United States Patent 5,778,313
Fougnies July 7, 1998
Pre-paid cellular telephone system
Abstract
A pre-pay service unit uses pseudo-numbers to identify subscribers and
substitutes actual numbers to complete a call after verification of authenticity
and verification of a positive balance in a subscriber's account. The service
unit and the cellular telephone exchange data in the process of authentication.
For outgoing calls, a cellular telephone first transmits an "800" number and an
ANI. The "800" number is the telephone number of the pre-pay service unit, which
then requests number actually dialed. The cellular telephone responds with
dialed digits, a security code, and status data. If the information is correct,
the dialed digits are then passed to a local exchange carrier to complete the
call. For incoming calls, a pseudo-number directs the call to the pre-pay
service unit, which converts the pseudo-number to the actual telephone number of
a subscriber's cellular telephone.
Inventors: Fougnies; Douglas V. (Tempe, AZ)
Assignee: Cellexis International, Inc. (Tempe, AZ)
Appl. No.: 569961
Filed: December 8, 1995
Current U.S. Class:455/406; 379/114; 379/127; 379/144; 455/408; 455/409
Intern'l Class: H04Q 007/00; H04Q 007/38
Field of Search: 455/408,406,410,418,419,564,409
379/144,114,130,113,112,127,355,356
References Cited [Referenced By]
U.S. Patent Documents
5187710Feb., 1993Chau et al.379/114.
5216703Jun., 1993Roy379/355.
5309501May., 1994Kozik et al.379/58.
5353335Oct., 1994D'Urso et al.379/67.
5384825Jan., 1995Dillard et al.455/564.
5396545Mar., 1995Nair et al.379/91.
5404580Apr., 1995Simpson et al.455/89.
5408513Apr., 1995Busch et al.379/91.
5485505Jan., 1996Norman et al.455/419.
5509056Apr., 1996Ericsson et al.379/114.
5550897Aug., 1996Seiderman379/144.
5579376Nov., 1996Kennedy, III et al.455/433.
5583918Dec., 1996Nakagawa455/409.
5592535Jan., 1997Klotz455/406.
5722067Feb., 1998Fougnies et al.455/406.
Primary Examiner: Bost; Dwayne D.
Assistant Examiner: Legree; Tracy M.
Attorney, Agent or Firm: Cahill, Sutton & Thomas P.L.C.
Claims
What is claimed as the invention is:
1. A pre-paid, cellular telephone system comprising:
a plurality of subscriber cellular telephones, each telephone capable of
auto-answer and silent ring and including internal memory, a microprocessor, and
means for transmitting data from said memory;
wherein each of said cellular telephones is programmed to transmit a
predetermined first telephone number instead of dialed digits, followed by a
unique ANI code, on outgoing calls and is programmed to transmit the dialed
digits upon request and to include a unique security code with the dialed
digits;
a pre-pay service unit including a plurality of telephone communication
channels;
wherein said pre-pay service unit is identified by said first telephone number
and wherein said pre-pay service unit is programmed to request said dialed
digits for completing an outgoing call after recognizing a subscriber cellular
telephone by said ANI code and said security code.
2. The pre-paid, cellular telephone system as set forth in claim 1 wherein said
means for transmitting data includes a DTMF encoder/decoder.
3. The pre-paid, cellular telephone system as set forth in claim 1 wherein said
means for transmitting data includes a modem.
4. The pre-paid, cellular telephone system as set forth in claim 1 wherein said
subscriber cellular telephone scrambles the dialed digits with said security
code.
5. The pre-paid, cellular telephone system as set forth in claim 1 wherein said
subscriber cellular telephone transmits said dialed digits and said security
code seriatim.
6. The pre-paid, cellular telephone system as set forth in claim 1 wherein the
subscriber cellular telephones are each identified by a unique pseudo-DID number
for incoming calls and wherein said pre-pay service unit stores the actual MIN
numbers of the subscriber cellular telephones and converts the pseudo-DID digits
into the actual MIN of a subscriber cellular telephone to complete an incoming
call to the subscriber cellular telephone using the MIN.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application relates to U.S. application entitled "Prepaid Security Cellular
Telecommunications System" filed Nov. 15, 1995 and assigned Ser. No. 08/559,283,
which application is a continuation-in-part of an application entitled "Security
Cellular Telecommunications System" filed Dec. 23, 1994 and assigned Ser. No.
