Near field communication surface and method for positioning on said surface

Abstract

The present invention relates to a near field communication surface (1) intended to communicate with at least one electronic tag D1 or D2. The surface comprises a plurality of antennas A1-A8, each antenna having a position x1-x8 along an axis X, a circuit (100) for reading electronic tags, which is connected to the antennas A1-A8 so as to power the antennas and communicate with the electronic tags D1 or D2, and a processing unit (200) which controls the antennas A1-A8 and the circuit (100) for reading electronic tags. The processing unit (200) is configured to activate only one antenna and a reader circuit (100) at a time so as to communicate with the at least one electronic tag D1 or D2, and locate the position of the electronic tag D1 or D2 along the X axis according to the number of responses or the response time of the electronic tag D1 or D2. The present invention also relates to a positioning method.

Description

Technical Field

[0001] The present invention relates to a near field communication surface and a method for positioning on said surface. The present invention makes it possible to position on a near field communication surface one or more electronic ID tags or devices placed on said surface. Background Art

[0002] Automatic tracking of objects in a given area can be achieved in various ways. With regard to electronic anti-theft, it is known to position electromagnetic terminals at store exits and to equip products with anti-theft devices that include a resonant circuit tuned to the frequency of the electromagnetic field of the terminal. Once the anti-theft device is placed in the field generated by the electromagnetic terminal, the device begins to resonate and creates a significant disturbance in the electromagnetic field. It has been found that this disturbance is easily detectable and can locate the presence of the anti-theft device in a given area. However, this tracking method does not accurately identify the object associated with the device.

[0003] Two recent technologies allow for a more precise identification of objects. RFID (Radio Frequency Identification) and NFC (Near Field Communication) technologies use an electronic chip coupled to an antenna, which enables communication with the reader while powering the electronic chip using an electric or magnetic field generated by the reader. Both technologies make it possible to send a generally unique identifier to the reader from the moment the identified object is located in the communication field of the reader, making it possible to precisely identify the objects in the determined area without the need for the identified object or the electronic tag to have an intrinsic energy source. RFID technology uses an electric field, making it possible to communicate with one or more identified objects at a distance of several meters, without the need to precisely locate the object. NFC technology uses a magnetic field and allows communication at a distance of several centimeters from the reader.

[0004] In the application of object positioning, there are special needs that require a high degree of positioning accuracy and object recognition accuracy. For example, in the field of interactive games, it is necessary to track game pieces on a game board. Patent US 5,853,327 and patent application EP-A-0737 933 disclose a game board using a matrix of crossed magnetic antennas, and game pieces including resonant circuits tuned to different frequencies. By continuously performing frequency scans on each antenna, each piece placed on the board can be located. This type of system requires a specific resonant circuit to track each piece on the game board.

[0005] Application FR-A-2 860 985 discloses a gaming board using a matrix of NFC technology readers, each covering a very small part of the board in order to track the electronic tags located there. To achieve accuracy in positioning, it is necessary to reduce the size of each antenna in order to position as many antennas as possible. Furthermore, the number of readers is proportional to the number of antennas, which is relatively expensive.

[0006] Patent US10,090,888 also uses NFC technology, but with crossed antennas, which makes it possible to reduce the number of antennas and readers. In addition, in order to accurately determine the position relative to the antenna, the patent discloses measuring the modulation rate achieved by the electronic tag in order to obtain the relative distance therefrom. The development of this method is relatively complex, so if a high degree of positioning accuracy is required, then this method can prove to be quite expensive.

[0007] In terms of applications, there is also a need to track objects on shelves or displays in stores. This type of application aims to alert the store owner when a display is empty so that it can be restocked. Usually, this type of application uses simple detectors to detect the presence of an object, which has the disadvantage of providing incorrect information when the customer replaces one or more products in an incorrect position. For this type of application, there are also RFID type solutions, especially to ensure inventory management, but despite this, RFID solutions do not determine with high accuracy the exact position of a product on a display or a set of shelves.

[0008] Therefore, there is a need to be able to accurately track pieces or products on a game board or display with high accuracy and low cost. Summary of the invention

[0009] The present invention proposes an improved near field communication surface provided with multiple antennas. The present invention implements a continuous query of one or more electronic ID tags through each antenna. The response obtained from the electronic ID tag is then used to determine the position of the electronic ID tag on the communication surface. In order to simplify the positioning method implemented by the communication surface, one method applied is to count the number of responses issued by the electronic ID tag, or to use its response cycle, so as to determine the corresponding position of the electronic ID tag.

[0010] According to a first embodiment, the present invention proposes a near field communication surface for communicating with at least one electronic ID tag. The surface includes a first plurality of antennas, at least one circuit for reading electronic tags, and a processing unit. Each of the first plurality of antennas has a position according to a first axis, which corresponds to the maximum flux of the antenna according to the first axis. At least one circuit for reading electronic tags is connected to the antenna so as to power the antenna and communicate with the at least one electronic ID tag. The processing unit controls the antenna and at least one circuit for reading electronic tags, and the processing unit is configured to activate only one antenna and the at least one reader circuit at a time to communicate with the at least one electronic ID tag. In order to locate the position of the at least one electronic ID tag along the first axis according to the number of responses or the response time of the at least one electronic ID tag, the processing unit is configured to send a command to the at least one electronic ID tag through each antenna.

[0011] Preferably, when the number of responses is used to locate an electronic ID tag, the processing unit can be configured to send a predetermined number of commands to at least one electronic ID tag through at least one reader circuit and each antenna; calculate the number of responses received by each antenna; and calculate the position of at least one electronic ID tag by taking a weighted average of the positions of the antennas according to the number of responses received by each antenna.

[0012] According to a variant, the processing unit can be configured to control the transmission power of said reader circuit so that a predetermined number of commands are sent with a predetermined amount of transmission power.

[0013] Preferably, when the response time is used to locate the tag, the processing unit can be configured to send at least one command to at least one electronic ID tag with the same transmission power through at least one reader circuit and each antenna; measure the response time of the at least one electronic ID tag of each antenna; and calculate the position of at least one electronic ID tag based on the difference between the measured response time and the expected response time.

[0014] Preferably, the processing unit can be configured to calculate the position of the at least one electronic ID tag by weighted averaging the positions of the antennas by taking the inverse of the difference between the measured response time and the expected response time.

