CN107064918B - High-precision radar ranging method - Google Patents
High-precision radar ranging method Download PDFInfo
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- CN107064918B CN107064918B CN201611162672.8A CN201611162672A CN107064918B CN 107064918 B CN107064918 B CN 107064918B CN 201611162672 A CN201611162672 A CN 201611162672A CN 107064918 B CN107064918 B CN 107064918B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/06—Systems determining position data of a target
- G01S13/08—Systems for measuring distance only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/28—Details of pulse systems
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Abstract
The invention discloses a high-precision radar ranging method, which forms a stable and minimum time difference between the period of a transmitting signal and the period of a sampling signal through a variable capacitance diode voltage oscillator, expands and amplifies the transmission time of electromagnetic waves by utilizing the small period difference of the transmitting pulse signal and the sampling signal so as to improve the precision of time measurement, measures a measured echo signal after expanding, and adopts a variable capacitance diode voltage-controlled oscillator to realize the control of frequency difference, so that two crystal oscillators generate a stable period difference and a signal with a numerically-controllable period so as to improve the precision of measurement. The time measuring precision of the invention can reach picosecond, namely the distance measuring precision can reach centimeter, the measuring precision is high, and the realization is easy, compared with the expensive microwave counter with the measuring precision reaching picosecond, the cost is greatly reduced; compared with the methods which are difficult to realize, such as high-precision time measurement based on FPGA, time-voltage conversion and the like, the method is much easier to realize.
Description
Technical Field
The invention belongs to the technical field of radar measurement, and particularly relates to a radar ranging method for improving accuracy.
Background
The radar ranging has stable measuring performance and good environmental adaptability, is little interfered by rain, snow and fog, and can adapt to various weather changes. The distance measurement using radar requires measurement of the time of transmission of electromagnetic waves in the air, so that the distance of transmission of electromagnetic waves in the air is calculated according to the measured time. However, because the propagation speed of the electromagnetic wave is close to the speed of light, the corresponding time interval is very short during short-distance transmission, and if the precision of centimeter-level distance measurement is required, the precision of the time measurement needs to reach picosecond level, so that the difficulty is high by adopting the current technical means. The following methods are commonly used for measuring time:
1. the time of pulse round trip is measured by direct counting, but the precision of the method is low and cannot reach the picosecond level requirement.
2. The measurement is carried out by adopting a microwave counter, the accuracy of the measurement can reach picosecond, but the measurement is expensive and is difficult to popularize.
It can be seen that the existing methods have the defects of insufficient precision or overhigh price.
Disclosure of Invention
In order to solve the problems, the invention discloses a radar ranging method, which forms a stable and minimum time difference between the period of a transmitting signal and the period of a sampling signal through a variable capacitance diode voltage oscillator, and expands and amplifies the transmission time of electromagnetic waves by utilizing the small period difference of the transmitting pulse signal and the sampling signal so as to improve the precision of time measurement, thereby ensuring high-precision distance measurement.
In order to achieve the purpose, the invention provides the following technical scheme:
a high-precision radar ranging method comprises the following steps:
step A, setting two clock signals with small period difference, wherein one clock signal is used as a main clock to control and generate a transmission pulse signal, and the period is T1; another clock is used to generate the sampling signal with a period T2, and T2> T1, the sampling signal will have a delay time Δ T with respect to each sampling of the fire pulse signal:
ΔT＝T2-T1 (1)
two identical clock circuits are used to generate clock signals, a varactor voltage-controlled oscillator is used in the clock circuit to control frequency difference, a capacitor, a varactor and a crystal are used to form a resonant loop, and the voltage of one clock circuit is first regulated to make the circuit f1Reaches a certain value, and then adjusts the frequency difference of the two circuits by adjusting the voltage value of the other clock circuit, therebySo as to form a stable and extremely small time difference Delta T;
step B, starting measurement, firstly, sampling and judging the emission pulse signal by using the sampling signal, and when the rising edge of the sampling signal detects the leading edge of the emission pulse, determining the emission starting moment t1(ii) a Starting sampling judgment of the received echo signal, clearing the counter to start timing, and confirming the echo receiving time t when detecting the corresponding received echo leading edge2(ii) a At the moment, the sampling judgment is carried out on the transmitted pulse signal, and the receiving time t is confirmed when the rising edge of the sampling signal detects the leading edge of the transmitted pulse3And resetting the counter; when the measurement is finished, starting the next measurement;
step C, according to the measured t1、t2、t3And T1 and T2, calculating the distance to be measured by the following formula
Where c is the speed of electromagnetic wave propagation in air.
