JP2945875B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a distance measuring device for measuring the length of the transmission path of the received signal containing a large noise component.

[0002]

2. Description of the Related Art In a satellite communication system using a communication satellite, a mobile communication system, an international communication system using an optical fiber, or the like, there are various reasons such as a long transmission path and a large output power. The received signal received by the receiving device has a low signal level, is mixed with high-level noise, and has a significantly reduced S / N ratio.

As a technique for detecting a weak signal from a received signal mixed with such large noise, a spread spectrum communication system (SSC Spread Spectum Communication) is employed. In this spread spectrum communication system,
As is well known, an information transmitting station spreads the spectrum of an information signal to be transmitted over a wide frequency band using, for example, a pseudo random signal (PN pattern signal) or the like and transmits the spread signal to a transmission path.

[0004] When the information receiving station receives the spread weak signal, it despreads (converges) the spectrum of the received signal and restores the original information signal. Further, by performing a correlation process on the restored signal, S / N
The ratio can be improved.

[0005] Among the test items for testing the quality of the transmission line in the above-mentioned satellite communication system, mobile communication system and optical fiber communication system, there is an item for measuring the distance (length) of the transmission line. In a distance measuring device for measuring the distance of such a transmission path, for example, a PN pattern signal is transmitted from a transmission side to a transmission path to be measured, and a PN pattern signal transmitted through the transmission path to be measured is received.
The distance is calculated from the time difference between the N pattern signal and the received PN pattern signal.

As a method of accurately measuring the time difference,
A correlation coefficient R between the reception PN pattern signal and a delay PN pattern signal obtained by delaying the transmission PN pattern signal by a delay time τ by a delay circuit is calculated. Then, the delay time τ is sequentially changed, and the delay time τ at which the maximum correlation coefficient R _max is obtained is determined as the time difference between the transmission PN pattern signal and the reception PN pattern signal. To calculate the distance.

FIG. 9 shows a schematic configuration of a distance measuring apparatus employing the above-described correlation function calculating method. FIG. 10 is a time chart showing the operation of the distance measuring device.

The PN pattern generator 1 comprises, for example, an N-stage shift register and one exclusive OR gate, and as shown in FIG. _In synchronization with a clock signal c having a frequency of ₀ (frequency f ₀ ), an M-series PN pattern signal a having a data period of (2 ^N −1) is output.

PN output from PN pattern generator 1
The pattern signal a is synthesized by the signal combiner (mixer) 2 with the carrier signal b output from the carrier oscillator 3 and having the carrier frequency f _c (period T _c f _c ≧ 2f ₀ ). The combined signal d output from the signal combiner (mixer) 2 is amplified by the amplifier 4 and then radiated through, for example, an antenna 5.

A radio signal radiated from the transmitting antenna 5 is received by the receiving antenna 6, and the received signal g is band-limited by a band-pass filter (BPF) 7 and then amplified by an amplifier 8. The received signal h amplified by the amplifier 8 is input to the next analog correlator 9.

On the other hand, the PN pattern signal a output from the PN pattern generator 1 is input to a signal synthesizer (mixer) 2 and also to a delay circuit 10. Delay circuit 1
The delayed PN pattern signal a ₁ delayed by a delay time τ ₁ designated externally at 0 is signal-synthesized with the carrier signal b by the signal combiner 11 having the same configuration as the signal combiner 2,
The signal is input to the analog correlator 9 as the delay composite signal d ₁ .

The analog correlator 9 includes a multiplier 9a and an integrator 9
b. The received signal h from the amplifier 8 and the delay combined signal d ₁ are input to the multiplier 9a. Multiplier 9a is a reception signal h and delayed composite signal d ₁ is multiplied in an analog manner, and sends the multiplied signal i to the next integrator 9b.

The integrator 9b is composed of, for example, a resistor and a capacitor, and accumulates the charge of the multiplication signal i in the capacitor. Then, the integrator 9b outputs the terminal voltage of the capacitor as the correlation coefficient j. Note that the integration time T _I in the integrator 9b is given in advance from the outside.

The correlation coefficient j output from the analog correlator 9 is converted by the next A / D converter 12 into a predetermined sampling period f
_{The signal} is A / D-converted by _S (f _S >> f ₀ ) and input to the next data processing unit 13.

The data processor 13 receives the delay time τ ₁ set in the delay circuit 10. Then, for example, the operator calculates the phase relationship number j in a case where began to sequentially change the delay time tau ₁ to be set in the delay circuit 10.

The data processing unit 13 determines a delay time τ _{s at} which the maximum correlation coefficient j _m is obtained, and determines this delay time τ _s as a transmission time of a signal on a transmission line formed between the antennas 5 and 6. By multiplying the delay time τ _s by the signal transmission speed V, the distance L (= τ _s × V) of the transmission path is calculated.

As described above, using the analog correlator 9,
Calculating the correlation coefficient j between the received signal h and the delay combined signal d ₁ is based on the fact that when the received signal h does not include any noise, the delayed combined signal d ₁ is delayed from the received signal h by the delay time τ _s. Since the signal is delayed, the analog correlator 9 receives the signal h
Is calculated. Generally, by calculating the autocorrelation coefficient of a signal, it is possible to remove a noise component having no frequency component contained in the signal.