[0015] To allow for locating the tag in two dimensions, the communication surface may further include a second plurality of antennas, each antenna having a position according to a second axis corresponding to a maximum flux of the antenna according to the second axis, the second axis intersecting the first axis, the second plurality of antennas being connected to the at least one circuit for reading electronic tags, and the second plurality of antennas being controlled by a processing unit. The processing unit may be configured to locate the position of the at least one electronic ID tag along the second axis based on the number of responses or the response time of the at least one electronic ID tag.

[0016] According to one variation, the shape of the first plurality of antennas may be elongated along the second direction, the shape of the second plurality of antennas may be elongated along the first direction, the surface area covered by the first plurality of antennas and the second plurality of antennas is substantially equal to the surface area of ​​the surface, and the first plurality of antennas and the second plurality of antennas overlap, so that at least one electronic ID tag may be positioned on the entire surface according to the first axis and the second axis.

[0017] To avoid interference in the measurement, each antenna may include at least one shunt switch which short-circuits the antenna when closed. When an antenna is selected, the at least one shunt switch may be opened, and when an antenna is not selected, the at least one shunt switch may be closed.

[0018] To reduce surface cost, at least one reader circuit may include a single modem circuit connected to each of the first plurality of antennas and / or the second plurality of antennas. Each antenna may include two connector switches for connecting it to the single reader circuit. When an antenna is selected, the connector switch may be closed, and when an antenna is not selected, the connector switch may be opened.

[0019] According to a second embodiment, the present invention proposes a method for locating an electronic ID tag on a near field communication surface, the surface comprising a plurality of antennas, each antenna having a position according to an axis corresponding to a maximum flux of the antenna according to the axis, and at least one circuit for reading the electronic tag connected to the antenna, so as to power the antenna and communicate with the electronic ID tag. The method comprises the following steps:

[0020] -sending a command to an electronic ID tag via an antenna selected from a plurality of antennas,

[0021] - receiving a response from an electronic ID tag via a selected antenna and storing the tag's response or non-response,

[0022] - repeating the steps of sending commands and receiving responses until at least one command has been sent to each of the plurality of antennas,

[0023] -Calculate the location of the electronic ID tag based on the number of responses or response time of the electronic tag.

[0024] According to the first embodiment, the steps of sending commands and receiving responses may be repeated until each of the plurality of antennas has sent a command to the electronic ID tag a predetermined number of times. The step of receiving responses may count the number of responses received. The step of calculating the position of the electronic ID tag may determine the position of the electronic ID tag by weighted averaging the positions of the antennas by the number of responses received.

[0025] In one variant, the predetermined number of commands may be sent with a predetermined amount of transmission power.

[0026] According to a second embodiment, the step of receiving a response may measure a response time of the electronic ID tag. The step of calculating the position of the electronic ID tag may determine the position of the electronic ID tag based on the difference between the measured response time and the expected response time.

[0027] In one variant, the step of calculating the position of the electronic ID tag may calculate the position of at least one electronic ID tag by weighted averaging the positions of the antennas by the inverse of the difference between the measured response time and the expected response time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention will be better understood, and other characteristics and advantages thereof will become more apparent, on reading the following description of particular embodiments of the invention given by way of illustrative and non-limiting examples, with reference to the accompanying drawings, in which:

[0029] [ Figure 1 ] shows a first embodiment of a communication surface comprising an antenna network compatible with the present invention,

[0030] [ Figure 2 ] shows a second embodiment of a communication surface comprising an antenna network compatible with the present invention,

[0031] [ Figure 3 ] shows a third embodiment of a communication surface comprising an antenna network compatible with the present invention,

[0032] [ Figure 4 ] can be used according to the present invention Figures 1 to 3 The first block diagram and wiring diagram of the antenna network used together,

[0033] [ Figure 5 ] can be used according to the present invention Figures 1 to 3 The second block diagram and wiring diagram of the antenna network used together,

[0034] [ Figure 6 ] is a functional flow chart of a first embodiment of a method for locating an electronic tag implemented by the surface according to the present invention,

[0035] [ Figure 7 ] shows the count of responses received, so that Figure 6 The method to locate the electronic tag is

[0036] [ Figure 8 ] shows a product arranged on a communication surface,

[0037] [ Fig. 9 ] is a functional flow chart of a second embodiment of the method for locating an electronic tag implemented by the surface according to the present invention,

[0038] [ Fig.10 ] shows the count of responses received, so that Fig. 9 The method to locate the electronic tag is

[0039] [ Fig.11 ] shows the measurement of the response period of the electronic tag,

[0040] [ Fig.12 ] is a functional flow chart of a third embodiment of the method for locating an electronic tag implemented by the surface according to the present invention,

[0041] [ Fig.13 ] shows the measurement of the response time of the electronic tag, so that Fig.12 The electronic tag is located by the method. DETAILED DESCRIPTION

[0042] The term "near field communication" refers to NFC technology limited to a few centimeters, and uses antennas implemented by forming conductive loops of half-transformers on the reader side and the electronic tag side. The communication thus achieved is achieved through a magnetic field that couples the reader's transmitting antenna and the antenna used to recover energy from the electronic tag.

[0043] The term "electronic tag" herein refers to an identification device that includes an electronic chip coupled to an antenna that forms a coil and powers itself through the magnetic field generated by the reader. Such identification devices are usually in the form of a tag that can be easily fixed to many types of packaging or products. Nevertheless, the present invention is not limited to a "tag" type form factor and can, for example, be in the form of a grain of rice or any other form of electronic device.

[0044] Before explaining the function of tag positioning in detail, it is first necessary to explain the function of near field communication between the reader and the electronic tag. The reader includes an antenna having one or more turns and tuned to a resonant frequency corresponding to the frequency of the emitted magnetic field, such as 13.56 MHz. The current flowing through the reader antenna turns generates a magnetic field that radiates near the antenna. The electronic tag includes an antenna having one or more turns and tuned to the magnetic field emitted by the reader. When the electronic tag is in the magnetic field of the reader, the antenna of the electronic tag begins to resonate and convert the magnetic field it receives. If the magnetic field is large enough, the antenna of the electronic tag can power the chip of the tag. The communication between the reader and the electronic tag is achieved by modulation of the magnetic field. On the reader side, the modulation of the field is achieved by modulating the current sent to the antenna, thereby modulating the emitted field. On the electronic tag side, the modulation is achieved by tuning and detuning the antenna of the electronic tag by performing a modulation disturbance of the magnetic field (also called retro-modulation). The modulation disturbance of the magnetic field causes the current flowing in the reader antenna to be modulated, which can be demodulated. For further details, those skilled in the art may refer to the standard ISO 14443 which defines the near field communication function.