Further, in the step a, a voltage required by the clock circuit to fine tune the frequency is generated by a digital-to-analog conversion module in the processor.
Further, the digital-to-analog conversion module is a 12-bit 2-channel voltage output digital-to-analog conversion module.
Further, the processor is an MCU.
Furthermore, in the step C, multi-period continuous measurement is performed, measured data are compared with each other, partial measured values with large deviation are removed, and finally, an average value of measurement effective values is calculated as a measurement result.
Further, the frequency difference in the step A is 11 Hz-20 Hz.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the measured echo signal is measured after being expanded, and the frequency difference is controlled by adopting a varactor voltage-controlled oscillator, so that two crystal oscillators generate stable periodic difference and a signal with a numerically controllable period, and the measurement precision is improved. The time measuring precision of the invention can reach picosecond, namely the distance measuring precision can reach centimeter, the measuring precision is high, and the realization is easy, compared with the expensive microwave counter with the measuring precision reaching picosecond, the cost is greatly reduced; compared with the methods which are difficult to realize, such as high-precision time measurement based on FPGA, time-voltage conversion and the like, the method is much easier to realize.
Drawings
FIG. 1 is a schematic diagram of ranging according to the present invention.
FIG. 2 is a schematic diagram of a clock generation circuit according to the present invention.
Fig. 3 is a diagram illustrating a relationship between a capacitance characteristic and a voltage of the varactor diode.
Fig. 4 shows the frequency difference corresponding to the DAC voltage value.
FIG. 5 is a timing diagram of ranging according to the present invention.
Fig. 6 is a table of correspondence between the cycle difference and the time.
Detailed Description
The technical solutions provided by the present invention will be described in detail below with reference to specific examples, and it should be understood that the following specific embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention.
The radar echo is nanosecond-level narrow pulse, and the time measurement precision cannot reach picosecond. Because the echo signal is periodic during ranging, the invention measures the measured echo signal after expansion, and adopts the varactor voltage controlled oscillator to realize the control of frequency difference, so that two crystal oscillators generate stable signal with period difference and controllable period, thereby improving the measuring precision.
The specific method comprises the following steps:
step A, as shown in FIG. 1, two clock signals with small period difference are set, one of the two clock signals is used as a master clock to control and generate a transmission pulse signal, and the period is T1; another clock is used to generate the sampling signal with a period T2, and T2> T1, the sampling signal will have a delay time Δ T with respect to each sampling of the fire pulse signal:
ΔT＝T2-T1 (1)
the key and difficulty for realizing high-precision measurement is that a period of a transmitting signal and a period of a sampling signal form a stable and extremely small time difference Δ T, and most of the existing methods are realized by phase locking and frequency synthesis technologies, which are relatively complex and difficult to achieve the required extremely small time difference.
The circuit shown in fig. 2 is adopted to generate a clock signal, and the frequency difference is controlled by using the varactor voltage-controlled oscillator in the circuit, so that the circuit is simple to implement and has low cost. The control voltage changes the equivalent capacitance of the variable capacitance diode so as to change the frequency of the crystal oscillator, so that the two crystal oscillators can generate stable signals with period difference and numerically-controlled period. The variable capacitance diode is a device which utilizes the change of potential barrier capacitance with the applied voltage under the condition of reverse bias of the diode, and the change law of the junction capacitance Gj and the applied voltage is
Cj＝Cj0/(1-VD/VB)n(2)
In the formula Cj0Is the value of the capacitance, V, at zero offsetBIs the potential difference of the barrier, and n is the index of change in capacitance. Capacitor C3、C4And the varactor and the crystal form a resonant circuit, and the crystal is inductive. The control voltage DAv changes the equivalent capacitance C of the varactorjThereby changing the frequency of the crystal oscillator. The voltage dependence of the capacitance characteristic of a varactor is shown in fig. 3.
The voltage is adjusted through DAv in the circuit, and the voltage at two ends of the varactor diode D1 is finely adjusted, so that the performance parameter Cj of D1 is finely adjusted, and the period difference of the emission pulse clock and the sampling signal clock is realized. The voltage DAv required to fine tune the frequency is generated directly by the DAC in the MCU. The DAC conversion module of the MCU is a digital-to-analog conversion module with 12-bit 2-channel voltage output, and the software selects 12-bit output; the internal 2.5V reference voltage is chosen so that DAv can be adjusted between 0V and 2.5V. The 2-channel voltage output can simultaneously adjust the voltage values of the two circuits, thereby easily controlling the frequency difference. In practice, two identical circuits are used, and f is first adjusted DAv1 to1Reaches 3.579545MHz, and then the voltage value of DAv2 is adjusted to adjust the twoThe frequency difference of the individual circuits. The frequency difference corresponding to the voltage value of the DAC is shown in fig. 4. DAv1 and DAv2 are generated by a 2-way DAC digital-to-analog conversion module of the MCU, the time spread is a measured value, and the frequency difference is a calculated value.
