WO2011054128A1

WO2011054128A1 - Device and method for precisely measuring near-field communication distance of radio frequency identification (rfid) tag

Info

Publication number: WO2011054128A1
Application number: PCT/CN2009/001220
Authority: WO
Inventors: 岳彦生; 梁敏
Original assignee: 北京简约纳电子有限公司
Priority date: 2009-11-03
Filing date: 2009-11-03
Publication date: 2011-05-12

Abstract

A system and method for short-distance wireless communication are provided. The system comprises: an antenna array, including a central antenna and at least two circumambient antennas which are centrosymmetrical with respect to the central antenna, and adapted to receive signals from a tag in the near field of the antenna array; a baseband processing unit (50), calculating and determining the distance of the tag in the near-field of the antenna array based on the phase difference of received signals, and determining whether to communicate with the tag according to the distance. The system and method are able to more precisely determine the near-field distance between the tag and the reader based on the phases of signals.

Description

Radio frequency identification (RFID) tag near field communication distance

Apparatus and method for accurate measurement

The present invention relates to electronic tag distance measurement, and more particularly to an apparatus and method for accurate measurement of near field communication distance of an RFID tag. Background technique

Radio Frequency Identification (RFID) technology is a non-contact automatic identification technology. RFID systems are generally composed of tags and readers. Among them, the tag consists of a chip and an antenna, and the reader also has an antenna. When the two communicate, the reader emits electromagnetic waves into its surrounding space, and the antenna tag is tuned to the corresponding frequency to receive electromagnetic waves. The tags are divided into active and passive. Passive tags take energy from the electromagnetic field generated by the reader to operate the chip circuit on it, operating only within close communication distances. Active tags can actively transmit higher power signals and can operate over longer communication distances.

Since the tag may be read by multiple RF readers, especially active tags, it is necessary to limit the communication distance from the reader to the tag, which requires accurate measurement of the tag to reader distance.

U.S. Patent No. 7,161,357, issued Jan. 9, 2007, discloses a device for measuring the reading distance between a tag and a reader. In the device, at least one unit cell is connected in a row to form an electromagnetic anechoic chamber, and each unit cell has electromagnetic wave absorbing material disposed on the inner wall and placed at the end of the electromagnetic anechoic chamber. The electromagnetic wave generating portion at the chamber transmits an electromagnetic wave through the antenna, and the electromagnetic wave measuring portion measures the electromagnetic wave field strength by using an electric field probe moving in the electromagnetic anechoic chamber, thereby analyzing the antenna pattern.

U.S. Patent Application Serial No. 2007/0290846 A1, which issued on Dec. 20, 2007, discloses a transducer transponder determined by inductive coupling in a radio system.

The method of position or orientation of (transponder). The radio system includes a transceiver having an antenna device. The method generates an alternating magnetic field by a transceiver and an antenna device to determine an associated signal indicative of a measure of inductive coupling between the antenna device and the transponder of the transceiver, wherein the distance or orientation of the transponder relative to the antenna device may be coupled to the inductive related.

"RADAR: An In-Building RF-based User Location and Tracking by Paramvir Bahl and Venkata N. Padmanabhan of Microsoft Research" System" is disclosed in {bahl, pad ma nab}@ mi crosoft.com. This article discloses the use of RADAR (Radio Frequency System) to locate and track users in buildings. RADAR works by recording and processing settings. It is used to provide signal strength information at a plurality of base stations whose coverage overlaps within a region of interest.

Christian Metzger, Alexander llic from ETH Zurich, Switzerland

Philippe Bourquin, Florian Michahelles, Elgar Fleisch et al., "Distance-sensitive High Frequency RFI D Systems" by {cmetzger, ailic, fmichahelles, efleisch}@ethz.ch, discloses a distance-dependent high-frequency RFID system. It allows the distance of the tag to the reader antenna to be solved. Depending on the signal strength of the transmitted data as a function of the distance of the tag from the reader antenna, it is also affected by the deflection of the tag relative to the parallel surface of the reader antenna. The solution uses a tilted sensor (such as an accelerometer on the tag) to provide the tag. Orientation.

As RFID is widely used in all walks of life, the problem of interference between tags is becoming more and more prominent. Based on the requirements of anti-interference and safety considerations, it is often desirable to limit the tag to a certain distance. When the communication distance between the tag and the reader is the same order of magnitude as the wavelength of the wireless signal, it belongs to near field communication. In near-field communication, the power transmitted by the tag or the reader receives little change with distance, so the actual distance of the tag cannot be accurately determined according to the power. Accurate measurement of the near-field communication distance is a challenging subject. . The techniques disclosed above are difficult to apply to near-field measurements. Summary of the invention

It is an object of the present invention to provide an apparatus and method that is capable of determining the distance of a tag located in the near field of a reader.

