Abstract:
A system and method to store a sequence of data records relating to attributes of interactions between fuel dispensers and tags. The data records may be stored on the tag or at a location remote from the tag, such as a fuel dispenser, central site controller or other network. The data records may contain the identity of the dispenser, tag and any attribute of a received signal, such as frequency band or signal strength, or other attribute indicative of proximity. Every dispenser that attempts to communicate with a tag in question adds its own interaction data to a limited history of a tag&#39;s past interactions with the same and other dispensers. When a dispenser or central site control system examines the contents of the interaction histories, the detected presence of other dispensers or the relative strength of the recorded interaction attributes will determine what, if any, action is to be taken by the dispensers or central site control system to communicate with the tag at issue.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to communicating with transponders in a fueling environment and, more particularly, to a dispensing system capable of arbitrating between competing tags and dispensers to ensure a dispenser communicates with the tag most proximate to that dispenser. 
     In recent years, traditional gasoline pumps at service stations have evolved into elaborate point-of-sale (POS) devices having sophisticated control electronics and user interfaces with large displays and touch pads (or screens). These dispensers include various types of payment means, such as card readers, to expedite and further enhance fueling transactions. A customer is not limited to the purchase of fuel at the dispenser. More recent dispensers allow the customer to purchase services, such as car washes, and goods such as fast food or convenience store products at the dispenser. Once purchased, the customer need only pick up the goods and services at the station store. 
     Given the ever increasing demand to increase transaction efficiency by both fuel suppliers and customers, transaction systems associated with the service stations are further evolving to provide fully automated authorization and purchasing. It would be advantageous if customers no longer needed to use a credit/debit card or smartcard to purchase fuel or other products or services. This can be accomplished if the customer, vehicle or both are equipped with a remote intelligent communications device, or transponder (hereinafter referred to as a tag for simplicity), capable of remotely communicating with fuel dispensers and other devices as desired. These tags and dispensers operate in conjunction to provide a cashless and cardless transaction system where transactions are automatically charged or debited without requiring any action by the customer. A tag is a remote communication device capable of unidirectional or bi-directional communications to and/or from a fuel dispenser&#39;s remote communications system. 
     Numerous patents have issued and foreign applications published relating to technology associated with communicating information between a tag or like transponder and the fuel dispenser. These patents disclose communicating between the tag and fuel dispenser with fiber optics, electromagnetic radiation, such as radio frequency transmissions, infrared, direct electrical connections and various others means or combination of these means. Various types of information are communicated between the tag and the dispenser including vehicle identification, customer identification, account information, fuel requirements, diagnostics, advertising, and various other types of solicited and unsolicited messages. Certain specific applications equip the tag and dispenser with cryptography electronics to encrypt and decrypt data transferred between the tag and dispenser. 
     Tag transponder technology is used in many areas of technology relating to vehicles. Such technology is used in tracking vehicles, navigational aids, toll collection, diagnostics, vehicle security and theft deterrence, keyless entry, refueling, collision avoidance, vehicle identification, surveillance and traffic control as well as transmitting and receiving financial data. 
     In theory, such communications between a tag and a fuel dispenser appear to be an answer to increasing transactional efficiencies. However, when multiple tags are used in an application where a single tag can be read by multiple devices, the problem of location arbitration becomes an issue. Location arbitration is defined as the process of determining the physical closest proximity of a tag to a dispenser in applications where the proximity of the tag to the dispenser basically determines which dispenser and dispenser side should interact with the tag. 
     One example is the use of a tag to authorize a credit card transaction at a gasoline dispenser in place of a credit card. In this instance, multiple dispensers might have the ability to read the same tag but, by nature of the application, only the dispenser that is closest to the tag is meant to interact with the tag. To further complicate the issue, numerous tags may be within a single dispenser&#39;s communication field to provide a situation where multiple dispensers are talking with multiple tags. Although current systems are available for determining the existence and identity of tags, applicants are not aware of any systems providing an economical and effective system and process to associate the proximity of a tag with the various dispensers in close proximity to each other, which may cause multiple tags to be read by multiple dispensers within a narrowly defined time frame. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system to store a sequence of data records relating to attributes of interactions between fuel dispensers and tags. The data records may be stored on the tag or at a location remote from the tag, such as a fuel dispenser, central site controller or other network. The data records may contain the identity of the dispenser, tag and an attribute of a received signal, such as frequency band or signal strength, or other attribute indicative of proximity. Every dispenser that attempts to communicate with a tag in question adds its own interaction data to a limited history of a tag&#39;s past interactions with the same and other dispensers. When a dispenser or central site control system examines the contents of the interaction histories, the detected presence of other dispensers or the relative strength of the recorded interaction attributes will determine what, if any, action is to be taken by the dispensers or central site control system to communicate with the tag at issue. 
