Abstract: A geographic-based communications service system has a mobile unit for transmitting/receiving information, and access points connected to a network. The access points are arranged in a known geographic locations and transmit and receive information from the mobile unit. When one of the access points detects the presence of the mobile unit, it sends a signal to the network indicating the location of the mobile unit and the information requested by the mobile unit. Based on the signal received from the access point, the network communicates with information providers connected to the network and provides data to the mobile unit through the access point corresponding to the location of the mobile unit.

Abstract: A wireless tracking system consists of a wireless target including a wireless communication system for transmitting a data packet over a communication path, and a locating station for determining a position of the target. The data packet transmitted from the target includes an identification code uniquely associated with the target. The locating station includes a configurable directional antenna, a communication interval processing system, a direction processing system, and a position processing system. The communication interval processing system is in communication with the directional antenna and determines the transmission interval of the transmitted data packet over the communication path. The direction processing system determines the transmission angle of the communication path, and is in communication with the directional antenna for controlling the configuration of the directional antenna so as to facilitate the determination of the transmission angle.

Abstract: A method of calculating the position or state of motion of one or more terminals is proposed in which each has a receiver capable of making measurements of signals received from one or more transmission sources for use in calculating the unknown position or state of motion of the or each terminal. At least one transmission source has a known directional transmission pattern, and the bearing from one of the receivers of the or each of the transmission source having a known directional transmission pattern is estimated. Weights are assigned to the measurements made by the one receiver, the weights being calculated from the bearing or bearings and the known directional transmission pattern of the transmission sources.

Abstract: A pseudolite for transmitting a global positioning system (GPS) signal having identification information for a GPS satellite that is currently out-of-view. The pseudolite mimics a global positioning system (GPS) signal by using a C/A pseudorandom (PRN) identification code for a GPS satellite that is allocated in the GPS system but is unreceivable in the local vicinity and location-determination information including ephemeris data corresponding to the geographical location of the pseudolite. In order to ensure that two of the GPS pseudolites in the same vicinity do not use the identification PRN code from the same out-of-view GPS satellite, the pseudolite listens first before transmitting to detect the identifications in the received GPS signals.

Abstract: A global positioning system (GPS) signal receiving and rebroadcasting device includes a first GPS antenna receiving GPS signals from a number of earth orbiting satellites, and a connector electrically connected to the first GPS antenna and configured for electrical connection to a voltage source. The connector supplies the voltage produced by the voltage source to the first GPS antenna via an electrical cable connected therebetween. The device further includes a second GPS antenna mounted within the connector and electrically connected to the first GPS antenna via a signal wire carried by the electrical cable. The first GPS antenna is operable to supply the received GPS signals to the second GPS antenna which, in turn, is operable to rebroadcast the GPS signals. The device is useful in enclosed environments requiring GPS access, wherein the first GPS antenna may be positioned to receive GPS signals.

Abstract: An apparatus, method, and computer-readable media. The apparatus comprises a receiver adapted to receive a plurality of broadcast signals; a signal processor adapted to determine a position based on the received plurality of broadcast signals; a signal generator adapted to generate a ranging signal comprising a known component of a television signal; and a transmitter adapted to broadcast a signal comprising the ranging signal and a position signal comprising a description of the position.

Abstract: The invention relates to control systems and is directed at defining the state of transportation means (TM) in normal and extreme conditions. Each TM is fitted with a power-on radio beacon station (RB) whose signals are retransmitted by means of geostationary Artificial Earth Satellites (AES) of the integrated variety to mated ground stations for reception of information. In extreme situations of TM, the transmission of information from RB is carried out continuously by signal sets with a gap of up to 1 within the narrow band in a wave-range of 400 MHz which is provided for transmitting emergency signals with the aid of AES. In the normal conditions, signal transmission is carried out in a narrow adjacent band with intervals between sets of greater than 10 sec. An 20-30-fold increase of a transfer bandwidth of the system is ensured by means of a synchronous transmission of the information sets from RB one after another with small time gaps.

Abstract: A navigation system is disclosed including at least one RF tag having a predetermined signature. The system also includes a receiver having an RF tag reader capable of reading the predetermined signature. A controller is communicatively coupled to the receiver, a memory and output device. The controller is arranged to receive the predetermined signature, based upon the predetermined signature, obtain at least one navigation instruction stored in the memory, and output the navigation instruction using the output device. Additional non-navigational information may also be provided using the output device. The receiver may also include an input device for inputting information into the navigation system.

