GB2522451A

GB2522451A - A system, method and server for locating and identifying a tag

Info

Publication number: GB2522451A
Application number: GB1401225.6A
Authority: GB
Inventors: Timothy John Hawley-Jones; Anthony Peter Hulbert
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2014-01-24
Filing date: 2014-01-24
Publication date: 2015-07-29
Also published as: GB201401225D0

Abstract

Each RID tag emits an rf electromagnetic signal in response to movement of the tag using a conductive plate, groundplate and electrets. A plurality of receivers provide data to a server that processes the data to determine tag location by time difference of arrival (TDOA), compares this with information concerning the known previous location of the tag and the most probable tag identity is determined corresponding with the known location. Speed may also be determined and used to predict location information for specific tags.

Description

A system, method and server for locating and identifying a tag The invention relates to a system, method and server for locating and identifying a tag emitting an electromagnetic signal.

D

Background

Wireless tracking of a device transmitting an electromagnetic signal is most commonly performed by a device using an internal positioning system to monitor its own location, for example a phone using Global Positioning System (UPS) signals broadcast by a plurality of satellites to detennine its location. This location information is then transmitted wirelessly over either a mobile network or a local area network to a server, which records the information.

Summary of the Invention

In a first aspect, the invention provides a system for locating and identiing tags, each tag arranged to emit an electromagnetic signal in response to movement of the tag, the system comprising: a plurality of receivers arranged to receive signals emitted from the tags; a server, coupled to said plurality of receivers, and arranged to receive data from the plurality of receivers; a database, accessible by the server, arranged to store information corresponding to a known location of each of the tags; wherein the server is arranged to: (i) process the data received from one or more of the plurality of receivers to calculate a position of a tag; (ii) compare the calculated tag position with the information corresponding to the known location of each of the tags; and (iii) when the calculated position corresponds to a known tag location, determining that the located tag is the tag with the knowi location.

In a second aspect, the invention provides a method of locating and identif'ing a tag that is arranged t.o emit an electromagnetic signal in response to movement of the tag, the method comprising: a tag emitting an electromagnetic signal in response to movement of the tag; receiving, at a plurality of receiven, the signal transmitted by the tag; transmitting data corresponding to the received tag signal from each of the plurality of receivers to a server; processing, at the server, the data received from the plurality of receivers to calculate a position of the tag; comparing the calculated tag position with information corresponding to a plurality of knoi locations of a plurality of tags at the server; and determining that the located tag is the tag with the known location when the calculated position corresponds to a known tag location at the server.

In a third aspect, the invention provides a server for locating and identifying a tag, wherein the tag is arranged to emit an electromagnetic signal, and the server is arranged to: receive information corresponding to a received lag signal from a plurality of receivers; process the data received from the plurality of receivers to calculate a position of the tag; compare the calculated tag position with information corresponding to a plurality of known locations of a plurality of tags; and determine that the located tag is the tag with the known location when the calculated position corresponds to a known tag location.

Further features of embodiments of the invention are recited in the appended claims.

Brief Description of the Drawings

Embodiment so the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a system in accordance with a first embodiment of the invention; Figure 2 is a flow chart illustrating the server steps when receiving information; 2$ Figure 3 is a flow chart illustrating the server steps after receiving information; Figure 4 is a schematic diagram of one of the receivers from Figure 1; Figure 5 is a schematic diagram of a receiver arrangement according to a further embodiment of the invention; Figure 6 is a perspective diagram of the tag shown in Figure 1; Figure 7 is a side-view diagram of the tag shown in Figure 6 in operation; Figure 8 is a further side-view diagram of the tag shown in Figure 6 in operation; Figure 9 is a further side-view diagram of the tag shown in Figure 6 in operation; and Figure 10 is a further side-view diagram of the tag shown in Figure 6 in operation.