[0045] In order to establish communication between the reader and the electronic tag, the electronic tag needs to be close enough to the reader to receive a magnetic field of sufficient power to power the chip of the electronic tag. The distance that allows communication between the reader and the electronic tag depends on the size of the antenna of the reader and the antenna of the electronic tag, and also on the transmission power of the reader. Using low transmission power on the reader side means that the electronic tag can only be detected when it is very close to the transmitting antenna, or in fact only when the electronic tag is superimposed on the transmitting antenna.

[0046] It is using this principle that it is possible to locate an electronic tag on a communication surface having multiple readers.

[0047] Figure 1 A first embodiment of a communication surface 1 is shown, which is intended for locating one or more electronic tags according to a single axis X. This type of communication surface 1 can be a game board, a display, a shelf or any other planar element intended to receive an electronic tag or a product comprising an electronic tag. For this purpose, the communication surface 1 comprises a plurality of coplanar antennas A1 to A8, which are placed side by side according to the axis X. The antennas are preferably aligned according to the axis X. The communication surface 1 also comprises a reader block 100 connected to the antennas A1 to A8, and a processing unit 200 connected to the reader block 100. The processing unit 200 also comprises a communication interface (not shown) for enabling the transmission of positioning information to a remote computer (not shown).

[0048] Each antenna A1 to A8 includes one or more turns for emitting a magnetic field when a current passes through it. The current flowing in each antenna A1 to A8 is provided by the reader block 100 under the control of the processing unit 200. When the reader circuit 100 supplies power to the antenna A1 to A8, the antenna A1 to A8 emits a magnetic field, and the magnetic field strength is maximum at the center of its turns. The maximum strength of the magnetic field of each antenna A1 to A8 projected on the axis X defines the position of the antenna A1 to A8 on the axis X. Therefore, each antenna A1 to A8 is associated with a position x1 to x8 on the axis X.

[0049] The operating principle of the near field communication system including the positioning of the electronic tag is to control the power supply of each antenna A1 to A8 so that a single selected antenna A1 to A8 emits a magnetic field at a given moment. If the electronic tag placed on the communication surface 1 is close enough to the selected antenna A1 to A8, communication is established between the selected antenna A1 to A8 and the electronic tag. Depending on the shape and position of the antenna of the electronic tag, and also on the transmission power, one or more of the antennas A1 to A8 can communicate with the tag. How to determine the position of the electronic tag will be described in detail below.

[0050] In order to be able to locate the position of a tag in two dimensions on a substantially flat communication surface, it is necessary to be able to track the antenna of the tag according to two intersecting and preferably perpendicular axes. Figure 2 A second embodiment of a communication surface 1' is shown, which is intended for positioning one or more electronic tags according to a first axis X and a second axis Y, the second axis Y being coplanar with the first axis, for example orthogonal to the first axis. For this purpose, the communication surface 1' comprises a plurality of antennas A11 to A27, which are arranged in a matrix comprising antennas arranged in a row according to the first axis X and in a column according to the second axis Y. The communication surface 1' also comprises two reader blocks 100' and 100", one of which is connected to the antennas A11 to A17 and the other to the antennas A21 to A27. More simply stated, the second embodiment amounts to a replication of the first embodiment, with as many rows as there are antennas. The communication surface 1' also comprises a processing unit 200 connected to the reader block 100 in order to control the block and select the transmitting antenna.

[0051] The point of maximum intensity of the magnetic field of each antenna A11 to A27 projected on the first axis X defines the position of the antenna A11 to A27 on the first axis X. The point of maximum intensity of the magnetic field of each antenna A11 to A27 projected on the second axis Y defines the position of the antenna A11 to A27 on the second axis Y. Therefore, each antenna A11 to A27 is associated with a position x1 to x7 on the first axis X and a position y1 to y2 on the second axis Y.

[0052] The positioning principle of the electronic tag in the second embodiment is the same as that in the first embodiment. However, the communication between each of the antennas A11 to A27 and the electronic tag will be used to determine the position of the electronic tag on each of the first axis X and the second axis Y, as will be explained in the subsequent description.

[0053] Figure 3A third embodiment of a communication surface 1" is shown, which is intended for positioning one or more electronic tags according to coplanar and intersecting first and second axes X and Y. For this purpose, the communication surface 1" comprises a first plurality of antennas AC1 to AC8 arranged side by side according to the first axis X, and a second plurality of antennas AL1 to AL4 arranged side by side according to the second axis Y. The first plurality of antennas AC1 to AC8 and the second plurality of antennas AL1 to AL4 overlap and occupy approximately the same surface area corresponding to the surface area of ​​the communication surface 1". The communication surface 1" also comprises a first reader block 100L connected to the first plurality of antennas AC1 to AC8, a second reader block 100C connected to the second plurality of antennas AL1 to AL4, and a processing unit 200 connected to the first reader block 100L and the second reader block 100C. More simply put, the third embodiment is equivalent to a replication of the first embodiment, but with the superposition of antennas oriented according to two axes X and Y.

[0054] For the first plurality of antennas AC1 to AC8, the maximum strength of the magnetic field projected by each antenna AC1 to AC8 on the first axis X defines the position of said antenna AC1 to AC8 on said first axis X. Thus, each of the first plurality of antennas AC1 to AC8 is associated with a position x1 to x8 on the first axis X. For the second plurality of antennas AL1 to AL4, the maximum strength of the magnetic field projected by each antenna AL1 to AL4 on the second axis Y defines the position of said antenna AL1 to AL4 on said second axis Y. Thus, each of the second plurality of antennas AL1 to AL4 is associated with a position y1 to y4 on the second axis Y.

[0055] The principle of positioning the electronic tag in the third embodiment corresponds to a replication of the first embodiment according to two different axes. Nevertheless, the positioning of the first plurality of antennas AC1 to AC8 and the second plurality of antennas AL1 and AL4 must be performed sequentially, as will be explained in the following description.

