WO2012044524A1

WO2012044524A1 - Method and reader device for identifying a location of a radio frequency identification (rfid) tag

Info

Publication number: WO2012044524A1
Application number: PCT/US2011/052926
Authority: WO
Inventors: Chandrashekhara Harischandra; Michael J. Koch; Miklos Stern
Original assignee: Symbol Technologies, Inc.
Priority date: 2010-09-28
Filing date: 2011-09-23
Publication date: 2012-04-05

Abstract

A method and device are provided for identifying a location of a radio frequency identification (RFID) tag using a reader device. The method includes determining a first position parameter at a first position of the reader device relative to the RFID tag, and then moving the reader device from the first position to a second position. A location of the second position of the reader device is then determined relative to the first position. Next, a second position parameter at the second position of the reader device relative to the RFID tag is determined. The location of the RFID tag relative to the reader device is then identified using the determined first and second position parameters and the location of the second position of the reader device relative to the first position.

Description

METHOD AND READER DEVICE FOR IDENTIFYING A LOCATION OF A RADIO FREQUENCY IDENTIFICATION (RFID) TAG

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a radio frequency identification (RFID) reader device, and in particular to identifying a location of a RFID tag relative to a location of the reader device.

BACKGROUND

Radio frequency identification (RFID) tags are now widely used to mark, inventory and track various products. RFID tags generally transmit to a reader device a radio frequency (RF) signal that includes product information. RFID tags generally include an integrated circuit for storing and processing information, a transceiver for transmitting and receiving RF signals, and an antenna. Some RFID tags are active RFID tags and include their own battery power source. Passive RFID tags do not have their own power source and require receiving a power signal from the reader device to operate. For interrogating passive RFID tags, a reader generally transmits a continuous wave (CW) or modulated RF signal to a tag. The tag receives the signal and responds by modulating the signal and then "backscattering" an information response signal to the reader device. The reader device receives the response signal from the tag, and the response signal is demodulated, decoded and further processed.

Handheld RFID reader devices are now widely used for identifying, cataloging, and locating various types of objects that are tagged with RFID tags. Such objects include relatively large products such as pallets, boxes, containers and big parts or components; and relatively small products such as fasteners, electronic components, and small parts that are stored in bins with large numbers of similar parts. However, it is sometimes difficult to identify a location of a desired object visually relative to an RFID reader device when numerous similar objects surround the desired object. There is therefore a need for an improved method and reader device for identifying a location of an RFID tag. BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.

FIG. 1 is a system diagram illustrating an environment where RFID reader devices communicate with an exemplary population of RFID tags, according to an

embodiment of the present disclosure.

FIG. 2 is a block diagram illustrating some elements of an RFID reader device, according to an embodiment of the present disclosure.

FIG. 3 is a close-up perspective view of a handheld RFID reader device, according to an embodiment of the present disclosure.

FIG. 4 is a diagram illustrating relative positions between an RFID tag, a reader device, and two measurement positions mi and m,₂, according to an embodiment of the present disclosure.

FIG. 5 is a diagram illustrating, using angle of arrival measurement techniques, the relative positions between an RFID tag at a position T, and a reader device at two measurement positions mi and w,₂, according to an embodiment of the present disclosure.

FIG. 6 is a diagram illustrating a graphical display shown to a user on a display screen of a reader device, according to an embodiment of the present disclosure.

FIG. 7 is a flow diagram illustrating a method for identifying a location of an RFID tag using a reader device, according to an embodiment of the present disclosure.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.

The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION

According to some embodiments of the present disclosure, a method is provided for identifying a location of a RFID tag using a reader device. The method includes determining a first position parameter, such as an angle or distance, at a first position of the reader device relative to the RFID tag, and then moving the reader device from the first position to a second position. Using, for example, an accelerometer in the reader device, a location of the second position of the reader device is then determined relative to the first position. Next, a second position parameter at the second position of the reader device relative to the RFID tag is determined. The location of the RFID tag relative to the reader device is then identified using the first position parameter, the location of the second position of the reader device relative to the first position, and the second position parameter. For example, a graphical representation of the relative location of the RFID tag can be displayed on a display screen of the reader device.

