JP2000031926A - Detector for characteristic deviation with respect to frequency between channels for fdma receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an inter-channel bias that is a deviation in a frequency characteristic of a group delay in an IF section without using a pseudo signal generating circuit in a frequency division multiple access FDMA receiver. SOLUTION: A frequency synthesizer (consisting of a phase comparator 304, a loop filter 302, a voltage controlled oscillator 301 and a frequency divider 303) is adopted for a local oscillator 30, an arithmetic section 40 changes an oscillated frequency of the frequency synthesizer to convert a frequency fRF of one RF signal from a satellite into plural IF frequencies fIF, and the arithmetic section 40 calculates a pseudo distance for each frequency fIF. A difference of the calculated pseudo distances is a deviation in a frequency characteristic of inter-channel group delay, so-called an inter-channel bias.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a global orbiting navigation satellite system.
, GLONASS. ), For example,
FDMA suitable for application to an FDMA receiver for receiving a spread spectrum signal wave transmitted from a GLONASS satellite by the FDMA method (frequency division multiple access method)
The present invention relates to a characteristic deviation detecting device for a frequency between channels for a receiving device.

[0002]

2. Description of the Related Art Global navigation system GLONASS
(Global Orbiting Navigation Satellite System)
Is a kind of navigation system using artificial satellites. Users of mobile objects such as aircraft, ships, and automobiles are equipped with satellite positioning devices including satellite signal receivers on mobile objects, and simultaneously receive radio waves emitted by four of the GLONASS satellites in satellite orbit. If the positioning operation is performed, 3
The dimensional coordinates (position) can be measured.

As this type of system, NAVSTA
R / GPS (Navigation System using Time and Rangi
ng / Global Positioning System, hereinafter abbreviated as GPS. )
Has been partially opened to the U.S. military for civilian use, and has recently become widely used as a means for measuring the position of a mobile object.

The basic principle of GLONASS is almost the same as that of GPS. The biggest difference is that in GPS, the frequency of radio waves (satellite signals) emitted by each satellite is the same, and the satellite signals of each satellite are distinguished by making the code code for modulating the radio waves different for each satellite. On the other hand, in GLONASS, on the contrary, the code code of each satellite is the same, and the difference is that the frequency is different for each satellite to distinguish each satellite signal.

An outline of satellite signals in GLONASS and a positioning method based on the satellite signals will be described. The carrier frequency of the satellite signal of the GLONASS satellite is 1598.0625 MHz.
From (Channel-7) to 1609.3125 MHz (Channel + 13), they are arranged at intervals of 0.5625 MHz for every 21 channels. Each satellite signal is modulated by a pseudo-noise code called a PN code common to all satellites and navigation data.

In the PN code, binary data having a predetermined length in which 0s and 1s are arranged seemingly irregularly are repeated. Irregularities in the data of a predetermined length cause characteristics similar to noise, and are called pseudo-noise codes. As is well known, such a modulation method has a feature of being resistant to radio wave interference.

Although the PN code has a noise-like property, it is only an artificial thing and a signal of the same pattern can be generated on the receiver side. When a PN code generated by a PN code generation circuit provided on the receiver side is collated with a satellite signal while being temporally shifted, there is a timing at which the two coincide.

[0008] The phase of each satellite signal is managed based on the time, and the relationship between the phase and the time is also known on the receiver side. Therefore, if the clock on the receiver side has the exact same time as the clock on the satellite, the radio wave propagation time between the satellite and the receiver can be known from the coincidence timing of the PN code. And the distance between the receiver and the receiver can be calculated.

However, it is actually difficult to guarantee the same time between the satellite and the receiver, and there is an unknown amount of time shift between the satellite and the receiver, and the distance has an error. .
For this reason, the above distance is called a pseudo distance.

On the other hand, the navigation data is the position information and time information of each satellite, and is transmitted in a form in which the PN code is subjected to secondary modulation. Therefore, the PN provided on the receiving device side
The received radio wave is demodulated (despread) by the PN code generated by the code generation circuit, and the signal radio wave can be extracted.