08/364,479.
BACKGROUND OF THE INVENTION
This invention relates to a cellular telephone system that allows only pre-paid
subscribers to complete cellular telephone calls and, in particular, to a fraud
resistant, pre-paid subscriber system that does not require special hardware
connections to existing telephone networks.
A cellular telephone is a multi-frequency, portable transceiver, typically
constructed with state of the art integrated circuits and capable of
transmitting voice and digital data reliably almost anywhere in the world.
Except for cost, a cellular telephone would likely be the appliance of choice
for every person in the country. A cellular telephone costs at least three times
as much, per month, as a "land line," i.e. as a telephone connected by wire to a
public switching network. Despite the sophistication and quality of cellular
telephones, the relatively high cost of a cellular telephone is not the
telephone itself but the charges for the use of the telephone. Unfortunately, a
significant portion of the cost of the system is due to theft of services and
many techniques for detecting or thwarting theft have been proposed or
implemented.
Some security systems rely on calling patterns to detect theft and such systems
are prone to false positives, i.e. incorrectly identifying a legitimate call as
an illegal call. Also, such systems require a number of calls to detect theft,
which means that, if the calls were illegal, the cost of the calls must be
absorbed by someone other than the caller. It is preferred to have a system that
can detect theft of service as soon as the theft is attempted.
Another aspect of cost is the ability of a subscriber to pay for services
compared to the subscriber's desire to use the services. Many subscribers sign
up on the basis that the cellular telephone will only be used for emergencies
and then find themselves defining "emergency" progressively more broadly. For
many subscribers, it has been found beneficial to provide a pre-paid
subscription that is self-limiting in the sense that the service is terminated
when the payments are used up. U.S. Pat. No. 5,353,335 (D'Urso et al.) describes
a modified network architecture in which a special platform for pre-paid calling
service is connected to a node in a public, switched telephone network.
The above-identified, related application also describes a pre-paid, cellular
system. The system disclosed in the application requires no modification to
cellular telephones and, for outgoing calls, uses the automatic number
identification (ANI) from each cellular telephone as a file link to identify and
to authenticate the cellular telephone. Incoming calls are transferred to the
mobile telephone switching office (MTSO) in which a number of lines are reserved
for pre-paid subscribers. An incoming call is screened for a valid number and a
positive, pre-paid balance by the subscription service and is then passed on to
the subscriber. If the MTSO will not dedicate lines to pre-paid subscribers, a
significant geographic area is unavailable to a specific but viable market.
A system requiring no modification to the cellular telephone is most easily
implemented but the security of such a system is not as great as when the
cellular telephone is modified. A problem with a system requiring modification
to the cellular telephone is that physical access to the telephone is required.
In view of the foregoing, it is therefore an object of the invention to provide
a cellular telephone system for pre-paid subscribers in which the system is
transparent to existing telephone networks.
Another object of the invention is to provide a prepaid subscription service
that detects theft as it occurs and terminates the call.
A further object of the invention is to provide a prepaid cellular telephone
system that monitors both outgoing and incoming calls without the need for
dedicated lines at an MTSO.
Another object of the invention is to provide a secure, pre-paid cellular
telephone system requiring only software modification to existing cellular
telephones to adapt the telephones to the system.
A further object of the invention is to provide a secure cellular telephone
system in which modifications to a cellular telephone do not require physical
access to the telephone.
SUMMARY OF THE INVENTION
The foregoing objects are achieved in this invention in which a pre-pay service
unit uses pseudo-numbers to identify subscribers and substitutes actual numbers
to complete a call after verification of authenticity and verification of a
positive balance in the subscriber's account. The service unit and the cellular
telephone exchange data in the process of authentication. The pseudo-numbers are
combined with other data to provide a secure check of the identity of the
cellular telephone and the authenticity of the call. It has been found that
modifying a cellular telephone to share identification between the system and
the telephone increases the security of the system and enables the operation of
the system to be transparent to an MTSO.
