PARTICULAR IN AN INDOOR ENVIRONMENT, AND METHOD

THEREOF

The present invention relates to a system for locating at least one RFID {“Radio Frequency IDentification ') tag in space, in particular in an indoor environment and a method thereof.

In particular, the present invention relates to a system for identifying in a spatial region (preferably arranged within an indoor environment) the position of one or more RFID tags, each of which can be associated with a product, a person or an animal, so as to identify the position of said product, said person or said animal within said spatial region.

Advantageously, the system and the method for locating an RFID tag, object of the invention, can be useful in the field of automatic identification systems, in which the identification of objects and/or living beings is automated in order to collect information on such objects and/or living beings.

Prior Art

In recent decades there has been a progressive development of identification systems designed to identify assets, people, etc., based on the transmission and reception of radiofrequency signals.

RFID technology is one of the most used technical solutions.

RFID technology allows to obtain information through an RFID system formed by at least one RFID tag or transponder and by a reader that can be configured to read the data contained in the RFID tag and/or to write data on said RFID tags.

Both the RFID tag and the reader are provided with a respective antenna and these antennas make radiofrequency communication between the RFID tags and the reader possible (th electromagnetic waves act as a transport channel for data from the RFID tag to the reader or vice versa).

With reference to the RFID tag, in general, this RFID tag substantially comprises a central processing unit, a memory, a transceiver antenna and a battery.

The RFID tag functions essentially consist of:

- store information relating to a predetermined entity, such as an identification code associated with that entity;

- receive a request for information from the reader; - send to the reader a reply to such a request for information.

With reference to the reader, as already said, the reader is intended to read and/or write data on said RFID tags.

The reader sends a radiofrequency signal and, if the RFID tag is in the receiving area to receive said radiofrequency signal, a bidirectional communication is established between said RFID tag and said reader.

Once a communication is established between the reader and the RFID tag, the reader can read and/or write data on the RFID tag.

The sectors of interest in which an RFID system can be used are numerous.

Below, an RFID system can be used in different areas, such as the monitoring of industrial production, the video surveillance of objects and/or people, the control of structures or environments, or the evaluation of product counterfeiting.

Furthermore, these RFID systems can also be used in the health sector.

The continuous growth of people's life expectancy leads to a consequent increase in chronic and disabling diseases for them.

Flence the need to continuously and non-invasively localize the different patients within appropriate structures, in order to monitor their psychophysical state and take appropriate action.

By way of example, it may be necessary to prevent the movements of a patient towards areas considered "at risk" due to his health, or to check that he is not subject to falls or that he remains in a certain position for prolonged periods of time.

As is known in the health sector, currently, different solutions are in use which provide for the simultaneous presence of multiple receivers, for example receivers of the UWB type {"Ultra Wide Band') capable of receiving large amounts of data from one or more transmitting antennas.

Furthermore, different solutions are used to monitor patients in the host structures (hospitals, nursing homes, etc.).

Flowever, these known solutions have drawbacks.

A first drawback of these known solutions is given by the need to install multiple electronic devices in order to guarantee the correct operation of an identification system.

A second drawback consists in the fact that they provide a processing of data a posteriori, which is expensive in terms of computation, energy and time. A third drawback of these known solutions is the fact that, if they are used in the health sector, it is necessary to request the consent for privacy.

A further drawback of these known solutions is that they do not allow to discriminate or interact with multiple RFID tags arranged in an environment, when said RFID tags are at a reduced distance from each other.

Aim of the invention

The aim of the present invention is to overcome the aforementioned drawbacks, by providing a system and a method for locating an RFID tag in space, in particular in an environment, in order to locate objects and/or living beings, to which a respective RFID tag is associated .

A further object of the invention is to provide a system and a method for locating an RFID tag, with a high precision, in particular in the order of centimeters in an environment with size up to about 20 square meters, in the presence of reflections, fading, etc.