Abstract: The invention relates to control systems and is directed at defining the state of transportation means (TM) in normal and extreme conditions. Each TM is fitted with a power-on radio-beacon station (RB) whose signals are retransmitted by means of geostationary Artificial Earth Satellites (AES) of the integrated variety to mated ground stations for reception of information. In extreme situations of TM, the transmission of information from RB is carried out continuously by signal sets with a gap of up to I within the narrow band in a wave-range of 400 MHz which is provided for transmitting emergency signals with the aid of AES. In the normal conditions, signal transmission is carried out in a narrow adjacent band with intervals between sets of greater than 10 sec. An 20-30-fold increase of a transfer bandwidth of the system is ensured by means of a synchronous transmission of the information sets from RB one after another with small time gaps.

Abstract: The invention relates to a method for positioning a wireless communication device (MS). In the method, position data of one or a plurality of reference points is stored into at least one data base (DB), and it is detected which of said reference points is located in the vicinity of the wireless communication device (MS). In the method, at least position data of said reference point located in the vicinity of the wireless communication device (MS) is transmitted to the wireless communication device (MS), wherein in order to perform the positioning, said reference point located in the vicinity of the wireless communication device (MS) is selected as the default location of the wireless communication device (MS).

Abstract: An emergency position information radio beacon utilized in conjunction with a global positioning system that receives latitude and longitude information continuously in which the GPS data is periodically transferred into the EPIRB before activation in order to preserve battery power in the EPIRB. The EPIRB includes a first micro controller that is connected by an electro/optical data input to the GPS with the first micro controller being a very low power drain. Periodically, such as every 10 minutes, latitude and longitude information is transferred from the GPS into the EPIRB memory after which the EPIRB memory and system is maintained in a sleep mode with no power consumption. This insures that the EPIRB has geographical position information data before activation that can be transmitted with the emergency signal to search and rescue at the same time preserving the battery power of the EPIRB which is utilized only during the emergency period. The system is power off 99.

Abstract: A method for mitigating multipath effects in radio systems which is based on searching for and finding a maximum likelihood estimate of range for a received signal is provided. In determining the maximum likelihood estimate, the correlation process uses a high resolution step method in processing the received signal sample values to develop an estimation statistic. The estimation statistic using the correlations of the received signal is based on a new derived representative set of coefficients formed from a nonlinear combination of parameters of the received signal transformed into a linearly solvable invertible parameter set allowing solution of the maximization process of the estimation statistic over a reduced dimension search space. Additionally there is a method of constraining the relative amplitude of received secondary signals to obtain a refinement of the optimal solution of range.

Abstract: A method of controlling an antenna signal combiner in a vehicle having multiple antenna elements. The method comprises the steps of receiving broadcast signals from the antenna elements. An antenna beam is steered toward a first steering angle. Navigation data is generated in response to a navigation sensor, the navigation data identifying a relative changes in vehicle direction. The antenna beam is steered toward a second steering angle in response to the relative change in vehicle direction.

Abstract: A method for correcting yaw in a DGPS (global positioning system) based guidance system mounted on a vehicle. The method corrects for a yaw induced heading/cross track error due to a DGPS antenna being mounted a significant distance from the point of operation (e.g., the vehicle operator's location, the center of the vehicle, etc.). The method determines a ground track of a vehicle using a DGPS system and a coupled antenna mounted on the vehicle. A heading of the vehicle is also determined using a compass mounted on the vehicle. The heading and the ground track are compared to determine whether a difference exits and the magnitude of the difference. Using the difference, the DGPS determined position is adjusted to be the position of the operator/center of the vehicle. Using this guidance information, an indication is generated operable for directing the vehicle to maintain a desired ground track.

Abstract: A geographic-based communications service system has a mobile unit for transmitting/receiving information, and access points connected to a network. The access points are arranged in a known geographic locations and transmit and receive information from the mobile unit. When one of the access points detects the presence of the mobile unit, it sends a signal to the network indicating the location of the mobile unit and the information requested by the mobile unit. Based on the signal received from the access point, the network communicates with information providers connected to the network and provides data to the mobile unit through the access point corresponding to the location of the mobile unit.

Abstract: In a mobile communication network, the accuracy of location determinations for mobiles based on TDOA measurements made by the mobiles is increased by measuring the TDOA of signals from base station pairs at a known location and generating correction factors for compensating timing and propagation errors in TDOA measurements made by the mobiles. Calibration terminals may be provided for measuring TDOAs at known locations. System processes and elements for applying data generated by calibration terminals are disclosed.