Therefore, as shown in FIG. 10, even if the received signal h contains noise having a level exceeding the signal level, the time difference between the received signal h and the original synthesized signal d can be accurately determined. And the correct transmission path distance L can be obtained.

[0019]

However, the distance measuring device shown in FIG. 9 still has the following problems to be solved.

That is, in the above-described distance measuring apparatus, the condition for accurately calculating the distance L of the transmission path is to accurately determine the delay time τ _{s at} which the maximum correlation coefficient j _m is obtained.

However, the correlation coefficient j obtained by the analog correlator 9 depends on the calculation accuracy of the analog multiplier 9a and the calculation accuracy of the analog integrator 9b, as shown in FIG. In general, the analog multiplier 9a is when a large level difference exists in the two input signals h, d ₁ mutual, large multiplication error is a concern to occur. This multiplication error appears as an offset (DC bias) of the output multiplication signal i.

Further, even if the signals h and d ₁ having substantially the same signal level are inputted, due to the ambient temperature and the like,
There is a concern that a DC drift occurs in the output multiplied signal i. When a DC drift occurs in the multiplied signal i output from the multiplier 9a, the DC drift remains as it is in the correlation coefficient j as an integration result of the analog integrator 9b including the above-described resistor and capacitor.

Also, in the analog integrator 9b,
There is a concern that a DC drift may occur in the output integration result due to an ambient temperature or the like.

As described above, S of the obtained correlation coefficient j
In order to increase the / N ratio, it is necessary to increase the integration time (measurement time) T _I in the integrator 9b. However, if the integration time T _I is increased, the DC drift included in the multiplication signal i has a phase relationship. Since it is included in the number j, it is difficult to obtain a correct correlation coefficient j as long as the analog correlator 9 is used.

Therefore, even if the delay time τ ₁ is the same, a different correlation coefficient j is obtained, and it is difficult to accurately determine the delay time τ _{s at} which the maximum correlation coefficient j _m is obtained. In addition, the distance measurement accuracy of the transmission path is reduced.

Further, analog multipliers 9a and integrators 9b that minimize the occurrence of DC drift are extremely expensive and have a problem that the circuit configuration is complicated.

The present invention has been made in view of such circumstances, and by using a digital correlator instead of an analog correlator, a signal can be detected from a received signal containing large noise, and the signal can always be detected. correct correlation coefficient is obtained, and an object thereof is to provide a distance measuring apparatus that can accurately measure the distance of the transmission path.

[0028]

[0029]

[Means for Solving the Problems] In order to solve the above problems
According to a first aspect of the present invention, a PN pattern generator for generating a digital PN pattern signal, a PN pattern signal output from the PN pattern generator and a carrier signal are combined and transmitted to a transmission path to be measured. A signal transmission processing unit,
A signal reception processing unit that receives a signal transmitted through the transmission path under test and demodulates the original PN pattern signal using a carrier signal, and A / D converts the demodulated PN pattern signal output from the signal reception processing unit. An A / D converter, a delay circuit for delaying a PN pattern signal output from the PN pattern generator, and a correlation coefficient between the A / D converted demodulated PN pattern signal and the delayed delayed PN pattern signal Digital correlator, delay time control means for controlling a delay time in a delay circuit so that a correlation coefficient calculated by the digital correlator becomes a maximum value, and delay time controlled by the delay time control means Distance calculating means for calculating the distance of the transmission path to be measured based on the distance.

Furthermore, the distance measuring apparatus according to claim 2, a PN pattern generator for generating a digital PN pattern signal, output from the PN pattern generator P
A signal transmission processing unit for synthesizing the N-pattern signal and the carrier signal and transmitting the resultant signal to the transmission path to be measured; receiving the signal transmitted through the transmission path to be measured;
The first demodulator demodulates one of the split received signals with a carrier signal, and the second demodulator shifts the other split received signal by 90 ° with a 90 ° phase shifter. A signal reception processing unit that demodulates with the carrier signal that has been converted, and a pair of demodulated signals output from the signal reception processing unit are A /
A pair of A / D converters for D-conversion, a delay circuit for delaying the PN pattern signal output from the PN pattern generator, and one of the A / D-converted demodulated signal and the delayed delayed PN pattern signal A first digital correlator for calculating a correlation coefficient, and a second digital correlator for calculating a correlation coefficient between the other A / D-converted demodulated signal and the delayed delayed PN pattern signal.
Digital correlator, vector computing means for performing a vector operation on each correlation coefficient obtained by the first and second digital correlators, and the value of the vector correlation coefficient obtained by the vector computing means becomes a maximum value. A delay time control means for controlling a delay time in the delay circuit; and a distance calculation means for calculating a distance of the transmission path to be measured based on the delay time controlled by the delay time control means.

