Stateful inventory for monitoring RFID tags

Abstract

Radio Frequency Identification (RFID) tags, or tags, are affixed to specific items and store unique identifying information about the item. They can be queried with a reader that transmits a radio signal to the tag and receives the tag's response, which can be correlated with information in an inventory record. Traditionally, when the reader stops receiving the tag's response to these queries, the inventory record is updated to indicate that the tag and associated item have been removed from the inventory. However, simply removing the tag and item can lead to inaccurate inventory records, since tags may stop generating detectable responses for other reasons, including being too close to other tags. Stateful inventory techniques address this issue by maintaining and transitioning tags between different states, including stale states for tags that have not been read recently, depending on when and where the tag was last read.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. patent application Ser. No. 63 / 304,760, filed Jan. 31, 2022, which is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] Radio Frequency Identification (RFID) tags are small transponders that are typically preprogrammed to emit a unique identification signal in response to a query or interrogation signal from an RFID tag reader. Passive RFID tags contain a microchip with a small memory and a coil or antenna that is powered by the interrogation signal itself. The interrogation signal typically begins with a continuous wave (cw) tone that charges the microchip through the coil or antenna. The RFID tag reader modulates a portion of the interrogation signal with a query or command for the RFID tag. The coil or antenna in the RFID tag backscatters a version of the cw tone in response to the query or command modulated with information such as an electronic product code (EPC) or other unique identifier stored in memory. The RFID tag reader detects the backscattered signal, also called a reply or response, and may update a database based on the information from the RFID tag.

[0003] RFID tags are used to identify and track objects in warehouses, stores, and other spaces or environments. They are cheap and easy to manufacture; for example, a microchip and antenna can be printed on sticky paper and then attached to the item. In a clothing store, for example, there may be a passive RFID tag on the price tag of each clothing item for sale in the store. A database stores a unique identifier for each RFID tag and information about the clothing item to which the RFID tag is attached. By querying the RFID tags with one or more readers distributed throughout the store, one can determine and track the store inventory, which is often considered to be a complete list of items (goods) available for sale (i.e., items received minus items sold or otherwise removed from the store). The system may also be able to locate tagged items within a particular portion of the store by sensing the power level and / or angle of arrival of the tag's response with RFID readers at different locations in the store. Readers at checkout or exit can be used to track items as they leave the store, for example for automated checkout or loss prevention. Similarly, readers in the inventory can be used to track items as they arrive at the store and are placed on the sales floor.

[0004] One challenge of using RFID technology in stores, warehouses, and other spaces or environments with many surfaces is getting enough power from the RFID reader to the tags due to shadowing, fading, ghosting, etc. Another challenge is that the response from each tag may propagate along many different paths from the tag to the reader. This phenomenon is known as multipath propagation and can result in interference that causes fading, ghosting, and / or other undesirable effects that complicate efforts to estimate the tag's location from the energy received by the reader. For example, a tag may respond to a query from a reader by backscattering incident radiation, for example, in a dipole pattern. A portion of this RF energy may propagate along a direct or line-of-sight (LOS) path from the tag to the reader. Some or all of the remaining RF energy may propagate along a reflected, indirect, or non-line-of-sight (NLOS) path from the tag to the reader, i.e., some or all of the remaining RF energy may reflect or scatter off one or more surfaces as it propagates from the tag to the reader. Radiation propagating along these different paths can interfere and cause fading in the signal received by the reader. Summary of the Invention

[0005] These problems with detecting replies from passive RFID tags can be addressed using a method for tracking items associated with each RFID tag that enters and leaves a store using an inventory database that stores the states of the RFID tags. These states include an available state, indicating that the item associated with the RFID tag is available for sale, an stale state, indicating that a predetermined period of time has passed since the RFID tag responded to an interrogation signal, and a sold state, indicating that the item associated with the RFID tag has been sold and / or removed from the store. The method can be performed by changing the state of the RFID tag to the stale state in response to not detecting a response to a first interrogation signal from an RFID tag in the available state, changing the state of the RFID tag from the stale state to an available state in response to detecting a response to a second interrogation signal from the RFID tag, and changing the state of the RFID tag to the sold state in response to detecting a sale of the item associated with the RFID tag and / or removal of the RFID tag from the store. The state of the RFID tag includes information about the estimated location of the RFID tag, an error associated with the estimated location of the RFID tag, and a timestamp associated with the last detected response from the RFID tag. The predetermined period of time may be based on the estimated location of the RFID tag and / or the last detected response from the RFID tag.

[0006] For example, such a method may be performed by transmitting a first interrogation signal by an RFID tag reader to a first RFID tag and detecting a response to the first interrogation signal from the first RFID tag by the RFID tag reader. The RFID tag reader and / or a controller appliance connected to the RFID tag reader estimates a location of the first RFID tag based at least in part on the response to the first interrogation signal. In response to detecting a response to the first interrogation signal from the first RFID tag, the controller appliance updates a status of the first RFID tag in an inventory database to an available status to indicate the location of the first RFID tag. The first RFID tag is then positioned within 20 centimeters of a second RFID tag (e.g., items associated with the first and second RFID tags are stacked on top of each other). The RFID tag reader (or possibly a different RFID tag reader) transmits a second interrogation signal to the first RFID tag but does not detect any response to the second interrogation signal from the first RFID tag due to tag shadowing, tag detuning, and / or re-radiation cancellation caused by the second RFID tag. The controller appliance, in response to not being able to detect any response to the second interrogation signal from the first RFID tag, changes a state of the first RFID tag in the inventory database from an available state to a stale state. After a time, the RFID tag reader (or possibly a different RFID tag reader) transmits a third interrogation signal to the first RFID tag and detects a response to the third interrogation signal from the first RFID tag. The controller appliance, in response to detecting a response to the third interrogation signal from the first RFID tag, changes a state of the first RFID tag in the inventory database from a stale state to an available state.

[0007] An embodiment of the method may also include, in response to detecting the RFID tag in a receiving area of ​​the store, creating an entry in an inventory database for the item associated with the RFID tag. The entry includes information about the item represented by an Electronic Product Code (EPC) stored in a memory of the RFID tag. The information about the item represented by the EPC may be verified and / or checked for accuracy prior to adding the RFID tag / item to the inventory database.

[0008] The state of the RFID tag can be changed to an ignored state in response to receiving an indication that the item is no longer part of the inventory. Similarly, the state of the RFID tag can be changed to a missing state in response to receiving an indication (e.g., input from a store associate via a computer, tablet, or smartphone) that the item cannot be found. In either case, an RFID tag remains in the inventory database (e.g., a stale state) even if no reader detects a response to an interrogation signal from the RFID tag, unless it is changed to a sold state or a person removes the RFID tag from the inventory database or changes its state (e.g., becomes missing or ignored).

[0009] Detecting the sale of the item can include updating a point of sale (POS) system to reflect that the item has been sold. Detecting the sale of the item can also include processing the sale with the POS system. Detecting the sale of the item can also include detecting that the RFID tag has been removed from the store.

[0010] The RFID tag may be moved, oriented, or otherwise arranged so as not to generate a detectable response to the second interrogation signal. For example, the items may be placed in a stack of items that prevents the RFID tag from generating a detectable response to the second interrogation signal. The RFID tag may also be placed within about 20 cm or less (e.g., within 1, 2, 5, 10, or 15 cm) of another RFID tag such that the other RFID tag causes tag shadowing, tag detuning, and / or re-radiation cancellation that makes it difficult or impossible to detect a signal from one or both RFID tags. The method may be implemented using a system that includes a plurality of RFID tag readers that transmit interrogation signals to the RFID tags and receive responses to the interrogation signals from the RFID tags, and a controller appliance operatively connected to the RFID tag readers. The RFID tag readers may transmit interrogation signals at different repetition rates based on the time of day (e.g., fast scans during the day and slow scans at night).

