System and procedure for improving portal directionality determination

Abstract

The disclosure is a system comprising a transceiver array containing at least a first pair of transceivers and a second pair of transceivers, wherein the first pair of transceivers includes a transceiver that is contained in the second pair of transceivers. Each transceiver in a pair is configured to monitor a plurality of zones for RFID tags, to transmit information relating to the monitoring of a portion of the plurality of zones for RFID tags to the other transceiver in the pair, and to determine the location of a monitored RFID tag based on the information acquired by monitoring the plurality of zones and the information received by the other transceiver in the first or second pair.

Description

background

[0001] Transceivers configured to function as overhead radio frequency identification (RFID) tag readers are commonly used to determine the location of an RFID tag in commercial environments, such as warehouses or distribution centers. In these environments, an array of overhead RFID tag readers is often used to determine the bearing (arrival angle) and pinpoint the location of an RFID tag. This is generally achieved by an RFID tag reader using beam steering technology to determine the tag's bearing, and the array of tag readers then determines the precise location of a tag using triangulation of multiple bearings from several tag readers that have a coverage overlap.However, implementing such an arrangement can, in some cases, lead to high costs to achieve RFID tag monitoring in potentially confined spaces, such as along the aisles in a distribution center where RFID-tagged items are typically loaded from within the center onto trucks for shipment via a dock door. These dock doors are usually arranged in a row along the length of an outer loading dock.

[0002] In such commercial environments, the precise location of an item with an RFID tag within a facility may not be as critical as determining whether the item has entered or exited a point of entry or exit, such as a portal. In such cases, the tag's directionality, an estimation of the tag's position over time at the entry or exit point, and the creation of an auditable track of the item can be of far greater value. Brief description of the different views of the drawings

[0003] The accompanying figures, in which the same reference numerals refer to identical or functionally similar elements in the individual views, are integrated into the specification together with the following detailed description and form a part thereof, serving to further illustrate embodiments of concepts that include the claimed invention and to explain various principles and advantages of these embodiments. Fig. Figure 1 is a diagram illustrating an overhead view of an exemplary embodiment of the system of the present disclosure. Fig. Figure 2 is a diagram of an exemplary embodiment of the system of the present disclosure, illustrating a linear arrangement of overhead transceivers along a series of portals. Fig. Figure 3 is a diagram of an exemplary embodiment of the system of the present disclosure, illustrating a linear arrangement of overhead transceivers along a series of portals. Fig. Figure 4 is a diagram showing an overhead view of an exemplary embodiment of the system of the present disclosure. Fig. Figure 5 is a block flow diagram of an exemplary embodiment of a method of the present disclosure.

[0004] Experts will recognize that elements in the figures are illustrated for the sake of simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of embodiments of the present invention.

[0005] Where appropriate, the apparatus and process components have been represented by conventional symbols in the drawings, which show only those specific details relevant to understanding the embodiments of the present invention, so as not to obscure the disclosure with details that are readily apparent to persons skilled in the art referring to the present description. Detailed description

[0006] In environments such as warehouses and distribution centers, accurately determining the directionality of an RFID tag at an entry or exit point, such as a portal, allows for precise tracking of the goods to which the RFID tag is attached. This can be crucial for inventory management or loss prevention. Many environments implement a cluster of multiple RFID tag readers to obtain several bearing estimates for a single tag and triangulate its location, and thus direction, over time across the entire cluster area. Deploying such a cluster can incur high associated costs for installation and operation, while providing little valuable information regarding the directionality of an RFID tag at an entry or exit point.One system that overcomes these disadvantages is provided, for example, by using a single overhead transceiver acting as an RFID tag reader to monitor two portals, including monitoring RFID tags coming from a warehouse and exiting through two separate dock doors, while having overlap in monitoring coverage for each portal with at least one other transceiver forming its own localized cluster.

[0007] Examples disclosed herein are directed to a system comprising: a linear transceiver array comprising at least a first pair of transceivers and a second pair of transceivers, wherein the first pair of transceivers includes a transceiver contained in the second pair of transceivers, each transceiver in a pair being configured to monitor a plurality of RFID tag zones, including at least a first zone and a second zone, each with a defined zone width, wherein a first portal is located at a boundary between the first zone and the second zone, and including at least a third zone and a fourth zone, wherein a second portal is located at a boundary between the third zone and the fourth zone; transmitting information relating to the monitoring of a portion of the plurality of RFID tag zones to the other transceiver in the pair;and to determine a location of a monitored RFID tag based on the information gathered by monitoring the multitude of zones and the information received by the other transceiver in the first or second pair, such that the first pair of transceivers works together to monitor and determine locations for RFID tags in the first zone and the second zone, and the second pair of transceivers works together to monitor and determine locations for RFID tags in the third zone and the fourth zone.