Further, in the distance measuring apparatus according to the third aspect , a PN pattern generator for generating a digital PN pattern signal, and a PN pattern signal output from the PN pattern generator and a carrier signal are combined to form a signal. A signal transmission processing unit for transmitting the signal to the measurement transmission path, a signal transmitted through the transmission path to be measured, and a splitter for splitting the signal into two reception signals; one of the split reception signals is output to the first demodulator; A signal reception processing unit that demodulates using the carrier signal and shifts the phase of the other branched reception signal by 90 ° using the 90 ° phase shifter and demodulates using the carrier signal with the second demodulator. A pair of A / D converters for respectively A / D converting the pair of demodulated signals output from the signal reception processing unit, a delay circuit for delaying the PN pattern signal output from the PN pattern generator,
A first digital correlator for calculating a correlation coefficient between one of the D-converted demodulated signals and the delayed delayed PN pattern signal, and the other A / D-converted demodulated signal and the delayed delayed PN pattern signal A second digital correlator for calculating a correlation coefficient between the first and second digital correlators, a vector operation unit for performing a vector operation on each correlation coefficient obtained by the first and second digital correlators, and a Delay time control means for controlling the delay time in the delay circuit so that the value of the vector correlation coefficient becomes a maximum value, and calculating the distance of the transmission path to be measured based on the delay time controlled by the delay time control means And distance calculating means for calculating the distance.

[0032]

First, the principle of operation for measuring a weak signal will be described. On the receiving side, a received signal containing a large noise component is first demodulated with a carrier signal to obtain a demodulated signal corresponding to the original PN pattern signal. This demodulated signal includes the large noise component described above and a minute PN pattern signal component embedded in the large noise component. This demodulated signal is A / D converted by an A / D converter at a sampling period. On the other hand, the original digital PN pattern signal is delayed by the delay circuit to become a delayed PN pattern signal.

Each time the clock cycle of the PN pattern signal elapses, the A / D converted demodulated signal and the delayed delay P
A correlation coefficient with the N pattern signal is calculated by a digital correlator and output as a reproduction pattern signal.

Specifically, for each sampling period, each signal value of the demodulated signal is multiplied by each signal value of the delayed PN pattern signal, and the multiplied values are added within the duration of the clock period. The added value (product-sum operation value) is output as one data value.

Generally, each sampled instantaneous value of the noise component is dispersed into various values including positive and negative polarities. On the other hand, since the signal component maintains a constant value, FIG.
As shown in (1), the noise component in the demodulated signal is reduced and the S / N ratio is improved in the product-sum operation process. FIG.
As shown in (b), when the signal component increases, the S / N ratio improves in the product-sum operation process for the same reason as described above, even when the noise component also increases.

Therefore, a weak signal buried in the noise component is detected from the demodulated signal having a large noise component.

In this case, since the accuracy of the correlation coefficient of the digital correlator is determined by the conversion accuracy of the A / D converter, a very high calculation accuracy can be maintained. That is, since an analog multiplier and an analog integrator are not incorporated as in the analog correlator, no DC drift occurs even if the product-sum operation is performed for a long time.

The distance measuring device according to the first aspect of the present invention is configured as described above.
The distance of the transmission path to be measured is measured by applying the operation principle of the weak signal measurement .

An analog composite signal obtained by synthesizing the digital PN pattern signal and the analog carrier signal from the transmission signal processing unit is transmitted to the transmission path to be measured. The reception signal processing unit demodulates the received composite signal with the carrier signal to obtain a demodulated signal corresponding to the original PN pattern signal, and performs A / D conversion.

The correlation coefficient between the demodulated signal corresponding to the A / D converted original PN pattern signal and the delayed PN pattern signal is calculated by a digital correlator. Then, the delay time in the delayed PN pattern signal is controlled so that the maximum correlation coefficient is obtained. Then, the distance of the measured transmission line is automatically calculated from the controlled delay time and the transmission speed of the signal of the measured transmission line.

In this case, the accuracy of measuring the distance depends on the accuracy of determining the delay time. As described above, the accuracy of calculating the correlation coefficient corresponds to the number of sampling data when calculating the correlation coefficient in the digital correlator. I do. However, in the digital correlator, even if the number of sampling data is increased (data collection period), no DC drift occurs, so that the calculation accuracy of the correlation coefficient can be increased. The delay time at which the value is obtained can be accurately calculated.

[0042] In the distance measuring apparatus according to claim 2, in the signal reception processing unit, the received signal is split into two received signals. One of the split received signals is demodulated into a demodulated signal corresponding to the original PN pattern signal by a carrier signal, and then A / D converted.

The other received signal is demodulated from the original PN pattern signal to a demodulated signal corresponding to the PN pattern signal shifted by 90 ° with the carrier signal shifted by 90 °, and then A / D converted. You.

For each demodulated signal that has been individually A / D converted, the correlation coefficient with the delayed PN pattern signal is calculated individually and individually.

Finally, these correlation coefficients are vector-combined, and the delay time is set so that the vector correlation coefficient becomes the maximum value.

That is, when a received signal is demodulated, even if a phase shift or the like occurs, an error due to the phase shift in the calculated correlation coefficient is suppressed by vector synthesis.

In the distance measuring device according to the third aspect, the received signal is branched into two received signals in the signal reception processing section. One of the split received signals is demodulated into a demodulated signal corresponding to the original PN pattern signal by a carrier signal, and then A / D converted.