[0011] The RFID tag readers may include first and second RFID tag readers configured to monitor first and second zones of the store, respectively (e.g., a shipping / receiving area and an entrance / exit area, respectively). The first and second RFID tag readers may transmit interrogation signals at different speeds, at different power levels, or with different Q parameters (the RFID tag readers may have two RFID tag readers configured to instruct the RFID tag to respond to an interrogation signal, where Q is the Q parameter). Q Randomly select one of the time slots.

[0012] The controller appliance may include a communications interface configured to communicate with at least one RFID tag reader, an inventory database that stores a state of the RFID tag, a processor operatively connected to the communications interface, and a non-volatile memory operatively connected to the processor that stores instructions that, when executed by the processor, cause the processor to update the state of the RFID tag based on responses from the RFID tag to interrogation signals from the RFID tag reader and failures by the RFID tag to respond to interrogation signals from the RFID tag reader.

[0013] The controller appliance can transition an RFID tag to a sold state in response to an indication from at least one of the multiple RFID tag readers that the RFID tag has been physically removed from the store. The controller appliance can transition a corresponding RFID tag to a sold state in response to an indication that an item has been sold, even if the RFID tag's starting state is a stale state or a missing state indicating that the RFID tag and associated item are missing. The indication can come from a point of sale (POS) system to which the controller appliance is communicatively connected. The controller appliance can also transition the state of the RFID tag in response to a command received via an application programming interface (API). The controller appliance can keep the RFID tag in the inventory database in a stale state despite the multiple RFID tag readers not detecting a response from the RFID tag.

[0014] All combinations of the foregoing concepts, and additional concepts discussed in more detail below (provided such concepts are not mutually inconsistent), are considered to be part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are considered to be part of the inventive subject matter disclosed herein. Terms explicitly used in any disclosure incorporated herein by reference should be given the meaning most consistent with the specific concepts disclosed herein. [Brief description of the drawings]

[0015] Those skilled in the art will appreciate that the drawings are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale, and in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and / or structurally similar elements).

[0016] [Figure 1A] A photograph shows items of clothing tagged with radio frequency identification (RFID) tags and stacked on metal shelves in the stockroom of a retail clothing store. [Figure 1B] 1 shows a photograph of clothing items tagged with RFID tags and stacked on wooden shelves on the sales floor / store front of a retail clothing store. [Figure 2A] Shows an RFID tag. [Figure 2B] 2B shows the antenna gain pattern of the RFID tag of FIG. 2A. [Figure 2C] 1 shows simulated antenna gain patterns for different RFID tags in a stack of five RFID tags. [Figure 2D] 1 shows simulated antenna gain patterns for different RFID tags in a stack of 24 RFID tags. [Figure 3A]Illustrates an RFID tag monitoring system deployed in a retail store or similar space. [Figure 3B] FIG. 3B is a block diagram of a controller appliance in the RFID tag monitoring system of FIG. 3A. [Figure 3C] 3B is a state transition diagram for an RFID tag monitored using the RFID tag monitoring system of FIG. 3A. [Figure 4] FIG. 1 illustrates a process for receiving and monitoring items using RFID tags. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Passive RFID tags are particularly useful for tracking or monitoring items in a retail store, warehouse, or other facility. RFID tags are affixed to the items to be monitored and are periodically queried or interrogated with an RFID tag reader, also called a sensor or simply a reader. These RFID tag readers may be handheld or may be fixed in certain locations, for example, above the exits and entrances to the facility. Each time the reader interrogates an RFID tag, it updates the status and location of the RFID tag, as well as the status and location of the corresponding item, in a database or inventory maintained by a system controller or appliance that communicates with the reader.

[0018] Under a naive approach to inventory management with RFID tags, when an RFID tag reader stops reading an RFID tag, the RFID tag and corresponding item are removed from inventory, assuming that the RFID tag and corresponding item have been removed from the premises. For example, when an item is purchased, the purchaser may remove the item and RFID tag from the store, or the purchaser or a store clerk may remove or deactivate the RFID tag affixed to the item before the purchaser removes the item from the store. As a result, the RFID tag will not show up in subsequent scans by a handheld or fixed RFID tag reader. After the RFID tag has not been seen for a predefined number of scans or for a predefined period of time (e.g., one or more days), the system controller may automatically remove the RFID tag and corresponding item from inventory.

[0019] Unfortunately, RFID tags may disappear from scanning by a reader for reasons other than being removed from the facility. For example, an RFID tag placed on a metal shelf as shown in FIG. 1A may not be read by a reader because the metal shelf may block both the interrogation signal and the response. Experiments show that placing an RFID tag on a metal shelf reduces the detection rate from about 99% to about 88%. Similarly, temporary obstacles, sometimes including people, shield RFID tags from an RFID tag reader. A metal cart or a crowd of people may prevent a reader from reading an RFID tag on the other side of the cart or crowd. In a store, a customer or store employee may inadvertently move an RFID tag to, for example, a lower shelf, where it cannot be effectively read by a ceiling-mounted reader. If the obstruction or repositioning lasts longer than the timeout period, the RFID tag and the corresponding item may be removed from inventory even though it is still on-site.

[0020] Other RFID tags can also interfere with RFID tag measurements. As shown in Figures 1A and 1B, RFID tags stacked on top of each other or placed near each other (e.g., within 1, 2, 5, or 10 cm of each other) can degrade each other's ability to be activated by and / or respond to interrogation signals from a nearby reader. Without being bound to any particular theory, this degradation of RFID tag performance can be caused by tag detuning, tag shadowing, and / or reradiation cancellation. Tag detuning within an RFID tag is caused by power loss due to impedance mismatch caused by coupling between the antenna and integrated circuit (IC) of the RFID tag to nearby RFID tags. Tag shadowing and reradiation cancellation are caused by interference between backscattered RF waves from other RFID tags and the incident interrogation signal from the reader. These effects operate at different length scales and can be difficult to model and predict given the numerous ways in which RFID tags can be stacked or positioned and interact with each other. These issues arise from how passive RFID tags work and are currently difficult to mitigate.

[0021] Performance degradation with stacked or closely spaced RFID tags 2A-2D illustrate how stacking RFID tags on top of each other can degrade tag performance. FIG. 2A shows a typical RFID tag 200 having an antenna 202 coupled to an integrated circuit (IC) 204, both of which are printed or otherwise disposed on a substrate 206, such as a piece of paper or cardboard. The antenna 202 receives RF energy in an interrogation signal from a reader and backscatters some of that RF energy as a tag response. The tag 200 modulates the backscattered RF energy according to a value stored in a memory that is part of the IC 204.

[0022] In this embodiment, the antenna 202 is a dipole antenna having a toroidal or doughnut-shaped antenna pattern 201, as shown in Figure 2B. The antenna pattern 201, also called the radiation or far-field pattern, describes the directionality or angular dependence of the strength of radio waves received or emitted by the antenna 202. The antenna pattern 201 in Figure 2B shows that the antenna 202 has lower gain along the length of the RFID tag 200 and higher gain along the width of the RFID tag 200 perpendicular to the substrate 206.

[0023] 2C and 2D illustrate how stacking several RFID tags 200 on top of each other distorts the antenna patterns of each of the RFID tags. FIG. 2C shows five RFID tags 200a-200e aligned on top of each other. Adjacent tags are separated from each other by about 1 cm, which represents the thickness of a folded article of clothing, for example, as shown in FIGS. 1A and 1B. FIG. 2C also shows simulated antenna patterns 201a-201e for different tags 200a-200e, where the change in shading of the radiation pattern indicates the change in gain or detuning of the dipole antenna. Although each antenna pattern is shown in FIG. 2B, tag detuning, tag shadowing, and / or reradiation cancellation distort the antenna pattern. This distortion for each RFID tag varies with the position of that RFID tag in the stack of RFID tags and may reduce the chances of successfully reading the RFID tag.

