generator 10 is detected by the demodulation unit 9, and the control unit 8 tracks the satellite signal code. Then, in the control unit 8, the demodulation unit 9
The position of the receiving antenna 2 is calculated based on the obtained data and output to the outside.

Next, the pseudo noise generator 10 will be described with reference to FIG. The pseudo noise generator 10 receives the phase data of the 13-bit pseudo noise code quantized at 1/8184 msec from the control unit 8. Two clocks are selected by the data selector from the clocks φ0 to φ7 having eight kinds of phases by the lower three bits of this data. The phase of the pseudo-noise code of the selected satellite signal is calculated by the latch 10-6.
Latch the pseudo-noise code with the phase advanced by 1/2 chip. Next, the latch 10-7 latches the pseudo noise code at the center phase of the pseudo noise code of the satellite signal. The latch 10-8 latches the pseudo-noise code at a phase delayed by 1/2 chip from the phase center of the pseudo-noise code of the satellite signal. Top 10 in phase data
Bits are preset to the preset counter at a cycle of 1 msec. Then, the pseudo-noise code written in the ROM is
Read at the timing according to the 10-bit phase data.
As described above, the phase of the pseudo noise code is set with a roughness of about 120 nsec. Next, FIG. 7 shows a detailed configuration of the demodulation unit 9. In FIG. 7, a detection circuit 9-1 for detecting a phase difference of a carrier wave, a detection circuit 9-2 for receiving data, and two detection circuits 9-3 and 9-4 for measuring a code phase are provided. Become.

Next, a detailed operation of the demodulation unit 9 will be described. The control section 8 predicts the code phase of the satellite signal and sets it in the pseudo-noise code generator 10. The code phase of the satellite signal and the generation of the pseudo noise are generated by using the detection result output from the detection circuits 9-3 and 9-4 in the control unit 8 and measured by the phase of the pseudo noise code whose phase is about 1/2 chip. The difference between the phases set in the detector is calculated. The obtained phase difference includes an error corresponding to the phase of the code phase of the satellite signal predicted by the control unit 8, which is rounded down or rounded up in the quantization. However, this error is a value known when quantizing the phase value. Therefore, in order to enhance the measurement accuracy of the satellite signal code phase, the demodulation unit 9
Using the output amplitude of the demodulation unit 9 and the response characteristic curve of the demodulation unit 9, the result of the phase difference is accurately calculated, and the error added in the quantization is compared with the code phase of the satellite signal and the receiver. The difference between the phases of the pseudo-noise codes predicted in is obtained, and the phase is measured using the result.

Problems to be Solved by the Invention However, the code tracking method of the conventional GPS receiver calculates the phase difference of the pseudo noise code for each measurement, so that the amount of calculation processing increases. In addition, when the received signal has much noise, there is a problem that a positioning error may be caused due to a non-linear effect. When the same detection circuit is used to detect the phase difference between the leading and lagging phases to simplify the demodulation circuit, and the phase difference is detected by switching the phase of the pseudo noise code in time series, the measurement time Therefore, there is a problem that an error easily occurs in position measurement because an error due to quantization of a pseudo noise code phase is different. An object of the present invention is to reduce the calculation processing time and the position measurement error as much as possible.

Means for Solving the Problems In order to achieve the above object, the technical solution of the present invention is to firstly provide a value of an error due to quantization in setting a pseudo noise code phase, a correlation characteristic curve of a demodulation unit, The measurement value when there is no quantization error is estimated based on the amplitude value of the detection result. Second, the measurement value when there is no quantization error is estimated, and the same detection circuit is used to compare the code phase difference between the leading and lagging phases of the pseudo-noise code. The phase difference is detected by switching in a sequence.