The two clock signals with the period difference of about delta f to 11Hz can be controlled and generated by the method.
The transmission pulse repetition period T1 is:
the sampling pulse repetition period T2 is:
then the measurement accuracy Δ T is:
ΔT＝T2-T1＝0.858ps (5)
therefore, the measuring precision of the invention can reach picosecond level. According to the measurement accuracy formula, the corresponding theoretical distance measurement accuracy is 0.0258 cm. However, in practical use, certain noise interference exists, and the measurement accuracy is also influenced by noise and the like and is lower than the theoretical measurement accuracy.
And step B, starting measurement, as shown in fig. 5, firstly, sampling and judging the transmission pulse signal by using the sampling signal, and confirming the starting moment. Determining a transmission start time t when the leading edge of the transmission pulse is detected by the rising edge of the sampling signal1. Starting sampling judgment of the received echo signal, clearing the counter to start timing, and confirming the echo receiving time t when detecting the corresponding received echo leading edge2. At the moment, the sampling judgment is carried out on the transmitted pulse signal, and the receiving time t is confirmed when the rising edge of the sampling signal detects the leading edge of the transmitted pulse3And the counter is cleared. When the measurement is completed, the next measurement is started. In fig. 5, the leading edge and the trailing edge of the timing signal are synchronized with the time when the transmitted pulse and the received echo are detected, so that there is no quantization error in counting the sampling pulses during the high level time of the timing signal, i.e. theoretically, the sampling pulses are spreadThe measurement error of the spread coefficient k tends to zero. When the small change of the electromagnetic wave in the atmosphere is not considered, the relative error of the distance measurement is mainly determined by the relative error of the period difference of the emission pulse signal and the sampling pulse signal. The time measurement accuracy is T2-T1 and the measured time value is T2-T1, i.e., k (T2-T1). The time interval t between the transmitting pulse to be measured and the receiving echo is expanded in a certain proportion by the method, and the whole expansion coefficient N can be confirmed by time expansion measurement of the transmitting pulse signal because the repetition period of the transmitting pulse signal is fixed. In order to reduce errors, multi-period continuous measurement can be carried out, measured data are compared with each other, partial measured values with large deviation are removed, and the influence of random interference signals in the measurement process is reduced. And finally, calculating the average value of the measurement effective values, and improving the measurement precision.
Step C, according to the measured t1、t2、t3And T1, T2 calculates the distance, and the process of deriving the distance conversion formula is as follows: suppose that a section of transmission delay t is amplified by N times after being measured by equivalent sampling time expansion, namely:
t2-t1＝Nt (6)
in the time period from t1 to t2, if the counter value is k when the echo signal is detected, the following are:
t2-t1＝kT2＝kT1+kΔT＝kT1+t (7)
the two formulas (6) and (7) can be obtained:
the formula (4-4) shows that the time interval T to be measured is quantized by the time difference, k is the expansion coefficient to be measured, Δ T is the time resolution during sampling, and when two clock periods are close enough, the quantized resolution can reach a very high level. Considering the path of the electromagnetic wave back and forth propagation in the distance measurement, the actual distance to be measured:
thus, with a known signal propagation speed and a difference of two clock cycles, the distance to be measured can be calculated by measuring k. When k is 1, the minimum distance resolution:
as can be seen from equation (10), since the distance resolution is related to the period difference Δ T between the transmission pulse signal and the sampling pulse signal, the period difference between the transmission pulse signal and the sampling pulse signal can be set according to the distance resolution to be achieved. In the case of a constant propagation velocity, decreasing Δ T increases the distance resolution, but the corresponding expansion coefficient k increases, and the time to complete the measurement increases accordingly. Therefore, the algorithm increases the measurement time and improves the measurement precision.
By the law of error synthesis, by fully differentiating equation (4-6) and then replacing the differentiation with increments, it can be derived:
when minute variations of electromagnetic waves in the atmosphere are not considered, the relative error of the distance measurement mainly depends on the relative error of the difference in the periods of the transmission pulse signal and the sampling pulse signal.