Another aim of the invention is to provide a system and a method for locating an RFID tag in order to monitor objects and/or subjects to which respective tags are associated over time.

This is achieved by means of a system and a method conceived to locate the position of said object/subject, to which an RFID tag is applied, by acquisition, on an azimuth plane and on an elevation plane, perpendicular to said azimuth plane, of power values of a signal received from one or more RFID tags present in a spatial region "read" by said reader, where said power values depend on the position of each RFID tag with respect to said reader, and through the acquisition of the distance between said reader and each RFID tag.

Object of the invention

It is therefore object of the invention a system for locating at least one RFID tag in a spatial region, in particular in an indoor environment, where a respective unique identification code is associated with said RFID tag and said system coprises:

- a reader configured to send/receive a RF signal to/from said RFID tag in said spatial region and comprising:

o a first antenna for sending a first RF signal and receiving a further first RF signal A from said RFID tag, a second antenna for sending a second RF signal and receiving a further second RF signal B from said RFID tag, a third antenna for sending a third RF signal and receiving a further third RF signal C from said RFID tag and a fourth antenna for sending a fourth RF signal and receiving a further fourth RF signal RF D from said RFID tag, where said RF signal sent from said reader is the sum of RF signals sent from each antenna;

o a first phase shifter for shifting the phase of said first RF signal, a second phase shifter for shifting the phase of said second RF signal, a third phase shifter for shifting the phase of said third RF signal, a fourth phase shifter for shifting the phase of said fourth RF signal; o a comparator, connected to each of said antennas and configured to generate a sum signal å = A + B + C + D, a first difference signal D _az = A - B - C + D on the azimuth plane, a second difference signal A _el = A + B - C - D on an elevation plane, perpendicular to said azimuth plane;

o a first logic control unit, connected to each phase shifter, and configured to receive from said RFID tag a power value associated with said RF signal received from RFID tag and said unique identification code and for controlling each phase shifter;

- a processing unit, configured to communicate with said first logic control unit.

In particular, said reader is configured in such a way that, in use, the variation of one or more phases changes the pointing direction of said RF signal sent from reader within said spatial region on said azimuth plane and/or said elevation plane.

Furthermore, said processing unit is configured to:

o create for said RFID a first matrix Mi associated with said sum signal å, a second matrix M2 associated with said first difference signal A _az , and a third matrix M3 associated with said second difference signal A _el , where each element of each matrix is a power value of the respective RF signal received by said RFID tag depending on a respective position of said RFID tag with respect to the pointing direction of the RF signal sent from said reader;

o calculate a first difference matrix MDI given by the difference between said first matrix Mi and said second matrix M2 and a second difference matrix MD2 given by the difference between said first matrix Mi and said third matrix M3;

o determine the maximum power value of said first difference matrix MD-I , associated with a first angular position of said RFID tag on said azimuth plane and the maximum power value of said second difference matrix MD2, associated with a second angular position of said RFID tag on said elevation plane;

o calculate a first distance between said reader and said RFID tag on said azimuth plane by the maximum power value of a predetermined raw of said first matrix Mi, and a second distance between said reader and said RFID tag on said elevation plane by the maximum power value of a predetermined column of said first matrix Mi ;

o determine a first coordinate x and a second coordinate y associated with the position of said RFID tag on said azimuth plane by said first distance and said first angular position, and a third coordinate z associated with the position of said RFID tag on said elevation plane by said second distance and said second angular position of said RFID tag.

Preferred embodiments of the system are defined in the dependent claims.

