CN113311384B - Unilateral two-way distance measurement method and device - Google Patents
Unilateral two-way distance measurement method and device Download PDFInfo
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Abstract
The invention discloses a unilateral two-way distance measurement method and a unilateral two-way distance measurement device, wherein the method comprises the following steps: s1, when a ranging message and a response message are transmitted between a sending device and a response device for ranging through a built-in radio frequency chip and an antenna, respectively acquiring the sending time and the receiving time of the ranging message and the response message, correcting by using the time delay of the antenna, and extracting the sending time stamp and the receiving time stamp of the ranging message and the response message transmitted between the sending device and the response device; s2, calculating an initial distance value between the sending equipment and the response equipment according to the extracted sending and receiving time stamps; s3, correcting the calculated distance initial value by using a preset model to obtain a corrected distance value; s4, filtering the corrected distance value by using a filter, and outputting a filtered measurement result. The invention has the advantages of simple implementation method, high measurement efficiency and precision, small error, time estimation and the like.
Description
Technical Field
The invention relates to the technical field of positioning and ranging equipment, in particular to a unilateral two-way ranging method and device.
Background
Under the condition that satellite navigation signals are absent or extremely easily disturbed, efficient and accurate real-time relative positioning and ranging are needed for both the indoor fast moving robot and the outdoor clustered flying robot so as to realize motion navigation and control and inter-individual collision prevention. In positioning and ranging applications, the conventional Ultra Wideband (UWB) technology is widely applied to the ranging and positioning of indoor mobile equipment and outdoor unmanned system clusters due to the characteristics of low cost, high ranging accuracy, strong anti-interference capability, low power consumption and the like of UWB technology equipment. Common UWB positioning methods generally include: time of arrival (TOA), time difference of arrival (TDOA), angle of arrival (AOA), received Signal Strength (RSS), etc. The TDOA directly obtains the user position information in a parallel mode, and the user is not required to be fed back with the information, but the interaction speed is high, the user capacity is large, the base station is required to keep time synchronization and provide accurate coordinates, and the requirement on layout conditions is high; the AOA calculates the position through the arrival angle and the transmission time, and the sensor fusion or the antenna array is required to provide angle information, so that the AOA is generally only suitable for the following of an unmanned system; TOA is a point-to-point ranging method based on time-of-flight conversion distance, no other sensors are needed, the algorithm is easy to realize, and the method has more advantages in cost and reliability, so that the TOA is widely concerned, time measurement and distance calculation involved in the scheme are the most critical factors, and the accuracy of the positioning algorithm can be directly influenced.
Among the point-to-point measurement methods, there are typically a single-side two-way ranging (SS-TWR) method and a double-side two-way ranging (DS-TWR) method, wherein the SS-TWR is a UWB ranging method in which a device transmits a message and receives a response, calculates the propagation time of electromagnetic waves, and converts the propagation time into a distance. Because the conventional SS-TWR only needs one information exchange, time and power are saved, and the response time length and clock drift determine the ranging value error, the ranging value error increases along with the increase of the response time length and clock offset. Therefore, the conventional SS-TWR error accuracy is usually tens to hundreds of centimeters, and is commonly used for fusing processing results in scenes or other positioning modes with less severe accuracy requirements. DS-TWR is an improved method of SS-TWR, four pieces of information are required to be sent between two ranging parties, a plurality of time stamps are obtained, clock offset is subtracted by calculation, the accuracy is replaced by prolonging the measuring period, and the accuracy of ranging errors is about +/-5 cm, so that the method is the current mainstream UWB ranging method.
In the application occasions such as an indoor fast moving micro-platform unmanned system and an outdoor large-scale unmanned aerial vehicle cluster which need high-frequency and high-precision position information, compared with the application occasions such as high SS-TWR frequency and low precision and low DS-TWR frequency and high precision, the method of combining with GPS, IMU, vision and the like is generally adopted to make up for the defects, and the sensor load, the computing resource and the energy cost of the unmanned platform are increased. That is, the conventional DS-TWR and SS-TWR methods have respective defects, cannot meet the requirements of efficiency, precision and the like at the same time, and cannot accurately realize time estimation in general.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems existing in the prior art, the invention provides the unilateral two-way ranging method and the unilateral two-way ranging device which are simple in implementation method, high in measurement efficiency and precision, small in error and capable of estimating time.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a unilateral two-way distance measurement method comprises the following steps:
s1, extracting propagation time: when a distance measuring device and a response device transmit a distance measuring message and a response message through a built-in radio frequency chip and an antenna, respectively acquiring the sending time and the receiving time of the distance measuring message and the response message, correcting by using the time delay of the antenna, and extracting the sending time stamp and the receiving time stamp of the distance measuring message and the response message transmitted between the sending device and the response device;
s2, calculating the distance: calculating the initial value of the distance between the sending equipment and the response equipment according to the sending and receiving time stamps extracted in the step S1;
s3, distance correction: correcting the distance initial value calculated in the step S2 by using a preset model to obtain a corrected distance value;
s4, filtering distance values: and (3) filtering the distance value corrected in the step (S3) by using a filter, and outputting a filtered measurement result.