     Accordingly, one aspect of the present invention provides a remote communication unit arbitration system including a control system that has associated memory and communication electronics operatively associated with the control system. The communication electronics may have a transmitter for transmitting signals to a remote communication unit and a receiver for receiving signals from the remote communication unit. The arbitration system also includes attribute monitoring electronics having an input associated with the control system and an output associated with the communication electronics. The attribute monitoring electronics are adapted to 1) monitor an attribute of a signal received by the communication electronics wherein the attribute is indicative of the relative proximity of the remote communication unit and the dispenser, and 2) provide the control system with a new proximity value indicative of the relative proximity of the remote communication unit and the dispenser. The control system is preferably adapted to compare the new proximity value with a prior proximity value from a prior communication with the remote communication unit and determine a relative proximity of the remote communication unit to the housing with respect to a communicative device associated with the prior communication based on the new and prior proximity values. For simplicity, the remote communication unit is referred to as either a tag or transponder, and the communication electronics are referred to as an interrogator. 
     The control system may also be adapted to obtain the prior proximity value from a record in an interaction attribute database having a listing of records wherein each record includes 1) a prior proximity value associated with a prior communication with the remote communication unit from a communicative device, and 2) communication indicia of the communicative device. The control system may also be adapted to cause the new proximity value to be added as a record to the interaction attribute database in association with a unique identification indicia representative of a communicative device. The control system may determine the relative proximity of the remote communication unit by determining the proximity value representative of the closest proximity. The interaction attribute database may be located at the remote communication unit wherein the control system is adapted to access the database via radio communications through the communication electronics, but is preferably located at a central control system apart from the dispensers. 
     The interaction attribute may be derived from a signal strength measurement provided by the interrogator and sent to the control system. In such an embodiment, the interrogator may include signal strength electronics configured to provide the interaction attribute proportional to a strength measurement of a signal received by the communication electronics. The signal strength electronics may include automatic gain control circuitry adapted to amplify the received signal to a nominal signal strength. The gain control circuitry may include an output proportional to the gain necessary to amplify the received signal to the nominal signal strength, wherein the output represents the interaction attribute. 
     In particular, the gain control circuitry may include a variable gain amplifier having a gain input and a signal wherein the signal input receives the received signal from a remote communication unit. The gain control circuitry also includes a gain control amplifier having an input derived from the normalized signal of the variable gain amplifier&#39;s output and an output representing the amount of gain necessary to normalize the received signal. The output also provides feedback to the variable gain amplifier. The output of the gain control amplifier may be fed into an analog-to-digital converter to provide a digital string representing an amount of gain necessary to normalize the received signal. Those skilled in the art will be aware of other common methods of determining signal strength. 
     Alternatively, the interaction attribute or proximity values may be derived from detecting a number of errors occurring during a communication between the remote communication unit and a communicative device. The control system may be adapted to count the number of errors during the communication to provide an interaction attribute wherein the number of errors occurring during a communication is indicative of a relative proximity. Similarly, the interaction attribute may be derived from detecting a number of attempts at communication without completion between the remote communication unit and a communicative device. In general, the interaction attribute may be virtually any attribute indicative of a relative proximity between the remote communication unit and the fuel dispenser. Furthermore, the interaction attributes may be monitored or checked to determine if other communicative devices have communicated with the remote communication unit, where the remote communication unit has been, its direction of travel and movement, as well as whether or not the remote communication unit is moving. 
     Yet another aspect of the present invention provides a method of independently arbitrating between remote communication units wherein records are either stored at a central control system or on the remote communication unit. The method typically comprises 1) transmitting a signal to a remote communication unit; 2) receiving an identification indicia from the remote communication unit; 3) determining an interaction attribute indicative of a relative proximity of communication between the remote communication unit and the dispenser based on the received signal; 4) obtaining from the remote communication unit a proximity value associated with a prior communication between the remote communication unit and a communicative device and an identification indicia of the communicative device; and 5) determining a relative proximity of the fuel dispenser with respect to the communicative device based on the interaction attributes associated with the fuel dispenser and the communicative device. 
     These and other aspects of the present invention will become apparent to those skilled in the art after reading the following description of the preferred embodiments when considered with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic of a service station constructed and implemented according to a preferred embodiment of the present invention including various possible tags interacting with fuel dispensers and a host network through a central control system. 
