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TIME BALANCE BASED PREPAID SUBSCRIBER DATABASE AND REPORTING
 This application is related to and claims priority from a co-pending U.S. Provisional Application No. 60/285, 990 to Ung et al., entitled "Prepaid First In-First Out Rating", and filed Apr. 25, 2001, the entirety of which is expressly incorporated herein by reference.
BACKGROUND OF THE INVENTION  1. Field of the Invention
 The present invention relates generally to wireless carriers, Internet Service Providers (ISPs), and information content delivery services/providers. More particularly, it relates to wireless telecommunications, ANSI-41D Wireless Intelligent Network (WIN) applications, and prepaid applications.
 2. Background of Related Art
 In recent years, the telecommunication industry has seen an explosive growth both in the particular types of services offered and in the number of service providers. Among the numerous services now being offered, prepaid call service may be one of the fastest growing segments in the telecommunication industry today, particularly in the wireless device sector.
 FIG. 4 depicts a simplified telecommunication system 100 including an Advanced Intelligent Network (AIN) associated with wireless services and landline services. Exemplary landline systems include a private branch exchange, public pay phones, or home or business telephones serviced by Plain Old Telephone Service (POTS) 111. Exemplary wireless systems include a Personal Communication Service 108, a paging system 109, or a cellular system 110 or other wireless digital telephone system.
 The system elements shown in FIG. 4 are linked via a separate high-speed messaging network called Signaling System 7 (SS7) 112, used to support a variety of special services and advanced call-handling features across multiple vendor domains. Signal Transfer Points (STPs) 106 are tandem packet switches that route SS7 messages among SCPs and SSPs. Switch Service Points (SSPs) 107 are distributed switching nodes that send and receive data from the wireless 110 or landline 111 telecommunication systems for interaction with a Services Control Point (SCP) 101. The SCPs 101 centrally control telephone services provided to subscribers from diversely located switching systems.
 An SCP 101 typically includes a computer 102, a database 103, and programmed service logic 104 which manages several system features, including prepaid services. By accessing SCP intelligent nodes, subscribers are able to design and control their own services and customize features without telephone company involvement, provided the feature is offered by the local carrier.
 With the advent of the AIN, advantages to the subscribers are numerous. For instance, the service logic 104 can be programmed to implement advanced call handling and service features such as Intelligent Caller Data, Disaster Routing, Intelligent Call Redirection, Intelligent One-Number Calling, Intelligent Call Screening, Automatic Callback, Interactive Voice Response (IVR) or speech recognition, bandwidth on demand in order to support multimedia appli
cations, custom billing and calling card services. The service logic 104 of the AIN can also be programmed to maintain subscriber accounts for prepaid services.
 A Service Management System (SMS) 113, linked to the SCP, creates and introduces subscriber services. A billing system 105 is generally linked to the SCP 101. The billing system is generally responsible for tracking and billing subscribers for various services, as well as for providing remaining balance information to prepaid subscribers.
 As the name implies, a prepaid call service allows a customer of the service to pay their service provider in advance for the use of their provider's network resources in making a telephone call, e.g., a wireless telephone call. The prepaid call service provides, among other things, an alternative option for a telephone user who might otherwise not be able to obtain the traditional postpaid telephone services because, e.g. of a bad credit rating, or of being in a geographical area where post paid service is unavailable. Also, prepaid call services allow a convenient way for a third party to prepay for a subscriber's subsequent calls (e.g., a parent or guardian prepaying for call services for their child away at college). The world-wide prepaid call services market is projected to grow tremendously in the next few years, encouraging service providers to add or upgrade their own prepaid service offerings to meet the demand.
 To implement a prepaid call service for a particular subscriber, that subscriber caller must first deposit a sufficient amount of funds into an appropriate account, e.g., using cash, credit card, debit card and/or other means, to enable the ability to place subsequent telephone calls.
 Alternatively, pre-deposited scratch card accounts are readily available for purchase in many convenience stores, providing a simple and direct method for a subscriber to initiate, maintain and/or replenish a prepaid account. Scratch cards may be utilized to repeatedly replenish a particular subscriber's prepaid account, even before a previous replenishment is exhausted. Scratch cards are typically available in varying pre-deposit amounts, e.g., $25, $50, etc. A given value card (e.g., a $30 card) provides a given amount of prepaid call minutes (e.g., 60 minutes) based on a desired call rating.
 While scratch cards are convenient, they cause some difficulty to service providers as compared to other replenishment methods (e.g., credit cards, etc.) For instance, each scratch card offer typically provides a different rate plan, and the service provider essentially "switches" to the new rate plan as prior scratch card replenishments become exhausted. As an example, a $30 scratch card might offer a rate plan of $0.50 per minute providing 60 minutes of time, while a $50 scratch card might offer a rate plan of $0.40 per minute providing 125 minutes of time.
