Abstract: A station-based method for use in a wireless location system determines the geographic location of a mobile wireless transmitter. The wireless location system includes signal collection systems and location processors for processing digital data provided by the signal collection systems. The station-based method comprises receiving a transmission from a wireless transmitter at multiple antennas and at multiple signal collection systems. The transmission is converted into a digital format in a receiver connected to each antenna at the multiple signal collection systems. At each signal collection system, digital data representative of the received transmissions are stored in a memory. The transmission is then demodulated at a first signal collection system, and appropriate phase correction intervals are determined.

Abstract: A method and a system for determining an altitude of an object of interest, for example, an airplane that transmits electromagnetic radiation in the form of radar signals. A number of sub-units that can detect the radar signals are spread out in an area, preferably in a large geographical area, where the radar signals of the airplane/object it is possible to detect. The sub-units communicate to the information center when they are able to detect the radar signals. The information center determines the altitude of the airplane based on the airplanes line of sight, i.e., its radar horizon, and thus which sub-units can detect the radar signals.

Abstract: An antenna array includes a reference antenna and a plurality of closely-spaced secondary antennas for mitigating the effects of multipath signals on a direct signal, each antenna connected to a corresponding receiver which outputs signal data. A computational device uses the post-correlation signal data to estimate the parameters of a virtual reflector and derive correction values for code data, signal noise, and carrier phase.

Abstract: A method and system for calculating the range between a source which emits electromagnetic energy having an unknown frequency and a first receiver of electromagnetic energy at at least three points along a portion of a source trajectory. The source trajectory portion is a substantially straight line which has two end points. The first receiver moves along a first, substantially straight-line receiver trajectory so that the frequency of the electromagnetic energy is Doppler-shifted. The first receiver measures the Doppler-shifted frequency at at least three predetermined times. Next, at least two ratios of frequencies are calculated, the ratios being functions of the Doppler-shifted frequencies and bearing angles. Finally, the range between the first receiver and the source is calculated from the frequency ratios at the at-least-three points. In a first preferred embodiment the source is stationary.

Abstract: A reference terminal used in positioning/locating of mobile terminals in a radiocommunication system is described. The reference terminal includes a time-of-arrival (TOA) receiver which is used to provide information associated with the location of mobile terminals. The TOA receiver also performs the function of calibrating the time delays within the reference terminal by measuring time delays associated with each time-sensitive component. For example, when the reference terminal transmits an uplink signal burst, e.g., reporting TOA information associated with a particular mobile terminal, a portion of this signal energy can be captured and propagated through antenna cables within the reference terminal. The TOA receiver can be used to determine time delays associated with the returned signal energy through various paths, which delays can be used to calibrate the positioning information generated by the reference terminal.

Abstract: An asset management radio location system uses time-of-arrival differentiation for random and repetitive spread spectrum, short duration pulse `blinks` from object-attached tags, to provide a practical, continuous identification of the location of each and every object within an environment of interest, irrespective whether the object is stationary or moving. Correlation-based RF processors determine which signals received spatially diverse antennas coupled to tag transmission readers are first-to-arrive signals as transmitted from any blinking tag. An object location processor carries out time-of-arrival differentiation of first-to-arrive transmissions from any blinking tag to determine where the respective object is located within the environment.

Abstract: The accuracy of multilateration systems can be greatly improved by using a correction method based on the SLS (Sideband Lobe Suppression) signal produced by a Secondary Surveillance Radar (SSR). Multilateration is a cooperative surveillance technique for aircraft equipped with Air Traffic Control Radar Beacon System (ATCRBS), Mode S, or Automatic Dependent Surveillance Broadcast (ADS-B) transponders. When one of these transponders aboard a vehicle is interrogated, it responds by broadcasting a message based on what the interrogation requests. These reply messages may be multilaterated to determine the source position of the transmission. Multilateration is a Time Difference of Arrival (TDOA) technique similar to triangulation. Multilateration can be performed to locate the transmission source of any SSR signal.