To this end, the present invention provides a short-range wireless communication system in a first aspect. The system includes:

An antenna array including a center antenna and at least two peripheral antennas symmetrical about a center antenna for receiving signals from tags located in a near field of the antenna array; a baseband processing unit, calculating according to a phase difference of signals received by different antennas Determining the distance of the tag located in the near field of the antenna, and determining whether to communicate with the tag based on the distance.

The present invention provides a short-range wireless communication method in a second aspect. The method includes utilizing an antenna including a center antenna and at least two peripheral antennas centered on the center antenna The array receives signals from tags located in the near field of the antenna array, determines the distance of the tag located in the near field of the antenna based on the phase difference of the signals received by the different antennas, and determines whether to communicate with the tag based on the distance.

The present invention can more accurately determine the near field distance between the tag and the reader based on the phase of the signal. DRAWINGS

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described in more detail with reference to the accompanying drawings in which:

1 is a schematic diagram of a short-range wireless communication system according to an embodiment of the present invention; FIG. 2 is a schematic diagram of a principle according to an embodiment of the present invention;

Figure 3 is a schematic illustration of a principle in accordance with another embodiment of the present invention;

Figure 4 is a schematic diagram showing the distances of D1, D2, and D3 with respect to points A and C, respectively.

Figure 5 is an equivalent diagram of D1, D2, and D3 relative to points A and C;

Figure 6 is an equivalent diagram of D1, D2, D3 relative to point B;

Figure 7 illustrates an antenna array consisting of five antennas;

Figure 8 illustrates an antenna array consisting of four antennas. detailed description

1 is a schematic diagram of a short-range wireless communication system in accordance with one embodiment of the present invention. As shown in Fig. 1, the reader system includes an antenna array consisting of three antennas 10, 20 and 30 for receiving incoming radio signals, respectively. The received signals are filtered and amplified by RF units 12, 22 and 32, respectively, and converted to intermediate frequency signals, which are then demodulated by I/Q demodulators 14, 24 and 34. The demodulated signal is converted by the AD unit 40 and processed by the baseband processing unit 50. When the signal needs to be transmitted, the signal from the baseband processing unit 50 is DA converted by the DAC 70, then loaded by the RF unit 80 onto the RF signal, and transmitted through the intermediate antenna 20. The same frequency complex is provided to the RF units 12, 22, and 32 by the SYN unit during communication, and the ADC channel performs AD conversion on signals from different antennas based on the same sampling clock.

In this embodiment, the three antennas are arranged in a row and are equidistant. The phase of the received signal using the three antennas determines the distance of the tag located in the near field of the antenna, and determines whether or not to communicate normally with the tag based on the distance.

The so-called near-field and far-field are defined based on the relationship between the communication distance and the wavelength of the wireless signal. Let r be the distance between the antenna and the receiving point, λ is the wavelength of the transmitted signal, =c/f, Where c = 3 x 10 ⁸ m / s, f is the communication frequency. In a nutshell, when r is at the same order of magnitude as λ, it is considered to be near-field, and Γ» λ is considered to be far-field. For a simple antenna, the electric field expression is a superposition of 1 / r, 1 / r ² and 1 / r ³ terms. When r is small, the third term plays a major role. When r is relatively large, the first term is dominant, generally the former is the near field, and the latter is the far field.

The boundary between the far and near fields can also be roughly summarized as 3 λ or 2D ² / , where D corresponds to the largest size of the antenna, the former is often used for linear antennas, and the latter is used for planar antennas such as parabolic and horn antennas.

For antennas, the antenna spacing is usually required to be d ≥ λ /2.

2 is a schematic diagram showing the principle of determining the distance by the phase difference of the received signals of the antenna array according to an embodiment of the present invention. As shown in FIG. 2, A, B, and C are three points of the three-point antenna array shown in FIG. 1, and A, B, and C are arranged in a row and are equidistant to form an antenna array. B is the center antenna, and A and C are the peripheral antennas, respectively. D is the position of the label. In this example, it is assumed that the longitudinal length direction of the label is substantially parallel to the longitudinal direction of the A, B, and C antenna arrays. The closer D is to A, B, and C, the greater the difference between the distance from 0 to person and C to the distance from point D to point B. Assuming that the distance between A and B is a, and the distance between B and D is x, the distance difference between AD and BD is y, and the condition y ² +2xy-a ² =0 is satisfied. It can be seen from this formula that as X decreases, y becomes inevitably large.