If there is no time lag between the satellite and the receiver, the pseudorange indicates the exact distance between the satellite and the receiver, so that the position of each satellite obtained from the satellite signals of the three satellites, The position of the receiver can be calculated and determined based on the pseudo distance.

However, in practice, as described above, since there is an unknown amount of time lag between each satellite and the receiver, the positions of the four satellites and the pseudo distance are removed to eliminate this. Is used.

FIG. 4 shows a conventional satellite signal receiving apparatus F.
2 shows a configuration of a downconverter for a DMA receiver.

The radio wave transmitted from the GLONASS satellite is received by an antenna unit installed on a moving body such as a ship or an automobile, and unnecessary radio waves outside the band are removed by a band-pass filter such as a dielectric filter. And is guided to the down converter shown in FIG.

A high-frequency signal having a frequency fRF (hereinafter referred to as an RF signal) is input to one input of the directional coupler 1 whose one end is terminated by a resistor 9. On the other hand, the other input of the directional coupler 1 receives the signal transmitted from the satellite, which is generated by the pseudo signal generating circuit 2 for correcting the in-band group delay characteristic of the band pass filter 5 of the IF unit 8. The pseudo-satellite signal can be input, and an RF signal in which a real satellite signal and a pseudo-satellite signal are mixed is obtained at the output end of the directional coupler 1.

The RF signal is mixed with a local signal LO having a frequency fLO of the local oscillator 3 by a mixer circuit 4, frequency-converted into an intermediate frequency signal having a frequency fIF (hereinafter referred to as an IF signal), and input to the IF section 8. . In the IF section 8, the IF signal in the GLONASS band is extracted by the band pass filter 5, amplified by the amplifier 6, finally converted into a digital signal by the A / D converter 7, and output to the arithmetic section.

[0017]

By the way, in the conventional satellite signal receiving apparatus including the down converter shown in FIG.
The following inconveniences existed.

That is, in a receiving apparatus for receiving a signal transmitted by the FDMA system, such as a satellite signal in GLONASS, the RF signal received by the antenna unit is transmitted by a transmission source, for example, a transmission frequency for each satellite (for each satellite channel). Therefore, the IF signal that has been frequency-converted in the down-converter circuit of the receiving device is also kept at a different frequency for each satellite.

In a circuit having frequency characteristics, such as a band-pass filter 5 provided in an IF signal band, it is generally difficult to keep the signal amplitude, phase, group delay time, and the like constant over a wide band. Frequency characteristics such as amplitude, phase, and group delay time are different for each satellite on the device side, and the distance between the satellite and the receiving device is measured using the group delay time of the PN code signal like GLONASS. In the satellite navigation system, this influences the error of the positioning position.

Therefore, in the conventional satellite signal receiving apparatus, the reception characteristic is corrected in order to correct the frequency characteristic of the group delay time, which is one of the deviations of the characteristic with respect to the frequency between channels (also referred to as inter-channel bias) in the receiving apparatus. A pseudo signal generating circuit 2 for generating a pseudo signal having the same frequency as that of the satellite is provided in the apparatus, and a method of correcting the frequency characteristic of the group delay time is adopted. However, the pseudo signal generating circuit 2 is provided. As a result, there has been a problem that the configuration of the receiving apparatus becomes complicated and power consumption increases.

The present invention has been made in view of such a problem, and without using a pseudo signal generation circuit,
Frequency characteristic deviation between channels (inter-channel bias)
It is an object of the present invention to provide a device for detecting a characteristic deviation with respect to the frequency between the channels for the FDMA receiving device, which can detect the frequency deviation.

Further, the present invention particularly enables FDMA to detect a group delay time, which is one of the inter-channel biases (deviation of characteristics with respect to frequency) in a satellite positioning device for measuring the position of a moving body or the like. It is an object of the present invention to provide a device for detecting a characteristic deviation with respect to a frequency between channels for a receiving device.

