JP3106829B2 - GPS receiver demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulation circuit for a GPS receiver in the field of satellite navigation, which measures a position using radio waves of artificial satellites.

[0002]

2. Description of the Related Art In recent years, GPS receivers that receive radio waves from positioning satellites and measure absolute positions have been widely used as navigation devices for cars, ships, and aircraft. 2. Description of the Related Art Conventional GPS receivers include, for example, those described in Japanese Patent Application Laid-Open No. 2-103487.

[0003] A conventional GPS receiver will be described below. FIG. 6 shows a demodulation circuit of a conventional GPS receiver when demodulating 32 signals of 8 channels. FIG.
, 1 is a U.S. positioning satellite NAVSTAR.
2 is an antenna, 3 is an amplifier, 4 is a mixer, 5 is a local oscillator, and 6 is an intermediate frequency amplifier. 7 is an orthogonal frequency converter, 8 is a local oscillator, 9 is 64 correlators, 10 is 32
Kind of pseudo-noise code generator, 11 is 64 filters,
Reference numeral 12 denotes 32 orthogonal frequency converters, 13 denotes eight types of local oscillators, 14 denotes 64 integrators, 15 denotes a control unit, 16 denotes a positioning operation unit, and 17 denotes an output unit.

The operation of the GPS receiver configured as described above will be described below. First, radio waves transmitted by a plurality of positioning satellites 1 are received by the antenna 2, and the received signals are amplified by the amplifier 3. The amplified signal is mixed with the signal of the local oscillator 5 in the mixer 4 and frequency-converted to an intermediate frequency signal. The converted signal is amplified by the intermediate frequency amplifier 6, and quadrature-converted by the signal of the local oscillator 8 by the quadrature frequency converter 7 to output the in-phase signal I and the quadrature signal Q. The pseudo-noise code generator 10 generates a total of 32 signals having four types of phases for each of the eight pseudo-noise codes specific to the satellites, and correlates this signal with the in-phase signal I and performs the orthogonalization. A total of 64 correlations with the signal Q are determined using the 64 correlators 9 and filters 11 respectively. The 32 sets of orthogonal correlation results are frequency-converted in 32 orthogonal frequency converters 12 by outputs of a local oscillator 13 that generates eight kinds of signals corresponding to eight satellites. The converted base frequency signal is time-integrated by the integrator 14 in accordance with the timing of each pseudo noise code, and the control unit 15 receives the integration result.

In accordance with the result of the integration, the control unit 15 determines the code phase of the pseudo-noise code generator 10 and the local oscillator 13
To control the frequency. A satellite signal can be detected only when the phase of the pseudo noise code of the satellite and the frequency of the carrier substantially match the phase of the pseudo noise code generated in the receiver and the frequency of the local oscillator. Further, the control unit 15 demodulates the signal, receives the orbit information, and measures the time indicated by each satellite.
The phase of the pseudo-noise code generator 10 and the frequency of the local oscillator 12 are controlled so as to track the pseudo-noise code and the carrier. From the obtained orbit information for each satellite and the measured time, the position of the antenna 2 is obtained by calculation in the positioning calculation unit 16 and output from the output unit 17. In order to capture the satellite signal, the phase of the pseudo-noise code and the frequency of the local oscillator are scanned, and the signal can be detected only when the two substantially match the satellite signal. But,
This receiver has 32 demodulators and scans the same satellite signal in parallel, so that the satellite signal can be found quickly.

[0006]

However, in the above-mentioned conventional configuration, the types of local oscillation signals generated by the local oscillation signal 13 correspond to the number of satellites, respectively, and correspond to the number of satellites. A large number of filters must be provided, so that the circuit scale becomes large, the power consumption increases, and the cost increases.

In another conventional example, a satellite signal is detected by performing a fast Fourier transform on the signal for which the correlation has been obtained. This method can detect a satellite signal at a plurality of frequencies at the same time, but the processing is complicated and the load is heavy.

The present invention solves the above-mentioned conventional problems, and does not increase the number of correlators, reduces power consumption and cost, and demodulates a GPS receiver that can quickly find a satellite signal. It is intended to provide a circuit.

[0009]

In order to achieve this object, a GPS receiver demodulation circuit according to the present invention comprises a pseudo-noise code generator for generating one pseudo-noise code unique to each satellite, and a pseudo-noise code generator for the pseudo-noise code generator. Multiplies the generated code by the received signal from the satellite
And a filter that integrates the output of the correlator over time
When the local oscillator simultaneously generating a plurality of different frequencies of the local oscillation signal to one satellite to receive, separately using the different local oscillator signals, said corresponding Fi
A frequency converter correlation result the frequency conversion respectively obtained Ri by the time integral with filter, the result of the frequency conversion into the different frequencies, and has a configuration including an integrator or filter for integrating each time.