[0008] Fig. Figure 1 illustrates an overhead view of an exemplary embodiment of a system of the present disclosure. A system 100 comprises a transceiver array 101a-c containing at least a first pair of transceivers 103 and a second pair of transceivers 104. The first pair of transceivers 103 includes a transceiver 101b, which is also included in the second pair of transceivers 104. For example, a first pair of transceivers 103 may contain the transceiver 101a and the transceiver 101b, and a second pair of transceivers 104 may contain the transceiver 101b and the transceiver 101c. Each transceiver 101a-c may be an overhead RFID tag reader, such as a beam-steerable phased array RFID reader.Although the transceivers in array 101a-c can be positioned in any arrangement that provides acceptable coverage over the relevant coverage area for which the directionality of RFID tags is of interest, the advantages of the present disclosure are generally greatest when the transceivers in the array are positioned in a linear arrangement. Additionally, the transceivers in the array can be placed at ground level or in any other position that provides acceptable coverage over the relevant coverage area for which the directionality of RFID tags is of interest.

[0009] Each transceiver in the first pair 103 or the second pair 104 is configured to monitor a variety of zones for RFID tags. An exemplary embodiment of the system 100 is illustrated in Fig. Figure 1 illustrates this monitoring of the plurality of zones with respect to the transceiver 101b, which is included in the first pair 103 and the second pair 104 of transceivers, as an example of the monitoring capabilities of any given transceiver in the system. The plurality of zones includes a first zone 110 and a second zone 115. A first portal 112 is located at the boundary between the first zone 110 and the second zone 115. Each transceiver is also configured to monitor at least a third zone and a fourth zone, for example, as shown in Fig. As shown in Figure 1, the transceiver 101b in the first pair 103 or the second pair 104 is also configured to monitor at least one third zone 120 and one fourth zone 125. A second portal 114 is located at the boundary between the third zone 120 and the fourth zone 125. The first zone 110, the second zone 115, the third zone 120, and the fourth zone 125 can each have a zone width defined in the settings of the transceivers 101a-c, which can be coordinated among the transceivers 101a-c in the system 100.

[0010] The first portal 112 and the second portal 114, for example, could be dock doors through which items containing RFID tags pass when being loaded from a warehouse into a truck for shipment, or vice versa. Each transceiver 101a-c can be positioned at a predetermined height above the zones it monitors. In a system of the present disclosure, the number of transceivers required may depend on the number of portals or entry / exit points for which the directionality of RFID tags is a concern. For example, to monitor zones assigned to ten different portals, such as dock doors in a row, at least eleven transceivers may be required, since each transceiver can be configured to monitor zones assigned to two portals.

[0011] Each transceiver in the first pair 103 or the second pair 104 is also configured to transmit information regarding the monitoring of a portion of the multiple RFID tag zones to the other transceiver in the pair. For example, with respect to the first pair of transceivers 103, transceiver 101b can be configured to monitor a first zone 110, a second zone 115, a third zone 120, and a fourth zone 125 for RFID tags. Transceiver 101a can also be configured to monitor the first zone 110 and the second zone 115 for RFID tags, as well as two additional zones not monitored by transceiver 101b (not shown).The transmitter-receiver 101b can transmit information to the transmitter-receiver 101a, which may include information relating to the location and directionality of RFID tags in the first zone 110 and the second zone 115, which are monitored by both transmitter-receivers 101a and 101b in the first pair 103. In an exemplary embodiment of the present disclosure, the transmitter-receiver 101b can be configured to transmit carrier information relating to an RFID tag identified in the first zone 110 to the transmitter-receiver 101a.