Abstract: A wireless location system receives signals transmitted by wireless telephones at a plurality of signal collection sites. To improve the accuracy of the location information, the system synthesizes greater bandwidth, and thus greater time resolution, than would otherwise be available. The location system commands an MTSO to make the wireless transmitter to be located change frequency channels, and a doubly-differenced carrier phase of the transmitted signal, or the time difference of arrival, is observed at each of many frequencies spanning the widest possible bandwidth. The phase-measurement data from these many frequencies are combined to resolve the inherent integer-wavelength ambiguity. To begin the process of ambiguity resolution, single-frequency channel, doubly-differenced, group delay measurements are used to resolve the ambiguity in the doubly-differenced phase difference between the most closely spaced frequency channels.

Abstract: A multi-dimensional tracking sensor for tracking a moving transmitter with particular applications in virtual reality and other real time computer applications. The system employs an electro-magnetic (EM) tracking sensor having a small lightweight transmitter with a transmitting antenna located on the target to be tracked and an array receiver with several local stationary antenna elements. Multiple antenna elements of the array receiver lie on the perimeter of the measured space in positions determined by a self-calibration procedure. The proposed device calculates a cross correlation function between two signals at each receiving unit to determine a spatial position of the tracked element via a system of linear equations.

Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Exemplary embodiments of the present invention provide improved techniques for using a system of monitoring or adjunct stations to provide this location information to the emergency service centers. For example, either time of arrival (TOA) or time difference of arrival (TDOA) techniques can be selectively used to process received signals and provide location information. Techniques for improving timing estimates are also disclosed.

Abstract: A method of determining the location of an unknown source (10) transmitting an unknown signal to satellite relays (14 and 16) comprises receiving the signal from the relays at respective receivers (18). The receivers (18) receive reference signals via respective relays from a common source (22). The unknown signal and reference signal received by each receiver (18) are processed coherently to preserve their timing and phase information relative to one another independently of signals received elsewhere. The signals are frequency downconverted and digitised, and transferred to a common processing computer (150). The computer (150) performs cross ambiguity function processing of the reference signals to determine their relative Differential Time Offset (DTO) and Differential Frequency Offset (DFO).

Abstract: A wireless system for locating a signal emitter includes at least three base stations for receiving the emitter signal, and a central processing site for converting information from the received signals into range estimates. Specifically, an antenna array at each base station for receives the emitter signal, and a beamformer isolates the direct path component of this received signal from interference and multi-path signals using cyclic phase minimizer techniques. In operation, an extractor is used to separate a cyclostationary feature from the direct path component of the emitter signal, and the cyclostationary feature is identified in an absolute time reference. The identified cyclostationary feature is then passed to the central processing site. At the central processing site, phase delay characteristics of the cyclostationary features from all participating base stations are compared with each other to obtain phase difference measurements.

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: An asset management radio location system uses time-of-arrival differentiation for random and repetitive spread spectrum, short duration pulse `blinks` from object-attached tags, to provide a practical, continuous identification of the location of each and every object within an environment of interest, irrespective whether the object is stationary or moving. Correlation-based RF processors determine which signals received spatially diverse antennas coupled to tag transmission readers are first-to-arrive signals as transmitted from any blinking tag. An object location processor carries out time-of-arrival differentiation of first-to-arrive transmissions from any blinking tag to determine where the respective object is located within the environment.

Abstract: To locate a person within a particular room inside a building or, if outside, within a small enough radius that enables a rapid identification of where that person is located, a system of sensors is strategically disposed throughout the building or area. The sensors are calibrated so that upon activation of an alarm the feedback from all of the sensors enables differentiation of the location of the alarm. To locate an object within a defined area, received values output by the sensors are compared to stored reference values received by the sensors when transmitting reference signals. A best fit of the received values against the reference values is performed to determine the location of the person. To create the stored reference values, a calibration of the sensors is performed. This includes transmitting one at a time a plurality of reference signal levels, and measuring an output of each of the sensors after each transmission.