[0010]

With this configuration, a satellite signal can be detected simultaneously at a plurality of frequencies, and a satellite signal can be quickly found. Further, it is easier to generate a plurality of local oscillation signals than to provide a large number of correlators, so that an increase in power consumption and an increase in cost can be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the first to fourth embodiments described below, 32 signals of 8 channels are demodulated, but it goes without saying that the number is not limited to this.

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In FIG.
Reference numeral 21 denotes a positioning satellite NAVSTAR. 22 is an antenna, 23 is an amplifier, 24 is a mixer, 25 is a local oscillator,
26 is an intermediate frequency amplifier. 27 is an orthogonal frequency converter, 28 is a local oscillator, 29 is 16 correlators, 30 is a pseudo-noise code generator for generating eight kinds of pseudo-noise codes,
31 is 16 filters, 32 is 32 orthogonal frequency converters, 33 is a local oscillator which outputs 32 kinds of oscillation signals,
34 is 64 integrators, 35 is a control unit, 36 is a positioning operation unit, and 37 is an output unit.

The operation of the demodulation circuits indicated by 27 to 35 in the GPS receiver configured as described above will be described. First, radio waves transmitted from a plurality of positioning satellites 21 are received by an antenna 22, and the received signals are amplified by an amplifier 23. The amplified signal is passed through a mixer 24 to a local oscillator 25.
And frequency-converted to an intermediate frequency signal. The converted signal is amplified by the intermediate frequency amplifier 26, and quadrature-converted by the quadrature frequency converter 27 using the signal of the local oscillator 28, to output the in-phase signal I and the quadrature signal Q. A pseudo-noise code generator 30 generates eight satellite-specific pseudo-noise codes, multiplies the correlation between the signals and the orthogonal signals I and Q in a correlator 29, and performs time integration in a filter 31. Ask. The eight orthogonal correlation results are frequency-converted using 32 orthogonal frequency converters 32 by the output of a local oscillator 33 that generates 32 types of signals corresponding to eight satellites. The converted 32 sets of base frequency signals are time-integrated by 64 integrators 34 in accordance with the timing of each pseudo noise code, and the control unit 35 receives the integration result. FIG. 2 shows the above 29 to 3
4 shows an example of a portion corresponding to one satellite.

The control unit 35 determines the phase of the code of the pseudo-noise code generator 30 and the local oscillator 33 according to the integration result.
To control the frequency. A satellite signal can be detected only when the phase of the pseudo noise code of the satellite and the frequency of the carrier substantially match the phase of the pseudo noise code generated in the receiver and the frequency of the local oscillator. Further, the control unit 35 demodulates the satellite signal, receives the orbit information, and measures the phase indicated by the pseudo noise code generator 30 and the local oscillator 33 so as to track the pseudo noise code and the carrier in order to measure the time indicated by each satellite. Control the frequency. Based on the obtained orbit information for each satellite and the measured time, the position of the antenna 22 is obtained by calculation in the positioning calculation unit 36 and output from the output unit 37. In order to capture the satellite signal, the phase of the pseudo-noise code and the frequency of the local oscillator are scanned, and the signal can be detected when both of them substantially match the satellite signal.

The demodulation circuit of the GPS receiver according to this embodiment is provided with a local oscillator for outputting 32 types of local oscillation signals.
Since the frequency is converted into two kinds of frequencies, signals can be simultaneously detected at four kinds of frequencies with respect to eight satellites, and the frequency can be scanned four times as fast as a conventional eight-channel receiver. Further, compared with the conventional demodulation circuit which captures a satellite at a high speed, a satellite signal can be quickly captured by simple processing with a small number of circuits.

As is apparent from the configuration shown in FIG. 1, the demodulation circuit of the GPS receiver according to the present embodiment can obtain an excellent effect of low power consumption in a high-performance receiver that can capture satellite signals at a high speed. .

As described above, according to the present embodiment, the correlation result obtained after the correlation with the pseudo noise code is obtained by the correlator is converted into the base frequency by a plurality of local oscillation signals. Thus, a high-performance receiver with little increase in power consumption and cost can be realized.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. In FIG. 3, 4
1 is a positioning satellite NAVSTAR. 42 is an antenna, 43 is an amplifier, 44 is a mixer, 45 is a local oscillator, 4
Reference numeral 6 denotes an intermediate frequency amplifier. 47 is an orthogonal frequency converter,
48 is a local oscillator, 49 is 16 correlators, 50 is a pseudo-noise code generator for generating eight kinds of pseudo-noise codes, 51
Represents 16 filters, 52 represents 32 orthogonal frequency converters, 53 represents a local oscillator for outputting 32 kinds of oscillation signals, 5
4 is 64 integrators, 55 is a control unit, 56 is a positioning operation unit, and 57 is an output unit. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 1 is that 58 switches are provided before the orthogonal frequency converter 52. With this switch 58, it is possible to select which channel a signal processing circuit processes after that.