[0056] Regardless of the implementation of the communication surface 1 , 1 ′ or 1 ″, the selection of the antennas A1 to A8 , A11 to A27 , AC1 to AC8 or AL1 to AL4 is performed jointly by the reader block 100 , 100 ′, 100 ″, 100L or 100C controlled by the processing unit 200 . Figure 4 and 5 Details of two possible embodiments of the reader block are shown. To simplify the representation, Figure 4 and Figure 5 Reused Figure 1 Reference numerals in the Figure 2 or Figure 3Furthermore, only three antennas are shown, but those skilled in the art will appreciate that some circuits are not shown for simplicity purposes and that duplication of the elements shown is sufficient.

[0057] exist Figure 4 In the reader block 100, for each antenna A1, Ai or An, the reader block 100 includes a modulation and demodulation circuit (MODEM) 110, an EMC filter 120 (electromagnetic compatibility) and a tuner circuit 130. The tuner circuit 130 is coupled to the antenna A1, Ai or An to form a resonant circuit tuned to the magnetic field frequency. The EMC filter 120 is located between the MODEM circuit 110 and the tuner circuit 130. The EMC filter 120 is implemented, for example, by two LC circuits forming a bandpass filter centered on the magnetic field frequency so as to allow only a narrow frequency band centered on the magnetic field frequency to pass. The EMC circuit 120 suppresses possible modulation images and interference received by the antenna. The tuner circuit 130 is located between the antennas A1 to An and the EMC filter 120, and the tuner circuit 130 is composed of a capacitor, the function of which is to form a resonant circuit with the antennas A1 to An at the magnetic field frequency. The dimensioning of the components of the EMC circuit 120 and the tuner circuit 130 is performed jointly so that the component consisting of the antennas A1 to An, the tuner circuit 130 and the EMC circuit itself is a resonant circuit at the frequency of the magnetic field. The MODEM circuit 110 is an active element that provides the carrier frequency of the magnetic field, modulates the magnetic field when information is to be sent, and demodulates the information sent by the electronic tag and received by the antenna. The MODEM circuits 110 associated with the antennas A1 to An, respectively, are connected to the processing unit 200 via a communication bus.

[0058] The processing unit 200 is, for example, a microcontroller or microprocessor including a volatile memory and a non-volatile memory. The non-volatile memory includes programs that, when executed, can manage the sending and receiving of information with an electronic tag, and can also implement a method for locating an electronic tag. The processing unit 200 can select a single MODEM circuit 110 via a communication bus so that only antennas A1 to An associated with the selected MODEM circuit 110 are activated. When the MODEM circuit 110 is activated, it provides an electrical signal to the antennas A1 to An through the EMC filter 120 and the tuner circuit 130. The electrical signal is a variable signal at the frequency of the magnetic field, which the antenna converts into a magnetic field. In order to send information, the processing unit 200 sends a modulation command, and then a binary sequence is sent to the selected MODEM circuit 110. The MODEM circuit 110 encodes the binary sequence in the baseband and then modulates the electrical signal provided to the antenna, which has the function of modulating the magnetic field. When the electronic tag modulates the magnetic field, the selected antennas A1 to An convert the modulated magnetic field into an electrical signal modulating the antenna. The MODEM circuit 110 demodulates the electrical signal and decodes the information which is retransmitted to the processing unit 200 .

[0059] When the MODEM circuit 110 and its associated antennas A1 to An are not selected, the antennas do not perform transmission. Depending on the type of MODEM circuit 110, the output of the MODEM circuit 110 can be grounded or set to high impedance. If the output of the MODEM circuit 110 is set to high impedance, antennas adjacent to the selected antenna may begin to resonate due to electromagnetic coupling; this resonance has the effect of increasing the magnetic field range of the selected antenna and improving communication with the electronic tag. However, the positioning of the tag is performed with consideration of the range limitations of the selected antenna. In order to prevent unwanted resonance, a shunt switch 140 can be set in parallel with the antennas A1 to An so as to short-circuit the antennas A1 to An when not selected.

[0060] Figure 5 An embodiment using only one MODEM circuit 110 and one EMC filter 120 for all antennas A1 to An is shown. This type of embodiment is more Figure 4 The embodiment is more economical. In addition, in response to the command of the processing unit 200, using only one MODEM circuit 110 makes it easier to ensure the same modulation power for each antenna A1 to An. The EMC filter 120 is connected to the plurality of tuner circuits 130 via two series of connector switches 150 corresponding to analog multiplexers, for example. The connector switches 150 are controlled by the processing unit 200 through n command signals S1 to S n (Also denoted as S 1-n ) to control, only one of which is active. Command signal S 1-nOne of the connector switches 150 is activated to close the connector switch 150 corresponding to the selected antenna A1 to An, the other connector switches 150 remain open, and the unselected antennas A1 to An are set to high impedance. In order to prevent the unselected antennas A1 to An from coupling through resonance, the shunt switch 140 is placed in parallel on each of the antennas A1 to An. The shunt switch 140 is connected to the antenna 11 to An by the same command signal S1 to S2 as the connector switch 150. n Controlled, but in an opposite manner, so that when antennas A1 to An are selected, the shunt switches 140 associated therewith are opened, and when antennas A1 to An are not selected, the shunt switches 140 associated therewith are closed.

[0061] The first positioning method implemented by the processing unit 200 refers to Figure 6 , and corresponds to a positioning method performed based on the number of responses of an electronic tag. When the processing unit 200 executes a program corresponding to the method for locating a tag, the processing unit initializes the method in step 600 by setting two loop indicators IB and JB to a value of "1". Then, in step 610, the processing unit 200 selects an antenna corresponding to the indicator IB to interrogate the tag, for example, through a REQA command defined in the standard ISO14443, so as to receive an ATQA response indicating the identification number of the tag. If an ATQA response is received, step 620 performed by the processing unit 200 stores the identifier of the electronic tag that has responded, and the indicator IB corresponds to the antenna A1 to An that has received the ATQA response. If no ATQA response is received within the reception waiting period, the processing unit 200 stores in step 620 that no tag response has been received. The principle implemented in this first embodiment relates to a non-systematic response of an electronic tag. In fact, since the electronic tag is powered by a magnetic field, the electronic tag must store a certain amount of energy in order to respond. A tag that is not positioned in an optimal manner relative to the magnetic field may not have enough energy to respond to the command systematically.

