HK1138952B - Item level inventory with a rodio frequency identification (rfid) system - Google Patents

Description

Item level inventory for radio frequency identification system

Technical Field

The present invention relates generally to Radio Frequency Identification (RFID) systems, and more particularly to RFID systems that acquire information from each of a plurality of items.

Background

Radio Frequency Identification (RFID) systems are used in many different applications, including, for example, in retail environments to obtain information about items tagged with RFID identifiers. For example, an RFID tag may be attached or incorporated within a product or product packaging. Using an RFID interrogator (which may be a fixed, portable, or handheld device), RFID tags within the interrogation zone of the interrogator may be activated and provide information about the item associated with the RFID tag (e.g., product descriptor, serial number, location, etc.). These RFID tags receive and respond to Radio Frequency (RF) signals to provide information, for example, about the product to which the RFID tag is attached. Such information may include inventory information relating to items on a shelf or items within a warehouse. Generally, the modulators of the RFID tags may use a transmitter to transmit back a signal or reflect back a signal to the RFID readers. Additionally, information can be transmitted to the RFID tags (e.g., encoding information) using an RFID encoder. In this way, RFID systems can be used to monitor the inventory of products in a retail environment and provide product identification through the use of storage and remote retrieval of data using RFID tags or transceivers.

RFID systems include RFID readers that are capable of detecting and receiving information from a large number of RFID tags simultaneously. In addition, the RFID reader is capable of transmitting and receiving simultaneously on the same frequency. For example, in a retail environment where RFID systems are used to track inventory, it is known to provide multiple read points, where each read point includes the use of multiple RF multiplexers and multiple cables to connect to each read point. Furthermore, in such known systems, a separate communication and control system is typically required to manage and control the RF multiplexers. Therefore, the cost and complexity of these RFID systems is typically high. In addition, the time and complexity of installing these components may also be high, for example, when bulky cable breakout clips or the like must be installed. Moreover, it is often difficult, if not impossible, to obtain a complete inventory of, for example, a complete pallet because of the materials used to package the contents. For example, metal foils or metallized plastic films and/or RF-absorbing materials can be used and are commonly used in the packaging of pharmaceuticals or food products. Such packaging can shield passive RFID tags attached to products within the packaging. Thus, with known RFID systems, only the outer layer of the RFID tag can be read. Therefore, it is often necessary to disassemble or open the pallet or case to inspect the contents and confirm the inventory.

It is also known to use multiple RFID interrogators in such systems to monitor RFID tags at different locations. The use of multiple RFID interrogators also increases the cost and complexity of the system. In addition, these RFID interrogators may need to be moved in order to interrogate the entire area. For example, individual RFID interrogators may have to be constantly moved in order to interrogate an entire shelf or shelf unit. This increases the time and cost of, for example, completing an inventory of RFIDs.

Disclosure of Invention

A method for performing Radio Frequency Identification (RFID) inventory may be provided. The method may include selectively controlling each of a plurality of multiplexers connected to a plurality of local antennas using an RF signal and selectively enabling the plurality of local antennas using the RF signal, the local antennas using the plurality of multiplexers to perform RFID interrogation on a plurality of RFID tags. The method further may include obtaining inventory information based on the RFID interrogation.

A method for controlling information acquisition during an RFID item level inventory may be provided. The method may include transmitting an Identification (ID) request command to each of the plurality of multiplexers during the ID acquisition state. The ID request command may activate multiple multiplexers within a transmission range. The method further may include identifying a plurality of antenna arrays available for use using the plurality of multiplexers to obtain the RFID tag information. The method may also include initiating an inventory acquisition process in which each of the plurality of local antennas of the antenna arrays is selectively activated to acquire the RFID tag information.

Radio Frequency Identification (RFID) inventory information may also be obtained by a method for completing a Radio Frequency Identification (RFID) inventory.

Drawings

For a better understanding of various embodiments of the present invention, reference should be made to the following detailed description taken in conjunction with the following drawings in which like numerals represent like parts.

FIG. 1 is a block diagram of an RFID system in association with which various embodiments of the invention may be implemented.

Fig. 2 is a block diagram of another RFID system in association with which various embodiments of the invention may be implemented.