Detailed Description of Embodiments of the Invention Figure 1 shows a system comprising a tag 1, wherein the tag 1 is arranged to emit an electromagnetic signal when moved. The precise construction and operation of the tag is not relevant to the understanding of this embodiment of the invention. However, in this embodiment the signal emitted by tag I. is not distinguishable from other similar tags, An example of a tag suitable for use in this embodiment is described in the applicants co-pendin.g UK patent application number 1300927.9. Such a tag will be described in more detail below.

The system also includes four receivers 10, 11, 12, 13. The receivers 10, Ii, 12, 13 are arranged to receive the electromagnetic signal emitted by the tag I. In other embodiments, there may be more or fewer than four receivers. As will be described in more detail below, the system uses Time Difference of Arrival (TDOA) techniques to determine the location of a tag.

In order to accurately locate a tag in three dimensions, four receivers are required, as would be understood by a person skilled in the art. However, three receivers may suffice for location in two dimensions. Additional receivers may improve the accuracy of the system. Each of the receivers 10, 1.1, 12, 13 is coupled to a server 30 and is arranged to transmit information relating to the emitted tag signal that has been received by the receiver to the server 30 over a network 20. In this embodiment, the network 20 comprises a single network connecting each of the receivers 10, 11, 12, 13 to the server 30. The single network may be an internet or the Internet. Additionally, or alternatively, the network 20 may include wired and/or wireless connections spanning one or more individual networks.

The server 30 comprises a processor 31; memory 32, which may be volatile or non-volatile; a data port 33 for communicating with external devices, such as the network 20; non-volatile data storage 34 for storing programs for execution by the processor 31; a database 35; and an internal data bus 36 for transmitting data within the server 30 between its various components.

S The database 35 may be incorporated into the memory 32 or the storage 34, or located on a separate medium either internally of the server 30, or externally of the server. in an embodiment where the database 35 is located externally of the server 30, the server 30 is arranged to connect to the database 35 over either the network 20 or another network.

The embodiment shown in Figure 1 has additional features, which are considered optional.

These include a mobile/cell network 40, a local mobile/cell base station 41 and a mobile/cell phone (or another mobile device) 42. The server 30 may communicate with the mobile handset 42 over (i) the network 20 or (ii) the mobile network 40 using a wireless signal broadcast and received by the mobile base station 41.

In one embodiment, the server 30 is arranged to follow the routine illustrated in Figure 2 to receive data from the receivers 1.0, Ii, 1.2, 13 Figure 2 shows a routine that may be perfonned by the server 30 of Figure 1. The routine may be implemented as a computer program stored in the server's storage 34. The routine starts s2,0 and proceeds to wait s2.l for information to be received from one of the receivers 10, 11, 12, 13. When a receiver 10. 11, 12. 13 receivers a signal from a tag, it generates an IP message that includes a timestamp indicating when the signal was received. When the server 30 receives an IF message from a receiver s2.2, the information is stored s2.3 in memory 32 of the server 30. A timer is started s2,4 and a counter ("responseNo") is incremented s2,5. The timer is checked to determine whether or not it has run for a predetermined amount of time s2.6, If not, the counter ("responseNo") is checked to determine if the number of pieces o LIP messages received from the receivers 10, 11, 12, 13 has reached a predetermined number s2.7. If not, the routine returns to wait s2.l to receive further messages. if either the timer has run for a predetermined amount of time s2.6, or the counter ("responseNo") has received the predetermined number of messages s2.7, the counter ("responseNo") and the timer are reset s2.8, s2,9 and the routine ends s2,l0.

The above-described embodiment limits the number of messages received and the duration over which the messages can be received, In alternative embodiments, either or both the number of messages received and/or the duration over which the messages can he received are not limited by the server.