Abstract: The disclosure describes a novel Time Difference of Arrival (TDOA) method and system for determining the position of a mobile radio terminal within an associated mobile radio system, which is based on Time of Arrival (TOA) measurements, including a plurality of radio base stations, measuring devices, network controller, and service node. The measuring devices are synchronized in otherwise unsynchronized radio base stations. The measuring devices measure TOA on demand and (optionally) Direction of Arrival (DOA), on a digital uplink time slot or on digital information on an analog uplink traffic channel in one or more radio base stations. The TOA and DOA information and the traffic channel number are reported to a Mobile Services Switching Center, which obtains the mobile terminal's identity from the traffic channel number and sends the terminal identity and TOA and DOA measurement information to a Service Node.

Abstract: A method for determining the position of a mobile station within a cellular telephone system having a plurality of base stations. A signal is transmitted at a low power level from the mobile station. The strength of the signal is then temporarily increased from the low power level to an increased power level, and the signal is temporarily transmitted from the mobile station at this increased power level. While the signal is being temporarily transmitted from the mobile station at the increased power level, the signal is used to make at least a first positional measurement. The position of the mobile station is determined in accordance with the first positional measurement.

Abstract: An asset management radio location system uses time-of-arrival differentiation for random and repetitive spread spectrum, short duration pulse `blinks` from object-attached tags, to provide a practical, continuous identification of the location of each and every object within an environment of interest, irrespective whether the object is stationary or moving. Correlation-based RF processors determine which signals received by tag transmission readers are first-to-arrive signals as transmitted from any blinking tag, and an object location processor carries out time-of-arrival differentiation of these first-to-arrive transmissions from any blinking tag to determine where the respective object is located within the environment. A low power interrogation wand may be employed to refine the location of an object by a user programmed transmission-response exchange between the wand and the tag associated with the object of interest.

Abstract: The system includes circuitry for measuring the distance between a transmitter and one or more receivers, and having a timing circuitry to measure the time-of-flight of an RF pulse and the transversed distance of the pulse. The use of two receivers in a single plane provides for the determination of the location of the transmitter with respect to a reference position created by the associated tracking system and the automatic tracking of the transmitter with the field of view of a camera by the tracking system.

Abstract: An adaptive signal level detector. The inventive detector includes a first circuit for receiving an input signal and providing a second signal identical to said input signal and delayed relative thereto. The amplitude of the delayed signal is compared to the maximum amplitude of the input signal. When the second signal is at a predetermined level relative to the input signal an output signal is provided. In a specific implementation, the invention (10) includes a first circuit (18) for detecting the signal level of the transmitted signal and providing a second signal in response thereto. The second signal is a logarithmic representation of the input signal The second signal is delayed (20) to provide a third signal. The third signal is subtracted (24) from the second signal to provide a fourth signal. When the fourth signal exceeds a predetermined threshold, an output signal is provided.

Abstract: A position location system includes multiple base stations spaced over a region. A portable unit within the region transmits a locating signal which is received by the base stations. The base stations report amplitude, phase and time data related to the locating signal to a control station. The control station includes a processor and memory that combine the data from all of the participating base stations to directly compute an optimal estimate of the location of the portable unit. The control station generates an ambiguity function based upon the probability that the portable unit is located at a particular position. By optimizing the ambiguity function, the error in the computation is minimized to produce an accurate position estimate.

Abstract: The invention is an electronic system for warning helicopter pilots of the presence of electric power lines during landing. The system detects electromagnetic fields created by electricity flowing through the power lines. When the helicopter is closer than a predetermined distance from the power line, visual and audio alarms alert the pilot of the danger. When the helicopter is a safe distance from the power line, the alarms reset.