The other of the received signals is phase-shifted by 90 °, then the carrier signal is used to demodulate the original PN pattern signal into a demodulated signal corresponding to the PN pattern signal phase-shifted by 90 °, and then A / D converted. Is done.

For each demodulated signal that has been individually A / D converted, a correlation coefficient with the delayed PN pattern signal is calculated individually and individually.

Finally, these correlation coefficients are vector-combined, and the delay time is set so that the vector correlation coefficient becomes the maximum value.

That is, when a received signal is demodulated, even if a phase shift or the like occurs, an error due to the phase shift in the calculated correlation coefficient is suppressed by vector combining.

[0052]

The embodiments of the present invention will be described below.

(First Embodiment) FIG. 1 is a block diagram showing a schematic configuration of a distance measuring apparatus according to a first embodiment. FIG.
Is a time chart showing the operation of the distance measuring device.

The PN pattern generator 21 has the same configuration as the PN pattern generator 1 in FIG. 9, and as shown in FIG.
In synchronization with a clock signal c having a predetermined clock period T ₀ (frequency f ₀ ) input from the clock generator 22, a digital PN having a data period of (2 ^N -1)
The pattern signal a is output.

The digital PN pattern signal a output from the PN pattern generator 21 has the carrier frequency f _C (period T _C f _C ≧ 2f ₀ ) output from the carrier oscillator 25 in the signal transmission processing unit 23. Carrier signal b
And the signal is synthesized by a signal synthesizer (mixer) 24. Specifically, the signal synthesizer (mixer) 24 changes the phase of the carrier signal b by 180 ° according to the level change of the [1] level or [0] level of the PN pattern signal a.

The combined signal d output from the signal combiner (mixer) 24 is amplified by an amplifier 26 and then radiated, for example, via an antenna 27.

The signal reception processing unit 28 receives the radio wave radiated from the antenna 27 of the signal transmission processing unit 23 via the antenna 29.

The antenna 27 of the signal transmission processing unit 23
The measured transmission path is between the antenna and the antenna 29 of the signal reception processing unit 28. In actual measurement, the measured transmission path is a round trip path to a communication satellite or an optical fiber laid between cities. Signal transmission processing unit 2
3 and the signal reception processing unit 28 are housed in the same case. Therefore, there is no time delay of the signal between the signal transmission processing unit 23 and the signal reception processing unit 28.

The received signal g received by the antenna 29 is band-limited by a band-pass filter (BPF) 30,
The signal is amplified by the amplifier 31. The received signal amplified by the amplifier 31 is input to the next demodulator 32.

The demodulator 32 outputs the received signal to the carrier wave oscillator 25
Is demodulated into a signal corresponding to the original PN pattern signal with the carrier signal b output from the PN signal. Demodulated signal output from the demodulator 32 is high-frequency noise component is removed by a low pass filter (LPF) 33, is input as a new demodulation signal h ₁ to the A / D converter 34.

The A / D converter 34 synchronizes with the sampling signal k having the frequency f _S (period T _S ) inputted from the clock input terminal 35 to input the demodulated signal h.
A / D conversion to the 8-bit data is set to ₁ for example, a positive or negative sign to the most significant bit. The digital demodulated signal h ₂ output from the A / D converter 34 is input to the next digital correlator 36.

On the other hand, the PN pattern signal a output from the PN pattern generator 21 is input to the signal transmission processing unit 23 and also to the delay circuit 37. Delay circuit 37
Delays the input PN pattern signal a by the delay time τ ₁ designated by the control section 39 and sends it to the next digital correlator 36 as a delayed PN pattern signal a ₁ .

The digital correlator 36 performs a product-sum operation based on the equation (1) between the demodulated signal h ₁ and the delayed PN pattern signal a ₁ in synchronization with the sampling signal k to obtain a correlation coefficient R (Τ ₁ ) is calculated.

[0064]

(Equation 1)

Here, T _M = M · T ₀ = m · T _S T _M : Measurement period of one correlation coefficient One correlation coefficient R corresponding to this one delay time τ ₁
The measurement time T _M corresponding to the number m of collected data when calculating (τ ₁ ) is the clock period T ₀ of the PN pattern signal a.
Is given by the operator in the form of an integer multiple M of

The correlation coefficient R (τ ₁ ) output from the digital correlator 36 is input to the next controller 39. Control unit 3
Reference numeral 9 denotes a type of microcomputer, which includes a delay time control unit 40 and a distance calculation unit 41 which are configured as software on an internal application program.

The delay time control unit 40 includes the digital correlator 3
The delay time τ ₁ in the delay circuit 37 is controlled so that the correlation coefficient R (τ ₁ ) output from 6 becomes the maximum value. Specifically, in response to a measurement start command from the operator, the measurement signal is transmitted to the delay circuit 37 every time a measurement time (measurement period) T _M obtained from a multiple M of the clock period T ₀ specified by the operator elapses. Delay time τ ₁ to a predetermined minimum value τ
It increases in order from _{1 min} to the maximum value τ _1max at predetermined intervals.