Abstract: A signalling device which is housed within a tubular container includes a mylar balloon; a pressurized, lighter-than-air gas source; and multiple beacon devices. The device signals its location and, as such, is useful in rescue or retrieval operations. A pressure vessel is connected to the balloon so that lighter-than-air gas contained within the pressure vessel can flow into the balloon. An RF transmitter, a Global Positioning System (GPS) receiver unit and a strobe light, are also coupled to the balloon. A valve separates located in the pressure vessel separates the lighter-than-air gas from the balloon until opened either manually or automatically. The balloon is inflated by the lighter-than-air gas which expands the balloon causing it to break through the top of the container and rise. As the balloon rises, the RF transmitter, the GPS receiver and the strobe light activate.

Abstract: A global positioning system (GPS) and auxiliary receiver receive limited range position signals broadcasted from telemetry transmitters when in an urban canyon environment. The limited range receivers preferably are implemented as part of the lighting infrastructure of the environment. The limited range receivers derive power from light from the lighting infrastructure. The receivers can also include a transmitter for retransmitting the receive position data and an ID code to a central processing center.

Abstract: A data-transmission device has a pulse generator (1) and a monitoring unit (20) for use in a vehicle. A signal generated by the sensor (2) is transmitted from the pulse generator (1) to the monitoring unit (20) by a signal line (9) and also, when requested by the monitoring unit, is transmitted in encrypted form along a data line (19). The signal generated by the pulse generator (1) is first stored in an intermediate store. Before transmission, the contents of this store are encrypted. On arrival in the monitoring unit, the encrypted signal is compared with the signal previously transmitted in the usual way and recorded there. This is a security check which reveals any manipulations which have been made during transmission.

Abstract: An autonomous formation flying sensor for precise autonomous determination and control of the relative position and attitude for a formation of moving objects.

Abstract: This invention involves a method for mitigating multipath effects in radio ranging systems which is based on searching for and finding a maximum likelihood estimate of range for a received signal in a signal ranging system. In determining the maximum likelihood estimate, the correlation process uses a high resolution step method in processing the received signal sample values to develop an estimation statistic. The estimation statistic using the correlations of the received signal is based on a new derived representative set of coefficients formed from a nonlinear combination of parameters of the received signal transformed into an invertible linear combination which allows solution of the maximization process of the estimation statistic. Additionally there is a method of constraining the relative amplitude of received secondary signals to obtain a refinement of the optimal solution of range.

Abstract: A position measuring apparatus includes a first position measuring device for position measuring a first position by receiving a first radio wave, a second position measuring device for position measuring a second position by receiving a second radio wave, an evaluating unit for evaluating uncertainty of data derived from the first position measuring device and/or the second position measuring device, and a selecting element for selecting data from the first position measuring device or the second position measuring device based on an output signal of the evaluating unit.

Abstract: A global positioning system (GPS) and auxiliary receiver receive limited range position signals broadcasted from telemetry transmitters when in an urban canyon environment. The limited range receivers preferably are implemented as part of the lighting infrastructure of the environment. The limited range receivers derive power from light from the lighting infrastructure. The receivers can also include a transmitter for retransmitting the receive position data and an ID code to a central processing center.

Abstract: A security system having two-way communication with a central monitoring station. The security system is equipped with a computerized control and communications unit. The control and communications unit is connected to a position determination device and to a calling unit. The control and communications unit is also connected to several intrusion detection devices. Upon direction of the control and communications unit, for example, in response to the detection of a violation of an intrusion detection device, the calling unit establishes a communications link with the central monitoring station and communicates thereto the status and location of the vehicle in which the security system is located. The control and communication device is operable to receive commands from a handset electrically connected thereto. The central monitoring station, by communicating with the control and communications unit, is operable to control functional units of the vehicle.

Abstract: A method for improving the provision of emergency assistance services for an emergency site. An observer of an emergency event contacts an Emergency Assistance Services (EAS) operator, using a telephone to describe the type of emergency event and any special circumstances present. The EAS operator also receives the present location of the observer, using a location determination system that is connected to the telephone used by the observer. The EAS operator is provided with an electronic map showing the location of the observer and the location of at least one available EAS responder for the type of emergency event that has occurred. The EAS operator determines whether a given EAS responder has the equipment and/or trained personnel required to respond to the emergency event and, from a group of EAS responders who do so qualify, selects an EAS responder who is estimated to be able to reach the emergency site in the shortest time.