Further, the step S1 specifically includes:
the transmitting device sends out a frame which has only a preamble, SFD and PHR and does not contain data, namely a message Poll, when a frame mark bit of the PHR leaves a built-in radio frequency chip of the transmitting device and is transmitted out from an antenna, a corresponding transmitting time tl is recorded, and the first transmitting time stamp poll_tx is obtained by adding the time delay of the antenna to the transmitting time tl;
when the response equipment receives the message Poll, recording the arrival time t2 of the frame marking bit, and subtracting the time delay of the antenna processed by the correction factor from the arrival time t2 to obtain a first receiving time stamp poll_rx;
acquiring the arrival time t3 of the frame marking bit, which is obtained by pre-calculation in the response equipment, controlling the frame marking bit to leave the response equipment at the arrival time t3, and adding the time delay of the antenna to the arrival time t3 to obtain a second sending timestamp answer_tx; the first receiving timestamp poll_rx and the second sending timestamp answer_tx are used as data to be written into a response message Answer and sent to the sending equipment;
after receiving the Answer message Answer, the sending device records the arrival time t4 of the frame mark bit, and obtains a second receiving timestamp answer_rx by subtracting the time delay of the antenna processed by the correction factor from the arrival time t 4.
Further, the sending time tl and the arrival time t4 specifically take the value of the clock counter in the built-in radio frequency chip of the sending device at the corresponding moment, and the arrival time t2 specifically takes the value of the clock counter in the built-in radio frequency chip of the response device at the corresponding moment.
Further, in the step S2, the time of flight of the ranging message between the sending device and the response device is calculated according to the extracted sending and receiving time stamps, and then the initial value of the distance is determined according to the calculated time of flight, where the time of flight is calculated according to the following formula:
T round ＝T Answer_rx -T Poll_tx
T reply ，＝T Answer_tx -T Poll_rx
wherein T is Answer_rx For the time value corresponding to the second receiving time stamp answer_rx, T Poll_tx For the time value corresponding to the first transmission time stamp poll_tx, T Answer_tx For the time value corresponding to the second transmission time stamp answer_tx, T Poll_rx And a time value corresponding to the first receiving time stamp poll_rx.
Further, the step S1 further includes correcting the clock in the rf chip by using an active temperature compensation crystal oscillator.
Further, in the step S3, the preset model is an error empirical model for correcting the antenna radiation near field region, and the constructed error empirical model is used to correct the distance initial value.
Further, in the step S4, a kalman filter is specifically adopted for filtering.
A single-sided two-way ranging apparatus, comprising:
the system comprises a propagation time extraction module, a transmission time judgment module and a transmission time judgment module, wherein the propagation time extraction module is used for respectively acquiring the transmission time and the receiving time of a ranging message and a response message when the ranging message and the response message are transmitted between a sending device and a response device for ranging through a built-in radio frequency chip and an antenna, correcting by using the time delay of the antenna, and extracting the transmission time stamp and the receiving time stamp of the ranging message and the response message propagated between the sending device and the response device;
the distance calculating module is used for calculating the initial value of the distance between the transmitting equipment and the response equipment according to the transmitting and receiving time stamps extracted by the propagation time extracting module;
the distance correction module is used for correcting the distance initial value calculated by the distance calculation module by using a preset model to obtain a corrected distance value;
and the distance value filtering module is used for filtering the distance value corrected by the distance correction module by using a filter and outputting a filtered measurement result.
Further, the system also comprises a clock correction module connected with the propagation time extraction module, and the clock correction module is used for correcting the clock in the radio frequency chip by using an active temperature compensation crystal oscillator.
A computer device comprising a processor and a memory for storing a computer program, the processor for executing the computer program to perform a method as described above.
Compared with the prior art, the invention has the advantages that:
1. the invention establishes a flow processing process from generating a measurement request to sending of a radio frequency module, correcting time delay to an antenna and then reversely returning a received signal, respectively acquires sending time and receiving time of a ranging message and a response message when the propagation time is extracted, and simultaneously, finally determines an accurate sending time stamp and an accurate receiving time stamp of the message based on the time delay of the antenna, calculates a distance initial value based on the sending time stamp and the receiving time stamp, and obtains a final distance value after correcting and filtering in sequence.
2. According to the invention, a data frame propagation time sequence relation is obtained by adopting an analysis method combining a physical frame structure and an equipment module, an accurate time point can be extracted, the time delay of an antenna between the arrival of data from the antenna and an antenna interface is introduced, the time delay of the antenna is used for correcting the message sending and receiving time, the corrected time is used as the accurate time to calculate the distance, meanwhile, the frame mark bit arrival time of a response frame is calculated in advance, a radio frequency chip is controlled to send a response message at the calculated sending time by using a timing sending function, the unilateral bidirectional ranging with accurately estimated time can be realized, the problem that the traditional SS-TWR method cannot estimate the time is solved, and compared with the traditional unilateral bidirectional ranging, the time point is directly used, the time extraction precision can be greatly improved, and the ranging error is reduced.
3. The invention further adopts the active temperature compensation crystal oscillator to carry out clock correction on the radio frequency chip, simultaneously introduces Kalman filtering to carry out fusion estimation on the measurement result, further reduces the measurement error and improves the accuracy of unilateral two-way distance measurement.
