RFID Antenna Array for Games

Abstract

This application relates to an RFID antenna array for gaming. An RFID system includes a plurality of antennas and uses amplitude and phase information of RFID signals received by each antenna to determine the location of nearby RFID tags. More than one antenna can receive the RFID signals during a single read cycle, enabling the RFID system to operate more quickly than a system that energizes the antennas individually.

Description

[0001] Relevant information on divisional applications

[0002] This application is a divisional application of the patent application for invention with the application date of November 15, 2018, application number 201811358220.6, and invention title "RFID Antenna Array for Games".

[0003] Cross-reference to related applications

[0004] This application claims priority to U.S. Patent Application No. 15 / 814,170, filed on November 15, 2017, with the title "RFID Antenna Array for Games", and U.S. Patent Application No. 16 / 114,018, filed on August 27, 2018, with the title "RFID Antenna Array for Games", both of which are incorporated herein by reference. Technical Field

[0005] The present invention relates to games, and in particular, to an RFID system having an antenna array for detecting the position of radio frequency identification (RFID) tags on a gaming table. Background Art

[0006] Unless otherwise indicated herein, the methods described in this section are not prior art to the claims in this application and are not admitted to be prior art merely by virtue of being included in this section.

[0007] The ability to track the position of game markers on a gaming table in real time has the potential to revolutionize the gaming industry by providing cash management and improved security. Binding this data to specific players allows casinos to create accurate player profiles while alleviating the day-to-day operations of gaming establishment owners.

[0008] Traditional RFID systems have attempted to cater to the gaming market with limited success. In a typical RFID system, an excitation antenna defines a "working volume" within which the energy projected by the antenna is sufficient to power an RFID tag. This "working volume" is typically poorly defined with the only option of increasing / decreasing the power to adjust the read range. However, doing so expands the read range in all directions, introducing crosstalk errors when multiple antennas are very close together. Existing products on the market suffer from a variety of drawbacks. First, they are limited to discrete game marker points. Second, they are limited in the height of the chip stack they can read. Third, there is very poor discrimination between adjacent game marker points. Fourth, they have a higher than acceptable read error. Fifth, they have a slow read rate, which can miss important events (such as placing and removing chips, etc.).

[0009] These drawbacks limit the techniques available for games in which game markers are widely distributed (e.g., a single "jug"), detect only an initial game marker (not capture instantaneous events such as payments), and identify counterfeit markers only before their use on the table (not during the game).

[0010] U.S. Application Publication No. 2013 / 0233923 discusses ferrite core technology. The ferrite core technology overcomes many of the above drawbacks, but does not address the need to track multiple independent game markers placed by different players on a single larger game marker point (e.g., when a "backward player" shares a game marker point with a seated player on a traditional Baccarat "pit" layout). There is also a need for the ability to distinguish the positions of game markers that are very close together (e.g., as may be found on a roulette table).

[0011] U.S. Application Publication No. 2017 / 0228630 discusses a solution involving two intersecting antenna arrays. A horizontal antenna array provides one coordinate, and a second vertical antenna array provides a second coordinate. Signal strength information comparing adjacent antennas can then be used to interpolate a set of higher-fidelity coordinates.

[0012] While the method of U.S. Application Publication No. 2017 / 0228630 does work, the practical problem it encounters is that reading RFID tags takes time and reading the tags multiple times for interpolation purposes doubles the time required, making it potentially infeasible to capture an accurate "snapshot" of an instantaneous event with a large number of tags in some gaming environments.

[0013] A typical RFID system solves the problem "Who's there?". The response is a series of unique item identifiers (e.g., serial numbers). As discussed above, the ferrite core technology discussed in U.S. Application Publication No. 2013 / 0233923 is directed at solving the additional problem "Where are you?" as a way to track individual game markers.

[0014] U.S. Application Publication No. 2016 / 0217645 discusses using a network analyzer device prior to RFID reading, thereby enabling the RFID reader to be directed only to those antennas where tags are present. This describes a series of methods for eliminating the "overhead" of using an RFID reader to look in places where there are no tags at all, because using a network analyzer device takes less time than using an RFID reader.

[0015] U.S. Application Publication No. 2013 / 0233923 and U.S. Application Publication No. 2016 / 0217645 both relate to placing game tokens in specific areas (game token points). RFID tags that are not placed in one of the defined areas will not be read correctly. Neither of these disclosures addresses the need to detect game tokens placed at any location on a larger defined area. The additional disclosure of U.S. Application Publication No. 2017 / 0228630 does satisfy placing multiple game tokens within a larger defined area. However, the system disclosed therein involves multiple RFID reads to define the coordinates of each game token, which is a time-consuming process.

[0016] U.S. Application Publication No. 2013 / 0233923, U.S. Application Publication No. 2016 / 0217645, and U.S. Application Publication No. 2017 / 0228630 all describe systems for identifying and locating RFID tags by determining proximity to a specific antenna using signal strength information measured by an RFID reader. U.S. Application Publication No. 2013 / 0233923 describes a system for increasing the signal strength at a suitable antenna to further improve accuracy. SUMMARY OF THE INVENTION

[0017] One problem with existing systems for locating tags within an array using an antenna array is the time it takes to power each antenna to read RFID tags near each antenna and then repeat the process for each subsequent antenna. There is a need for a faster method for accurately locating and tracking individual, very closely spaced game tokens that can be placed anywhere within a defined boundary on a game table. There is a need to increase the speed at which the system applies game rules to calculate the quantity and location of the original game tokens and to associate instantaneous events such as payments with winning game tokens.

[0018] Given the above, embodiments are directed to using the phase information of detected RFID signals to improve the operation of the system.

[0019] According to an embodiment, a system determines the position of an object in a gaming environment. The system includes a main antenna associated with an area on a gaming table; a first plurality of antennas oriented in a first direction and associated with the area on the gaming table; a second plurality of antennas oriented in a second direction; a main radio frequency identification (RFID) transmitter coupled to the main antenna; a main RFID receiver coupled to the main antenna; a first plurality of RFID receivers coupled to the first plurality of antennas; a second plurality of RFID receivers coupled to the second plurality of antennas; and a controller that controls the main RFID transmitter to generate an RFID inventory command. The second direction is different from the first direction, the second plurality of antennas overlap the first plurality of antennas, the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the area, and each of a plurality of RFID tags in the area responds to the RFID inventory command according to an anti-collision process. In response to the RFID inventory command, the main RFID receiver receives a first plurality of responses from the plurality of RFID tags, the first plurality of RFID receivers receive a second plurality of responses from the plurality of RFID tags, and the second plurality of RFID receivers receive a third plurality of responses from the plurality of RFID tags. The controller determines an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses, the second plurality of responses, and the third plurality of responses, and the controller determines the position of each of the plurality of RFID tags by correlating amplitude information and phase information of the first plurality of responses, amplitude information and phase information of the second plurality of responses, and amplitude information and phase information of the third plurality of responses.

[0020] For a particular RFID tag of the plurality of RFID tags, the controller can simultaneously determine the identifier and position of the particular RFID tag.

[0021] The RFID inventory command can be a single RFID inventory command that causes the controller to determine the identifiers and positions of all of the plurality of RFID tags.

[0022] The first plurality of antennas and the second plurality of antennas can overlap and intersect to define the position of each of the plurality of RFID tags in two dimensions within the area. The first plurality of antennas and the second plurality of antennas can intersect perpendicularly and define the position of each of the plurality of RFID tags in the x-dimension and y-dimension within the area.

[0023] The first plurality of antennas and the second plurality of antennas can define the position of each of the plurality of RFID tags using polar coordinates within the area.

[0024] The first plurality of antennas may be formed as a first non-overlapping single layer, and the second plurality of antennas may be formed as a second non-overlapping single layer. The first plurality of antennas may be formed as an overlapping double layer.

[0025] The controller may determine the position of each of the plurality of RFID tags using interpolation of the amplitude information of the second plurality of responses and the amplitude information of the third plurality of responses.

[0026] The controller may determine that a subset of the plurality of RFID tags are grouped together when the position of each RFID tag of the subset is within a defined range of at least one other RFID tag of the subset.

[0027] The controller may determine, based on the position of a first subset and the position of a second subset, that the first subset of the plurality of RFID tags corresponds to a game token and the second subset of the plurality of RFID tags corresponds to a payment associated with the game token.

[0028] The controller may determine an identifier of each of the plurality of RFID tags using at least one of the second plurality of responses and the third plurality of responses.

[0029] The controller may use the first plurality of responses as reference information for normalizing the second plurality of responses and the third plurality of responses. The controller may normalize the amplitude information of the second plurality of responses and the amplitude information of the third plurality of responses using the amplitude information of the first plurality of responses.

[0030] The controller may determine the relative phase information of the second plurality of responses and the relative phase information of the third plurality of responses using the phase information of the first plurality of responses.

[0031] When a first group of the plurality of RFID tags is associated with a first position and when a second group of the plurality of RFID tags is associated with a second position, the controller may determine that the first group and the second group are a group when the first position and the second position are within a threshold distance.

[0032] According to an embodiment, a system determines the location of an object in a gaming environment. The system includes a main antenna associated with an area on a gaming table; a first plurality of antennas oriented in a first direction and associated with the area on the gaming table; a second plurality of antennas oriented in a second direction; a main radio frequency identification (RFID) transmitter coupled to the main antenna; a main RFID receiver coupled to the main antenna; a first plurality of RFID receivers coupled to the first plurality of antennas; a second plurality of RFID receivers coupled to the second plurality of antennas; and a controller that controls the main RFID transmitter to generate an RFID inventory command. The second direction is different from the first direction, the second plurality of antennas overlap the first plurality of antennas, and the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the area. Each of a plurality of RFID tags in the area responds to the RFID inventory command according to an anti-collision process. In response to the RFID inventory command, the main RFID receiver receives a first plurality of responses from the plurality of RFID tags, and the first plurality of RFID receivers receive a second plurality of responses from the plurality of RFID tags, and the second plurality of RFID receivers receive a third plurality of responses from the plurality of RFID tags. The controller determines an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses, the second plurality of responses, and the third plurality of responses. The controller determines the location of each of the plurality of RFID tags by correlating amplitude information of the first plurality of responses, amplitude information and phase information of the second plurality of responses, and amplitude information and phase information of the third plurality of responses.