Abstract: A system and method are provided for communicating between a person, object, and/or vehicle carried transceiver and a monitor station to locate and track the movement of the same for security or anti-crime purposes. A portable computing and communication device carried by a person or located (hidden) in an object generates and transmits via radio signals a plurality of codes when remotely activated. One (or more) code(s), identifying or descriptive of the person, object or vehicle to be tracked, is (are) generated and transmitted to a monitor station to display character and/or video picture information describing and/or physically displaying a picture of a select person and/or vehicle and license plate information to permit police or security personnel to recognize the same. Such coded information may be immediately transmitted or retransmitted from the monitor station to a radio receiver carried by a policeman or in one or more police vehicles.

Abstract: Survival radio interrogator (1) transmits upon request a message including an identification of survival radio (3). Upon receiving and processing this message, survival radio (3) determines its position from the Global Positioning System and transmits a message back to the search aircraft (2) with the survival radio interrogator (1). The processor (10) of the survival radio interrogator 1 determines a range and bearing of the survival radio (3) and processes data from the survival radio 3 which data includes identification, position and messaging information for display on the LCD display 14. All message transmissions are conducted via the aircraft's (2) radio/intercom system (30).

Abstract: A bi-static radar configuration measures the direct time-of-flight of a transmitted RF pulse and is capable of measuring this time-of-flight with a jitter on the order of about one pico-second, or about 0.01 inch of free space distance for an electromagnetic pulse over a range of about one to ten feet. A transmitter transmits a sequence of electromagnetic pulses in response to a transmit timing signal, and a receiver samples the sequence of electromagnetic pulses with controlled timing in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample the sequence of electromagnetic pulses such that the time between transmission of pulses in the sequence and sampling by the receiver sweeps over a range of delays.

Abstract: A method and apparatus for locating and tracking a portable transmitter that may be deposited with currency or other items desired to be tracked, comprising a doppler antenna array, analog antenna switching, radio frequency and intermediate frequency circuitry and a digital signal processor, exhibiting increasing sensitivity, accuracy, and range.

Abstract: A GPS system that includes a GPS beacon beacon that receives a plurality of GPS signals. Each of the GPS signals haa a carrier component and a pseudo-random code component. The beacon generates in response to the received GPS signals a plurality of beacon signals. Each of the plurality of beacon signals has a carrier component phase locked to one of the carrier components of the received GPS signals and a pseudo-random code component phase locked to one of the pseudo-random code components of the received GPS signals. The beacon then transmits the plurality of beacon signals. The system also includes a GPS receiver. The GPS receiver can make Code Based Differential GPS position determinations by making range measurements for each of the pseudo-random code components of the GPS and beacon signals and in response computing values representing a position.

Abstract: A GPS system and method for generating precise position determinations. The GPS system includes a ground based GPS reference system which receives with a reference receiver GPS signals and makes phase measurements for the carrier components of the GPS signals. The GPS reference system then generates and broadcasts an initialization signal having a carrier component and a data link signal having a data component. The data component of the data link signal contains data representing the phase measurements made by the reference receiver. The GPS system also includes a GPS mobile system which receives with a mobile position receiver the same GPS signals as were received by the reference system. In addition, the GPS position receiver receives the data link and initialization signals broadcast by the reference system.

Abstract: An arrangement for simulating indirect fire in military combat training exercises in which each individual exercise participant is not required to be equipped with an individual position-locating device. The arrangement uses a technique of grouping (20, 30) the players (1-7,11-17) and equipping only one member of the group with a position-locating device (43). The position of the single player equipped with the position-locating device is used to determine if the group is located within the area affected by simulated indirect fire. Once the group has been determined to be within the affected area, individual players within the group assess their own casualties based on weapon-target pairing and random chance.

Abstract: A security system having two-way communication with a central monitoring station. The security system is equipped with a computerized control and communications unit. The control and communications unit is connected to a position determination device and to a calling unit. The control and communications unit is also connected to several intrusion detection devices. Upon direction of the control and communications unit, for example, in response to the detection of a violation of an intrusion detection device, the calling unit establishes a communications link with the central monitoring station and communicates thereto the status and location of the vehicle in which the security system is located. The control and communication device is operable to receive commands from a handset electrically connected thereto. The central monitoring station, by communicating with the control and communications unit, is operable to control functional units of the vehicle.

