Method and apparatus for tracking a moving object

A system for determining with a high degree of accuracy the location of an object based upon signals transmitted from a plurality of satellites, which are disposed in known orbits about the earth, the object being capable of moving selectively throughout a geographical area, said system comprising:

• a) a command center;
• b) a plurality of differential stations distributed throughout the geographical area at a plurality of corresponding fixed points, each fixed point of a known location, each of said plurality of differential stations comprising means for receiving and processing signals from a corresponding subset of the plurality of satellites presently in sight of said corresponding fixed point to provide a signal indicative of the approximate location of said corresponding fixed point and differential station;
• c) means coupled to said receiving and processing means of each of said plurality of differential stations for comparing the approximate and accurate locations of each of said plurality of fixed points to provide differential data;
• d) a unit mounted on the object and movable with the object throughout the geographical area, said unit having means for receiving and processing signals from a given subset of the plurality of satellites presently in sight of its object to provide a signal indicative of the approximate location of its object, and first actuable means for transmitting a message indicative of the location of its object;
• e) said command center having first means for receiving said differential data and said approximate object location signal from said first actuable transmitting means of said unit, and means for determining based upon said approximate object location and said known locations of said plurality of the fixed points a determined one of said corresponding differential stations which is presently in sight of the same subset of satellites as the object;
• and
• f) means for combining said approximate object location signal and said differential data from said determined one differential station to provide an indication of the object's location with greater accuracy.

A method of determining with a high degree of accuracy the location of an object based upon signals transmitted from a plurality of satellites disposed earth in known orbits about the earth, said method comprising the steps of:

• a) determining with accuracy the latitude and longitude of a fixed point, the object being capable of moving with respect to the fixed point;
• b) receiving at the fixed point and processing the satellite signals to determine the approximate latitude and longitude of the fixed point;
• c) taking a first difference between the accurate and approximate latitudes to provide a differential latitude correction of a magnitude corresponding to said first difference and of a direction to the north or south, and taking a second difference between the accurate and approximate longitudes to provide a differential longitude correction of a magnitude corresponding to said second difference and of a direction to the east or west;
• d) receiving at the object and processing the satellite signals to determine the approximate latitude and longitude of the object;
• and
• e) combining the approximate object latitude and differential latitude correction to provide a corrected object latitude of improved accuracy, and the approximate object longitude and differential longitude correction to provide a corrected object longitude of improved accuracy.

A method of operating apparatus for determining the location of an object based on signals transmitted from a plurality of satellites, which are disposed in known orbits about the earth, said satellite signals comprising satellite orbit data, the location determining apparatus comprising a memory for storing the satellite orbit data and a clock for providing the current time, said method comprising the steps of:

• a) upon detecting the cessation of receiving the satellite signals, storing the last received satellite orbit data in the apparatus' memory;
• b) detecting the recapture of the satellite signals to determine a length of time that the apparatus was not receiving satellite signals;
• c) comparing said determined length of time with a given period and, if less, accessing from the apparatus' memory the stored satellite orbit data and from the apparatus' clock the current time to determine the present subset of the plurality of satellites that is in direct view of the object, before restarting the location determining apparatus to receive again the signals from the determined subset of satellites;
• and
• d) if said determined length of time is greater than said given period, sequentially searching the plurality of satellites one at a time until a satellite transmitting a signal having a greater than a threshold strength is detected and the signal from the one detected satellite is recaptured.

Security apparatus adapted to be mounted on a vehicle, said security apparatus utilizing signals received from a plurality of satellites which are disposed in known orbits about the earth to determine a current location of the vehicle, said security apparatus comprising:

• a) means for receiving and processing the satellite signals to provide said current location of the vehicle;
• b) actuable means for transmitting an alarm message to a remote station;
• and
• c) means responsive to an unauthorized use of the vehicle for accessing said current location of the vehicle from said receiving and processing means and for actuating said transmitting means to transmit said alarm message indicative of the unauthorized use of the vehicle and said current location of the vehicle to the remote station.

Apparatus adapted to be mounted on a vehicle for determining the location of the vehicle based upon signals transmitted from a plurality of satellites disposed in orbit about the earth and for transmitting messages to a remote command center indicative of the current location of the vehicle, said apparatus comprising:

• a) means for receiving and repetitively processing the satellite signals to provide a series of current locations of the vehicle;
• b) memory means coupled to said receiving and processing means for receiving said series of current vehicle locations and for storing the last received vehicle location until replaced with the next processed vehicle location;
• and
• c) means for receiving prompt messages from the command center and responsive thereto for accessing from said memory means said last received vehicle location and transmitting said message with said received vehicle location to the command center.