[0012] Each transceiver in the first pair 103 or the second pair 104 is configured to determine the location of an RFID tag within a monitored zone 110, 115, 120, or 125 based on information gathered by monitoring the multitude of zones and information received from the other transceiver in the first or second pair 103 or 104. For example, an RFID tag can enter the first zone 110, and each transceiver in the first pair 103 can identify the RFID tag. Transceiver 101b can determine an xy position according to the information in Fig. The transceiver 101b can estimate the coordinate plane of the RFID tag shown in Figure 1 using the carrier information related to the RFID tag, assuming a fixed height of the RFID tag from the ground. In entry or exit areas, such as near a portal, the transceiver 101b can use this position information to determine that the RFID tag has moved from the first zone 110 through the first portal 112 and into the second zone 115. The transceiver 101a can estimate the bearing of the same RFID tag that has entered the first zone 110 or second zone 115, and the transceiver 101a can transmit this bearing estimate and / or position information to the other transceiver in the first pair 103, transceiver 101b.The transceiver 101b can use the information it receives from the transceiver 101a, in conjunction with its own estimations, to determine a more precise location / direction of the RFID tag. This results in a system 100 in which the first pair of transceivers 103 work together to monitor and determine carrier information for RFID tags in the first zone 110 and the second zone 115, and the second pair of transceivers 104 work together to monitor and determine carrier information for RFID tags in the third zone 120 and the fourth zone 125.

[0013] By using the carrier information received from transceiver 101a, transceiver 101b can determine a more accurate position of an RFID tag and thus a more accurate direction of an RFID tag moving through a portal separating two zones, such as the first portal 112. The physical separation between the transceivers in a pair improves read diversity by providing a bearing estimate from two different positions (one from each transceiver in a pair). Estimating the location from the carrier information shared by multiple readers improves the accuracy of tag location determination and the ability to read tags in cases where one reader in the pair covering a common zone fails to read a tag, while the other transceiver in the pair does.This improved accuracy of location estimation leads to improved accuracy of directionality determination, which can improve the accuracy of RFID tag tracking systems, for example, systems used when an auditable trace is required for inventory and loss prevention purposes.

[0014] This improved location estimation, resulting from readers monitoring shared zones sharing monitoring information, leads to improved directionality determination. Each transceiver in each pair of transceivers, for example, the first pair of transceivers 103, is required to actively monitor each zone it is capable of monitoring, for example, with respect to transceiver 101b, the first zone 110, the second zone 115, the third zone 120, and the fourth zone 125. This monitoring, combined with the time required to transmit information about a jointly monitored zone to the other transceiver in a pair, results in increased computation time for determining an improved location and directionality.

[0015] Fig. Figure 2 illustrates an exemplary embodiment of a system of the present disclosure. Each pair of transmitters / receivers can cooperate in monitoring common zones with each transmitter / receiver in a pair, sharing information relating to this monitoring with the other transmitter / receiver in the pair. For example, a system 100 can include a first pair of transmitters / receivers 103, comprising transmitter 101a and transmitter 101b; a second pair of transmitters / receivers 104, comprising transmitters 101b and 101c; and a third pair of transmitters / receivers 106, comprising transmitters 101c and 101d. Transmitter 101a can be configured to monitor the first zone 110, the second zone 115, and two additional zones (not shown). The 101b transceiver can be configured to monitor the first zone 110, the second zone 115, the third zone 120 and the fourth zone 125.The 101c transceiver can be configured to monitor the third zone 120, the fourth zone 125, zone 140, and zone 145. The 101d transceiver can be configured to monitor zone 140, zone 145, and two additional zones (not shown). The 101b transceiver can send information regarding its monitoring of the first zone 110 and the second zone 115 to the 101a transceiver and information regarding its monitoring of the third zone 120 and the fourth zone 125 to the 101c transceiver.

[0016] Similarly, each transceiver in any pair in System 100 can communicate with the other transceiver in the pair regarding jointly monitored zones. For example, transceiver 101c can send information regarding its monitoring of the third zone 120 and the fourth zone 125 to transceiver 101b, and information regarding its monitoring of zone 140 and the fourth zone 145 to transceiver 101d.