It is therefore also object of the invention a method for locating at least one RFID tag in a spatial region, in particular in an indoor environment, where a respective unique identification code is associated with said RFID tag and said method coprises the following steps:

A) providing a reader provided with a first antenna, a second antenna, a third antenna and a fourth antenna,

B) sending a RF signal in said spatial region given by the sum of a first RF signal sent through said first antenna, a second RF signal sent through said second antenna, a third RF signal sent through said third antenna, and a fourth RF signal sent through said fourth antenna,

C) shifting the phase of said RF signal and/or the phase of said second RF signal and/or the phase of said third RF signal and/or the phase of said fourth RF signal for shifting the pointing direction of said RF signal within said spatial region, on said azimuth plane and/or on said elevation plane,

D) receiving by said reader a further first RF signal A through said first antenna, a further second RF signal B through said second antenna, a further third RF signal C through said third antenna, a further fourth RF signal D through said fourth antenna,

E) generating a sum signal å = A + B + C + D , a first difference signal D _az = A - B - C + D on an azimuth plane, a second difference signal A _EL = A + B - C - D on an elevation plane, perpendicular to said azimuth plane,

F) receiving by said reader a power value associated with to the RF signal received by said RFID tag, G) creating a first matrix Mi associated with said sum signal å, a second matrix M2 associated with said first difference signal D^ _z , and a third matrix M3 associated with said second difference signal A _EL , where each element of each matrix is a power value of the respective RF signal received by said RFID tag depending on a respective position of said RFID tag with respect to the pointing direction of the RF signal sent from said reader,

FI) calculating a first difference matrix MDI given by the difference between said first matrix Mi and said second matrix M2 and a second difference matrix MD2 given by the difference between said first matrix Mi and said third matrix M3,

I) determining the maximum power value of said first difference matrix MD-I , associated with a first angular position of said RFID tag on said azimuth plane, and the maximum power value of said difference matrix MD2, associated with a second angular position of said RFID tag on said elevation plane,

L) calculating a first distance between said reader and said RFID tag on said azimuth plane by the maximum power value of a predetermined raw of said first matrix Mi, and a second distance between said reader and said RFID tag on said elevation plane by the maximum power value of a predetermined column of said first matrix Mi,

M) determining a first coordinate x and a second coordinate y associated to the position of said RFID tag on said azimuth plane by said first distance and said first angular position, and a third coordinate z associated to the position of said RFID tag on said elevation plane by said second distance and said second angular position of said RFID tag.

Figures list

The present invention will be now described, for illustrative, but not limitative purposes, according to its embodiments, making particular reference to the enclosed figures, wherein:

Figure 1 is a schematic view of a system for locating at least one RFID tag in a spatial region, according to the present invention, configured to identify the position of said at least one RFID tag in said spatial region;

Figure 2 is a block diagram of the reader forming part of the system of Figure 1 ;

Figure 3 is a schematic view of a surface of the reader for showing the antennas which it is provided with;

Figure 4 is a schematic view of a comparator arranged on a further surface of the reader, opposite to the surface on which the antennas are arranged;

Figure 5 is a schematic view of the essential parts of the physical structure of the reader.

Detailed description

In the different figures the similar parts will be indicated with the same numerical references.

Anywhere in this description and in the claims, it is is included the case in which the term "comprises" is replaced by the term "consists of".

With reference to the figures, a system is described for locating at least one RFID tag in space, in particular in an indoor environment, where a respective unique identification code is associated with said RFID tag.

Said system 1 comprises:

- a reader 2 configured to send/receive a RF {“Radio Frequency’) signal to/from said RFID tag 3 (in order to read or read and write data on said RFID tag) in a spatial region or “spatial region to be read” and comprises:

o a first antenna 21 A for sending a first RF signal and receiving a further first RF signal A from said RFID tag 3, a second antenna 21 B for sending a second RF signal and receiving a further second RF signal B from said RFID tag 3, a third antenna 21 C for sending a third RF signal and receiving a further third RF signal C from said RFID tag 3 and a fourth antenna 21 D for sending a fourth RF signal and receiving a further fourth RF signal RF D from said RFID tag 3;

o a first phase shifter 22A for shifting the phase of said first RF signal, a second phase shifter 22B for shifting the phase of said second RF signal, a third phase shifter 22C for shifting the phase of said third RF signal, a fourth phase shifter 22D for shifting the phase of said fourth RF signal;

o a comparator 23, connected to each of said antennas 21 A, 21 B, 21 C, 21 D and configured to generate a sum signal å = A + B + C + D, a first difference signal A _AZ = A - B - C + D on the azimuth plane, a second difference signal A _EL = A + B - C - D on an elevation plane, perpendicular to said azimuth plane;

o a first logic control unit 20A, connected to each phase shifter 22A,22B,22C,22D, and configured to control (indipendentely) each phase shifter 22A,22B,22C,22D.