The first aspect of the present invention estimates the correlation result in the case where there is no quantization error from the value of the error due to quantization in setting the pseudo noise code phase, the correlation characteristic curve of the demodulation unit, and the amplitude value of the detection result. In this way, a quantization error in setting the pseudo-noise code phase is removed, and a plurality of measurement results are filtered to reduce the noise component, thereby suppressing an increase in the positioning error. Furthermore, the same detection circuit is used for detecting the phase difference between the leading and lagging phases, the phase of the pseudo-noise code is switched in time series to detect the phase difference, and a method for simplifying the circuit of the demodulation unit is employed. By estimating the correlation result when there is no quantization error from the measurement of the correlation that sets the quantized phase, the difference in the measurement error at different times, except for the difference in the error due to quantization that differs depending on the measurement time, is obtained by using the satellite. A phase difference between a signal and a pseudo-noise code predicted in a receiver is obtained.

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a characteristic diagram showing response characteristics of a demodulation unit in a circuit configuration of a GPS receiver according to a first embodiment of the present invention. The present invention employs the conventional GP shown in FIGS.
A circuit configuration similar to that of the S receiver is used, and the description thereof is omitted here, and only the parts unique to the present invention will be described.

First, in order to increase the position measurement accuracy, when setting the phase, the quantization error is calculated from the output amplitude of the demodulation unit 9 using the phase error due to the truncated or rounded-up quantization and the response characteristic of the demodulation unit 9. Estimate the measurement results obtained when setting a phase with no parameters.

FIG. 1 is a diagram for explaining a response characteristic of the demodulation unit 9 for explaining a specific method of the estimation. The horizontal axis is the phase difference τ between the received signal and the pseudo-noise code generated in the receiver, and the vertical axis is the predicted correlation result. The phase difference between pseudo-noise code of the satellite signal and the receiver, corresponding to the correlation result in positive and negative half chip including a quantization error, the detection result of the demodulation unit 9 outputs k ⁺ and k ^-, phase quantization Let Δτ be the phase error due to the rounded down or rounded up quantization. This error Δτ is calculated by the controller 8
The phase of the pseudo-noise code of the satellite signal is predicted, and the predicted value is obtained when quantizing to set the pseudo-noise generator 10. Where a is the signal strength, f (τ) is the correlation response of the demodulation unit 9 to the phase difference τ of the pseudo noise code, and g () is the amplitude response of the demodulation unit 9.

Then, the correlation result K ⁺ obtained when there is no quantization error
And K ^- estimate. K error of the predicted value as ^{ε + = g {a · f} (0.5 + Δτ + ε)} k - = a relationship of g {a · f (-0.5 + Δτ + ε)}. If the inverse function of the function g () is represented by G (), G (k ⁺ ) = af (0.5 + Δτ + ε) G (k ⁻ ) = af (−0.5 + Δτ + ε) K ⁺ = af (0.5 + ε) ≒ G ( k +) {F + (Δτ) + {F + (Δτ)} '· ε} K - = a · f (-0.5 + ε) ≒ G (k -) {F - (Δτ ^{) + {F - (Δτ)} } '· ε} However, Becomes As the tracking becomes more accurate, ε becomes smaller.

Thus ^{K + ≒ G (k +)} · F + (Δτ) K - ≒ G (k -) · F - (Δτ) does not lead to tracking errors as. This calculation is performed by the control unit 8 in FIG.

^{F + (Δτ), F -} (Δτ) and G (k) is a function determined by the characteristics of the receiver, .DELTA..tau in a storage device such as a ROM, k
Is obtained in advance as a table for, and is calculated by reading from the table.

K ⁺ obtained in this way, K ^- is the gradual time change as compared with .DELTA..tau, the tracking filter time constant of 1sec Numerical about time, after removing a sufficient noise, 200 msec
The phase error of the code is obtained by comparing with each other at a period of and the phase is corrected.

According to the above processing method, a measurement value in the case where there is no quantization error can be estimated from the value of the error due to quantization in setting the phase of the pseudo noise code, the correlation characteristic of the demodulation unit, and the amplitude value of the detection result. By eliminating the quantization error in the phase setting of the pseudo-noise code, it is possible to reduce the noise component by filtering the measurement results several times and suppress the increase in the positioning error, and to simplify the pseudo-noise code generator. Can be realized by easy processing.

