Rfid system using distributed exciter network

The present invention relates generally to RFID systems, and more specifically to RFID systems incorporating at least one RFID receiver system and a distributed exciter architecture defining multiple interrogation spaces.

Signal detection in difficult environments, such as very low signal-to-noise ratios and / or very strong interference from other signals, has always been a challenging task.

<p> Described in US Patent Application No. 11/971678 filed on January 9, 2008, which is incorporated herein by reference in its entirety, and the title of the invention "RFID system with low implementation complexity and pallet coding error correction". In RFID systems, such as RFID systems, RFID receiver subsystems detect very low power signals in indoor or outdoor radio propagation channels with the additional white Gaussian noise with additional channel distortion. On the other hand, it depends on the enhancement of the RF front end as well as the processing power. These techniques are particularly applicable to radio frequency identification (RFID) systems. FIG. 12 shows a transmit / receive RFID reader similar to the specifications of the transmit / receive reader and RF front end described in US Patent Application No. 11/971678. The reader (12-9) tracks the RFID tag protocol and communicates with the tag (12-5) using the same transmit and receive frequencies. A timeline showing this communication is shown in FIG. The protocol sends the reader data (13-2) to the tag as well as the continuous wave (CW) (13-4) transmission (12-4) and the tag data (13-10) reception (12-2). to manage. From FIG. 13, the reader transmits a CW signal (13-4) during the period when the tag backscatters the packet to the reader. That is, the received signal is a composite of the transmitted CW and the received tag signal (12-7). Receiver subsystem (12-9) performs baseband down-conversion (12-12, 12-14), filtering (12-16, 12-18), and amplification (12-20, 12-22) To do. At the output of the baseband amplifier, there is a signal from the tag along with a strong DC component. This DC component is erased using DC blocking capacitors (12-27, 12-29). To further improve the performance of DC erasure, the input to the DC blocking capacitors (12-27, 12-29) is a switch that closes only while the system is receiving data from the tag, as shown in Figure 13. It is controlled through (12-24, 12-26). The digital processor (12-46) maintains system timing control of the switch control and opens the switch during the transmission period of the reader (13-2, 13-6, 13-14, 13-18) and is expected. The switch is closed during the reception period (13-4, 13-10, 13-16). The output of the DC erasing capacitor is followed by an AGC loop (12-32, 12-34), an analog-to-digital converter (12-36, 12-38), and a digital processor (12-40) containing a control algorithm. To do.</p>

<p> RFID systems according to many embodiments of the present invention include one or more RFID receiver systems for many distributed transmitters, called RFID tag exciters (or simply "exciters"). The exciter can act as a signal repeater from the RFID receiver system, allowing the tag signal to be transmitted to the distant exciter, and then this distant exciter for the intended RFID tag collection within the exciter's line of sight. , Filter the signal, amplify it, and retransmit it. Logical interconnects and communication topologies scale from centralized control points to full connectivity graphs. Physically, the communication network can be either wired or wireless.</p><p> Each exciter may or may not include dynamic regeneration of the transmitted signal into an RFID tag, but in many embodiments, each exciter has sufficient power and an electronic product code. -Emit a waveform that is compatible with the standard requirements presented by Global (EPC Global) or the International Organization for Standardization (ISO). Transmission from RFID receiver systems to exciters may be compatible with these standards and / or regulatory requirements stated, for example, by the Federal Communications Commission (FCC) or other international coordinating agencies. Other waveforms compatible with may be used.</p><p> One embodiment of the present invention includes an RFID receiver system configured to detect information from an RFID tag within a receive cover area, the plurality of exciters within the receive cover area of the RFID receiver system. Define the response command space. In addition, the RFID receiver system is configured to identify one of a plurality of exciters and transmit a control signal including information indicating an RFID tag response command signal, so that the plurality of exciters receive the control signal. The exciter identified by the control signal is configured to illuminate the response command space using the RFID tag response command signal.</p>