     FIG. 2A is a block representation of the tag constructed according to the preferred embodiment. 
     FIG. 2B is a block representation of the tag having integrated electronics constructed according to the preferred embodiment. 
     FIG. 3 is a an elevational view of a fuel dispenser constructed according to a preferred embodiment. 
     FIG. 4 is a block diagram of a fuel dispenser and central control system constructed according to the preferred embodiment. 
     FIG. 5 is an electrical schematic of a fuel dispenser&#39;s control system having communication electronics and automatic gain control circuitry designed according to the present invention. 
     FIGS. 6A and 6B are a flow chart of a first tag arbitration process according to the present invention. 
     FIG. 7 is a schematic diagram of three fuel dispensers and a tag associated with the arbitration process of FIGS. 6A and 6B. 
     FIG. 8 is a schematic diagram exemplary of a tag memory associated with the process shown in FIGS. 6A and 6B. 
     FIGS. 9A and 9B are a flow chart of a second tag arbitration process according to the present invention. 
     FIG. 10 is a schematic diagram of three fuel dispensers, a transponder and a central control system associated with the arbitration process of FIGS. 6A and 6B. 
     FIG. 11 is a schematic exemplary of a central control memory associated with the process shown in FIGS. 6A and 6B. 
     FIGS. 12A through 12C are a flowchart of an arbitration process controlled from a central control system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, like reference characters designate like or corresponding parts throughout the several figures. Referring now to the drawings in general, and FIG. 1 in particular, please understand that the illustrations are for the purpose of describing preferred embodiments of the invention and are not intended to limit the invention thereto. As best seen in FIG. 1, a retail transaction system generally designated  10 , is shown constructed according to a preferred embodiment of the present invention. The transaction system  10  typically includes or is associated with three subsystems: a remote communication unit  100  (hereinafter a tag); a fuel dispenser  200  and a host network  300 . In general, remote communication units  100  are adapted to communicate with and through the fuel dispenser  200  in order to obtain authorization and communicate information to and from the various subsystems. The tag  100  may also communicate with other local sources  32  directly. 
     Various means of security are employed depending on the information being communicated and the source and destination of the information. The tag  100 , POS device  200  and host network  300  may be adapted to encrypt and decrypt certain communications there-between. For additional detail relating to secure communications, attention is drawn to U.S. application Ser. No. 08/895,417, filed Jul. 16, 1997, entitled Cryptography Security for Remote Dispenser Transactions, in the name of William S. Johnson, Jr.; U.S. application Ser. No. 08/895,282, filed Jul. 16, 1997, entitled Memory and Password Organization for Remote Dispenser Transactions, in the name of William S. Johnson, Jr.; and U.S. application Ser. No. 08/895,225, filed Jul. 16, 1997, entitled Protocol for Remote Dispenser Transactions, in the name of William S. Johnson, Jr. The disclosures of each of these applications are incorporated herein by reference. U.S. application Ser. Nos. 08/649,455 and 08/759,733 and provisional application Ser. No. 60/060,066 disclose further details on similar communications systems and are also incorporated herein by reference. 
     The tag  100  is preferably integrated into a small carrying medium, such as a module mounted in or on a vehicle  12 , a transaction card  14  or a key fob  16 . Regardless of the medium carrying the tag  100 , the tag is preferably designed to provide remote bi-directional communications with the fuel dispenser  200 . Preferably, the fuel dispenser  200  is placed in a fuel dispensing environment  20 , and in particular, at each of two fueling positions  24  of the fuel dispenser  22 . The dispensers are operatively associated with a central station store  26  by a conventional wire system. The store  26  may house a convenience store as well as one or more restaurants, a car wash or other commercial establishment. 
     Many fuel dispensing environments  20  provide other goods and services, such as fast food and car washes. Generally the store  26  will include a central site controller  28  to provide central control functions for the entire site including each dispenser  22 . Each dispenser, and its respective POS (point-of-sale) electronics, generally communicates either directly, or indirectly with the central site controller  28 , which in turn may communicate with the host network  300  via a telephone network  30 . The host network  300  generally provides authorizations and other data for the various transactions attempted at each fuel dispenser  200 . 
     In addition to communicating with the fuel dispensers  200 , the transponders  100  are also adapted to communicate with various other local sources  32  for various informational and transaction-type functions. These local sources  32  may include any number of goods or service providers, such as local quick-serve restaurants. 