Abstract: The multi-dimensional tracking sensor especially for virtual reality and other real time computer applications. The disclosure describes an electro-magnetic (EM) tracking sensor that consists of a small lightweight transmitter with a transmitting antenna located on the target to be tracked and an array receiver with several local stationary antenna elements (FIG. 1). Multiple antenna elements of the array receiver lie on the perimeter of the measured space in positions determined by a self-calibration procedure. The proposed device calculates a cross correlation function between two signals at each receiving unit to determine a spatial position of the tracked element.

Abstract: Method which involves determining the position of a number of measured objects by determining a number of directions to the measured objects from at least two measuring stations, of which at least one is mobile, the method being used to decide which of the points of intersection between the directions correspond to measured objects and which ones do not correspond to measured objects. Changes in the mutual movements between the measuring stations and the points of intersection are in this case determined by comparison between the paths in which the points of intersection and the measuring stations are moving. The points of intersection whose movement is not affected by changes in the movement of other points of intersection, or by changes in the movement of at least one measuring station, correspond to positions of measured objects.

Abstract: A system and method for determining the geolocation of a transmitter within or without a set of receiving stations. The system includes plural receiving stations which determine the time of arrival and the angle of arrival of a signal from a target unit. The signal determinations are communicated to a central processing unit which determines the geolocation of a radiating unit which would provide such times of arrival and angles of arrival. By use of both time of arrival and angle of arrival information at the central processing unit, the need for receiving stations to cover a desired geographic area is reduced.

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 population of locatable personal detection units (PDUs) (20) are worn by users. Any number of locators (14) are placed at known locations within an area (10) where the users tend to be. When an alarm event for an individual user occurs, a request signal is transmitted from the user's PDU (20). The request signal is received at several of the locators (14), each of which measure the power level of the request signal. A central computer (16) selects some of these locators (14) in response to the power level measurements. In sequence, the selected locators (14) transmit an interrogation signal to the PDU (20), the PDU (20) replies to the interrogation signal, and the locators (14) measure the duration transpiring between the interrogation and the reply. Based on the durations measured for at least three of the locators, the central computer (16) uses a multilateration process to localize the PDU (20).

Abstract: Measuring the difference in dihedral angles formed by planes defined by a pair of passive sensors, a target, and a reference plane to determine whether both sensors are tracking the same target. The reference plane is defined by the positions of the two sensors and the origin of the system's reference coordinates. A sensor-target plane is determined by the sensor's position, the position of the other sensor, and the position of its target. If the target is the same for both sensors, the sensor-target planes will be substantially the same and their dihedral angles formed with the reference plane will be substantially equal. If the target is not the same for both sensors, then a statistic relating to the dihedral angles with the reference plane will be significant. A decision based on the dihedral angle statistic and a statistic derived from the tracking predictor, e.g., the Kalman Filter Residual, can be made whether the target is maneuvering, has been lost, is correctly tracked.

Abstract: A differential ranging location system is described which uses a modified time-of-arrival technique to determine the location of a frequency hopped spread spectrum radio signal. The transmitter simultaneously transmits two radio frequency carriers having different frequencies such that a phase difference is observed between the two carriers at a distance from the transmitter. The phase difference is proportional to the range from the transmitter that the carrier signals are observed. The two carrier signals from the single transmitter are received by at least three and in special cases four base stations which calculate the differential time of arrival based on the phase differences of the received carriers. The calculated phase differences are then sent to a central location which locates the position of the transmitter based upon a planer hyperbolic location algorithm.

Abstract: A radio location system comprises a wireless transmitter that outputs two megahertz period bursts of two gigahertz radar carrier signals. A receiver system determines the position of the transmitter by the relative arrival of the radar bursts at several component receivers set up to have a favorable geometry and each one having a known location. One receiver provides a synchronizing gating pulse to itself and all the other receivers to sample the ether for the radar pulse. The rate of the synchronizing gating pulse is slightly offset from the rate of the radar bursts themselves, so that each sample collects one finely-detailed piece of information about the time-of-flight of the radar pulse to each receiver each pulse period. Thousands of sequential pulse periods provide corresponding thousand of pieces of information about the time-of-flight of the radar pulse to each receiver, in expanded, not real time. Therefore the signal processing can be done with relatively low-frequency, inexpensive components.