4. The invention further considers the error of the antenna radiation field, and corrects the distance initial value by constructing an error experience model for correcting the antenna radiation near field region and using the constructed error experience model, thereby further improving the ranging precision and reducing the measuring error.
Drawings
Fig. 1 is a schematic structural diagram of a single-sided two-way ranging method according to the present embodiment.
Fig. 2 is a schematic diagram of an implementation flow of the single-sided two-way ranging method in this embodiment.
Fig. 3 is a schematic diagram of a physical layer frame structure based on the UWB system employed in the present embodiment.
Fig. 4 is a schematic diagram of each time point in the single-sided two-way ranging method according to the present embodiment.
Fig. 5 is a schematic diagram of the principle of extracting propagation time in the single-sided two-way ranging method of the present embodiment.
Fig. 6 is a schematic diagram of message propagation between devices in a specific application embodiment of the present invention.
FIG. 7 is a schematic diagram of the result of empirical model modification in a specific application example of the present invention.
Fig. 8 is a schematic diagram of ranging comparison under active and passive crystal conditions in a specific application embodiment.
FIG. 9 is a time-consuming comparison of using the single-sided two-way ranging method of the present invention with a conventional DS-TWR in a specific application embodiment.
Fig. 10 is a schematic diagram of a movement error simplified model employed in the present embodiment.
Fig. 11 is a schematic diagram showing the result of the movement speed-error relationship obtained in the specific application example.
Detailed Description
The invention is further described below in connection with the drawings and the specific preferred embodiments, but the scope of protection of the invention is not limited thereby.
As shown in fig. 1, the single-sided two-way ranging method of the present embodiment includes the steps of:
s1, extracting propagation time: when the distance measuring device and the response device transmit the distance measuring information and the response information through the built-in radio frequency chip and the antenna, respectively acquiring the transmitting time and the receiving time of the distance measuring information and the response information, correcting by using the time delay of the antenna, and extracting the transmitting time stamp and the receiving time stamp of the distance measuring information and the response information transmitted between the transmitting device and the response device;
s2, calculating the distance: calculating the initial value of the distance between the transmitting equipment and the response equipment according to the transmitting and receiving time stamps extracted in the step S1;
s3, distance correction: correcting the distance initial value calculated in the step S2 by using a preset model to obtain a corrected distance value;
s4, filtering distance values: and (3) filtering the distance value corrected in the step (S3) by using a filter, and outputting a filtered measurement result.
The method is improved on the basis of a single-side two-way ranging (SS-TWR) method, a flow processing process from generating a measurement request to transmitting a radio frequency module, correcting time delay of an antenna and then reversely returning a received signal is established, when propagation time is extracted, the transmitting time and the receiving time of a ranging message and a response message are respectively obtained, meanwhile, the transmitting time stamp and the receiving time stamp of the message are finally determined on the basis of the time delay of the antenna, a distance initial value is calculated on the basis of the transmitting time stamp and the receiving time stamp, and the final distance value is obtained after correction and filtering in sequence, so that time-estimated single-side two-way ranging can be realized, and compared with the traditional double-side two-way ranging (DS-TWR), single-time measuring time can be shortened, measuring frequency can be increased, and meanwhile, the number of error frames can be reduced.
Because unilateral two-way ranging is to send an inquiry message from one device to another device and receive a response message, ranging is achieved, wherein a key link is precise time of message receiving and sending, namely, time point determination of message receiving and sending is a key point affecting ranging accuracy. Such as DW1000 chips based on UWB systems, etc., are capable of providing accurate time stamping (time stamping) and delayed transmission functions, but have no spontaneous time synchronization function. As shown in fig. 2, the transmitting/answering device includes three main parts, namely an upper computer, a radio frequency chip and an antenna, wherein the upper computer is responsible for controlling calculation and packaging of unpacked data frames, the radio frequency chip is responsible for transmitting modulation and receiving demodulation data frames and extracting time sequences, and the antenna is responsible for interconversion of electric signals and electromagnetic waves. In order to make the calculation of the air propagation time more accurate, the embodiment adopts an analysis method combining a physical frame structure and an equipment module to obtain a data frame propagation time sequence relationship and extract a more accurate time point. The method for realizing unilateral two-way ranging based on the UWB system in the embodiment and extracting accurate propagation time based on arrival time, as shown in fig. 2-5, the step S1 in the embodiment specifically includes:
the transmitting device issues a frame (the "query" frame) with only (Preamble), SFD (start of frame delimiter), PHR (physical layer header) and no Data in the Data field (Data), i.e. a message Poll, as shown in fig. 3, wherein the Preamble: for informing the receiver that the data synchronization reception preparation is ready; SFD: for indicating the start of a frame, PHR: the first bit is a ranging tag, rmaroker, whose time to and from the rf chip may be provided by a clock counter; data field: data can be left empty or piggybacked; when the frame marking bit (first character RMARKER) of PHR leaves the built-in radio frequency chip of the transmitting device and is transmitted from the antenna, recording the corresponding transmission time tl, and adding the delay of the antenna to the transmission time tl to obtain a first transmission time stamp poll_tx;
when receiving the message Poll, the response equipment records the arrival time t2 of the frame mark bit, subtracts the time delay of the antenna processed by the correction factor from the arrival time t2, and obtains a first receiving time stamp poll_rx;
acquiring the arrival time t3 of the frame marking bit obtained by pre-calculation in the response equipment, controlling the frame marking bit to leave the response equipment at the arrival time t3, and adding the time delay of the antenna to the arrival time t3 to obtain a second sending timestamp answer_tx; the first receiving time stamp poll_rx and the second sending time stamp answer_tx are used as data to be written into the response message Answer and sent to the sending equipment;
after receiving the Answer message Answer, the sending device records the arrival time t4 of the frame mark bit, and subtracts the time delay of the antenna processed by the correction factor from the arrival time t4 to obtain a second receiving time stamp answer_rx.
