CN101666878A - Passive RFID positioning method and system for improving signal to noise ratio and positioning accuracy - Google Patents
Passive RFID positioning method and system for improving signal to noise ratio and positioning accuracy Download PDFInfo
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Abstract
The invention relates to a method for positioning a passive RFID, which the following steps: sending a radio-frequency signal through a transmitter aerial by a reader; receiving the radio-frequency signal sent by the reader through an aerial by a passive transponder to be positioned; converting the received radio-frequency signal into a DC voltage for powering the passive transponder; detecting the peak value of the signal received by the aerial to obtain the analog quantity of signal intensity, carrying out the AD conversion on the analog quantity, and converting the detected analog quantityof the signal intensity represented by a signal peak amplitude into a digital quantity; storing the digital quantity representing the signal intensity; sending the modulated digital quantity to the reader by the aerial of the transponder; and positioning the transponder by a computer according to two digital quantities sent and received by the reader. Meanwhile, the invention also provides a positioning system for realizing the method. The invention greatly improves the signal to noise ratio and the positioning accuracy of the passive RFID positioning system.
Description
Technical field
The present invention is applicable to closely or the localization method and the system of the interior space, use radio-frequency (RF) identification (RFID, RadioFrequency IDentification) technology is finished the location to object, relates to a kind of passive RFID localization method and system that can improve signal to noise ratio (S/N ratio) and bearing accuracy.
Background technology
The develop rapidly of mobile computing technology and wireless local area network technology has promoted advancing by leaps and bounds of mobile positioning technique.For outdoor positioning system, the application of foremost global position system GPS is seen everywhere, but for being applied to closely or positioning system in the interior space, gps system has tangible limitation, carry out location in the indoor enclosure space and use radio-frequency (RF) identification (RFID) technology be born in automatic identification field, with other location technology incomparable advantage such as its noncontact, non line of sight, bearing accuracy height and cost are low, obtained more and more people's concern.
In the whole bag of tricks that applying RFID technology positions, a kind of very important location thought is by obtaining the range difference between several groups of (be generally 3 or more than) readers and the transponder, and the reader of having determined according to the position is finished the location to transponder then.In the whole bag of tricks that the acquisition range difference positions, the RFID localization method that is mapped to range difference based on RSSI (Received SignalStrength Indication) received signal field strength attenuation has low-power and advantage cheaply, this makes this method be used for business-like positioning system, for example LANDMARC etc.
Can be divided into two kinds based on the used transponder of the RFID localization method of RSSI: active balise and passive balise.Because passive balise has the advantage that a series of active balises such as cost is low, simple in structure, applied widely, long service life do not have, passive balise replaces active balise in extensive fields will become trend.Basic thought based on the rfid system of passive balise is: oneself does not have power supply transponder, and its work capacity need obtain from the radiofrequency signal that reader sends.Power supply generation module among the present invention just is being based on this NE BY ENERGY TRANSFER and obtaining mode realization.
Use the RFID positioning system of passive balise mainly to adopt following working method at present: reader sends radiofrequency signal, this signal arrives transponder, produce the voltage that activates transponder work by the power supply generation module, transponder is again with radiofrequency signal reflected back reader.As shown in Figure 1, signal in two-way process through 1., thereby 2. twice decay of two paths, compare with the signal of original transmission by the signal that reader finally receives, the degree of measuring-signal decay, come the round distance of decision signal according to the signal attenuation and the relation of transmission distance, thereby obtain the distance between reader and the transponder.If the position of reader is determined, then by 3 readers with to locate transponder and obtain corresponding 3 groups of range differences, just can position transponder, we call this localization method: the passive RFID that arrives reader based on the RSSI signal is located, and the data computation of this location can be finished by relevant location algorithm program.It need not change and is used to read and write the conventional reader of identification and the hardware configuration of transponder, only need read the signal strength that the signal strength that sent by reader and reader finally receive, by the decay in the signal calculated transmission way, finally finish location by the located in connection algorithm routine to transponder.
(a) by top analysis, the reflected energy P that reader obtains from transponder
RXTherefore and the biquadratic of distance R is inversely proportional between the two, and in reader and transponder distance location occasion far away slightly, R is bigger at this moment, the P after then being inversely proportional to the biquadratic of R
RXCan be very little, promptly can be very faint by the final received signal strength of reader.General reader receives for the signal that can realize great dynamic range, all there is automatic gain control agc circuit module inside, this module can be amplified to the size that is fit to read with the faint signal that receives, and also the very big signal that receives can be contracted to suitable value.Existing based in the RSSI signal arrival reader localization method, when R gets higher value and makes P
RXWhen very little, the AGC module can automatically be amplified the signal that receives, thereby the intensity level of the received signal of using during calculations for signal attenuation is no longer true, thereby has a strong impact on bearing accuracy.For the authenticity and the accuracy of positioning result, P
RXShould not get too for a short time, so the R value should not get too greatly, and promptly existing to arrive in the reader localization method orientation distance and scope based on the RSSI signal very restricted.