FIG. 3 is a block diagram of one embodiment of an RFID tag for use in an RFID system.

FIG. 4 is a block diagram of another embodiment of an RFID tag for use in an RFID system.

Fig. 5 is a block diagram of an RFID communication system that may be controlled by various embodiments of the present invention.

Fig. 6 is a flow diagram of a method for completing an RFID item level inventory in accordance with various embodiments of the invention.

FIG. 7 is a perspective view of an inventory system that can be controlled by various embodiments of the present invention.

Fig. 8 is a flow diagram of a method for controlling information acquisition during an RFID item level inventory process in accordance with various embodiments of the invention.

Detailed Description

For simplicity and convenience of illustration, the invention will be described herein in connection with various embodiments thereof. Those skilled in the art will recognize, however, that the features and advantages of the various embodiments may be implemented in a variety of configurations. It is to be understood, therefore, that the embodiments described herein are presented by way of illustration, not of limitation.

In summary, various embodiments of the present invention provide a method and system for completing an item level inventory. The item level inventory is generally performed using Radio Frequency (RF) controlled multiplexers. Thus, various embodiments may provide a method for obtaining a real-time inventory of items tagged with RFID identifiers.

Specifically, and with reference to fig. 1 and 2, various embodiments of the present invention may be implemented in connection with controlling the acquisition of information from various types of RFID systems, including, for example, an RFID system 50. The RFID system 50 may include an RFID communication device, such as an RFID reader or interrogator 52 (which may optionally also include an RFID encoder) and a plurality of identification devices (not shown), such as RFID tags, that are attached to or integrated with different objects 54 (e.g., DVDs or CDs). The objects 54 may be supported by a plurality of support structures, such as a plurality of shelves 55 (e.g., a plurality of movable shelves on a peg board). The RFID interrogator 52 and the RFID tags may communicate via Radio Frequency (RF) and generally operate in accordance with known RFID communication methods. For example, as shown in FIG. 1, a plurality of objects 54 may be supported on a plurality of shelves 55, each object 54 having one or more RFID tags attached thereto or integrated therewith as is known. For example, the objects 54 may be products, such as retail products, and a plurality of shelves 55 may form a display for displaying the objects 54. It should be noted that these objects 54 may have different sizes and shapes. In addition, the objects 54 may be constructed of different materials, such as RFID tags located on the exterior or interior of the product or product packaging as is known.

Referring to FIG. 2, as another example, a plurality of objects 54 may be located within a support structure 56. For example, the plurality of objects 54 may be boxes or cases and the support structure 56 is a crate/pallet or similar structure for transporting the structure (e.g., a plurality of medication containers within one or more pallets). The RFID interrogator 52 may be used to communicate with RFID tags that are attached to the objects 54 while the support structure 56 is stationary or in motion.

In various embodiments, RFID tag 60 may be a passive radio reflective identification tag or a passive RFID tag, as shown in FIG. 3. The passive RFID tags 60 do not include a battery or other power source, and when the radio waves 62 from the RFID interrogator 52 are detected by an antenna 64 of the RFID tag 60, the power is converted by the antenna 64 into electrical power that may power, for example, a processor, such as a microprocessor 66 within the RFID tag 60. Thus, the RFID tag 60 is able to communicate, and more specifically, transmit the information stored within the microchip 66 to the RFID reader 52. For example, the information transmitted may include the type of object to which the RFID tag 60 is attached, including, for example, a serial number, the time and date of the transmission, the location of the RFID tag 60 transmitting the information, and the like, and will be referred to herein collectively as RFID tag information.

In other various embodiments, the plurality of RFID tags 70 may be active radio-reflective identification tags or active RFID tags, as shown in FIG. 4. The active RFID tags 70 also include a transmitter 72 to communicate and, more particularly, transmit signals 74 to (as opposed to reflecting back to) the RFID reader 52 having the RFID tag information. Active RFID tag 70 transmits these signals 74 to RFID reader 52 using a battery (not shown) or other power source, such as a photo-powered power source.

It should be noted that the objects 54 or other objects shown in fig. 1 and 2 may include only active RFID tags, only passive RFID tags, or a combination of active and passive RFID tags. The decision as to which type of RFID tag to use may be based on the particular application, e.g., the coverage distance (e.g., long versus short) over which the RFID tag must be detected. This may be determined, for example, based on the type of product and the location of the product having the RFID system implemented in association therewith.