[0024] FIG. 2D shows that the distortion worsens as more tags 200 are added to the stack. In FIG. 2D, there are 24 RFID tags stacked on top of each other in the environment 20, with adjacent RFID tags separated from each other by 1 cm. FIG. 2D also shows simulated antenna patterns 203a-203f for six RFID tags 200 at the bottom of the stack stacked on the environment 20. These patterns are severely distorted due to tag detuning, tag shadowing, and / or reradiation cancellation. With this level of distortion, RFID tags 200 at the bottom or middle of the stack cannot be reliably read by the ceiling reader, even though they are still in stock.

[0025] Tag detuning, tag shadowing, re-radiation cancellation, and temporary obstructions reduce the ability to maintain an accurate inventory with an RFID system. In a naive approach to inventory management, a temporary failure to read an RFID tag can lead to the associated item being removed from inventory even though it is still in stock. This in turn can lead to an inability to find an item that is actually in stock, or to ordering unnecessary replacements for "out of stock" inventory. Other inventory problems caused by or related to temporary failure to read an RFID tag include carrying excess safety stock to offset inventory errors. Safety stock is the extra inventory that a retailer carries because their inventory is inaccurate, to ensure that they have (enough) product to sell, knowing that their inventory is inaccurate. Safety stock is typically held for all colors and sizes of an item, even for items that are not particularly popular. This causes the retailer to buy and / or store more inventory than is actually needed, potentially discarding unsold or undesirable items.

[0026] Stateful inventory monitoring system 3A-3C illustrate a system 300 that can monitor and locate passive RFID tags 312 with greater than 99% accuracy despite tag detuning, tag shadowing, re-radiation cancellation, and temporary obstructions that may temporarily prevent the reading of a particular RFID tag 312. The system 300 includes one or more RFID tag readers 310a-g (collectively, readers 310), which are shown deployed in a retail clothing store in FIGURE 3A. The readers 310, also referred to as sensors or interrogation devices, are connected to a controller appliance 320, also referred to as a system controller or controller, via respective Ethernet connections 314 or other suitable wired or wireless connections.

[0027] The readers 310 can be fixed in place, for example, on the ceiling or from the ceiling, to monitor different areas of the store. In this example, reader 310a monitors the shipping and receiving area 31, reader 310b monitors the goods storeroom 33, reader 310c monitors the hallway connecting the goods storeroom 33 to the sales floor / storefront 35, reader 310d monitors the changing room 37, and readers 310e-310g monitor the sales floor / storefront 35. For areas monitored by multiple readers 310, the readers 310 may be assigned to monitor zones or sub-areas within the larger area. In FIG. 3A, reader 310e covers a zone including a checkout counter 41 such as a cash register and a point of sale (POS) 42, and reader 310g is positioned to cover the entrance / exit zone 39.

[0028] In operation, the readers 310 scan the store for RFID tags 312 affixed to items 314 for sale within the store. The readers 310 scan the store by transmitting wireless ultra-high frequency (UHF) interrogation signals (e.g., carrier frequencies of 865-868 MHz or 902-928 MHz) and detecting responses from the RFID tags 312. The antenna array of the readers 310 may sweep or scan the interrogation signals over different angular ranges and detect responses from tags 312 that are activated by those interrogation signals. Additionally, the readers 310 may act in a coordinated manner, e.g., one reader 310 activates an RFID tag 312 and all readers 310 within range detect the RFID tag's response (e.g., as disclosed in International Patent Application No. PCT / US2022 / 026198, which is incorporated herein by reference in its entirety for all purposes).

[0029] These scans may include quick and frequent scans of certain high traffic areas, such as the entrance / exit zone 39 or checkout zone 41, when the store is open, to detect tags 312 that are likely to have moved or changed status. Other scans may be longer, less frequent scans of the entire store, including the stockroom 35 and the dressing rooms 37, when the store is closed (e.g., overnight), to perform a complete inventory of all RFID tags 312, including those that are unlikely to have moved or changed status and those that did not respond to recent previous scans. The readers 310 may not detect all tags 312 in every scan. For example, the reader 310b monitoring the stockroom 33 may not detect tags 312 on the metal shelves 34. Similarly, the readers 310e-310g monitoring the sales floor 35 may not detect tags 312 on items 314 stacked on top of each other or hidden by fixtures 36, such as shelves or furniture.

[0030] The reader 310 reports tag responses to a controller appliance 320, shown in detail in FIG. 3B. The controller appliance 320 may include one or more processors, non-volatile memory, and other logic devices implemented as integrated circuits and powered by appropriate power supplies and other housekeeping electronics. These processors and logic devices may include individual components performing separate functions and / or more general purpose components that are programmed to perform various functions by themselves or in cooperation with other components of the controller appliance 320. For example, the controller appliance 320 may include a central processor unit (CPU) 322 that runs an operating system (e.g., Alpine Linux OS) that manages the hardware and software resources of the controller appliance, including communication interfaces shown as Ethernet connections Eth0 and Eth1 connected to the reader 310, the POS system, and / or other devices. The non-volatile memory of the controller appliance may store the operating system, and other firmware and software, and tag state information.

[0031] Fading channels and increased scanning frequency for more accurate estimation In a store, warehouse, or other space or environment in which the reader 310 is deployed, there may be many objects that scatter the wireless radio frequency (RF) signals propagating between the reader 310 and the RFID tags. This means that the channel between the RFID tags and the reader can be modeled or approximated using an appropriate statistical model, such as a Rayleigh or Rician channel model. If there are many objects that attenuate, reflect, or scatter the signal such that there is no line of sight (LOS) path between the transmitter and the receiver (i.e., between the reader and the RFID tag), the channel can be modeled using Rayleigh fading, and the envelope of the channel response follows a Rayleigh distribution. Often, the signal travels from the transmitter (RFID tag) to the receiver (reader) via many paths simultaneously, with one or more paths changing (e.g., length or loss) over time and interfering at the receiver. When the signal arriving along one of these paths, usually the LOS path, is much stronger than the other signals, the environment can be modeled using Rician or Rician fading, which is a probabilistic model for radio propagation anomalies caused by partial cancellation of the radio signal by itself. Rayleigh fading is sometimes considered Rician fading without the LOS signal.

[0032] Conversely, a Rayleigh channel may be considered a Rician channel, without the LOS signal. The Rician fading channel model has a coefficient that represents the ratio of the power in the LOS path to the total power of the reflected paths. The Rician channel devolves into a Rayleigh channel as the strength of the LOS signal decreases relative to the total power of the non-LOS signals. When the coefficient becomes zero, the distribution becomes a Rayleigh distribution. In practice, RFID systems may experience both types of channels.

[0033] In a Rayleigh fading channel, moving the antenna more than a half wavelength will result in approximately statistically independent fading. In other words, in a Rayleigh fading channel, interrogating an RFID tag at a first location with a reader, moving the RFID tag from the first location to a second location that is approximately a half wavelength away from the first location (e.g., 16.4 cm at a carrier frequency of 915 MHz) or changing the orientation of the RFID tag relative to the reader, and interrogating the RFID tag at the second location or orientation with the reader will generate two statistically independent measurements of the RFID tag. If each of these read opportunities independently has an 80% probability of success, then combining both opportunities will result in a 96% probability that at least one read opportunity will be successful in a measurement (accurate location estimate). In other environments, the RFID tag may be stationary, but a person or other object moving at 1-2 meters / second will cause fading changes that will result in statistically independent measurements at a tag read rate of once every few seconds even if the RFID tag does not move. This means that reading an RFID tag frequently (e.g., once every 1, 2, 3, 4, or 5 seconds) in an area or zone where RFID tags and / or other objects are likely to move (e.g., a sales floor) is more likely to result in at least one successful measurement or estimation of the RFID tag's location than reading an RFID tag in an area or zone where movement is less likely (e.g., a storeroom).