Abstract: A multi-path resistant frequency-hopped spread spectrum mobile vehicle or personal location system is described which provides low cost manufacture and low power operation while still enabling the accurate location of the mobile unit over long distances and in moderate to severe multi-path conditions. The frequency-hopped spread spectrum mobile vehicle or personal location system consists of a central station, a plurality of base stations and a plurality of mobile transmitters which transmit using a frequency-hopped spread-spectrum differential bi-phase shift keying communication signal. Frequency Shift Keying modulation may also be used. Each of the plurality of base stations include an array of receiving dipole antennas and employs special algorithms for retrieving very low power frequency-hopped spread spectrum signals in a noisy and multi-path environment.

Abstract: A multilateration location system (12) includes a locatable unit (16) and any number of known-position locators (14). A time of arrival detector (22) determines instants in time when a location signal (20) transmitted by the locatable unit (16) arrives at various known-position locators (14). For each combination of two known-position locators (14) that receive the location signal (20), a pre-estimation process (32) determines whether the difference in arrival times is less than or equal to a maximum propagation duration for the locator pair. The maximum propagation duration is based upon the distance between the locators (14) in the locator pair. If the difference is greater than the maximum propagation duration, the difference is omitted from the data set processed by a multilateration calculation process (34). A post estimation filtering process (36) screens out location estimates that are too distant from a predicted position.

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 of analysing clusters of bearings (A, B, C, D) taken of distant sources by an array of direction finding stations. Each bearing has an error +E and a triangulation process is used to fix the position of the sources. A combination of bearings is taken one each from the stations. Each bearing of the combination is taken in turn as a spoke (3) directed at a source. The triangulation process generates a bar (31, 32, 33) of intersection points along the spoke for each other bearing of the combination, each bar corresponding to the error +E of each bearing. The number of overlaps between pairs of bars along a spoke is totalled to give a spoke score. The spoke scores of all spokes of the combination is summed to form a fix confidence score for a source which may be associated with the combination, or cluster, of bearings. Methods are also provided for rejecting redundant fixes associated with subsets of bearings within a cluster.

Abstract: RF energy radiated by impacting munition rounds is used to provide an indication to a gunner where the rounds from his gun are striking, or to control a gun servo (158) to automatically correct the aiming of the gun. The RF energy from the rounds is received by several antennas (32, 34, 36) in a known geometry and the angle of arrival computed from the differences in the times of arrival at each antenna. The impact locations can be displayed in the existing gun sight, or in a head up display for the gunner. The angle of arrival information can further be used to control a gun aiming servo (158) to correct the aim of the gun to improve accuracy.

Abstract: A system for accurately locating a mobile cellular radio includes plural radio receivers, the position of each being precisely known, a satellite-based time source for providing the actual time of arrival of a radio signal at the plural radio receivers, and a device for removing multipath and cochannel interference from the received signals so that actual time of arrival of the radio signal may be determined accurately. The Global Positioning System (GPS) may be used to provide the time signal and to provide the precise location of the plural radio receivers. The system may be used to passively determine the location of the mobile radio and is accurate enough to use with a computer generated map system.

Abstract: A system for measuring a position of an object moving in a limited area includes a transmitter provided on the moving object for periodically transmitting pseudo-noise signals at time intervals in accordance with an intrinsic period assigned to the object, and a plurality of stations located at predetermined coordinates, each of the stations including a receiving part for receiving the signals so that pulse signals whose period is matched with the intrinsic period are output, and a detecting part for detecting correlative pulses from the pulse signals. The system further includes a delay detecting part for detecting a time difference between reception of a first correlative signal by one of the stations and reception of each of the subsequent correlative pulses by the other stations, and a control part for calculating coordinates of the position of the moving object based on the time differences and based on the given coordinates of the stations, so that the calculated coordinates of the position are output.