In practical engineering applications, the transmission delay t cannot be measured accurately, so equation (6) is transformed into
t3-t1I.e. the time after spreading of the transmitted pulse, which is the repetition period T of the transmitted pulse1The ratio of (b) is the magnification factor N.
The relation between the time after the echo signal is widened and the echo transmission time is
From the equations (12), (13)
The distance to be measured is
Where c is the speed of electromagnetic wave propagation in air.
The distance to be measured D is calculated based on the formula (15).
The repetition period difference of the emission pulse and the sampling pulse can be adjusted within a certain range according to the characteristics of the crystal oscillator, so the measurement precision can be adjusted within a certain range. The measurement accuracy is adjusted to be suitable according to the actual use condition. The relationship between the time difference corresponding to the cycle difference and the theoretical measurement accuracy can be calculated according to the formulas (3), (4) and (5), as shown in fig. 6, wherein Δ f is 11 to 20Hz, and Δ T is 0.78 picosecond to 1.56 picoseconds. The measurement accuracy in actual measurement is greatly affected by system noise.
The technical means disclosed in the invention scheme are not limited to the technical means disclosed in the above embodiments, but also include the technical scheme formed by any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and such improvements and modifications are also considered to be within the scope of the present invention.
Claims (6)
1. A high-precision radar ranging method is characterized by comprising the following steps:
step A, setting two clock signals with small period difference, wherein one clock signal is used as a main clock to control and generate a transmission pulse signal, and the period is T1; another clock is used to generate the sampling signal with a period T2, and T2> T1, the sampling signal will have a delay time Δ T with respect to each sampling of the fire pulse signal:
two identical clock circuits are used to generate clock signals, a varactor voltage-controlled oscillator is used in the clock circuit to control frequency difference, a capacitor, a varactor and a crystal are used to form a resonant loop, and the voltage of one clock circuit is first regulated to make the circuit possess high stability
Reaches a certain value, and then the frequency difference of the two circuits is adjusted by adjusting the voltage value of the other clock circuit, thereby forming a stable and tiny time difference
；
Step B, starting measurement, firstly, sampling and judging the emission pulse signal by using the sampling signal, and determining the emission starting moment when the rising edge of the sampling signal detects the leading edge of the emission pulset 1 (ii) a Starting sampling judgment of the received echo signal, clearing the counter to start timing, and confirming the echo receiving time when detecting the corresponding received echo front edget 2 (ii) a At the moment, the sampling judgment is carried out on the transmitted pulse signal, and the receiving moment is confirmed when the rising edge of the sampling signal detects the leading edge of the transmitted pulset 3 And resetting the counter; when the measurement is finished, starting the next measurement;
step C, according to the measuredt 1 、t 2 、t 3 And T1 and T2, calculating the distance to be measured by the following formula
In the formulacIs the speed at which electromagnetic waves propagate in air.
2. The high accuracy radar ranging method of claim 1, wherein: in the step a, the voltage required by the clock circuit to fine tune the frequency is generated by a digital-to-analog conversion module in the processor.
3. The high accuracy radar ranging method of claim 2, wherein: the digital-to-analog conversion module is a 12-bit 2-channel voltage output digital-to-analog conversion module.
4. A high accuracy radar ranging method according to claim 2 or 3, wherein: the processor is an MCU.
5. The high accuracy radar ranging method of claim 1, wherein: and C, continuously measuring for multiple periods, comparing the measured data with each other, removing part of measured values with larger deviation, and finally calculating the average value of the effective values of the measurement as a measurement result.
6. The high accuracy radar ranging method of claim 1, wherein: the frequency difference in the step A is 11 Hz-20 Hz.
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| CN109374087B (en) * | 2018-10-31 | 2020-12-01 | 苏州热工研究院有限公司 | Method for extending measurement distance of guided wave radar liquid level meter and guided wave radar liquid level meter |
| CN111812619B (en) * | 2020-06-23 | 2023-03-21 | 深圳市精嘉微电子有限公司 | Device and method for measuring edge arrival time of picosecond-level resolution electric signal |
| CN114167396A (en) * | 2020-09-10 | 2022-03-11 | Oppo广东移动通信有限公司 | Control method based on ultra-wideband ranging and related device |
| CN115372985A (en) * | 2022-08-19 | 2022-11-22 | 厦门大学 | Pulse laser distance measuring device based on correlated sampling time-expanding algorithm |
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