JP2537802B2 - GPS receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to a GPS (Golobal Positioneng) that performs positioning by using radio waves from the NAVSTAR satellite of the global positioning satellite system.
System) is related to the receiver.

2. Description of the Related Art Recently, GPS receivers have attracted attention in the field of navigation. For this GPS receiver, for example, a reception method described in "GDM / GPS Receiver Implementation" (NAECON) 1977, 303P-309P and the like is known. A conventional GPS receiver will be described below with reference to FIGS. 6 and 7.

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

2 is an antenna for receiving the radio wave of the satellite 1, 3 is a preamplifier for amplifying the received signal, 4 and 5 are local oscillators and mixers for frequency-converting the output signal of the preamplifier 3, and 6 is a mixer 5. A bandpass filter for filtering the output intermediate frequency signal, 7 an amplifier for amplifying the output of the bandpass filter 6, and 9 for demodulating the signal output by the amplifier 7 and then converting it into a digital signal and outputting it to the control unit 8. , 10 is a pseudo noise generator for generating a code signal for despreading the spread spectrum signal from the satellite, and 11 is a numerically controlled oscillator for reproducing a carrier wave. Reference numeral 12 is a numerically controlled oscillator that generates the timing of the output signal of the pseudo noise generator 10. Reference numeral 8 is a numerically controlled oscillator 11 and a numerically controlled oscillator 12, which measures the received signal and calculates the measured signal. It is a control unit that obtains the position where the antenna is installed and outputs the obtained position and other information.

The operation of the above configuration will be described below. First, with the omnidirectional antenna 2, four satellites 1
Received by the preamplifier 3, and the output signal of the local oscillator 4 and the mixer 5 perform frequency conversion. This signal is band-limited by the band filter 6 and then amplified by the amplifier 7. This output signal contains the signals of four satellites 1, which are individually separated and demodulated by the four demodulators 9, digitized to about 8 bits, and output to the controller 8. The satellite 1 is identified by the Gold code generated by the pseudo noise generator 10. This pseudo-noise code is unique to the satellite and has a code length of 1023 bits. Then, when the phase of the satellite signal and the phase of the pseudo noise code generated in the receiver match, the demodulation unit 9 obtains the maximum amplitude. Further, for satellite signals having different pseudo noise codes, the output amplitude of the demodulation unit 9 is small regardless of the phase of the pseudo noise code.

The control unit 8 controls the phase of the pseudo noise code output by the pseudo noise generator 10 by changing the frequency of the numerically controlled oscillator 12 so that the output amplitude of the demodulation unit 9 becomes as large as possible. Track your code. The control unit 8 also corrects the Doppler shift caused by the relative speed between the receiver and the satellite 1 and the frequency error of the local oscillator, and controls the frequency of the numerically controlled oscillator 11 so as to track the carrier wave of the satellite signal. . The reproduced carrier wave is supplied to the demodulation unit 9, the phase difference between the carrier wave of the satellite signal and the reproduced carrier wave is measured, and the frequency of the numerically controlled oscillator 11 is controlled so as to reduce the phase difference, whereby tracking can be performed. By tracking the carrier wave, the control unit 8 can demodulate the data signal sent from the satellite 1 as a two-phase phase-modulated signal as an output of the demodulation unit 9.

Further, the control unit 8 reads the data sent from each satellite 1 from the output of the demodulation unit 9, and reads the orbital elements of each satellite 1 and the GPS time which is the reference of the satellite 1. This GPS time read is the satellite 1 received
The time when the radio wave was emitted from is shown, which is the apparent time. Using the obtained GPS times of the four satellites 1, the simultaneous equations are established regarding the propagation time of the radio wave and the position of the satellite 1 with the three-dimensional position of the receiving point and the current true GPS time as unknowns. The position is obtained by solving this and output to the outside.

