Method and apparatus for determining the precise location of a modified cellular telephone using registration messages and reverse control

Claims

What is claimed is:

1. A system for tracking an object comprising,

a first cellular radiotelephone system comprising cellular radiotelephones, cellular transmitting/receiving cells and a mobile telephone switching office,

a command and control center coupled to said first cellular radiotelephone system,

a modified cellular radiotelephone actable to automatically switch to a power on state, initiate a call to said command and control center, transmit a message including its identification; and maintain a communication channel with said command and control center,

said modified cellular radiotelephone and first cellular system automatically performing a cell registration process which identifies to the first cellular system and said command and control center the cell in which said modified radiotelephone is located,

said command and control center including a computer for computing and displaying the location of said modified cellular radiotelephone,

a second cellular radiotelephone system comprising cellular radiotelephones, cellular transmitting/receiving cells and a mobile telephone switching office,

said modified cellular radiotelephone performing a cell registration process with said second cellular radiotelephone system which registration information is forwarded to said command and control center and

said command and control center using the registration information received from said first cellular radiotelephone system and said second cellular radiotelephone system to determine the location of said cellular radiotelephone.

2. A system for tracking an object as in claim 1 including one or more additional cellular radiotelephone systems in which said modified radiotelephone registers and provides cell registration information to said command and control center for determining the location of said modified cellular radiotelephone.

3. A system for tracking an object as in claim 1 wherein said command and control center is coupled to said cellular radiotelephone systems via a public telephone switching network.

4. A system for tracking an object as in claim 3 wherein said modified cellular radiotelephone alternately registers with said cellular radiotelephone systems.

5. A system for tracking an object as in claim 2 further comprising an external device connected to said modified cellular radiotelephone, said external device being responsive to commands from said command and control center to turn on, turn off, accept a digital message, or send a digital message.

6. A system for tracking an object as in claim 1, further comprising

a mobile component for precision tracking and locating said modified cellular radiotelephone which includes direction finding equipment.

7. A system for tracking an object as in claim 6 wherein

said modified cellular radiotelephone is responsive to commands from said command and control center to lock onto the weakest forward control channel of the cell in which it is located and transmit a message, including its identity, on the reverse control channel associated with said weakest forward control channel, and

said mobile component, upon being directed by the command and control center to the vicinity of said modified cellular radiotelephone and being given the identity being transmitted, acquiring with said direction finding equipment said cellular radiotelephone transmission, and locating and tracking said modified cellular radiotelephone.

8. A system for tracking an object comprising,

a cellular radiotelephone system comprising cellular radiotelephones, cellular transmitting/receiving cells and a mobile telephone switching office,

a command and control center coupled to said cellular radiotelephone system,

a modified cellular radiotelephone actuable to automatically switch to a power on state, initiate a call to said command and control center, transmit a message including its identification, and maintain a communication channel with said command and control center,

said modified cellular radiotelephone and cellular system automatically performing a cell registration process which identifies to the cellular system and said command and control center the cell in which said modified radiotelephone is located,

said command and control center including a computer for computing and displaying the location of said modified cellular radiotelephone,

an actuation device for turning on power to said modified cellular radiotelephone,

a battery supplying power to said modified cellular radiotelephone,

a circuit for monitoring the condition of said battery and providing a message on battery condition for sending to said command and control center,

tagging logic including alert mode logic, registration and tracking mode logic, and acquisition mode logic,

a memory for storing the command and control center phone number, an alert message, and the electronic identification number of the unit, and

a controller coupled to said tagging logic and said memory.

9. A modified cellular radiotelephone unit comprising

a battery power supply, a circuit for monitoring the status of the battery and

an activation switch for activating the radiotelephone unit,

radiotelephone logic and tagging logic coupled to a controller,

I/O ports for connecting external devices to said controller,

a memory and a transmit/receive unit coupled to said controller, and wherein said memory contains stored therein the telephone number of a command and control center, the electronic serial number of the unit, an alert message and an acquisition message.

10. A modified cellular radiotelephone unit as in claim 9 wherein said tagging logic comprises

alert logic for calling said command and control center,

registration and tracking logic for providing said command and control center with information pertaining to the location of the unit in a cell of one or more cellular radiotelephone systems, and

acquisition logic for scanning a cell of one of said cellular telephone systems to find and lock onto the weakest or an unused forward control channel and transmitting on its associated reverse control channel said acquisition message.

11. A method of locating a cellular radiotelephone in a geographic region served by at least two cellular radiotelephone systems comprising,

placing a call from said cellular radiotelephone to a command and control center over each cellular system,

performing a registration process in each cellular radiotelephone system,

communicating the registration information to said command and control center,

computing from said registration information the cell or sector location of said cellular radiotelephone in each cellular radiotelephone system, and

determining the geographic subarea of a cell or sector of one cellular system in which said cellular radiotelephone is located by the overlapping of said cell or sector by the cell or sector of one or more other cellular systems in which said cellular radiotelephone has been determined to be located.