 Since most service providers offer scratch cards that have different face values and/or rate plans, it is likely that a particular subscriber will replenish their prepaid accounts with scratch cards of differing amounts and/or differing rate plans. Thus, a particular subscriber might have various rate plans "in queue" as their prepaid amounts become used up.
 Conventional prepaid services utilize a First-In/ First-Out (FIFO) control and billing method to handle
switch card replenishments. This conventional FIFO billing and control method typically chronologically stores and manages a list of scratch card face values and associated rate plans for each prepaid subscriber. Usually the rate plan of the next stored replenishment for any particular subscriber will take effect only after depletion of any prior replenishment.
 The FIFO control and billing technique can report an accurate dollar amount remaining to a particular subscriber, but can provide only an estimate as to their remaining time. This is because the FIFO control and billing technique calculates the total available minutes provided by the various scratch cards by dividing the total dollar value of all replenishments (e.g., the current and all subsequently loaded scratch cards) by the replenishment rate plan which is currently active (i.e., which is currently being depleted) in dollars per minute.
 For example, if a subscriber replenishes with a $25 scratch card providing a rate of $0.35 per minute, then later replenishes with a $50 dollar scratch card providing a rate of $0.25 per minute, the conventional FIFO billing and control approach would divide the total balance of $25+$50=$75 by the current (older) rate plan (e.g., ($75)/($0.35 per minute), resulting in an indication to a subscriber that their remaining prepaid balance is adequate to purchase 214 more minutes. However, the subsequent rate plan is lower than the prior rate plan, and errors and confusion result to the subscriber, who actually has 57 minutes more than the 214 minutes reported to them, i.e., they will actually have 271 minutes remaining once the rate plan changes. Ultimately, this leads to confusion on the part of the subscriber who was notified that only 214 minutes remained.
 To avoid this confusion, the service provider has to ensure its subscribers that their available minutes will be recalculated and re-reported after the depletion of the active card balance. Once the final scratch card balance is used, the time remaining will finally be accurately reported. However, if the subscriber has a number of replenishment cards in queue, the current approach may not accurately or correctly track or report the correct total minutes available to the subscriber.
 FIG. 5 shows the data elements of a single prepaid subscriber in a conventional subscriber database. As shown in FIG. 5, information must be maintained in the subscriber database 103 for each replenishment. In particular, for a single subscriber, multiple replenishment entries 700 must be maintained if they have not yet been depleted by the subscriber. Each entry includes both the dollar value 704712 of the various entries, together with the corresponding rate 720-728. This database technique can become quite large, particularly if subscribers tend to have multiple replenishments remaining. Moreover, the technique is boundless for any particular subscriber (unless the service provider limits the number of un-depleted replenishments that a subscriber may store in their prepaid accounts).
 Valuable computer processing time and database capacity is conventionally expended to manage and store replenishment data with respect to each subscriber account, which might be better utilized for other purposes, e.g., other services offered by the service provider.
 Accordingly, there is a need for a prepay method and apparatus implemented in a telecommunications system
that more accurately and efficiently determines and reports the remaining time available for a given prepaid account balance replenished with scratch cards.
SUMMARY OF THE INVENTION
 In accordance with the present invention, a subscriber database in a prepaid system comprises a subscriber database entry for a plurality of prepaid subscribers. Each subscriber database entry comprises an amount of time remaining for subscriber use based on a plurality of replenishments having at least two different rate plans.
 A method of maintaining subscriber account balance information in a prepaid system in accordance with another aspect of the present invention comprises firstly recording a first replenishment of the subscriber account having a first rate. A second replenishment of the subscriber account having a second rate is recorded. A total dollar amount of the subscriber account is revised, including at least a portion of a dollar value of the first replenishment together with a dollar value of the second replenishment both based on the second rate.
BRIEF DESCRIPTION OF THE DRAWINGS
 Features and advantages of the present invention will become apparent to those skilled in the art from the following description with reference to the drawings, in which:
 FIG. 1 shows a block diagram of a telecommunication system including a time remaining determination module, in accordance with the principles of the present invention.
 FIG. 2 shows a flow chart of an exemplary process by which the time remaining determination module of FIG. 1 operates.
 FIG. 3 shows the data elements of an entry of a single prepaid subscriber in a subscriber database in a service provider network including a time remaining determination module, in accordance with the principles of the present invention.
 FIG. 4 shows a conventional telecommunication system.
 FIG. 5 shows the data elements of a single prepaid subscriber in a conventional subscriber database.
DETAILED DESCRIPTION OF PREFERRED
 The present invention provides an improved account balance reporting mechanism for a prepaid service in a communications system, particularly in a wireless telecommunications system.
 In particular, the inventive approach utilizes a reporting module which accurately accounts for and determines the total minutes remaining in a subscriber's account by accommodating and adjusting for each potentially different rate plan associated with each recharge or replenishment. This enables the service provider not only to accurately report the account balance in terms of time remaining at any convenient time (e.g., during the call process), but also to correctly manage the subscriber account and call duration.