The phase of the pseudo noise code included in the satellite signal indicates a fine satellite time, and it is necessary to accurately measure the phase of the pseudo noise code of the satellite in order to accurately measure the observation position. Therefore, a numerically controlled oscillator that can be numerically controlled is suitable for the timing generation of the pseudo noise generator. The method of directly making the output timing of the pseudo noise generator 10 by the digital circuit cannot set a finer phase than the clock cycle of the digital circuit itself which makes the output timing. Therefore, a phase fluctuation corresponding to the clock interval of the digital circuit itself occurs, which becomes noise for the satellite time measurement. The numerically controlled oscillator 12 controls the phase with high accuracy by setting the timing signal generated by the digital circuit to a low frequency, and also removes the phase jitter etc. with the analog circuit, so that the output of the pseudo noise generator 10 is more accurate. I try to make the timing.

FIG. 7 is a block diagram for explaining the numerically controlled oscillator 12 in detail. 11-1 is a latch for holding the frequency setting value, 11
-2 is a cumulative adder for cumulatively adding the latched data, 11
-3 is a ROM in which a conversion table for converting the 8-bit phase value output by the cumulative adder into the amplitude value of the sine wave is written, 11-
4 converts the amplitude value of this sine wave into analog amplitude
D / A converter, 11-5 is a synthesizer for producing a local signal for frequency converting the output of the D / A converter, 11-6 is a mixer for this frequency conversion, 11-7 is an image of the frequency conversion. A band filter that removes the signal and excess jitter components, and a limiter 11-8 that shapes the analog signal output by the band filter into a logic signal.

First, a 22-bit precision frequency setting value is input from the control unit 8 and held in the latch 11-1. The cumulative adder 11-2 holds the 22-bit addition result, and when 41944 is set as the frequency, it overflows after 100 cumulative additions
It becomes the cycle of. This cumulative addition value divided by 4194304 corresponds to a semi-circle. And the frequency resolution is about 2.
The jitter of 4 Hz and phase is about 1/417 radian, which is 0.1 m when converted to distance resolution, which is sufficient resolution.

The cumulative adder 12-2 outputs the upper 8 bits of the cumulative added value at the cycle of the reference clock. This signal is the phase of the signal that changes the frequency by ± 10 KHz around 100 KHz. This 8
The phase value of the bit is converted into the amplitude value of the sine wave by the ROM 11-3 and converted into the analog signal by the D / A converter 11-4. Furthermore, this analog signal and the 1.123MHz signal that the synthesizer 11-5 can output are mixed by the mixer 11-6, the unnecessary components are removed by the bandpass filter 11-7, and the frequency is converted to the 1.023MHz ± 10KHz analog signal. . The frequency-converted signal is further waveform-shaped by the limiter 11-8 and output to the pseudo noise generator 10. The 1.023 MHz ± 10 KHz signal described above generates four independent signals for four satellites 1, so the numerically controlled oscillator 12 includes four circuits.

However, in the above configuration, the timing at which the pseudo noise generator 10 generates the pseudo noise code is the numerical control oscillator.
Since 12 signals are used, a complicated circuit structure is required as shown in FIG. 7, and not only the scale of the receiver becomes large, but also the price is high and the power consumption is large. .

The present invention solves the above problems of the prior art, and an object of the present invention is to realize an inexpensive, small-sized, lightweight, and low-power-consumption GPS receiver by improving the tracking method of the pseudo noise code.

Means for Solving the Problems The present invention relates to a pseudo noise generating means for generating a pseudo noise code unique to a satellite, a demodulating means for obtaining a correlation between the pseudo noise code and a signal from a satellite, and the pseudo noise generating means. A clock signal of a constant period is supplied to the pseudo-noise code, the pseudo-noise code phase-controlled by the quantized phase data is output, and the phase difference between the satellite and the pseudo-noise generating means is quantized from the correlation result of the demodulating means. In this case, satellite means for calculating the pseudo-noise code of the satellite numerically is provided by calculating with an accuracy equal to or less than the quantization unit in the case of.