12. A method of locating a cellular radiotelephone as in claim 11 wherein said cellular radiotelephone has stored in its memory its own electronic serial number and the phone number of a central command and control center, and an activating unit for automatically placing the cellular radiotelephone into operation, said method further comprising,

actuating said activating unit and automatically placing calls to said command and control center using the command and control center phone number and identifying itself using said electronic serial number.

13. A method of locating a cellular radiotelephone as in claim 12 further comprising

storing in said cellular radiotelephone memory a prearranged message,

sending said prearranged message to said command and control center upon being connected to said command and control center, and

receiving from said command and control center a confirmation that said prearranged message was received.

14. A method of locating a cellular radiotelephone as in claim 11 including the step of increasing the frequency of performing the registration process upon command from command and control center.

15. A method of precisely locating a modified cellular radiotelephone comprising,

activating said modified cellular radiotelephone to a power on state,

automatically placing a call to a command and control center over a cellular radiotelephone system and establishing a telephone communication link,

sequentially registering with the cellular radiotelephone system whereby the cell or cell sector in which said cellular radiotelephone is located is identified,

forwarding the registering information to said command and control center over said communication link,

computing and displaying at the command and control center the geographic location of the cell or cell sector in which said modified cellular radiotelephone is located,

sending a command to said modified cellular radiotelephone to implement an acquisition mode, said acquisition mode comprising

a) searching all available forward control channels of the cell and identifying an unused or weakest forward control channel,

b) locking onto said identified forward control channel, and

c) transmitting a prearranged message for a short time period on the reverse control channel associated with said locked on forward control channel,

directing a mobile acquisition unit with radio direction finding equipment to the cell or cell sector in which said modified cellular radiotelephone has been determined to be located, and

using radio direction finding techniques acquiring the signal being transmitted on the reverse control channel.

16. A method as in claim 15 wherein said transmitting of said prearranged message includes transmitting the electronic serial number of said modified cellular radiotelephone and said acquiring of the signal includes detecting the reception of the electronic serial number.

17. A method as in claim 15 wherein the transferring of location from one cell to another is registered and forwarded to said command and control center, and the transferring of location to a cell outside the geographic area of the cellular system in which the modified cellular telephone is currently registered induces a roaming mode and registration in another cellular system.

18. A method as in claim 15 including the step of increasing the frequency of registering.

19. A method as in claim 15 including the step of cycling between transmitting said prearranged message on said reverse control channel associated with the unused or weakest forward control channel and registering with said cellular system on the reverse control channel associated with another forward control channel of the cell in which the modified cellular radiotelephone currently resides.

TECHNICAL FIELD

The invention relates generally to communication systems, and in particular to a method of managing a unique cellular radiotelephone within a cellular telephone system from a remote command and control center for the purposes of locating and recovering this uniquely identified cellular radiotelephone.

BACKGROUND AND DISCUSSION OF PRIOR ART

Contemporary law enforcement and private security organizations must be able to surreptitiously follow vehicles, aircraft, objects, and people. In the past, small relatively low powered radio transmitters were secreted on the object to be followed. Radio direction finding equipment was then deployed to locate and acquire the object. The transmitting device is generally referred to as a beacon or tag, the process of placing the device on the object is referred to as tagging, and locating and following the tag is referred to as tracking.

Today's typical tag is a relatively low powered very high frequency radio transmitter that is manually activated when placed on the object to be tracked. It continually transmits a code of some sort until either the battery energy is depleted or the tracking operation is completed (U.S. Pat. No. 4,021,807 to Culpepper et al). Some tags can change their transmitted code based on local activity (motion, temperature change, etc.). These tags must have external sensors and specially designed electronic logic to accomplish their tasks. Other more advanced tags are commandable (U.S. Pat. No. 4,596,988 to Wanka). A radio signal from a remote unit can cause the transmissions to be turned on or off, or the transmission pattern can be modified as the situation dictates. This kind of tag needs a radio receiver to acquire the command signals, logic of some type to interpret and translate the signals into instructions, and a transmitter that is capable of carrying out the instructions.

Conventional tags have inherent weaknesses. Since a low power tag transmits over a relatively short distance, the only way to track it is to constantly monitor its transmissions with an appropriate radio receiver. Either full time field staff follow and monitor the tag during the tracking period, or a central office monitors the tag by using a system of dedicated receiving antennas that have been installed throughout the tracking area. Both choices are costly and impractical for a realistic national system. Further, the mission fails if the tag moves outside of the effective range of the tracking radio or of the antenna field.

There have been several creative enhancements to the conventional tag. Transmission characteristics have been modified to lower the probability of electronic detection (spread spectrum, microburst, etc.). Transmitters have been miniaturized for such applications as avian research (Telonics, Inc.). Several manufacturers have integrated position location systems, such as LORAN (U.S. Pat. No. 4,742,357 to Rackley) and GPS, with tags to allow tracking from a centralized location. QUALCOMM, GEOSTAR, and others have integrated position location systems with satellite transmitters. Cellular radiotelephones have been proposed as transmitting and receiving conduits for large, complex vehicle location systems (U.S. Pat. No. 5,218,367). Each of these techniques works in its intended application area. However, none adequately addresses the situation of tracking small, light, valuable objects in an urban environment.