[0023]

SUMMARY OF THE INVENTION The present invention relates to an input R
A characteristic detecting unit that includes at least one frequency synthesizer as a local oscillator of a downconverter that converts the F signal into a predetermined IF signal, and performs frequency conversion of an RF signal of one channel frequency into a plurality of IF signals of different frequencies. Thus, it is possible to detect the deviation of the characteristic with respect to the frequency in the IF frequency band in the FDMA receiver, that is, the so-called inter-channel bias (the invention according to claim 1).

According to the present invention, one of the RF signals input from the antenna unit is converted into an IF frequency corresponding to all the RF channels by sequentially changing the oscillation frequency of the frequency synthesizer of the local oscillator, that is, the local frequency. It is configured to be able to. As a result, the R signal received by the antenna unit without using the pseudo signal generation circuit
Using the F signal as one reference, the inter-channel bias in the circuit after the IF can be measured. By performing an operation for removing the inter-channel bias, the inter-channel bias can be removed.

In this case, when the input RF signal of one channel is a received signal of a radio wave transmitted from a GLONASS satellite, the characteristic detecting section determines the pseudo distance from each of the obtained IF frequencies. By measuring the pseudo distance, the pseudo distance can be detected as a characteristic of the group delay time, which is one of the characteristics with respect to the frequency between the channels (the invention according to claim 2).

[0026]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing an F to which this embodiment is applied.
1 shows a configuration of a DMA receiving device 10.

The FDMA receiver 10 basically includes a down converter 1 including a mixer circuit 101 for frequency-converting a high-frequency signal (RF signal) having a frequency fRF obtained from an antenna section into an intermediate frequency signal (IF signal) having a frequency fIF.
1, an IF unit 20 that converts an IF signal into a digital IF signal, and an arithmetic unit 40 that also functions as a characteristic detecting unit that detects a characteristic of a frequency between channels based on the obtained IF signal.

The local oscillator 30 includes a crystal oscillator (TCXO) 306 whose oscillation frequency is temperature-compensated and the TCXO3
The reference frequency of the reference signal output from the number 06 is divided by 26.
305, and a phase comparison for comparing the phases of a frequency-divided reference signal having a frequency fPD and a signal obtained by dividing a local signal LO having a frequency fLO by a frequency divider 303 having a frequency division number N. , A loop filter 302 for smoothing the output of the phase comparator 304, and a local signal LO having a predetermined frequency fLO based on the output voltage of the loop filter 302.
And a voltage controlled oscillator (VCO) 301 for generating

Phase comparator 304, loop filter 30
2. The VCO 301 and the frequency divider 303 constitute a frequency synthesizer. Although one frequency synthesizer may be used as in this embodiment, a plurality of frequency synthesizers having different oscillation frequency bands may be switched and used.

The IF section 20 includes a band-pass filter 20
1, an IF amplifier 202 and an A / D converter 203.

The arithmetic unit 40 is composed of a microcomputer or the like, and performs a positioning operation and a correction operation of the inter-channel bias, and has a memory 401 for storing the inter-channel bias.

First, radio waves transmitted from satellites in GLONASS will be described. GLONASS is 24
Satellites orbit around the earth at an altitude of about 20,000 km. As described above, the PN code of the radio wave transmitted from each satellite is common to all satellites, and the frequency differs for each satellite. This makes it possible to identify each satellite. The frequency of the radio wave transmitted from the satellite is the L band, and the carrier frequency of the satellite signal of the GLONASS satellite is
160 from 1598.0625 MHz (channel-7)
0.56 up to 9.3125 MHz (channel +13)
21 channel frequencies are arranged at intervals of 25 MHz.

Each satellite has a center frequency of one of the 21 channels, and a radio wave having a bandwidth of about 1 MHz which is spread spectrum with a PN code of 0.511 MHz with a chip rate (1 bit frequency of the PN code). Has been sent.