[0034] To take advantage of the statistical independence of measurements at relatively slightly different locations, the reader 310 of the system 300 of FIG. 3A operates at different read rates depending on the nature of RFID movement in each zone. The read rate and type also depends on the time of day / if the store is open or operational. The read rate can be selected or optimized to read areas with tag movement and may read less frequently or not at all in areas with little tag movement. Sensors (readers) can be positioned (including utilizing beam steering) to better cover and isolate foot / tag traffic areas.

[0035] When a large number of items do not appear in the traffic path, the reader can operate with a lower Q parameter that adjusts the probability of a tag response. For tags that receive an interrogation signal, the reader uses a set of zeros and twos to select a time slot in which to respond to the interrogation signal. Q -1. The reader then begins the next sequence of transmitting interrogation signals and waits for the tag to reply. Q Each sequence is called a round and can be the same carrier frequency (also called frequency hop or hop for short) or a different carrier frequency for the interrogation signal. A larger value of Q reduces the chance of two tags responding during the same time slot, known as a collision. Reducing the Q parameter can increase the chance of a collision, but allows the reader to read tags faster because there are fewer time slots for a response, and can send more rounds per hop or make each hop shorter. For example, with Q=5, a maximum of 2 5 = 32 query slots, in total taking much less time than a slow hop (e.g., 400 ms). Also, with a shorter hop, the reader can scan frequencies faster and take advantage of frequency diversity to improve the chances of powering / receiving a tag response.

[0036] Additionally, reducing the reader transmit power above the traffic path reduces the number of tags that are powered only to those in or close to the traffic path (again, allowing for a smaller Q and faster reads).If the Electronic Product Code (EPC) stored on an item's RFID tag at the time of movement is known, the system 300 can track that particular RFID tag (EPC) directly through the use of the RFID SELECT command, eliminating conflicts between RFID tags activated by the reader 310.

[0037] More specifically, some or all of the readers 310 may perform fast scans of high traffic areas during opening hours or business hours (e.g., when associates and / or customers are in the store) to interrogate RFID tags that are likely to be in motion. The readers 310 may also perform slower, deep scans to interrogate all RFID tags for inventory purposes when the RFID tags are unlikely to be in motion, e.g., because the store is closed and / or unattended. For example, the reader 310b in the product stockroom 33 may perform slow, deep scans of RFID tags in the product stockroom 33 at night when the store is closed to perform a complete inventory of the product stockroom 33. Other readers, including the readers 310d in the sales floor 35 and the dressing rooms 37, may similarly perform slow, deep scans at night or when the store is unattended. During a slow deep scan, each reader 310 reads RFID tags at a slower rate, pointing to more / finer sectors and giving equal time to interrogate each sector. Each reader 310 spends more time emitting and receiving signals from each location. If necessary, the readers and RFID tags can operate at a lower modulation rate (e.g., 80 kbps instead of 640 kbps) to increase the likelihood of detecting an RFID tag response in the presence of noise. Each reader 310 can also change the transmission (interrogation signal) characteristics that excite each RFID tag to make it more likely to produce a detectable response or to perform faster reads / interrogations. This compensates to some degree for stacking or obstructions that reduce the likelihood of successfully interrogating an RFID tag.

[0038] During deep scanning, more than one reader 310 at a time (e.g., two, three, four, or more readers 310) may interrogate RFID tags. For deep scanning, each reader 310 uses multiple pointing sectors (e.g., one for each antenna element of the reader) and uses a higher elevation angle for each pointing sector to read RFID tags on shelves, racks, or other furniture. For example, a reader may use elevation angles of 135° and 155° for deep and fast scanning, respectively (180° in this case points straight down from the ceiling-mounted reader to the floor). The reader may operate at azimuth angles of 0°, 45°, 90°, 135°, ... 315° for deep scans, and 45°, 135°, 225°, and 315° for fast scans, where the angles are changed (somewhat) during fast scans for sensors covering special volumes such as entry / exit zones and goods warehouses to better exploit activity within those volumes. The control appliance may take these different elevation and azimuth angles into account by using different boxing techniques to eliminate poor position estimates. The control appliance may also remove outliers by comparing the detected position to the illuminated position, which ideally should be consistent instead of widely separated.

[0039] During rapid scanning, some or all of the readers scan areas where RFID tags are likely to be moved (frequently) by salespeople or customers, such as the sales floor 35, the entrance / exit zone 39, the checkout zone 41 (aka the cash register zone), and the hallways between the sales floor 35 and the goods stockroom 33. If the system includes a camera, images from the camera may be used to detect areas that are (generally) free of motion or fixtures, and target scanning to areas with motion and / or areas without fixtures. For example, the camera may detect that a person is standing near fixtures and picks up an item from the fixtures. Because the system has estimated which items are on the fixtures (or otherwise within reach of the human hand), it can target the scan to only those items, so that only the tags on those items respond to the interrogation signal. If this is a small set of tags, the system may use a smaller Q parameter for more efficient and faster scanning. Once the system identifies a tag in motion (i.e., picked up by a human), the SELECT aspect of the RFID protocol can be used to track the remainder of the tag's journey through the store or space.

[0040] Alternatively, or in addition, the control appliance may instruct the reader 310 to scan areas with aisles or other areas where customers and store personnel are likely to move (and move RFID tags). Scanning tags in areas without furniture, fixtures, or many other tags improves the likelihood of activating a tag and receiving a detectable response from the tag, in part because there are fewer tags in the area being interrogated, and therefore less contention between tags to respond in different (unique) time slots. Additionally, rapid and frequent reading of RFID tags in these areas increases the detection rate of items, given the movement of RFID tags by store personnel and / or customers.

[0041] Scanning parameters during fast scans are typically different from those used in slow deep scans and may even vary from reader to reader. For example, fast scans may have a higher scan repetition rate, a lower scan (hop) period (e.g., 30-50 ms instead of 400+ ms), a lower Q parameter, fewer scan angles, fewer and coarser scan sectors, and a different time spent interrogating each sector. For example, the hallway reader 310c may scan in only two directions (left and right in FIG. 3A). In addition, the readers may employ interrogation signals with different amplitude / power characteristics, assuming the sensor is closer to the location of the tag being interrogated. While fast scans may be much shorter than slow deep scans, fast scans may extend or be repeated over a greater number and / or a wider range of carrier frequencies to increase carrier diversity. In addition, multiple readers (e.g., three or more) may scan simultaneously during fast scans, each scanning a separate section of the store. During fast scans, the sensors may operate at different scan speeds and / or duty cycles, with many short fast scans by sensors on high traffic areas (e.g., readers 310c, 310e, and 310g) and fewer scans by other sensors, as directed by the controller appliance 320.