Tags that use dedicated on board position location systems suffer from other problems. Their size, weight, and power consumption levels render them unacceptable for many tagging applications. The combined size and combined weight of the position location device, and the transmitter and receiver (for a commandable tag), could easily be greater than the object to be tracked. This is unfeasible.

Ideally a tag designed specifically for small objects would be installed long before the tracking need arose. It would lie dormant, in a power off state and thus retain sufficient battery energy to carry out its mission when activated. The tag would be commandable, would be tracked remotely, and would require intervention by field personnel only during final acquisition and apprehension. It would also have wide, and preferably, national coverage. There is no currently available tag with these characteristics. The disclosed tagging/tracking system meets these criteria. It solves the problems of size, weight, and energy consumption, and provides urban position location adequate for most law enforcement purposes.

SUMMARY OF THE INVENTION

The invention uses available cellular telephone infrastructure and is designed to adapt to any future advances in cellular technology. Contemporary mobile cellular radiotelephones are small and light. Complete mobile cellular radiotelephones with batteries weigh in the seven ounce range and measure less than two inches by six inches by one-half of an inch. For most small object tagging applications this is an acceptable size/weight combination. A mobile cellular radiotelephone modified to accept a set of tracking commands in addition to its cellular radio commands can easily function as an effective tag. Since a cellular telephone switch, referred to as a mobile telephone switching office (MTSO), knows the approximate location of all cellular mobile radiotelephones in its system, a tag that is a fully compliant cellular radiotelephone meets most of the requirements of remote tracking. The coverage of cellular telephone systems is virtually national, and all cellular telephones must comply with a national standard. Accordingly, the cellular tag's area of application is considerable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a modified cellular radiotelephone;

FIG. 2 is a pictorial representation of the complete system;

FIG. 3 illustrates two cellular systems "A" and "B";

FIG. 4 illustrates two subsectors provided by the overlap of two cellular systems; and

FIG. 5 is a diagram of the tagging logic.

DETAILED DESCRIPTION OF THE INVENTION

The system has four components, a modified commercially available mobile cellular radiotelephone, at least one cellular system, a command and control center, and a direction finding receiver set. The system operates in three modes, an alert mode, a registration/tracking mode, and an acquisition mode.

A modified mobile cellular radiotelephone or tag 1 is illustrated in block form in FIG. 1. The principal units of this component comprise tagging logic 2, cellular radiotelephone logic 3, controller 4, memory 5, battery 6, battery monitor 7, activator 8, I/O ports 9 and transceiver 10. The memory 5 has stored therein the phone number of the command and control center, the electronic serial number (ESN) of the cellular radiotelephone, an alert message, an acquisition message, and a prearranged telephone number. The I/O ports are for connection to an external device that is either subject to being sent control signals from the command and control center or a sensor that is able to provide information for the command and control center.

The tagging logic can be placed on an added integrated circuit chip or can be inserted into the cellular radiotelephone's cellular logic, should room be available. The tag is placed on the object to be tracked some time (e.g., months) before the anticipated tracking operation. It remains in a power off state until activated. If battery 6 is a secondary (rechargeable) battery, it will be subjected to a constant trickle charge to maintain its viability. A primary (non-rechargeable) battery that will remain in a power off state until activation and be replaced periodically can be used.

Activator 8 includes at least one switch that is actuated to apply battery power from battery 6 to the components of the radiotelephone. One technique for activating the switch is to have the radiotelephone normally placed in a holding unit such that the switch is held in a deactivated position until the radiotelephone is removed from the holding unit. Another technique involves the radiotelephone being held in a direct or inductively coupled trickle charging holster whereupon a breaking of the trickle charge coupling causes activation of the switch. Other techniques or means for activating the unit or for actuating a switch, or one of a plurality of parallel connected switches, will be apparent to those skilled in this art.

FIG. 2 shows the overall system. An object, here a brief case, contains the modified cellular radiotelephone 1 of FIG. 1 which has been activated. The cell of a cellular system wherein the object resides relays the communique along with cell location data from the cellular telephone to the MTSO 20 which forwards it over available communication links to the command and control center 30. During the acquisition mode the command and control center guides the pursuers 40 of the object to the cell where the object is located. Direction finding equipment is employed by the pursuers for precisely locating the object in the cell.

Upon activation, registration will occur and the tagging logic will direct that a telephone call be placed to the command and control center component of the system. The command and control center includes digital computers that receive the call and log the binary coded message sent by the tag. The message consists of a preassigned alert code and, most critically, the tag's unique identification--its electronic serial number (ESN). This initial telephone call serves as a fail safe mechanism, which will become evident later. The tagging logic will seek a message from the command and control center acknowledging the receipt of the alert message. The tag's unique identification code keys the command and control center's operational data base, which provides system operators with all available information about the tagged object's description and location, and any special