<figref num="1">FIG. 5 is a network diagram of an RFID system including a distributed exciter architecture according to an embodiment of the present invention, in which the exciter is connected to the RFID system via a cable.</figref><figref num="2">FIG. 5 is a network diagram of an RFID system including two RFID receiver systems and a distributed exciter architecture according to an embodiment of the present invention, in which the exciter is connected to the RFID receiver system via a cable.</figref><figref num="3">FIG. 5 is a network diagram of an RFID system including two RFID receiver systems and a distributed exciter architecture according to an embodiment of the present invention, in which the exciter wirelessly communicates with the RFID receiver system.</figref><figref num="4">FIG. 5 is a schematic circuit diagram of an exciter configured to be connected to an RFID receiver system via a coaxial cable according to an embodiment of the present invention.</figref><figref num="5">FIG. 5 is a schematic circuit diagram of an exciter configured to connect to an RFID receiver system via twisted pair according to an embodiment of the present invention.</figref><figref num="6">FIG. 5 is a schematic circuit diagram of an exciter configured to wirelessly communicate with an RFID receiver system according to an embodiment of the present invention.</figref><figref num="7">It is a schematic circuit diagram of the wireless reproduction exciter which concerns on one Embodiment of this invention.</figref><figref num="8">It is a top view of the antenna element which concerns on one Embodiment of this invention.</figref><figref num="9">It is sectional drawing of the antenna assembly which concerns on one Embodiment of this invention.</figref><figref num="10">It is a top view of the array of the receiver antenna which concerns on one Embodiment of this invention.</figref><figref num="11">FIG. 5 is a cross-sectional view of an array of receiver antennas according to an embodiment of the present invention, similar to the array shown in FIG.</figref><figref num="12">It is a schematic circuit diagram of a transmission / reception RFID reader.</figref><figref num="13">It is a chart which conceptually shows a tag protocol timing.</figref><figref num="14">FIG. 5 is a conceptual diagram of software used for setting an RFID application server according to an embodiment of the present invention.</figref><figref num="15">FIG. 5 is a flow chart of a method for determining whether or not an RFID tag is detected from a tag in a predetermined response command space according to an embodiment of the present invention.</figref><figref num="16">FIG. 6 is a schematic diagram showing an RFID system including a distributed exciter architecture in which exciters are paired to facilitate the distinction of tag reading locations according to an embodiment of the present invention.</figref><figref num="17">17a and 17b are conceptual diagrams showing frequency allocation and scheduling for a plurality of exciters according to an embodiment of the present invention.</figref><figref num="18">It is a block diagram which shows the state measurement of an input level, and the feedback control loop of an output level which concerns on one Embodiment of this invention.</figref><figref num="19">FIG. 5 is a block diagram showing a wirelessly or wired controlled exciter having a return path of radio status information that enables wireless communication of messages from the exciter to the RFID receiver system according to an embodiment of the present invention.</figref><figref num="20">It is a conceptual diagram of RFID tag movement between two hypothetical regions.</figref><figref num="21">Between the exciter and the RFID tag, which can be used to determine the excitation link margin in the exciter / hypothetical topology, exciter transmission output, exciter emission pattern, and normal RFID tag emission pattern according to an embodiment of the present invention. It is a conceptual diagram of a spatial relationship.</figref><figref num="22">It is a chart which shows the probability function which describes the probability of the RFID tag reading rate with respect to the RFID tag arranged in the given hypothesis region excited by a given exciter which concerns on one Embodiment of this invention.</figref>

Returning to the drawing, an RFID system including at least one RFID receiver system and a distributed exciter architecture is shown. In some embodiments, the entire desired interrogation space is decomposed into a set of response command spaces, and exciters are placed in each target response command space. This RFID system acquires information from the collection of RFID tags in a specific response command space by controlling the activation of the exciter. The RFID tag in the response command space is manipulated by irradiating the response command space with the RFID tag response command signal provided to the exciter by the RFID receiver system. The illuminated RFID tag backscatters the information, which can be detected by the RFID receiver system.

The RFID receiver system can control the size of each response command space by adjusting the total radiated power from the exciter. In many embodiments, the overall system performance is improved by selecting the type of transmitting antenna for each exciter that provides the desired level of directivity, thereby controlling the beamwidth with respect to the target response command space. .. In some embodiments, the exciter is connected to the RFID receiver system via a cable. In many embodiments, the exciter is wirelessly connected to the RFID receiver system.

Once the topology of the response command space is defined, the RFID system according to the embodiment of the present invention can control the irradiation of the individual response command space and acquire the position information about the article having the RFID tag. In many embodiments, the RFID system polls the exciter. In some embodiments, RFID systems can incorporate additional sensors to detect changes (eg, movement) within the response command space, and RFID systems are associated with adjacent response command spaces with corresponding exciters and corresponding exciters. / Or you can activate the exciter and get information about any article that has an RFID tag and moves between response command spaces.