Embodiments of the present disclosure thus enable a RFID reader device to effectively "triangulate" a relative position of an RFID tag using only a single antenna in the reader device. Identifying a position of a particular RFID tag relative to, for example, a handheld reader device can be very advantageous, as it can enable quick location and observation of tagged items that may otherwise be difficult to locate when grouped among similar items.

Before describing embodiments of the present disclosure in detail, it is helpful to describe an example of an RFID communications environment in which the invention may be implemented. FIG. 1 is a system diagram illustrating an environment 100 where RFID reader devices 104 communicate with an exemplary tag population 120. As shown in this example, the tag population 120 includes seven tags 102a-102g; however, the tag population 120 may include any number of tags 102.

The environment 100 may include any number of one or more reader devices 104. For example, the environment 100 includes a first reader device 104a and a second reader device 104b. An external application may request reader devices 104a and/or 104b to address the population of tags 120. Alternatively, reader device 104a and/or reader device 104b may have internal logic that initiates communication, or may have a trigger mechanism that an operator of a reader device 104 uses to initiate

communication. Reader devices 104a and 104b may also communicate with each other in a reader network.

As shown in FIG. 1, reader device 104a transmits an interrogation signal 110a having a carrier frequency to the population of tags 120. Reader device 104b transmits an interrogation signal 110b having a carrier frequency to the population of tags 120. Reader devices 104a and 104b typically operate in one or more of the frequency bands allotted for this type of RF communication. For example, frequency bands of 902-928 MHz and 2400-2483.5 MHz have been defined for certain RFID applications by the United States Federal Communication Commission (FCC).

Various types of tags 102 may be present in tag population 120 that transmit one or more response signals 112 to an interrogating reader device 104, including by alternately reflecting and absorbing portions of signal 110 according to a time -based pattern or frequency. This technique for alternately absorbing and reflecting signal 110 is referred to herein as backscatter modulation. Reader devices 104a and 104b receive and obtain data from response signals 112, such as an identification number of the responding tag 102. In the embodiments described herein, a reader may be capable of communicating with RFID tags 102 according to any suitable communication protocol, including Class 0, Electronic Product Code (EPC) Gen 2, International Organization for Standardization/International Electrotechnical Commission

(ISO/IEC) 18000-6, other binary traversal protocols and slotted aloha protocols, any other protocols mentioned elsewhere herein, and future communication protocols. FIG. 2 is a block diagram of an example RFID reader device 104. The reader device 104 includes an antenna 202, a receiver and transmitter portion 220 (also referred to as transceiver portion 220), a processor 212, and a network interface 216. These components of the reader device 104 may include software, hardware, and/or firmware, or any combination thereof, for performing their functions. For example, the reader device 104 may be a handheld reader device 104 comprising only one antenna 202.

The processor 212 and the network interface 216 are optionally present in the reader device 104. The processor 212 may be present in the reader device 104, or may be located remote from the reader device 104. For example, in an embodiment, the network interface 216 may be present in the reader device 104, to communicate between the transceiver portion 220 and a remote server that includes the processor 212. When the processor 212 is present in the reader device 104, the network interface 216 may be optionally present to communicate between the processor 212 and a remote server. In another embodiment, the network interface 216 is not present in the reader device 104. The processor 212 also processes computer readable program code components stored in a memory 226 of the reader device 104 to implement various methods and functions of the reader device 104 as described herein.

In one embodiment, the reader device 104 includes the network interface 216 to interface the reader device 104 with a communications network 218. As shown in FIG. 2, the processor 212 and the network interface 216 communicate with each other via a communication link 222. The network interface 216 is used to provide an

interrogation request 210 to the transceiver portion 220 (optionally through processor 212), which may be received from a remote server coupled to the communications network 218. The processor 212 optionally processes the data of interrogation request 210 prior to being sent to the transceiver portion 220. The transceiver portion 220 transmits the interrogation request via the antenna 202.