It should be noted that the RFID interrogator 52 may be a stand-alone unit, such as a portable or handheld unit, or may be integrated with another communication device (e.g., a mobile or cellular telephone, a Personal Digital Assistant (PDA), a blackberry device, etc.). Alternatively, the RFID interrogator 52 may be formed as part of the backplane as described in detail below. Also, for example, various components within the cellular telephone, such as the transceiver, processor, and/or software may be altered to provide the same functionality and operation of the RFID interrogator 52. Still other alternatives include a plug-in or add-on unit, such as a plug-in module for a PDA that includes the RFID interrogator 52 therein.

In various embodiments, the RFID interrogator 52 may include an interrogator antenna 80, which, as shown in FIG. 5, may include one or more antenna elements or coils. The interrogator antenna 80 is configured to communicate with a main antenna 82 of an RFID inventory communication system 90. Communication between interrogator antenna 80 and main antenna 90 is provided by any type of wireless RFID communication link using any type of RF signal and any type of protocol. The main antenna is connected to one or more multiplexers 84 that are connected to one or more local antennas 86. Each of the one or more local antennas 86 communicates with one or more RFID tags 88 using any known RFID communication method. It should be noted that the local antennas 86 may form one or more antenna arrays, each of which is provided with a main RF switch (not shown) to allow selection of the activation of the antenna array or passing of the received signal. Additionally, the multiplexers 84 may include or be configured to operate as switches and have control lines that may be activated to select different local antennas 86 or an antenna array.

In operation, and with reference to the one or more multiplexers 84, the devices may be configured as switches to control switching between the local antennas 86. The operation of the one or more multiplexers 84 causes the multiplexers 84 to appear as passive RFID tags to the RFID interrogator 52. The RFID interrogator 52 transmits at least one of data and power to the main antenna 82 via the interrogator antenna 80. For example, a high frequency signal may transmit RFID control commands to control the switching and interrogation of the RFID tags 88 through the local antennas 86, and a low frequency signal may transmit power to the one or more multiplexers 84. Specifically, the one or more multiplexers 84 do not include a battery or other power source, and when radio waves from the RFID interrogator 52 or other RFID transmitter (as is known) are detected by the main antenna 82, this energy is converted into electricity that can power the one or more multiplexers 84. The one or more multiplexers are then able to control, for example, switching and communication between the local antenna 86 and the RFID tag 88. The one or more multiplexers 84 may be configured in different ways. One configuration for one or more multiplexers 84 is described in a co-pending U.S. patent application serial No. 11/520,123, assigned to the assignee of the present application, the entire disclosure of which is incorporated herein by reference. It should also be noted that the power signal from the RFID interrogator 52 may also power any passive RFID tags 88.

The one or more multiplexers 84 each include a unique identification number and may be controlled by RFID interrogator commands from the RFID interrogator 52. For example, a write command from the RFID interrogator 52 may be sent to one or more multiplexers 84 to power and control the switching of the one or more multiplexers 84.

Different embodiments may be implemented in different applications to communicate using one RFID system and to obtain, for example, inventory information that may be provided in real time or automatically updated (e.g., periodically performing interrogations of multiple RFID tags). For example, an RFID shelf inventory system may be provided as described in co-pending U.S. patent application serial No. 11/520,123, entitled Radio Frequency Identification (RFID) system for item level inventory, assigned to the assignee of the present application, the entire disclosure of which is incorporated herein by reference. These various embodiments are not limited to, for example, shelf inventory. For example, RFID inventory of multiple pallets, multiple moving objects, multiple boxes, etc. may be performed.