Abstract: An apparatus determines the location of a signal source having coordinates x,y). The source may be located as far away as two thousand km and does not require knowledge of ionospheric height or layer structure. The apparatus comprises at least three receivers adapted to receive the signals from the signal source. The coordinates, (x.sub.1,y.sub.1), (x.sub.2,y.sub.2) and (x.sub.3,y.sub.3), of each of the receivers are very precisely known. One receiver is capable of receiving signals from the other two receivers through different means (e.g. a wide-band telephone link). A plurality of at least three timers, one connected to each receiver, measures precisely the time difference of arrival (TDOA) of the signals from the signal source. A plurality of at least three means, connected one to each of the receiving means, determine the vertical angles .phi. at which the signal from the signal source is received by each of the receivers.

Abstract: Position location processing using a series of processing routines for enhanced position location in a hyperbolic ranging system adapted to more accurately indicate the position of mobile transmitters within the system. These routines incorporate data in an overdetermined system to refine the position estimate and speed up computation time. The processing utilizes all data received and filters out data caused by radio propagation measurement error that contributes to overall position error. It selects the optimum subset of data to process prior to performing time-intensive mathematical operations which results in a substantial reduction in computation time, allowing for many more overall position computations per second. The advantages of the present position location processing include its ability to incorporate all data received to reduce the overall position error. Processing filters that provide for data extraction and position verification enhance the accuracy and reliability of the position estimate.

Abstract: A virtual secondary surveillance radar (VSSR) of the type described in U.S. Pat. No. 4,115,771 can produce inaccurate or indeterminate range information for a transponder positioned on or near a line between the actual SSR and the VSSR, owing to unfavorable geometrical relationships. This can be avoided by receiving the SSR interrogation and reply signals at two or more separated locations and processing the signals to provide positional information at a display site. No radar transmissions other than those of the existing ATCRBS are required.

Abstract: A radiolocation system for multipath environments, such as for tracking objects in a semiconductor fabrication facility (FIGS. 1a-1b), includes an array of receivers (20) distributed within the tracking area, coupled to a system processor (40) over a LAN. A TAG transmitter (30) located with each object transmits, at selected intervals, spread spectrum TAG transmissions including at least a unique TAG ID. In a high resolution embodiment, object location is accomplished by time-of-arrival (TOA) differentiation, with each receiver (FIG. 2b) including a TOA trigger circuit (64) for triggering on arrival of a TAG transmission, and a time base latching circuit (65) for latching the TOA count from an 800 MHz time base counter. In a low resolution embodiment, each receiver of the array is assigned a specific location-area, and receives TAG transmissions almost exclusively from TAGs located in that area, thereby eliminating the need for any time-of-arrival circuitry.

Abstract: Differential phase measurement techniques and apparatus for accurately loing unknown transmitters over great distances at radio frequencies below HF. A network of separated, time- and phase-synchronized, pairs of receiving stations having vertical whip antennas and having a known base-line geometry with respect to each other are used to accurately measure VLF phase differentials. The measured phase differences are compared against theoretical calculated values to provide highly accurate transmitter location information.

Abstract: According to a target locating method and system, each of a plurality of sensing stations, for example HFDF sensors, senses a nominal value of a predetermined measurement variable such as a bearing, differential times of arrival, etc., relating the location of a potential target in a target area to the location of each respective sensing station. Error models associated with each sensing station, along with the nominal measured variable for each sensing station, are transmitted to a central data collector. A central processor receives the collected data and directs a monitor to display a representation of the target area. The invention also provides a method for estimating the position of the target based on the nominal measurements of the location variable and also on the error models for each sensing station. The target area is divided into a grid of target area segments.