[0017] Fig. Figure 3 illustrates an exemplary embodiment of a system of the present disclosure. In a system 100, each pair of transmitters / receivers can temporally synchronize and divide the monitoring of a common zone between the transmitters / receivers in the pair. For example, the second pair of transmitters / receivers 104, which includes transmitter 101b, which has the capability to monitor the first zone 110, the second zone 115, the third zone 120, and the fourth zone 125, and transmitter 101c, which has the capability to monitor the third zone 120, the fourth zone 125, and two additional zones 140 and 145, can temporally synchronize and divide the monitoring of jointly monitored zones, e.g., the third zone 120 and the fourth zone 125, between transmitter 101b and transmitter 101c. As shown in Figure 3, the system can be configured to perform a multi-level monitoring function. Fig. As shown in Figure 3, the second pair of transceivers 104 can divide the monitoring in such a way that transceiver 101b is configured to monitor the third zone 120, and transceiver 101c is configured to monitor the fourth zone 125, where an arrow extending from a transceiver 101a-d to a zone represents the coverage zones or zones of that specific transceiver in which that transceiver monitors RFID tags. In addition to coordinating with transceiver 101b to monitor common zones, transceiver 101c can also be included in a third pair of transceivers 106, where transceiver 101c is coordinated with transceiver 101d to monitor common zones 140 and 145, and a third portal 116 serves as the boundary between zone 140 and zone 145.In a System 100 implemented in an environment experiencing a high volume of RFID tags passing through multiple portals at a relatively high speed, such as a warehouse with a series of dock doors used to load and unload items into and out of the warehouse, subdividing the common zones can lead to more optimized and up-to-date coverage along the entire path.

[0018] For example, the second pair of transceivers 104 can be time-synchronized so that transceivers 101b and 101c begin monitoring simultaneously to determine an accurate bearing and direction estimate over time. The second pair of transceivers 104 can also divide the monitoring so that transceiver 101b is configured to monitor the third zone 120, and transceiver 101c is configured to monitor the fourth zone 125. When an RFID tag enters the third zone 120, transceiver 101b can detect the tag and transmit information related to this detection to transceiver 101c. The synchronized transceiver 101c can then confirm that the tag is not in the fourth zone 125 and subsequently report the tag's location and direction to a remote host (not shown).When the RFID tag moves from the third zone 120, through the second portal 114, and into the fourth zone, the transceiver 101c can detect the tag. Based on information received from transceiver 101b, transceiver 101c can then confidently report the tag's location and precise direction to a remote host (not shown). In cases where system 100 monitors a tag's directionality, the current zone occupancy is important for accurately estimating the direction. Sharing information between a pair of transceivers monitoring shared zones advantageously enables rapid confirmation of zone occupancy and, over time, rapid confirmation of an RFID tag's direction in scenarios where a large volume of tags move along the path at high speed.

[0019] In some RFID tracking applications, such as tracking RFID tags near entry or exit points, the exact location of the tagged item is not what the end user needs to track their goods accurately and promptly. End users in such applications can benefit from knowing the tag's directionality—knowing whether a transition between two zones of interest has occurred. When a transition is detected by a monitoring transceiver, the transceiver can report the transition, along with information about the source and destination zones, to the other transceiver in the pair capable of monitoring shared zones, and / or to a remote host (not shown). In some cases, it may be critical to detect the transition as quickly as possible.For example, the situation where a forklift moves into the wrong trailer must be detected as quickly as possible so that the driver can be alerted before loading or unloading items from the incorrect truck. By subdividing the coverage areas between two adjacent transceivers configured to be in a pair monitoring common zones, there is little to no overlap in monitoring by the two readers, resulting in improved real-time detection of a transition.

[0020] Fig. Figure 4 illustrates an overhead view of an additional embodiment of the present disclosure. A system 100 can contain at least one first pair of transceivers 103 and a second pair of transceivers 104. The first pair of transceivers 103 contains a transceiver 101b, which is also included in the second pair of transceivers 104. Each transceiver can be configured to monitor a first track 126 extending in a first direction 130 from the first zone 110 to the second zone 115 and in a second direction 132 from the second zone 115 to the first zone 110. The first track 126 can extend through the first portal 112. Each transceiver, e.g., the transceiver 101b in Fig. 3 can also be configured to monitor a second lane 128 extending in a third direction 134 from the third zone 120 to the fourth zone 125 and in a fourth direction 136 from the fourth zone 125 to the third zone 120. The second lane 128 can extend through the second portal 114.

[0021] Fig. Figure 5 is a flowchart illustrating a procedure of the present disclosure. Although the exemplary procedure 500 refers to the one in Fig.As described in the illustrated flowchart 5, it is understood that many other methods can be used to perform the steps associated with Procedure 500. For example, the order of some of the blocks can be changed, certain blocks can be combined with other blocks, blocks can be repeated, and some of the described blocks are optional. Procedure 500 can be implemented by processing logic, which may include hardware (circuits, dedicated logic, etc.), software, or a combination of both.