[0033] Details of this embodiment may additionally be similar to details of previous embodiments.

[0034] According to an embodiment, a method determines the location of an object in a gaming environment. The method includes generating an RFID inventory command by a primary radio frequency identification (RFID) transmitter coupled to a primary antenna, where the primary antenna is associated with an area on a gaming table. The method further includes each of a plurality of RFID tags in the area responding to the RFID inventory command according to an anti-collision process. The method further includes receiving, by a primary RFID receiver coupled to the primary antenna, a first plurality of responses from the plurality of RFID tags in response to the RFID inventory command. The method further includes receiving, by a first plurality of RFID receivers coupled to a first plurality of antennas, a second plurality of responses from the plurality of RFID tags in response to the RFID inventory command, where the first plurality of antennas are oriented in a first direction and are associated with an area on the gaming table. The method further includes receiving, by a second plurality of RFID receivers coupled to a second plurality of antennas, a third plurality of responses from the plurality of RFID tags in response to the inventory command, where the second plurality of antennas are oriented in a second direction different from the first direction, where the second plurality of antennas overlap the first plurality of antennas, and where the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the area. The method further includes a controller determining an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses, the second plurality of responses, and the third plurality of responses. The method further includes the controller determining the location of each of the plurality of RFID tags by correlating amplitude information of the first plurality of responses, amplitude information and phase information of the second plurality of responses, and amplitude information and phase information of the third plurality of responses.

[0035] The step of determining the location of each of the plurality of RFID tags may further include the controller determining the location of each of the plurality of RFID tags by correlating amplitude information and phase information of the first plurality of responses, amplitude information and phase information of the second plurality of responses, and amplitude information and phase information of the third plurality of responses.

[0036] Details of this embodiment may further be similar to details of previous embodiments.

[0037] According to an embodiment, a system determines the location of an object in a gaming environment. The system includes a main antenna associated with an area on a gaming table; a first plurality of antennas oriented in a first direction and associated with the area on the gaming table; and a second plurality of antennas oriented in a second direction; a main radio frequency identification (RFID) transmitter coupled to the main antenna; a first plurality of RFID receivers coupled to the first plurality of antennas; a second plurality of RFID receivers coupled to the second plurality of antennas; and a controller. The second direction is different from the first direction, the second plurality of antennas overlaps with the first plurality of antennas, and the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the area. The controller controls the main RFID transmitter to generate an RFID inventory command, wherein each of a plurality of RFID tags in the area responds to the RFID inventory command according to anti-collision processing. In response to the RFID inventory command, the first plurality of RFID receivers receive a first plurality of responses from the plurality of RFID tags, and the second plurality of RFID receivers receive a second plurality of responses from the plurality of RFID tags. The controller determines an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses and the second plurality of responses. The controller determines the location of each of the plurality of RFID tags by correlating amplitude information of the first plurality of responses and amplitude information of the second plurality of responses.

[0038] The controller may determine the location of each of the plurality of RFID tags by correlating the amplitude information and phase information of the first plurality of responses with the amplitude information and phase information of the second plurality of responses.

[0039] Details of this embodiment may additionally be similar to details of previous embodiments.

[0040] According to an embodiment, a method determines the location of an object in a gaming environment. The method includes generating an RFID inventory command by a master radio frequency identification (RFID) transmitter coupled to a master antenna, where the master antenna is associated with an area on a gaming table. The method further includes each of a plurality of RFID tags in the area responding to the RFID inventory command according to an anti-collision process. The method further includes a first plurality of RFID receivers coupled to a first plurality of antennas receiving a first plurality of responses from the plurality of RFID tags in response to the RFID inventory command, where the first plurality of antennas are oriented in a first direction and are associated with the area on the gaming table. The method further includes a second plurality of RFID receivers coupled to a second plurality of antennas receiving a second plurality of responses from the plurality of RFID tags in response to the RFID inventory command, where the second plurality of antennas are oriented in a second direction different from the first direction, where the second plurality of antennas overlap the first plurality of antennas, and where the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the area. The method further includes a controller determining an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses and the second plurality of responses. The method further includes the controller determining the location of each of the plurality of RFID tags by correlating amplitude information of the first plurality of responses and amplitude information of the second plurality of responses.

[0041] The step of determining the location of each of the plurality of RFID tags may include the controller determining the location of each of the plurality of RFID tags by correlating the amplitude information and phase information of the first plurality of responses with the amplitude information and phase information of the second plurality of responses.

[0042] Details of this embodiment may additionally be similar to details of previous embodiments.

[0043] The following detailed description and the drawings provide a further understanding of the nature and advantages of the present invention. Description of the Drawings

[0044] Figure 1 is a block diagram of an RFID system 100.

[0045] Figure 2 is a flowchart of a method 200 of operating an RFID system (e.g., Figure 1 the RFID system 100).

[0046] Figure 3 is a diagram showing when a chip moves across an antenna by antenna 104 or 106 (see Figure 1A graph of the detected amplitude and phase information in

[0047] Figure 4 A graph showing the amplitude and phase information detected by two of the antennas 104 or by two of the antennas 106 (see Figure 1 ) of the graphs 400 and 402.

[0048] Figure 5 Is Figure 1 A top view of the antennas 104 and 106 of

[0049] Figure 6 A block diagram of the RFID system 600. The RFID system 600 shows a specific implementation of the RFID system 100 (see Figure 1 ).

[0050] Figure 7 A block diagram of the receiver 700.

[0051] Figure 8 A block diagram of the RFID system 800.

[0052] Figure 9 A top view of a set of overlapping antennas 900 in one direction.

[0053] Figure 10 A top view of the antenna array 1000.

[0054] Figure 11 A top view of the polarized antenna array 1100.

[0055] Figure 12A A top view of the baccarat table 1200, and Figure 12B A top view of a part of the baccarat table 1200 showing the corresponding part of the antenna array 1202.

[0056] Figure 13 A top view of the roulette table 1300 having the antenna array 1302.

[0057] Figure 14 Is Figure 1 A top view of the antennas 104 and 106 of Detailed Description

[0058] Techniques for determining the location of RFID tags are described herein. In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention, as defined by the claims, may include some or all of the features in some or all of these examples (either individually or in combination with other features described below), and may additionally include modifications and equivalents of the features and concepts described herein.

[0059] In the following description, various methods, processes, and procedures are detailed. Although specific steps may be described in a particular order, such order is mainly for convenience and clarity. A particular step may be repeated more than once, may occur before or after other steps (even if those steps are described in a different order in other ways), and may occur in parallel with other steps. A second step is required to follow a first step only when the first step must be completed before the second step can begin. Such cases will be specifically indicated when not clear from the context.

[0060] In this document, the terms "and", "or", and "and / or" are used. Such terms are to be understood in an inclusive sense. For example, "A and B" may mean at least the following: "both A and B", "at least both A and B". As another example, "A or B" may mean at least the following: "at least A", "at least B", "both A and B", "at least both A and B". As another example, "A and / or B" may mean at least the following: "A and B", "A or B". When an exclusive or is intended, this will be specifically indicated (e.g., "either A or B", "at most one of A and B").

[0061] In this document, the terms "RFID tag", "RFID game tag", "RFID chip", "RFID game chip", "game chip", and "game marker" are used. Such terms are to be understood as being synonymous in a broad sense. (More precisely, an "RFID chip" may be used to refer to the integrated circuit component of an "RFID tag", which also includes additional components such as an antenna, a rigid housing, etc. However, this document mainly concerns the broad use of these terms.) RFID tags typically respond to radio frequency signals from an RFID reader with their serial numbers or other identifiers, enabling the RFID reader to obtain an inventory of nearby RFID tags. In a gaming context, according to various game rules, RFID game tags may be placed on a game table, removed from the game table, and moved around the game table during play and payment. RFID game tags may be marked with value identifiers (e.g., $1).

[0062] Figure 1is a block diagram of an RFID system 100. The RFID system 100 includes a main antenna 102, a first set of antennas 104a - 104d (collectively referred to as antennas 104), a second set of antennas 106a - 106d (collectively referred to as antennas 106), a main RFID transmitter 108, a main RFID receiver 112, a first set of RFID receivers 114a - 114d (collectively referred to as RFID receivers 114), a second set of RFID receivers 116a - 116d (collectively referred to as RFID receivers 116), and a controller 120. Generally, the main RFID transmitter 108 generates radio frequency energy that is radiated by the antenna 102 and received by any RFID tag; responses from the RFID tags are then received by the antennas 102, 104, and 106. The responses from the RFID tags can be amplitude and phase information. The amplitude information can be in the form of received signal strength (RSSI) information, and the phase information can be in the form of in-phase (I) and quadrature (Q) information.