The sending time tl and the arrival time t4 specifically take the value of the clock counter in the built-in radio frequency chip of the sending equipment at the corresponding moment, and the arrival time t2 specifically takes the value of the clock counter in the built-in radio frequency chip of the response equipment at the corresponding moment. Because the radio frequency chip is internally provided with the high-frequency counter, the accurate time stamp can be obtained by reading the numerical value of the counter.
The ranging device (transmitting device, answering device) can obtain the time information of the data frame in different transmission stages through the data interface of the radio frequency chip, and considering that four time points of transmission and reception between the transmitting device and the answering device can not be directly obtained, the main factors have two aspects: on the one hand, the radio frequency chip can only read the value of the high-speed clock counter when the frame mark bit passes through the antenna interface, namely the time for reaching the antenna interface, and the data reach the antenna interface from the antenna, not the speed of light, but a delay time, namely the time delay of the antenna, is generated, so the time obtained by the radio frequency chip cannot be directly used for calculation. On the other hand, the transmission time of the response frame cannot be obtained by reading. When the tag bit of the reply frame passes through the reply-end antenna interface, the read time cannot be packed into the data payload of the reply frame. The embodiment considers the problems of the two aspects, adopts an analysis method combining a physical frame structure and an equipment module, introduces the time delay of data from an antenna to an antenna interface, corrects the time for transmitting and receiving the information by using the time delay of the antenna, calculates the distance by taking the corrected time as accurate time, calculates the arrival time of a frame mark bit of a response frame in advance, controls a radio frequency chip to transmit a response message at the calculated transmission time by using a timing transmission function, can realize unilateral bidirectional ranging with accurate time estimation, solves the problem that the traditional SS-TWR method cannot estimate the time, can greatly improve the time extraction precision and reduce the ranging error compared with the traditional unilateral bidirectional ranging by directly using the time point. The detailed process of realizing unilateral two-way ranging based on the UWB system in the embodiment is as follows:
the transmitting device sends out an inquiry frame, when the first character RMARKER of PHR leaves the radio frequency chip and is transmitted from the antenna, the value t1 of the system clock counter is recorded, after the measured antenna delay 1 is added, the inquiry frame is recorded as a transmission time stamp, and the inquiry frame is written into a register;
since the antenna has no clock and counter, the time for the rmaroker to reach the antenna cannot be recorded. The radio frequency chip of the transmitting device detects that the RMARKER leaves the record time t1, an electric signal containing the RMARKER information is converted into an electromagnetic wave containing the RMARKER information through an antenna and is transmitted into the air, and the time used in the whole process is the antenna delay. The electromagnetic wave reaches the antenna of the response equipment through air propagation, and is also converted into an electric signal through antenna delay, the radio frequency chip records the RMARKER arrival time t2, the antenna delay 2 is subtracted from the t2, and finally, a receiving timestamp 'inquiring and receiving' is obtained and written into a register;
the upper computer of the response device firstly transmits the pre-calculated RMARKER transmission time t3 to the radio frequency chip, and the RMARKER leaves the radio frequency chip at t3 by a timing transmission function; adding the antenna delay 3 to t3, and then writing the antenna delay 3 into a register as a transmission time stamp response; finally, the timestamp 'inquiry receiving', 'response sending' is written into a 'response' frame data field and is sent to the sending equipment;
after receiving the response frame, the transmitting device records the rmaroker arrival time t4, subtracts the antenna delay 4, marks the receiving time stamp as response receiving, and reads out the time stamp as inquiry sending and response sending. The above-described timings are shown in detail in table 1.
Table 1: time sequence calculation table
The propagation time extraction method of the present embodiment will be further described below by taking a case where a DW1000 chip is used for performing one-sided two-way ranging in the device a and the device B as an example.
As shown in fig. 6, the parameters specifically related are:
table 2: time point parameter table
Table 3: parameter table for each time period
As shown in fig. 6, the detailed flow of the ranging message propagated between the device a (transmitting device) and the device B (responding device) is:
device a issues a frame with only preambles (Preamble), SFD (start of frame delimiter), PHR (physical layer header) and no data, i.e. message Poll. When the first character (rmacker, frame marker bit) of PHR leaves DW1000 and is transmitted from the antenna, the value of the system clock counter (time point (2)) is recorded, and after the measured antenna delay is added, the value is recorded as a transmission time stamp poll_tx (time point (3)), and the transmission time stamp poll_tx is written into a register.
The device B receives the message Poll, records the arrival time of the frame mark bit (time point (5)), subtracts the antenna delay after the correction factor processing, finally obtains a receiving time stamp poll_rx (time point (4)), and writes the receiving time stamp poll_rx into a register.