The correlation coefficient R output from the digital correlator 36 every time the measurement time (measurement period) T _M elapses.
(Τ ₁ ) is compared in order, and the maximum correlation coefficient R
(Τ ₁ ) Determine the delay time τ _{1S at} which _max is obtained.

The distance calculation unit 41 uses the determined delay time τ _1S as the transmission time of the signal on the transmission path to be measured formed between the antennas 27 and 29, and sets the transmission time of the signal to the delay time τ _1S. By multiplying by V, the distance L (= τ _1S × V) of the transmission path to be measured is calculated.

Next, in the distance measuring apparatus thus configured, a signal component embedded in noise is calculated from the demodulated signal h ₁ received and demodulated by the signal reception processing unit 28 to calculate a correlation coefficient. The reason why the signal can be detected at a high S / N ratio will be described in detail with reference to FIGS.

Each sampled instantaneous value of the noise component is dispersed over a positive / negative polarity over a wide range represented by, for example, a normal distribution. On the other hand, since the signal component maintains a constant value, as shown in FIG. 5A, the noise component is reduced during the execution of the product-sum operation represented by the equation (1) during the fixed measurement period T _M. , Since the signal component maintains a constant value,
The / N ratio is improved.

Next, as shown in FIG. 5B, a case will be described where the noise component increases as the signal component increases.

As described above, when the magnitude of the signal and the magnitude of the noise have a correlation, if the product-sum operation represented by the equation (1) is executed N times, the S / N ratio may increase by N ^1/2. Are known. This is shown below.

Now, assuming that N times of product-sum operations are performed, supposing that the signal component of the i-th correlation coefficient measurement data Xi (t) is si and the noise component is ni, the signal component of the N-times measurement is The sum is given by equation (2).

[0075]

(Equation 2)

Is obtained. In equations (2) and (3), s and n are the average amplitudes of the signal and noise. As a result, S after product-sum operation
/ N is S / N = Ns / (N ^1/2 n) = N ^1/2 (s / n)
… (4). In the equation (3), the signal component becomes N times and the noise component becomes N
^It can be seen that the S / N ratio is N ^1/2 times as a whole.

Therefore, a weak signal buried in the noise component is detected from the demodulated signal having a large noise component.

The degree of improvement in the S / N ratio is shown in FIG.
As shown in (a) and (b), in addition to the measurement time T _M (product-sum operation time), the frequency f _S of the sampling signal in the case of A / D conversion of each signal is increased to perform the product-sum operation. The number of data in the case of implementation may be increased.

In the first embodiment,
As shown in the time chart of FIG.
3 is transmitted through the antenna 27,
In the process of being propagated through the transmission path to be measured is received by the reception signal processing section 28, a large noise is mixed, S / N ratio of the received signal g and the demodulated signal h ₂ is substantially reduced. However, by calculating the correlation coefficient R (τ ₁₎ between the demodulated signal h ₂ and the delayed PN pattern signal a ₁ by a digital correlator 36, the maximum correlation coefficient in the case of changing the delay time tau ₁ R ( τ ₁ ) _max can be detected with high accuracy.

[0080] Incidentally, by setting the measurement time T _M greater correlation coefficient in one of the delay times τ ₁ R (τ _1), the measurement accuracy of the correlation coefficient R (τ ₁₎ in the delay times tau ₁ Since the accuracy can be further improved, the measurement accuracy of the finally obtained distance L of the measured transmission path can be further improved.

Next, the reason why the distance L of the transmission path to be measured can be accurately measured using the PN pattern signal and the digital correlator 36 will be described with reference to FIGS.

As described above, the M-sequence PN pattern signal is a periodic signal having a data period of (2 ^N -1).
Therefore, the PN pattern generator 21 outputs the clock signal c
And one cycle T is T = T _C (2 ^N −1) = Δ (2 ^N −1) where T _C = Δ. Therefore, the autocorrelation coefficient R as a function of the elapsed time t of each data of the PN pattern signal
When (t) is calculated, as shown in FIG.
A sharp peak value of [1] is generated each time. On the other hand, at other time positions, the autocorrelation coefficient R (t) is [1 / n].
It is.

As in the apparatus of the embodiment, two
The correlation coefficient R (τ ₁ ) between two PN pattern signals is
When both PN pattern signals are completely synchronized, FIG.
Shows a sharp peak value. Therefore, the sharp peak value can be detected with high accuracy, and the delay time τ _1S at the sharp peak value can be specified with high accuracy.

FIGS. 4A and 4B show the signal transmission processing section 23.
5 is a frequency characteristic diagram of a synthesized signal d output from the signal synthesizer 24 of FIG. When the carrier suppression ratio is sufficient, FIG.
As shown in FIG. 4, when the composite signal d does not include the component of the carrier frequency f _C and the carrier suppression ratio is insufficient,
As shown in (b), the component of the carrier frequency f _C is included in the composite signal d.

As described above, the carrier frequency f
_{If the C} component is included, the demodulated signals h ₁ and h ₂ have specific frequency components remaining as noise, so even if the digital correlator 36 calculates the correlation coefficient R (τ ₁ ),
It is difficult to obtain a high S / N ratio at the correlation coefficient R (τ ₁ ). Therefore, the signal level of the carrier signal b is adjusted so as to obtain the optimum carrier suppression ratio.