In the embodiment being disclosed, said system 1 comprises a processing unit 4 (such as a computer or a tablet) which can be used by a user 6, where said processing unit is connected to said first logic control unit 20A of said reader 2, and configured to communicate with said first logic control unit 20A, as well as storage means 5, connected to said processing unit 4, for storing data sent by said reader 2 (which can be data associated with said reader 2 and/or said RFID tag 3).

Although not shown in Figures, said processing unit 4 can be included in said reader 2, without for this reason departing from the scope of the invention.

As an example, the communication between said processing unit 4 and said first logic control unit 20A can be a serial communication of the UART type (“Universal Asynchronous Receiver-Transmitter’).

With particular reference to the RF signal sent by said reader 2 to said RFID tag, said RF signal is the sum of the RF signals sent from each antenna 21 A, 21 B, 21 C, 21 D of the reader itself and the variation of one or more phases (through a respective phase shifter) of a respective RF signal sent by a respective antenna determines the pointing direction of the RF signal sent from reader 2 within said spatial region, on said azimuth plane and/or said elevation plane.

In other words, an irradiated beam, which has an orientation defined by the phases of the respective signals sent by each antenna 21 A, 21 B, 21 C, 21 D both on the azimuth plane and on the elevation plane, is associated with the RF signal sent by said reader 2.

This beam is the combination of the wavefronts of the respective RF signals sent by each antenna 21 A, 21 B, 21 C, 21 D in said spatial region (i.e. "spatial region to be read").

This spatial region corresponds to the region of the space in which said reader 2 is capable of locating each RFID tag 3 present in said spatial region.

Although in the example being disclosed only an RFID tag 3 is present in this spatial region, a multiplicity of RFID tags 3 may be present, without departing from the scope of the invention.

With particular reference to the RFID tag 3 identified by said reader, said RFID tag 3 is a RFID tag of known type of the type configured to: o receive said RF signal sent by said reader 2;

o store a power value of said RF signal;

o send said power value and the respective unique identification code to said reader 2. With particular reference to the reader 2, the first logic control unit 20A of said reader 2 is configured to receive by said RFID tag 3 a power value of said RF signal received by said RFID tag and the respective unique identification code.

With particular reference to the processing unit 4, said processing unit 4 is configured to:

o create for said RFID tag 3 a first matrix Mi associated with said sum signal å, a second matrix M2 associated with said first difference signal D^ _z , and a third matrix M3 associated with said second difference signal A _EL , where each element of each matrix is a power value of the respective RF signal received by said RFID tag 3 depending on a respective position of said RFID tag 3 with respect to the pointing direction of the RF signal sent from said reader 2 in said spatial region;

o calculate a first difference matrix MDI given by the difference between said first matrix Mi and said second matrix M2 and a second difference matrix MD2 given by the difference between said first matrix Mi and said third matrix M3;

o determine the maximum value of said first difference matrix MDI and the maximum value of said second difference matrix MD2, where a first angular position of said RFID tag 3 on said azimuth plane is associated with the maximum value of said first difference matrix MDI and a second angular position of said RFID tag 3 on said elevation plane is associated with the maximum value of said second difference matrix MD2;

o calculate a first distance between said reader 2 and said RFID tag 3 on said azimuth plane based on the maximum power value of a predetermined raw of said first matrix Mi, and a second distance between said reader 2 and said RFID tag 3 on said elevation plane based on the maximum power value of a predetermined column of said first matrix Mi ;

o determine a first coordinate x and a second coordinate y associated with the position of said RFID tag 3 on said azimuth plane by said first distance and said first angular position, and a third coordinate z associated with the position of said RFID tag 3 on said elevation plane by said second distance and said second angular position of said RFID tag 3.