A problem that can be encountered when using a distributed exciter architecture is the possibility that RFID tags will be read (false reads) outside the exciter response command space. In some embodiments, information about various characteristics of RFID systems is used to detect the occurrence of false reads. In many embodiments, the data from the sensor in the response command space, the RFID tag information detected in the other response command space and / or the RF feature of the detected RFID tag information is whether a false read has occurred. Can be used to determine. In many embodiments, statistical analysis is used to detect false reads based on predicted read rates for RFID tags located within the response command space. In these embodiments, the repeated irradiation of the response command space and the RFID tag detection rate are compared with the predicted detection rate for determining the likely position of the RFID tag. In some embodiments, the predictive detection rate is obtained using knowledge of the exciter topology of the RPI D system.

An RFID system including a distributed exciter architecture according to an embodiment of the present invention is shown in FIG. RFID system (1-1) is an RFID receiver system via an array of receiver antennas (1-4) and cables (1-10, 1-9, 1-16, 1-22, 1-26). Includes RFID receiver system (1-2) connected to multiple exciters (1-6, 1-14, 1-18, 1-23, 1-28) daisy-chained to. The RFID receiver system (1-2) is also connected to the LAN (1-32) via the connection (1-34). The RFID application server (1-30) is connected to the LAN via the connection (1-36). Although the plurality of exciters are shown as wired, in many embodiments the exciters communicate wirelessly with the RFID receiver system.

During operation, the RFID receiver system (1-2) controls the activation of the exciter. Cable segments (1-10, 1-12, 1-16, 1-22, 1-26) from RFID receiver system (1-2) to each exciter, both direct current (DC) power and control commands. To carry. The "return signal" transmitted from the RFID receiver system (1-2) to the exciter embeds all the necessary signal features and parameters to generate the desired waveform output from the exciter module to the ID tag. .. In some embodiments, each exciter can be commanded and addressed by N-bit address, where N ranges from 16 to 32 bits. Depending on the number of beams that the RFID receiver system can support, the exciters (1-8, 1-14, 1-18, 1-23, 1-28) can operate continuously or in parallel. In the illustrated embodiment, the RFID receiver system (1-2) includes a single antenna array (1-4) and can generate a single beam. In other embodiments, the RFID receiver system may include multiple antenna arrays and generate multiple beams (see description below).

The response command space and transmission power of each exciter can be managed and controlled by the RFID receiver system (1-2). In the illustrated embodiment, the RFID receiver system (1-2) controls the exciter and provides different sized response command spaces (1-8, 1-15, 1-20, 1-24 and 1-28). create. In addition, the receive cover area is configurable. The RFID receiver system can receive signals from the entire coverage area (1-11). Alternatively, the RFID receiver system can optimally beam form in the designated exciter response command space (1-12, 1-21).

RFID application servers (1-30) plan to operate each exciter in harmony in multiple dimensions: time, frequency and space. In many embodiments, the RFID application server (1-30) includes a scheduler for S / TVFDM (spatial, time and frequency division multiplexing), which displays all RFID tags within the target response command space. Use an optimization algorithm that maximizes the probability of successful operation. In addition, the controller can utilize frequency hopping in the scheduling of frequency channels for each exciter for the purpose of satisfying various tuning constraints.

The exciter layout and timeline showing the frequency channels assigned by the RFID application server according to the embodiment of the present invention are shown in FIGS. 17a and 17b. The timeline (17-4) represents the channel selection for the timeline within the 900MHz ISM band (17-10). In the exemplary embodiment of time "1", exciters 12, 15, 7, 11, 10, 3, 9, 4, 2, 1, 6, 14, 16, 8, 13, and 5, respectively, channel 7, Invoked for operation on 16, 23, 25, 34, 40, 44, 46, 49, 50, 51, and 52. Note that collisions can occur up to the extent that multiple exciters occupy a given channel and these exciters are located in the same topology (eg, exciters 7 and 11). Therefore, it is possible that a better choice could have been made in the frequency / exciter mapping program. However, in the exemplary embodiment, a working exciter (17-8) is assigned a random frequency, which is a collision of frequencies sharing a place (eg, on channel 23, exciter 7 in time example 1). Means that there can be (between 11 and 11). Frequency reuse and exciter placement schemes (14-12) (S / T / FDM) can be used to reduce overall buffering while adhering to regulatory constraints. An RFID system including two RFID receiver systems and a distributed exciter architecture according to an embodiment of the present invention is illustrated in FIG. This RFID system includes two RFID receiver systems (2-2, 2-20), each with a separate array of receiver antennas (2-4, 2-22) and connections (2-23). , 2-25) to LAN (2-21). Multiple exciters (2-6, 2-52, 2-58, 2-64, 2-32, 2-28, 2-38, 2-48, 2-44, 2-72, 2-70) Connect to two RFID receiver systems and have multiple response command spaces (2-13, 2-54, 2-69, 2) -66, 2-34, 2-28, 2-40, 2-46, 2-49, 2-72). In the illustrated embodiment, the exciters form two groups, each group having a separate cable (2-24, 2-30, 2-36, 2-42, 2-50 and 2-10, 2-12, It is connected to the RFID receiver system by 2-56, 2-62, 2-68). The RFID application server (2-51) works with the RFID receiver system (2-2, 2-20) through LAN (2-21) to control, control, coordinate, calibrate and optimize the exciter response command space. Manage exciter operations, including conversion. The functions of the RFID application server according to the embodiment of the present invention will be further described below.