Furthermore, by storing the correlation characteristics of the demodulation unit in a table and storing it in a recording device, and searching the table, it is possible to perform simple processing such as multiplication and addition / subtraction twice for one phase measurement.

Hereinafter, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing a response characteristic of a demodulation unit in a circuit configuration of a GPS receiver according to a second embodiment of the present invention. The configuration of the receiver is the same as that of the conventional example, and the description is omitted. In this embodiment, the correlation characteristic of the demodulation unit 9 in FIG. 5 is linear. The phase setting error due to quantization and
The procedure for estimating a measurement result obtained when a phase without a quantization error is set by the output amplitude of the demodulation unit 9 using the response characteristics of the demodulation unit 9 will be described with reference to the diagram showing the response of the demodulation unit 9 in FIG. Will be explained. The horizontal axis is the phase difference τ between the received signal and the pseudo-noise code generated in the receiver, and the vertical axis is the predicted correlation result. When the phase difference between the satellite signal and the pseudo-noise code is a positive / negative 1/2 chip including a quantization error, the correlation result is k ⁺
, K ⁻ , and a phase error Δτ. Here, A is the response of the demodulation unit 9 to the signal strength and the phase difference τ of the pseudo noise code is f (τ). Then, the correlation results K ⁺ and K ⁻ obtained when there is no quantization error are estimated. Assuming that the phase error of the predicted value is ε, K ⁺ = A · f (0.5 + ε) K ⁻ = A · f (−0.5 + ε) k ⁺ = A · f (0.5 + Δτ + ε) k ⁻ = A · f (−0.5 + Δτ + ε). Therefore, as the ε is sufficiently small ^{K + ≒ k + · F +} (Δτ) K - ≒ k - · F - (Δτ) However, And

This calculation is performed by the control unit 8 in FIG. F ⁺ (Δ
τ) and F ⁻ (Δτ) are functions determined by the characteristics of the receiver, and are previously written in a storage device such as a ROM as a table for Δτ, and are calculated by reading from the table.

K ⁺ obtained in this way, K ^- is the gradual time change compared with .DELTA..tau, the tracking filter time constant of 1sec Numerical about time, after removing a sufficient noise, to each other through a period of 200msec The phase error of the code is obtained by comparison, and the phase is corrected.

As described above, by making the demodulation unit 9 have a linear characteristic, the retrieval of the table can be reduced by half, the processing time can be reduced, and the table can be reduced.

Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. FIG. 3 is a configuration diagram showing the configuration of the demodulator in the circuit configuration of the GPS receiver according to the present invention. In FIG. 3, 5-1, 5-2, 5-3, and 5-4 are mixers, respectively, and 9-1 and 9-2 are detection circuits, respectively. Other configurations are the same as those of the conventional example. The operation of the above configuration will be described below. In FIG. 3, a detection circuit 9 for detecting the phase of a carrier wave is used as a detection circuit.
-5 and a detector 9-6 for measuring the phase difference of the code and receiving the data. The detection circuit 9-5 detects a phase difference between the received signal and the quadrature signal of the reproduced carrier generated by the numerically controlled oscillator 11. On the other hand, the detection circuit 9-6 measures the code phase difference and receives the data at the timing shown in FIG. FIG. 4A shows the phase difference of the code supplied to the detection circuit 9-6 with respect to the code tracked by the receiver in the time division processing. However, the previous embodiment and similar to the code phase includes a displacement that corresponds to the error of .DELTA..tau _m due to quantization. Then, as shown in (b), the correlation results k ⁰ , k ⁺ and k ^- are output. Then, k ⁺ and k ^- depending .DELTA..tau _m corresponding to each previous embodiment as well as (c) shows K ⁺ or K ^- is calculated. k ⁺ and k ^- is a time varying by the error component and the noise due to the quantization, K ⁺ and K ^- since excluding change due .DELTA..tau, be only changed by the noise, K ⁺ and K ^- when the each The variation can be improved by a code tracking filter that samples through a filter of a constant 1 sec and samples once every 200 msec.