[0022] In exemplary method 500, each transceiver in a transceiver array, including at least a first pair of transceivers 103 and a second pair of transceivers 104, wherein the first pair 103 contains a transceiver that is also included in the second pair of transceivers 104, monitors a plurality of zones for RFID tags (block 505). For example, the transceiver 101b can be included in both the first pair 103 and the second pair of transceivers 104, and the transceiver 101b can monitor the first zone 110, the second zone 115, the third zone 120, and the fourth zone 125 for RFID tags.

[0023] Exemplary procedure 500 also includes each transceiver transmitting information relating to the monitoring of shared zones (block 510). For example, transceiver 101b can detect an RFID tag in the first zone 110 and estimate the bearing of the RFID tag. Transceiver 101b can then transmit this bearing information and other information relating to the RFID tag, such as a tag identification number, to transceiver 101a, the other transceiver in the first pair, which also monitors the first zone.

[0024] In exemplary procedure 500, each transceiver also determines the location of a monitored RFID tag using information from monitoring the plurality of zones and information received from the other transceiver in the pair (block 515). For example, transceiver 101a can also detect the same RFID tag in the first zone 110 and estimate the bearing of the RFID tag based on its detections and the bearing estimate / information from transceiver 101b, which is then used to determine a location and precise directionality of a monitored RFID tag.

[0025] The present disclosure provides, for example, an efficient system that uses pairs of transceivers working together to coordinate the monitoring and detection of RFID tags in an area and the determination of a tag's directionality based on information from both transceivers in the pair. This results in a more accurate estimation of a tag's directionality. Additionally, in busy commercial environments where large volumes of RFID tags move in and out of portals, a system of the present disclosure provides multiple different readings of a tag's bearing, leading to improved accuracy and increased confidence in determining a tag's location and direction.The cover overlap and transmitter-receiver coordination in a system of the present disclosure also provide additional protection for the system in the event that a transmitter-receiver does not function correctly due to the use of multiple, different readings in determining the position and direction of a label.

[0026] Specific embodiments have been described in the foregoing specification. However, a person skilled in the art will recognize that various modifications and changes can be made without departing from the scope of the invention, as set forth in the claims below. Accordingly, the specification and the figures are to be regarded in an illustrative rather than a limiting sense, and all such modifications are to be included within the scope of the present teachings.

[0027] The benefits, advantages, problem solutions, and any element(s) that may lead to or enhance a benefit, advantage, or solution shall not be construed as critical, necessary, or essential features or elements of any claim or all claims. The invention is defined exclusively by the attached claims, including all amendments made during the pendency of this application, and all equivalents of these claims as granted.

[0028] Furthermore, in this document, relational expressions such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another, without necessarily requiring or implying any actual relationship or order of such entities or actions. The expressions "includes," "comprising," "has," "exhibiting," "contains," "containing," "incorporating," "including," or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, procedure, article, or device that includes, has, contains, or includes a list of elements may not only contain those elements but may also contain other elements not expressly listed or inherent in such process, procedure, article, or device. An element that "includes," "has," orThe phrases "a," "contains ... a," or "include ... a" preceding a statement do not, without further limitations, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, contains, or includes the element. The terms "a" and "a" are defined as one or more unless expressly stated otherwise herein. The terms "essentially," "generally," "approximately," "about," or any other version thereof are defined in a manner that would be closely understood by a person skilled in the art, and in one non-restrictive embodiment, the term is defined as being within 10%, in another embodiment within 5%, in another embodiment within 1%, and in yet another embodiment within 0.5%.The term "coupled," as used herein, is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in a particular way is configured at least in that way, but may also be configured in ways not listed.

[0029] The summary of disclosure is provided to enable the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it is not intended to interpret or limit the scope or meaning of the claims. Furthermore, it is evident from the detailed description above that various features in different embodiments have been grouped together for the purpose of simplifying the disclosure. This method of disclosure should not be construed as reflecting an intention that the claimed embodiments require more features than are expressly stated in each claim. Rather, as reflected in the following claims, the inventive step lies in fewer than all the features of any single disclosed embodiment.Therefore, the following claims are hereby included in the detailed description, each claim being a separate subject matter claimed on its own.