The reader device 104 includes the antenna 202 for communicating with tags 102 and/or other reader devices 104. The antenna 202 may be any type of reader antenna known to persons skilled in the relevant art, including, but not limited to, a dipole, loop, Yagi-Uda, slot, or patch antenna type. For description of an example antenna suitable for reader device 104, refer to U.S. Patent 7,551,140, titled "Low Return Loss Rugged RFID Antenna," issued 23 June 2009, which is incorporated by reference herein in its entirety.

The transceiver portion 220 receives a tag response via the antenna 202. The transceiver portion 220 outputs a decoded data signal 214 generated from the tag response. The network interface 216 is used to transmit decoded data signal 214 received from the transceiver portion 220 (optionally through the processor 212) to a remote server coupled to the communications network 218. The processor 212 optionally processes the data of decoded data signal 214 prior to being sent over the communications network 218.

In some embodiments, the network interface 216 enables a wired and/or wireless connection with the communications network 218. For example, the network interface 216 may enable a wireless local area network (WLAN) link (including an Institute of Electrical and Electronics Engineers (IEEE) 802.11 WLAN standard link), a

BLUETOOTH (Registered Trademark) link, and/or other types of wireless communication links. The communications network 218 may be a local area network (LAN), a wide area network (WAN) (e.g. the Internet), and/or a personal area network (PAN).

In various embodiments, a variety of mechanisms may be used to initiate an interrogation request by the reader device 104. For example, an interrogation request may be initiated by a remote computer system/server that communicates with the reader device 104 over the communications network 218. Alternatively, the reader device 104 may include a finger-trigger mechanism, a keyboard, a graphical user interface (GUI), and/or a voice activated mechanism with which a user of the reader device 104 may interact to initiate an interrogation by the reader device 104.

In the example of FIG. 2, the transceiver portion 220 includes a RF front-end 204, a demodulator/decoder 206, and a modulator/encoder 208. These components of the transceiver portion 220 may include software, hardware, and/or firmware, or any combination thereof, for performing their functions. An example description of these components is provided as follows. The modulator/encoder 208 receives the interrogation request 210, and is coupled to an input of RF front-end 204. The modulator/encoder 208 encodes interrogation request 210 into a signal format, modulates the encoded signal, and outputs the modulated encoded interrogation signal to RF front-end 204. For example, pulse- interval encoding (PIE) may be used in an EPC Gen 2 protocol embodiment.

Furthermore, double sideband amplitude shift keying (DSB-ASK), single sideband amplitude shift keying (S SB- ASK), or phase-reversal amplitude shift keying (PR- ASK) modulation schemes may be used in an EPC Gen 2 protocol embodiment. Note that in an embodiment, the processor 212 may alternatively perform the encoding function of the modulator/encoder 208.

The RF front-end 204 may include one or more antenna matching elements, amplifiers, filters, an echo-cancellation unit, a down-converter, and/or an up-converter. The RF front-end 204 receives a modulated encoded interrogation signal from the modulator/encoder 208, up-converts (if necessary) the interrogation signal, and transmits the interrogation signal to the antenna 202 to be radiated. Furthermore, the RF front-end 204 receives a tag response signal through the antenna 202 and down- converts (if necessary) the response signal to a frequency range amenable to further signal processing.

The demodulator/decoder 206 is coupled to an output of the RF front-end 204, receiving a modulated tag response signal from the RF front-end 204. In an EPC Gen 2 protocol environment, for example, the received modulated tag response signal may have been modulated according to amplitude shift keying (ASK) or phase shift keying (PSK) modulation techniques. The demodulator/decoder 206 demodulates the tag response signal. For example, the tag response signal may include backscattered data formatted according to FM0 or Miller encoding formats in an EPC Gen 2 protocol embodiment. The demodulator/decoder 206 outputs decoded data signal 214. Note that in one embodiment, the processor 212 may alternatively perform the decoding function of the demodulator/decoder 206.

The configuration of the transceiver portion 220 shown in FIG. 2 is provided for purposes of illustration, and is not intended to be limiting. The transceiver portion 220 may be configured in numerous ways to modulate, transmit, receive, and demodulate RFID communication signals, as is known to persons skilled in the relevant art(s).