(Second Embodiment) When the measurement time T _M of the digital correlator 36 in the distance measuring device in FIG. 1 is set to the clock period T ₀ of the PN pattern signal a (M =
1) The distance measuring device can be used as a weak signal detecting device.

That is, the range of the product-sum operation shown in the above equation (1) is the duration T ₀ of one data of the PN pattern signal a.
Becomes During this time T ₀ , as shown in FIG. 2, the signal component buried in the large noise component of the demodulated signal h ₂ maintains a constant value, so that it is synchronized with the measurement time T _M , that is, in synchronization with the clock cycle T _0. Thus, the correlation coefficient R (τ ₁ ) output from the digital correlator 36 becomes the reproduced PN pattern signal itself from which the noise component has been removed.

Then, the output reproduced PN pattern signal may be converted into a digital reproduced PN pattern signal by an A / D converter. Therefore, a weak signal buried in the noise component can be accurately detected from the received signal g.

In this case, the S / N of the reproduced PN pattern signal
To improve the ratio, instead of increasing the measurement time T _M ,
The sampling frequency f _S in the A / D converter 34 may be increased to increase the number of sampling data in the product-sum operation.

Before actually using the device as a weak signal detection device, the control unit 39 is started to activate the maximum correlation coefficient R
By setting the delay time τ _{1S at} which (τ ₁ ) _max is obtained in the delay circuit 37, the S / N ratio of the reproduced PN pattern signal can be further improved.

(Third Embodiment) FIG. 6 is a block diagram showing a schematic configuration of a distance measuring apparatus according to a third embodiment of the present invention.
The same parts as those in the first embodiment shown in FIG. Therefore, the detailed description of the overlapping part is omitted.

In this embodiment, a signal splitter 42 and a 90 ° phase shifter 44 are incorporated in the signal reception processing section 28a.

The reception signal output from the amplifier 31 in the signal reception processing section 28a is split in two directions by the signal splitter 42. One of the received signals branched in two directions is input to the demodulator 32 as in the first embodiment shown in FIG. Then, the received signal is converted by the demodulator 32 into a carrier signal b.
And demodulated using the low pass filter 33
/ D converter 34 are converted A / D, is input as a demodulation signal h ₃ corresponding to the original PN pattern signal a to a first digital correlator 36 as a digital correlator. Digital correlator 36 calculates the correlation coefficient R _X between the demodulated signal h ₃ delayed delayed PN pattern signal a ₁ and the delay circuit 37.

The other received signal branched in two directions by the signal splitter 42 is input to another demodulator 32a. The phase of the carrier signal b is shifted by 90 ° to the demodulator 32a.
4 in transportable carrier signal b ₁ which is 90 ° phase-shifted is input. The other received signal is supplied to the demodulator 32a by the carrier signal b.
₁ and demodulated by the A / D converter 34a as a first A / D converter via the low-pass filter 33a.
/ D converted and inputted as a demodulated signal h ₄ corresponding to the PN pattern signal 90 ° phase shift of the original PN pattern signal a to the second digital correlator 36a as a digital correlator.

The digital correlator 36a has the same configuration as the other digital correlators 36, and has a correlation coefficient R _Y between the delayed PN pattern signal a ₁ delayed by the delay circuit 37 and the demodulated signal h _4. Is calculated.

The correlation coefficients R _X and R _Y calculated by the digital correlators 36 and 36a are input to the control unit 39a.
The control unit 39a includes a vector calculation unit 43, a delay time control unit 40a, and a distance calculation unit 41a.

The vector operation unit 43 combines the correlation coefficients R _X and R _Y input from the digital correlators 36 and 36 a every time the measurement time T _M (measurement period) elapses. This vector synthesis method will be described with reference to FIG.

Since the phases of the demodulated signal h ₃ and the demodulated signal h ₄ are different from each other by 90 °, the obtained correlation coefficients R _X ,
_RY also differ in phase by 90 °.

Therefore, each vector correlation coefficient R _X , R
_Y can be defined by equations (5) and (6).

R _X = A COS ωt (5) R _Y = A COS (ωt + π / 2) = A sin ωt (6) where A is a value independent of the phase (scalar amount).

Therefore, the synthetic vector correlation function R
(Τ ₁ ) is given by equation (7).

[0102] _{R (τ 1) = R X} + R Y ... (7) scalar quantity of the resultant vector correlation function R (tau ₁₎ (absolute value) R (tau ₁₎ is represented by equation (8).

[0103] _{R (τ 1) = | R} (τ 1) | = [| R X | 2 + | R Y | 2] 1/2 = A [COS 2 ωt + sin 2 ωt] = A ... (8) The correlation function R (τ ₁ ) thus obtained is sent to the next delay time control unit 40a.

The delay time control section 40a includes the vector operation section 4
3 and a correlation function R (τ) input every time the measurement time T _M elapses.
₁ ) delay time τ _{1S at} which the maximum correlation function R (τ ₁ ) _max
Is determined and sent to the next distance calculation unit 41a. The distance calculation unit 41a multiplies the delay time τ _1S by the transmission speed V of the signal to obtain the distance L (= τ _1S ×
V) is calculated.