[0063] The RFID system 100 can be implemented as part of a gaming table (see, for example Figures 12A - 12B the roulette and baccarat examples of

[0064] and 13). For example, the antennas 102, 104, and 106 can be embedded beneath the playing surface of the gaming table (to detect the position of RFID gaming tags during play on the gaming table), and the remaining components of the RFID system 100 can be embedded within the structure of the gaming table. The gaming environment can have several gaming tables, each including an RFID system 100; multiple RFID systems 100 can be connected to each other or to other components via a network. Figures 12A - 12B The main antenna 102 is located beneath the playing surface of the gaming table. As part of playing a game using the gaming table, an RFID gaming tag is placed on, removed from, and moved around an area above the main antenna 102. This area on the gaming table can be marked to show various sub - areas according to the particular game being played (see, for example

[0065] the roulette and baccarat examples of Figure 1 and 13). The main antenna 102 can be implemented on a printed circuit board. The main RFID transmitter 108 and the main receiver 112 are coupled to the main antenna 102.

[0066] Antenna 106 is located below the playing surface of the game table and is associated with the game area, just like main antenna 102. Antenna 106 is oriented in a second direction that is different from the first direction of antenna 104. As Figure 1 shown, antenna 106 is oriented in the east-west (or x) direction. In other embodiments, antenna 106 may be oriented in other directions. Antenna 106 may be implemented on a printed circuit board or as a layer of a multi-layer circuit board that also includes main antenna 102 or antenna 104. RFID receiver 116 is coupled to antenna 106.

[0067] Antenna 106 overlaps with antenna 104; this overlap is shown using a dashed line in Figure 1 . In addition to main antenna 102, this overlap generally also allows antennas 104 and 106 to be associated with the game area. Generally speaking, this allows at least three antennas (e.g., one of main antenna 102, one of antennas 104, and one of antennas 106) to be associated with each position within the game area. The spacing between each of antennas 104 and the spacing between each of antennas 106 can be adjusted as needed.

[0068] Antennas 104 and 106 together form what can be referred to as an antenna array. As Figure 1 shown, antennas 104 and 106 intersect at a right angle. In other embodiments, antennas 104 and 106 may intersect at other angles. As Figure 1 shown, antennas 104 and 106 are shaped like rectangles. In other embodiments, antenna 104 may have other shapes, such as a circular shape, a pie shape, a curved shape, a rounded rectangle shape, etc. The sizes of antennas 104 and 106 can be adjusted as needed.

[0069] Figure 1 Four antennas 104 and four associated RFID receivers 114, as well as four antennas 106 and four associated RFID receivers 116 are shown in

[0070] Figure 1 . These quantities can be adjusted as needed to cover a larger or smaller area and / or increase or decrease the spatial resolution.

[0071] Generally speaking, main RFID receiver 112 is used to generate the reference amplitude and phase information that controller 120 uses when processing the amplitude and phase information from antennas 104 and 106. Although main RFID receiver 112 is shown as an independent component in Figure 1 , main RFID receiver 112 may be a sub-component of main RFID transmitter 108.

[0071] The controller 120 generally controls the operation of the RFID system 100. The controller 120 can be connected to a computer (e.g., a personal computer) and can be a component of the computer. The controller 120 can be connected to other components or can itself include components that implement other functions such as RFID tag identification, RFID tag location determination, game rule verification, etc. The controller 120 can access various data memories or databases, such as a game rule database, an RFID tag database, etc.

[0072] The RFID system 100 generally operates as follows. The transmitter 108 generates a radio frequency signal that is transmitted by the main antenna 102. Any RFID game tags in the game area respond to the radio frequency signal. Responses from the RFID game tags are received by at least one of the main receiver 112 (via the main antenna 102), at least one of the receivers 114 (via at least one of the antennas 104), and at least one of the receivers 116 (via at least one of the antennas 106). The controller 120 determines the location of each RFID game tag by correlating the responses received by each of the receivers. Refer Figure 2 for more details.

[0073] According to another embodiment, the main receiver 112 can be omitted.

[0074] Figure 2 is a flowchart of a method 200 for operating an RFID system (e.g., Figure 1 the RFID system 100). A controller (e.g., Figure 1 the controller 120) can control the method 200, for example, according to the execution of a computer program. Generally speaking, the method 200 describes a single RFID read cycle. Between read cycles, the RFID game tags are not powered and do not send signals. During an RFID read cycle, each RFID game tag in the game area responds. The RFID read cycle ends after each RFID game tag has responded. Thus, each RFID read cycle causes all the RFID game tags in the game area to respond once but be read by multiple receivers.

[0075] At 202, the controller controls the main RFID transmitter (e.g., Figure 1 the main RFID transmitter 108) to generate an RFID inventory command. Generally speaking, the main RFID antenna is energized, and the RFID inventory command is one of several commands that can be included in the radio frequency energy generated by the main RFID transmitter. Additional details of the RFID inventory command are provided below. The main antenna (e.g., Figure 1 the main antenna 102) coupled to the main RFID transmitter transmits the RFID inventory command. The main antenna is associated with an area on the game table that contains one or more RFID tags (e.g., RFID game tags).

[0076] At 204, each of the RFID tags responds to the RFID inventory command according to an anti-collision process. Generally speaking, the anti-collision process helps ensure that only one of the RFID tags responds at a given time. Additional details of the anti-collision process are provided below.

[0077] At 206, a primary RFID receiver (e.g., Figure 1 primary RFID receiver 112) coupled to the primary antenna receives a first set of responses from the RFID tags in the area in response to the RFID inventory command.

[0078] At 208, a first set of RFID receivers (e.g., Figure 1 RFID receivers 114) coupled to a first set of antennas (e.g., Figure 1 antenna 104) receive a second set of responses from the RFID tags in the area in response to the RFID inventory command. The first set of antennas is oriented in a first direction and is associated with an area on the game table.

[0079] At 210, a second set of RFID receivers (e.g., Figure 1 RFID receivers 116) coupled to a second set of antennas (e.g., Figure 1 antenna 106) receive a third set of responses from the RFID tags in the area in response to the RFID inventory command. The second set of antennas is oriented in a second direction different from the first direction, the second set of antennas overlaps the first set of antennas, and the first set of antennas and the second set of antennas intersect at several positions within the area.

[0080] As mentioned above, each RFID tag responds once, but each response is received by multiple antennas. For ease of description, these received responses are referred to above in 206 - 210 as "the first set of responses", "the second set of responses", and "the third set of responses". Generally speaking, each of the multiple antennas receives a particular response simultaneously.

[0081] Due to the anti-collision process, ideally, only one of the RFID tags responds at a given time, so the controller can associate the response received by each of the antennas at the given time with the one responding RFID tag. Thus, generally, 206 - 210 occur in parallel, where each RFID tag (ideally) responds at a given time and is detected by multiple receivers. For example, at a given time, a response from one RFID tag is received by the primary RFID receiver, at least one of the first set of RFID receivers, and at least one of the second set of RFID receivers.

[0082] A brief description of the anti-collision process is as follows. The controller outputs the start of an inventory command that includes a 5-bit cyclic redundancy check (CRC). This command also defines how many time slots there are. The tag generates a random number and compares it with a specific time slot number. If it matches, the tag responds with the 5-bit CRC from the command and a 16-bit CRC of its serial number. If the controller receives this without detecting a collision, it re-sends the 5-bit CRC and the 16-bit CRC to the tag. The tag then responds by sending out its serial number and setting its flag, so that when the RF power is removed, it does not respond to further queries until the flag is reset. Thus, sending the CRC before actual data acceleration is actually a shorter message to determine whether there is a collision.

[0083] At 212, the controller (e.g., Figure 1 controller 120) determines an identifier for each of the RFID tags using at least one of a first set of responses, a second set of responses, and a third set of responses. As discussed above, when a given tag responds with its serial number according to the anti-collision process, multiple RFID receivers may receive this response (e.g., the primary RFID receiver receives the first set of responses, including the response from the given tag; the first set of RFID receivers receives the second set of responses, including the response from the given tag; etc.). The controller may use one of the RFID receivers (e.g., the primary RFID receiver) to determine the identifier and may use the information from the other RFID receivers for verification or confirmation purposes. When the current read cycle ends, the RFID tag loses power, the flag is cleared, and the RFID tag responds arbitrarily during the next read cycle.

[0084] At 214, the controller determines the position of each of the RFID tags by correlating the amplitude and phase information of the first set of responses with the amplitude and phase information of the second set of responses and the amplitude and phase information of the third set of responses. Additional details of this correlation process are provided below. Generally, the controller uses the information from the first set of responses to modify the second set of responses in order to determine one dimension of the position (e.g., the x dimension), and uses the information from the first set of responses to modify the third set of responses in order to determine the other dimension of the position (e.g., the y dimension); the intersection point of the x dimension and the y dimension then indicates the position of the RFID tag in the play area.

[0085] As an alternative to 214, the controller may determine the position of each of the RFID tags by correlating only the amplitude information (no phase information) of the first set of responses with the amplitude and phase information of the second set of responses and the amplitude and phase information of the third set of responses. In this alternative, the primary RFID receiver only performs excitation, and its amplitude information is used for normalization purposes; the phase information from the first set of antennas and the second set of antennas is used to determine the position.

[0086] As another alternative in 214, the controller can determine the position of each of the RFID tags by correlating the amplitude information of the first set of responses with the amplitude information of the second set of responses and the amplitude information of the third set of responses.

[0087] The controller can perform 212 - 214 in parallel, or can perform 214 before 212.

[0088] Once all the RFID tags have responded, the current read cycle is completed. When the controller executes the next read cycle, the controller executes method 200 again.

[0089] The controller can then use the identifier and position of each of the RFID tags to perform other game functions, such as verifying the amount and placement of game tokens and payments, verifying the compliance of the RFID tag placement with the respective game rules, etc. Additional details of these game functions are provided below.

[0090] As discussed above with reference to Figure 1 the alternative embodiments omit the main RFID receiver. In such embodiments, the controller determines the identifier (see 212) and the position (see 214) without using the first set of responses.