[0062] To this end, the method implemented by the processing unit 200 consists in sending a command using each antenna A1 to An during step 610. The processing unit 200 controls the MODEM circuit 110 so as to send the REQA command on the antennas A1 to An at a power that does not allow the electronic tag to respond if the tag is located at a distance greater than a predetermined distance. If the electronic tag is located at a distance less than the predetermined distance, the energy received by the tag may not be sufficient for the system to respond, for example if the tag is not positioned in an optimal manner relative to the selected antenna. During step 620, when the antennas A1 to An receive an ATQA response, the MODEM circuit 110 sends the response to the processing unit 200, which identifies the electronic tag in the ATQA response to store the response received by each of the antennas A1 to An. During step 630, after the index IB is increased, steps 610 and 620 are repeated until the index reaches a value "n" corresponding to the number of antennas A1 to An. When steps 610 and 620 have been performed "n" times, the indicator JB is increased in step 640 and the indicator IB is reinitialized to the value "1" in order to re-interrogate all antennas A1 to An. All these steps 610 to 650 are repeated until the indicator JB reaches a value "p" corresponding to the maximum number of interrogations performed by all antennas. Thus, each antenna A1 to An has sent p REQA commands and the ATQA responses (if any) have been stored by the processing unit 200. The processing unit 200 then performs a step 660 of calculating the position of the detected tag.

[0063] According to a variant, the order in which the antennas are selected can be changed so that the REQA command is sent so that the previous charging condition of the tag is changed. In fact, a charged tag has a charge retention capacity of about ten microseconds. If the interrogation of an adjacent antenna occurs too quickly, that is, before the electronic tag has time to discharge, the interrogated tag needs to accumulate less energy than an uncharged tag. Changing the order of interrogation can avoid the residual charge phenomenon, thereby shortening the interval time for another antenna to send a command. In order to change the order of interrogation, a correspondence table with indicators IB and JB as input can give antenna indicators that are different from indicator IB.

[0064] As an example, two electronic tags D1 and D2 are placed Figure 1On the network of antennas A1 to A8, the value "n" is fixed to the value "8". The electronic tag D1 is configured in a manner that straddles antennas A2 and A3, and receives a larger magnetic flux from antenna A3 than antenna A2. The electronic tag D2 is located on antenna A7, slightly biased toward antenna A6. The power of the MODEM circuit 110 is fixed by the processing unit 200 so that the predetermined distance is equal to the spacing separating the two antennas. For example, the value "p" is fixed to the value "10", and the received responses are collected for each antenna A1 to A8.

[0065] Figure 7 A number of ATQA responses received from said tags D1 and D2 are graphically illustrated by way of non-limiting example. Antenna A2 has received six ATQA responses from tag D1, antenna A3 has received eight ATQA responses from tag D1. Antenna A6 has received four ATQA responses from tag D2, antenna A7 has received ten ATQA responses from tag D2, and antenna A8 has received eight ATQA responses from tag D2. In order to obtain the position of tag D1 or D2, during step 660, processing unit 200 calculates the average of the positions of antennas A1 to A8, the average being weighted by the number of responses received, for example by the following formula:

[0066] [Formula 1]

[0067]

[0068] where x(Dj) corresponds to the position of tag Dj, n is the number of antennas, Ri(Dj) is the number of ATQA responses received by antenna Ai and originating from tag Dj, and xi is the position of antenna Ai.

[0069] For example, if the positions of antennas A1 to A8 are four centimeters apart, and antenna A1 corresponds to the origin of the X-axis, then the positions x1 to x8 of antennas A1 to A8 correspond to distances of 0, 4, 8, 12, 16, 20, 24, and 28 centimeters relative to the origin, respectively. Figure 6 The ATQA response represented in , applying the above formulas yields a position x(D1) at 6.28 cm from the origin, and a position x(D2) at 23.76 cm from the origin. The error margin of this method depends on the power of the magnetic field, the distance that can separate the surface area of ​​the surface from the location of the tag, the orientation of the tag, and more generally, the coupling coefficient between the antennas A1 to A8 of the communication surface 1 and the antenna of the electronic tag D1 or D2.

[0070] In order to achieve two-dimensional positioning of the label position, the same operation needs to be performed on the Y axis. Figure 2For a communication surface 1', the responses of the antennas A11 to A27 must be considered according to the first axis X and the second axis Y so as to calculate a weighted average according to each axis. In one embodiment, two indicators IB can be used, one for the rows and the other for the columns. According to another embodiment, the value "n" can be equal to the total number of antennas, and the antennas are selected by a correspondence table according to the indicator IB. Whatever the selection method, the following formula can be used, for example:

[0071] [Formula 2]

[0072]

[0073] Wherein, x(Dj) is the position of tag Dj according to the first axis X, y(Dj) is the position of tag Dj according to the second axis Y, n is the number of antennas according to the first axis X, m is the number of antennas according to the second axis Y, xi is the position of antenna Aik according to the first axis X, yk is the position of antenna Aik according to the second axis Y, and Rik(Dj) is the number of ATQA responses received by antenna Aik placed at positions xi and yk and originating from tag Dj.

[0074] for Figure 3 The calculation of the tag position according to the first axis only takes into account the responses received by the first plurality of antennas AC1 to AC8, and the calculation of the tag position according to the second axis only takes into account the responses of the second plurality of antennas AL1 to AL4. As described above, the selection of antennas can be scanned using one or two indicators IB. For example, the calculation of the position can be obtained from the following formula:

[0075] [Formula 3]

[0076]

[0077] Wherein, x(Dj) is the position of tag Dj according to the first axis X, y(Dj) is the position of tag Dj according to the second axis Y, n is the number of antennas according to the first axis X, m is the number of antennas according to the second axis Y, xi is the position of antenna ACi according to the first axis X, yk is the position of antenna ALk according to the second axis Y, RCi(Dj) is the number of ATQA responses received by antenna ACi placed at position xi and originating from tag Dj, and RLk(Dj) is the number of ATQA responses received by antenna ALk placed at position yk and originating from tag Dj.

[0078] Therefore, by means of the REQA command and the associated ATQA response, it is possible to locate an electronic tag placed on a communication surface fairly easily. The same mechanism can be used with other commands defined in the standard ISO 14443, such as the WUPA command.