In particular, for outgoing calls, the cellular telephone first transmits an
"800" number and the ANI. The "800" number is the telephone number of a pre-pay
service unit which receives the call. A switching network in the service unit
then requests the dialed number, which the cellular telephone transmits with a
security code and status data. If the data is authentic, the dialed digits are
then passed to a local exchange carrier to complete the call. For incoming
calls, a pseudo-number directs the call to a pre-pay service unit, which
converts the pseudo-number to the actual telephone number of a subscriber's
cellular telephone. After exchanging data with the subscriber's telephone, and
after verifying authenticity and credit balance, the call is completed. Both
incoming and outgoing calls can be monitored for charges and a call is
terminated if a subscriber's balance reaches zero.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the invention can be obtained by considering
the following detailed description in conjunction with the accompanying
drawings, in which:
FIG. 1 illustrates an outgoing call from a cellular telephone in accordance with
the prior art;
FIG. 2 illustrates an outgoing call from a cellular telephone in accordance with
the invention;
FIG. 3 illustrates an incoming call to a cellular telephone in accordance with
the prior art;
FIG. 4 illustrates an incoming call to a cellular telephone in accordance with
the invention;
FIG. 5 is a flow chart of an outgoing call in accordance with a preferred
embodiment of the invention;
FIG. 6 is a flow chart of an incoming call in accordance with a preferred
embodiment of the invention;
FIG. 7 is a block diagram of a cellular telephone suitable for use in the
invention; and
FIG. 8 is a block diagram of the apparatus used by the pre-pay service unit .
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an outgoing call from a cellular telephone to a conventional
telephone. Cellular telephone 10 transmits the dialed number followed by the
automatic number identification code that uniquely identifies telephone 10. This
data is received by mobile telephone switching office 12, wherein the number is
verified as a valid subscriber and, if so, the call is transferred to local
exchange carrier 14. Local exchange carrier 14 switches the call to the
appropriate land line connecting carrier 14 with telephone 16.
FIG. 2 illustrates the path of an outgoing call from a pre-pay subscriber
through a pre-pay service unit. The subscriber enters the desired destination
telephone number on cellular telephone 20 and then presses the "send" button.
Telephone 20 displays the dialed number but actually transmits a pseudo-number,
viz. an "800" number to mobile telephone switching office 12, followed by the
automatic number identification code of cellular telephone 20. The pseudo-number
is the number of a pre-pay service unit. An "800" number is used to obtain the
automatic number identification code of telephone 20.
Switching office 12 passes the call through local exchange carrier 14 and tandem
switch 22 to pre-pay service unit 24. Service unit 24 recognizes the automatic
number identification as a pre-pay subscriber and transmits back to cellular
telephone 20 a request for the number actually dialed. Cellular telephone 20
responds with the dialed number, which passes through switching office 12,
carrier 14, switch 22, and service unit 24 to local exchange carrier 26, which
switches the call to the appropriate land line for connection to telephone 16.
Thus, the number initially transmitted by a pre-paid subscriber is the number of
a pre-pay service unit, which then completes the call with the dialed number. In
the process, the pre-pay service unit monitors the calls and the account of the
subscriber to be sure that the call is genuine and that the account of the
subscriber is has a positive balance.
In FIGS. 1-4, a pre-pay subscriber is indicated by a cellular telephone symbol
and a non pre-pay subscriber is represented by a symbol of a conventional
telephone. This is solely for the sake of clarity. A pre-pay subscriber can call
anyone, including another subscriber. An outgoing call from a subscriber's
telephone is always a call to an "800" number and, therefore, always includes
the dialed number and the automatic number identification code. This
characteristic of cellular telephone service is used to direct all outgoing
calls to the pre-pay service unit, enabling the pre-pay service unit to monitor
all subscriber calls for authenticity and appropriate charges.
FIG. 3 illustrates an incoming call to a cellular telephone in accordance with
the prior art. In this case, the user dials the destination number on telephone
16 and the number is recognized as a cellular telephone number by local exchange
carrier 14. Carrier 14 transfers the call to mobile telephone switching office
12, which then authenticates the call and pages cellular telephone 10.
In accordance with the invention, the actual telephone number of the cellular
phone is known only by the pre-pay service unit and a pseudo-number is provided
to the public, including the subscriber. The pseudo-number is actually a number
belonging the pre-pay service unit. Thus, as illustrated in FIG. 4, a user dials
the pseudo-number on telephone 16 and local exchange carrier 26 recognizes the
number as belonging to pre-pay service unit 24. Upon receipt of the incoming
call, pre-pay service unit 24 looks up the actual number of cellular telephone
20 in a conversion table and transfers the number to local exchange carrier 14.