Abstract: A target electronic system forms part of a marker beacon. The target system ids in detecting the marker beacon upon deployment. A seeking electronic system for locating the target system may be mounted on an air vehicle, land vehicle, sea vehicle, or backpack. The target system, upon deployment of the marker beacon, sends out signals identifying the marker beacon's use, identity, and direction. The seeking system then responds by querying the target system of its distance. The target system then responds to this query. The seeking system then has the option of sending a signal to have the target system initiate the activation of a flare. The activated flare can then be used for visual and infrared detection.

Abstract: A bi-static radar configuration measures the direct time-of-flight of a transmitted RF pulse and is capable of measuring this time-of-flight with a jitter on the order of about one pico-second, or about 0.01 inch of free space distance for an electromagnetic pulse over a range of about one to ten feet. A transmitter transmits a sequence of electromagnetic pulses in response to a transmit timing signal, and a receiver samples the sequence of electromagnetic pulses with controlled timing in response to a receive timing signal, and generates a sample signal in response to the samples. A timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample the sequence of electromagnetic pulses such that the time between transmission of pulses in the sequence and sampling by the receiver sweeps over a range of delays.

Abstract: A plurality of movable objects, such as aircraft, are provided with GPS receivers, enabling the individual determination of longitude and latitude. Further, the receiver also receives a very precise time base from the GPS satellites. This very precise time base is used to enable all of the plurality of movable objects to transmit in a predetermined radio frequency their identities and positions in precisely determined time blocks. By limiting the range of the frequencies used by the movable objects to transmit, the range of receivability is limited, such that the system may be implemented as a worldwide overlapping mosaic. The transmissions of each movable object may be received by all of the plurality of movable objects, as well as by air traffic monitoring centers on the ground.

Abstract: An electronic device for multiplexing several loads to the terminals of a source of alternating electrical energy. The source(4) of alternating electrical energy is coupled by electromagnetic flux to the loads by using primary excitation windings 71, 81 and 91 connect to the terminals of the source (4) of alternating electrical energy and secondary windings respectively corresponding to the number of loads. The secondary windings are at least partially coupled to the primary winding and are each connected to the terminals of a load. The coupling is inhibited by auxiliary winding 73 which are each totally coupled with the secondary winding 72. The inhibition function is controlled in order to inhibit all the magnetic couplings except for one and this particular one changes as a function of the respective load to be coupled to the source 4 of alternating electrical energy.

Abstract: A survey system including a survey instrument operable to receive signals indicating the Easting, Northing and elevation of a surveyed point. The survey instrument transmits data regarding the surveyed point coordinates to a radio terminal mounted on the survey instrument and having a command keyboard associated therewith. The radio terminal is operable to communicate with a base radio and controller connected to a digital computer which stores survey data for a predetermined number of survey points and is capable of performing calculations of at least elevations of points disposed intermediate a set of coordinates on a survey grid and calculating hole depth for blastholes based on the elevation of a surveyed point on the surface of material from which the hole is to be drilled. The base radio and controller are operable to communicate with plural survey instrument and radio terminal units.

Abstract: A marker beacon deployable by being launched through overhead foliage is able of landing atop and settling on the foliage for visual and infrared detection. A tether limits the flight range of the beacon and operates a switch to the electronic portion of the device to initiate radio signalling. The radio information assists in initial detection of the beacon by a seeking craft. Received signals from the seeking craft activate a flare stored within the beacon unit to further assist in locating the beacon. The beacon is also deployable by launch at sea, and by both place-and-leave and hand-held means on land and sea.

Abstract: A phase modulator for a position indicating radio beacon which includes a digital memory circuit having a plurality of sets of stored numerical amplitude values with each set corresponding to a sine wave of a given phase and with at least three values in each set. A selection circuit selects phase values from the memory circuit in steps between a predetermined angular range in response to input data and, for each phase value, transfers the set of amplitude values in series at spaced apart time intervals to a digital to analog converter. A high frequency filter has an input coupled to an output of the digital to analog converter such that a sine wave is produced at an output of the high frequency filter.

Abstract: This device is easily detachable. When the arrow makes impact, the dart with the transmitter remains in the target. The impact activates the transmitter which puts out a signal that can be picked up by the receiver.Because the device is small and ver light and has a counter-balance, it won't interfere with the accuracy and the flight of the arrow. This allows the archer to find the game faster and easier.

Abstract: A microwave system for locating a mobile element comprises a hollow tube forming a waveguide fed with microwave signals. A location beacon radiates into free space an electromagnetic wave derived from the microwave signals propagating in the waveguide. A location antenna attached to the mobile element receives the electromagnetic wave radiated by the beacon. The location beacon transmits to the antenna a single electric field signal enabling transmission of a location message.