In particular, the first angular position associated with the maximum power value of said first difference matrix MDI is the angular position of the RFID tag 3 on the azimuth plane, and the second angular position associated with the maximum power value of said second difference matrix MD2 is the angular position of the RFID tag 3 on the elevation plane.

In particular, said first difference matrix MDI and said second difference matrix MD2 are respectively calculated by the following formulas:

Consequently, the maximum power value of each of said difference matrices MD-I , MD2, as calculated above, will be determined to obtain a respective angular position on the azimuth plane and on the elevation plane.

In case of a plurality of RFID tags present in said spatial region, the processing unit is configured to create with reference to each RFID tag a respective first matrix Mi associated with the sum signal å, a respective second matrix M2 associated with the first difference signal D^ _z , and a respective third matrix M3 associated with said second difference signal A _el , calculate a respective first difference matrix and a respective second difference matrix, determine the maximum value of each difference matrix associated with the respective angular position of the respective RFID tag on the azimuth plane and on the elevation plane, c alculate a respective first distance and a respective second distance, and determine the respective coordinates x and y associated with the position of the respective RFID tag 3 on said azimuth plane and a respective third coordinate z associated with the position of the respective tag 3 on said elevation plane.

Each raw of each matrix corresponds to a respective azimuth plane and each column of each matrix corresponds to a respective elevation plane.

In the embodiment being disclosed, said first logic control unit 20A is connected (directly) to said first phase shifter 22A and is configured to control said first phase shifter 22A and is connected to the other phase shifters through respective logic control units by means of which said first logic control unit controls said phases shifters.

In particular, said first logic control unit 20A is connected to said second phase shifter 22B through a second logic control unit 20B, to said third phase shifter 22C through a third logic control unit 20C and to said fourth phase shifter 22D trhough a fourth logic control unit 20D.

In particular, said second logic control unit 20B is configured to receive a control signal by said first logic control unit 20A and control said second phase shifter 22B, said third logic control unit 20C is configured to receive a control signal by said first logic control unit 20A and control said third phase shifter 22C, and said fourth logic control unit 20D is configured to receive a control signal by said first logic control unit 20A and control said fourth phase shifter 22D.

In other words, said first logic control unit 20A is a master device, whilst the second logic control unit 20B, the third logic control unit 20C and the fourth logic control unit 20D are slave devices, controlled by said first logic control unit 20A.

Consequently, the first phase shifter 22A is controlled directly by sid first logic control unit 20A, whilst the second phase shifter 22B, the third phase shifter 22C and the fourth phase shifter 22D are controlled by the respective logic control units 20B,20C,20D, on the basis of the respective control signals sent by said first logic control unit 20A to each of said logic control units.

Each phase shifter is controlled independently of the other phase shifters and then the phase of a RF signal sent by a respective antenna can be shifted regardless of whether the phases of the RF signals sent by the other antennas are shifted or not.

In the embodiment being disclosed, said control logic units 20A, 20B, 20C, 20D are microcontrollers, connected to each other by means of a serial communication. By way of example, this serial communication between said microcontrollers takes place preferably via the SPI protocol (“ Serial Peripheral Interface’).

Furthermore, said reader 2 comprises:

- a first power supply unit 24A for supplying said first antenna 21 A,

- a second power supply unit 24B for supplying said second antenna 21 B,

- a third power supply unit 24C for supplying said third antenna 21 C,

- a fourth power supply unit 24D for supplying said fourth antenna 21 D.

In the embodiment being disclosed, each power supply unit 24A, 24B, 24C, 24D is made by a microstrip.

With reference to the phase shifters, said first phase shifter 22A is connected to said first power supply unit 24A, said second phase shifter 22B is connected to said second power supply unit 24B, said third phase shifter 22C is connected to said third power supply unit 24C and said fourth phase shifter 22D is connected to said fourth power supply unit 24D.