Incidentally, K ₊ and K _- not only filter interpolates the time, may be compared among the same time. Furthermore, a filter such as a Kalman filter that can combine two persons having different times 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, the phase of the pseudo noise code is switched in time series to detect the phase difference, and the phase of the quantized pseudo noise code is detected. By using the measured value and the error due to quantization to estimate the measured value when there is no quantization error, the difference in quantization error that differs depending on the measurement time is removed. The code phase difference between the satellite signal and the pseudo noise code measured at the receiver can be accurately obtained, and the circuit of the demodulation unit can be further simplified. Further, since the correlation between the leading phase and the late phase is measured by the same detection circuit, errors caused by differences in detection characteristics are reduced as compared with the case where separate detectors are used.

Although a single-channel receiver has been described above for the sake of simplicity, a multi-channel receiver can be provided by providing a plurality of demodulators, pseudo-noise generators, and numerically controlled oscillators.

Effect of the Invention As described above, as the effect of the present invention, simplification of the pseudo-noise code generator can be realized by easy processing. By making the demodulation unit have a linear characteristic, the number of table searches can be reduced by half, the processing time can be reduced, and the number of tables can be reduced. By using the same detection circuit for detecting the phase difference between the leading phase and the lagging phase, the circuit of the demodulation unit can be further simplified and
Compared to using separate detectors, there is less error due to differences in detection characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a response characteristic of a demodulation unit of a GPS receiver for explaining a first embodiment of the present invention, and FIG. 2 is a GPS receiver for explaining a second embodiment of the present invention. FIG. 3 is a diagram illustrating a response characteristic of a demodulation unit of the present invention, FIG. 3 is a configuration diagram of a demodulation unit of a GPS receiver for explaining a third embodiment of the present invention, and FIG. FIGS. 5, 6, and 7 are processing timing diagrams of the demodulation unit of the GPS receiver for explanation.
FIG. 1 is a block diagram of a GPS receiver, a block diagram of a pseudo-noise generator, and a block diagram of a demodulation circuit for explaining a conventional GPS receiver. 1 ... satellite, 2 ... antenna, 8 ... control unit, 9 ... demodulation unit, 1
0: pseudo-noise code generator, 11: numerical control generator.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-142429 (JP, A) JP-A-63-215140 (JP, A) JP-A-63-15181 (JP, A)

Claims (4)

(57) [Claims] 1. An antenna for receiving a radio wave from a satellite, an amplifier for amplifying a received signal, a pseudo-noise code generator, a numerically controlled oscillator for reproducing a carrier wave, a demodulation unit for detecting a received signal, and controlling a receiver. The control unit quantizes and sets the phase of the pseudo-noise code in the pseudo-noise code generator. The error caused by rounding down or rounding-up in the quantization and the response characteristic of the demodulation unit Estimate the correlation result obtained when a phase without quantization error is set using the output amplitude of the demodulator and the output amplitude of the demodulator, find the phase with the pseudo-noise code of the satellite signal, and track the pseudo-noise code GPS receiver code tracking method. 2. The correlation characteristic and the amplitude characteristic of the demodulation unit are registered in a table in a storage device, and the table is obtained by using this table to set a phase without a quantization error by the output amplitude of the demodulation unit. 2. The GP according to claim 1, wherein the correlation result is estimated.
S receiver code tracking method. 3. A demodulator having a linear characteristic, a correlation characteristic of the demodulator being registered in a storage device as a table, and a phase having no quantization error being set based on the output amplitude of the demodulator using the table. The code tracking method for a GPS receiver according to claim 1, wherein the correlation result obtained in (1) is estimated. 4. The same detection circuit is used for measurement for obtaining a correlation with the phase of a pseudo-noise code as an early phase and a late phase, and a phase difference is detected by switching the phase of a pseudo-noise code in a time series, and the measurement is performed. 4. The code tracking method for a GPS receiver according to claim 1, wherein a phase difference between a received signal and a pseudo-noise code predicted by the receiver is obtained between measurement results at different times.