The reader device 104 may further include an inertial locationing unit (ILU), which may include an accelerometer 224, such as a built-in three-axis accelerometer, as known in the art, or similar device, which is sensitive to general hand initiated movement of the reader device 104. According to some embodiments, the ILU may also include a gyroscope (not shown), compass, or other rotation sensors to provide rotation data. Also, the memory 226 may store operating code (OC) for the processor 212 and code for performing functions associated with an RFID reader device. For example, the memory 226 can store computer readable program code components configured to cause execution of a method for identifying a location of an RFID tag using a reader device, as described herein.

The present disclosure is applicable to any type of RFID tag. It will be recognized by persons skilled in the relevant art(s) that tags 102 may include any number of modulators, demodulators, charge pumps, and antennas. Tags 102 may additionally include further elements, including an impedance matching network and/or other circuitry.

Embodiments described herein are also applicable to tag "inlays" and "labels." A "tag inlay" or "inlay" is defined as an assembled RFID device that generally includes an integrated circuit chip (and/or other electronic circuit) and antenna formed on a substrate, and is configured to respond to interrogations. A "tag label" or "label" is generally defined as an inlay that has been attached to a pressure sensitive adhesive (PSA) construction, or has been laminated, and cut and stacked for application. One form of a "tag" is a tag inlay that has been attached to another surface, or between surfaces, such as paper, cardboard, etc., for attachment to an object to be tracked, such as an article of clothing, etc.

Example embodiments of the present disclosure are described in further detail below. Such embodiments may be implemented in the environments, reader devices, and tags described above, and/or in alternative environments and alternative RFID devices. FIG. 3 is a close-up perspective view of a handheld RFID reader device 104, according to an embodiment of the present disclosure. As shown, the handheld reader device 104 may further include a display screen 305, a keypad 310, and/or an optical barcode reader 315. A user's hand 320 is illustrated as gripping a triggering mechanism of the device 104.

As an example embodiment of the present invention, use of a handheld reader device 104 for locating a particular tag 102 in the environment 100 is described below in detail. First, consider that the user seeks to identify a location of a particular item that has been tagged with RFID tag 102c. After identifying the tag 102c, such as by entering a serial number of the tag 102c into the keypad 310 of the device 104, the user points the reader device 104 at the environment 100 that includes the tag 102c and transmits a signal from the reader device 104 to the tag 102c. The tag 102c is then activated by the signal and responds by "backscattering" an information response signal to the reader device 104.

A user may also point the reader device 104 towards a group of tagged items, pull a trigger on the reader device 104 and record all the tags 102 within the reader device's field of view. The user may also waive the reader device 104 around in order to increase the probability that all tags 102 within range are effectively read.

According to some embodiments of the present invention, there are at least two ways to determine the location of a tag 102 using a single reader device 104. One approach is to estimate the distance between the reader device 104 and the tag 102 when the reader device 104 is in two or more positions. The other is to measure an angle between the reader device 104 and the tag 102, again with the reader device 104 in two or more positions. In both approaches, at least one relative position parameter at the two or more reader positions is measured. For example, there are several possible ways to inertially determine the relative positions of the reader device 104. One possibility is to use accelerometers in three orthogonal axes, and gyroscopes in two orthogonal angular directions. Another possibility is to use a three axes gyroscope with two axes accelerometers. Accelerometers alone can be confused under circumstances where the reader device 104 is also rotated during translational movement. In order to obtain an accurate estimate of the relative distance between reader positions, angular motion sensing devices also can be used.

FIG. 4 is a diagram illustrating, using distance measurement techniques, the relative positions between the tag 102c at a position T, the reader device 104 at position R, and two measurement positions ni\ and m,₂, according to an embodiment of the present disclosure. For example, consider that the user first holds the reader device 104 about one foot to his or her left, at position mi, and determines the distance a between mi and the tag 102c. For example, based on the signaling between the reader device 104 and the tag 102c, those skilled in the art will recognize that such measurement determinations can be made by various known techniques, such as received signal strength indication (RSSI) techniques, phase frequency techniques, and other well- known techniques to determine a distance. Phase frequency techniques are described in detail in US patent no. 7,119,738 to Bridgelall et al, which patent is hereby incorporated by reference herein in its entirety. Assuming that the tag 102c is located somewhere in a horizontal plane in front of the user, based solely on the distance a between mi and the tag 102c, it can be determined that the tag 102c is located somewhere along an arc 405.