In particular, the variation of phase of the RF signals sent by the respective antennas 21 A, 21 B, 21 C, 21 D through the respective phase shifter 22A,22B,22C,22D, allows to control the pointing direction of the beam irradiated by said reader 2 on said azimuth plane and/or on said elevation plane.

To each combination of phase variation corresponds a respective direction of pointing of the RF signal sent by the reader 2 inside said spatial region.

In the embodiment being disclosed, sid pointing direction of the beam irradiated by said reader 2 ranges from about -45 ° to + 45 ° both on said azimuth plane and on said elevation plane with respect to a direction perpendicular to a plane on which said antennas 21 A, 21 B, 21 C, 21 D are arranged (as explained later, the antennas are arranged on a first substrate of which the reader is provided).

With reference to the comparator 23, said comparator 23 comprises:

- a first rat-race coupler 25 comprising:

o a first input 251 for receiving said first RF signal A and a second input 252 for receiving said fourth RF signal D,

o a first output 253 for providing as output the sum of said first RF signal A and said fourth RF signal D, and a second output 254 for providing as output the difference between said first RF signal A and said fourth RF signal D,

- a second rat-race coupler 26 comprising:

o a first input 261 for receiving said second RF signal B and a second input 262 for receiving said third RF signal C,

o a first output 263 for providing as output the sum of said second RF signal B and said third RF signal C, and a second output 264 for providing as output the difference between said second RF signal RF B and said third RF signal C,

- a third rat-race coupler 27, connected to said first rat-race coupler 25 and said second rat-race coupler 26, comprising:

o a first input 271 for receiving the sum of said first RF signal A and said fourth RF signal D, and a second input 272 for receiving the sum of said second RF signal B and said third RF signal C, o a first output 273 for providing as output said sum signal å and a second output 274 for providing as output said difference signal

^AZ

- a fourth rat-race coupler 28, connected to said first rat-race coupler 25 and said second rat-race coupler 26, comprising:

o a first input 281 for receiving the difference between the first RF signal A and said fourth RF signal D,

o a second input 282 for receiving the difference between the second RF signal B and said third RF signal C,

o a first output 283 for providing as output said second difference signal A _EL .

Furthermore, in the embodiment being disclosed, it is preferable that said comparator 23 is configured to generate an auxiliary signal A _q - A B + C - D.

In the specific case, said fourth rat-race coupler 28 comprises a second outout 284 for providing as output said auxiliary signal A _Q .

In particular, in the embodiment being disclosed, said comparator is a monopulse comparator.

With reference to the arrangement of the antennas 21 A, 21 B, 21 C, 21 D of the reader 2, as can be seen from Figure 3, said first antenna 21 A and said second antenna 21 B are arranged on a first axis T1 , and said third antenna 21 C and said fourth antenna 21 D are arranged on a second axis T2, parallel to said first axis T 1.

Moreover, the position of said first antenna 21 A and the position of said fourth antenna 21 D are respectively symmetrical to the position of said second antenna 21 B and to the position of said third antenna 21 C with respect to a third axis L, perpendicular to said first axis T1 and said second axis T2.

In other words, the four antennas 21 A, 21 B, 21 C, 21 D of the reader 2 are arranged at the vertices of a square.

With reference to the physical structure of the reader 2, said reader 2 comprises a first substrate 29A, on which each antenna 21 A, 21 B, 21 C, 21 D is arranged, and a second substrate 29B, on which said comparator 23 and each logic control unit 20A, 20B, 20C, 20D and each phase shifter 22A, 22B, 22C, 22D are arranged, where said second substrate 29B is spaced from said first substrate 29A.