Figure 3 shows an additional routine that may be performed by the server 30 of Figure 1. The routine may be implemented as a computer program stored in server storage 34. The routine starts s3.0 and proceeds to load information s3.l received from the receivers 10. 11, 12. 13 relating to the detection of a tag 1 signal from the server memory. The server calculates s3.2 a position for the emission of the detected tag signal. This is performed using a time of arrival technique and, preferably, using a multilateration technique, such as Time Difference of Arrival (TDOA) where the difference in time between receipt of the tag emission at three or more receivers 10, II, 12, 13 is compared. Such a method is disclosed in a number of the applicant's UK patents and applications. Other methods for calculating the position of the emitted tag signal known in the art may be used in other embodiments. The database 35 of the server 30 holds information regarding the known locations of a number of tags. The processor 31 compares s3.3 the calculated position with the known tag locations and determines which of the tags is mast lihely to have emitted the tag signal based on the known tag locations. The tag most likely to have emitted the tag signal is associated s3,4 with the calculated location, The new location information for that tag is transmitted to the database 35 where it is stored s3.5. The routine ends s3.6.

The above-described embodiment therefore enables a tag to be located, and further enabks the identity of the tag to be determined using a database of known tag locations, An advantage of this system is that in a system having several tags, where the signal transmitted by each tag is identical for detection purposes, a tag which is moved, and hence caused to emit a signal, can not only be located but also identified, This means that that tags may remain simple devices, which arc not required to transmit a unique identifier. In this sense, the system enables tags have signals which cannot be disambiguated, to be disambiguated, Figure 4 illustrates a schematic diavam of a receiver 50. The receiver 50 is the same as receivers 10, 11, 12, 13, The receiver comprises two antennas Sla, 52a each coupled to a respective receiver 51, 52. The first antenna and receiver 51 a, 51 is tuned to receive an electromagnetic signal emitted by the tag 1. The second antenna and receiver 5Th, 52 are tuned to receive a satellite positioning signal, such as a GPS signal. The second antenna and receiver 52a, 52 are optional. The receiver 50 frirther comprises a processor. 55; memory 56, which may he volatile or non-volatile; a data port 57 for communicating with external devices, such as the network 20; non-volatile data storage 54 for storing programs for execution by the processor 55; and an internal data bus 58 for transmitting data within the receiver 50 between its various components. A wired lead 59 is shown extending from the data port 57, and may connect to a network or the network 20 to couple the receiver 50 to the server 30.

The first antenna and receiver 5*l a, 51 are arranged to detect an emitted tag signal. The time of receipt of the signal and other characteristics of the signal such as the received power, duration., frequency and/or any other information modulated onto the signal are stored in the memory 56. In one embodiment, characteristics of the received tag signal are automatically transmitted to the server 30. In other embodiments, the received signal is evaluated to decide whether or not its characteristics are to be transmitted to the server 30. The evaluation may be based on the characteristics of the received tag signal, such as the tag signal strength, or on other measures, such as the previous rate at which signals had been detected by the receiver 50, The evaluation parameters may be based on a computer program stored in the receiver 50.

The program may be preloaded into the storage 54 when the receiver is initialised.

Alternatively, the evaluation may be based on data transmitted to the receiver 50 by the server 30.

As stated above, the second antenna and receiver 52a, 52 are optional. In an embodiment where the second antenna and receiver 52a, 52 are not present, the location of the receiver 50 is either stored in the receiver storage 54 to be transmitted to the server 30 over the network.

or the location of the receiver 50 is stored in the server storage 30.

The second antenna and receiver 52a, 52 detect the location of the receiver 50. TIns location information may be transmitted to the server 30 when the receiver 50 is initialised, on a regular basis thereafter, or when other information is transmitted to the server 30, such as that relating to a received tag emission. The second antenna and receiver 52a, 52 may provide location information for the receiver 50, For this the receiver will track as many satellites as possible to provide the most accurate geo-Ioeation information. Additionally, the second antenna and receiver 52a. 52 may be used to monitor a clock signal transmitted by a specific satellite, which will provide a highly accurate multilateration system.

Figure 5 illustrates a specific receiver and tag arrangement. The receiver 10, 11. 12, 13 are arranged in an identical pattern to those of Figure 1. The previous location of the tag (with respect to Figure 1) is shown as a cross I. The new location of the tag is shown as a circle 2. It is described above how the receivers 10, 11, 12, 13 detect a first tag signal and transmit the information to the server 30 where a location for the tag is calculated. The calculated location is then compared to known tag locations stored in the database 35 and the calculated location is associated with the most probable tag identity. The calculated tag position is then stored in the database 35 associated with the most probable tag identity.