With the above-described configuration, the present invention uses the output value of the demodulation means, which is a correlation result, while controlling the clock input by the pseudo noise generation means to a constant cycle and controlling the pseudo noise code to be output with a quantized phase. By pattern matching with the correlation characteristics, the phase difference between the pseudo noise code of the satellite signal and the output of the pseudo noise generator is rounded down or rounded up when performing the quantization, which is a finer phase difference than the unit phase of the quantization. By including the measured portion by calculation, by controlling the phase of the pseudo noise generating means by the quantized phase value according to the calculation result, by tracking the pseudo noise code more accurately on calculation, The above object is achieved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block connection diagram of a GPS receiver according to the first embodiment of the present invention.

In FIG. 1, 2 is an antenna for receiving radio waves from four satellites 1, 3 is a preamplifier for amplifying the received signals,
4 is a local oscillator that frequency-converts the output signal of the preamplifier 5, 5 is a mixer for frequency conversion, 6 is the output of the mixer 5, that is, a bandwidth for filtering only the intermediate frequency signal from the output signal of frequency conversion 2 MHz band filter, 7 an amplifier for amplifying the output of the band filter 6, 28 a control unit for controlling the receiver, 9 demodulates the output signal of the band filter 6 to the control unit 28 and outputs it after digital conversion. Demodulation unit, 30 is a pseudo noise generator that outputs four Gold codes unique to the satellite 1 which are pseudo noise codes to the demodulation unit 9, and 11 is demodulated data sent from the satellite 1 by two-phase phase modulation. It is a numerically controlled oscillator that regenerates a carrier wave.

FIG. 2 is a block connection diagram for explaining the pseudo noise generator 30 of FIG. 1 in more detail. 30-1 is φ ₀ ~ φ ₇ with a phase difference of 8 equal intervals by the clock of 8.184MHz
Shift register that generates 1.023MHz clock,
2 was 1msec 1023 minutes outputted by once control unit 28 in 1msec units, to preset the 10 bit phase pseudonoise code, from 0 to count up the clock of the phi ₇ 1
A counter for circulating the count value up to 022, 30-3 is a ROM in which a gold code unique to the satellite 1 which is determined by a satellite selection signal from the control unit 28 is written according to the 10-bit count value of the counter 30-2. , 30-4 is this ROM 30-3
A latch 30-5 for adjusting the output timing of the pseudo-noise code, which is quantized in units of 1 / 8,184 msec output from the control unit 28, receives the lower 3 bits of the phase data, and the lower 3
A data selector that selectively outputs the output clock of the shift register 30-1 corresponding to the bit value and the value obtained by adding 4 to this, and 30-6 is a pseudo according to the clock selected corresponding to the value of the lower 3 bits. Latch for latching noise code, 30-7 is a latch for latching the output of latch 30-6 by the clock selected according to the value obtained by adding 4 and 30-8 is selected according to the value of the lower 3 bits. It is a latch that latches the output of the latch 30-7 by the clock.

The operation of the above configuration will be described below. The operation except for the control unit 28 and the pseudo noise generator 30 is almost the same as that of the conventional example shown in FIG. That is, the radio waves from the four satellites 1 are received by the omnidirectional antenna 2, amplified by the preamplifier 3, and the local oscillator 4
The frequency of the output signal is converted by the mixer 5. This signal is band-limited by the band filter 6 and then amplified by the amplifier 7. This output signal is for all satellites 1 received by the antenna 2.
Contains the signal of. The four demodulators 9
Separated and demodulated for each, digitized to 8 bits, and the control unit 28
Output to. The satellite 1 is identified by the Gold code generated by the pseudo noise generator 30. This pseudo-noise code is unique to the satellite and has a code length of 1023 bits. Then, when the phase of the satellite signal and the phase of the pseudo noise code generated in the receiver match, the demodulation unit 9 obtains the maximum amplitude. Further, for satellite signals having different pseudo noise codes, the output amplitude of the demodulation unit 9 is small regardless of the phase of the pseudo noise code.