A method for tracking at a command center one or more vehicles which moves about an extended geographical area based upon signals transmitted from a plurality of satellites disposed in orbits about the earth, said method comprising the steps of:

• a) receiving and processing at the one vehicle the satellite signals to provide a signal indicative of the location of the one vehicle;
• b) storing at least at one of the command center and the vehicle in an addressable memory a plurality of sub area maps corresponding to the extended geographical area;
• and
• c) transmitting the vehicle location signal to the memory and using the transmitted location signal to address and obtain from the memory a selected one sub area map corresponding the present location of the one vehicle.

A system for determining with accuracy the location of an object movable within a geographic area based upon signals transmitted from a plurality of satellites, which are disposed in orbit about the earth, said system comprising:

• a) a command center;
• b) at least one differential station disposed at a fixed point, within the geographical area, said fixed point having a location known with accuracy, said differential station comprising first means for receiving and processing signals from the plurality of satellites to provide a signal indicative of the approximate location of the fixed point, an antenna coupled to said first receiving and processing means and oriented at the fixed point, and means coupled to said first receiving and processing means to provide a first differential signal;
• c) a unit mounted on the object and movable with the object throughout the geographical area, said unit having second means for receiving and processing signals from the plurality of satellites to provide a second signal indicative of the approximate location of its object;
• d) first means coupled to said unit and said command center for bidirectionally transmitting signals between said unit and said command center;
• e) second means coupled to said differential station and said command center for transmitting said first differential signal from said differential station to said command center;
• and
• f) means disposable at least at one of said command center and said unit and coupled to receive said first and second signals for combining said first and second signals to provide an indication of the object's location with an accuracy greater than that of said second approximate object location signal.

A system for displaying with accuracy the location of an object movable within a geographic area based upon signals transmitted from a plurality of satellites, which are disposed in orbit about the earth, said system comprising:

• a) a command center;
• b) a unit mounted on the object and moveable with the object throughout the geographical area, said unit having first means for receiving and processing the signals from the plurality of satellites to provide a signal indicative of the approximate location of its object;
• c) memory means disposed at least at one of said command center and the object for storing at least one map of at least a portion of the geographical area, said map comprising information to a level of detail to include a plurality of streets the geographical area;
• d) display means disposed at least at one of said command center and the object and coupled to said memory means for displaying said map and a mark superimposed on said displayed map to indicate the relative position of the object with respect to said plurality of streets;
• e) at least one differential station disposed within the geographical area at a fixed point, said fixed point having a location known with accuracy, said differential station comprising second means disposed at the fixed point for receiving and processing signals from the plurality of satellites to provide a signal indicative of the approximate location the fixed point, and means coupled to said second receiving and processing means to receive the signal therefrom for comparing the approximate location with the accurate location to provide a differential signal indicative of any difference therebetween;
• f) transmission means coupled to said unit, said command center and said one differential station for transmitting signals bidirectionally therebetween;
• and
• g) means disposed at least at one of said command center and the object and coupled to said unit and to said transmission means for combining said differential signal and said approximate object location signal to provide an accurate vehicle location signal and for imposing said mark on said street level map displayed by said display means in a position relative to said plurality of streets dependent upon said accurate vehicle location signal, said given level of accuracy of said differential signal being sufficiently high so that said mark is displayed to a level of accuracy corresponding to a street address of one of said plurality of streets.

A security vehicle system utilizing signals received from a plurality of satellites disposed in orbit about the earth, said vehicle security system comprising:

• a) an alarm unit adapted to be mounted on a vehicle for communication with a remote station, said alarm unit comprising:
• 1) means for receiving and processing the satellite signals to provide information as to the location of the vehicle,
• 2) first wireless means for transmitting radio signals bearing information from the vehicle to the remote station,
• 3) first means for nondestructively storing a unique ID identifying the vehicle, and
• 4) control means for obtaining and applying the vehicle location information and the ID from said receiving means and from said storing means respectively to said first wireless means to be transmitted by said wireless means from the vehicle to the remote station;
• and
• b) a monitoring unit disposed at the remote station, said monitoring unit comprising:
• 1) second wireless means for receiving radio signals bearing the vehicle location and ID from the vehicle,
• 2) second means for storing addressable files of data related to a plurality of vehicles, and
• 3) addressing means coupled to said second wireless means for address said second storing means with the received ID to output from said second storing means the data file corresponding to the received ID.