[0042] Controller Appliance Architecture 3B illustrates the controller appliance 320 as a block diagram, with each block representing a different function or sub-function performed by the controller appliance 320. To monitor and update tag status, the controller appliance 320 includes or implements an in-store message router 324, an RFID interrogation controller (RFID-IC) 326, a location state manager 328, a tag state manager 330, and a retail back-end application programming interface (API) 332. The in-store message router 324 queues and routes messages exchanged between the reader 310 and the RFID-IC 326 over the Ethernet connection 314. The RFID-IC 326 employs a split media access controller (MAC) design with a lower MAC layer implemented in the reader 310 and an upper MAC layer implemented in the RFID-IC 326 to process messages exchanged with the reader 310. The lower MAC layer determines timestamps and parameters estimated from the backscatter response of the RFID tag that are useful for determining the location of the tag. The upper MAC layer schedules the hop transmissions and the general purpose of each hop. The lower MAC layer performs more time-critical functions such as actually scheduling when to send commands and how to react to replies within a hop. The positioning layer, including the RFID-IC and / or reader 310, calculates the location of the RFID tag in a 3D coordinate system (e.g., Cartesian coordinates with an origin at a known location in a store or room) from data from the MAC and PHY layers. Messages from the reader 310 may also include data read from the RFID tag, including the RFID tag's EPC and other metadata.

[0043] A location state manager 328 and a tag state manager 330 track the location and state, respectively, of the RFID tag. The location state manager 328 receives the estimated location of the RFID tag from the RFID-IC 326 (e.g., in a Cartesian coordinate frame with the origin at one corner of the store) and determines the room and zone within the store in which the RFID tag is located. The rooms and zones may be extracted from a 3D model of the store or space. In FIG. 3A, the rooms include a receiving area 31, a merchandise storeroom 33, a sales floor 35, and a dressing room 37, with the sales floor 35 further divided into an entrance / exit zone 39 and a checkout zone 41. The location state manager 328 updates the location of each RFID tag in an inventory database 334, which may be hosted locally or off-site (e.g., in the cloud), based on the location changes detected by the reader 310.

[0044] The tag state manager 330 manages the tag states, including the tag's location and availability, according to a state diagram shown in FIG. 3C and described in more detail below. There are several possible availability states, including, but not limited to, (1) available, (2) stale (optional), (3) ignored, (4) missing, and / or (5) sold. Other states may also exist. These states and transitions between these states are described in more detail below. The tag state manager 330 transitions the RFID tag 312 between these states based on the tag's response (or lack of response) to queries from the reader 310 that include information about the tag's location, and the tag's state stored in the inventory database 334. The tag state manager 330 updates the tag state stored in the inventory database 334 and forwards both the tag state and the tag location estimate to the retail backend light API 332, which implements backend functionality for inventory, restocking, and product lookup 332. The Retail Backend Lite API 332 can implement these functions through a Web App Gateway 342 that implements a Hypertext Transfer Protocol (HTTP) proxy and redirects Representational State Transfer (REST) ​​requests to the appropriate backend servers (not shown). The Web App Gateway 342 can also provide user authentication and authorization, and serves static files that are used by browsers to render web pages.

[0045] Also shown in FIG. 3B are several optional components of the controller appliance 320, including a spatial server 338, a raw tag server 336, a Trivial File Transfer Protocol (TFTP) server 340, a Network Time Protocol (NTP) server 344, a multicast domain name service (mDNS) server 342, a Secure Shell (SSH) server 346, and a Secure Sockets Layer (SSL) certificate store 348. The spatial server 338 handles firmware lifecycle management and configuration of the sensor 310 and a Power-over-Ethernet (PoE++) switch (not shown) that connects the controller appliance 320 to the sensor 310. The raw tag server 336 retrieves tag metadata for legacy APIs, such as those used by API clients for system debugging. Upon booting, the sensor 310 downloads an executable image from a TFTP server. The NTP server 344 connects and synchronizes with a remote (e.g., Internet-based) NTP server and provides NTP services to the sensor 310. An mDNS server 342 allows the controller appliance 320 to advertise itself using the mDNS and DNS-SD protocols, for example, during debugging. An SSH server 346 is also used for debugging. An SSL certificate store 348 also hosts server certificates used by the sensors 310 and web server certificates used by REST clients to authenticate the controller appliance 320.

[0046] Stateful inventory tracking Together, the location state manager 328, tag state manager 330, and inventory database 324 in the controller appliance 320 track the state of each RFID tag based on the tag response (or lack of response) detected by the sensor 310. The tag state includes two variables: the tag's location state and its availability state. The location state includes the tag's last estimated location (e.g., two-dimensional or three-dimensional Cartesian coordinates), a timestamp of the last location update, and an estimate of the error in the estimated location (e.g., x , y , z ), and optionally a flag indicating whether the tag and associated item are in a warehouse. A sales manager, store associate, or other user can view the tag's status, including availability and location state variables, using a browser or app running on a computer, tablet, smartphone, or other device that queries the controller appliance 320 via a REST API or other suitable interface or API that makes inventory data available. The sensors 310 and / or RFID-IC 326 generate an estimated location, timestamp, and error estimate from the RFID tag's response to the interrogation signal from the sensor 310. The location state manager 328 maps each estimated location to a room and, if applicable, a zone of the store, sets or resets an optional warehouse flag, and then appends this information to the tag read event and forwards the event to the tag state manager 330.

[0047] The tag state manager 330 is responsible for maintaining the availability state of each RFID tag according to the state transition diagram of Figure 3C. As shown in Figure 3C, tags have five availability states: (1) AVAILABLE, indicating that the item associated with the tag is available for sale; (2) SOLD, indicating that the item associated with the tag has left the store and is considered sold or the POS system has processed and / or recorded the item for sale; (3) IGNORANT, indicating that the item associated with the tag is no longer part of the inventory, for example because the tag was attached to the wrong item or the item is damaged and unsuitable for sale; (4) Stale, indicating that the tag has not been read within a predefined timeout period (e.g., minutes, hours, days, or weeks depending on the item and / or zone in which the tag was last read); and (5) MISSING, indicating that a store associate searched for an item associated with an old tag and was unable to find the item in the store. Other states may also exist, including, but are not limited to, stolen, damaged, reserved for pick-up or exchange (e.g., in response to an online sale or exchange process), and / or custom state, and may be used to represent items or tags that have been stolen, destroyed, or otherwise manipulated.

[0048] When the sensor 310 first reads the tag 312 (360), the tag state manager 330 creates a record of the tag 312, including a timestamp indicating when the tag 312 was first detected and the associated item, and enters the record into the inventory database 334. In response to creating the record, the tag state manager 330 sets the tag's available state variable to available. If the reader 310 continues to detect responses from the tag 312 during subsequent scans (the tag 312 is read before the timeout period expires 362), the location manager 328 updates the location state variable as necessary, and the tag state manager 330 keeps the tag's available state variable in available state. If a store associate or other user determines that the item associated with the tag is incorrect or otherwise unsuitable for sale, the store associate sets the tag's available state variable to ignored by accessing an API (370) with an app on a smartphone, tablet, or other suitable computing device. (This can occur during the receiving process when a store associate checks the shipping manifest against the actual items received.) The tag state manager 330 keeps the tag's availability state variable as "ignored" unless a store associate or another user uses the API to change the tag's availability state variable to available (372), sold (374), or missing (376). A store associate or user can use the API to force transitions between any pair of tag states, including those shown in FIG. 3C.

[0049] If the reader 310 does not detect a response from the tag 312 for a predefined timeout period and / or after a predefined number of scans, the tag status manager 328 sets (380) the tag's availability status variable to "stale." The timeout period and / or number of scans may vary depending on the tag's last estimated location, e.g., if the tag was last read at a storeroom, the predefined timeout period may be seven days, whereas if the tag was last read at a sales floor, it may be three days. The tag status manager 330 does not remove the tag or associated item from inventory in response to this change in status, even though the tag 312 has not been read, possibly for an extended period of time (e.g., a week or more). In other words, stale does not mean that the tag or associated item has been removed from inventory. It means that the tag 312 has not been read for at least as long as the timeout period because it is on a metal shelf or stacked near other tags (e.g., within 1, 2, 5, or 10 cm of other tags).