[0079] Already described Figure 6 A positioning method in which there is only one electronic tag in the magnetic field of the antenna. This positioning method can also be applied when there are multiple electronic tags in the magnetic field of one antenna. Therefore, steps 610 and 620 must be adjusted. In the case where there are multiple tags in the field of one antenna on the communication surface, the ATQA response indicates the beginning of an identifier that is common to all tags present in the magnetic field of the antenna, and these tags have sufficient energy to respond. When the tag detects that the ATQA response does not conform to the content of its modulation, that is, when multiple tags modulate the same bit differently, the electronic tag stops modulating. The processing unit 200 that receives an incomplete identifier via the MODEM circuit 110 therefore executes an anti-collision cycle defined in the standard ISO14443, replacing steps 610 and 620. The processing unit 200 sends a selection command SEL containing the beginning of the received identifier, and the additional bit is fixed to 1 and then fixed to 0 so as to select the minimum number of electronic tags. If only one tag is selected, the SAK response sent by the tag contains the identifier of the tag. If multiple tags are selected, the SAK response is incomplete, and the selection operation is repeated for another bit of the identifier. Thus, the selection operation is repeated until all tags present in the field of the antenna have been completely identified. During the progress of the anti-collision cycle, the processing unit 200 stores the identifiers of the detected tags. For more details on the anti-collision mechanism, a person skilled in the art can refer to the standard ISO 14443.

[0080] The above method uses the low power of the MODEM circuit 110, which is limited, for example, by the distance separating the two antennas. If the communication surface is used as a product display, the antenna of the electronic tag can be placed on the top of certain packages, so that it is a few centimeters away from the display location. In order to allow detection of tags farther away, a higher transmission power can be used, which makes it possible to read the electronic tag at a distance of, for example, twice the above. If the electronic tag is close to the surface, the use of a stronger magnetic field may result in more antennas being detected. In particular, the number of antennas that receive ATQA responses to all REQA commands may increase, which may hinder its accuracy. In order to increase the detection range of the electronic tag without losing accuracy, the above method is modified using variable power.

[0081] Figure 8 A communication surface 1 for product display is shown, on which two products P1 and P2 have been placed. Each of the products P1 and P2 comprises an electronic tag D1 and D2, respectively, at the bottom of its packaging. Nevertheless, the product P2 is inadvertently placed upside down on the communication surface 1. As a result, the tag D2 is located at a certain distance from the surface 1. As far as the positioning on the communication surface 1 is concerned, it is assumed that the placement of the tags D1 and D2 is the same as Figure 1 For example, it is assumed that the distance between the communication surface 1 and the tag D2 is between one and two times the distance between the two separated antennas A1 to A8.

[0082] In this improvement of the positioning method, the processing unit 200 controls the transmission power of the MODEM circuit 110 so that each detection is performed with a different power. Fig. 9 Repeat and combine the positioning methods shown Figure 6 The same steps of the method described above are performed, but an initialization step 900 is added, during which the processing unit 200 initializes the transmission power of the MODEM circuit 110 to the maximum power Pmax. For example, the maximum power is fixed so that the tag can be detected at a distance twice as long as the distance separating two antennas A1 to A8 adjacent to each other. The processing unit 200 then performs steps 610 to 620 through each of the antennas A1 to A8. Then, in step 910, during the increment of the indicator JB, the processing unit 200 reduces the transmission power of the MODEM circuit 110. For example, for a value "p" of the indicator JB equal to "10", the power is reduced by 5%. Those skilled in the art can consider the maximum transmission power and the minimum transmission power, and gradually reduce the power of the maximum power to the minimum power according to the number of inquiries performed by each antenna, that is, the value "p". According to a variant, a step 900 including initializing the transmission power to the minimum power and a step 910 including gradually increasing the power to the maximum power can be provided.

[0083] Fig.10 The multiple ATQA responses received by each of antennas A1 to A8 from the electronic tags D1 and D2 are graphically illustrated by way of non-limiting example. Antenna A1 receives four ATQA responses from electronic tag D1, antenna A2 receives eight ATQA responses from electronic tag D1, antenna A3 receives nine ATQA responses from electronic tag D1, and antenna A4 receives five ATQA responses from tag D1. Antenna A6 receives one ATQA response from electronic tag D2, antenna A7 receives three ATQA responses from electronic tag D2, and antenna A8 receives one ATQA response from electronic tag D2. In order to obtain the position of electronic tag D1 or D2, the processing unit 200 calculates the average of the positions of antennas A1 to A8, which is weighted by the number of responses received. As described below: For example, if the positions of antennas A1 to A8 are four centimeters apart, and antenna A1 corresponds to the origin of the X-axis, then the positions x1 to x8 of antennas A1 to A8 are located at distances of 0, 4, 8, 12, 16, 20, 24, and 28 centimeters relative to the origin, respectively. Considering Figure 8The ATQA response represented in , can calculate the position x(D1) of 6.31 centimeters from the origin, and the position x(D2) of 24 centimeters from the origin. Those skilled in the art will note that these measurements are different from but close to the measurements made above, and the detection of these measurements is improved.

[0084] The above method requires executing multiple instances of the send command using each antenna. In order to achieve a faster method that is equally simple to implement, the present invention proposes measuring the response time of the tag in order to locate the tag.

[0085] The ISO 14443 standard states that after receiving a command, the tag must send a response within the time limit FDT (Frame Delay Time). FDT is defined in the ISO 14443 standard as the time separating the last modulation pulse of the reader from the first modulation pulse of the electronic tag.

[0086] Fig.11 The top of the figure shows the modulated magnetic field, and the bottom of the figure shows the pulse sequence that modulates the magnetic field. The REQA command corresponds to the first cycle, followed by the ATQA response corresponding to the second cycle. The baseband modulation is achieved by pulses, and the offset of the pulses is different depending on whether the bit sent is a "0" or a "1". The FDT measurement is performed between the end of the last pulse of the REQA command modulated by the reader and the beginning of the first pulse of the ATQA response modulated by the tag, as shown in Figure 1. Fig.11 As shown. Fig.11 As shown by the dotted line in , the last pulse of the REQA command can be generated at the end of the REQA command or before the end, depending on the value of the last bit transmitted.

[0087] The standard ISO14443 defines the duration of the FDT in terms of the number of cycles of the magnetic field frequency. Depending on the value of the last bit modulated by the reader, this time period may be increased by an additional time period, which corresponds to the end of the symbol. The number of cycles of the FDT also depends on the command sent so that the electronic tag has time to respond to the command. For example, for the REQA command, the FDT period for sending the ATQA response is fixed to 1172 cycles of the magnetic field frequency, plus 64 additional cycles when the last bit is "1". In addition, the standard ISO14443 provides a tolerance of + / -1 cycle for the FDT of the reader, and a tolerance of +0.4 microseconds for the electronic tag. For further definition of FDT, those skilled in the art can refer to the ISO 14443 standard.