Since device B cannot intercept the transmission timestamp answer_tx packet into the message Answer when the message Answer is transmitted, the delayed transmission function of DW1000 must be used. This function requires that the pre-calculated frame marker bit arrival time be sent to the DW1000 first, and the first character of the PHR will leave the DW1000 at the calculated frame marker bit arrival time (time point (6)). The frame marker bit arrival time plus the antenna delay is written into the register as a transmission time stamp answer_tx (time point (7)). The time stamps poll_rx and answer_tx are transmitted to the device a as a data write message Answer.
After receiving the message Answer, the device a records the arrival time of the frame flag bit (time point (9)), subtracts the antenna delay after the correction factor processing, marks the received time stamp answer_rx (time point (8)), and reads out the time stamps poll_rx and answer_tx.
In step S2 of this embodiment, the flight time of the ranging message between the sending device and the responding device is calculated according to the extracted sending and receiving time stamps, and then the initial value of the distance is determined according to the calculated flight time, specifically, the distance between the devices is obtained by multiplying the time by the speed of light. The flight time is calculated according to the following formulas (1) to (3):
T round ＝T Answer_rx -T Poll_tx (1)
T reply ＝T Answer_tx -T Poll_rx (2)
wherein T is Answer_rx For the time value corresponding to the second receive timestamp answer_rx, T Poll_tx For the time value corresponding to the first transmission time stamp poll_tx, T Answer_tx For the time value corresponding to the second transmission timestamp answer_tx, T Poll_rx The time value corresponding to the first reception time stamp poll_rx.
The ranging values calculated according to the distance calculation in the step S2 may have errors, and the errors may be classified into two types: one is random error, the main causes are clock drift and noise, wherein the clock drift causes the clocks between two ranging devices to be asynchronous, and errors are caused when the distance is calculated through the air propagation time; noise present in the system causes small range fluctuations in the final ranging value; the other type is a system error, mainly because the equipment types are different, and the antenna structures and materials are different, so that the generated radiation field and the antenna delay are different, and the overall offset of the ranging value is caused.
The accurate time stamp is needed for distance measurement, a high-frequency counter is arranged in the radio frequency chip, the time stamp is obtained by reading the numerical value of the counter, and meanwhile, the radio frequency chip is externally connected with a high-quality crystal oscillator as a reference clock, so that the built-in counter can provide stable high-frequency counting. Clock skew generated by the crystal oscillator remains a major source of error in the SS-TWR method, affecting the accuracy of the acquisition of t1, t2, t3, t4 in table 1 above.
This example further analyzes the error caused by clock drift in the SS-TWR:
setting the clock offset of the transmitting device to e A The clock offset of the answering device is set to e B Using the single-sided two-way ranging SS-TWR described above, the exact representation of the time of flight should be the following expression containing the error e:
in engineering operation, time of flight T prop Typically in nanoseconds, and T round 、T reply In the course of 2-3 milliseconds,can approximate T at the time of analysis round ≈T reply The preparation method comprises the following steps:
for crystal oscillator clock drift and response time, the error of the flight time can be calculated as follows:
table 4: flight schedule
The range error resulting from a time-of-flight error of 1ns is typically about 0.3m, at a response time T reply In a fixed condition, a crystal oscillator with smaller clock offset is used, so that even e A -e B ＝|e A |+|e B |，e t And still remain at a small value, the error can be controlled to an acceptable range (in the sub-nanosecond range). The embodiment further uses the active temperature compensation crystal oscillator on the basis of the unilateral two-way distance measurement method, so that SS-TWR errors can be effectively controlled.
Conventionally, a passive crystal oscillator is used, and the temperature stability is a main error source, so that the passive crystal oscillator is very sensitive to temperature, and small temperature changes during the working period of the passive crystal oscillator can cause the change of system errors, so that the calculation results of the table are met. According to the calculation, even if the active temperature compensation crystal oscillator of +/-1 ppm is adopted, the recovery time period T reply When the frequency is 4ms, an error of +/-2 ns (equivalent to +/-0.6 m) still occurs, but because the active temperature compensation crystal oscillator has good temperature stability, a temperature error curve is stable, no error jump occurs greatly in the working temperature, so that the frequency accuracy can be controlled to be +/-0.2 ppm, namely, only an error of +/-0.4 ns (equivalent to +/-0.12 m) is generated, the error and the noise are superimposed together, and the error still is a Gaussian distribution error, and because the error caused by Gaussian white noise is still Gaussian distribution, the noise can be effectively reduced by further using a Kalman filtering algorithm.
As shown in fig. 1, in this embodiment, a measurement system is formed by five modules including clock correction, air propagation time extraction, distance calculation, distance correction by an empirical model, and distance value filtering, a distance calculation module extracts a time stamp of transmission/reception of a ranging message propagating in the air, and calculates a distance initial value by using an SS-TWR method, and after correcting a systematic error by the empirical model, noise is eliminated by a filter to form a measurement result output by the system. Because the extraction of the air propagation time module is dependent on accurate time information, an external crystal oscillator is further used for correcting a clock in the chip so as to reduce time errors.