[0050] If one or more of the readers 310 receives a response from a tag 312 with an outdated available state variable, the location state manager 328 updates the tag's location availability variable and the tag state manager 330 changes the tag's state availability variable from outdated to available (364). If a store associate searches for the tag and associated item, for example based on the tag's last estimated location, but is unable to find the tag or associated item, the associate can change the tag's state availability variable from outdated to missing via the API (376). If the tag and associated item are later found, the tag's state availability variable can be changed from missing to available via the API.

[0051] Tags can also be automatically transitioned from a stale state to a missing state based on timeout conditions specific to the area of ​​the store where the tag stales. For example, tags should not remain near checkouts beyond the store's operating hours, so stale tags near checkouts can be set to missing after a predefined timeout period, e.g., 6, 12, 18, or 24 hours. Typically, a store's inventory is completely turned over at some multi-month interval (e.g., 1, 2, or 3 months), so stale tags on the sales floor can be set to missing after staleness at that multi-month interval to ensure that stale tags that have been removed (e.g., due to uncaptured theft) do not remain in inventory forever.

[0052] The tag state manager changes the tag's state availability variable to sold (382) in response to a positive indication that the item associated with the tag has been purchased. (Failure to read the tag in a given period or number of scans changes the tag's state to stale, rather than sold.) This positive indication can include a sale (384) processed using the POS 42, or detection of a tag 312 leaving the store by a reader 310g monitoring the entry / exit zone 39. For example, a customer may purchase an item at the checkout 41, where a store clerk registers the sale at the POS 42. The customer then removes the purchased item from the store. The tag state manager 330 receives an indication of the sale from the POS 42 via the API and changes the tag's state availability variable to sold, even if the tag was missing or stale. If the tag is still active, readers 310e-310g detect the tag leaving the store, in which case the location state manager 328 determines that the tag has left the store and the tag state manager 330 changes the tag's state availability variable to sold.

[0053] The state of an object's tag can transition directly from old or missing to sold based on the POS data, even if the tag was not read during checkout. For example, a sale processed at the POS 42 can trigger a tag state transition from old or missing to sold. Without this change in tag state, old tags would need to be marked as sold upon leaving the store, which means the tag state transitions from old to available for sale, rather than transitioning directly from old to sold.

[0054] Once the tag's status availability variable is changed to a sold state, the tag and associated item may be retained at least temporarily to perform sales and inventory reporting before being removed from the inventory database 334 or purged to prevent the inventory database from becoming too large. If a customer returns an item, the tag and associated item are restored to inventory when the tag is read by an RFID reader and the tag's status availability variable is set to an available state (368). Similarly, if the reader receives a response from a missing tag, the tag's status availability variable is set to an available state (366).

[0055] Optionally, the tag state manager 330 can maintain a history of recent tag state transitions for each and every RFID tag. This transition history can include timestamps indicating when a state transition occurred. This is useful for debugging the system.

[0056] Inventory Web Application Store associates, sales managers, and other users can view the inventory database 334 through an inventory web application on a computer, tablet, smartphone, or other device that connects to the controller appliance 320 via the Internet or another computer network or connection (e.g., a direct WiFi or Ethernet connection). Store associates, sales managers, and other users can query the inventory database 334 using different APIs. These APIs may allow users to query the inventory database 334 for complete inventory, items or units that meet a certain criteria or set of criteria (e.g., the color or size of the unit or tag status), or the history of the units.

[0057] Using the inventory web application and / or API, users can retrieve and view lists of items and associated RFID tags and the status of the associated RFID tags, including location and availability state variables. Users can view inventory items by row or column, and can enter entries for location and availability state variables, including the room in which the item is (presumably) located, and the number of items by type on the sales floor and in the stockroom. In these views, users can sort, filter, and reposition items, for example, by item type, item color, item size, item stock keeping unit (SKU) number, RFID EPC, location, availability state variables, etc. These numbers are particularly useful when receiving a shipment of new items and adding those items and associated RFID tags to the database inventory. The inventory web application also allows users to view state transition times, location times, and history, which show the time that a particular item has spent in different states and / or locations. Users can also use the inventory web application to change the status of an item, for example, to out of stock or sold.

[0058] Confidence index of estimated tag location In addition to managing the location state variables, the location manager 328, retail backend light server, or other processor may also manage a separate reliability index or level. The reliability index may be another number that represents the likelihood that an item or RFID tag is still at its last known location (even after some time has passed since the tag was last read). When a RIFD tag is read, the RFID-IC develops both a location estimate and an error estimate, and after some time has passed, if the tag has not moved, the location / error should still be valid. However, if a lot of time has passed, the tag may have been moved but for some reason the system missed it. In other words, the reliability index represents the probability that the RFID tag and associated item are actually located at the (last) estimated location of the RFID tag. This reliability index may be another input of the location state variables, or a separate optional parameter or variable. The reliability index may be calculated and displayed in a quantitative manner, a qualitative manner, or both a quantitative and qualitative manner. For example, it can be a numerical value ranging from 0 indicating no reliability to 1 indicating complete reliability, or a qualitative value such as excellent, good, fair or poor. The qualitative value can be linked to a quantitative value (for example, excellent may correspond to a numerical reliability of 0.76-1.0, good may correspond to a numerical reliability of 0.51-0.75, etc.).

[0059] The reliability index may depend in part on the tag's status (e.g., available, stale) and its last estimated location. The reliability level or index may have little or no meaning if the tag is in a ignored, missing, or sold state. The reliability level may degrade, for example, exponentially or stepwise, with time since its last detected response. If a tag was last detected at a goods warehouse, it may have a relatively high reliability index, for example, even though its status may be stale. On the other hand, if the tag has been located in a high traffic room or zone, such as the receiving area 31, the entrance / exit zone 39, or the checkout zone 41, for a longer than usual time, the reliability index may be low even if the tag's status is available.

[0060] Table 1 (below) shows one way to calculate or assign a reliability index to an RFID tag based on the time T since the tag was last read by a sensor. The times in Table 1 are examples and should not be taken as limiting, and other times are possible. This time depends on the last estimated location of the tag, which is longest for tags in a warehouse and shortest for tags in temporary zones such as pick-up areas, checkout zones, and entrance / exit zones. This can range from hours or days for warehouses, minutes to hours for sales floors, and seconds to minutes for temporary zones. [Table 1]

[0061] The inventory web application may depict the reliability indicator to a store associate or other user via a graphical user interface (GUI) displayed on a computer, tablet, or laptop. For example, if the GUI shows the (last) estimated location of the tag as a dot superimposed on a store floor plan, the color of the dot may reflect the reliability indicator, e.g., green or blue representing a higher reliability level, and yellow, orange, or red indicating a lower reliability level. The shading may be discrete or graded depending on the range or scale of the reliability level, with additional icon, text, or other indication (e.g., if the reliability level is poor) indicating when the tag was last read / detected. The GUI may also depict the estimation error of the tag's estimated location as the size or radius of the dot, with a larger dot indicating a larger estimation error. The shape or opacity of the dot may indicate whether the tag is in an available (opaque) or stale (semi-transparent) state.

[0062] A store associate can use the tag status and reliability index to quickly and efficiently locate an item, for example, for inventory management, replenishing, or fulfilling a customer request. For example, assume a customer is looking for the next larger size shirt, or a shirt in a different color. The store associate can query the inventory database 334 via an inventory web application to see if the item is in stock, and if so, its estimated location, along with the reliability index and uncertainty (error estimate radius). If multiple copies of the item are in stock, the GUI can display all of the items, along with a visual indication of the associated reliability index and error estimate. The store associate can then select the item with the closest and / or highest reliability index and lowest error estimate to keep in stock. The store associate may interpret an estimated location with a low reliability index as a place where the item is unlikely to be found, but may interpret it as a reasonable location to begin searching for the item as part of the process to determine if the item is missing. The GUI shows items associated with both available and old RFID tags, allowing store associates to find and remove items that may be stacked on metal shelves, piled in tall piles, or temporarily blocked from the reader 310 by furniture or other objects.