The technical effect of the distance measuring device thus configured will be described.

For example, the reception direction of the antenna 29 of the reception signal processing section 28 of the distance measuring apparatus shown in FIG. The transmission path to be measured is shown in FIG. In the case of a coaxial cable, an optical fiber, or the like instead of the radio wave path shown in FIG. 6, the required transmission time may change due to expansion and contraction of the cable.

In any case, when the demodulator 32 demodulates the received signal g, there is a concern that a phase shift occurs in the demodulated signal. Therefore, even when the delay time is set to the same delay time τ ₁ in the delay circuit 37, if the measurement timing is different, the correlation function R (τ
There is a disadvantage that ₁ ) has a different value.

However, as in the device of the third embodiment shown in FIG.
By demodulating the correlation coefficients R _X and R _Y into signals h ₃ and h ₄ corresponding to two PN pattern signals, a vector correlation function R
As shown in FIG. 7, since the absolute value A of (τ ₁ ) moves on the circumference even if the phases of both are relatively shifted,
Always maintain a constant value. Therefore, the delay time τ _{1S at which} the correlation function R (τ ₁ ) due to the phase shift generated in the demodulators 32 and 32a becomes the maximum correlation function R (τ ₁ ) _max is determined, and the distance to the transmission path to be measured is calculated thereafter. A decrease in accuracy is prevented beforehand.

(Fourth Embodiment) FIG. 8 is a block diagram showing a schematic configuration of a distance measuring apparatus according to a fourth embodiment of the present invention. The same parts as those in the third embodiment shown in FIG. 6 are denoted by the same reference numerals. Therefore, the detailed description of the overlapping part is omitted.

[0110] In this example system, the received signal processing section 28b, the received signal g ₁ of the one which is branched at splitter 42 as it is sent to the demodulator 32, branched to the other received signal g ₂ The 90 ° phase shifter 44a shifts the phase by 90 ° and sends it to the other demodulator 32a. The carrier signal b having the same phase is input from the carrier oscillator 25 to each of the demodulators 32 and 32a.

Also in the distance measuring apparatus having such a configuration, the demodulated signals output from the A / D converters 34 and 34a are demodulated signals h ₃ and h ₃ corresponding to two PN pattern signals having phases different from each other by 90 °. It becomes ₄ . The correlation coefficient R _X output from the digital correlator 36, 36a, each vector correlation coefficient of R _Y R _X, R _Y, as shown in FIG. 7,
Since the phase difference of 90 ° is relatively maintained, the third
It is possible to obtain substantially the same effects as those of the embodiment device.

[0112]

As described above, in the distance measuring apparatus according to the present invention, on the receiving side, a received signal containing a large noise component is demodulated by a carrier signal to correspond to the original PN pattern signal. A demodulated signal is obtained, and the demodulated signal is further converted to A /
A digital correlator obtains a correlation coefficient between the demodulated signal of the A / D conversion and the delayed PN pattern signal obtained by delaying the original PN pattern signal, and the correlation coefficient is used as a reproduced PN pattern signal.

Accordingly, since no analog multiplier or analog integrator is incorporated, no DC drift occurs even if the product-sum operation is performed for a long time. Accuracy can be improved.

[0114] Also, self employed very high PN pattern signal correlation coefficient, the A / D conversion value of the demodulated signal corresponding to the original PN pattern signal demodulated from the received signal and the delayed PN pattern signal A / D A digital correlation coefficient with the converted value is calculated, and the distance of the transmission path to be measured is calculated from the correlation coefficient.

Therefore, even if the number of sampling data is increased (data collection period), no DC drift occurs, so that the accuracy of calculating the correlation coefficient can be increased.
As a result, the delay time at which the maximum value of the correlation coefficient is obtained can be accurately calculated, and the distance measurement accuracy of the transmission path to be measured is improved.

Further, in another invention, in the signal reception processing section, the received signals are different in phase by 90 ° from each other.
The signal is demodulated into two signals corresponding to one PN pattern signal. That is, when a received signal is demodulated, even if a phase shift or the like occurs, an error due to the phase shift in the calculated correlation coefficient is suppressed by vector combining. Therefore, distance measurement accuracy can be further improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a distance measuring device according to a first embodiment of the present invention.

FIG. 2 is a time chart showing the operation of the first embodiment.

FIG. 3 is a characteristic diagram showing an autocorrelation coefficient of a PN pattern signal used in the first embodiment.

FIG. 4 is a frequency characteristic diagram of a combined signal output from the signal combiner of the first embodiment.

FIG. 5 is a diagram showing a relationship between a signal and noise in a reception signal of the signal reception processing unit of the first embodiment.

FIG. 6 is a block diagram showing a schematic configuration of a distance measuring device according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a vector of each correlation coefficient in the third embodiment.

FIG. 8 is a block diagram showing a schematic configuration of a distance measuring device according to a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a schematic configuration of a conventional distance measuring device using an analog correlator;

FIG. 10 is a time chart showing the operation of the conventional device.