Abstract: A method of determining the position of an object comprising the steps of: producing a plurality of hyperbolic electromagnetic wave patterns; calculating from said patterns at least three lines of position; identifying the lane of each line of position by two independent methods; comparing the size of the area enclosed by the lines of position based on the lanes identified by a first of said methods with the size of the area enclosed by the lines of position identified by a second of said methods and producing therefrom an indication as to whether the lanes identified by the first method are more likely to be correct than those identified by the second method; and computing the position of the object using the lines of position based on the lanes identified as being more likely to be correct.

Abstract: A time transfer position location method and arrangement. A mission control station initiates a number of relays placed throughout a simulated battlefield. Each of the relays then obtains position and time information from a Global Positioning System (GPS) satellite. Each relay repeatedly transmits position information (timing pulse) in a particular time slot over the playing field. In addition, fire mission information which includes type of munition deployed and its range and affects is also transmitted.

Abstract: Method and apparatus are described for the integration of global positioning system (GPS) or LORAN positioning information into the transmission of an emergency locator transmitter (ELT) radio beacon signal. Signals from NAVSTAR satellites or LORAN system are received by a receiver. The calculated position, and then subsequent updates, are processed and alternately stored in two locations on a static random access memory chip. Upon activation of the ELT transmitter, the updated position information, or the latest stored information, is combined with aircraft information stored on an EPROM chip. The aircraft information and position information is preferably converted from a digital-to-speech signal, by a voice synthesizer. All this information is then integrated into the radio beacon signal and broadcast by the ELT. This new ELT-GPS storing and processing package is self-contained, independently powered, and crash resistant. This system avoids loss of time in establishing the location of the beacon signal.

Abstract: Method and apparatus for reporting of an emergency event experienced by a marine vessel, an airborne vessel or by an occupant of the vessel. The present vessel position, accurate to within a few tens of meters, and (optionally) the vessel velocity and local air quality, is determined at an ordered sequence of times, using a position-determining Global Positioning System, such as the Navstar system or the GLONASS system. If an emergency occurs on the vessel, the approximate present position and time of occurrence of this event is broadcast on one or more of the mobile communication or emergency radiowave bands. Optionally, the type of emergency event that has occurred, drawn from a predetermined list of such types, is also broadcast by a vessel in distress, for receipt by an emergency response facility or by another vessel that can respond to a call for assistance. Optionally, vessel velocity heading and/or vessel position quality of fix information is also broadcast by a vessel in distress.

Abstract: The navigation receiver with coupled-tracking channels is intended for use in radio navigation systems based on trilateration wherein the times of arrival of radio signals transmitted by a plurality of ground- or space-based terminals are measured by a user terminal and utilized by the user terminal in calculating its position and orientation.

Abstract: A dual mode electronic identification system using a tag which has a RF receiver and transmitter contained therein. In the first mode the tag responds to an interrogation signal by transmitting identification data to the interrogator. In the second mode the tag periodically transmits an identification beacon signal to a directional sensing antenna which uses the signal to compute the position of the tag. The power supply for the tag operates from an internal battery or from power received from a portal signal via a tag receiving antenna. The battery can be automatically turned off when the tag is in the portal area and the unit can be shifted into the battery operated beacon mode when the tag is removed from the portal area.

Abstract: A system receives and demodulates spread spectrum positional signals such as those generated by a GPS satellite by frequency shifting the signals substantially to baseband and utilizing digital signal processing techniques. The digital signal processing techniques utilized can be implemented by a standard audio digital signal processor due to the circuit design. The spread spectrum signal is frequency shifted substantially to baseband, forming in-phase and quadrature components which are processed substantially in parallel. Pseudo-range, carrier phase and doppler frequency, and the underlying data are thereby derived.

Abstract: A GPS system and method for generating precise position determinations. The GPS system includes a ground based GPS reference system which receives with a reference receiver GPS signals and makes phase measurements for the carrier components of the GPS signals. The GPS reference system then generates and broadcasts an initialization signal having a carrier component and a data link signal having a data component. The data component of the data link signal contains data representing the phase measurements made by the reference receiver. The GPS system also includes a GPS mobile system which receives with a mobile position receiver the same GPS signals as were received by the reference system. In addition, the GPS position receiver receives the data link and initialization signals broadcast by the reference system.