As can be seen from the embodiments illustrated in FIG. 2, each RFID receiver system has a separate receive coverage area (2-5, 2-29). Therefore, the use of multiple RFID receiver systems allows for increased coverage of the system. In addition, exciters in different coverage areas can be activated at the same time. In the illustrated embodiment, some exciters (2-32, 2-44) occupy a place in both coverage areas of the RFID receiver system. When two exciters (and RFID tags) transmit simultaneously in different response command spaces, beam formation in each RFID receiver system allows null placement in the response command space of the other RFID receiver system. Avoid collisions.

FIG. 3 shows an RFID system including a plurality of RFID receiver systems and a distributed exciter architecture constructed by using the RFID receiver system according to the embodiment of the present invention and the exciter for wireless communication. This RFID system is similar to the system shown in FIG. 2, with the exception that the exciter is configured to wirelessly communicate with the RFID receiver system. Each RFID receiver system (2-2', 2-20') has a receiver (2-4', 2-22') and a transmit antenna (3-6, 3-8). The transmitting antenna radiates a forward link to the exciter, while the receiving antenna array receives a signal from the RFID tag within the response command space of each exciter. Forward links also carry exciter identification (ID) numbers, commands, control and management information. In the illustrated embodiment, the receive coverage area for two RFID receiver systems (2-5', 2-29') is shown. The overlapping region between the covering regions (2-5', 2-29') is managed through beam formation in the receiving region and adjustment of the frequency or time of the exciter operation. The RFID application server (3-7) works with two RFID receiver systems (2-2', 2-20') through LAN (2-21'), as well as optimizing the response command space. Manages the operation of the exciter, including control, command, adjustment and calibration of the exciter.

The implementation of the wired exciter according to the embodiment of the present invention is shown in FIGS. 4 and 5. FIG. 4 represents an exciter according to an embodiment of the invention configured to connect to an RFID system via coaxial cable. FIG. 5 represents an exciter according to an embodiment of the invention configured to connect the exciter to an RFID system via a general purpose twisted pair (UTP) that can be connected via CAT-5 or 6 leads.

Leader coaxial interfaces (4-2, 4-4, 4-6, 4-8, 4-12) and interfaces for daisy-chaining multiple exciters (4-52) in the embodiments illustrated in FIG. (4-14) is shown. Received signals from RFID receiver systems typically carry control signals, which are processed by demodulation and modulation commands, and control message modules (4-10), self-calibration and automatic level control (ALC) loops (ALC). To control 4-18, 4-20, 4-48, 4-34, 4-36, 4-32) or to set the transmit power according to the manual setting (4-38, 4-30) Used for. The command and control messages for the wired exciter include a message that causes the exciter to perform power calibration (discussed below), turn the transmit signal on and off, and control the reporting of the exciter's status information (see below for Figure 19). , Refer to the description of wireless / wired hybrid exciter). The received RF signal is split using a coupler (4-8) between the next exciter (4-52) and the transmitting RF chain (4-40). The RF chain consists of a receiving low noise amplifier (4-16) and an ALC loop (4-22, 4-20, 4-24, 4-48) consisting of a feedback loop and a power amplifier (PA) (4-24). And include. After PA output, follow the transmit antenna patch (4-28). In addition, the exciter has an interface to one or more external alarms (4-58), which is linked to the internal processor (4-47).

A self-calibration and automatic level control loop according to an embodiment of the present invention is shown in FIG. This block measures the power levels of inputs (18-1) and outputs (18-4). Input power levels between -10 dB milliwatts and 27 dB milliwatts are considered to be acceptable. If the input signal is within this range, the block of output power level measurement (18-3) feeds the signal back to the amplifier module (18-2) so that the total output power level is 30 dB milliwatts. , Control the gain of the power amplifier. This output level complies with the FCC's total radiated power regulations for frequency hopping systems operating in the 900MHz band. In other embodiments, the total output power level of the exciter can be controlled according to the constraints of other applications. The embodiments illustrated in FIG. 18 are particularly useful in applications where the exciter regenerates the receive control signal. The radio exciter that synthesizes the RFID tag ring waveform according to some embodiments of the present invention can utilize an automatic control loop that simply monitors the output level and adjusts the transmitter power accordingly.