Next, consider that the user moves the reader device 104 from the first position mi to a second position m₂ located about 1.5 feet to his or her right, and determines a distance b between m₂ and the tag 102c. Based solely on the distance b between m₂ and the tag 102c, it can be determined that the tag 102c is located somewhere along an arc 410. The actual position of the tag 102c in a horizontal plane is then known to be at the intersection of the arc 405 and the arc 410. Finally, the reader device 104 is moved back in front of the user at position R.

Based on the movement of the reader device 104, double integration of data from the accelerometer 224, or similar device, augmented for example with data obtained from a gyroscope in the reader device 104, as is well known in the art, can be used to provide the distance / between mi and m₂. Assuming again a two-dimensional example where the tag 102c and all movements of the reader device 104 occur in a horizontal plane, triangulation and basic trigonometry then can be used to determine a relative position of the reader device 104 and the tag 102c. For example, the following equations can be used to calculate a distance r between the reader device 104 and the tag 102c, and an angle Θ that points to the tag 102c. First, a distance x between a perpendicular line d and position ni₂ can be calculated as follows using the Pythagorean Theorem for two right triangles: d² + (/ - x)² =a² Eq. 1 d² + X ² = b² Eq. 2 Subtracting the two equations and solving for x provides: l² + b² - a²

x = Eq. 3

21

Substituting in Equation 2 above for x provides:

Next, considering that position m; is the origin of our coordinate system with coordinates (0, 0), and given /, x, and d, the coordinates of point Ί{χ_τ, yr) with respect to the position mi can be determined. In particular, the coordinates are T(l-x, d). Because the coordinates of point R(X_R, J¾) are known from the

accelerometer/gyroscope data, the distance r and angle Θ between points R and T can be determined as follows:

Θ = tan^"1 y_T - y_R

Eq. 6

FIG. 5 is a diagram illustrating, using angle of arrival measurement techniques, the relative positions between the tag 102c at a position T, and the reader device 104 at two measurement positions mi and m,₂, according to an embodiment of the present disclosure. For example, consider that the user first holds the reader device 104 about one foot to his or her left, at position mi, and determines a distance angle ψ between a reference direction at mi and the tag 102c. The reference direction can be

conveniently aligned along the length of the reader device 104, but can be determined in various other ways as well. Assuming that the tag 102c is located somewhere in a horizontal plane in front of the user, based solely on the distance angle ψ between mi and the tag 102c, it can be determined that the tag 102c is located along the line 415 extending from mi along the angle ψ.

Next, consider that the user moves the reader device 104 from the first position mi to a second position m2 located about 1.5 feet to his or her right, and determines an angle between the reference line in the reader located at m2 and the tag 102c. Based solely on the angle between m2 and the tag 102c, it can be determined that the tag 102c is located somewhere along the line 420. The actual position of the tag 102c in a horizontal plane is then known to be at the intersection of the line 415 and the line 420.

Based on the movement of the reader device 104, double integration of data from the accelerometer 224, or similar device, augmented with data obtained from a gyroscope in the reader device 104, as is well known in the art, can be used to provide the coordinates of the reader device 104 at m2. For convenience, the origin of the coordinate system is located at position mi, and the y-axis is along the reference direction chosen at mi, while the x-axis is perpendicular to the y-axis. Assuming again a two-dimensional example where the tag 102c and all movements of the reader device 104 occur in a horizontal plane, the following approach can be used to determine a relative position of the reader device 104 and the tag 102c. For example, the loci of the points along a line in general can be determined from the following equation: y - y₀ = m(x - x₀ ) , _Eq. 7 where m is the slope of the line with respect to the x-axis of the coordinate system. For line 415 the slope is mi and it is equal to tan(90 degrees - ψ. For line 415, yo = xo = 0, since the line 415 passes through the origin by construction. Line 420 follows a similar equation, but with different constants, such that: y - y = m₂ (x - x₂ ) , Eq. 8 which is the equation of a line passing through a point (x₂,y₂) with slope m₂. The slope of the line 420 is then determined with respect to the x-axis. An inertial locationing unit, which may include the accelerometer 224, provides the angle for the direction of the new reference at m,₂ with respect to the original reference direction at mi, which is chosen to be the y-axis. The reader device 104 provides the angle between a new reference axis and the tag location using angle-of-arrival techniques. The angle between the original reference axis and the line 420 is: β = δ - γ Eq. 9