(b) the more above-mentioned existing reflection interference that arrives in the reader localization method based on the RSSI signal is once analyzed below: with accompanying drawing 2 is example, an if reflecting object, can be other transponder or other objects, be in the R/2 place of be positioned transponder and reader, at this moment, the interfering energy P of the reflecting object that receives of reader
INFor
Here other object spheres the reflection cross section identical with transponder.Compare P
RXAnd P
INAs can be known, interfering energy is bigger 16 times than signal, at this moment probably can cause the useful reflected signal reflected by objects signal that is reflected to flood, and useful signal can't be extracted.This shows,, bring huge interference in the system that arrives the reader location based on signal, can for original location for the object that is between reader and the transponder.
Summary of the invention
Existing based on positioning error fainter owing to received signal in the passive RSSI signal arrival reader localization method or that the reflected by objects interference brings for overcoming, the present invention proposes a kind of passive RFID localization method that arrives transponder based on the RSSI signal.Technical scheme of the present invention is as follows:
A kind of passive RFID localization method that can improve signal to noise ratio (S/N ratio) and bearing accuracy utilizes at least three readers, adopts based on the locator meams of RSSI arrival transponder passive balise is located, and comprises the following steps:
(1) radiofrequency signal sent through transmitting antenna of reader;
(2) passive balise to be positioned utilizes antenna to receive the radiofrequency signal that reader sends;
(3) radiofrequency signal that receives is carried out converting the DC voltage of supplying with passive balise work to behind bridge rectifier, low-pass filtering, voltage stabilizing and the amplitude limit successively;
(4) signal that antenna is received carries out the peak value detection, represents the analog quantity of the received signal intensity of transponder with detected signal peak amplitude;
(5) analog quantity after peak value is detected is carried out the AD conversion, and the analog quantity of detected signal peak amplitude institute characterization signal intensity is converted to digital quantity;
(6) digital quantity of preservation characterization signal intensity;
(7) to digital quantity is modulated after transponder antenna sends to reader;
(8) reader sends to computing machine with two digital quantities of its characterization signal intensity that receives with it that sends out, the mapping relations that are directly proportional with the quadratic power of signal transmission distance according to the signal attenuation degree by computing machine, to become three range differences from least three group digital signal attenuation map that different readers obtain, according to the position of corresponding reader, finish location again to transponder.
The present invention provides a kind of positioning system that realizes said method simultaneously, comprise: at least three are used for reader that transponder reads identification, be connected with reader three and are used to receive and dispatch the antenna of radiofrequency signal, passive balise and computing machine to be positioned, it is characterized in that, described passive balise comprises:
An antenna is used to receive the radiofrequency signal that is sent by each reader, and utilizes backscattering principle return path signal.
A power supply generation module is used for the radiofrequency signal that receives is carried out converting the DC voltage of supplying with passive balise work to behind bridge rectifier, low-pass filtering, voltage stabilizing and the amplitude limit successively;
A peak detctor is used for signal that antenna receives and carries out peak value and detect, and represents the analog quantity of the received signal intensity of transponder with detected signal peak amplitude;
An AD converter, its effect are that the analog quantity after peak value is detected is carried out the AD conversion, and the analog quantity of detected signal peak amplitude institute characterization signal intensity is converted to digital quantity;
A digital buffer process module is preserved the digital quantity of characterization signal intensity, and when transponder passback data, issues modulator;
A modulator is to modulating digital quantity after transponder antenna sends to reader;
Described reader is used for two digital quantities of its characterization signal intensity that receives with it that sends out are sent to computing machine; The mapping relations that described computing machine is directly proportional with the quadratic power of signal transmission distance according to signal attenuation, to become three range differences from least three group digital signal attenuation map that different readers obtain, according to the position of corresponding reader, finish location again to described transponder.
Passive RFID positioning system of the present invention, described peak detctor can be the RC charging circuit.Through the detected signal of peak filtering, be admitted to the comparer that is set with threshold value, the output of comparer is admitted in the Sheffer stroke gate after swinging to through impact damper, the enable signal of Sheffer stroke gate and the acquired signal of radiofrequency signal are synchronous, and the time of opening of Sheffer stroke gate is proportional to the crest voltage of peak detctor output.