[0091] Figure 3 is a diagram of graph 300 showing the amplitude and phase information detected by one of antennas 104 or 106 (see Figure 1 ) as the chip moves across the antenna. Graph 300 represents the amplitude and phase information generated by the response of a single RFID tag at each given x - position. For viewing purposes, it is contemplated that antenna 104a (see Figure 1 ) is used to detect the RFID tag at each position. In Figure 3 , antenna 104a has a width of approximately 2 inches and is positioned between approximately 1.8 inches and 3.8 inches from zero position 302. Thus, it is contemplated that the RFID tag starts at zero position 302. This is outside of antenna 104a and has zero amplitude, corresponding to the RFID tag not being detected. The left side of antenna 104a starts at 304. As the RFID tag moves from 302 to 304, antenna 104a detects the amplitude of the response from the RFID tag, which increases as the RFID tag approaches antenna 104a. (The response received by the main antenna 102 of Figure 1 will Figure 3The amplitude normalization shown in. Note that the amplitude of the graph 300 is negative between 302 and 304; this is attributed to the comparison of the phase information of the RFID tag detected by the main antenna 102 with the reference line 104a. Specifically, the phase information detected by the main antenna 102 is out of phase with the phase information detected by this antenna 104a; this out-of-phase result is shown as Figure 3 the negative amplitude in. The negative phase information indicates that the RFID tag is detected outside the antenna 104a.

[0092] When the RFID tag reaches 304 (directly above the left loop of the antenna 104a), the amplitude information is zero, corresponding to the RFID tag not being detected. As the RFID tag moves towards the center of the antenna 104a, the amplitude increases and reaches a maximum of approximately 0.75 at 306. Since the phase information detected by the main antenna 102 is in phase with the phase information detected by the antenna 104a, this indicates that the RFID tag is inside both antennas, and is shown by the positive amplitude curve of the graph 300 between 304 and 308. As the RFID tag moves towards the right loop of the antenna 104a, the amplitude decreases to zero at 308.

[0093] As the RFID tag continues past 308, the antenna 104a detects that the amplitude information increases (negatively) by one bit before returning to zero at 310. As previously mentioned, the amplitude is shown as negative due to the comparison of the phase information between the main antenna 102 and the antenna 104a. Since the RFID tag is inside the main antenna 102 but outside the antenna 104a between 308 and 310, the comparison result is out of phase, and the amplitude of the graph 300 is shown as negative between 308 and 310.

[0094] As an example, assume that the antenna 104a detects an amplitude of 0.2. Using only the amplitude information, the RFID tag can be in a position corresponding to one of the following six points: 320, 322, 324, 326, 330, or 332. If the phase information indicates out of phase, then the RFID tag can be in a position corresponding to one of the following four points: 320, 322, 324, or 326. If the phase information indicates in phase, then the RFID tag can be in a position corresponding to one of the two points 330 or 332. Next, Figure 4 shows how this multiple positions can be narrowed down to a single position using adjacent antennas.

[0095] Figure 4 is a diagram showing the graphs 400 and 402 of the amplitude and phase information detected by two of the antennas 104 or by two of the antennas 106 (see Figure 1 ) For illustrative purposes, assume that the graph 400 corresponds to the signal received by the antenna 104a, similar to the graph 300 (seeFigure 3 ); The graph 402 corresponds to the signal received by the adjacent antenna 104b. The antennas 104a and 104b can be referred to as adjacent antennas. The graphs 400 and 402 are further similar to the graph 300 (see Figure 3 ).

[0096] Due to the distance between the antennas 104a and 104b, there is a certain overlap between the graphs 400 and 402. This overlap provides the RFID system 100 (see Figure 1 ) with the ability to correlate the amplitude and phase information detected by each antenna with the position of the RFID tag.

[0097] Returning to the example discussed above regarding Figure 3 , suppose the antenna 104a detects an in-phase amplitude of 0.2, which indicates that the RFID tag may be located at a position corresponding to one of the following two points: 430 or 432. Suppose the antenna 104b detects an out-of-phase amplitude of 0.2, which indicates that the RFID tag may be located at a position corresponding to one of the following four points: 450, 452, 454, or 456. By correlating these measurements, the RFID system 100 determines that the position of the RFID tag is the position corresponding to point 432 (antenna 104a) and point 450 (antenna 104b); on the game table, this position is slightly inside the right hand side of the antenna 104a. (Note that Figure 4 corresponds to a side view of the antenna 104a, so in the Figure 1 top view, the position of the RFID tag corresponds to a position on the line slightly inside the right hand side of the antenna 104a.) Next, Figure 5 shows how to extend this example to two dimensions.

[0098] Figure 5 is Figure 1 a top view of the antennas 104 and 106. Continuing with the hypothetical experiment discussed above regarding Figure 4 , suppose the RFID system 100 uses the antenna 104 to determine that the RFID tag is located at a position corresponding to the line 502, due to the amplitude and phase information detected by the antennas 104a and 104b. Further suppose the RFID system 100 uses the antenna 106 to determine that the RFID tag is located at a position corresponding to the line 504, due to the amplitude and phase information detected by the antennas 106a and 106b (in a manner similar to that discussed above regarding the antennas 104a and 104b). The RFID system 100 can then determine the position of the RFID tag as the intersection point of the lines 502 and 504, i.e., the position 506. In this way, the RFID system 100 can determine the position of one or more RFID tags near the antenna array.

[0099] Figure 6is a block diagram of an RFID system 600. The RFID system 600 shows a specific implementation of the RFID system 100 (see Figure 1 ). The RFID system 600 includes a main antenna 602, a first set of antennas 604a - 604d (collectively referred to as antennas 604), a second set of antennas 606a - 606d (collectively referred to as antennas 606), an RFID reader 608, a main RFID receiver 612, a first set of RFID receivers 614a - 614d (collectively referred to as RFID receivers 614), a second set of RFID receivers 616a - 616d (collectively referred to as RFID receivers 616), and controllers 620a and 620b (collectively referred to as controllers 620). These components are similar to the components discussed above with respect to the RFID system 100 (see Figure 1 ). The RFID system 600 also includes an oscillator 630, a signal divider 632, microprocessors 640a - 640i (collectively referred to as microprocessors 640), a bi - directional coupler 650, and a diode detector 652.

[0100] The RFID reader 608 includes an RFID transmitter and an RFID receiver. The RFID transmitter is similar to the main RFID transmitter 108 (see Figure 1 ). When needed, the RFID receiver enables the RFID reader 608 to read the identifier of an RFID tag. The RFID reader 608 can be a "stockpiled" or "off - the - shelf" RFID reader. The RFID reader 608 generates a radio - frequency signal provided to the bi - directional coupler 650. The RFID reader 608 can also read the identifier of the response from any RFID tag in the area.

[0101] The oscillator 630 generates a first local oscillator signal at the desired frequency. For the RFID system 600, the RFID tags are designed to operate at a frequency of 13.56 MHz. In other embodiments, this frequency can be adjusted as needed. The oscillator 630 provides this first local oscillator signal to the receivers 612, 614, and 616 (as also Figure 7 shown), and to the signal divider 632.

[0102] The signal divider 632 divides the first local oscillator signal from the oscillator 630 to generate a second local oscillator signal. For the RFID system 600, the RFID tags are designed to operate with a modulation frequency of 424 kHz. Thus, the signal divider 632 divides the 13.56 MHz signal by 32 to obtain 424 kHz. In other embodiments, the modulation frequency can be adjusted as needed. The signal divider 632 provides this second local oscillator signal to the receivers 612, 614, and 616 (as also Figure 7 shown).

[0103] The microprocessor 640 processes the amplitude and phase information from the receivers 612, 614, and 616, and provides the amplitude and phase information from each of the receivers to the controller 620b. The microprocessor 640 receives an enable signal from the controller 620b to selectively enable the microprocessor.

[0104] The bi - directional coupler 650 generally couples the RFID reader 608, the main antenna 602, the main RFID receiver 612, and the controller 620b (via the diode detector 652). The bi - directional coupler 650 couples the radio - frequency energy transmitted by the RFID reader 608 to the main antenna 602, and directs a portion of the transmitted radio - frequency energy to the controller 620b (via the diode detector 652). The bi - directional coupler 650 couples the radio - frequency energy received by the main antenna 602 to the RFID reader 608, and directs a portion of the received radio - frequency energy to the main RFID receiver 612.

[0105] The diode detector 652 generally acts as an envelope detector. The controller 620b uses the output of the diode detector to determine the time at which the tag can respond. This allows the controller 620b to cause the receivers 614 and 616 to begin sampling the antenna signal.

[0106] The controller 620 generally controls the operation of the RFID system 600, as discussed above with respect to the controller 120 (see Figure 1 ) and the method 200 (see Figure 2 ). The controller 620a generally controls the RFID reader 608, and processes the data collected by the controller 620b in order to determine the location of the RFID tag. The controller 620a may be connected to the RFID reader 608 via an Ethernet connection, and may be connected to the controller 620b via a Universal Serial Bus (USB) connection. The controller 620a may be implemented as a computer that is connected to other devices via a network (e.g., a personal computer). The controller 620b generally collects the amplitude and phase information received by the receivers 612, 614, and 616. The controller 620b may be implemented as a microprocessor or a programmable logic device.