Carrier 14 recognizes the number as a cellular number and passes the call to
mobile telephone switching office 12 which authenticates the number and pages
cellular telephone 20.
For both incoming and outgoing calls, the pre-pay service unit is interposed in
the path of a call and converts the dialed number into a second number for
completing the telephone call. The pre-pay service unit is independent of the
mobile telephone switching office and is connected into the system by way of
land lines or its own cellular connections.
While intercepting telephone calls to or from a subscriber, the pre-pay service
unit exchanges data with the subscriber cellular telephone prior to completing
the call. The data exchange between the pre-pay service unit and a subscriber's
cellular telephone is illustrated in FIGS. 5 and 6. In FIGS. 5 and 6, a small
dot in the lower left hand corner of a rectangle indicates an action by the
subscriber's cellular telephone. A small dot in the lower right hand corner of a
rectangle indicates an action taken by the pre-pay service unit. A rectangle
with a dot in neither location represents an action taken by a public switching
network.
FIG. 5 is a flow chart of an outgoing call from a subscriber's cellular
telephone. In step 51, the subscriber dials the desired phone number. If the
cellular telephone has a display, the dialed number is displayed. In step 52,
the subscriber's cellular telephone actually transmits an "800" number followed
by the automatic number identification code. The telephone call is passed to the
pre-pay service unit, which stores the automatic number identification and opens
a channel to the subscriber's telephone. The pre-pay service unit then requests
the dialed number (step 54) and the subscriber's telephone responds (step 55)
with the number actually dialed and other data, such as roaming information, and
a security code. "Roaming" is the situation in which the cellular telephone is
outside of the service area of the subscriber. Service within the area is
considered a local call and service outside the area is subject to additional
charges for "roaming" and long distance.
After receiving the data from the subscriber's telephone, the pre-pay service
unit uses the automatic number identification to check the subscriber's account
for a positive balance and verifies the automatic number identification code
with the security code transmitted by the subscriber's telephone. If there is a
positive balance and the codes are authentic, the pre-pay service unit sends an
"off hook" signal to the mobile telephone switching office, step 57, and
transfers the call to the local exchange carrier, step 58, completing the call.
FIG. 6 illustrates the exchange of information between the pre-pay service unit
and a subscriber's cellular telephone for an incoming call. In step 61, a party
dials what he believes is the actual telephone number of a subscriber's cellular
telephone. In step 62, the local exchange carrier recognizes the number as
belonging to the pre-pay service unit and transfers the call accordingly. In
step 63, the pre-pay service unit looks up the pseudo-number in a table and
replaces the pseudo-number with the actual number of the subscriber's telephone.
In step 64, the pre-pay service unit checks the subscriber's account for a
positive balance, based upon the actual number of the subscriber, also known as
the mobile identification number (MIN).
In step 65, the pre-pay service unit retrieves a security code for the
subscriber's account and then passes the actual telephone number to a local
exchange carrier (step 66). The carrier passes the call to a mobile telephone
switching office for paging the subscriber's cellular telephone. Upon receipt of
the page, the subscriber's telephone goes off-hook, in what is known as
auto-answer mode, but does not ring. In other words, the subscriber's cellular
telephone must have the features of auto answer and silent ring. These features
are used in many, but not all, commercially available cellular telephones. To be
compatible with the invention, a cellular telephone must have both features.
After the subscriber's telephone goes off-hook, the pre-pay service unit sends a
security code to the subscriber's telephone, step 73. The subscriber's telephone
verifies the code, step 74, sends a verification code to the pre-pay service
unit and provides an audible ring, step 75. The pre-pay service unit verifies
the code and monitors the account of the subscriber for call duration and
billing. The subscriber "answers" the telephone call by pressing "send", step
77.
The exchange of data between the subscriber's telephone and the pre-pay service
unit makes it very difficult to steal services. If desired, the data transferred
between the subscriber's telephone and the pre-pay service unit can be scrambled
or encrypted. For example, in step 55 (FIG. 5) the DID number, roam code, and
security code need not be sent consecutively but can be mixed in a predetermined
sequence and sent as a single block of data. Similarly, the subscriber's
telephone can verify the code (step 74, FIG. 6) as it is received from the
pre-pay service unit or it can re-order the digits in a predetermined manner
prior to verification. Alternatively, one can use a checksum to verify the
digits or a checksum of selected digits for verification. The particular manner
for scrambling or encrypting data is a matter of choice.