In summary, the various embodiments provide a method 100, as shown in FIG. 6, for completing an RFID item level inventory. The method 100 may include, at 102, transmitting a signal to obtain unique IDs from each of a plurality of multiplexers associated with, for example, different levels of a shelf unit or different rows in a pallet. This may include communicating with the multiplexers through an interface device that includes, for example, an antenna external to the pallet (e.g., may be exposed outside of the pallet packaging). Essentially, an RFID interrogator reads a unique ID from each of these multiplexers. Once the unique ID is known, individual multiplexers may be individually and selectively controlled and/or addressed. More specifically, thereafter at 104, control commands may be transmitted from the RFID interrogator to a first identified multiplexer. The RFID interrogator may write a command to the first multiplexer device to control the operation of the local antennas connected to the multiplexer. For example, the RFID interrogator may issue a command to the multiplexer to select a first local antenna in an array of local antennas controlled by the first multiplexer. For example, the local antenna array may be positioned at intervals along a shelf, or at intervals between rows of a pallet. The intervals may be fixed, varied, or selected based on the positioning of items to be inventoried.

The local antennas are selectively activated by a first multiplexer. For example, a first local antenna may be activated to transmit an RFID interrogation signal to activate RFID tags associated with items on a row of the shelf or pallet using any known RFID transmission scheme. It should be noted that the RFID interrogation signal originates from an RFID interrogator. As is known, these RFID tags respond with item or product information. For example, an Electronic Product Code (EPC) and/or a Universal Product Code (UPC) is read for each item in accordance with the contents stored in these RFID tags. Thereafter, a determination is made at 110 whether other local antennas are connected to the first multiplexer. If other local antennas are connected to the first multiplexer, then the local antennas are selectively activated at 106. This process is repeated using each of the plurality of local antennas associated with the first multiplexer. If it is then determined at 110 that no more local antennas are connected to the first multiplexer, then a determination is made at 112 whether there are additional multiplexers. If other multiplexers are present, e.g., provided as part of the shelf unit or within the pallet (e.g., in another row), local antennas connected to the multiplexer, e.g., a second multiplexer, third multiplexer, etc., are activated at 106. It should be noted that multiple multiplexers may be controlled by a single master multiplexer. If no other multiplexers are present, the item level inventory is completed at 114. The acquired item information may then be communicated to, for example, an inventory management program, an item reordering system, a accounting system, and the like.

Thus, in operation, the RF interrogator 52 (shown in FIGS. 1 and 2) may perform an inventory information acquisition process on a pallet 140 (shown in FIG. 7) as follows:

1. each unique ID is read from the multiplexer 84 associated with each of the plurality of interface devices 122. These interface devices may be manually or automatically inserted between rows of boxes on the pallet 140 and include a plurality of multiplexers 84 and local antennas 86.

2. A command is written to a first multiplexer 84 (e.g., associated with the interface device 122 between the bottom two rows of boxes) to select a first local antenna 86 within an array (e.g., one row) and read or retrieve the EPC code from one or more RFID tags 150 that are in communication with the local antennas 86 (e.g., interrogated by the local antennas 86). It should be noted that one or more RFID tags 150 may be located at different locations within a particular portion of the pallet (e.g., within a box).

3. This process is repeated (2 above) for each local antenna 86 within one interface device 122, for example, along a row of boxes.

4. This process is repeated for each of these interface devices 122 between each row of boxes (2 and 3 above).

It should be noted that this process is not limited to obtaining information from one pallet, but may also be used to obtain information from other structures, objects, etc.

Thus, different embodiments may be used, for example, to complete an RFID inventory, such that the same RF channels and wireless protocols are used to control a multiplexed antenna array when the RFID tags are inventoried. It should be noted that different embodiments may be used in association with different types of RFID systems that operate using different RFID protocols. For example, the various embodiments are not limited to the EPC Class1 Gen 1 and EPC Class1 Gen 2 wireless protocols.

Fig. 8 illustrates a method 170 for controlling information acquisition within an RFID item level inventory. Although the method 170 is illustrated in connection with obtaining inventory information (e.g., quantity of products, location of products, etc.), the method 170 may be used to obtain other types of information. Specifically, the RFID interrogator may transmit an ID request command at 172 that activates each multiplexer controller within range of the RFID interrogator antenna, and specifically within a near field range of the RFID interrogator's RF transmissions and that conforms to the RFID interrogator's wireless protocol. In this process, the RFID interrogator attempts to determine a unique ID, which may be a unique EPC code, for each multiplexer controller. These multiplexer controllers are responsive to the respective unique IDs. It should be noted that in the ID acquisition state, the main RF switch of each antenna array is set to a "pass-through" mode so that all multiplexers within the antenna array chain (e.g., all local antennas) are able to provide a unique ID. It should also be noted that power for the multiplexer functions may be provided by the RF signal generated and transmitted by the RFID interrogator.