In the present embodiment, when reducing noise by Kalman filtering, a system state vector x is established specifically by a distance value and a distance change rate k Based on the previous state of the system, predicting the current state, and establishing a state equation of a distance model:
x k ＝Ax k-1 +w k (8)
wherein the state transition matrix [15] Is thatDeltaT is the sampling interval of UWB, w k The covariance matrix of the system noise at the moment k is Q k 。
The system observation equation is as follows:
Z k ＝Cx k +v k (9)
wherein the observation transfer matrix takes c= [ 10 ]]，v k The covariance matrix of the measurement noise at the moment k is R k . In practice, the covariance matrix adopts an empirical model Q k =q and R k ＝R。
The established measurement distance model is a linear system, and the standard Kalman filtering algorithm is as follows:
wherein the method comprises the steps ofFor predicting state vector, ++>To predict state covariance, K k For Kalman gain matrix, X k-1 And X k Estimated state vector for k-1 and k-time, P k-1 And P k For the estimated state covariance matrix at k-1 time and k time, I is an identity matrix and an empirical model->R＝[0.4]。
The antenna surrounding field is divided into three areas: reactive power station field region (also called inductive field region), radiation near field region (also called Fresnel region) and radiation far field region (also called Fulange field region), the interface between the two isThe interface between the two is +.>The electric field and the magnetic field of the reactive power station field perform energy oscillation and do not radiate outwards. The electromagnetic wave can stably propagate in the far field region of radiation to establish a relatively fixed mathematical model, and in the near field region of radiation, due to the coupling effect of capacitance and inductance, complex signal propagation is formed, the receiving antenna and the transmitting antenna can interfere with each other due to the coupling effect of capacitance and inductance, the fixed mathematical model is difficult to establish, and the air propagation model cannot be directly used.
The maximum dimension L of the UWB device antenna is 0.2m, the light speed C is 299702547m/s, the central frequency omega of the working channel 2 is 3993.6MHz, and the wavelength of electromagnetic wave isSince the UWB band is large, the bandwidth of the working channel 2 is 499.2MHz, and the boundary distance between the radiation near field region and the far field regionIs not clear, R 2 Between 0.999m and 1.113m, mathematical models with two antennas less than 1.113m apart are difficult to derive. In the embodiment, the error of the antenna radiation field is further considered, the error experience model for correcting the antenna radiation near field region is constructed, and the constructed error experience model is used for correcting the distance initial value, so that the ranging accuracy can be further improved, and the measuring error is reduced. In a specific application embodiment, the existing system errors are approximately corrected using an empirical error table, as shown in fig. 7, where the abscissa is distance and the ordinate is error correction. Besides the influence of the antenna radiation field, the propagation speed of electromagnetic waves in different antenna media is different, so that fixed and measurable time delay is generally called as the time delay of the antenna, and the correction can be performed by constructing an empirical model.
The embodiment is specifically directed to a method such as a UWB measurement system, which uses an improved time-estimatable single-side two-way ranging (SS-TWR), and establishes a flow processing system from generating a measurement request to transmitting to a radio frequency module, correcting the time delay of an antenna, and returning a received signal reversely. Under the condition of adopting active temperature compensation crystal oscillator, kalman filtering is introduced to carry out fusion estimation on the measurement result, and the measurement error can be further reduced.
In order to verify the effectiveness of the invention, an SS-TWR passive crystal oscillator and active temperature compensation crystal oscillator comparison experiment is carried out in a specific application embodiment, and a BP-400 module with infinite blue points (Infinite of Blue Point) is adopted as a main body of the device. When a 38.4MHz crystal oscillator is selected, the group A uses a passive crystal oscillator with the error of 10ppm which is commonly used for UWB modules, the group B uses an active temperature compensation crystal oscillator with the error of 1ppm for improvement, and other devices are the same, so that a test is performed. The experimental field selects an indoor open area, the length of the square floor tile can be measured, the square floor tile is uniformly paved, the A group is used as a reference group for measuring the true value of the length of the distance, the distance between two devices is 3 meters, and the measurement result is shown in figure 9. As can be seen from the ranging result of FIG. 9, the passive crystal oscillator has a large time drift along with the temperature change after the start-up, so that the positioning error reaches hundreds of centimeters, the ranging value is unreliable, and the error of the device using the active temperature compensation crystal oscillator fluctuates within +/-10 cm and is Gaussian, and the error can be processed by Kalman filtering during the ranging.
In the embodiment, a Kalman filtering method experiment is further carried out, and the ranging effect obtained after the standard Kalman filtering algorithm is applied can reach +/-5 cm.
In this embodiment, the comparison experiment between the SS-TWR algorithm and the conventional DS-TWR algorithm of the present invention is further performed, first, the fixed distance accuracy is compared, two algorithms of SS-TWR and DS-TWR are used in a pair of identical modules, 3000 ranging data are cut from four distances of 1, 3, 5 and 10 meters, and the results are shown in fig. 8. According to the graph, under the condition of active temperature crystal oscillation compensation, the SS-TWR ranging method and the traditional DS-TWR ranging method achieve the accuracy of +/-5 cm.