If the three points A, B, and C are strictly synchronized in time and the same frequency, the time at which the signal transmitted at point D reaches A, B, and C will be different due to the distance, and the gap will be reflected in the reception. On the phase of the signal. The three RF channels at points A, B, and C send the demodulated baseband signal to the baseband processor for processing. The three baseband signals will have a fixed deviation in phase: The phase difference between D->A and D->C points should be [艮 close, and the larger the deviation from the phase difference, the closer the tag is to the array antenna.

Assuming that the RF signal frequency is 2.4 GHz, the RF signal has a wavelength of approximately 12.5 cm. If the label D is at a position 6 cm from point B, the card is in the near field. If the position between the human, B, and C antennas is as shown, the difference between 0->person and 0->B is

((8.48-6) cm/(3*10 ⁸ m/s)) *360*2.4G=71.4 degrees.

If the card retreats further, for example to a position of 10 cm, the above difference will result in ((11.7-10) cm/(3*10 ⁸ m/s)) *360*2.4G=49 degrees.

According to the above principle, the position of the three points of the antenna array is designed, and the transmission power of the tag is controlled so that the amplitude of the signal received by the reader is moderate, and the distance between the tag and the antenna can be determined more accurately. The system can determine if it is communicating with this tag based on the distance.

In one embodiment, the phase difference between D->A and D->C is measured, and when the phase difference is within a certain threshold range, such as greater than 10 degrees, the aforementioned label and reading are determined. The distance of the device is appropriate.

The above is an ideal case where the physical size of the tag is assumed to be small, and the transmitted and received signals are only performed at point D. However, there are some factors that may introduce errors. For example, the label has a certain size and is the same order of magnitude as the measured distance. In addition, if the tag is located in a terminal such as a cell phone, the signal may leak from some unclosed structure at the edge of the terminal, which may make the measured distance inaccurate.

Fig. 3 is a schematic diagram showing the principle of determining the distance by the phase difference of the received signal of the antenna array according to another embodiment of the present invention. Assuming that the size of the label is large, there are three signal transmission points of D1, D2, and D3 as shown in the terminal. Since it is near field communication, it can be considered that the power radiated from three points is basically equivalent. There is a certain phase difference between the signals radiated from these three points.

If D2 is the center of the signal, the D1/D3 radiated signal has a certain phase difference with respect to D2. As shown in Figure 4, the signal received at point A will be the result of a vector superposition of three signal sources.

Suppose the distance between D1--D2, D2--D3 is X, where x is half the width of the phone, then the distance between A and D1 is dl=sqrt (6 ² + (6-χ) ² ), Α The distance from D3 is

D2=sqrt (6 ² + (6+χ) ² ), so the phase of the D1 to A point signal is (( x+dl-8.48 ) cm/ (3*10 ⁸ m/s) ) *360*2.4GHz. The same method can calculate the phase from point D3 to point A.

Take x=3 as an example. H does not signal D2 point to reach the signal phase of point A is 0, then the signal from point D1 reaches the signal phase of point A should be

((3+6.7-8.48) cm/ (3*1 Om/s) ) *360*2.4GHz=35 degrees. The signal from point D3 reaches the signal phase at point A.

((3+10.8- 8.48) cm/(3*10 ⁸ m/s)) *360*2.4 GHz=153 degrees. Then, the phase combination of D1, D2, and D3 reaching the point A signal results in a phase of about 118 degrees. Equivalent to point A receives a signal transmitted from a central source point farther than the position of D2.

Similarly, the signal received at point C is from Dl, D2, and D3, which is equivalent to a signal transmitted from a source point of 9.22 cm from point B and 11 cm from point A and point C. See Figure 5, where

D12 and D23 represent the virtual transmission points of the signal from the tag seen at points A and C, respectively.

Look at the signal received at point B.

As shown in Fig. 6, the signals at points D1 and D3 reaching point B are out of phase with respect to point D2 ((3+6.7-6) cm/(3*10 ⁸ m/s)) *360*2.4 GHz = 107 degrees. The signals at point D1 and point D3 reaching point B are superimposed in phase, and the result of superposition of the signal vector at point D2 to point B is equivalent to the signal transmitted from the source of D22 from 9.125 cm. Based on the above analysis, it can be seen that due to the divergence of a signal in the tag structure, errors in the calculation may result. 2厘米。 The original setting of a label of 6cm, due to the existence of three signal radiation points, the final calculation result is close to 9. 2cm. However, it can also be seen from this calculation that as long as the size of the label (especially the wireless radiation portion) is within a range, the phase difference calculated according to this method can still determine the distance more accurately. For example, the indicator is a communication distance of <4 cm, and a threshold of a phase difference between an AC point and a point B of a label size of not more than 6 cm can be agreed, and the threshold can be calculated according to the case where only one signal source point is 8 cm.