The slope m₂ is negative in the example shown in FIG. 5. Whether the slope m₂ is positive or negative can be automatically detected based on the sign and magnitude of the angles and γ. In practice, an algorithm can check for all different variations of such signs and magnitudes. Given the simple example shown in FIG. 5, the angle and in turn the slope m₂ can be calculated as shown below:

^ = 180^° - (90^° - /?) = 90^° + /? _Eq. io m₂ = - tan(l 80^° - φ) = - tan(90^° - β) _Eq. 11

By construction, the two lines 415, 420 intersect at the same coordinate point (x_T, y_T), which is the location of the tag 102c to be located. Hence, the equations for the two lines 415, 420 are equated and the resulting equation for x is solved, obtaining:

m_x = tan(90^° - ψ) Eq. 13 m₂ = - tan(90^° + γ - δ) Eq. 14

Using x, one can substitute in one of the equations for the line 415 or the line 420, and obtain the coordinates of the tag 102c at (x_T, y_T). With the knowledge of those coordinates, it is straightforward to determine the location of the tag 102c with respect to mi, ni₂, or any other known reader location, as explained in the first example above that uses a distance measurement method to locate the tag 102c.

Various alternative techniques can be used to determine the relative x-y position of m; and ni₂ using data from the accelerometer 224. For example, such alternative techniques include time of arrival techniques, time difference of arrival techniques, frequency domain techniques, and orthogonal frequency division multiplexing (OFDM) techniques. Based on the movement of the reader device 104, and data from the accelerometer 224, attributes of phase, frequency, or time can be used to uniquely solve the coordinates of point Ί{χ_τ, yr) with respect to the position of the reader device 104.

FIG. 6 is a diagram illustrating an example of a graphical display shown to a user on the display screen 305 of the reader device 104, according to an embodiment of the present disclosure. In particular, an identification of the location of the tag 102c relative to the reader device 104 is displayed on a display screen 305 of the reader device 104. For example, referring again to the circumstances described above in relation to FIG. 4, the display screen 305 may graphically display various icons 500 that represent the relative locations of the various tags 102 in the environment 100. The display screen 305 thus comprises a map that includes a plurality of icons 500 illustrating a location of the RFID tag 102c relative to another RFID tag 102, or relative to a known position.

Using the techniques described herein, the relative locations of a plurality of tags 102 can be determined simultaneously. For example, the relative locations of all the various tags 102 can be determined by a sequential or simultaneous reading of each of the various tags 102 by the reader device 104 using the above-described techniques and the above equations. The display screen 305 further includes a line 505 that indicates relative two-dimensional positions of the user, the reader device 104, the position mi and the position m,₂.

The identification of the location of a tag 102 relative to the reader device 104 may comprise the display of a vector including a distance value and at least one angle value. For example, a vector 510 is displayed to indicate an angle Θ, such as 70 degrees, and a distance value, such as 5 feet, between the reader device 104 and the tag 102c. A search box 515 is also shown, which may enable a user to search for tagged items using various criteria such as, for example, serial number, item name, brand, size, or various other identifiers. In addition, a search box 520 can be used to display search entries provided by a user.