Claims

[1] System, encompassing: a transmit-receiver array comprising at least a first pair of transmit-receivers and a second pair of transmit-receivers, wherein the first pair of transmit-receivers includes a transmit-receiver that is contained in the second pair of transmit-receivers, and wherein each transmit-receiver in a pair is configured to to monitor a multitude of zones for RFID tags, each with a defined zone width, including at least a first zone and a second zone, wherein a first portal is located at a boundary between the first zone and the second zone, and including at least a third zone and a fourth zone, wherein a second portal is located at a boundary between the third zone and the fourth zone; To transmit information relating to the monitoring of a portion of the multitude of zones for RFID tags to the other transceiver in the pair; and to determine the location of a monitored RFID tag based on the information gathered by monitoring the multitude of zones and the information received by the other transceiver in the first or second pair, so that the first pair of transceivers works together to monitor and determine locations for RFID tags in the first zone and the second zone, and the second pair of transceivers works together to monitor and determine locations for RFID tags in the third zone and the fourth zone. [2] System according to claim 1, wherein each transmitter-receiver is further configured to monitor a first track extending in a first direction from the first zone to the second zone, in a second direction from the second zone to the first zone and extending through the first portal, and a second track extending in a third direction from the third zone to the fourth zone, in a fourth direction from the fourth zone to the third zone and extending through the second portal. [3] System according to claim 1, wherein each transmitter receiver is further configured to determine a directionality for a monitored RFID tag based on the information acquired by monitoring the plurality of zones by the transmitter receiver and the information received by the other transmitter receiver in the first or second pair. [4] System according to claim 1, wherein the transmit-receiver array is a linear transmit-receiver array. [5] System according to claim 1, wherein each transmitter receiver is a beam-steerable phased array RFID reader. [6] System according to claim 1, wherein the first portal and the second portal are dock doors. [7] System according to claim 1, wherein each pair of transmitters / receivers is further configured to subdivide the monitoring of zones that are monitored by both transmitters / receivers in the pair. [8] System according to claim 7, wherein the subdivision of the monitoring of zones monitored by both transmitters in the pair comprises one transmitter in the pair monitoring RFID tags with an even tag identification number and the other transmitter in the pair monitoring RFID tags with an odd tag identification number. [9] Methods for reading RFID tags, comprising: Monitoring a plurality of zones for RFID tags via a linear array of transceivers, including at least a first pair of transceivers and a second pair of transceivers, wherein the first pair of transceivers contains a transceiver that is included in the second pair of transceivers, and wherein each transceiver is configured to to monitor a number of the plurality of zones for RFID tags, each with a defined zone width, including at least a first zone and a second zone, wherein a first portal is located at a boundary between the first zone and the second zone, and including at least a third zone and a fourth zone, wherein a second portal is located at a boundary between the third zone and the fourth zone; To transmit information relating to the monitoring of the part of the plurality of zones to the other transmitter-receiver in the pair that monitors the same part of the plurality of zones; to determine the location of a monitored RFID tag based on the information acquired by monitoring the plurality of zones by one transceiver in the first or second pair and the information received by the other transceiver in the first or second pair, wherein the first pair of transceivers works together to monitor and determine locations for RFID tags in the first zone and the second zone, and the second pair of transceivers works together to monitor and determine locations for RFID tags in the third zone and the fourth zone. [10] Method according to claim 9, wherein each transmitter-receiver is further configured to monitor a first track extending in a first direction from the first zone to the second zone, in a second direction from the second zone to the first zone and extending through the first portal, and a second track extending in a third direction from the third zone to the fourth zone, in a fourth direction from the fourth zone to the third zone and extending through the second portal. [11] Method according to claim 9, wherein determining a location of a monitored RFID tag based on the information acquired by monitoring the plurality of zones by a transmitter-receiver in the first or second pair and the information received by the other transmitter-receiver in the first or second pair further comprises determining a directionality of the monitored RFID tag. [12] Method according to claim 9, wherein each transmitter receiver is a beam-steerable phased array RFID reader. [13] Method according to claim 9, further comprising, wherein each pair of transmitters / receivers is configured to subdivide the monitoring of zones that are monitored by both transmitters / receivers in the pair. [14] Method according to claim 13, wherein the monitoring of a common zone via a pair of transceivers is divided between the transceivers in the pair, wherein one transceiver in the pair monitors RFID tags with an even tag identification and the other transceiver in the pair monitors RFID tags with an even tag identification number.

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