A second tag signal may he emitted and this will be detected by the receivers 10, 11, 12, 1 3 and one or more characteristics relating to the detected signal will then be transmitted to the server 30. The server will calculate a location for the emission of the second signal in the same manner as described for the first emitted signal. This second calculated signal emission location will be compared to both the known tag locations in the database 35 and to th.e location calculated for the emission of the first signal, which is also stored in the database 35.

If the server calculates that the tag which emitted the first signal is also most probable to have emitted the second signal, the second signal is associated with the same tag and the second emission location is store in the database 35.

The distance between the first and second tag emissions, and the time between the two emission can be used to calculate a speed for the corresponding tag. Further, the locations of the first and second tag emissions, and the time between the two emission can be used to calculate the vector of the corresponding tag.

In one embodiment, the server monitors the speed of a lag and raises an alarm should the speed exceed a predetermined speed. The predetermined speed may be a global value, i.e. identical for all the tags, or a speed for a specific tag. Raising an alarm may comprise merely of flagging the tag as exceeding the speed within the server memory or database 35, Alternatively, an alarm may be raised by the server 30 contacting a party via the mobile network 40 delivering a message to a specific mobile handset 42. In an alternative

S

embodiment, the server monitors how far the tag has moved from its origin, and raises an alarm should the tag exceed a given distance from the origin.

Calcuiating a vector for a tag allows a more accurate prediction of a future rag position and therefore the accuracy in associating a tag to a tag emission can be increased.

An area may be designated wherein if a specific tag either enters or exits, the server raises an alarm as described above.

The tag of the above described system emits an electromagnetic signal, which does not require identifying information to be included in the tag emission for the tag to be tracked.

This is due to the lag identifying and location information being contained within the database.

In another embodiment, the tag is arranged to emit a second type of electromagnetic signal.

The second signal type being of shorter range than the first signal type, but containing information identi'ing the tag. The second signal type may be an Radio Frequency Identification (RFID) signal, wherein the tag is either an active or passive REID device. In this embodiment, One or more of the receivers are adapted to read RFID signals and can therefore identify a tag passing within REID signal range (up to 200 meters for an active or serniactive RFID device operating between 3.1 and 10 0Hz; however, shorter range passive may be used). In this embodiment, a tag may be tracked using (i) the first signal type over a relatively long distance and identified using the tag location database, which may only provide a probably identification of a tag to a tag identified in the location database; and (ii) the second signal type over a relatively short distance, but allowing the tag to be definitively identified and an accurate location recorded in the database. In this embodiment, each receiver may be arranged. to detect either one or both of the first and second type signals emitted by a tag.

Figure 6 is simplified diagram of tag I as shown in Figure 1. Tag 1 is an RE (radio frequency) device. The tag 1 includes an eleetret 60! and a conductive plate 602. The eleetret 601. and the conductive plate 602 are arranged in parallel. The conductive plate 602 is arranged to move between a first position in which it is in contact with the electret 601 and a second position in which it is separated from the elecret 601. In Figure 6. the conductive plate is shown between the first and second positions. The tag I also includes a first contact 603, a second contact 604 and an antenna 605. Both contacts 603, 604 are coupled to the antenna 605. The tag I also includes a resonant circuit, which is not shown in Figure 6. The resonant circuit is also coupled to the antenna 605. The tag I further includes a ground plane 606, to which the electret 601 and the resonant circuit are coupled.