Compare with existing passive RFID localization method based on signal arrival reader, the present invention has following outstanding advantage:
1, existing passive RFID localization method arrives reader based on signal strength, 4 powers of signal strength that reader receives and reader and transponder distance are inversely proportional to, the inventive method arrives transponder based on signal, 2 powers of the signal strength that reader receives and this distance are inversely proportional to, this method has improved the positioning signal field intensity that reader receives greatly, increase distance and the space that to locate, improved antijamming capability.
2, this method arrives transponder based on signal strength, signal strength has been converted into digital quantity in transponder, passback reader after modulating, there is corresponding circuit module to separate in the reader and reads this digital quantity of representation signal intensity, finally finish location to transponder by the located in connection algorithm routine, the reflected by objects that this method greatly reduces in the positioning system is disturbed, and has improved bearing accuracy.
Description of drawings
Fig. 1 is based on the passive RFID positioning system block diagram that signal arrives.
Fig. 2 is the passive RFID positioning system block diagram based on signal arrival when considering the reverberation interference.
Fig. 3 is based on the transponder structural drawing in the RSSI signal arrival transponder localization method.
Fig. 4 is transponder power supply generation module circuit theory diagrams.
Fig. 5 is the peak detection circuit of transponder.
Fig. 6 is the single-slope A/D convertor circuit of transponder.
Embodiment
The workflow that the passive RFID based on RSSI signal arrival transponder that the present invention proposes is located is: reader sends signal by antenna, receive by transponder antenna, and by transponder circuit the power of signal is carried out peak value and detect, the analog value of the gained after then peak value being detected obtains representing the numeric results of signal power after the AD conversion, numeric results after will modulating with modulator is then returned reader through antenna transmission, and the reader demodulation obtains numeric results.Because this numeric results has been represented the strong and weak size of the received signal of transponder, just can calculate the decay of signal in mailing to the transponder way thus, and then the distance between definite response device and reader.Thisly arrive the transponder localization method based on signal and only need consider the transmit path of signal from the reader to the transponder, and do not need to go again to consider that signal is from the return path of transponder reflected back reader in last a kind of method, compare with the localization method that arrives reader based on signal, the signal strength values that this method can make reader receive is enhanced can reduce simultaneously reflection interference in the positioning system greatly, divides the concrete analysis of two aspects below.
(a) in this localization method, only considered the transmit path of signal from the reader to the transponder, i.e. reader demodulation and the P after digital-to-analog conversion
TagFor
The intensity level of the received digital quantity signal of reader this moment and R square are inversely proportional to, compare with the biquadratic that is inversely proportional to R based on the received signal intensity of reader in the passive RSSI signal arrival reader localization method, make reader can receive onesize signal strength values, it is very big that R value in the inventive method can become, and promptly realizes that with this method the location can enlarge the distance and the scope of positioning system greatly.In like manner, for same R value, and arrive the reader localization method based on the RSSI signal and compare, the signal intensity that reader receives also strengthens greatly, positioning result can be better than faint positioning signal greatly, and under the promptly same orientation distance, the inventive method makes the better of locating effect change.Simultaneously owing to only need to demodulate digital quantity in the transponder reflected back signal with reader, and need not go again to consider this signal whether the automatic gain control module AGC in reader to its amplification or dwindle, therefore, under the prerequisite that does not change existing common reader hardware circuit structure, this method makes bearing accuracy higher, and the result is truer.
(b) be example with accompanying drawing 2, if adopt signal to arrive the transponder location, in the accompanying drawing 2 2. the path owing to just be used for transmitting on the 1. path signal after the modulation of the digital quantity of intensity after the signal attenuation, and the reader end generally can directly accurately demodulate this digital quantity, therefore 2. the decay on the path is not considered, to not influence of measurement result.Only need to consider of the influence of the signal of interfering object reflected back reader now to measurement result.In accompanying drawing 2, by the analytical approach of front, 3., 4. reverberation finally reflects the energy P that gives reader through the path
INFor
Transponder is about to P owing to only considered the decay that 1. go up in the path
TagSend to reader, reader demodulation and the P after digital-to-analog conversion after being converted to digital quantity and modulation
TagFor
This moment P
IN/ P
TagFor
With G
TagUsual value be 3dBi, when communicating with 900MHz, this λ is about 33cm, R gets 3m, this moment P
IN/ P
TagValue be about 0.005, promptly the signal of interfering object reflected back reader only is 0.005 times of transponder reflected back signal intensity, and arrives P in the reader locator meams based on signal
IN/ P
TagValue is 16 to compare, and the localization method that arrives transponder based on signal has reduced the reflection interference in the positioning system greatly, even can eliminate this type of interference substantially.