Thus, the icons 500 and the vector 510 can be used to display relative two- dimensional locations of the reader device 104 and various tagged items using the techniques described and illustrated with reference to FIG. 4. For example, such items may include stacked boxes, parts or components piled in a large container, or various other conglomerations of items. Further, according to an alternative embodiment, those skilled in the art will appreciate that the display screen 305 may also be used to illustrate three-dimensional relative locations of the reader device 104 and various tagged items. In that case, a distance is determined between the reader device 104 and a known third position, ni₃ (not shown), where ni₃ is not on a line connecting mi and m,₂. Basic trigonometry then can be used to determine the relative three-dimensional locations of the reader device 104 and the tag 102c. The

calculations are similar to the two-dimensional case outlined above, but

understandably more complicated due to the three dimensional nature of the problem.

FIG. 7 is a flow diagram illustrating a method 700 for identifying a location of an RFID tag using a reader device, according to an embodiment of the present disclosure. At step 705, a first position parameter is determined at a first position of the reader device relative to the tag. For example, the distance a shown in FIG. 4 at mi relative to tag 102c is determined. Alternatively, the angle

in FIG. 5 between a reference direction of the reader device 104 and the line 405 connecting mi and the tag 102c is determined. At step 710, the reader device is moved from the first position to a second position. For example, the reader device 104 is moved from position mi to position m,₂, as shown in FIG. 4.

At step 715, a location of the second position of the reader device relative to the first position is determined. For example, the distance / between position mi and position ni₂, as shown in FIG. 4, is determined.

At step 720, a second position parameter at the second position of the reader device relative to the tag is determined. For example, the distance b shown in FIG. 4 between m,₂ and tag 102c is determined. Alternatively, the angle shown in FIG. 5 between a reference direction of the reader device 104 and the line 410 connecting m,₂ and the tag 102c is determined.

At step 725, the location of the tag relative to the current position of the reader device is identified using the first position parameter, the location of the second position of the reader device relative to the first position, and the second position parameter. For example, the location of the tag 102c relative to the reader device 104 is identified and then displayed on the display screen 305, as shown in FIG. 6. As shown in FIG. 4, a final viewing position R of the reader device 104 may be different from both position mi and position m₂.

Alternatively, the method 700 can be modified such that a three dimensional location of the tag relative to the reader device can be identified. In that case, the reader device is moved from the second position to a third position. A location of the third position of the reader device is then determined relative to the second position.

Finally, a position parameter is determined at the third position of the reader device relative to the tag.

Advantages of some embodiments of the present disclosure therefore include enabling an RFID reader device to effectively "triangulate" a relative position of an RFID tag using only a single antenna in the reader device. Such a relative position then can be employed, such as through the use of a graphical user interface or display screen of the device, to assist a user in quickly identifying or finding a particular tagged object or locating all items in an inventory. In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. For example, determining the location of the second position of the reader device relative to the first position may alternatively use data received from an ultra wide band (UWB) system used to locate the reader device. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present teachings. The benefits, advantages, solutions to problems, and any

element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," "has", "having," "includes", "including," "contains", "containing" or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, or contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by "comprises a ...", "has a ...", "includes a ...", or "contains a ..." does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, or contains the element. The terms "a" and "an" are defined as one or more unless explicitly stated otherwise herein. The terms "substantially", "essentially", "approximately", "about" or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1% and in another embodiment within 0.5%. The term "coupled" as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

It will be appreciated that some embodiments may be comprised of one or more generic or specialized processors (or "processing devices") such as microprocessors, digital signal processors, customized processors and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the method and system described herein. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used.

Moreover, an embodiment can be implemented as a computer-readable storage medium having computer readable code stored thereon for programming a computer (e.g., comprising a processor) to perform a method as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a read only memory (ROM), a programmable read only memory (PROM), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM) and a flash memory. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

We claim:

1. A method for identifying a location of a radio frequency identification (RFID) tag using a reader device, the method comprising:

determining a first position parameter at a first position of the reader device relative to the RFID tag;

moving the reader device from the first position to a second position;

determining a location of the second position of the reader device relative to the first position;

determining a second position parameter at the second position of the reader device relative to the RFID tag; and

identifying the location of the RFID tag relative to the reader device using the first position parameter, the location of the second position of the reader device relative to the first position, and the second position parameter.