FIG. 7 illustrates a cellular telephone suitable for use in the invention. In
particular, cellular telephone 80 includes microprocessor 81 coupled to memory
82 and to an I/O device such as encoder 83 and transceiver 84. Antenna 85 is
coupled to transceiver 84 for emitting the high frequency radio waves that
couple cellular telephone to the mobile telephone switching office. Most
cellular telephones transmit data in what is known as multiple frequency (MF) or
dual tone multiple frequency (DTMF) form. In accordance with the invention, a
cellular telephone, in addition to providing silent ring and auto answer,
includes at least a decoder for MF/DTMF signals.
A DTMF encoder/decoder handles numbers in base 10, i.e. the digits 0-9, as
opposed to binary numbers, the digits 0-1. In a preferred embodiment of the
invention, a cellular telephone includes a modem for transmitting binary data to
and from microprocessor 81 through transceiver 84. Some commercially available
cellular telephones include an encoder, a decoder, and a modem. For such
telephones, only the software and the data stored in memory 82 need be modified
to implement the invention. Transmitting a pseudo-number, waiting for a request
for data, comparing data with stored data, and sending a code stored in memory
are tasks that are easily implemented in software whether microprocessor 81 has
a rich instruction set or a reduced instruction set.
An advantage of the invention over the prior art is the ability to encode a
subscriber's cellular telephone remotely. Because the telephone includes a
modem, data can be transferred over telephone lines to the subscriber's
telephone, for example to change security codes or to modify the programming
within the telephone. Not only is physical access not required but this
capability enables one to sell telephones through a national chain of stores and
activate the telephones remotely. Similarly, if a subscriber moves, the
subscriber's "home" cell can be changed remotely to the new location. The memory
in the cellular telephone need only include an EAROM (electrically alterable,
read-only memory).
FIG. 8 is a block diagram of a pre-pay service unit. Unit 90 includes
microprocessor 91 connected to memory/mass storage 92 and line interface 93.
Memory/mass storage 92 contains the codes, account information, and tables for
translating incoming calls to the appropriate destination telephone number and
for monitoring the accounts of subscribers. Line interface 93 includes
appropriate circuitry for coupling land lines to microprocessor 91, encoding and
decoding MF/DTMF signals, and modems for transferring data to and from
subscribers. Printed circuit boards or cards are commercially available for
performing these functions and a array of cards is used in unit 90 for
connecting lines 96 to a public switching network. Lines 96 can be implemented
by wire, optical fiber, microwave links, or a cellular network. Line 94 is a
"WATS" or "800" line. More than one "800" number can be used, depending upon
loading.
A system incorporating the invention operates conventionally for billing, busy
signals, inadequate prepaid balance, and the like. A distinct advantage of the
invention is that attempted theft of services is immediately detected because of
the data exchange between a subscriber's cellular telephone and the pre-pay
service unit. Referring to FIG. 4, for example, if someone obtained the actual
dial-in number is for telephone 20, the pre-pay service unit cannot be by-passed
because telephone 20 awaits a security code before proceeding. Without the code,
the call is terminated and is counted as suspect in telephone 20. In a preferred
embodiment of the invention a fixed number of suspect calls, e.g. three,
disables telephone 20 until the telephone is physically returned to the pre-pay
service provider for correction. Similarly, without the security code, a call
cannot be placed from telephone 20.
The invention thus provides a cellular telephone system for pre-paid subscribers
in which the system is transparent to existing telephone networks and can
monitor both outgoing and incoming calls without the need for dedicated lines at
an MTSO. Theft is detected as soon as an attempt is made and the call is
terminated. The invention can be implemented with commercially available
cellular telephones and switching equipment, requiring only software
modification.
Having thus described the invention, it will be apparent to those of skill in
the art that various modifications can be made within the scope of the
invention. For example, a rotating coding system can be used within the cellular
telephone. That is, for step 55 (FIG. 5), one of several possible codes is
transmitted for each outgoing call. Both the telephone and the pre-pay service
unit have the same table of codes and increment through the table in step.
Attempted thefts of service will very likely send the wrong code. The tables and
codes are different for each subscriber.
* * * * *