See Figure 5 to show an exciter with a UTP interface using CAT-5 or 6 cables (5-4, 5-72). When the UTP interface is used, the interface between the exciter and the RPI D system (5-4) is in baseband. The exciter detects the baseband signal and modulates it to the specified RF frequency. When a coaxial interface is used, the interface is at high frequencies, which are repeated and the baseband carries the control signal. The raw data that the RFID receiver system sends to the exciter includes the data that is modulated and sent to the RFID tag, along with control and command signals. Like the coaxial version, the UTP exciter uses a UTP connector to daisy chain (5-2, 5-4, 5-6, 5-8, 5-10, 5-12, 5-14, 5-72, 5-74) is possible. Demodulation and decoding commands and control message modules (5-18) include RF synthesizer (5-22), modulator (5-26), self-calibration and ALC control loops (5-24), and manual transmit power configuration. Decrypt the command and control data used to calibrate the subsystem (5-20). The data decoder and modulator (5-26) detect and remodulate the transmitted data according to the relevant standards, to which it is up-converted (5-28, 5-60, 5-58) and automatic gain control (5). -32, 5-34, 5-36, 5-24) follows. The amplified signal is fed to the transmitting antenna patch (5-40) via the connection (5-66). The exciter also has an interface (5-76) for one or more external alarms (5-80), which works with the internal processor (5-16).

The radio exciter according to the embodiment of the present invention is shown in FIG. RFID receiver systems use transmit antennas (6-4) to communicate with radio exciters at one frequency, while using an array of receiver antennas to receive data from tags at different frequencies. In the illustrated embodiment, the radio exciter operates as an RF repeater utilizing the 900 MHz ISM band. In other embodiments, other frequency bands can be used. The RF signal is down-converted from the signal transmitted by the transmit antenna (6-4) of the RFID receiver system to the baseband in the down-convert output connection (6-20), and then the baseband signal is up-converted output connection. It is up-converted to the selected frequency in (6-30). The frequencies specified for down and up-conversion are communicated to the exciter using the RF command channel, for example using the 900MHz ISM band. The same method can be used for other frequency bands. The exciter patch antenna (6-6), which will be further described later, includes two wires for receiving and transmitting RF signals. The RFID receiver system sends commands, controls, and transmit frequency planning information to the exciter. Commands are detected by demodulation and decryption commands and control message modules (6-74), dual synthesizers (6-66), self-calibration and ALC loops (6-54, 6-36, 6-50, 6-). 38), and the transmission power manual setting loop (6-56, 6-48) is processed to control.

Instructions and control messages to the wireless exciter cause the exciter to calibrate the power, turn the transmit signal on and off, control the reporting of the exciter's status information (see description of the wireless / wired hybrid exciter below), and transmit. It can include a message that allows the frequency to be selected and other parameters that define the characteristics of the various transmitted waveforms to be selected. In other embodiments, commands and control messages can provide other instructions to the exciter.

The exciter configures the dual synthesizer (6-66) with the transmit and receive frequencies in response to instructions received from the RFID receiver system. The reception frequency is down-converted (6-18) and then up-converted (6-28) to a specific transmission frequency. Transmission power is self-calibrated through the control loop (6-52, 6-62, 6-50) and TX power calibrated through the ALC module (6-54) and control loop (6-48, 6-58). Configuration and calibration are performed using the subsystem (6-56) to be configured. The RF path includes filters (6-22, 6-32, 6-42) and amplifiers (6-10, 6-24, 6-38) necessary to maintain signal integrity and quality. The output of the final stage (6-42) is followed by an antenna element (6-46) to which the exciter transmission wiring is connected. In addition, the exciter has an interface to one or more external alarms (6-80), which works with the internal processor (6-70).

The regenerative radio exciter according to the embodiment of the present invention, wherein the receiver system demodulates and detects the data supplied by RFID at the first frequency, and then modulates and transmits this RF signal at different frequencies. Shown in 7. The forward link from the RPID receiver system to the exciter (7-2, 7-5) can carry the raw data along with the control and command signals. The reader forward link (7-5) to the exciter can use any modulation format, such as spectral diffusion or arbitrary simple suppression carrier modulation. In the illustrated embodiment, the operating frequency and transmit power of this link are configured to meet regulatory requirements. For example, the FCC Part 15 specified by the Federal Communications Commission (FCC) standard can be met by frequency hopping.