[0107] The RFID system 600 generally operates as follows. The controller 620a instructs the RFID reader 608 to transmit an inventory command. The RFID reader 608 turns on its radio frequency output and sends a signal to the RFID tag (e.g., by amplitude modulating the carrier signal of its radio frequency output). The directional coupler 650 directs a portion of this signal to the diode detector 652. The controller 620b monitors the output of the diode detector 652 to determine when to start sampling the receiver for RFID tags that can respond to the RFID reader 608. At this time, the controller 620b instructs the microprocessor 640 to start sampling the RSSI information using an enable signal. When the controller 620b determines that the RFID tag has finished responding, the controller 620b uses the enable signal to instruct the microprocessor 640 to sample the I and Q levels from the receivers 612, 614, and 616, and process the RSSI information to determine the data returned by the RFID tag. (In response to the inventory command, this data is typically the serial number of the RFID tag.) The I and Q information determines the phase of the modulated second local oscillator signal from the RFID tag (e.g., at 424 kHz). It should be noted that when using only one of the receivers 614 or 616, the phase of the modulated second local oscillator signal is not determined. However, by comparing the phase detected by one of the receivers 614 or 616 with the phase detected by the receiver 612, the controller 620b can determine whether the RFID tag is inside or outside a given antenna loop.

[0108] The oscillator 630 provides a first local oscillator signal (e.g., 13.56 MHz) to the receivers 612, 614, and 616, and to the signal divider 632. The signal divider 632 generates a second local oscillator signal (e.g., 424 kHz) and provides this second local oscillator signal to the receivers 612, 614, and 616. The RFID tag responds to the inventory command by loading and modulating a subcarrier signal onto the carrier signal transmitted by the RFID reader 608. The receivers 612, 614, and 616 determine the modulated subcarrier signal from the RFID tag by first mixing the antenna signal with the first local oscillator signal. After filtering and amplification, the signal is mixed with the second local oscillator signal to demodulate the modulated subcarrier signal to baseband to determine the I and Q components.

[0109] The controller 620b analyzes the data from the receiver 614 and the data from the receiver 612 to determine the position of the RFID tag on the x-axis. Similarly, the controller 620b analyzes the data from the receiver 616 and the data from the receiver 612 to determine the position of the RFID tag on the y-axis. The controller 620b can use the RSSI normalization from the receiver 612 to normalize the signals received from the other receivers 614 and 616 so that higher fidelity position information can be obtained.

[0110] Although four sets of antennas 604 and antennas 606 (and their associated receivers 614 and 616) are shown, these numbers can be adjusted as needed. Similarly, the shapes of the antennas 604 and 606 can be adjusted.

[0111] Figure 7 is a block diagram of the receiver 700. The receiver 700 can be a specific implementation for one or more of the receivers 612, 614, or 616 (see Figure 6 ). The receiver 700 includes a mixer 702, a band-pass filter 704, an amplifier 706, a band-pass filter 708, a limiting amplifier 710, mixers 712a and 712b, a phase shifter 714, resistors 716a and 716b, and capacitors 718a and 718b.

[0112] The receiver 700 is connected to one of the antennas (e.g., Figure 6 one of the antennas 602, 604, or 606). The receiver 700 receives a first local oscillator (LO) signal 730 (e.g., at 13.56 MHz) from the oscillator 630 (see Figure 6 ), and receives a second local oscillator signal 732 (e.g., at 424 kHz) from the signal divider 632 (see Figure 6 ).

[0113] The mixer 702 mixes the radio frequency signal received by the antenna (e.g., Figure 6 one of the antennas 602, 604, or 606) with the first local oscillator signal 730 to generate a modulated subcarrier signal 734 (e.g., at 424 kHz). Due to the RFID tag in the area modulating the radio frequency energy from the RFID reader (e.g., Figure 6 608 in ), the subcarrier signal 734 is a modulated subcarrier signal.

[0114] The band-pass filter 704 performs band-pass filtering on the modulated subcarrier signal 734 to reduce noise and generates a modulated subcarrier signal 736. The band-pass filter 704 has a center frequency around the desired frequency of the subcarrier signal (e.g., 424 kHz).

[0115] Amplifier 706 amplifies the modulated subcarrier signal 736 and generates a modulated subcarrier signal 738. Bandpass filter 708 performs bandpass filtering on the modulated subcarrier signal 738 to further reduce noise and generates a modulated subcarrier signal 740. Bandpass filter 708 has a center frequency around the desired frequency of the subcarrier signal (e.g., 424 kHz).

[0116] Limiting amplifier 710 drives the modulated subcarrier signal 740 into limiting (e.g., by having a high gain) such that the I and Q phase signals are independent of the signal amplitude, thereby generating a modulated subcarrier signal 742. Limiting amplifier 710 also outputs an RSSI signal 744 proportional to the level of the modulated subcarrier signal 740 (e.g., in dB). The RSSI signal 744 is then provided to Figure 6 controller 620b and corresponds to the RSSI or amplitude information discussed above.

[0117] Mixer 712a mixes the modulated subcarrier signal 742 with the second local oscillator signal 732 in order to extract a modulated signal 746. The modulated signal 746 corresponds to the modulation of the subcarrier signal (e.g., at 424 kHz) performed by RFID tags in the area. Resistor 716a and capacitor 718a form a low-pass filter that performs low-pass filtering on the modulated signal 746, thereby generating an in-phase (I) signal 748. The in-phase signal 748 is then provided to Figure 6 controller 620b and corresponds to the in-phase (I) signal component discussed above.

[0118] Phase shifter 714 performs a 90-degree phase shift on the second local oscillator signal 732 to generate a phase-shifted second local oscillator signal 733.

[0119] Mixer 712b mixes the modulated subcarrier signal 742 with the phase-shifted second local oscillator signal 733 in order to create a demodulated signal 750. The demodulated signal 750 corresponds to the unfiltered quadrature (Q) signal. Resistor 716b and capacitor 718b form a low-pass filter that performs low-pass filtering on the demodulated signal 750 to generate a quadrature (Q) signal 752. The quadrature signal 752 is then provided to Figure 6 controller 620b and corresponds to the quadrature (Q) signal component discussed above.

[0120] As discussed above, controller 620 (see Figure 6 ) is able to determine whether a given RFID tag is internal or external to one or more of antennas 604 and 606 by comparing the I and Q components received by the antenna with the I and Q components received by main antenna 602.

[0121] According to another embodiment, instead of the receiver 700, the receiver may be implemented as a software-defined radio. Generally, a software-defined radio samples the signal from the antenna with a high-speed analog-to-digital converter and then processes the signal digitally to detect the amplitude and phase.

[0122] Figure 8 is a block diagram of an RFID system 800. The RFID system 800 shows a specific implementation of the RFID system 100 (see Figure 1 ). The RFID system 800 includes a main antenna 802, a first set of antennas 804a - 804d (collectively referred to as antennas 804), a second set of antennas 806a - 806d (collectively referred to as antennas 806), an RF transmitter 808, a main RFID receiver 812, a first set of RFID receivers 814a - 814d (collectively referred to as RFID receivers 814), a second set of RFID receivers 816a - 816d (collectively referred to as RFID receivers 816), controllers 820a and 820b (collectively referred to as controllers 820), an oscillator 830, and a signal divider 832. These components are similar to those discussed above with respect to the RFID system 100 (see Figure 1 ) or the RFID system 600 (see Figure 6 ). The RFID system 800 also includes a directional coupler 850.

[0123] The RFID system 800 is similar to the RFID system 600 (see Figure 6 ), where the main differences are that the RFID reader 608 (see Figure 6 ) is replaced by an RF transmitter 808, the controller 620b is replaced by a controller 820b, and the bi-directional coupler 650 is replaced by a directional coupler 850. Briefly, the RFID system 600 (see Figure 6 ) is for using a "stock" or "off-the-shelf" RFID reader (RFID reader 608), and the RFID system 800 is for using a controllable RF transmitter (RF transmitter 808).

[0124] The oscillator 830 generates a first local oscillator signal at the desired frequency. For the RFID system 800, the RFID tags are designed to operate at a frequency of 13.56 MHz. In other embodiments, this frequency can be adjusted as needed. The oscillator 830 provides the first local oscillator signal to the receivers 812, 814, and 816. The receivers 812, 814, and 816 can be implemented in a manner similar to the receiver 700 (see Figure 7 ), in which case this signal corresponds to the first local oscillator signal 730.

[0125] The signal divider 832 divides the first local oscillator signal from the oscillator 830 to generate a second local oscillator signal. For the RFID system 800, the RFID tags are designed to operate at a modulation frequency of 424 kHz. Thus, the signal divider 832 divides the 13.56 MHz signal by 32 to obtain 424 kHz. In other embodiments, the modulation frequency can be adjusted as needed. The signal divider 832 provides this second local oscillator signal to the receivers 812, 814, and 816 (also as shown in Figure 7 ), in which case this signal corresponds to the second local oscillator signal 732.

[0126] The directional coupler 850 generally couples the RF transmitter 808, the main antenna 802, and the main RFID receiver 812. The directional coupler 850 couples the radio frequency energy transmitted by the RF transmitter 808 to the main antenna 802. The directional coupler 850 couples the radio frequency energy received by the main antenna 802 to the RF transmitter 808 and directs the received radio frequency energy to the main RFID receiver 812.

[0127] The controller 820 generally controls the operation of the RFID system 800, as discussed above with respect to the controller 120 (see Figure 1 ) and the method 200 (see Figure 2 ). The controller 820a generally serves as an interface to other components. The controller 820a can be connected to the controller 820b via an Ethernet connection. The controller 820a can be implemented as a computer (e.g., a personal computer) connected to other devices via a network connection. The controller 820b generally controls the RF transmitter 808, collects the amplitude and phase information received by the receivers 812, 814, and 816, and processes the amplitude and phase information to determine the position of the RFID tag. The controller 820b can be implemented as a microprocessor or a programmable logic device.