[Explanation of symbols]

21 ... PN pattern generator, 22 ... Clock generator, 2
3 ... Signal transmission processing device, 24 ... Signal combiner, 25 ... Carrier wave oscillator, 26,31 ... Amplifier, 27,29 ... Antenna, 28 ... Signal reception processing unit, 30 ... Band pass filter, 32,32a ... Demodulator, 33, 33a ... low-pass filter, 34, 34a ... A / D converter, 36, 36a ...
Digital correlator, 37 delay circuit, 39, 39a control unit, 40, 40a delay time control unit, 41, 41a
Distance calculation unit, 43 ... vector calculation unit, 44, 44a ... 9
0 ° phase shifter

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Horiuchi 2-3-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo International Telegraph and Telephone Corporation (72) Inventor Shu Yamamoto 2-3-Nishi-Shinjuku, Shinjuku-ku, Tokyo (2) Inside the International Telegraph and Telephone Corporation (72) Shigeyuki Akiba 2-3-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo International Telegraph and Telephone Corporation (72) Hiroharu Wakabayashi 2, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. 3-2, International Telegraph and Telephone Corporation (56) References JP-A-55-34578 (JP, A) JP-A-2-246542 (JP, A) JP-A-5-145521 (JP, A) JP-A-5-281340 (JP, A) JP-A-7-12930 (JP, A) JP-A-7-35849 (JP, A) JP-A-7-321611 (JP, A) JP-A 8-278362 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , D B name) H04J 13/00 G01S 13/10

Claims (3)

(57) [Claims] 1. A PN pattern generator (21) for generating a digital PN pattern signal; a PN pattern signal output from the PN pattern generator and a carrier signal are synthesized and transmitted to a transmission path to be measured. A signal transmission processing unit (23); a signal reception processing unit (28) that receives a signal transmitted through the transmission path under measurement and demodulates the signal into an original PN pattern signal using the carrier signal; An A / D converter (34) for A / D converting the demodulated PN pattern signal output from the PN pattern signal; a delay circuit (37) for delaying the PN pattern signal output from the PN pattern generator; A digital correlator ( 36 ) for calculating a correlation coefficient between the converted demodulated PN pattern signal and the delayed delayed PN pattern signal; and The delay circuit Definitive and the delay time control means for controlling the delay time (40), the distance calculating means for calculating the distance of the measured transmission path based on the delay time controlled by the delay time control means (41)
A distance measuring device comprising: 2. A PN pattern generator (21) for generating a digital PN pattern signal, and a PN pattern signal output from the PN pattern generator and a carrier signal are combined and transmitted to a transmission path to be measured. A signal transmission processing unit (23), receives the signal via the transmission path to be measured, and a splitter (42)
The first demodulator (32) demodulates one of the branched reception signals with the carrier signal.
In the second demodulator (32a), the other of the branched reception signals is converted by the 90 ° phase shifter (44) to the phase of the carrier signal by 90 °.
Signal reception processing unit (28a) that demodulates with the phase-shifted carrier signal
A pair of A / D converters (34.34a) for A / D converting the pair of demodulated signals output from the signal reception processing unit; and delaying the PN pattern signal output from the PN pattern generator. A delay circuit (37); a first digital correlator (36) for calculating a correlation coefficient between one of the A / D-converted demodulated signals and the delayed delayed PN pattern signal; A second digital correlator (36a) for calculating a correlation coefficient between the other converted demodulated signal and the delayed delayed PN pattern signal; and each of the digital correlators obtained by the first and second digital correlators. Vector operation means (43) for performing a vector operation on the correlation coefficient, and delay time control means (for controlling the delay time in the delay circuit so that the value of the vector correlation coefficient obtained by the vector operation means becomes a maximum value) 40a) and this delay time control means Distance calculating means for calculating the distance of the measured transmission path on the basis of the control delay time (41
a) a distance measuring device comprising: 3. A PN pattern generator (21) for generating a digital PN pattern signal; a PN pattern signal output from the PN pattern generator and a carrier signal are synthesized and transmitted to a transmission path to be measured. A signal transmission processing unit (23), receives the signal via the transmission path to be measured, and a splitter (42)
The first received signal is demodulated using the carrier signal in a first demodulator (32), and the other received signal is phase-shifted by 90 °. Container (4
4a) the signal is shifted by 90 °, and the second demodulator (32a) demodulates using the carrier signal (28b).
A pair of A / D converters (34.34a) for A / D converting the pair of demodulated signals output from the signal reception processing unit; and delaying the PN pattern signal output from the PN pattern generator. A delay circuit (37); a first digital correlator (36) for calculating a correlation coefficient between one of the A / D-converted demodulated signals and the delayed delayed PN pattern signal; A second digital correlator (36a) for calculating a correlation coefficient between the other converted demodulated signal and the delayed delayed PN pattern signal; and each of the digital correlators obtained by the first and second digital correlators. Vector operation means (43) for performing a vector operation on the correlation coefficient, and delay time control means (for controlling the delay time in the delay circuit so that the value of the vector correlation coefficient obtained by the vector operation means becomes a maximum value) 40a) and this delay time control means Distance calculating means for calculating the distance of the measured transmission path on the basis of the control delay time (41
a) a distance measuring device comprising: