JPH05281340A - Range finder - Google Patents

Abstract

PURPOSE:To obtain such a constitution that no phase synchronization is required between PN codes on a convolver for a range finder of a spectrum spread system using the convolver as a correlator. CONSTITUTION:When switches 21, 22, 23 are respectively connected to their a-terminal sides, sweep carriers are transmitted toward an object from a VCO 30 through a high-frequency section 32. Upon receiving the reflected waves of the carriers, a convolver 34 auto correlates the reflected waves with the carriers through a high-frequency section 33 and an arithmetic section 40 calculates the propagating time tauby processing the correlated output. When the switches 21, 22, and 23 are then connected to their b-terminal sides, the above-mentioned carriers are supplied to one input of the convolver 34 after phase modulation by transmitting burst-like SS signals by phase-modulating singlefrequency carriers from the VCO 30 by using a PN code from a PNG 26 and sending another PN code inverted in time to a multiplier 25 from another PNG 27 through a delay time setting section 39 and received signals are supplied to the other input, and then, the carriers are correlated with the received signal. Then the section 40 calculates the propagating time tau' from the maximum correlation peak and finds the distance to the object from the time tau' by further correlating the carriers with the received signals by changing the initial phase of the receiving-side PN code.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a distance measuring device using a spread spectrum transmission / reception system.

[0002]

2. Description of the Related Art Since the propagation velocity of all high-frequency signals has a constant value, two points are obtained by obtaining the time difference between the transmission signal waveform and the signal waveform that is received after the transmission signal is reflected by the object and returned. It is possible to measure the distance between them.
Generally, as a method of measuring the distance between such two points (reference point and measurement point), (a) a method of emitting a radio wave from the reference point and receiving a reflected wave reflected at the measurement point at the reference point (b) There is a method in which radio waves are emitted from a reference point, received at a measurement point, and the received signal is sent back to be received at the reference point. In any case, the distance d between the two points is calculated by the following equation: d = C / 2τ C: speed of light, τ: propagation time of radio wave (1).

There are various methods for measuring the propagation time,
One of them is the pulse method. This method transmits a pulse wave with a sufficiently short time width compared to the propagation time,
This is a method of receiving a pulse wave reflected at a measurement point (object) and measuring its delay time τ with respect to the transmission pulse wave.

In general, the distance measuring method by the spread spectrum method is a method in which the carrier wave is phase-modulated with a PN code, the autocorrelation of the received signal is obtained, and the delay time at which the correlation value becomes maximum is measured. It is a transformation. FIG. 6 shows an example of such a conventional distance measuring device.

In the figure, in the transmitter T, the carrier wave from the local oscillator 1 is multiplied by the PN code generated by the PN code generator 2 by the multiplier 3 to perform phase modulation, and the high frequency unit 4
A spread spectrum signal (SS) is transmitted via. At the same time, the start bit of the PN code is input to the time counter of the receiving unit R.

The receiving section R receives the transmission signal reflected by the object 5 and returned, and inputs it to the correlator 7 via the high frequency section 6. The correlator 7 calculates the autocorrelation of the received signal.
A matched filter is used for this correlator 7, and therefore, the same PN code pattern as the PN code used for the transmitter T is set. Then, when the received signal and the PN code pattern of the matched filter match, a sharp correlation peak output is obtained. The correlation output (correlation peak) obtained by the correlator 7 is detected by the detector / waveform shaper 8 and waveform-shaped into a digital signal, and then input to the time counter 9.

The time counter 9 calculates the time difference between the start bit and the correlation peak output. Then, the result is given to the distance calculation unit 10, and the distance calculation unit 10 calculates the distance to the object 5 based on the equation (1). However, when a matched filter is used for the correlator 7 as described above,
Since the PN code used in the set PN code pattern is uniquely determined, the random PN code cannot be changed, and measurement becomes impossible at the time of interference of the same PN code. Therefore, as another method for solving the above problem, there is a distance measuring method using a convolver as a correlator. This method is shown in FIG.

The basic operation of this system is the same as that described with reference to FIG. The different point is that the carrier wave whose phase is modulated by the multiplier 11 by the PN code transmitted and the time-inverted PN code is added as a reference signal to the other input of the correlator (convolver) 7. This enables a programmable distance measuring method by changing the PN code sequence.

[0009]

However, in the above-mentioned apparatus, when transmitting SS signals that are continuous in time, the measurable distance is determined by the gate length τg (delay time) of the convolver. That is, if τ> τg, it will be difficult to measure because it overlaps with the next PN code period in time series.

As a method for solving this problem, for example, the SS signal is not transmitted continuously but is transmitted as a burst-like signal for one period of the PN code (may be longer than that) (provisionally referred to as pulsed SS system). Method) is possible. However, in order to maximize the autocorrelation of the received signal, the PN of the reference signal and the received signal on the convolver is
It is necessary to synchronize the phases of the codes. Here, it is assumed that the convolver gate length τg and the PN code one cycle length are equal, for example. Therefore, a training period is required until phase synchronization is achieved on the convolver, and it is obvious that the above-mentioned problem cannot be solved even by the pulsed SS method due to the constraint of burst time and the like.

An object of the present invention is to provide a range finder which uses a spread spectrum system using a convolver as a correlator and which does not require phase synchronization of the PN code on the convolver.

[0012]

In order to achieve the above object, the distance measuring apparatus of the present invention provides a PN code and a reverse PN code which is time-inverted with respect to the PN code at a predetermined cycle based on a control signal. PN code generation means for generating and shifting the phase of the code generated based on the phase data signal,
A first switch for selecting and outputting a drive signal composed of a predetermined voltage and the PN code based on a start signal, and an oscillator for selectively outputting a swept carrier wave and a carrier wave of a predetermined frequency based on the start signal. And a first modulator that modulates the output of the oscillator by the output of the first switch,
The transmitting high-frequency section for transmitting the output of the modulator to the object, the delay time setting section for variably delaying the time-reversal PN code in response to the delay time setting signal, and the output of the oscillator for delaying A second modulator that modulates with the output of the time setting unit, a high-frequency unit for reception that receives a transmission signal returned from the object, an output of the second modulation based on the activation signal, and a reception signal. Is selectively output, a convolver that correlates the received signal with the output of the second switch, and the output of the convolver is selectively detected with a frequency divider based on the activation signal. A third switch supplied to the detector, a first propagation time is calculated based on the output of the swept carrier and the frequency divider, and the delay time setting signal and the phase data signal are output. Based on the output of The maximum peak point of the output of the wave filter is detected, the second propagation time is calculated based on the phase shift time and the first propagation time at that time, and based on the second propagation time, The gist is to have a computing unit that calculates the distance to the object.

[0013]

When the drive signal is selected by the first switch, the sweep carrier wave is modulated by the drive signal and transmitted to the object. The reflected signal from the object at this time is received, the autocorrelation of the received signal is obtained, and the first propagation time is calculated from the correlation output and the swept carrier.

Next, the PN code is selected by the first switch and the SS signal is transmitted to the object. At this time, the autocorrelation between the reflection signal from the object and the reference signal based on the time-reversed PN code is obtained. In this case, the phase of the PN code is shifted by the phase data signal, and the time-reversal PN code is delayed by the delay time setting signal. Then, a second propagation time is obtained from the phase shift time at the time of detecting the correlation output and the first propagation time, and the distance to the object is calculated based on the second propagation time.

[0015]

Embodiments of the present invention shown in the drawings will be described below.
FIG. 1 shows an embodiment of the distance measuring device according to the present invention. Reference numerals 21, 22 and 23 are first, second and third switches, 24 and 2, respectively.
5 is a first and second multiplier, 26 and 27 are first and second PN code generators (PNG), 28 and 29 are first and second drivers, 30 voltage controlled oscillator (VCO), 3
2 and 33 are high-frequency units on the transmitting side and receiving side, 34 is a convolver, 35 is an amplifier, and 36 is a bandpass filter (BP).
F), 37 is a frequency divider, 38 is a wave detector, 39 is a delay time setting unit, 40 is a computing unit, and 41 and 42 are transmitting and receiving antennas, respectively.

First, each switch 21, 22, 2
3 is connected to the a terminal. In the transmitter T, an appropriate electric potential (+ V) is given to the multiplier 26 via the terminal a so that the multiplier 26 can be driven, and the repeated sweep (sweave) carrier wave from the voltage controlled oscillator (VCO) 30 is supplied to the radio frequency unit (RF). Part)
Sent via 32.

The receiving section R receives the transmission signal reflected by the object and returned, and inputs it to one input terminal of the convolver 34 via the high frequency section (RF section) 33. At the same time, the switch 22 is connected to the other input of the convolver 34.
To input the same signal.

In the convolver 34, the autocorrelation of both input signals is obtained, but since both input signals are swept carrier waves, they are multiplied and output as a result. Then, the output correlation output is amplified by the amplifier 35, filtered by the BPF 36, and frequency-divided by the frequency divider 37 via the switch 23 to 1/2, and the arithmetic unit 4
Input to 0. The swept carrier wave used for transmission is also input to the arithmetic unit 40. If the delay time of the processing system from the receiving antenna 42 to the arithmetic unit 40 is very small and can be ignored, fT and fR have the relationship shown in FIG. When the transmission frequency fT is changed at a repetition frequency fm with a maximum deviation Δf centered on fo, the waveform becomes a triangular wave.
The received wave fR is delayed by the propagation time τ.

As a result, fT and f
If R is mixed, the beat frequency fb is obtained, and by obtaining this beat frequency fb, the propagation time τ can be calculated from the following equation. τ = fb / 2fmΔf (2) However, τ <1 / 2fm The calculation section 40 performs the above calculation and gives the delay time data to the delay time setting section 39.

Next, after calculating the delay time, the arithmetic unit 40 gives an activation signal to each of the switches 21, 22, and 23 to connect each switch to the b terminal. Also, based on the start signal, VC
The O30 is controlled to generate a single frequency (for example, fo which is also equal to the center frequency of the convolver). Then, the burst period (τ1) signal from the arithmetic unit 40 is passed through the drivers 28 and 29 to drive the PN code generators 26 and 27 to burst one PN code period (τ0) as shown in FIG. The SS signal is transmitted. Note that the gate length of the convolver 34 and the PN code 2 periods are equal. Further, the PN code used for transmission and the PN code temporally inverted is input to the delay time setting unit 39, delayed by τ, and multiplied by the multiplier 2.
The carrier wave is phase-modulated by 5, and then input to the other input terminal of the convolver 34.

As a result, the autocorrelation with the received transmission signal is obtained by the convolver 34. However, since the PN code of the reference signal is delayed by the propagation time in advance, the code phases of the convolver 34 are substantially the same. .. Therefore,
When they match, a sharp correlation peak output is obtained and the amplifier 3
5, after being detected by the wave detector 38 via the BPF 36, it is input to the arithmetic unit 40. In the arithmetic unit 40, the driver 28,
A burst period signal is given to 29, and initial phase data of the PN code used in the receiving section R is given (the following phase is dithered by ± n chips with respect to the current phase).

By repeating this, the convolver 3
4, the autocorrelation of one cycle of the PN code which is completely set is obtained, and the maximum correlation peak can be detected. That is, finally, the propagation time τ ′ converged with the accuracy within one chip of the PN code is obtained. Then, the calculation unit 40 outputs the result of calculating the distance d from the propagation time τ ′ based on the equation (1). Although it is possible to calculate the distance at the time when the propagation time τ is obtained by the calculation unit 40 by the equation (2), if the Doppler frequency shift or the like occurs depending on the state of the object, the distance can be calculated. The accuracy of will deteriorate. Therefore, this series of operations does not require phase synchronization of the PN code on the convolver 40, and at the same time improves the distance accuracy.

FIG. 4 is a flow chart showing details of the operation after the delay time is calculated in the above embodiment. Step ST
1, the burst period signal from the arithmetic unit 40 is given to the PNGs 26 and 27 via the drivers 28 and 29,
The PN code of the transmitting and receiving side is output, and bursty SS of τo
The signal is transmitted. The transmission / reception side PN code is inverted in time.

In step ST2, the receiving side PN code is
The multiplier 2 is set via the delay time setting unit 39 in which τ time is set.
5, the carrier is modulated by this signal and applied to the other input terminal of the convolver 34. Step ST
In 3, the arithmetic unit 40 calculates the maximum level α of the correlation peak output from the convolver 34.

In step ST4, the arithmetic unit 40 supplies the burst period signal to the PN code generators 26 and 27 through the drivers 28 and 29, and at the same time, the receiving side PN code generator 27 (or the transmitting side PN code generator 26 also). ) To the PN code initial phase data θ. θ = γ−ε + n where γ is the initial phase data (or address Ao) in the equation (1), and ε is an offset value (for example; Ao−
2) and n are the number of dither chips (Defult1). In step ST5, the calculation unit 40 calculates the maximum level β of the correlation peak output from the convolver 34.

Next, steps ST6 to ST11 show the arithmetic operations performed by the arithmetic unit 40. In step ST6, the maximum levels α and β of the correlation peaks are compared. If α ≧ β, the process proceeds to step ST9. If α ≧ β is not satisfied (NO), τ ′ = τ + η is calculated in step ST7. Then, in step ST8, α = β. However, η = T _pn × (−ε +
n), T _PN is the PN clock time.

At step ST9, it is determined that n = 4, and N
If it is O, n = n + 1 is set in step ST10, the process returns to step ST4, and if YES, step ST
At 11, the distance d to the object is calculated from τ ′ or τ and output.

FIG. 5 shows another embodiment of the present invention. The same reference numerals as those in FIG. 1 represent the same or similar circuits, and the portion A in FIG. 5 has the same configuration as that in FIG. In the example,
The second switch and divider are not needed.

The basic operation of the embodiment of FIG. 5 is the same as that of FIG. 1, except that the received signal is directly input to the arithmetic unit 40 via the high frequency unit 33 in the process of obtaining the propagation time τ, and the transmitted signal is This is the point of mixing with fT. Since the subsequent operation is the same as that in FIG. 1, the description thereof will be omitted.

In the embodiment shown in FIGS. 1 and 5, P
Although the initial phase data of N code is given to the PNGs 26 and 27, instead of this, the delay time setting data K may be given to the delay time setting 39. K = ψ−ε + n where ψ is data (or its address A ₁ ) corresponding to the delay time τ.

[0031]

As described above, according to the distance measuring apparatus of the present invention, it is possible to use the spread spectrum method using the convolver as the correlator and to eliminate the need for the phase synchronization of the PN code on the convolver. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the above embodiment.

FIG. 3 is an operation explanatory diagram of the above embodiment.

FIG. 4 is a flowchart showing an operation after calculation of a delay time in the embodiment.

FIG. 5 is a block diagram showing another embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a conventional distance measuring device.

FIG. 7 is a block diagram showing another example of a conventional distance measuring device.

[Explanation of symbols]

 21, 22, 23 1st, 2nd, 3rd switches 24, 25 1st and 2nd multipliers 26, 27 1st and 2nd PN code generators (PNG) 28, 29 1st and 2nd Driver 30 Voltage controlled oscillator (VCO) 32, 33 Transmission side and reception side high frequency section 34 Convolver 35 Amplifier 36 Bandpass filter (BPF) 37 Frequency divider 38 Detector 39 Delay time setting section 40 Computing section 41, 42 Transmission and Receiving antenna

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[Procedure amendment]

[Submission date] May 8, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Next, after calculating the delay time, the arithmetic unit 40 gives an activation signal to each of the switches 21, 22, and 23 to connect each switch to the b terminal. Also, based on the start signal, VC
The O30 is controlled to generate a single frequency (for example, fo which is also equal to the center frequency of the convolver). Then, the burst period (τ1) signal from the arithmetic unit 40 is passed through the drivers 28 and 29 to drive the PN code generators 26 and 27 to burst one PN code period (τ0) as shown in FIG. The SS signal is transmitted. The gate length of the convolver 34 and one cycle of the PN code are assumed to be equal. Further, the PN code used for transmission and the PN code temporally inverted is input to the delay time setting unit 39, delayed by τ, and multiplied by the multiplier 2.
The carrier wave is phase-modulated by 5, and then input to the other input terminal of the convolver 34.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

In step ST4, the arithmetic unit 40 supplies the burst period signal to the PN code generators 26 and 27 through the drivers 28 and 29, and at the same time, the receiving side PN code generator 27 (or the transmitting side PN code generator 26 also). ) To the PN code initial phase data θ. θ = γ−ε + n where γ is the initial phase data (or address Ao) in the equation (1), and ε is an offset value (for example; Ao).
-2), n is the number of dither chips (Default is 0 ). In step ST5, the calculation unit 40 calculates the maximum level β of the correlation peak output from the convolver 34.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

At step ST9, it is determined that n = 4, and N
If it is O, n = n + 1 is set in step ST10, the process returns to step ST4, and if YES, step ST
At 11, the distance d to the object is calculated from τ ′ or τ and output. This series of operations is based on the initial phase of the PN code.
Controlling two chips before and after based on the data,
If you want to change the control amount further, change the ε value and n value.
You can correspond with.

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

Claims (1)

[Claims] 1. A PN code that generates a PN code and an inverted PN code that is temporally inverted with respect to the PN code in a predetermined cycle based on a control signal, and shifts the phase of the code generated based on a phase data signal. A first switch for selecting and outputting the generating means, a drive signal composed of a predetermined voltage and the PN code based on the start signal, a sweep carrier wave and a carrier wave of a predetermined frequency based on the start signal. , A first modulator that modulates the output of the oscillator by the output of the first switch, a transmission high-frequency unit that transmits the output of the modulator to an object, and a delay time setting signal Corresponding to the above, a delay time setting section for variably delaying the time-reversal PN code, a second modulator for modulating the output of the oscillator with the output of the delay time setting section, and returning from the object Incoming high frequency section, a second switch for selectively outputting the output of the second modulation based on the activation signal, the second switch, the received signal and the second A convolver that correlates with the output of the switch, a third switch that selectively supplies the output of the convolver to the divider and the detector based on the start signal, and the output of the swept carrier and the divider Calculating the first propagation time based on the above, outputting the delay time setting signal and the phase data signal, detecting the maximum peak point of the output of the detector based on the output of the detector, A second propagation time is calculated based on the phase shift time and the first propagation time, and based on the second propagation time,
A distance measuring device comprising: a calculation unit that calculates a distance to the object.