The operation of the demodulation circuit of the GPS receiver configured as described above will be described below. The general operation is the same as that of the first embodiment, but the operation after capturing satellite signals on some channels is different. Initially, the switch 58 connects the input signal in the same way as in FIG. 1, but after a certain channel captures a satellite signal, a single orthogonal frequency converter necessary for tracking the satellite signal on this channel is used. The remaining orthogonal frequency converter 52 can be switched to the output of the filter 51 corresponding to another channel while leaving 52.

As described above, by providing the switch 58, after some channels capture satellite signals,
The assignment of the orthogonal frequency converter to the remaining channels allows the remaining channels to catch the satellite signal faster.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. In FIG.
1 is a positioning satellite NAVSTAR. 62 is an antenna, 63 is an amplifier, 64 is a mixer, 65 is a local oscillator, 6
Reference numeral 6 denotes an intermediate frequency amplifier. 67 is an orthogonal frequency converter,
68 is a local oscillator, 69 is 16 correlators, 70 is a pseudo-noise code generator for generating eight types of pseudo-noise codes, 71
Is 16 filters, 72 is one orthogonal frequency converter,
73 is a local oscillator for sequentially outputting 32 kinds of oscillation signals;
4 is an integrator, 75 is a control unit, 76 is a positioning operation unit, 77 is an output unit, and the above is the same as the configuration of FIG. FIG.
The configuration is different from that of the first embodiment in that 79 parallel-to-serial converters are provided before the orthogonal frequency converter 72, the orthogonal frequency converter 72 is set as one set, and the local oscillator 73 outputs 32 kinds of signals periodically and sequentially. , The integrator 74 is composed of 64 memories and one adder. In the present embodiment, it is appropriate that the blocks from 72 to 79 use equivalent arithmetic processing using a digital circuit or an arithmetic device.

The operation of the demodulation circuit of the GPS receiver configured as described above will be described below. The general operation is the same as that of the first embodiment, except that the code rate of the pseudo noise code is f, the intermediate frequency is f, and the orthogonal frequency converter 72 is
Processes the received signal sampled at 4f. Local oscillator 6
8 is 1f, the output after frequency conversion is an orthogonal signal Q of the base frequency, and a carrier wave of a frequency obtained by combining the Doppler shift of the satellite signal and the frequency error of the receiver is a signal modulated by a pseudo noise code and data. . Next, the signal obtained by filtering the output of the correlator 69 is a signal modulated only by data, and the sampling cycle is f / 32. Next, the parallel signal of eight channels is converted into a time sequential signal by the parallel / serial converter 79. The converted received signal is output at a period of f / 4. Next, the sequential signals I and Q are subjected to orthogonal frequency conversion, and the I and Q frequency-converted signals are further integrated into an integrator 74.
, The cumulative addition is sequentially performed on the 64 memories. The result of the cumulative addition 74 with an integer multiple of the pseudo noise code as a delimiter is output to the control unit 75.

As described above, by providing the parallel-serial converter 79, the number of orthogonal frequency converters can be reduced, and the configuration of the accumulator can be simplified.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. In this embodiment, FIG.
Has the configuration shown in FIG. Reference numeral 81 denotes eight frequency memories for storing the frequency set by the control unit 75 in FIG. 4, 82 a phase memory for storing the phases of eight channels, 83 an adder for updating the phase, and 84 a triangle for converting the phase to amplitude. It is a function table. The above is the numerically controlled oscillator constituting the eight-channel local oscillator. In this embodiment, the following configuration is added. 85 is a 5-bit counter, 86 is a shifter that carries the output of the counter, 8
7 is an adder / subtracter for changing the phase.

The operation of the demodulation circuit of the GPS receiver configured as described above will be described below. The general operation is the same as that of the third embodiment. As for the local oscillator 73 shown in FIG. 4 which periodically and sequentially outputs 32 kinds of signals, eight numerically controlled oscillators corresponding to channels are stored in a memory 82.
In the phase of the eight channels stored in
The frequency information of the channel is added to the adder 8 at a period of f / 32.
3 is realized by successively adding for each channel. Further, with respect to the result of the addition, assuming that the phase of the cycle is n / 32 with respect to the value n of the counter 85, −1 times, 0 times,
By the control of the control unit, four types of phases, 1 times and 2 times,
Using a shifter 86 and an adder / subtractor 87, 32 types of local oscillation signals are generated by sequentially adding the phases to the eight channels. Further, the counter 86 counts at a period of f / 32. By such processing, the oscillation frequency of the numerically controlled oscillator of each channel is substantially -1 KHz, 0 KH
Signals of z, +1 KHz, and +2 KHz are sequentially output. As described above, the phase of the signal generated by the numerically controlled oscillator
By adding the value of the counter, the types of signals can be easily increased.

In the first and second embodiments, the blocks showing the functions have been described. However, each block can be composed of an analog circuit and a digital circuit, and equivalent arithmetic processing using an arithmetic unit can be used. In the third and fourth embodiments, the demodulation unit is constituted by a digital circuit. However, equivalent arithmetic processing using an arithmetic unit may be used. In the second embodiment, the switching device 58 is initially connected to the input signal in the same manner as the first connection, but is not limited to this.
In the fourth embodiment, -1 KHz, 0 KHz, +1 KHz,
Although a signal having a frequency difference of +2 KHz is generated, a different frequency difference can be realized by changing the sampling cycle and the counter 86. Further, the adder 83 can realize the same function with another element.

[0027]

As described above, the present invention provides a pseudo-noise code generator for generating one pseudo-noise code unique to a satellite, and multiplies the generated code by a signal received from the satellite.
And a filter that integrates the output of this correlator over time.
And a local oscillator for simultaneously generating a plurality of local oscillation signals of different frequencies for one satellite to be received, and separately using the plurality of different local oscillation signals for the one satellite to be received. a frequency converter for frequency-converting the correlation results more obtained to the time integral with the filter into a plurality of frequency by the result of the frequency conversion into the different frequency, with an integrator or filter for integrating each time, at the same time Signals can be detected for a plurality of frequencies, and there is no need to provide many correlators for increasing the circuit scale. Therefore, it can be configured with a small amount of hardware, and therefore, an excellent GPS that can find a satellite quickly with little increase in power consumption and cost.
This is to realize a demodulation circuit of the receiver.

[Brief description of the drawings]

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

FIG. 2 is a block diagram of a portion corresponding to one channel in the embodiment.

FIG. 3 is a block diagram of a demodulation circuit of a GPS receiver according to a second embodiment of the present invention.

FIG. 4 is a block diagram of a demodulation circuit of a GPS receiver according to a third embodiment of the present invention.

FIG. 5 is a block diagram of a local oscillator according to a fourth embodiment of the present invention.

FIG. 6 is a block diagram of a demodulation circuit in a conventional GPS receiver.

[Explanation of symbols]

 Reference Signs List 21 positioning satellite 22 antenna 23 amplifier 24 mixer 25 local oscillator 26 intermediate frequency amplifier 27 orthogonal frequency converter 28 local oscillator 29 correlator 30 pseudo-noise code generator 31 filter 32 orthogonal frequency converter 33 local oscillator 34 integrator 35 controller 36 Positioning calculation unit 37 Output unit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-178372 (JP, A) JP-A-3-170890 (JP, A) JP-A-5-164834 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01S 5/00-5/14

Claims (4)

(57) [Claims] 1. A kind of pseudo-noise code unique to a satellite to be received
A pseudo-noise code generator generated one by one in each class, a correlator for multiplying the generated code by a received signal from a satellite,
A filter for time-integrating the output of the correlator, a local oscillator for simultaneously generating a plurality of local oscillation signals of different frequencies for at least one received satellite, and separately using the plurality of different local oscillation signals, A frequency converter for converting the correlation result obtained by time integration by the filter corresponding to the one received satellite into a plurality of frequencies, and a result of frequency conversion to the different frequencies , A demodulation circuit of a GPS receiver including an integrator or a filter for time-integrating. 2. The demodulation circuit of a GPS receiver according to claim 1, wherein the demodulation circuit has a plurality of reception channels and has a switching function of changing a connection between a plurality of correlation results and a plurality of frequency converters. 3. A parallel-serial converter having a plurality of reception channels and converting a plurality of correlation results into a time-sequential signal, a number of frequency converters smaller than the number of reception channels for sequentially frequency-converting the output signal, and 3. The demodulation circuit of a GPS receiver according to claim 1, further comprising: an oscillator for generating local signals having different frequencies; and an integrator or a filter for sequentially and individually time integrating the frequency conversion results. 4. A means for changing the phase of a local oscillation signal corresponding to a channel, and a counter for determining a method of changing the phase, wherein a plurality of frequency-changed local oscillation signals are changed by changing the frequency of the local oscillation signal. 4. The G according to claim 1, further comprising a local oscillator for outputting a local oscillation signal.
Demodulation circuit of PS receiver.