[0088] In practice, it is found that the reaction time of the NFC chip depends on the power of the received magnetic field, which itself depends on the distance from the antenna. Therefore, the change in response time represents the distance between the electronic tag and the reader antenna. In addition, this change occurs in a time period corresponding to +0.4 microseconds, or a time period exceeding 5.4 magnetic field cycles. FDT can be measured by simply counting the cycles of the magnetic field. This cycle counting is specifically done to determine the absence of a response.

[0089] Fig.12 A method for measuring the position of an electronic tag using response time measurement is shown, which is easy to implement. When the processing unit 200 executes a program corresponding to the method for locating a tag, in step 1200, the processing unit initializes the method by setting a loop index IB to a value of "1". Then, in step 1210, the processing unit 200 controls the MODEM circuit 110 to send a command, such as REQA, at a specified power on the antennas A1 to An corresponding to the index IB in order to receive an ATQA response indicating the identification number of the electronic tag. For all antennas, the specified transmission power is the same, or at least substantially the same. During step 1220, when the antennas A1 to An receive the ATQA response, the MODEM circuit 110 sends the response and the measured value of the response time TR to the processing unit 200. The processing unit 200 stores the identifier of the electronic tag that has responded, the response time TR, and the index IB corresponding to the antennas A1 to An that have received the ATQA response. For example, the response time TR is measured, for example, in the number of periods of the magnetic field that separates the last modulation pulse of the REQA command from the first pulse of the ATQA response.

[0090] During step 1230, steps 1210 and 1220 are repeated after the index IB is increased until the index IB reaches a value "n" corresponding to the number of antennas A1 to An. When steps 1210 and 1220 have been performed "n" times, the processing unit 200 performs step 1240 of calculating the position of the detected tag.

[0091] In order to perform the calculation of the position, it is necessary to take into account the difference between the measured response time TR and the expected response time corresponding to the FDT. In addition, the shorter the response time, the smaller the distance between the tag and the maximum field of the antenna. A first method can consist in determining the distance relative to each antenna, which depends on the difference between the measured response time TR and the expected response time FDT. Then, a triangulation process can locate the position of the tag more accurately. However, this method requires the classification of the response time of the tag, which can only be achieved if the circuit of the tag is accurately known.

[0092] In addition, the present invention proposes a simple calculation method based on the average value of the antenna position, which performs a weighted average of the antenna position based on the inverse of the difference between the measured response time and the expected response time. Figure 1 For an antenna network, the following formula can be used:

[0093] [Formula 4]

[0094]

[0095] where x(Dj) corresponds to the position of tag Dj, n is the number of antennas, TRi(Dj) is the response time of tag Dj measured by antenna Ai, FDT is the expected response time, and xi is the position of antenna Ai.

[0096] As an example, Fig.13 Shown according to Figure 1 The difference between the measured response time and the expected response time of the located electronic tags D1 and D2. Antenna A2 can measure the delay of four cycles of the ATQA response of the electronic tag D1, and antenna A3 can measure the delay of three cycles of the ATQA response of the electronic tag D1. Antenna A6 can measure the delay of four cycles of the ATQA response of the electronic tag D2, antenna A7 can measure the delay of two cycles of the ATQA response of the electronic tag D2, and antenna A8 can measure the delay of five cycles of the ATQA response of the electronic tag D2.

[0097] For example, if the positions of antennas A1 to A8 are four centimeters apart, and antenna A1 corresponds to the origin of the X-axis, then the positions x1 to x8 of antennas A1 to A8 are located at distances of 0, 4, 8, 12, 16, 20, 24, and 28 centimeters relative to the origin, respectively. Fig.13 The difference between the measured response time and the expected response time of the electronic tags D1 and D2 is shown for a position x(D1) of 6.29 cm from the origin and for a position x(D2) of 23.78 cm from the origin. The error range of this method depends on the power of the magnetic field, the distance that can separate the surface area of ​​the surface from the location of the tag, the orientation of the tag, and more generally, the coupling coefficient between the antennas A1 to A8 of the communication surface 1 and the antenna of the electronic tag D1 or D2.

[0098] Reference Figure 1 The calculation formula of the communication surface 1 can be applied to Figure 2 The communication surface 1' or Figure 3 The communication surface 1". To scan in rows and columns, two indicators can be used instead Fig.12 The indicator IB in the method, or a correspondence table is used for the correspondence between a single indicator IB and each antenna.

[0099] As an example, use Figure 2 The formula of the communication surface 1' can be, for example:

[0100] [Formula 5]

[0101]

[0102] Wherein, x(Dj) is the position of tag Dj according to the first axis X, y(Dj) is the position of tag Dj according to the second axis Y, n is the number of antennas according to the first axis X, m is the number of antennas according to the second axis Y, xi is the position of antenna Aik according to the first axis X, yk is the position of antenna Aik according to the second axis Y, and TRik(Dj) is the response time of tag Dj measured by antenna Aik placed at positions xi and yk, and FDT is the expected response time.

[0103] As an example, use Figure 3 The formula of the communication surface 1" can be, for example:

[0104] [Formula 6]

[0105]

[0106] Wherein, x(Dj) is the position of tag Dj according to the first axis X, y(Dj) is the position of tag Dj according to the second axis Y, n is the number of antennas according to the first axis X, m is the number of antennas according to the second axis Y, xi is the position of antenna ACi according to the first axis X, yk is the position of antenna ALk according to the second axis Y, and TRCi(Dj) is the response time of tag Dj measured by antenna ACi placed at position xi, TRLk(Dj) is the response time of tag Dj measured by antenna ALk placed at position yk, and FDT is the expected response time.