When the tag is physically shaken or moved, the conductive plate 602 moves between the flrst and second positions, The electret 601 is an insulating material with an implanted fixed charge. The electret 601 produces a strong electric field in the area through which the conductive plate 602 moves. As the conductive plate 602 moves, a charge is induced in the plate. In this sense, the conductive plate is an inducer. The conductive plate 602 discharges through the contacts 603, 604, causing the resonant circuit to resonate, and an RI? signal to be transmitted from the antenna 605. All of the energy used to generate the sial is derived from the movement of the tag. No energy is drawn from the electret itself Figure 7 is a more detailed diagram of the tag I shown in Figure 6.All of the components shown in Figure 6 are also shown in Figure 7. In addition, resonant circuit 607 is shown in Figure 7, coupled between the groundplane 606 and the antenna 605. In Figure 7, the conductive plate 602 is shown to be moveable in a direction perpendicular to the plane of the electret 601. However, in alternative embodiments, the conductive plate 602 may move side-to-side or rotate relative to the electret, as will be described in more detail below.

The electret 601 is positioned parallel and adjacent to the groundplane 606. Here, the eletret 601 is positioned in contact with the groundplane 606, and the groundplan.e 606 i.s a metal haek.plate. The electrct 60.1 has an implanted negative charge. There is an. induced positive charge in the groundplane 606. This induced charge is a result of the electret charging process. In Figure 7, the first contact 603 is located close to the electret 601. The second contact 604 is situated close to the conductive plate's second position. When the conductive plate 602 is in the first position, it makes contact with the first contact. 603 and the eleetret 601. When the conductive plate 602 is in the second position, it makes contact with the second contact 604 and is separated from the electret 601.

As noted above, the tag I is designed such that motion of the tag results in the conductive plate 602 moving toward and away front the electret 601. Initially, to a first order approximation, the entire electric field (F-field) is contained within the eiectret 601. The E-field in the electret 601 is dependent on: the charge density, a; the area, A; and the pcrniittivity, a.

C---(1)

The surface voltage of the electret 601 and the groundplane 606 is determined by the charge and the distance of separation between the el.ectret 601 and the groundplane 606.

V=E.d (2) where d is the distance of separation. Is

Figure 8 shows the tag I when the conductive plate 602 is in the first position and is in contact with the eleeret 601 and first contact 603. Charge redistributes between the conductive plate 602 and the groundplane 606 as they have to be at the same potential. Current i flows through the resonant circuit 607 and the antenna 605 radiates energy. Assuming that conductive plate 602 and the groundplane 606 are equidistant from the charge in the ekctret, 50% of the charge is transferred onto the conductive plate 602. Ft should be noted that the conductive plate 602 and the eleetret 601 do not need to make contact. For example, in this embodiment, the conductive plate 602 and the electret 601 may move close to the charged electret, and make contact with the groundplane 606. Such an arrangement would also he effective at charging the condcutive plate 602.

If the direction of motion (of the tag 1) is now reversed, the conductive plate 602 moves away from the electret 601. The charge on the conductive plate 602 is captured as no circuit is made with the groundplane 606. This is shown in Figure 9.

As the motion forces the conductive plate 602 and electret 601 apart, work is being done, The electric field between the conductive plate 602 and the electret 601 remains constant since the captured charge remains constant: ii (3) As described above, the electric field is constant hut the separation (d) is increased.

S Therefore, the voltage on the conductive plate 602 increases since: V=E.d (4) In the second position. the conductive plate 602 contacts with the second contact 604 and makes a circuit with the groundplane 606, as shown in Figure 10. To a first approximation, the charge reverts to the initial state with aU the charge residing in the groundplane 606. The current / that results flows through the resonant circuit and results in radiation from the antenna 605.

The tag I described above requires that a metal struciure (the conductive plate 602) moves close to an clectret (the electret 601) and that additional motion moves the now charged metal away from the electret. Once separated, the metal structure is connected to the groundplane discharging the metal structure, Accordingly, so long as these requirements are met, it is possible to design structures to scavenge energy front different types of motion, for example rotational and sliding motion. The above-described tag is one way in which the tag may be implemented. Other designs may be used to work with the above-described system.

In the above-described embodiments, we refer to known locations'. A known location may be "known' because the tag was knowingly placed in that location, Alternatively, the tag may have a "known' location because the system has located the tag, and hence "knows" it is in a particular location.

It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

Embodiments of the present invention may be implemented in software, hardware, or a combination of software and hardware.