Although three arrayed and equidistant array antennas are employed in the foregoing embodiments, other types of antenna array schemes may be employed, such as a circularly symmetric pattern centered on the center of the circle.

Figure 7 illustrates an antenna array consisting of five antennas. The peripheral antennas A1-A4 are located on a circumference centered on the center antenna B and are circularly symmetric with respect to the center B. In one example, A1-A4 are formed in a square shape; in another example, A1-A4 form a rectangle. The distance of the tag located in the near field of the antenna can be determined based on the phase difference of the signals received by one of the antennas A1-A4 and the antenna B, and whether the tag is off center according to the phase of the signal received by the antennas A1-A4.

Figure 8 illustrates an antenna array consisting of four antennas. The peripheral antennas A1-A3 are located on a circumference centered on the center antenna B and are circularly symmetric with respect to the center B. The distance of the tag located in the near field of the antenna can be determined based on the phase difference of the signals received by one of the antennas A1-A3 and the antenna B, and whether the tag deviates from the center based on the phase of the signal received by the antennas A1-A3.

It should be noted that the foregoing embodiment refers to the use of the same frequency synthesizer and the same sampling clock, the role of which is to ensure that the phase difference of the signals received by the different antennas is substantially only related to the transmission distance of each signal. One of ordinary skill in the art recognizes that the phase difference can be obtained in different ways, so that the intermediate frequency and the ADC are not necessary, such as signals that are received at different times but are delayed calibrated, because the phase difference eliminates errors introduced by the communication system. It is therefore also possible to carry out the treatment using the method and system of the invention, and should also fall within the scope of the invention. It should be noted that the present invention can be applied to near field communication situations including mobile payment, access control, identification, and garage.

Furthermore, the present invention can be applied to various RF I D tags including RFS IM.

It is apparent that there are many variations to the invention described herein, and such variations are not to be construed as a departure from the spirit and scope of the invention. All changes that are obvious to those skilled in the art are therefore intended to be included within the scope of the claims.

Claims

Claim

1. A short-range wireless communication system, comprising:

An antenna array including a center antenna and at least two peripheral antennas centered on the center antenna for receiving signals from tags located in the near field of the antenna array;

The baseband processing unit determines the distance of the tag located in the near field of the antenna based on the phase difference using the received signal, and determines whether to communicate with the tag based on the distance.

2. The system of claim 1 wherein the at least two perimeter antennas and the center antenna are arranged in a row.

3. The system of claim 1, wherein the at least two peripheral antennas are arranged on a circumference centered on the center antenna and are circumferentially symmetric with each other.

4. The system according to claim 1, wherein the baseband processing unit determines a tag distance according to a phase difference between a signal received by one of the at least two peripheral antennas and the center antenna, and according to a phase between the at least two peripheral antennas The difference determines whether the aforementioned label distance is reliable.

5. The system of claim 1 wherein the baseband processing unit utilizes a threshold associated with the size of the wireless radiating portion of the tag to determine the tag distance.

6. The system of claim 1 including a frequency synthesizer for controlling the operating frequencies of the plurality of radio frequency units of the antenna array to be identical; said baseband processing unit issuing the same control signal to control said plurality The radio unit receives the signal at the same time.

7. A short-range wireless communication method, the method comprising receiving a signal from a tag located in a near field of an antenna array using an antenna array comprising a center antenna and at least two peripheral antennas symmetrical about a center antenna, according to different antennas The phase difference of the received signal determines the distance of the tag located in the near field of the antenna, and determines whether to communicate with the tag based on the distance.

8. The method of claim 7, wherein the at least two peripheral antennas and the center antenna are arranged in a row.

9. The method of claim 7, wherein the at least two peripheral antennas are arranged on a circumference centered on the center antenna and are circumferentially symmetric with each other.

10. The method according to claim 7, wherein the step of determining a distance of a tag located in an antenna near field according to a phase difference of signals received by different antennas comprises: according to one of at least two peripheral antennas and a center antenna The phase difference of the received signal determines the tag distance, and determines whether the aforementioned tag distance is reliable based on the phase difference between the at least two peripheral antennas.

The method of claim 7 wherein the step of determining the distance of the tag located in the near field of the antenna based on the phase difference of the signals received by the different antennas utilizes a threshold associated with the size of the wireless radiating portion of the tag to determine the tag distance.