Being used to of the reader of using in the methods of the invention and routine reads and writes the reader of identification and compares, hardware circuit need not to change, only need demodulate the digital quantity of representation signal intensity, and this digital quantity is offered the location algorithm program carry out next step data processing with its intrinsic AD module.For transponder structure designed in this localization method as shown in Figure 3, its main circuit is formed structure and is comprised: the digital buffer process module of (1) power supply generation module circuit (2) peak detection circuit (3) A/D convertor circuit (4) (5) modulation circuit.
Below in conjunction with accompanying drawing 1,3,4,5,6 introduce the embodiment of the inventive method in detail.In accompanying drawing 1, reader through radiofrequency signal that transmitting antenna sends behind certain transmission path, receive and carry out certain amplification by the antenna of transponder, extract signal envelope and signal envelope is carried out the peak value detection through the peak detection circuit module then, promptly extract the maximal value of signal envelope, the peak value that peak value detects the signal envelope of back gained is an analog quantity, it has represented the power of the received radiofrequency signal of transponder, then this analog value is carried out analog to digital conversion through the A/D convertor circuit module, obtain representing the numeric results of signal power, simultaneously by digital buffer process module with this digital quantity buffer memory.For this numeric results is sent, the modulation module of transponder is modulated to high band with this digital quantity, the radio frequency signal frequency of sending with reader is consistent, and the numeric results after the modulation is sent to reader after the antenna of transponder amplifies, the digital quantity before the reader demodulation obtains modulating.Because this digital quantity has been represented the strong and weak size of the received signal of transponder, just can calculate the decay of signal in mailing to transponder way thus, this attenuation map be become distance between reader and the transponder according to the relation of radiofrequency signal decay in the varying environment and distance.Three data that reader read utilize serial ports or USB interface communication or additive method to be admitted in the computing machine, finally utilize three readers of known location finally to obtain 3 groups of distance measurements by computing machine, finally calculate the particular location of the transponder in closely indoor or the enclosure space then according to 3 of known location methods of then this point being carried out position calculation with any range difference, this a part of specific implementation is finished by relevant location algorithm program, only needs reader to provide the intensity level of the digital quantity that demodulates to get final product before.
Arrive the designed transponder structure of the passive RFID localization method of transponder as shown in Figure 2 based on the RSSI signal, it is as follows with function in the localization method specific implementation process that arrives transponder based on signal that its main circuit is formed modular structure:
(1) power supply generation module
Circuit such as accompanying drawing 4 are the voltage sources of an alternation because antenna ends senses from radio-frequency field, so current rectifying and wave filtering circuit of needs be translated into direct supply.Because the actuator internal circuit is the DC source except requiring power supply, also must be able to not surpass the voltage breakdown of devices such as metal-oxide-semiconductor, triode, so need to introduce the amplitude limit module.Final generation can be supplied with the DC voltage of each circuit module of transponder.
(2) peak detection circuit
Circuit such as accompanying drawing 5, it has comprised envelope detector and peak filter, so envelope detector and envelope detector in the common RFID transponder be identical can be shared, extract the radiofrequency signal envelope that reader sends with it, peak filter is used for extracting the signal amplitude maximal value, thereby obtain the expression reader and send the analog quantity of back by the received signal intensity size of transponder, this analog value is compared with the intensity size of the radiofrequency signal that the reader end sends out, its amplitude has had decay to a certain degree, and direct relation being arranged with the propagation distance of signal, this also is based on the fundamental starting point of the passive RFID localization method that the RSSI signal reaches.
(3) A/D convertor circuit
Adopt the simple single-slope AD conversion of circuit as shown in Figure 6, the groundwork process is that RESET makes the G conducting, and Sheffer stroke gate is opened, and reception voltage signal charges to C by R.The time that charging voltage reaches Vth voltage is directly proportional with the received signal crest voltage, is inversely proportional to RC.The comparer counter-rotating made Sheffer stroke gate close again after impact damper is swung to when C was charged to Vth, and at this moment the number of output pulse width or counting clock is proportional to the time that Sheffer stroke gate is opened, and promptly is proportional to the received signal crest voltage.Represent that the most at last the analog quantity that reader sends to the signal intensity size of transponder is converted to digital quantity.Whole A/D convertor circuit is simple, is easy to transponder integrated.
(4) digital buffer process module
Digital quantity behind the AD commentaries on classics back is carried out buffer memory, before transponder is to reader passback reflected signal, digital quantity is passed to modulator.