Furhtermore, in the embodiment being disclosed, each power supply unit 24A,24B,24C,24D is arranged on said second substrate 29B. With particular reference to Figure 5, said reader 2 comprises a first ground plane 30A and a second ground plane 30B, arranged between said first substrate 29A and said second substrate 29B, where said first ground plane 30A is in contact with said first substrate 29A and said second ground plane 30B is in contact with said second substrate 29B.

Said ground plane 30A is glued to said second ground plane 30B by an adhesive layer (not shown).

In other words, the reader 2 comprises in succession:

a first substrate 29A,

a first ground plane 30A,

an adhesive layer (for example a layer of adhesive),

a second ground plane 30B,

a second substrate 29B.

In particular, said first ground plane 30A is provided with four openings 215A,215B,215C,215D and said second ground plane 30B is provided with further four openings 216A,216B,216C,216D.

Said ground plane 30A and said second ground plane 30B are arranged in such a way that each opening 215A, 215B, 215C, 215D of the first ground plane 30A is overlapped on a respective further opening 216A, 216B, 216C, 216D of the second ground plane 30B.

In particular, said first power supply unit 24A is connected to the first input 251 of the first rat-race coupler 25, said second power supply unit 24B is connected to the first input 261 of the second rat-race coupler 26, said third power supply unit 24C is connected to the second input 262 of the second rat-race coupler 26, and said fourth power supply unit 24D is connected to the second input 252 of the first rat-race coupler 25.

Each power supply unit 24A,24B,24C,24D is electromagnetically coupled with a respective antenna 21 A,21 B,21 C,21 D through a respective pair of openings, formed by an opening 215A,215B,215C,215D of the first ground plane 30A and a further opening 216A,216B,216C,216D of the second ground plane 30B, overlapped on a respective opening of said first ground plane 30A.

According to the invention, said processing unit 4 is configured to divide said spatial region in two or more predetermined zones on said azimuth plane and in two or more further predetermined further zones on said elevation plane and said first logic control unit 20A is configured to shift the phases of each RF signal sent bya respective antenna 21 A, 21 B, 21 C, 21 D so as to change the pointing direction of said RF signal sent by said reader 2 toward said two or more predetermined zones and/or said two or more predetermined further zones.

Furthermore, said processing unit 4 is configured to select one of said predetermined zones on the basis of the maximum value of said first difference matrix MDI and/or one of said predetermined further zones on the basis of the maximum value of said second difference matrix MD2.

Said first distance is calculated according to the following formula: where

i=1 ...M is the index of the number of zones in which the spatial region is divided in the azimuth plane, and M is a positive integer,

P _Q AZ _I is a predetermined reference power value on the azimuth plane associated with a respective zone,

PR I is the maximum power value of a predetermined raw of said first matrix Mi,

n _lt is a known attenuation coefficient associated with a respective zone. Said second distance is calculated according to the following formula: where

j=1 ... K is the index of the number of further zones in which the spatial region is divided in the elevation plane, and K is a positive integer,

Po _ELj is a predetermined reference power value on the azimuth plane associated with a respective further zone,

PR 2 _I is the maximum power value of a predetermined column of said first matrix Mi,

n _2j is a known attenuation coefficient associated with a respective further zone.

In the embodiment beung disclosed, said processing unit 4 divides the spatial region (i.e. the spatial region to be read) irradiated by the beam of said reader 2 into three different zones on the azimuth plane and into three further zones on the elevation plane.

Below, the three zones on the azimuth plane:

- a first zone or Zone 1 : from -45 °to -22.5 °; - a second zone or Zone 2: from -22.5 ° to + 22.5 °;

- a third zone or Zone 3: from + 22.5 ° to + 45 °.

Below, the three further zones on the elevation plane:

- a first further zone or Zone 1 : from -45 ° to -22.5 °;

- a second further zone or Zone 2: from -22.5 ° to + 22.5 °;

- a third further zone or Zone 3 from + 22.5 ° to + 45 °.

It is not necessary for the number of said predetermined zones on the azimuth plane to be equal to the number of said predetermined further zones on the elevation plane.