The radio exciter uses a data demodulator and decoder module (7-70) to detect command and control data and decode the command and control message module (7-74). This command and control data configures the RF synthesizer (7-62), modulator (7-31), self-calibration and ACL control loop (7-58), and transmit power manual configuration subsystem (7-86). Used by wireless exciters for this purpose. The data encoder and modulator (7-31) detect the transmitted data and remodulate it to the standard, which is then managed by the upconvert (7-34) and the ALC loop control module (7-58). An automatic gain control loop (7-42, 7-60, 7-44, 7-48) follows. The amplified signal (7-52) is followed by the transmit antenna wiring and patch (7-54). In addition, the exciter has an interface to one or more external alarms (7-90), which works with the internal processor (7-80).

A hybrid wireless / wired exciter according to an embodiment of the present invention is shown in FIG. In addition to the features supported by wired and / or wireless exciters mentioned above, this design provides status (19-9) or sensor (19-12) information via the same waveform nominally used by RFID tags. It is possible to reply wirelessly. The hybrid exciter is a wired interface (nominally coaxial cable) (19-1), receiving antenna interface (19-2), frequency converter (19-5) and wired output (daisy chain) interface (19-6). ) Consists of. The wireless or wired interface signal undergoes down-conversion using the mixed frequency produced by the received frequency synthesizer (19-10). After analog-to-digital conversion (19-7), the digital processor (19-8) builds a modulated waveform for digital-to-analog conversion (19-13). These waveforms can describe tag commands (ie, the signals used to manipulate the tags) or exciter status information (ie, information transmitted over the return channel to the RFID receiver system). .. In many embodiments, the exciter status information includes sensor trigger event data (19-11, 12), exciter calibration information, and / or any other information that describes the status of the exciter or its surroundings. .. The low-pass filter (19-14, 19-15) precedes the frequency up-conversion (19-16) with the mixed frequency determined by the synthesizer block (19-19). The variable gain block (19-17) calibrates the output level so that it does not exceed a given threshold (eg, 30 dBm) before bandpass filtering the output signal (19-18). The final generated signal is radiated through the transmitting antenna (19-21).

Hybrid wireless / wired exciter shown in FIG. 19, RFID receiving to communicate information to signal system can generate the same waveform as that of the irradiated tag. In many embodiments, the exciter allows the hardware configuration of the same RFID receiver system to be used both to detect the irradiated RFID tag and to receive a status signal from the exciter. , Can generate waveforms that mimic the irradiated RFID tags. In other embodiments, the return channel from the exciter to the RFID receiver system is a conventional radio communication channel, where the RFID receiver has a separate receiving mechanism to communicate with the exciter and receive information from the RFID tag. Use RFID / hardware.

FIG. 8 shows an antenna that can be used in the structure of the transmission / reception array of the reader or the transmission / reception element of the exciter according to the embodiment of the present invention. This antenna is made using a brass, copper or aluminum plate (8-2). The plate (8-2) has four slots (8-22, 8-24, 8-28, 8-30), which are circular through cuts (8-4, 8-6, 8-- End with 8, 8-26). Two through holes (8-10, 8-12) for connecting transmit and receive wiring, and four through holes (8-14, 8-16, 8-18, 8-20) for plastic insulators ).

FIG. 9 shows an antenna element similar to the antenna shown in FIG. 8 attached to the housing according to the embodiment of the present invention. In the antenna assembly (9-2), the bushing (9-10, 9-12) connects the antenna element (9-4) to the printed circuit board (PCB) (9-18), which serves as the antenna ground plane. Also works. This connection is made by a bushing pin (9-14, 9-16) to the PCB and a through screw (9-6, 9-8) to the element. The antenna element is covered with a radome cover (9-11) at a distance from the element. Plastic pins (9-5, 9-9) further stabilize the antenna element.

The reception array configuration according to the embodiment of the present invention is shown in FIGS. 10 and 11. This array consists of four elements, similar to the antenna assembly (9-2) shown in Figure 9. The four antenna elements (10-4, 10-6, 10-8, 10-10) are connected to the antenna PCB (10-2). Figure 11 shows the PCB (10-2), bushing (11-8, 11-10), element (10-4, 10-6, 10-8, 10-10), and radome cover (11-2). The cross-sectional view of is shown. In the illustrated embodiment, the distance from the center of the device to the center is 164 mm (10-5). In other embodiments, the center-to-center spacing of the device is determined according to the requirements of the application.