[0063] Example stateful inventory tracking scenario FIG. 4 illustrates an exemplary life cycle of an RFID tag affixed to an item sold in a store such as that shown in FIG. 3A, beginning with receipt (402). The item arrives at the store. A store associate removes the item from its shipping materials and reads the affixed RFID tag with a handheld or fixed reader, which records the tag's response, including its EPC. A controller appliance connected to the reader adds a new record to the tag's inventory database containing information about the item and initializes the tag's state to available. (If the item does not have an RFID tag affixed to it, the associate affixes the RFID tag to the item before reading the RFID tag with the reader, and similarly, if reading the RFID tag does not automatically add the RFID tag or the item to inventory, the associate can manually add them to inventory.) The associate compares the item information gleaned from the tag's EPC in the inventory database to the shipping manifest, and if there is a mismatch, the associate can set the tag's state to ignored and remove the item.

[0064] Once the item is received and successfully added to the inventory database, the clerk may move the item and tag to a stockroom (404). The reader may sense this transition from a change in the tag's estimated location as it moves to the stockroom. In the stockroom, the clerk may place the item among a pile of items, on a metal shelf, etc. This may cause the tag to "disappear," meaning that, as discussed above, the reader may not be able to effectively read the tag due to interference from nearby tags or metal. If the reader stops reading the tag, the tag and associated item will remain in inventory, although it will eventually change from available to stale.

[0065] For example, assume there are 10 items of a particular SKU on a stock shelf. If a shipment arrives with 10 more items of the SKU, the store attendant may stack the new item on top of the old one for a stack of 20 items, even though the sensor can read up to 16 items in the stack, causing at least 4 items to stop emitting a detectable response. All 20 items will remain in stock, the "missing" item will eventually have an obsolete status, and the others will have an available status.

[0066] Finally, the sales associate moves the items from the stockroom to the sales floor (406). An RFID tag reader may frequently scan the hallways or other spaces between the product stockroom and the sales floor to detect tags, as described above, or may simply detect the tags once they reach the sales floor. In either case, the controller appliance updates the location state of the tags and, if applicable, changes the availability state of the tags from stale to available. From time to time, sales associates and / or customers may move or reposition items and tags on the sales floor (408), for example, when customers try on items, when other items are moved or purchased, or when sales displays are repositioned. When this happens, the items and tags are scanned frequently to detect their change of position. Items and tags may also be stacked with other items and tags such that the tags are no longer readable, in which case the tag's state will eventually transition from available to stale. Even if the tag is unreadable, the controller appliance keeps the item in the inventory database, even in its stale state. When the tag becomes readable again, the controller appliance changes the tag's state to available.

[0067] When a customer purchases an item (410) and / or removes the item from the store (412), the controller appliance may change the item's status to sold and ultimately remove the item from the (potentially) available inventory in the inventory database. More specifically, the controller appliance changes the item's status to sold in response to receiving a message from the POS system that the item has been sold and / or a reader sensing an associated tag that is tracking its trajectory out of or outside the store. This may trigger restocking the item from a stockroom and / or ordering a replacement item.

[0068] conclusion While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art can readily envision various other means and / or structures for performing the functions and / or results and / or obtaining one or more advantages described herein, and each such variation and / or modification is deemed to be within the scope of the inventive embodiments described herein. More generally, those of ordinary skill in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary, and that the actual parameters, dimensions, materials, and / or configurations will depend on the particular application or applications in which the teachings of the present invention are used. Those of ordinary skill in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. Thus, the foregoing embodiments are presented by way of example only, and it will be understood that, within the scope of the appended claims and equivalents thereof, the inventive embodiments may be practiced otherwise than as specifically described and claimed. The inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods is within the inventive scope of the present disclosure, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent.

[0069] Also, various inventive concepts may be embodied as one or more methods, examples of which have been provided. The acts performed as part of a method may be ordered in any suitable manner. As a result, embodiments may be constructed in which acts are performed in an order different from that illustrated, which may include performing some acts simultaneously, even when shown as sequential acts in the example embodiments.

[0070] All definitions and those used herein should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0071] The indefinite articles "a" and "an," as used in the specification and claims, unless expressly indicated otherwise, should be understood to mean "at least one."

[0072] The term "and / or" as used herein and in the claims should be understood to mean "either or both" of the conjoined elements, i.e., elements that are conjunctive in some cases and disjunctive in other cases. Multiple elements listed with "and / or" should be construed in the same manner, i.e., "one or more" of the conjunctive elements. Other elements may optionally be present other than the elements specifically identified by the "and / or" clause, whether related or unrelated to the elements specifically identified. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," can refer to A only (optionally including elements other than B) in one embodiment, B only (optionally including elements other than A) in another embodiment, both A and B (optionally including other elements) in yet another embodiment, and so forth.

[0073] As used herein and in the claims, "or" should be understood to have the same meaning as "and / or" as defined above. For example, when separating items in a list, "or" or "and / or" shall be construed as inclusive, i.e., including at least one, but not one or more, of a number or list of elements, and optionally including additional items not in the list. Only terms clearly indicating the contrary, such as "only one of," "exactly one of," or, when used in the claims, "consisting of," shall refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be construed to indicate exclusive alternatives (i.e., "one or the other but not both") when preceded by an exclusive term, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0074] As used herein and in the claims, the phrase "at least one" in reference to a list of one or more elements should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed in the list of elements, and not excluding any combination of elements in the list of elements. This definition also allows that elements other than those specifically identified in the list of elements to which the phrase "at least one" refers may optionally be present, whether or not related to the specifically identified elements. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B" or, equivalently, "at least one of A and / or B") can refer to, in one embodiment, the inclusion of at least one, optionally one or more, A, in which B is absent (and optionally including elements other than B); in another embodiment, the inclusion of at least one, optionally one or more, B, in which A is absent (and optionally including elements other than A); in yet another embodiment, the inclusion of at least one, optionally one or more, A, and at least one, optionally one or more, B (and optionally including other elements), etc.

[0075] In the claims, as well as in the above specification, all transitional phrases, such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like, are to be understood as open-ended, i.e., meaning including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" shall be closed or semi-closed transitional phrases, respectively, as defined in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

1. 1. A method for tracking items associated with each radio frequency identification (RFID) tag that enters and leaves a store using an inventory database that stores states of the RFID tags, the states including an available state indicating that the item associated with the corresponding RFID tag is available for sale, an stale state indicating that a predetermined period of time has passed since the corresponding RFID tag responded to an interrogation signal, and a sold state indicating that the item associated with the corresponding RFID tag has been sold and / or removed from the store, the method comprising: changing the state of the RFID tag to the old state in response to not detecting a response to the first interrogation signal from the available RFID tag; changing the state of the RFID tag from the old state to the available state in response to detecting a response to the second interrogation signal from the RFID tag; changing the status of the RFID tag to the sold status in response to detecting a sale of an item associated with the RFID tag and / or removal of the RFID tag from the store; A method comprising:

2. 2. The method of claim 1, wherein the state of the RFID tag includes information about an estimated location of the RFID tag, an error associated with the estimated location of the RFID tag, and a timestamp associated with the last detected response from the RFID tag.