[0128] The RFID system 800 typically operates as follows. The controller 820b controls the RF transmitter 808 using the modulation signal 860. The RF transmitter 808 applies the modulation signal 860 to its RF carrier signal to command the tag (e.g., transmit an inventory command using amplitude modulation of a subcarrier signal on the carrier signal of its radio frequency output). The directional coupler 850 directs this signal to the main antenna 802. The controller 820b receives amplitude and phase information (RSSI, I, and Q) from the receivers 812, 814, and 816. (In response to the inventory command, this data is typically the serial number of the RFID tag.) The I and Q information determines the phase of the modulated subcarrier of the response from the RFID tag (e.g., at 424 kHz). It should be noted that when using only one of the receivers 814 or 816, the phase of the modulated subcarrier is not determined. However, by comparing the phase detected by one of the receivers 814 or 816 with the phase detected by the receiver 812, the controller 820b can determine whether the RFID tag is inside or outside a given antenna loop.

[0129] The oscillator 830 provides a first local oscillator signal (e.g., 13.56 MHz) to the receivers 812, 814, and 816, and to the signal divider 832. The signal divider 832 generates a second local oscillator signal (e.g., 424 kHz) and provides this signal to the receivers 812, 814, and 816. The RFID tag responds to the inventory command by loading and modulating a subcarrier signal onto the carrier signal transmitted by the RF transmitter 808. The receivers 812, 814, and 816 determine the modulated subcarrier signal from the RFID tag by mixing the detected subcarrier signal with the first local oscillator signal from the oscillator 830. The receivers 812, 814, and 816 demodulate the modulated subcarrier signal to baseband to determine the I and Q components.

[0130] The controller 820b analyzes the data from the receiver 814 and the data from the receiver 812 to determine the position of the RFID tag on the x-axis. Similarly, the controller 820b analyzes the data from the receiver 816 and the data from the receiver 812 to determine the position of the RFID tag on the y-axis. The controller 820b can use the RSSI normalization from the receiver 812 to normalize the signals received from the other receivers 814 and 816 so that higher-fidelity position information can be obtained.

[0131] Although four sets of antennas 804 and antennas 806 (and their associated receivers 814 and 816) are shown, these numbers can be adjusted as needed. Similarly, the shapes of the antennas 804 and 806 can be adjusted.

[0132] Figure 9Is a top view of a set of overlapping antennas 900 in one direction. The overlapping of antennas 900 increases the number of antennas that can receive responses from a given RFID tag, which increases the amount of data available to the RFID system and may increase the accuracy of RFID tag location determination. Antennas 900 include antennas 900a, 900b, 900c, 900d, 900e, 900f, and 900g. Antennas 900 are associated with RFID receivers (not shown); these RFID receivers may be similar to RFID receivers 114, 116 (see Figure 1 ), 614, 616 (see Figure 6 ), 700 (see Figure 7 ), 814 or 816 (see Figure 8 ). It should be noted that for clarity of illustration, antennas 900e, 900f, and 900g are shown slightly offset.

[0133] Antennas 900 can be used to replace one of the set of antennas in a specific direction. For example, antennas 900 can be used to replace antenna 104 in the x direction (see Figure 1 ), or antenna 106 in the y direction (see Figure 1 ). Antennas 900 can be used to replace antenna 604 in the x direction (see Figure 6 ), or antenna 606 in the y direction (see Figure 6 ). Antennas 900 can be used to replace antenna 804 in the x direction (see Figure 8 ), or antenna 806 in the y direction (see Figure 8 ).

[0134] Antennas 900 can be printed as a double layer on a printed circuit board. The number and shape of antennas 900 can be adjusted as needed.

[0135] Figure 10 Is a top view of antenna array 1000. Antenna array 1000 includes a first set of antennas 1004a, 1004b, 1004c, and 1004d (collectively referred to as antennas 1004), and a second set of antennas 1006a, 1006b, 1006c, 1006d, 1006e, 1006f, 1006g, 1006h, 1006i (collectively referred to as antennas 1006). Compared with other antenna arrays (e.g., Figure 1 's antennas 104 and 106), antennas 1004 and 1006 do not intersect at right angles. Antenna array 1000 can be used to replace antennas 104 and 106 (see Figure 1 ), 604 and 606 (see Figure 6 ), or 804 and 806 (see Figure 8 ). Antenna 1004, antenna 1006, or both can overlap in a manner similar to that of antennas 900 (see Figure 9 ).

[0136] The number and shape of antennas 1004 and 1006 can be adjusted as needed.

[0137] Figure 11 is a top view of a polar antenna array 1100. The polar antenna array 1100 includes overlapping circular antennas 1104a, 1104b, 1104c, and 1104d (collectively referred to as circular antennas 1104), and radial antennas 1106a, 1106b, 1106c, and 1106d (collectively referred to as radial antennas 1106). The antennas 1104 are shown in dashed lines. Compared with other antenna arrays (e.g., Figure 1 antennas 104 and 106), the antenna array 1100 does not generate x and y position information, but instead generates polar position information (e.g., magnitude and direction). The circular antennas 1104 are used to determine the distance from the center point 1110, and the radial antennas 1106 are used to determine the angle. The polar antenna array 1100 can be used instead of antennas 104 and 106 (see Figure 1 ), 604 and 606 (see Figure 6 ), 804 and 806 (see Figure 8 ), or the antenna array 1000 (see Figure 10 ).

[0138] As an example, it is considered that the system detects an RFID tag inside the circular antenna 1104d and outside the circular antenna 1104c. If the system further detects outside the radial antenna 1106a of the RFID tag, then the system determines that the position of the RFID tag is near the point 1110. The accuracy of the position determination can be determined according to the value of the detected signal, as discussed above with respect to Figures 3 - 4 (or further detailed in the position determination section below).

[0139] As an option, the circular antennas 1104 do not need to overlap. Similarly, the radial antennas 1106 do not need to overlap. As another option, the circular antennas 1104 can be loops or rings, and can overlap, not overlap, or partially overlap.

[0140] Figure 12A is a top view of a baccarat table 1200, and Figure 12B is a top view of a part of the baccarat table 1200, which shows the corresponding part of the antenna array 1202. In Figure 12A there is the entire antenna array 1202, but it is not shown. In Figure 12BIn [the figure], the antenna array 1202 includes a first set of antennas 1204a, 1204b, 1204c, 1204d, 1204e, 1204f, 1204g, and 1204h (collectively referred to as antennas 1204) and a second set of antennas 1206a, 1206b, 1206c, and 1206d (collectively referred to as antennas 1206). The baccarat table 1200 also includes one or more main antennas (not shown), similar to the main antenna 102 (see Figure 1 ). For one main antenna, it can surround the entire playing area of the baccarat table 1200. For two main antennas, each main antenna can cover a part of the baccarat table 1200. For example, one main antenna can surround the gaming marker positions (positions 7 - 12) on the left side of the baccarat table 1200, and the other main antenna can surround the gaming marker positions (positions 1 - 6) on the right hand part of the baccarat table 1200. Alternatively, the main antenna can define a delimited area for some (or all) of a single type of gaming marker (e.g., a player). Such an array can be used to track individual gaming markers within the delimited area.

[0141] The antennas 1204 and 1206 (and the main antenna) are connected to an RFID reader (not shown) in a manner similar to the RFID readers 114 or 116 (see Figure 1 ). The antenna 1204 is wider at one end than at the other. The antenna 1206 is slightly bent or curved to conform to the baccarat table 1200.

[0142] As an option, the antenna 1204, the antenna 1206, or both can overlap in a manner similar to the antenna 900 (see Figure 9 ).

[0143] Figure 13 is a top view of a roulette table 1300 having an antenna array 1302. The antenna array 1302 includes a first set of antennas 1304a, 1304b, 1304c, 1304d, and 1304e (collectively referred to as antennas 1304) and a second set of antennas 1306a, 1306b, 1306c, 1306d, 1306e, 1306f, 1306g, 1306h, 1306i, 1306j, 1306k, 1306l, 1306m, and 1306n (collectively referred to as antennas 1306). The roulette table 1300 also includes a main antenna (not shown) surrounding the playing area, similar to the main antenna 102 (see Figure 1 ). The antennas 1304 and 1306 (and the main antenna) are connected to an RFID reader (not shown) in a manner similar to the RFID readers 114 or 116 (see Figure 1 ).

[0144] As an option, antenna 1304, antenna 1306, or both can overlap in a manner similar to that of antenna 900 (see Figure 9 ).

[0145] Finally, with regard to the sizing of the antennas discussed herein, generally, the width of each antenna should be less than the diameter of the RFID tag (or within about + / - 0.5 inches of the diameter of the RFID tag), and the spacing between each antenna should also be less than the diameter of the RFID tag.

[0146] Reading the RFID tag

[0147] As discussed above, an RFID reader (e.g., Figure 1 's RFID transmitter 108) sends an inventory command (e.g., 202 in Figure 2 ), and the RFID tag responds to the inventory command (e.g., 204 in Figure 2 ). The RFID tag includes anti-collision features to reduce interference that results when two or more RFID tags respond at the same time. One anti-collision feature is the pseudo-random selection of time slots in which the RFID tag responds. Statistically, different pseudo-random time slots among multiple RFID tags help prevent them all from responding at the same time.

[0148] Another anti-collision feature is a 5-bit CRC added to the inventory command sent from the tag to the reader and a 16-bit CRC of the serial number of the tag. If the CRC is incorrect, there may be a collision. When all RFID tags have been read, the RFID reader stops radiating energy, which causes the RFID tag to clear its flag; in the case where the flag has been cleared, when the RFID reader starts radiating energy again in the case of sending the next inventory command, the RFID tag is free to respond.