The L-band radio wave transmitted from the GLONASS satellite is received by an antenna unit installed on a moving body such as a ship or an automobile, and unnecessary out-of-band radio waves are removed by a band-pass filter such as a dielectric filter. It is amplified by the noise amplifier and guided to the down converter 11 shown in FIG.

The RF signal of the frequency fRF input to the down converter 11 is mixed with the local signal LO of the local oscillator 30 by the mixer circuit 101, frequency-converted into an IF signal, and input to the IF unit 20.

In the IF section 20, the band-pass filter 20
After the desired IF signal is extracted in step 1, the IF amplifier 20
The digital signal is amplified by the A / D converter 203 and finally converted into a digital signal by the A / D converter 203 and input to the arithmetic unit 40. Arithmetic unit 40
Can use a processing device used for a normal satellite positioning device.

Here, a SAW filter is usually used as the band-pass filter 201 of the IF unit 20.
If the difference of the group delay time at the IF frequency corresponding to each satellite of the SAW filter is not constant regardless of the GLONASS channel, an error occurs when the arithmetic unit 40 calculates the pseudo distance between the satellite and the receiving device. Will be lost.

For example, within the IF band of GLONASS,
If there is a difference in the group delay time of 0 ns, the DOP (Dilution Of Precisio
n: accuracy reduction rate) 2, an error of about 18 m occurs.

In this embodiment, the local oscillator 30 uses a frequency synthesizer in order to detect the bias of the group delay time due to the channel and remove the bias error by the calculation in the calculation unit 40.

That is, the local frequency fLO which is the oscillation frequency of the local signal generated by the VCO 301 is
In order to set the ONASS channel interval to 0.5625 MHz, the oscillation frequency of the TCXO 306 is set to, for example, 14.6.
The frequency is divided by 26 by the frequency divider 305, and the reference frequency fPD of the frequency synthesizer is set to 0.5625 MHz and input to the phase comparator 304.

Oscillation frequency fLO generated by VCO 301
Is input to the mixer circuit 101, is also frequency-divided by the frequency divider 303, and is input to the phase comparator 304. The phase comparator 304 compares the phases of the two input signals, converts the phase error into a voltage, and outputs the voltage to the loop filter 302.

The phase error voltage is input to the voltage control terminal of the VCO 301 after the high frequency noise component is removed by the loop filter 302. Thus, finally, V
The oscillation frequency fLO of the CO 301 is equal to the reference frequency fPD =
The frequency is multiplied to N times the frequency of 0.5625 MHz.

Here, the dividing number N of the divider 303 is N = 2.
496, the output frequency fLO of the local oscillator 30
Is fLO = 1404 MHz. At this time, as shown in the table of FIG. 2, for example, the channel number n is n = −7, the RF frequency fRF = 1598.0625 MHz is the IF frequency fIF = 194.0625 MHz, and the channel number n is the RF frequency n = + 3. fRF = 1603.6875
MHz is the IF frequency fIF = 199.6875 MHz
Where the channel number n is the RF frequency fRF of n = + 13 =
1609.3125 MHz is IF frequency fIF = 20
The frequency is converted to 5.3125 MHz.

The IF section 20 includes an element having a frequency characteristic represented by the SAW band-pass filter 201.
The group delay characteristic has a ripple in the pass band as shown in FIG. 3 in which the horizontal axis indicates the IF frequency (MHz) and the vertical axis indicates the group delay time, and the ripple width is about 30 ns.

In order to remove the inter-channel group delay bias of the IF section 20 represented by the band-pass filter 201, the frequency division number N of the frequency divider 303 of the local oscillator 30 is set from the arithmetic section 40.

For example, GL where the channel number n is n = + 3
Assuming that an ONASS satellite signal is being received, a method of measuring the group delay time using this satellite, in other words, using the RF frequency (one RF frequency) of this satellite will be described.