Further intercepting the average value of 500 times of the time duration taken from sending out the polling information to receiving the last message when the SS-TWR and DS-TWR of the invention are measured at 1, 3, 5 and 10 meters, and comparing and analyzing, wherein the SS-TWR only needs 34.58% of the time duration of the DS-TWR algorithm as shown in figure 9. The electromagnetic wave propagation time only needs a few nanoseconds to a few microseconds, the equipment processing calculation time is about 4 milliseconds, and the equipment processing time occupies more than 99 percent of the whole distance measurement time, so the method can reduce the information exchange times between the equipment, can obviously reduce the whole distance measurement time, and can improve the distance measurement refreshing frequency to 2.89 times.
Further, the method of the invention also carries out a mobile ranging experiment: in the case of positioning an object moving at a high speed, there is an error, taking a simplified model as shown in fig. 10 as an example, when the Tag moves to the Anchor, the positions of the transmitted signal and the received signal are not the same, the position of the received signal is taken as the actual position, and the calculated measured distance has an error Δd from the actual distance. Taking SS-TWR one-time ranging time to be 5ms, and under the condition that the error delta d can be allowed to be 10cm, passing through a motion formulaThe moving speed can be calculatedThe error due to the degree is calculated and the simulation result is shown in fig. 11. Under the condition that the error delta d can allow 10cm, the maximum speed of the movement of the Tag can be 40m/s (144 km/h), and the distance measurement requirement of most indoor high-speed mobile robots can be met.
By adopting the unilateral two-way distance measurement method, after using an active temperature compensation crystal oscillator, the SS-TWR error is effectively controlled, the error is reduced from hundreds of centimeters to about + -10 cm, the noise is effectively reduced by using filtering energy, and the error is reduced from + -10 cm to + -5 cm; compared with the traditional double-side two-way ranging (DS-TWR), the one-time ranging duration is reduced to 34.58%, the ranging refresh frequency can be increased to 2.89 times, and for mobile ranging, the maximum moving speed is 40m/s under the condition that an error is allowed to be 10 cm. The method has high ranging efficiency and refreshing frequency, can control the error of unilateral two-way ranging, and effectively reduces noise.
The unilateral two-way distance measuring device of this embodiment includes:
the transmission time extraction module is used for respectively acquiring the transmission time and the receiving time of the ranging message and the response message when the ranging message and the response message are transmitted between the transmitting device and the response device for ranging through the built-in radio frequency chip and the antenna, correcting by using the time delay of the antenna, and extracting the transmission time stamp and the receiving time stamp of the ranging message and the response message transmitted between the transmitting device and the response device;
the distance calculating module is used for calculating the initial value of the distance between the transmitting equipment and the response equipment according to the transmitting and receiving time stamps extracted by the propagation time extracting module;
the distance correction module is used for correcting the distance initial value calculated by the distance calculation module by using a preset model to obtain a corrected distance value;
and the distance value filtering module is used for filtering the distance value corrected by the distance correction module by using a filter and outputting a filtered measurement result.
In this embodiment, the device further includes a clock correction module connected to the propagation time extraction module, for correcting a clock in the radio frequency chip by using the active temperature compensation crystal oscillator.
The structural principle of the unilateral two-way distance measuring device in this embodiment is shown in fig. 1. The single-sided two-way ranging device in this embodiment corresponds to the single-sided two-way ranging method in a one-to-one manner, and will not be described in detail herein.
The embodiment also provides a computer device, which comprises a processor and a memory, wherein the memory is used for storing a computer program, the processor is used for executing the computer program, and the processor is used for executing the computer program so as to execute the unilateral two-way distance measurement method.
The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention shall fall within the scope of the technical solution of the present invention.
Claims (8)
1. The unilateral two-way distance measurement method is characterized by comprising the following steps of:
s1, extracting propagation time: when a distance measuring device and a response device transmit a distance measuring message and a response message through a built-in radio frequency chip and an antenna, respectively acquiring the sending time and the receiving time of the distance measuring message and the response message, correcting by using the time delay of the antenna, and extracting the sending time stamp and the receiving time stamp of the distance measuring message and the response message transmitted between the sending device and the response device;
s2, calculating the distance: calculating the initial value of the distance between the sending equipment and the response equipment according to the sending and receiving time stamps extracted in the step S1;
s3, distance correction: correcting the distance initial value calculated in the step S2 by using a preset model to obtain a corrected distance value, wherein the preset model is an error experience model for correcting the antenna radiation near field region, and the constructed error experience model is used for correcting the distance initial value, wherein the distance between a receiving antenna and a transmitting antenna is smaller than 1.113m;
s4, filtering distance values: filtering the distance value corrected in the step S3 by using a filter, and outputting a filtered measurement result;
the step S1 specifically includes:
the transmitting device transmits a frame which has only a preamble, SFD and PHR and does not contain data, namely a message Poll, when a frame mark bit of the PHR leaves a built-in radio frequency chip of the transmitting device and is transmitted from an antenna, the corresponding transmitting time tl is recorded, and the transmitting time tl is added with the time delay of the antenna to obtain a first transmitting time stamp poll_tx;
when the response equipment receives the message Poll, recording the arrival time t2 of the frame marking bit, and subtracting the time delay of the antenna processed by the correction factor from the arrival time t2 to obtain a first receiving time stamp poll_rx;
acquiring the arrival time t3 of the frame marking bit, which is obtained by pre-calculation in the response equipment, controlling the frame marking bit to leave the response equipment at the arrival time t3, and adding the time delay of the antenna to the arrival time t3 to obtain a second sending timestamp answer_tx; the first receiving timestamp poll_rx and the second sending timestamp answer_tx are used as data to be written into a response message Answer and sent to the sending equipment;
after receiving the Answer message Answer, the sending device records the arrival time t4 of the frame mark bit, and obtains a second receiving timestamp answer_rx by subtracting the time delay of the antenna processed by the correction factor from the arrival time t 4.