     One embodiment of the tag  100  is shown in FIG.  2 A. Communications electronics  102 , adapted to provide remote communications with various remote sources, includes a transmitter  106  and receiver  108  having associated antennas  110 ,  112 . The transmitter  106  and receiver  108  operate to transmit data from and receive data into the remote communications unit  100 . The communications electronics  102  may also include a battery power supply  114 , a communication controller  116  associated with a memory  120  having the software  122  necessary to operate the communications electronics  102  and communicate with the control electronics  104 . Serial communications between the communication electronics  102  and the control electronics  104  is provided via the input/output (I/O) ports  124 ,  138  associated with the respective electronics. The communication electronics  102  provide a clock  128  signal to the I/O port  138  of the control electronics  104 . The control electronics  104  may include a controller  130 , memory  132  and software  134  to provide remote processing. The memory  120 ,  132  may include random access memory (RAM), read only memory (ROM), or a combination of both. Notably, the communication controller  116  and the general controller  130  may be integrated into one controller. Similarly the software and memory of the communication and general control modules may be merged. Notably, the communication electronics  104  and communication electronics  102  may be combined, and may also include encryption hardware or software. 
     As shown in FIG. 2B, the communication and general control electronics, as well as any associated controllers may be integrated into a single controller system and/or integrated circuit. In such cases, a single controller  115  is associated with memory  117  having any software  119  necessary for operation. In such an integrated system, the controller  115  will carryout any control functions. 
     The communication electronics  102  may be the Micron MicroStamp™ produced by Micron Communications, Inc., 8000 South Federal Way, Boise, Id. 83707-0006. A detailed description of the MicroStamp™ is provided in the data sheets and the MicroStamp Standard Programmers Reference Manual provided by Micron Communications, Inc. These references and the information provided by Micron Communications on their website at HTTP://WWW.MCC.MICRON.COM are incorporated herein by reference. The Micron MicroStamp™ is an integrated system implementing a communications platform referred to as the MicroStamp™ standard on a single CMOS chip. The communications controller  116  preferably provides a spread spectrum processor associated with an eight-bit microcontroller. The memory  120  includes 256 bytes of RAM. The receiver  108  operates in conjunction with the spread spectrum processor and is capable of receiving direct sequence spread spectrum signals having a center frequency of 2.44175 GHz. The transmitter  106  is preferably a differential phase shift key (DPSK) modulated back-scatter transmitter transmitting DPSK modulated back-scatter at 2.44175 GHz with a 596 KHz sub-carrier. Notably, any type of communications scheme is acceptable, and the invention should not be limited to those discussed in the preferred embodiment. 
     In order to save power and extend battery life, the communication electronics  102  may operate at a low-current sleep mode until an internal programmable timer causes it to wake up. The communication electronics  102  determines whether there is a properly modulated signal present and, if not, immediately returns to the sleep mode. The modulated signal, which the communication electronics  102  monitors once it awakens, is provided by the fuel dispenser  200  or one of the local sources  32 . If a properly modulated signal is present, the communication electronics  102  processes the received command and sends an appropriate reply. The communication electronics  102  then returns to the sleep mode. The communications electronics  102  causes the control electronics  104  to awaken as necessary to process data, receive information, or transmit information. 
     As seen in FIGS. 3 and 4, a fuel dispenser  200  will preferably include a control system  202  having communications electronics or interrogator  204  associated with an automatic gain control electronics  206  and one or more antennas  208 . The control system  202  will also have sufficient memory  210  for operation. The control system  202  may also be associated with various displays  212  and input devices  214 , such as keypads or touch screens. An audio system  215  may also be provided. 
     The dispenser  200  may also be equipped with a card reader  216 , cash acceptor  218  and a receipt printer  220  for memorializing transactions. Each dispenser  200  is typically equipped with a conventional fuel supply line  222 , metering device  224 , delivery hose  226  and a nozzle  228 . The metering device  220  communicates data relating to the volume of fuel dispensed along line  229  to the control system  202 . In addition to the hardware described, the dispenser may include a vapor recovery system, flow control valves and related control hardware and electronics. 
     With reference to FIG. 4, the dispenser  200  is adapted to communicate with a tag (not shown) and the central control system  28 , which may also communicate with the host network  300  through a standard telephone interface  30 . The central control system  28  may include communications electronics  34  and a memory  36  having the requisite capacity and software necessary to run the control system and facilitate communications to and from the dispenser and host network. 
     As shown in FIG. 5, the dispenser control system  202  and communications electronics  204  will preferably operate in association with automatic gain control electronics  206 . These systems will operate together to amplify a signal received from a tag to a normalized level to ensure proper reception and demodulation at receiver  240 , which provides a demodulated output to a microcontroller  230  of the control system  202 . The demodulated output represents information transmitted from the transponder to the dispenser. The microcontroller  230  will receive the demodulated information and process the information accordingly. 
     The signal received at antenna  208  is initially sent to a low-noise amplifier (LNA)  241  having feedback resulting in the normalized output, which is sent to receiver  240 . The normalized output is also sent to the feedback circuitry in the automatic gain control electronics  206 . These feedback components include a diode  242 , capacitor  244 , amplifier  248 , and a potentiometer  246 . The potentiometer  246  is connected between power (vcc) and ground and is used to provide a reference voltage at the inverting input of amplifier  248 . 
     The normalized signal from the low noise amplifier  241  is rectified through the diode  242  and charges capacitor  244  to a DC level indicative of the normalized output level of the low noise amplifier  241 . The amplifier  248  provides an output indicative of the voltage differences received at the inverting and non-inverting inputs. This difference is indicative of the difference between the normalized output of the low noise amplifier  220  and the voltage reference set by the potentiometer  246 . The output of amplifier  248  is proportional to the difference between the reference and the normalized output of the low noise amplifier  241  and is used to control the gain of the low noise amplifier  241 . Thus, amplifier  248  will adjust the gain of the low noise amplifier  241  so that the normalized output of the low noise amplifier  240  results in a DC value at the non-inverting input equal to the reference value appearing at the inverting input of the amplifier  248 . The output of the amplifier  248  is also sent to the analog to digital converter  234 , which provides a digital string indicative of the amount of gain necessary to bring the signal originally received at antenna  208  up to a normalized level at the output of the low noise amplifier  241  and received by the receiver  240 . The microcontroller will receive the digital string and preferably associate the string with a tag identification number (ID) in memory  2   10 . Preferably, the signal received at the antenna  208  will include the tag ID. 
     In other words, when a signal from a tag appears at antenna  208 , the communication electronics  204  and automatic gain control electronics  206  operate to normalize the signal for reception at the receiver  240 , provide a value indicative of the amount of gain necessary to provide the normalized signal for reception and demodulate information on the received signal for the microcontrol system  202 . Preferably, the communication electronics will take the form of an interrogator having the automatic gain control electronics integrated therein. The interrogator will provide an indicator of signal strength as well as the received signal itself to the control system  202 . 
     In operation, tag arbitration may operate according to one of two basic processes. The first process creates a memory stack inside the intrinsic memory of the applicable tag. The tag records the short term history of any attempts by dispensers to access the tag along with attributes that indicate the quality of the interaction. Examples of these attributes include signal strength (i.e., the inverse of the gain signal determined above), number of errors recorded per transmission, and number of attempts at communication without completion. These latter attributes may be determined using hardware, software and techniques apparent to those of ordinary skill in the art. All of these attributes, or similar attributes, would indicate the quality of the interaction between the tag and the dispenser. Since signal strength, error rates and successful connection rates degrade with physical distance from the dispenser&#39;s communication electronics, degradation of the attributes is a representative indicator of the physical distance between the dispenser and the tag. For arbitration, the dispensers place their interaction data and attributes into any tag they read and other dispensers do the same, while preserving the data from past interactions. The dispensers retrieve the information stored in the tags. The multiple dispensers review the memory records within the tag and can determine that other dispensers have recently been writing to the tag. Each dispenser independently makes a determination based on the interaction attribute history as to which of the dispensers was closest to the tag and, thus, should be allowed to communicate solely with the tag in question. 
     The second, and preferred, process provides similar arbitration, with the exception that arbitration data is not stored in the tag, but is stored at the central site control system memory  36  (or perhaps in the dispensers or other associated system). In the latter process, the tag ID is stored in association with the dispenser communicating with the tag and the attribute indicative of proximity. The central control system  28  polls the various dispensers, updates the attribute records, and determines the dispensers closest to the respective tags. In any of the systems, the respective control systems may monitor movement, location and continued presence of any tag with respect to any of the dispensers communicating with the tag. 
     Turning now to FIGS. 7 and 8, the process of the first embodiment will be described. In this embodiment, interaction histories between the various dispensers and the given tag are stored in the tag&#39;s memory  132 . The dispenser communicating with the tag will examine the accumulated data stored on the tag and update the data as necessary for each interaction. As shown in FIG. 7, dispensers A, B and C either are or have recently communicated with the tag shown. The most recently updated history of interactions are shown in FIG. 8, which depicts the tag memory  132  and the history stored therein. The tag memory includes a series of interaction fields linking a dispenser with the relative strength of the communication associated therewith. For example, the tag memory indicates the most recent communication was made with dispenser A and the strength field has a value  200  stored in association with the communication with dispenser A. In this example, the strength field value (i.e., the gain required to normalize the reception) is inversely proportional to the distance between the tag and the dispenser. 
     In this embodiment, the data string from the automatic gain control electronics  206  will be lower for strong signals because the amount of gain necessary to amplify the signal received at the antenna  208  to a normalized level is low. As can be seen in FIG. 8, the most recent communications with dispensers A, B and C (i.e., the top three records) indicate interaction strength values of  200 ,  35  and  5 , respectively. This means that dispenser C is the closest to the tag, dispenser A is the furthest from the tag, and dispenser B is between A and C. The last three fields indicate communications with dispensers A, C and B, in that order, with resulting strength values of 175, 15 and 55, respectively. The values indicate that during the earlier sequence of communications with the three dispensers, dispenser C remained the closest and dispenser A was the furthest away from the tag. The strength values also indicate the tag was further away from dispenser C and closer to dispensers B and A than at the times of the more recent series of communications. From these values, the control system can determine that the tag is moving left to right, across drawing FIG. 7 (i.e., towards dispenser C from a direction closer to dispenser A). 
     With these concepts in mind, FIGS. 6A and 6B illustrate the flow of the process that begins in block D 400 . The dispenser transmits an interrogation signal (block D 402 ), which may include a dispenser and/or position identification number, to any of the tags within communication range. A tag receives the interrogation signal (block T 404 ), determines the dispenser ID (block T 406 ) and transmits a response signal including the transponder ID and dispenser ID (block T 408 ). The dispenser receives the response signal (block D 410 ) and monitors an attribute of the signal (block D 412 ) to determine the relative signal strength and/or proximity of the responding tag to the dispenser. Notably, the response signal transmitted from the tag may be received at various dispensers simultaneously and each dispenser will receive the signal, monitor for signal attributes and otherwise function concurrently as discussed herein. 
     The dispenser may determine the transponder ID and the dispenser ID from the received response signal (block D 414 ) and transmit the attribute values, the associated transponder ID and the dispenser ID (block D 416 ). The various tags in the communication field receive the transmission and determine whether to accept or ignore the transmission based on the transponder ID. In other words, the tags likely receive signals intended for other tags in the communication field. Preferably, the transponder ID of the intended tag or other indicia allow the receiving tag to recognize communications intended for that particular tag and ignore communications directed to another tag. Thus, the receiving tag receives the transmitted attribute values and the transponder and dispenser ID&#39;s (block T 418 ) and determines if communications were directed at the particular tag (block T 420 ). If the communications were not meant for the tag, the transmission is ignored (block T 422 ) and the tag waits to receive a communication directed to the tag (block T 418 ). 
     If the communications are directed to the tag, the tag stores the attribute values in association with the dispenser ID (block T 421 ) and transmits historical information relating to the historical interaction information, including attribute values and associated dispenser ID&#39;s (block T 426 ). The dispenser receives the historical information (block D 428 ) and analyzes the attribute values therein associated with each dispenser for the various communication entries (block D 430 ). The dispenser determines the most proximate dispenser based on the current and historical information (block D 432 ). The dispenser next determines if it is the most proximate dispenser to the tag (block D 434 ). If it is not the most proximate dispenser, communications with that particular tag are discontinued (block D 436 ) and the process returns to the beginning (block  438 ). If the dispenser is the most proximate to the tag, the dispenser continues with communications and possibly the fueling operation (block D 440 ). During this period, the dispenser may continue to monitor communication attributes to derive the tag&#39;s location, determine if the tag is moving, and/or check for the continued presence of the tag. 
     Preferably, the dispenser updates the tags and transmits new attributes with each series of communications to the tag throughout the communication process (block D 442 ) and, at the end of fueling, the process will return to the beginning (block D 444 ). Notably, each dispenser in the fueling environment may be operating in the same manner. That is, various dispensers may be communicating with various tags to independently determine the dispenser closest to the tag, and each tag may communicate with various dispensers in a complementary fashion. Thus, each dispenser independently and concurrently arbitrates among the various tags to select the tag most likely to be associated with a fueling operation. 
     If a dispenser reads an attribute history and determines its identity as the last recorded contact, the dispenser may simply overwrite the last entry. If the dispenser sees its identity in the record along with the identities of other dispensers that have entered attribute records subsequent to the dispensers last communication, then the currently communicating dispenser may add additional records and preserve all past records, including those of other dispensers. Given that the number of records are of the finite number, it is preferred that new entries will destroy old entries in a first in-first out record structure. 
     Furthermore, the memory record  132  may be configured so that two or more competing dispensers are allowed to record a number of record attributes into the attribute history. The memory record would recycle and overwrite its oldest entries after a maximum number of entries for a particular dispenser is reached. In this way, a number of entries can be supported from each of the competing dispensers in order for each dispenser to independently calculate any average or normalized results so that a location decision can be made. 
     In the second and preferred embodiment, the attribute and communication history is not stored in the tag&#39;s memory. The historical information is stored in a database apart from the tag and, preferably, at the central site control system  28 . This process is shown in the flow chart of FIGS. 9A and 9B in association with FIGS.  10  and  11 , which depict the dispenser and central control system communicating with a transponder (FIG. 10) and the central control system&#39;s memory record associated with the transponder ID, communicating dispenser, and corresponding attribute value (FIG.  11 ). Like the historical record shown in FIG. 8 for the first embodiment, the attribute record shown in FIG. 11 represents historical communication attributes recorded during prior communications. These records are associated with a particular transponder since they are not stored on the transponder. In other words, the historical data is simply stored in a different location than the first embodiment and associated with the transponder to which the communication relates. 
     In operation, the process begins (block D 500 ) where an interrogation signal is transmitted with a dispenser ID to the various tags in the communication field (block D 502 ). The tag receives the interrogation signal (block T 504 ) and transmits a response with the tag ID and dispenser ID (block T 506 ). 
     Next, the dispenser receives the response signal having the tag ID and dispenser ID (block D 508 ) and monitors attributes of the received signal (block D 510 ). The dispenser determines the transponder and dispenser ID from the received signal (block D 512 ) and sends these ID&#39;s along with the associated attribute values to the central control system (block D 514 ). The central control system receives the transponder ID, dispenser ID and associated attribute value (block C 516 ) and stores this information in the central control system&#39;s memory  36  (block C 518 ). 
     The central control system then analyzes the attribute values of the various transponders with respect to the various dispensers (block C 520 ). The central control system determines the transponder most proximate to the dispenser based on this information (block C 522 ) and operates to have the dispensers communicate with the transponders most proximate thereto in a fashion similar to that shown in blocks C 502  through C 520  (block C 524 ). 
     The control system continues to monitor the location of the transponders, the movement of the transponders with respect to the dispensers and/or the presence or absence of the transponders in the various communication fields (block C 526 ). Throughout the communication iterations, the various attribute values and historical records for each of the communications between the dispensers and transponders will be updated (block C 528 ) until the fueling operation is ended, wherein the process will return to the beginning (block C 530 ). As can be appreciated, if during fueling this continued monitoring indicates movement of the vehicle equipped with the tag in question, fueling can be terminated to avoid fuel spillage, and alarms can sound to remind the driver that the nozzle is still in his filler pipe. 
     Preferably, each dispenser will have communication electronics associated with each fueling position. For example, one interrogator may be controlled in cooperation with antennas for two fueling positions. The interrogator may have automatic gain control electronics  206  and be configured to transmit proximity values and transponder ID&#39;s to the central control system  28  for arbitration. The central control system  28  will know from which dispenser and fueling position the information is to be received or each dispenser will transmit the information along with the transponder ID&#39;s and proximity values. Arbitrating at the central control system allows overall transponder monitoring throughout the fueling environment. The database kept at the central control system  28  will preferably include transponder ID&#39;s associated with fueling positions or interrogator and proximity values received therefrom. The central control system will be able to effect polling at any interrogator at each dispenser by causing the interrogator&#39;s transmitter to transmit a polling signal causing the transponders receiving the polling signal to transmit a response signal including the transponder ID. Any of the interrogators receiving the response signal will generate a proximity value, preferably using the automatic gain control electronics. The proximity values and transponder ID&#39;s will be sent to the central control system for arbitration to determine the interrogator most proximate to the transponder. 
     Referring now to FIGS. 12A-12C, a basic overview of the preferred operation of the central control system is shown. The process begins at block  1200  where the central control system effects polling (block  602 ) of the interrogators throughout the dispenser forecourt. Preferably, the dispenser interrogators are caused to transmit the polling signal independently of other interrogators to reduce the possibility of confusing response signals from the various transponders present in the forecourt. Preferably, each interrogator is sequentially activated to transmit the polling signal and receive response signals. Although each of the interrogators may be activated to transmit polling signals simultaneously, activating individual interrogators or certain groups of interrogators is preferred. Once polling is effected, the control system will receive proximity values (block  604 ) and transponder ID&#39;s (block  606 ) from the dispensers. The control system will check to see if any new tags responded in the most recent polling (block  608 ) by comparing the received transponder ID&#39;s with the ID&#39;s already stored in the database. If a new transponder is present, a timer is set (block  610 ) and the new transponder is assigned to the first dispenser recognizing its presence. This is referred to as assigning a control token for the transponder to the corresponding dispenser fueling position or interrogator (block  612 ). 