First, the frequency division number N of the frequency divider 303 is set to N = 25.
06, the IF frequency f of the same n = + 3 satellite
Since the IF becomes fIF = 194.0625 MHz, the pseudo distance between the satellite and the receiving device is calculated (measured) by the arithmetic unit 40.
I do. Next, when the frequency division number N is set to N = 2505, the IF frequency fIF of the same n = + 3 satellite is fIF = 19.
It becomes 4.6250 MHz, and the pseudo distance between the satellite and the receiving device is measured in the same manner.

In this case, the dividing number N = 2506 and the dividing number N
= 2505 and the difference in the pseudo distance measured is IF section 2
A group delay time difference of 0 results. At this time, even if the satellites have the same channel number of n = + 3, since the satellites themselves are moving, the pseudoranges differ depending on the measurement time.
It is needless to say that the movement of the satellite must be extrapolated to cancel the difference in the position of the satellite.

In this way, the group delay characteristic with respect to the frequency of the IF unit 20 can be measured by repeating the above calculation 21 times from the division number N = 2506 to the division number N = 2486, 21 times. By storing this in the memory 401 in the arithmetic unit 40 and using it for correction of the group delay time, the group delay time bias between channels can be removed, and accurate positioning can be performed.

In the above embodiment, the group delay time is described as an example of the bias between channels. However, the present invention is not limited to the detection of the group delay time, but can be applied to the detection of amplitude and phase. Of course.

[0052]

As described above, according to the present invention, by using a frequency synthesizer as a local oscillator and changing the oscillation frequency of this frequency synthesizer, one RF signal from one satellite can be changed to a different IF frequency. , And measures the frequency characteristics of the bias between channels. For this reason, it is possible to detect the bias between channels without using a pseudo signal generation circuit which has been required in the past, and furthermore, it is possible to achieve the effect of simultaneously reducing the size and power consumption of the receiving device. Can be

A configuration using a frequency synthesizer in the FDMA receiving method is described in Japanese Patent Application Laid-Open No. 60-27250, which discloses that a single synthesizer uses a plurality of FDMA signals in an intermediate frequency band. It merely describes a technique that enables frequency conversion to a baseband signal, and does not disclose anything about detecting an inter-channel bias as in the present invention.

[Brief description of the drawings]

FIG. 1 is an FDMA to which an embodiment of the present invention is applied.
FIG. 3 is a circuit block diagram illustrating a configuration of a receiving device.

FIG. 2 is a diagram showing a table provided for explaining the operation of the present invention;

FIG. 3 is a diagram showing group delay characteristics as an example of an inter-channel bias.

FIG. 4 is a circuit block diagram showing a configuration of a downconverter for an FDMA receiver according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... FDMA receiving apparatus 20 ... IF part 30 ... Local oscillator 40 ... Calculation part 101 ... Mixer circuit 201 ... Band pass filter 202 ... IF amplifier 203 ... A / D converter 301 ... Voltage control oscillator (VCO) 302 ... Loop filter 303 ... frequency divider 304 ... phase comparator 305 ... frequency divider 306 ... crystal oscillator (TCXO) 401 ... memory

Claims (2)

[Claims] 1. An RF signal of one channel frequency corresponding to an RF signal of another channel frequency by using at least one frequency synthesizer as a local oscillator and changing the frequency division number of the frequency synthesizer. A down converter for converting the frequency into a plurality of IF signals, and a plurality of I
A characteristic detecting unit for detecting a characteristic of a frequency between channels based on an F signal; a characteristic deviation detecting device for a frequency between channels for an FDMA receiving device. 2. The apparatus according to claim 1, wherein the input RF signal of one channel is GLON.
When the signal is a reception signal of a radio wave transmitted from an ASS satellite, the characteristic detecting unit measures a pseudo distance from each of the obtained IF frequencies, and determines the pseudo distance as one of characteristics with respect to the frequency between the channels. A characteristic deviation detector for a frequency between channels for an FDMA receiver, wherein the characteristic deviation is detected as a characteristic of a group delay time.