(5) modulator
To modulate through resulting digital quantity behind the A/D convertor circuit, signal after will modulating then sends to reader through transponder antenna, reader receives this modulation signal and demodulation obtains this digital quantity, and then carries out correlation computations, finishes the location to transponder.
Claims (4)
1. the passive RFID localization method that can improve signal to noise ratio (S/N ratio) and bearing accuracy utilizes at least three readers, adopts based on the locator meams of RSSI arrival transponder passive balise is located, and comprises the following steps:
(1) radiofrequency signal sent through transmitting antenna of reader;
(2) passive balise to be positioned utilizes antenna to receive the radiofrequency signal that reader sends;
(3) radiofrequency signal that receives is carried out converting the DC voltage of supplying with passive balise work to behind bridge rectifier, low-pass filtering, voltage stabilizing and the amplitude limit successively;
(4) signal that antenna is received carries out the peak value detection, represents the analog quantity of the received signal intensity of transponder with detected signal peak amplitude;
(5) analog quantity after peak value is detected is carried out the AD conversion, and the analog quantity of detected signal peak amplitude institute characterization signal intensity is converted to digital quantity;
(6) digital quantity of preservation characterization signal intensity;
(7) to digital quantity is modulated after transponder antenna sends to reader;
(8) reader sends to computing machine with two digital quantities of its characterization signal intensity that receives with it that sends out, the mapping relations that are directly proportional with the quadratic power of signal transmission distance according to the signal attenuation degree by computing machine, to become three range differences from least three group digital signal attenuation map that different readers obtain, according to the position of corresponding reader, finish location again to transponder.
2. passive RFID positioning system that can improve signal to noise ratio (S/N ratio) and bearing accuracy, comprise: at least three are used for reader that transponder reads identification, be connected with reader three and are used to receive and dispatch the antenna of radiofrequency signal, passive balise and computing machine to be positioned, it is characterized in that, described passive balise comprises:
An antenna is used to receive the radiofrequency signal that is sent by each reader, and utilizes backscattering principle return path signal.
A power supply generation module is used for the radiofrequency signal that receives is carried out converting the DC voltage of supplying with passive balise work to behind bridge rectifier, low-pass filtering, voltage stabilizing and the amplitude limit successively;
A peak detctor is used for signal that antenna receives and carries out peak value and detect, and represents the analog quantity of the received signal intensity of transponder with detected signal peak amplitude;
An AD converter, its effect are that the analog quantity after peak value is detected is carried out the AD conversion, and the analog quantity of detected signal peak amplitude institute characterization signal intensity is converted to digital quantity;
A digital buffer process module is preserved the digital quantity of characterization signal intensity, and when transponder passback data, issues modulator;
A modulator is to modulating digital quantity after transponder antenna sends to reader;
Described reader is used for two digital quantities of its characterization signal intensity that receives with it that sends out are sent to computing machine; The mapping relations that described computing machine is directly proportional with the quadratic power of signal transmission distance according to signal attenuation, to become three range differences from least three group digital signal attenuation map that different readers obtain, according to the position of corresponding reader, finish location again to described transponder.
3. the passive RFID positioning system that can improve signal to noise ratio (S/N ratio) and bearing accuracy according to claim 2 is characterized in that described peak detctor is the RC charging circuit.
4. the passive RFID positioning system that can improve signal to noise ratio (S/N ratio) and bearing accuracy according to claim 2, it is characterized in that, through the detected signal of peak filtering, be admitted to the comparer that is set with threshold value, the output of comparer is admitted in the Sheffer stroke gate after swinging to through impact damper, the enable signal of Sheffer stroke gate and the acquired signal of radiofrequency signal are synchronous, and the time of opening of Sheffer stroke gate is proportional to the crest voltage of peak detctor output.
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| CN108919808B (en) * | 2018-07-19 | 2022-01-25 | 石家庄铁道大学 | Rail transverse moving vehicle position synchronous control system and position synchronous method |
| WO2021068106A1 (en) * | 2019-10-08 | 2021-04-15 | Huawei Technologies Co., Ltd. | Towards scalable, robust and cost-efficient mechanism for multiple object localization in smart indoor environment |
| CN114365421A (en) * | 2019-10-08 | 2022-04-15 | 华为技术有限公司 | Scalable, robust, and cost-effective mechanism for multi-object positioning in smart indoor environments |
| CN112606879A (en) * | 2020-12-29 | 2021-04-06 | 卡斯柯信号有限公司 | Vehicle positioning system and method for railway traffic |
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