Then, at 174, after identifying and storing a list of available antenna arrays determined by the multiplexers in response to the ID request command, an inventory acquisition process may be initiated to determine an inventory of items associated with each local antenna. Specifically, as described in greater detail herein, each of the plurality of local antennas is selectively activated by a write command sent to a corresponding multiplexer. Specifically, each of the local antennas is individually activated and identifies items having responsive RFID tags within range of the local antenna. Essentially, an inventory of all items with RFID tags that respond to RFID interrogation by the local antenna is determined. With respect to write commands for selectively activating multiplexers connected to local antennas, a control word is written to, for example, a controller (e.g., a master multiplexer) to determine which local antenna should be enabled. One shown sequence is as follows:

1. the system writes "01" to controller ID0XFFF 000000000000000000001.

2. The controller 0X0000000000000000000000001 switches a main RF switch to access the antenna array connected thereto and enables a first antenna (e.g., antenna 1) by setting the corresponding switch and multiplexer control line to activate the first antenna (e.g., initiate an RFID interrogation).

3. The system then makes an inventory round at 176. For example, the active controller and all RFID tags within range of the selected antenna respond with a corresponding ID, such as:

a.0XFFF000000000000000000001 (controller)

b.0X0000000000000000000000001 (article 1)

c.0X0000000000000000000000002 (article 2)

d.0X0000000000000000000000003 (article 3)

e.0X0000000000000000000000004 (article 4)

f.0X0000000000000000000000005 (article 5)

g.0X0000000000000000000000006 (article 6)

4. Thereafter, at 178, the items located during the inventory round (e.g., the items located at controller 1, antenna 1) are stored in a database. This may include storing item information such as a UPC or EPC, an item description, the location of the item based on the interrogation controller and antenna, and so forth.

5. At 180, a determination is made whether other controllers are present and available for use based on the initial list of identifications. If other controllers are available, for example, a second controller (controller 2), then the system writes "02" to controller ID0XFFF 000000000000000000001.

6. The second controller 0X 00000000000000000000000000001 switches a main RF switch to access the antenna array connected thereto and enables a second antenna (e.g., antenna 2) by setting the corresponding switch and multiplexer control line to activate the second antenna (e.g., start an RFID interrogation).

7. The system then makes an inventory round again at 176. For example, the active controller and all RFID tags within range of the selected antenna respond with a corresponding ID, such as:

a.0XFFF000000000000000000001 (controller)

b.0X0000000000000000000000007 (article 7)

c.0X0000000000000000000000008 (article 8)

d.0X0000000000000000000000009 (article 9)

e.0X0000000000000000000000000000A (article 10)

f.0X0000000000000000000000000000B (article 11)

g.0X000000000000000000000000C (article 12)

8. Thereafter, at 178, the items located during the inventory round (e.g., the items located at the controller 2, antenna 2) are stored in a database. This again may include storing item information (e.g., UPC or EPC), an item description, the location of the item based on the interrogation controller and antenna, and so forth.

9. At 180, a determination is again made whether other controllers are present and available for use based on the initial identification list. If other controllers are available, for example, a third controller (controller 2), then the system writes "03" to controller ID0XFFF 000000000000000000001 and makes a stock form round again at 176. This process is repeated for each antenna in the array controlled by 0XFFFF 00000000000000001.

10. When the inventory of the first antenna array is complete, the system writes "00" to controller ID0XFFFF000000000000000000001, which sets the main RF switch of the first antenna array to "pass" to allow access to the other controllers within the antenna array chain. The inventory round at 176 is repeated again for each antenna in the other array.

11. Thereafter, if no other controller is used for the inventory process, such that the antennas in all arrays have been used for inventory, then at 182 the system waits for the next scheduled inventory and repeats the method 170.

It should be noted that the address, ID, and control command of the memory are merely exemplary and may be modified based on the type of system, and the like.