2. The method of claim 1, further comprising:

moving the reader device from the second position to a third position;

determining a location of the third position of the reader device relative to the second position; and

determining a third position parameter at the third position of the reader device relative to the RFID tag;

whereby a three dimensional location of the RFID tag relative to the reader device is identified.

3. The method of claim 1, wherein the first and second position parameters comprise distances or angles.

4. The method of claim 1, further comprising displaying an identification of the location of the RFID tag relative to the reader device on a display screen of the reader device.

5. The method of claim 4, wherein the identification of the location of the RFID tag relative to the reader device displayed on the display screen comprises a vector including a distance value and at least one angle value.

6. The method of claim 4, wherein the display screen comprises a map that includes a plurality of icons illustrating a location of the RFID tag relative to another RFID tag or relative to a known position.

7. The method of claim 1, wherein determining the location of the second position of the reader device relative to the first position uses data received from an inertial locationing unit of the reader device.

8. The method of claim 1, wherein determining the location of the second position of the reader device relative to the first position uses data received from an ultra wide band system used to locate the reader device.

9. The method of claim 1 , wherein determining the first position parameter and determining the second position parameter use at least one of the following techniques: received signal strength indication (RSSI) techniques; time of arrival techniques, time difference of arrival techniques, angle of arrival techniques, frequency domain techniques, phase frequency techniques, and orthogonal frequency division multiplexing (OFDM) techniques.

10. The method of claim 1, wherein the reader device is a hand held reader device comprising only one antenna.

11. The method of claim 1 , wherein the relative locations of a plurality of RFID tags are determined simultaneously.

12. A radio frequency identification (RFID) reader device, comprising:

a processor;

a transceiver portion operatively coupled to the processor;

an inertial locationing unit operatively coupled to the processor; and a memory operatively coupled to the processor, wherein the memory includes: computer readable program code components for determining, based on data received from the transceiver portion, a first position parameter at a first position of the reader device relative to a RFID tag;

computer readable program code components for determining, based on data received from the inertial locationing unit, a location of a second position of the reader device relative to the first position;

computer readable program code components for determining, based on data received from the transceiver portion, a second position parameter at the second position of the reader device relative to the RFID tag; and

computer readable program code components for identifying a location of the RFID tag relative to the reader device using the first position parameter, the location of the second position of the reader device relative to the first position, and the second position parameter.

13. The RFID reader device of claim 12, further comprising:

computer readable program code components for determining a location of a third position of the reader device relative to the second position; and

computer readable program code components for determining a third position parameter at the third position of the reader device relative to the RFID tag, whereby a three dimensional location of the RFID tag relative to the reader device is identified.

14. The RFID reader device of claim 12, further comprising computer readable program code components for displaying an identification of the location of the RFID tag relative to the reader device on a display screen of the reader device.

15. The RFID reader device of claim 14, wherein the identification of the location of the RFID tag relative to the reader device displayed on the display screen comprises a vector including a distance value and at least one angle value.

16. The RFID reader device of claim 14, wherein the display screen comprises a map that includes a plurality of icons illustrating a location of the RFID tag relative to another RFID tag or relative to a known position.

17. The RFID reader device of claim 12, wherein determining the location of the second position of the reader device relative to the first position uses data received from an accelerometer of the reader device.

18. The RFID reader device of claim 12, wherein determining the first position parameter and determining the second position parameter use at least one of the following techniques: received signal strength indication (RSSI) techniques; time of arrival techniques, time difference of arrival techniques, angle of arrival techniques, frequency domain techniques, phase frequency techniques, and orthogonal frequency division multiplexing (OFDM) techniques.

19. The RFID reader device of claim 12, wherein the reader device is a hand held reader device comprising only one antenna.

20. A reader device, comprising:

means for determining a first position parameter at a first position of the reader device relative to a radio frequency identification (RFID) tag;

means for determining a location of a second position of the reader device relative to the first position;

means for determining a second position parameter at the second position of the reader device relative to the RFID tag; and

means for identifying a location of the RFID tag relative to the reader device using the first position parameter, the location of the second position of the reader device relative to the first position, and the second position parameter.