[0149] The RFID reader can implement a slotted Aloha system or a binary tree search. In a slotted Aloha system, the RFID reader broadcasts initialization commands and parameters, and the tags individually use the initialization commands and parameters to pseudo-randomly delay their responses. In a binary tree search, the RFID reader sends an initialization symbol and then transmits the identification data one bit at a time; only the RFID tags with a matching bit respond, and ultimately only one RFID tag matches the complete identification string.

[0150] Each RFID tag can contain 96 bits of identification information, which allows a total of 2^96 RFID tags to be individually identified by the system. The RFID tag can send its response using Manchester coding of its modulation of the carrier signal from the RFID reader.

[0151] Due to the anti-collision feature, the system is typically operable as if only one RFID tag responds at a given time. This allows all receivers that receive a response at a given time (e.g., Figure 1 receivers 112, 114, and 116) to associate the respective responses received by each receiver together. For the sake of clarity of illustration, the remainder of this document assumes that only one RFID tag responds at a given time.

[0152] Determining Location

[0153] As discussed above, at least three receivers of an RFID system (e.g., an RFID system 100) (e.g., Figure 1 at least one of receivers 112, at least one of receiver 114, and at least one of receiver 116) receive responses from a given RFID tag. For a given antenna in the x direction (e.g., antenna 104b), the RFID system can determine whether the given RFID tag is inside or outside the given antenna by comparing the signal phase between the given antenna in the x direction and the main antenna (e.g., main antenna 102). Similarly, for a given antenna in the y direction (e.g., antenna 106b), the RFID system can determine whether the given RFID tag is inside or outside the given antenna by comparing the signal phase between the given antenna in the y direction and the main antenna. When the RFID system determines that the given RFID tag is inside both the x-direction antenna and the y-direction antenna, the RFID system determines that the location of the given RFID tag on the game table is at the location where the two antennas intersect. In a simple case, the RFID system assumes that the location is at the midpoint of the intersection area.

[0154] When the RFID system determines that the given RFID tag is outside the x-direction antenna or the y-direction antenna, the RFID system needs to determine in which direction it is outside. As an example in the x direction, if it is detected that the given RFID tag is outside antenna 104b, then the given RFID tag can be on the left or right side of antenna 104b. At this time, the RFID system looks at the responses received by the antennas adjacent to antenna 104b (e.g., antennas 104a and 104c). If antenna 104a receives the response and antenna 104c does not, then the RFID system determines that the location of the given RFID tag is on the left side of antenna 104b. Similarly, if antenna 104c receives the response and antenna 104a does not, then the RFID system determines that the location of the given RFID tag is on the right side of antenna 104b. In a simple case, the RFID system assumes that the location is at the midpoint between the two antennas (104b and 104a, or 104b and 104b). A similar result occurs in the y direction.

[0155] Interpolation

[0156] Instead of assuming the position is at the midpoint as discussed above, an RFID system (e.g., Figure 1 RFID system 100) can interpolate the position based on the amplitude of the received signal. For example, the RFID system can store Figure 3 graph 300 as a look-up table (e.g., in controller 120). Table 1 is an example look-up table with 7 entries corresponding to 7 sections of graph 300 (where section 1 is the descent from point 302 to the most negative value of graph 300; section 2 is the ascent from said point to point 304; section 3 is the ascent from point 304 to near the most positive value of graph 300; section 4 is the part around the most positive value; section 5 is the descent from near the maximum value to point 308; section 6 is the descent from point 308 to the most negative value of graph 300; and section 7 is the ascent from the most negative value to point 310):

[0157] Section Amplitude Position 1 From 0 to -0.25 0.5 (near point 320) 2 From -0.25 to 0 1.4 (near point 322) 3 From 0 to 0.7 1.9 4 Higher than 0.7 2.5 5 From 0.7 to 0 3.2 6 From 0 to -0.25 3.75 (near point 324) 7 From -0.25 to 0 4.2 (near point 326)

[0158] Table 1

[0159] (Since graph 300 is symmetric, the data in Table 1 can be reduced to 4 entries, such as offset around the center point.) As discussed above, there can be multiple points for a given amplitude detected by a single antenna, so the RFID system uses adjacent antennas to eliminate impossible points.

[0160] The position data in Table 1 corresponds to the midpoint of each section of graph 300. Instead of using the midpoint when the amplitude drops at any position within the appropriate range, the RFID system can use the exact amplitude for interpolation. For example, if the amplitude is at -0.125 and (using adjacent antennas) it is determined that the position is within the first section, then instead of using 0.5 as the position, the RFID system interpolates the position midway between 0.5, i.e., 0.25. The RFID system can use linear interpolation.

[0161] The number of entries in the look-up table can be increased or decreased as needed. As more entries appear in the look-up table, the interpolation becomes more accurate for the actual position.

[0162] Generally, the values in Table 1 apply to antennas of uniform width, such as in Figure 5 For other antennas, such as Figure 11 radial antenna 1106, or Figure 12B antenna, the values in the corresponding look-up table can be determined empirically.

[0163] Integrated game rules

[0164] RFID system (e.g., Figure 1The RFID system 100) can control various events in the gaming environment using the determined RFID information (e.g., detected RFID tag identifiers and locations). Generally, these events are managed according to the game rules, and different game rules are applied in different gaming environments (referred to as game states). When the RFID system detects a violation of the game rules, the RFID system can generate a warning. The RFID system can determine the detected RFID tag identifiers and locations (commonly referred to as chip data) using the RFID readers described herein, and can determine the value of the card dealt (commonly referred to as card data) using the meter box.

[0165] Generally, game states are customized for a particular game. For example, baccarat can have the following game states: pre-game, new game, game marker locked, payout, and game over. In the pre-game state, the RFID system does not monitor RFID tag identifiers or locations. In the new game state, the RFID system can track RFID tag identifiers and locations (and can display and record the resulting data), but no illegal movement alarms are generated because the game rules allow the chips to move freely in this state. (Exceptions for detecting illegal chips can be generated, which can cause illegal chip alarms.) In the game marker locked state, chip movement is not allowed, so any detected RFID tag movement can result in an alarm. In the payout state, the RFID system monitors that the correct payout amount is made to the correct location, and generates a correct collection from the correct location by correlating the RFID tags placed (or removed from) each location. At the end of the game state, the RFID system records the end of the current game and returns to the new game state for the next game.

[0166] A particular game state can contain one or more sub-states (which can also be referred to as game states). For example, in blackjack, the dealer is obligated to deal another card to the dealer's hand based on the total number of points in the dealer's hand (e.g., 17). Thus, within the game state of "dealing a card to the dealer's hand", there are sub-states of "deal another card" and "stop dealing cards". There are similar states and sub-states for each hand. Similarly, if the dealer deals an initial blackjack, the RFID system can transition from the "dealing" state to the "collecting / paying out" state. As another example, baccarat has multiple sub-states within the game state that depends on the card dealt, and each playing position transitions between these sub-states. For example, the transition from playing to paying can be staggered for each player.

[0167] The RFID system is particularly helpful during the collection and payment phases. For example, the RFID system determines that Location 1 is the winner and Location 2 is the loser based on the game result. The RFID system knows the identifiers of the RFID tags associated with the locations and verifies that additional chips corresponding to the correct payment are generated for Location 1 and collects the chips associated with Location 2.

[0168] Other information regarding the game rules and game state can be found in U.S. Application Publication No. 2015 / 0312517 and U.S. Application Publication No. 2016 / 0217645, which are incorporated herein by reference.

[0169] Grouping

[0170] An RFID system (e.g., Figure 1 RFID system 100) can associate RFID tags with similar locations into a single group. (These similar locations refer to the x-y plane; for example, two RFID tags stacked on top of each other will have similar x-y locations but different z locations.) For example, if the locations of two identified RFID tags are less than approximately 0.75x the diameter, the RFID system can consider the two RFID tags to be associated in a group. For example, for an RFID tag with a diameter of 1.5 inches, grouping occurs when two RFID tags are within approximately 1.125 inches of each other. Similar groups can be formed by adjacent stacked RFID tags. The controller can then consider the group of RFID tags as a single unit. For example, instead of interpreting a first RFID tag and an adjacent second RFID tag as two separate game tokens (e.g., $100 and $200), the controller groups the two RFID tags as a single game token (e.g., $300). Generally, when the location of each RFID tag in a group of RFID tags is within the defined range (e.g., 0.75x the diameter) of at least one other RFID tag in the group, the RFID system can consider the group as a group. For example, a "stack" of RFID tags will have similar locations (e.g., much less than 0.75x the diameter), so the RFID system determines the stack as a group. As another example, a "bump" of RFID tags may have locations that exceed the defined range after aggregation, but as long as each RFID tag in the bump is within the defined range of at least one other RFID tag in the bump, the RFID system determines the bump as a group.

[0171] Grouping can also be used in conjunction with game rules (e.g., game states and sub - states). For example, in blackjack, a player is allowed to "double down" (double the amount of the initial game token) in certain situations. In this case, the RFID system first uses card data to determine that doubling down is allowed. Second, the RFID system uses RFID data to verify that the accurately doubled game tokens have been placed as a group with the initial game tokens. (The RFID system can determine that the initial game tokens are in a first group and the doubled game tokens are in a second group.) Third, the RFID system uses card data to determine whether the player's hand is a winner or a loser; for a winner, the RFID system uses chip data to verify that the correct payout has been placed as an additional group with the initial game tokens and the doubled game tokens; and for a loser, the RFID system uses chip data to verify that all groups (the initial game tokens and the doubled game tokens) have been collected. If any data indicates a violation of the game rules, the RFID system can generate an alert.

[0172] The defined range used by the RFID system to determine groups can be adjusted as needed. For example, when the defined range is 1.5x the diameter, the RFID system determines that two adjacent stacks are a group.