Thus, various embodiments of the present invention may acquire inventory information and allow for a permanent RFID shelf inventory in which communication to complete the inventory is provided wirelessly. It should be noted that the power for the controllers (e.g., the multiplexers) to interrogate the RFID tags may be provided by the RF signal from the RFID interrogator. The RFID interrogator may also wirelessly activate selected local antennas to perform RFID inventory operations to identify, for example, item IDs and locations (e.g., locations within a rack or shelf unit).

Different embodiments or components for completing an RFID inventory may be implemented as part of one or more computer systems. The computer system may include a computer, an input device, a display unit, and an interface, for example, for accessing the internet. The computer may include a microprocessor. The microprocessor may be connected to a communication bus. The computer may also include a memory. The memory may include Random Access Memory (RAM) and Read Only Memory (ROM). The computer system further may include a storage device, which may be a hard disk drive or a removable storage drive such as a floppy disk drive, optical disk drive, and the like. The storage device may also be other similar means for loading computer programs or other instructions into the computer system.

The term "computer" as used herein may include any processor-based or microprocessor-based system including systems using microcontrollers, Reduced Instruction Set Circuits (RISC), Application Specific Integrated Circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term "computer".

The computer system executes a set of instructions stored in one or more storage elements to process input data. These storage elements may also store data or other information as desired or needed. The memory element may be in the form of an information source or a physical memory element within the processor.

The set of instructions may include various commands that instruct the computer to perform specific operations as a processing machine, such as the methods and processes of the various embodiments of the present invention. The set of instructions may be in the form of a software program. The software may be in different forms, such as system software or application software. Additionally, the software may be in the form of a collection of separate programs, a program module within a larger program or a portion of a program module. The software may also include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to a user command, or in response to a previous processing result, or in response to a request made by another processing machine.

The terms "software" and "firmware" as used herein are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (nvram) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the various embodiments of the invention can be practiced with modification within the spirit and scope of the claims.

Claims (12)

1. A method for performing a Radio Frequency Identification (RFID) inventory, the method comprising:

selectively controlling each of a plurality of multiplexers connected to a plurality of local antennas by an RF signal;

selectively enabling, by an RF signal, local antennas that perform RFID interrogation on RFID tags using the plurality of multiplexers; and is

Inventory information is obtained based on the RFID interrogation,

the method further comprises the following steps:

controlling information acquisition in an RFID item level inventory process, comprising:

transmitting an Identification (ID) request command to each of the plurality of multiplexers during an Identification (ID) acquisition state, the ID request command causing the plurality of multiplexers to activate within a transmission range;

setting an RF switch of each antenna array formed by the local antennas to a pass-through mode during the ID acquisition state, enabling the multiplexer to provide the ID;

identifying a plurality of antenna arrays available for use using the plurality of multiplexers to obtain RFID tag information; and is

An inventory acquisition process is initiated in which each of the plurality of local antennas of the antenna arrays is selectively activated to acquire the RFID tag information.

2. The method of claim 1, further comprising determining identification information for each of the plurality of multiplexers.

3. The method of claim 2, further comprising communicating with individual ones of the plurality of multiplexers based on the identification information.

4. The method of claim 1, further comprising selectively energizing the plurality of multiplexers with the RF signal.

5. The method of claim 1, wherein the selectively controlling comprises transmitting a write command to the plurality of multiplexers.

6. A method according to claim 1, further comprising receiving the RF signal on an antenna exposed outside a container, the antenna being connected to at least one of the plurality of multiplexers.

7. The method of claim 1, further comprising positioning an RFID interface between stacks of boxes on a pallet, the RFID interface device including the plurality of multiplexers and local antennas.

8. The method of claim 1, further comprising using the plurality of multiplexers to direct control commands.

9. The method according to claim 1, wherein the plurality of local antennas are selectively activated using write commands from an RFID interrogator.

10. A method according to claim 9, wherein the write commands include control words written to a controller for the plurality of multiplexers.

11. The method according to claim 1, further comprising selectively setting a switch and multiplexer control line to selectively activate the antenna arrays, wherein the RFID tag information comprises information about one or more items, the information comprising at least one of: a Universal Product Code (UPC), an Electronic Product Code (EPC), an item description, and a location of the item based on an interrogation controller and antenna.

12. The method of claim 1, further comprising performing a plurality of inventory rounds to acquire the RFID tag information using each antenna array.