     At this point, the control system may effect another polling (block  614 ), receive proximity values and transponder ID&#39;s (block  616 ), and wait for the timer to time out (block  618 ). The timer is set for a predetermined time likely to give the new transponder time to settle or stop at a particular fueling position associated with an interrogator. Once the timer times out, the control system effects polling (block  602 ), receives proximity values (block  604 ) and associated ID&#39;s (block  606 ), and checks for the presence of any new tags (block  608 ). 
     Assuming there are no new tags during this polling, the control system updates the database with the new proximity values for each dispensing position or interrogator and arbitrates tag location (block  620 ). Arbitration preferably includes a comparison of proximity values for any given transponder associated with any interrogator receiving response signals from that transponder. The control system will determine which interrogator is most proximate to the responding transponders (block  622 ) and determine if any transponder assignments need to be changed. In other words, the arbitration process determines if the assignment of one transponder to a certain interrogator needs to be changed because that transponder is closer to a different interrogator than it was during a previous polling. If a change is necessary, the control token associated with the transponder will be associated with the interrogator most proximate the transponder during the most recent polling. If a change is necessary, the control system will assign the control token to the interrogator most proximate the transponder (block  624 ). If no change is necessary, the control token assignment remains the same for the particular transponder. 
     The process will next determine if the tag is at a standstill (block  626 ). This is accomplished by comparing proximity values for a certain transponder at an assigned interrogator over consecutive pollings. If the tag is not at a standstill, the process will again effect polling (block  602 ) and continue the process as described above. 
     If the tag is at a standstill, the control system will start a tag session (block  628 ) and begin to authorize the tag (block  630 ). During authorization, the control system will send the transponder ID along with any available account information to the host (block  632 ). The control system will request authorization (block  634 ) and receive an answer accepting or declining authorization for the given transponder (block  636 ). If authorization is declined (block  638 ), the process ends for that particular transponder (block  640 ). If the transponder is authorized, the control system will preferably effect polling (block  642 ) and receive proximity values and transponder ID&#39;s from the various interrogators. Polling after a transponder is authorized is preferred because during the authorization process the transponder may have moved or communications may have been lost between the associated interrogator and the transponder. Thus, after receiving the additional polling after authorization, the control system will determine if the transponder has been moved or removed (block  646 ). If the transponder is moved, the control system will effect additional polling (block  648 ) and check earlier arbitration results to see if the tag has moved or if communications have been reestablished. Next, the control system will determine whether to pass control of the transponder or token to another interrogator (block  652 ). If communications are reestablished and it is determined that the transponder has not moved from earlier pollings, the control system initiates the start of a fueling operation (block  654 ) and continues with the operation until fuel has ended (block  656 ) wherein the process ends (block  658 ). If communications are not reestablished or it is determined that the transponder has moved during the authorization process, the central control system will revert back to block  602  to effect polling and rearbitrate to determine to which interrogator the transponder is most proximate and if the transponder needs to be reassigned to new interrogator or fueling position. 
     Determining whether to keep historical data in the tags or at the central control system will depend upon the requirements of the application. Keeping the information in the respective tags allows each dispenser to independently arbitrate which tag is most proximate. These decisions are going on in parallel and do not require communications between the dispensers to facilitate the arbitration. Since each dispenser is provided with identical historical data and operates on that data with identical decision processes, each dispenser will arrive at the same decision. However, certain applications may find benefit in allowing communications between the dispensers through the central control system. The first embodiment allows communications to occur between the dispenser and tag at a much higher rate, because communications are not required between the dispenser and central control system for arbitration. The second embodiment may reduce communication rates, but will provide more centralized control and location monitoring throughout the fueling environment. 
     Various other modifications and improvements will occur to those skilled in the art upon reading the foregoing description. As noted, it is preferable to use one interrogator in cooperation with communication electronics and/or antennas configured to cover both dispenser positions. Alternatively, each side may have dedicated communication electronics and/or interrogators. In either situation, arbitration will typically determine not only the dispenser, but also the position a transponder is most proximate. It should be understood that all such modifications and improvements have been omitted for the sake of conciseness and readability but are properly within the scope of the following claims.