For example, the number of said predetermined zones may be equal to three and the number of said predetermined further zones may be equal to five.

In the embodiment said reader 2 allows to locate the position of the RFID tag 3 in space identified by the coordinates x,y,z.

In particular, when in use, said processing unit 4 determines both the x and y coordinates, associated with the position of said RFID tag 3, on the basis of said angular position on said azimuth plane and of said first distance between said RFID tag 3 and said reader 2, and the z coordinate associated with position of said RFID tag 3, on the basis of said angular position on said elevation plane and of said second distance between said RFID tag 3 and said reader 2.

The present invention also relates to a method for locating at least one RFID tag 3 in space, in particular in an indoor environment, where a respective unique identification code is associated to said RFID tag.

Said method comprises the following steps:

A) providing a reader 2 provided with a first antenna 21 A, a second antenna 21 B, a third antenna 21 C and a fourth antenna 21 D,

B) sending a RF signal in a spatial region given by the sum of a first RF signal sent through said first antenna 21 A, a second RF signal sent through said second antenna 21 B, a third RF signal sent through said third antenna 21 C, and a fourth RF signal sent through said fourth antenna 21 D,

C) shifting the phase of said RF signal and/or the phase of said second RF signal and/or the phase of said third RF signal and/or the phase of said fourth RF signal for changing the pointing direction of said RF signal within said spatial region (in other words, the phases are shifted to orientate said RF signal inside the spatial region, on the azimuth plane and/or on the elevation plane), D) receiving by said reader 2 a further first RF signal A through said first antenna 21 A, a further second RF signal B through said second antenna 21 B, a further third RF signal C through said third antenna 21 C, a further fourth RF signal D through said fourth antenna 21 D,

E) generating a sum signal å = A + B + C + D , a first difference signal D _az = A - B - C + D on an azimuth plane, a second difference signal A _EL = A + B - C - D on an elevation plane, perpendicular to said azimuth plane,

F) receiving by said reader 2 a power value associated with to the RF signal received by said RFID tag 3,

G) creating a first matrix Mi associated with said sum signal å, a second matrix M2 associated with said first difference signal A _az , and a third matrix M3 associated with said second difference signal _EL , where each element of each matrix is a power value of the respective RF signal received by said RFID tag 3 depending on a respective position of said RFID tag 3 with respect to the pointing direction of the RF signal sent from said reader 2 in a spatial region,

FI) calculating a first difference matrix MDI given by the difference between said first matrix M1 and said second matrix M2 and a second difference matrix MD2 given by the difference between said first matrix Mi and said third matrix M3,

I) determining the maximum power value of said first difference matrix MD-I , associated with a first angular position of said RFID tag 3 on said azimuth, and the maximum power value of said difference matrix MD2, associated with a second angular position of said RFID tag 3 on said elevation plane,

L) calculating a first distance between said reader 2 and said RFID tag 3 on said azimuth plane by the maximum power value of a predetermined raw of said first matrix Mi, and a second distance between said reader 2 and said RFID tag 3 on said elevation plane, by the maximum power value of a predetermined column of said first matrix Mi,

M) determining a first coordinate x and a second coordinate y associated to the position of said RFID tag 3 on said azimuth plane by said first distance and said first angular position, and a third coordinate z associated to the position of said RFID tag 3 on said elevation plane by said second distance and said second angular position of said RFID tag 3.

Advantages

As already mentioned, the system object of the invention allows to locate objects and/or living beings, to which a respective RFID tag is associated, which move in space, in particular inside an indoor environment.

Advantageously, the system allows to locate an object/subject with a high precision in the order of centimeters for environments with size up to about 20 square meters in the presence of reflections, fading, etc.

Another advantage of the system is that it allows to monitor objects/subjects to which a tag is applied over time.

The present invention has been described for illustrative, but not limitative purposes with reference to its preferred embodiments, but it well evident that one skilled in the art can introduce variants and/or modifications to the same, without departing from the relevant scope as defined in the enclosed claims.