2. The unilateral two-way distance measurement method according to claim 1, wherein the sending time tl and the arrival time t4 specifically take the value of the clock counter in the built-in radio frequency chip of the sending device at the corresponding time, and the arrival time t2 specifically takes the value of the clock counter in the built-in radio frequency chip of the response device at the corresponding time.
3. The unilateral two-way distance measurement method according to claim 1, wherein in step S2, the flight time of the distance measurement message between the sending device and the responding device is calculated according to the extracted sending and receiving time stamps, and then the initial value of the distance is determined according to the calculated flight time, and the flight time is calculated according to the following formula:
T round ＝T Answer_rx -T Poll_tx
T reply ＝T Answer_tx -T Poll_rx
wherein T is Answer_rx For the time value corresponding to the second receiving time stamp answer_rx, T Poll_tx For the time value corresponding to the first transmission time stamp poll_tx, T Answer_tx For the time value corresponding to the second transmission time stamp answer_tx, T Poll_rx And a time value corresponding to the first receiving time stamp poll_rx.
4. A unilateral two-way distance measurement method according to any one of claims 1 to 3, characterized in that: and the step S1 also comprises the step of correcting the clock in the radio frequency chip by using an active temperature compensation crystal oscillator.
5. A unilateral two-way distance measurement method according to any one of claims 1 to 3, wherein in step S4, a kalman filter is specifically adopted for filtering.
6. A single-sided two-way ranging apparatus, comprising:
the system comprises a propagation time extraction module, a transmission time judgment module and a transmission time judgment module, wherein the propagation time extraction module is used for respectively acquiring the transmission time and the receiving time of a ranging message and a response message when the ranging message and the response message are transmitted between a sending device and a response device for ranging through a built-in radio frequency chip and an antenna, correcting by using the time delay of the antenna, and extracting the transmission time stamp and the receiving time stamp of the ranging message and the response message propagated between the sending device and the response device;
the distance calculating module is used for calculating the initial value of the distance between the transmitting equipment and the response equipment according to the transmitting and receiving time stamps extracted by the propagation time extracting module;
the distance correction module is used for correcting the distance initial value calculated by the distance calculation module by using a preset model to obtain a corrected distance value, the preset model is an error experience model for correcting the antenna radiation near field region, the constructed error experience model is used for correcting the distance initial value, and the distance between a receiving antenna and a transmitting antenna is smaller than 1.113m;
the distance value filtering module is used for filtering the distance value corrected by the distance correction module by using a filter and outputting a filtered measurement result;
the propagation time extraction module specifically comprises:
the transmitting device transmits a frame which has only a preamble, SFD and PHR and does not contain data, namely a message Poll, when a frame mark bit of the PHR leaves a built-in radio frequency chip of the transmitting device and is transmitted from an antenna, the corresponding transmitting time tl is recorded, and the transmitting time tl is added with the time delay of the antenna to obtain a first transmitting time stamp poll_tx;
when the response equipment receives the message Poll, recording the arrival time t2 of the frame marking bit, and subtracting the time delay of the antenna processed by the correction factor from the arrival time t2 to obtain a first receiving time stamp poll_rx;
acquiring the arrival time t3 of the frame marking bit, which is obtained by pre-calculation in the response equipment, controlling the frame marking bit to leave the response equipment at the arrival time t3, and adding the time delay of the antenna to the arrival time t3 to obtain a second sending timestamp answer_tx; the first receiving timestamp poll_rx and the second sending timestamp answer_tx are used as data to be written into a response message Answer and sent to the sending equipment;
after receiving the Answer message Answer, the sending device records the arrival time t4 of the frame mark bit, and obtains a second receiving timestamp answer_rx by subtracting the time delay of the antenna processed by the correction factor from the arrival time t 4.
7. The single-sided two-way distance measuring device of claim 6, further comprising a clock correction module coupled to the propagation time extraction module for correcting a clock within the radio frequency chip using an active temperature compensated crystal oscillator.
8. A computer device comprising a processor and a memory for storing a computer program, the processor being for executing the computer program, characterized in that the processor is for executing the computer program to perform the method according to any of claims 1-5.
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| CN114265049B (en) * | 2022-03-02 | 2022-06-14 | 华南理工大学 | UWB-based real-time ranging method, network structure and network node |
| CN114689056B (en) * | 2022-04-08 | 2023-04-18 | 上海柯锐芯微电子有限公司 | Accurate ranging method based on UWB SS-TWR |
| CN115397014A (en) * | 2022-08-19 | 2022-11-25 | 中铁建电气化局集团第三工程有限公司 | High-precision fusion positioning system and method and electronic equipment |
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