[0173] Figure 14 Yes Figure 1 Top view of antennas 104 and 106. Compared with Figure 5 Compared with Figure 14 contains five RFID tags 1402, 1404, 1406, 1408, and 1410. Assume that each RFID tag takes 10 milliseconds (ms) to respond. Assuming no collisions, the read cycle takes 50 ms (10 ms per RFID tag): during this time, power is supplied to the main antenna (not shown), and the RFID readers connected to antenna 104a receive responses from RFID tags 1402 and 1404; the RFID readers connected to antenna 104b receive responses from RFID tags 1402, 1404, and 1406; the RFID readers connected to antenna 104c receive responses from RFID tags 1406, 1408, and 1410; and the RFID readers connected to antenna 104d receive responses from RFID tags 1408 and 1410. (These responses correspond to those described above in Figure 2The "second set of responses" discussed at 208 above.) During the same time period, the RFID reader connected to antenna 106a receives responses from RFID tags 1402 and 1408; the RFID reader connected to antenna 106b receives responses from RFID tags 1402, 1406, and 1408; the RFID reader connected to antenna 106c receives responses from RFID tags 1404, 1406, and 1410; and the RFID reader connected to antenna 106d receives responses from RFID tags 1404 and 1410. These responses correspond to the "third set of responses" discussed at 210 above in Figure 2 above.

[0174] Compare the above with a system that powers each antenna individually (e.g., no master antenna). In this system, the RFID reader connected to antenna 104a takes 20 ms to perform the read (10 ms for each of RFID tags 1402 and 1404), the RFID reader connected to antenna 104b takes 30 ms to perform the read (10 ms for each of RFID tags 1402, 1404, and 1406), the RFID reader connected to antenna 104c takes 30 ms to perform the read (10 ms for each of RFID tags 1406, 1408, and 1410), and the RFID reader connected to antenna 104d takes 20 ms to perform the read (10 ms for each of RFID tags 1408 and 1410); thus, reading the x direction takes 100 ms (20 + 30 + 30 + 20). Similarly, for a total read time of 200 ms, reading the y direction also takes 100 ms. This is significantly greater than the 50 ms discussed above.

[0175] Therefore, compared to existing systems that power each antenna individually, the RFID system described herein results in a significant improvement in read time.

[0176] The above description illustrates various embodiments of the invention and examples of how aspects of the invention may be implemented. The above examples and embodiments should not be considered the only embodiments, and the above examples are presented to illustrate the flexibility and advantages of the invention as defined by the appended claims. Based on the above disclosure and the appended claims, other arrangements, embodiments, implementations, and equivalents will be apparent to those skilled in the art and may be used without departing from the spirit and scope of the invention as defined by the claims.

Claims

1. A system for determining the position of an object in a gaming environment, the system comprising: a main antenna associated with an area on a gaming table; a first plurality of antennas oriented in a first direction and associated with the area on the gaming table; a second plurality of antennas oriented in a second direction, wherein the second direction is different from the first direction, wherein the second plurality of antennas overlaps with the first plurality of antennas, and wherein the first plurality of antennas and the second plurality of antennas intersect at a plurality of positions within the area; a main radio frequency identification (RFID) transmitter coupled to the main antenna; an RFID receiver; and a controller that controls the main RFID transmitter to generate an RFID inventory command, wherein each of a plurality of RFID tags in the area responds to the RFID inventory command according to an anti-collision process, wherein in response to the RFID inventory command, the RFID receiver receives a first plurality of responses from the plurality of RFID tags via the first plurality of antennas and a second plurality of responses from the plurality of RFID tags via the second plurality of antennas, wherein the controller determines an identifier of each of the plurality of RFID tags using at least one of the first plurality of responses and the second plurality of responses, and wherein the controller determines the position of each of the plurality of RFID tags by correlating phase information of the first plurality of responses and phase information of the second plurality of responses.

2. The system according to claim 1, wherein in response to the RFID inventory command, the RFID receiver receives a third plurality of responses from the plurality of RFID tags via the main antenna, and wherein the controller determines the position of each of the plurality of RFID tags by correlating the phase information of the first plurality of responses, the phase information of the second plurality of responses, and the phase information of the third plurality of responses.

3. The system according to claim 2, wherein the controller uses the phase information of the third plurality of responses to determine relative phase information of the first plurality of responses and relative phase information of the second plurality of responses, wherein the controller determines the position of each of the plurality of RFID tags by correlating the relative phase information of the first plurality of responses and the relative phase information of the second plurality of responses.

4. The system according to claim 1, wherein the controller determines the position of each of the plurality of RFID tags by correlating amplitude information and phase information of the first plurality of responses with the phase information of the second plurality of responses.

5. The system according to claim 1, wherein in response to the RFID inventory command, the RFID receiver receives a third plurality of responses from the plurality of RFID tags via the main antenna, and The controller determines the position of each of the plurality of radio frequency identification tags by correlating the amplitude information and the phase information of the first plurality of responses, the phase information of the second plurality of responses, and the phase information of the third plurality of responses.

6. The system of claim 1, wherein for a particular radio frequency identification tag of the plurality of radio frequency identification tags, the controller simultaneously determines the identifier and the position of the particular radio frequency identification tag.

7. The system of claim 1, wherein the radio frequency identification inventory command is a single radio frequency identification inventory command that causes the controller to determine the identifiers and the positions of all of the plurality of radio frequency identification tags.

8. The system of claim 1, wherein the first plurality of antennas and the second plurality of antennas overlap and intersect to define the position of each of the plurality of radio frequency identification tags in two dimensions within the region.

9. The system of claim 1, wherein the first plurality of antennas and the second plurality of antennas intersect perpendicularly and define the position of each of the plurality of radio frequency identification tags in the x-dimension and the y-dimension within the region.

10. The system of claim 1, wherein the first plurality of antennas and the second plurality of antennas define the position of each of the plurality of radio frequency identification tags using polar coordinates within the region.

11. A method of determining the position of an object in a gaming environment, the method comprising: generating, by a master radio frequency identification transmitter coupled to a master antenna, a radio frequency identification inventory command, wherein the master antenna is associated with a region on a gaming table; responding, by each of a plurality of radio frequency identification tags in the region, to the radio frequency identification inventory command according to an anti-collision process; receiving, by a radio frequency identification receiver, a first plurality of responses from the plurality of radio frequency identification tags via a first plurality of antennas in response to the radio frequency identification inventory command, wherein the first plurality of antennas are oriented in a first direction and are associated with the region on the gaming table; receiving, by the radio frequency identification receiver, a second plurality of responses from the plurality of radio frequency identification tags via a second plurality of antennas in response to the radio frequency identification inventory command, wherein the second plurality of antennas are oriented in a second direction different from the first direction, wherein the second plurality of antennas overlap the first plurality of antennas, and wherein the first plurality of antennas and the second plurality of antennas intersect at a plurality of locations within the region; determining, by a controller, the identifier of each of the plurality of radio frequency identification tags using at least one of the first plurality of responses and the second plurality of responses; and determining, by the controller, the position of each of the plurality of radio frequency identification tags by correlating the phase information of the first plurality of responses and the phase information of the second plurality of responses.

12. The method of claim 11, further comprising: receiving, by the radio frequency identification receiver, a third plurality of responses from the plurality of radio frequency identification tags via the master antenna in response to the radio frequency identification inventory command, The step of determining the position of each of the plurality of radio frequency identification tags includes determining the position of each of the plurality of radio frequency identification tags by the controller by correlating the phase information of the first plurality of responses, the phase information of the second plurality of responses, and the phase information of the third plurality of responses.

13. The method according to claim 12, further comprising: by the controller, determining the relative phase information of the first plurality of responses and the relative phase information of the second plurality of responses by using the phase information of the third plurality of responses, wherein the step of determining the position of each of the plurality of radio frequency identification tags includes determining the position of each of the plurality of radio frequency identification tags by the controller by correlating the relative phase information of the first plurality of responses and the relative phase information of the second plurality of responses.

14. The method according to claim 11, wherein the step of determining the position of each of the plurality of radio frequency identification tags includes determining the position of each of the plurality of radio frequency identification tags by the controller by correlating the amplitude information and the phase information of the first plurality of responses with the phase information of the second plurality of responses.

15. The method according to claim 11, further comprising: by the radio frequency identification receiver, receiving a third plurality of responses from the plurality of radio frequency identification tags via the main antenna in response to the radio frequency identification inventory command, wherein the step of determining the position of each of the plurality of radio frequency identification tags includes determining the position of each of the plurality of radio frequency identification tags by the controller by correlating the amplitude information and the phase information of the first plurality of responses, the phase information of the second plurality of responses, and the phase information of the third plurality of responses.

16. The method according to claim 11, wherein for a particular radio frequency identification tag among the plurality of radio frequency identification tags, the step of determining the identifier of the particular radio frequency identification tag is performed simultaneously with the step of determining the position of the particular radio frequency identification tag.

17. The method according to claim 11, wherein the radio frequency identification inventory command is a single radio frequency identification inventory command, and wherein the steps of determining the identifier of each of the plurality of radio frequency identification tags and determining the position of each of the plurality of radio frequency identification tags result in determining a plurality of identifiers and a plurality of positions of all the plurality of radio frequency identification tags.

18. The method according to claim 11, wherein the first plurality of antennas and the second plurality of antennas overlap and intersect to define the position of each of the plurality of radio frequency identification tags in two dimensions within the region.

19. The method according to claim 11, wherein the first plurality of antennas and the second plurality of antennas intersect perpendicularly and define the position of each of the plurality of radio frequency identification tags in the x dimension and the y dimension within the region.

20. The method according to claim 11, wherein the first plurality of antennas and the second plurality of antennas define the position of each of the plurality of radio frequency identification tags using polar coordinates within the area.

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