Although specific antenna configurations are shown in FIGS. 8 to 11, other antenna configurations that are capable of transmitting and / or receiving signals according to the particular embodiment may be used in the embodiments of the present invention. it can.

In many embodiments, the behavior of the exciter in a distributed architecture is managed and controlled by an RFID system using command, control and processing algorithms. FIG. 14 shows a series of methods adjusted by the RFID system that controls the operation of the distributed exciter according to the embodiment of the present invention. This method (14-1) includes an exciter network interface and a control process (14-2) that provides control messages and manages communication protocols. In many embodiments, various methods determine the mode in which the exciter is controlled, and the exciter network interface and control process (14-2) are used to communicate control information to the exciter. In the illustrated embodiment, the exciter transmits a power control process (14-4) and from each exciter optimizes, controls, manages and calibrates the transmit power as specified by the user. In some embodiments, the message containing the transmit power control information is provided to the exciter using the exciter network interface and control process (14-2).

The reader-to-exciter frequency hopping and management process (14-6) includes the exciter management, scheduling and optimization process (14-10) to optimize the deployment of single and multiple RFID receiver systems. Combine with RFID frequency reuse, planning and optimization process (14-8). Exciter frequency hopping and management process (14-6) adjusts frequency hopping. In some embodiments, the frequency hopping and management process assigns a random frequency to the operating exciter. In other embodiments, this process works in conjunction with the RFID frequency reuse, planning and optimization process (14-8) to use an algorithm that optimizes frequency reuse based on the location of the exciter. To do. In many embodiments, other algorithms suitable for the application are used for frequency allocation. In some embodiments, the exciter management, scheduling and optimization process (14-10) coordinates the activation of the exciter. In many embodiments, this process polls the exciter periodically. In some embodiments, the sensor detects a possible presence of an article with an RFID tag within the calling region of the exciter, and the sensor information is used to control the activation of individual exciters by this process.

The RFID read error discrimination process (14-12) detects and flags RFID tags that do not belong to the specified calling area. The RFID reading error discrimination process according to the embodiment of the present invention is shown in FIG. This process (15-1) takes sensor data from the response command space (15-4), detects RFID tag data including the tag's identification code (15-06), signal strength, signal-to-noise ratio. Determine the RF characteristics of the detected tag information, including (SNR) and direction of arrival (15-8). This process uses the collected sensor data, RFID tag data and RF features to determine if the RF tag data was located outside the response command space of the exciter activated by the RFID system. Various methods can be used to determine if RFID tag data was read from a tag located outside the response command space, based on the collected methods similar to the information above. The specific process is further described below.

FIG. 16 shows an RFID system deployment including a distributed exciter architecture according to an embodiment of the present invention. This expansion includes three response command spaces (16-14, 16-16, 16-18). In this deployment, each response command space utilizes two exciters (16-2, 16-4 and 16-6, 16-8, and 16-10, 16-12). In many embodiments, the RFID system utilizes a process similar to that shown in FIG. 15 to illuminate each response command space and read RFID tag data from tags located within the exciter's response command space. Identify if it was done.

For example, when the reader (16-22) intends to read an RFID tag in the first response command space (16-16), the reader (16-22) has the tag "x" (16-34) and the tag "y" (16). Read -36). Data can also be collected from other exciters (eg, "x" was read by exciters (16-6 and 16-8), while "y" is exciter (16-10, 16-6). And 16-12), the SNR for each signal is compared (eg, the SNR for the tag "y" is the tag "x" when using the exciters (16-6 and 16-8). It was low compared to). Using the information collected, the RFID application server can conclude that the tag "y" (16-36) actually belongs to the first response command space (16-16).

The method used to determine whether RFID tag data is associated with an RFID tag located within the response command space can be application dependent. In some embodiments, read rate information is used to identify the relationship between RFID tags and exciters. Various read-rate-dependent methods for drawing conclusions about the location of RFID tags according to embodiments of the present invention will be described later.

Many processes according to the embodiment of the present invention determine the position of the RFID tag for which the information was received by accumulating the information on the RFID tag reading rate, and obtain the reading rate information for the purpose of determining the tag position. , Exciter and region topology description. The combination of read rate and topology description allows the detection of read errors when the tag is not located within the region of interest by addressing the issue of read distinction for "event sensing". In particular, RFID systems are interested in events that include tags that are moving from one "hypothetical area" to the other. These events can be called "transition events". In some embodiments, the probability of a transition event (or transition hypothesis) informs the process of distinguishing reads.