The control unit 28 controls the phase of the pseudo noise code output by the pseudo noise generator 30 so that the output amplitude of the demodulation unit 9 becomes as large as possible, and tracks the pseudo noise code of the satellite 1. Further, the control unit 28 corrects the Doppler shift caused by the relative speed between the receiver and the satellite 1 and the frequency error of the local oscillator, and controls the frequency of the numerically controlled oscillator 11 so as to track the carrier wave of the satellite signal. . The reproduced carrier wave output from the numerically controlled oscillator 11 is supplied to the demodulator 9, the phase difference between the carrier wave of the satellite signal and the reproduced carrier wave is measured, and the frequency of the numerically controlled oscillator 11 is controlled so as to reduce the phase difference. You can track it. By tracking the carrier wave, the control unit 28 can demodulate the data signal sent from the satellite 1 as a two-phase phase-modulated signal as the output of the demodulation unit 9. Further, the control unit 28 reads the data transmitted from the satellite 1 from the output of the demodulation unit 9 and reads the orbital elements of each satellite 1 and the GPS time indicated by the satellite 1.
The obtained GPS time indicates the time when the satellite 1 emitted the radio wave. Using these four apparent GPS times,
Regarding the propagation time of the radio wave and the position of the satellite 1, the three-dimensional position of the receiving point and the GPS time at the time of reception are used as unknowns, and simultaneous equations are set up, and by solving this, the position is obtained and output to the outside.

Next, the pseudo noise derivation device 30 will be described in more detail with reference to FIG. The pseudo noise generator 30 receives the phase data of the 13-bit pseudo noise code quantized in 8.184 msec from the control unit 28. By the lower 3 bits of this data, from clocks φ _{0 to} φ ₇ having 8 kinds of phases,
The data selector 30-5 selects two clocks. FIG. 3 shows an example of this selected clock. In FIG. 3, (a) is the 8.184 MHz clock, and (b) is the φ ₀ clock. When the value of the lower 3 bits of the phase data is 3, the data selector 30-5 has the φ shown in FIG. 3 (c).
3 is output to the latches 30-6 and 30-8, and φ ₇ shown in FIG. 3 (d) is output to the latch 30-7. When the lower 3 bits are n, φ _n is output to the latches 30-6 and 30-8, and φ _m is output to the latch 30-7. (However, m is the remainder obtained by dividing n + 4 by 8.) Therefore, when the latch 30-7 outputs the pseudo noise code as the center, the latch 30-6 has a half.
Chip (1 / 046msec) advanced phase and latch 30
-8 is a phase delayed by one half chip. The upper 10 bits of the phase data of the 13-bit pseudo noise code is preset in the preset counter 30-2 at a cycle of 1 msec. After that, the preset counter 30-2 sequentially counts up by the clock φ7 having a cycle of 1023 msec. Furthermore, the value of the pre-set counter 30-2 is used as an address,
The Gold code written in ROM30-3 is read out sequentially. Therefore, the gold output from the latch 30-4
The code has the same code rate as the Gold code of the satellite signal. The preset timing of the 1 msec cycle is common to all the satellites 1 and is a timing that precedes the 1 msec step in the internal clock of the receiver by 13/8 chips. Also, the gold output from the latch 30-4
The code has a phase advanced by 5/8 chip from the timing with the upper 10 bits of the phase data of the 13-bit pseudo noise code as the phase, with the internal clock of the receiver as a reference. Latch 30-6, Latch 30-7, Latch 30-8
The Gold code output by the above-mentioned signal is a phase advanced by one-half chip, a matched phase, and a phase delayed by one-half chip with respect to the timing with the 13 bits as a phase. As described above, the pseudo noise generator 30 is 1 / 8,184 msec.
By setting the phase of the pseudo noise code, which is quantized in units of about 120 nsec, the Gold code that matches the set timing is output.