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claimL Li

Claims

CLAIMS: 1. A system for locating and identifying lags, each tag arranged to emit an electromagnetic signal in response to movement of the tag, the system comprising: a plurality of receivers arranged to receive signals emitted from the tags; a server, coupled to said plurality of receivers, and arranged to receive data from the plurality of receivers; a database, accessible by the server, arranged to store information corresponding to a known location of each of the tags; wherein the server is arranged to: (1) process the data received from one or more of the plurality of receivers to calculate a positiDn of a tag; (ii) compare the calculated tag position with the information corresponding to the known location of each of the gs,and (iii) when the calculated position corresponds to a known tag location, determining that the located tag is the tag with the known location.
2. A system according to claim 1, wherein step (iii) further comprises determining if the calculated position is within a predetermined distance of a known location.
3. A system according to claims I or 2, wherein the plurality of' receivers are arranged to record the time of arrival of a received signal.
4. A system according to claim 3, wherein the plurality of receivers are further arranged to generate a message, comprising said time of arrival information, and send the message to the server.
5. A system according to any preceding claim, wherein the plurality of receivers each comprise a clock, the time of each clock being synchronised with timing information provided by a space-based satellite location system.
6, A system according to any of the preceding claims, wherein the data received by the server from one or more of the plurality of receivers does not identit' which of the one or more tags emitted the received electromagnetic signal.
7. A system according to claim 3, wherein the server is arranged to calculate the position of the tag using Time Difference of Arrival (TDOA).
8, A system according to any of the preceding claims, wherein the server is fru'ther arranged to store in the dacabase the calculated tag position as a location for the identified tag.
9, A system according to claim 8, wherein the server is further arranged to receive data from one or more of the Plurality of receivers associated with receipt of a further electromagnetic signal, process the received data to calculate a position of the tag that emitted the signal, compare the calculated tag location to the database locations, and identify a tag that transmitted the signal; and calculate a speed for the tag based on the distance and times between the two locations.
10. A system according to claim 9, wherein the server is further arranged to: predict a tag location using the calculated speed of the tag and the time since the previous tag emission; and compare a calculated tag position with the predicted location information.
ii. A system according to any of the preceding claims, wherein, the server is further arranged to: compare the calculated tag position to a predetermined area and raise an alarm if the calculated position for the associated tag is outside the predetermined area specific to the associated tag.
12. A system according to any of the preceding claims, wherein the electromagnetic signal emitted by the one or more tags is in a frequency range of between 400 MHz and 1 0Hz,
13. A system according to any of the preceding claims, wherein the electromagnetic signal emitted by each of the tags is a first type of electromagnetic signal; one or more of the tags is arranged to emit a second type of electromagnetic signal; the second type of electromagnetic signal is a radio frequency identification (RFID) signal identifying the tag that emitted the RFID signal; the plurality of receivers are arranged to receive the RFID signal and transmit the tag identi'ing information to the server.

I 4. A method of locating and identi'ing a tag that is arranged to emit an electromagnetic signal in response to movement of the tag, the method comprising: a tag emitting an electromagnetic signal in response to movement of the tag; receiving, at a plurality of receivers, the signal transmitted by the tag; transmitting data corresponding to the received tag signal from each of the plurality of receivers to a server; iS processing, at the server, the data received from the plurality of receivers to calculate a position of the tag; comparing the calculated tag position with information corresponding to a plurality of known locations of a plurality of tags at the server,; and determining that the located tag is the tag with the known location when the calculated position corresponds to a known tag location at the server.1 5 A method of identifying a tag according to claim 14, the method further comprising the step of retrieving, from a database, the known locations of the plurality of tags.16. A server for locating and identi'ing a tag, wherein the tag is arranged to emit an electromagnetic signals and the server is arranged to: receive information corresponding to a received tag signal from a plurality of receivers; process the data received from the plurality of receivers to calculate a position of the tag; compare the calculated tag position with information corresponding to a plurality of known locations of a plurality of tags; and determine that the located tag is the tag with the known location when the calculated position corresponds to a]wown tag location.