3. The method of claim 2 , wherein the predetermined period of time is based on the estimated location of the RFID tag.

4. The method of claim 2 , wherein the predetermined period is based on a last detected response from the RFID tag.

5. 2. The method of claim 1, comprising, in response to detecting the RFID tag in a pickup area of ​​the store, creating an entry in the inventory database for the item associated with the RFID tag, the entry including an Electronic Product Code (EPC) stored in a memory of the RFID tag, the EPC representing the item associated with the RFID tag.

6. The method of claim 5 , further comprising verifying that the EPC correctly represents the item associated with the RFID tag.

7. The method of claim 1 , wherein detecting the sale of the item comprises updating a point of sale (POS) system to reflect that the item has been sold.

8. The method of claim 1 , wherein detecting the sale of the item comprises transacting the sale of the item with a point of sale (POS) system.

9. The method of claim 1 , wherein detecting the sale of the item includes detecting that the RFID tag has been removed from the store.

10. The method of claim 1 , further comprising arranging the items to prevent the RFID tags from generating a detectable response to the second interrogation signal.

11. The method of claim 1 , further comprising placing the item in a stack of items that prevents the RFID tag from generating a detectable response to the second interrogation signal.

12. 2. The method of claim 1, further comprising, in response to receiving an indication that another item associated with another RFID tag is no longer part of the inventory tracked using the inventory database, changing the state of the other RFID tag to an ignored state.

13. 13. The method of claim 1, further comprising, in response to receiving an indication that another item associated with another RFID tag cannot be found, changing the status of the other RFID tag to a missing status.

14. 2. The method of claim 1, further comprising: maintaining the RFID tag in the inventory database in the stale state despite not detecting the response to the first interrogation signal from the available RFID tag.

15. The method of claim 1 , further comprising transitioning a state of the RFID tag in response to a command received via an application programming interface (API).

16. 1. A controller appliance for monitoring the status of radio frequency identification (RFID) tags, the statuses including an available status indicating that an item associated with a corresponding RFID tag is available for sale, an stale status indicating that a predetermined period of time has elapsed since the corresponding RFID tag responded to an interrogation signal, and a sold status indicating that the item associated with the corresponding RFID tag has been sold, the controller appliance comprising: a communications interface configured to communicate with at least one RFID tag reader and to communicate with an inventory database that stores the status of the RFID tags; a processor operatively connected to the communication interface; a non-volatile memory operatively connected to the processor and storing instructions that, when executed by the processor, cause the processor to update a state of the RFID tag based on responses from the RFID tag to interrogation signals from the at least one RFID tag reader and failure by the RFID tag to respond to the interrogation signals from the at least one RFID tag reader.

17. 1. A system for monitoring radio frequency identification (RFID) tags, comprising: a plurality of RFID tag readers for transmitting interrogation signals to RFID tags and receiving responses to the interrogation signals from the RFID tags; a controller appliance operatively connected to the plurality of RFID tag readers and configured to update a state of the RFID tags based on the responses from the RFID tags; Equipped with the states being an available state indicating that an item associated with the corresponding RFID tag is available for sale, an stale state indicating that a predetermined period of time has passed since the corresponding RFID tag responded to an interrogation signal, and a sold state indicating that the item associated with the corresponding RFID tag has been sold. Including, the system.

18. 20. The system of claim 17, wherein the plurality of RFID tag readers are configured to vary a rate at which they transmit the interrogation signal based on a time of day.

19. The plurality of RFID tag readers a first RFID tag reader configured to monitor a first zone of the store; a second RFID tag reader configured to monitor a second zone of the store; and The system of claim 17, comprising:

20. 20. The system of claim 19, wherein the first RFID tag reader is configured to emit a first interrogation signal at a first rate and the second RFID tag reader is configured to emit a second interrogation signal at a second rate different than the first rate.

21. 20. The system of claim 19, wherein the first RFID tag reader is configured to emit a first interrogation signal at a first power level and the second RFID tag reader is configured to emit a second interrogation signal at a second power level different from the first power level.

22. 20. The system of claim 19, wherein the first RFID tag reader is configured to emit a first interrogation signal with a first Q parameter and the second RFID tag reader is configured to emit a second interrogation signal with a second Q parameter that is different from the first Q parameter.

23. 20. The system of claim 19, wherein the first zone comprises a shipping / receiving area of ​​the store and the second zone comprises an entrance / exit of the store.

24. 20. The system of claim 17, wherein the status of the corresponding RFID tag includes information about an estimated location of the corresponding RFID tag, an error associated with the estimated location of the corresponding RFID tag, and a timestamp associated with the last detected response from the corresponding RFID tag.

25. 25. The system of claim 24, wherein the predetermined period of time is based on the estimated location of the corresponding RFID tag.

26. 25. The system of claim 24, wherein the predetermined period is based on a last detected response from the corresponding RFID tag.

27. 20. The system of claim 17, wherein the controller appliance is configured to transition an RFID tag to the sold state in response to an indication from at least one of the plurality of RFID tag readers that the RFID tag has been physically removed from the store.

28. 20. The system of claim 17, wherein the controller appliance is communicatively connected to a point of sale (POS) system and configured to transition the corresponding RFID tag to the sold state in response to an indication from the POS system that the item has been sold.

29. 20. The system of claim 17, wherein the controller appliance is configured to transition a state of an RFID tag in response to a command received via an application programming interface (API).

30. 20. The system of claim 17, wherein the controller appliance is configured to transition the state of the corresponding RFID tag from the old state to the sold state in response to an indication that the item associated with the corresponding RFID tag has been sold.

31. 20. The system of claim 17, wherein the controller appliance is configured to transition the state of the corresponding RFID tag from a missing state, indicating that the item associated with the corresponding RFID tag is missing, to the sold state in response to an indication that the item associated with the corresponding RFID tag has been sold.

32. 20. The system of claim 17, wherein the controller appliance is configured to keep the RFID tag in the inventory database in the stale state even though the multiple RFID tag readers do not detect a response from the RFID tag.

33. 1. A method for tracking items associated with each radio frequency identification (RFID) tag that enters and leaves a store using an inventory database that stores states of the RFID tags, the states including an available state indicating that the item associated with the corresponding RFID tag is available for sale, an stale state indicating that a predetermined period of time has passed since the corresponding RFID tag responded to an interrogation signal, and a sold state indicating that the item associated with the corresponding RFID tag has been sold and / or removed from the store, the method comprising: transmitting, by at least one RFID tag reader, a first interrogation signal to a first RFID tag; detecting, by the at least one RFID tag reader, a response to the first interrogation signal from the first RFID tag; estimating a location of the first RFID tag based at least in part on the response to the first interrogation signal; updating a status of the first RFID tag in the inventory database to the available status to indicate the location of the first RFID tag in response to detecting the response to the first interrogation signal from the first RFID tag; positioning the first RFID tag within 20 centimeters of a second RFID tag; transmitting, by the at least one RFID tag reader, a second interrogation signal to the first RFID tag using the at least one RFID tag reader; not detecting any response to the second interrogation signal from the first RFID tag due to tag shadowing, tag detuning, and / or re-radiation cancellation caused by the second RFID tag; changing the status of the first RFID tag in the inventory database from the available status to the stale status in response to not detecting any response to the second interrogation signal from the first RFID tag; transmitting, by the at least one RFID tag reader, a third interrogation signal to the first RFID tag; detecting, by the at least one RFID tag reader, a response from the first RFID tag to the third interrogation signal; changing the status of the first RFID tag in the inventory database from the stale status to the available status in response to detecting the response to the third interrogation signal from the first RFID tag; A method comprising:

34. 34. The method of claim 33, wherein positioning the first RFID tag within 20 centimeters of the second RFID tag comprises stacking an item associated with the first RFID tag on an item associated with the second RFID tag.

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