FIG. 4 shows changes in the output of the demodulation unit 9 with respect to the phase difference between the phase of the pseudo noise code generated by the receiver and the received satellite signal. FIG. 4 (a) shows the correlation result with the output of the latch 30-7, which is shown in absolute value. The solid line and the broken line show changes in the input amplitude to the demodulation unit 9. As a phase reference, the phase where the pseudo noise code output from the latch 30-7 matches the code of the satellite 1 is set to zero. On the other hand, FIGS. 4 (b) and 4 (c) respectively show
It is the amplitude obtained when the correlation is obtained in the demodulation unit 9 by the latches 30-8 and 30-6, and the solid line and the broken line show the change in the amplitude. FIG. 4 (d) is the same figure (b) and (c).
Shows that the phase difference τ of the pseudo noise code between the satellite signal and the pseudo noise generator 30 is zero, this value is also zero,
If the absolute value of τ is 1.5 chips or less, τ and the sign of the difference shown in FIG.

Assuming that the amplitude of the input signal is A, the correlation result K _O of the output of the latch 30-7 and the demodulation unit 9 of the received signal is (However, f {} is the amplitude characteristic of the demodulation unit 9). Similarly correlation result latch 30-6 and 30-7 K _+, K _-
Respectively Becomes Therefore, K ₊ , K _O , and K ₋ are all monotonic functions in the intervals where τ is minus one half to 0 and zero to one half. Since the phase of the pseudo noise code is quantized and set by 1/8 chip, when the satellite signal is tracked by the pseudo noise code, the value quantized and set as the phase of the pseudo noise code is the disturbance. It is possible to hold τ including ± and ± ½ or less. Also, τ
Whether is positive or negative is determined by the difference between K ₊ and K ₋ shown in FIG. 4 (d). Value to evaluate the error of τ regardless of whether τ is positive or negative (τ, A) Τ and A are determined so that Note that k ₊ , k _O , k
_- The K _+, K _O, K _- is the measured value of. The sum of the value of τ obtained by the above calculation and the phase actually set by quantizing the phase of the pseudo noise code is the value obtained by measuring the phase of the pseudo noise code of the satellite signal. Using this result,
The control unit 28 tracks the pseudo noise code so that τ becomes small. The phase of the pseudo noise code managed by the tracking calculation has a fine precision, but the pseudo noise generator
The quantized value is set to 30.

As is clear from the above description, according to this embodiment,
The pseudo noise generator 30 is driven by a clock with a constant cycle,
A pseudo noise code is generated by setting the quantized phase, the correlation with the received signal from the satellite 1 is obtained, and the pseudo noise generator 30 and the satellite signal between the pseudo noise generator 30 and the satellite signal are obtained by pattern matching between the correlation result and the characteristics of the demodulation unit 9. By obtaining the phase difference, in the pseudo noise generator 30, the tracking of the phase is performed with higher accuracy in calculation than the phase of the pseudo noise code which is actually quantized and set. Therefore, according to the present embodiment, the numerically controlled oscillator 12 shown in FIG. 6 can be simplified, and an inexpensive, compact and lightweight GPS receiver can be realized.

In addition, the error between the pseudo noise generator clock and the satellite pseudo noise code clock caused by the Doppler shift of the received signal and the accuracy of the oscillator that creates the reference timing due to the relative speed between the satellite and receiver is at most It is about 4 ppm, and the amount of change in the set phase at the beginning and end when the phase is set with a constant clock for a period of 1 msec can be 4 nsec or less. The distance between the satellite and the measurement point is 1.2 m or less, which is not a problem. Also,
Since this error is a clock error obtained in position calculation, it is easy to correct it by calculation.

Next, a second embodiment of the present invention will be described. First
In the same configuration as in FIG. 2 and FIG. 2, the procedure of calculating the phase difference between the pseudo noise generation circuit 30 and the pseudo noise code of the satellite signal is different in this embodiment. In the first embodiment, A and τ are determined so that the equation (4) is minimized.
In this embodiment, in the range where the absolute value of τ is smaller than ½ chip, It is obtained by solving the equation of.

According to this embodiment, the phase of the pseudo noise code can be obtained by a simpler calculation.

Next, a third embodiment of the present invention will be described. First
In the same configuration as FIG. 2 and FIG. 2, the demodulation unit 9 of FIG.
For this, a mixer with linear input / output characteristics is used. Due to this linear characteristic, the correlation characteristic of the pseudo noise code changes from FIG. 4 (a) to (d) to FIG. 5 (a) to (d). Therefore, equation (5) is Next Becomes

Therefore, the phase of the pseudo noise code can be obtained by a very simple calculation by using a mixer having a linear characteristic.