The transition hypothesis is<maths num="1"><img file="JP2013059093A_D0001.tif" /></maths>The amount is that the tag is the area x_aIt can be determined by defining it as a posterior probability that it is in the exciter e_iTag observables by<maths num="2"><img file="JP2013059093A_D0002.tif" /></maths>The exciter is in polling or sensor drive mode. Exciters in polled drive mode are activated by the RFID receiver system in a strictly cyclical manner. When a sensor event (eg, beam interruption or machine vision operation) is detected, the exciter in sensor drive mode is activated. Most of the time, the exciter operates in polling mode, where access to the RFID receiver system is evenly timed among a series of possible exciters. This occurs when a subset of exciters are given exclusive access to the RFID receiver system until the perceived event is triggered.

Events related to the transition hypothesis can be illustrated. A series of regions of interest and multiple distributed exciters are shown in FIG. In the illustrated embodiment, the article bearing the RFID tag (20-1) is the first place x₁From the second place x₅Move to. The tag is the hypothesis area x₁Or x₃From area x₅The posterior probability of moving to can be determined by evaluating the probability of the following equation.<maths num="3"><img file="JP2013059093A_D0003.tif" /></maths>

The normalization parameters Cx and p (y) can be removed (normalization can be treated as a final separate step). The probabilities of similar transition events can be described more generally using the product of the following sums.<maths num="4"><img file="JP2013059093A_D0004.tif" /></maths>In the formula, A_originIs a set of hypotheses that can be transitioned to the goal hypothesis, E_destIs a set of exciters around the goal hypothesis.

Below, the system<maths num="5"><img file="JP2013059093A_D0005.tif" /></maths>I will focus on how to get the sum of the formulas.

Where the hypothetical region x₁Exciter e against^j21, which provides a description of the topological form of. For each of these combinations, a typical exciter link margin (the amount of power that reaches the tag that exceeds the absolute minimum amount of power required to activate the same tag) can be determined. This link margin is well approximated using knowledge of the exciter power level, Pt, the angle θ from the exciter boresite, the average distance d from the exciter to the hypothesis, and the expected radiation pattern of the exciter and tag. To.

Referring to FIG. 22, the exciter link margin generated from FIG. 21 is the hypothetical region x.₁Used to generate a probability function (pmf) that describes the likelihood of a percentage of the time a tag is read (reading rate) when located within. Readability (RR) is empirically determined by counting the number of times a tag is read within a fixed time interval and dividing this amount by the number of readable times possible during the same time period. (Note that the reading rate is given to the tripartite set of exciter ID, hypothesis area, and tag ID). The reading rate is the exciter (e) and the hypothesis area (x)._j) As a subscript, the code RR_{e, x}Is used. The associated read rate is implicitly considered to be determined by the position of the hypothetical region by the exciter (e) in polling or sensor driven mode. The target hypothesis area is usually read using the sensor drive mode. Given the above definition, the product of interest can be identified as a point on the following Gaussian probability function.<maths num="6"><img file="JP2013059093A_D0006.tif" /></maths> This is simply the product of two Gaussian functions. Note that all probabilities associated with a given exciter, e, are normalized as follows, prior to performing the product of the total transition probabilities.<maths num="7"><img file="JP2013059093A_D0007.tif" /></maths>In the equation, H is a set of all hypothetical regions.

The process described above can also include a model of the probability of reading a tag at a given position in relation to the exciter's beam and tag environment. Such models include a spatial multipath field in which large structures are somehow sampled by frequency hopping. This predicted probability can be used for each reading opportunity to update the Bayesian inference for each hypothesis, whether the tag was read or not. Each of these hypotheses has a specific spatial trajectory with respect to time, some tags are fixed (in the same position for all measurements), and some are moving (doors). Usually constant speed in a specific direction, such as passing through a loading / unloading area). Sensors outside the RFID system are used to arrange the trajectories that are estimated to move in time, so a simplified guess for all read-opportunity approaches, ie, read part statistics, are before and after the event. Make a guess that it can be maintained during the major time intervals of. Statistics on the average of the read portion often follow Poisson statistics, which are based on the individual probabilities of reads and the number of opportunities to read at intervals (the exception to this is for stationary tags, during the read portion over time. Has a strong correlation, which can be included in a spatial correlation function that has a roughly wavelength / half-wavelength correlation distance). In the inventor's preferred embodiment (above), the inventor uses a Gaussian distribution for the reading portion to approximate Poisson statistics.

While the above description includes many specific embodiments of the invention, they should be construed as an example of one embodiment thereof rather than a limitation within the scope of the invention. Therefore, the scope of the present invention must be determined not by the illustrated embodiments but by the appended claims and their equivalents.