[0107] Already described Fig.12A positioning method in which there is only one electronic tag in the magnetic field of the antenna. This positioning method can also be applied when there are multiple electronic tags in the magnetic field of one antenna. Therefore, steps 1210 and 1220 must be adjusted. As described above, in the case where there are multiple tags in the field of one antenna on the communication surface, the ATQA response indicates the beginning of an identifier that is common to all tags present in the magnetic field of the antenna. When the tag detects that the ATQA response does not conform to the content of its modulation, the tag stops modulating. The processing unit 200 that receives the incomplete identifier via the MODEM circuit 110 therefore executes the anti-collision cycle defined in the standard ISO 14443, replacing steps 1210 and 1220. The processing unit 200 sends a selection command SEL containing the beginning of the received identifier, and the additional bit is fixed to 1 and then fixed to 0 so as to select the minimum number of electronic tags. If only one tag is selected, the SAK response sent by the tag contains the identifier of the tag. In addition, the SAK response must be sent within the FDT after the SEL command, which is the same as the FDT after the ATQA response. If multiple electronic tags are selected, the SAK response is incomplete and the selection operation is repeated for another bit of the identifier. Therefore, the selection operation is repeated until all tags present in the field of the antenna have been fully identified. The identifiers of the electronic tags are stored together with the response times corresponding to the SAK responses they return. At the end of the anti-collision cycle, the processing unit 200 can proceed to step 1230 or 1240. For more details on the anti-collision mechanism, those skilled in the art can refer to the standard ISO14443.

[0108] The described embodiments relate to contactless devices, referred to as Class A in standard ISO 14443. Class A devices correspond to electronic tags comprising simplified electronic circuits that are used only to return an identifier. Class A devices are often used for marking and identification of commercial products due to the low cost of their electronic circuits, and are also often used in games using communication game boards. However, position positioning can also be applied by counting the number of responses to Class B devices, using equivalent commands and anti-collision management applicable to Class B. In fact, steps 610 and 620 can be replaced by the overall detection of Type A or Type B electronic tags, the important issue being the identification of the electronic tags in the field of the antenna, and the calculation of the number of responses of each tag to each antenna.

[0109] Similarly, the method of positioning by measuring the response time can also be applied to Class B devices. However, Class B devices use a response time window. Therefore, it is necessary to consider the time window that the electronic tag uses to determine the expected response time. Steps 1210 and 1220 can be replaced by the overall detection of Class B electronic tags, step 1210 corresponds to sending a REQB command, and step 1220 corresponds to receiving one or more ATQB responses in one of the response time windows. The important issue is to identify the electronic tag and measure its response time in the field of each antenna.

[0110] exist Figure 2 and 3 In the embodiment of the invention, the antenna is represented according to two perpendicular axes. Those skilled in the art will appreciate that it is not necessary to position the axes perpendicular to each other and that the positioning of the axes can be adjusted as desired. Likewise, two axes are generally sufficient to position the tag on a flat surface. To increase positioning accuracy, three or four intersecting axes may be used.

Claims

1. A near field communication surface for communicating with at least one electronic identification tag, the surface comprising: - a plurality of antennas, each antenna having a position along a first axis corresponding to a maximum flux of the antenna according to said first axis, - at least one reader circuit for reading an electronic identification tag, connected to said antenna so as to power said antenna and communicate with said at least one electronic identification tag, a processing unit controlling an antenna and at least one reader circuit for reading an electronic identification tag, and said processing unit being arranged to activate only one antenna and said at least one reader circuit at a time in order to communicate with said at least one electronic identification tag, It is characterized in that, in order to locate the position of the at least one electronic identification tag along the first axis according to the response times of the at least one electronic identification tag, the processing unit is configured to send a command to the at least one electronic identification tag through each antenna.

2. The near field communication surface according to claim 1, wherein: The processing unit is configured to - send a command to at least one electronic identification tag via at least one reader circuit and each antenna a predetermined number of times, - count the number of responses received by each antenna, and - Calculating the location of at least one electronic identification tag by taking a weighted average of the locations of the antennas by the number of responses received by each antenna.

3. The near field communication surface according to claim 2, wherein: The processing unit is configured to control the transmission power of the reader circuit so that a predetermined number of commands are sent with a predetermined amount of transmission power.

4. The near field communication surface according to any one of claims 1 to 3, wherein: The communication surface also includes: - a second plurality of antennas, each antenna having a position according to a second axis, the position corresponding to a maximum flux of the antenna according to the second axis, the second axis intersecting the first axis, the second plurality of antennas being connected to at least one reader circuit for reading electronic identification tags, and the second plurality of antennas being controlled by a processing unit, wherein the processing unit is configured to locate the position of the at least one electronic identification tag along the second axis based on the number of responses of the at least one electronic identification tag.

5. The near field communication surface according to claim 4, wherein: The shape of the first plurality of antennas is elongated along the second direction, the shape of the second plurality of antennas is elongated along the first direction, the surface area covered by the first and second plurality of antennas is substantially equal to the surface area of ​​the surface, and the first and second plurality of antennas overlap, thereby enabling at least one electronic identification tag to be positioned on the entire surface according to the first and second axes.

6. The near field communication surface according to any one of claims 1 to 3, wherein: Each antenna includes at least one shunt switch that short-circuits the antenna when closed, and wherein the at least one shunt switch is opened when the antenna is selected and the at least one shunt switch is closed when the antenna is not selected.

7. The near field communication surface according to any one of claims 1 to 3, wherein: At least one reader circuit includes a single modem circuit connected to each antenna of the first plurality of antennas and / or the second plurality of antennas, wherein each antenna includes two connector switches for connecting it to the single reader circuit, and wherein the connector switches are closed when the antenna is selected and open when the antenna is not selected.

8. A method of locating an electronic identification tag on a near field communication surface, the surface comprising a plurality of antennas, each antenna having a position according to an axis corresponding to a maximum flux of the antenna according to the axis, and at least one circuit for reading the electronic identification tag, the at least one circuit being connected to the antenna to power the antenna and communicate with the electronic identification tag, characterized in that The method comprises the following steps: - sending a command, which sends a command to the electronic identification tag through an antenna selected from a plurality of antennas, - receiving a response, which receives a response from the electronic identification tag through a selected antenna and stores the response or non-response of the electronic identification tag, - repeating the steps of sending commands and receiving responses until at least one command has been sent to each of the plurality of antennas, - calculating the position of the electronic identification tag, which calculates the position of the electronic identification tag according to the number of responses of the electronic identification tag.

9. The method of claim 8, wherein the steps of sending commands and receiving responses are repeated until each of the plurality of antennas has sent a predetermined number of commands to the electronic identification tag, wherein the step of receiving responses is to count the number of responses received, and wherein the step of calculating the position of the electronic identification tag is to determine the position of the electronic identification tag by taking a weighted average of the positions of the antennas by the number of responses received.

10. The method of claim 9, wherein the predetermined number of commands are sent with a predetermined amount of transmission power.

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