In the above description, a multi-channel GPS receiver has been described, but the present invention is not limited to this and can be applied to a single-channel receiver.

Further, although the preset counter 30-2 is used in the pseudo noise generator 30, the output of the reference counter and the control unit
The phase data from 28 is added and the address is calculated by adding the most significant carry signal to the lower digit.
Other configurations, such as using RAM for 0-3, can also be used.

Further, the quantization of the phase output from the pseudo noise generator 30 is set to ⅛ chip, but it may be ½ chip or less.

Further, in the calculation of the pseudo noise code, even when the demodulation unit 9 is not linear, sufficient accuracy can be obtained by linearly approximating it using a table.

As described above, according to the present invention, although the clock of the pseudo noise generating means is fixed and the numerical control oscillating means is simplified, the pseudo noise code is accurately tracked by calculation and the phase is measured. As a result, it is possible to measure the position with high accuracy, and it is possible to realize a compact, lightweight and low-priced GPS receiver.
The effect is great.

[Brief description of drawings]

FIG. 1 is a block connection diagram of a GPS receiver in one embodiment of the present invention, FIG. 2 is a detailed block connection diagram of the pseudo noise generator of FIG. 1, and FIG. 3 is a timing waveform diagram of FIG. 4 and 5 are characteristic diagrams for the phase difference of the pseudo noise code of the demodulator, FIG. 6 is a block diagram of the conventional GPS receiver, and FIG. 7 is a numerical control for generating the clock of the pseudo noise generator. It is a block connection diagram of an oscillator. 9 ... Demodulator, 11 ... Numerically controlled oscillator, 28 ... Controller,
30 ... Pseudo noise generator, 30-1 ... Shift register, 30
-2 ... Counter, 30-3 ... ROM, 30-5 ... Data selector, 30-4 to 30-8 ... Latch.

 ─────────────────────────────────────────────────── ───Continued from the front page (56) Reference JP-A-63-36622 (JP, A) THE INSTITUTE OF NAVIGATION ed. "Global Positioning System M Vol. ▲ II ▼ P. 25-35

Claims (2)

(57) [Claims] 1. A pseudo noise generating means for generating a pseudo noise code specific to a satellite, a demodulating means for obtaining a correlation between the pseudo noise code output from the pseudo noise generating means and a pseudo noise code of a satellite signal, and the demodulating means. Has control means for controlling the phase of the pseudo noise code output by the pseudo noise generating means according to the correlation result output by the pseudo noise generating means. The pseudo noise generating means has a clock signal of a constant cycle and a time corresponding to the cycle of the clock signal. The phase data of the pseudo noise code quantized by is input, and the pseudo noise code of the phase corresponding to the input phase data is output, and the control means numerically compares the phase of the pseudo noise code included in the satellite signal. When the phase of the pseudo noise code to be tracked is controlled and the phase of the numerically controlled pseudo noise code corresponds to the cycle of the clock signal. , The pseudo noise code is set in the pseudo noise generating means, the demodulating means calculates the correlation between the pseudo noise code of the satellite signal and the pseudo noise code output by the pseudo noise generating means, and the control means calculates the correlation result. The phase difference of the satellite is tracked by correcting the phase of the pseudo noise code that is numerically tracking managed so that the measured phase difference becomes small. In the measurement of, the correlation characteristic of the demodulation means, and the pseudo noise code phase numerically managed by using the residual phase when the phase of the numerically managed pseudo noise code is quantized, and The difference between the phase of the pseudo noise code of the satellite signal and the phase of the pseudo noise code, which is numerically controlled, is obtained by calculation with accuracy less than the quantization unit. GPS receiver, characterized in that tracking the pseudo noise code in the satellite Te. 2. The GPS receiver according to claim 1, wherein the output amplitude characteristic with respect to the input amplitude of the demodulating means is made linear, and the phase difference of the pseudo noise code is calculated.