 FIG. 1 shows a block diagram of a telecommunication system including a time remaining determination module, in accordance with the principles of the present invention.
 In particular, as shown in FIG. 1, a Switching Control Point 401 includes a time remaining determination module 400 and suitable scratch card replenishment log 407. Suitable service logic 404 is implemented to control the reporting of time remaining to the subscriber's as calculated by the time remaining determination module 400. The remaining elements shown in FIG. 1 are substantially otherwise as shown in FIG. 3 and as generally known in the art.
 While shown in FIG. 1 implemented in an SCP 101 of a wireless system, the time remaining determination module 400 may alternatively be implemented in a landline system, e.g., in an individual central office switch of a Public Switched Telephone Network (PSTN).
 The service logic 404 and time remaining determination module 400 shown in FIG. 1 are suitably adapted to perform the exemplary process shown in FIG. 2. FIG. 2 shows a flow chart showing exemplary replenishment or account recharge process 200 controlled by the service logic 404 and reported (at least in part) by the time remaining determination module 400.
 In step 201 of FIG. 1, a particular subscriber accesses a prepay call service of a particular service providers network 100, e.g., by dialing a telephone number supplied on the replenishment card.
 In step 203, the prepay call service may prompt the subscriber to enter a personal code or other password to properly authorize access to their prepay subscriber account. Thus, the subscriber is prompted by an IVR controlled by the SCP 401. Then the subscriber enters their personal code or other password using the dual tone, multi-frequency (DTMF) keypad, or by verbalizing the same if voice recognition capability is provided. The IVR passes the collected information to the SCP service logic 404.
 In response, the service logic 404 of the SCP 401 accesses the time remaining determination module 400 to obtain the time remaining balance of a relevant subscriber, as well as other otherwise conventional account information (e.g., dollar balance, account status such as active or closed, etc.) and reports the same to the relevant subscriber. The report may be provided to the relevant subscriber at the relevant wireless device, or at a different remote device (e.g., at a landline telephone).
 To provide an accurate measurement of time remaining (particularly in light of the possibility that the account may have been replenished at different rates), the time remaining determination module 400 accesses a scratch card log 401. The scratch card log 401 may maintain information regarding remaining replenishments, e.g., the dollar amount and rate for remaining value in the subscriber's account.
 Generally, the subscriber selects a replenishment (scratch) card to replenish their prepaid account selected according to the face value of "$Balance" and associated "Available Minutes". Given the selected card, consider the following equations:
Plan Rate=$Balance/Available minutes
Available minutes=$Balance/Plan Rate.
 Extending these equations to multiple replenishment scenarios, if Ratel=rate of the first replenishment card used, $Balancel=$Balance of the first replenishment card used, Rate2=rate of the second replenishment card used, and $Balance2=Balance of the second replenishment card used, then the total number of minutes purchased may be calculated as:
%Balancel %Balance2 Adjusted$Batance
 The Adjusted$Balance is preferably determined such that the Total Minutes is correctly calculated with most recent replenishment rate (e.g., Rate2). Solving the above equation for Adjusted $Balance, yields:
 This formula provides the basis for accurately calculating Total Minutes remaining based on the current stored dollar balance and plan rate in view of a subsequently deposited $Balance and associated plan rate.
 For example, suppose a subscriber has a stored account balance of $25 ($Balance) with a rate plan of $0.35 per minute. Thereafter, the subscriber replenishes an additional $50 with a scratch card (replenishment card) bearing a plan rate of $0.25 per minute. Given this scenario, the time remaining determination module 400 re-determines time remaining for the subscriber, preferably substantially at the time of the deposit, Adjusted$Balance=$25x(0.25/0.35)+ $50=$67.8571. If desried, the account balance may be preferably rounded in favor of the subscriber, e.g., to $67.86.
 Note that the Adjusted$Balance is a value for internal computational purposes for use by the time remaining determination module 400. In a case where there is a fee associated with a subscriber account such as a monthly surcharge, a rate plan change fee, a maintenance fee, etc., the prepaid system preferably debits this fee from the subscriber remaining balance. The Adjusted$balance can be used for such purpose, noting that this would effect (i.e., reduce) the number of minutes available or remaining.
 Total Minutes is also recalculated at the time of replenishment by dividing the Adjusted$Balance by the most recent plan rate as follows: Adjusted$Balance/Rate (new)=271 minutes.
 The Total Minutes are stored in the appropriate location (e.g., data entry 502) in the subscriber data entry 500 in the subscriber account database 403, and may be reported to the subscriber in accordance with otherwise conventional methods.
 This approach does not require the prepaid service database to store and manage a list of each unused replenishment deposit (e.g., as shown in FIG. 5). Rather, only the Total Minutes remaining 502, the current Adjusted$Balance 504, and most recently deposited rate plan rate 506 need be maintained for each subscriber entry 500, as shown in FIG. 3.