Abstract: A precision aircraft landing system comprising at least four receivers which are located at different predetermined positions. Each receiver includes a precision timer for measuring the timer interval between the receiver's detection of an interrogation signal and a reply signal from a transponder onboard the aircraft. The system also includes a central processing unit (computer) at a base station which collects the time measurements from the receivers, and calculates the location of the aircraft. Because more than three independent measurements are used, the base station can compute not only the three-dimensional coordinates of the aircraft, but also the transponder reply time. Preferably estimation filtering calculations, such as Kalman filtering, are used to improve the accuracy. The aircraft's position is compared with a mathematical description of a desired approach path, and the position error is then communicated to the aircraft.

Abstract: A method and a system are disclosed for measuring the baseline vector b between a pair of survey marks on the ground by radio interferometry using radio signals broadcast from the earth orbiting satellites of the NAVSTAR Global Positioning System (GPS), the radio signals broadcast by the satellites being double-sideband modulated with their carriers suppressed. The signals received by one antenna during a predetermined time span are separated into upper and lower sideband components. These separate components are filtered, converted to digital form, and then multiplied together. Differences in Doppler shift are utilized to distinguish the carriers of different satellites. Thus, the powers and carrier phases of the signals from a plurality of satellites are measured simultaneously and numerical data representing the measurement results are obtained at each survey mark.

Abstract: The method of locating an unknown radio-frequency transmitter includes: (a) receipt of signals radiated from the transmitter by a plurality of receivers; (b) retransmission of the received signals to a plurality of antennas; (c) performing a time difference of arrival (TDOA) calculation which compensates for a relative delay value, which is a function of the distances from the transmitter to each of the receivers, the distances from each of the receivers to the antennas, and the speed of light; (d) performing a frequency difference of arrival (FDOA) calculation which compensates for a relative frequency value, which is a function of the relative velocity of each receiver with respect to the velocity of the Earth; (e) repeating these steps a plurality of times; and (f) determining the location of the unknown transmitter based on the plurality of TDOA and FDOA calculations.

Abstract: A stolen vehicle recovery system (20) in which a vehicle transceiver (30) is disposed on each vehicle (28) for cyclically transmitting a pulsed signal which is modulated by a data stream comprising a verification code, a unique identity code associated with the vehicle (28), and a code which corresponds to whether the detected vehicle (28) is moving or stationary. The vehicle transceiver (30) is automatically activated if a proper authorization signal is not provided to the transceiver (30) by a verification unit. A scanning receiver (42) decodes the pulsed signal and provides the information to a control processor (40) which, in turn, sets remote direction finding receivers (44, 46, 48), set up in a triangulation antenna array, to the appropriate channel. The D.F.

Abstract: A synchronization system and method for a lightning location system having a plurality of remote lightning detectors transmitting data to a lightning position analyzer via a communication system having variable transmission delays. Each lightning detector includes a clock for identifying the time of occurrence of a lightning event such as cloud to ground lightning discharge, the time of occurrence data being transmitted to the position analyzer along with other data representing the lightning event. The position analyzer also includes a clock for identifying the time of arrival at the analyzer of data representing a lightning event. Lightning events are correlated by the position analyzer by comparing the time intervals between the occurrence of lightning events detected by one detector and the time intervals between the occurrence of lightning events detected by a second detector.

Abstract: A method for detecting lightning as an electrical atmospheric disturbance and for providing an indication of the geographic position of that disturbance includes the stationing of at least three receivers at known geographic locations in spaced relationship to each other. Signals are encoded at each of the receivers representative of the time of arrival of an electrical indication of an emission from the lightning strike, in relation to a common timing source. All of the encoded signals are transmitted to a central facility and thereafter processed for deriving the position of the lightning strike irrespective of whether the position of the lightning occurred within or outside the perimeter bounded by the three receivers. The system is synchronized with the U.S. Coast Guard LORAN navigation network, and includes various features which permit a more accurate analysis of lightning position.

Abstract: A radiolocation system for multipath environments, such as for tracking objects in a semiconductor fabrication facility (FIGS. 1a-1b), includes an array of receivers (20) distributed within the tracking area, coupled to a system processor (40) over a LAN. A TAG transmitter (30) located with each object transmits, at selected intervals, spread spectrum TAG transmissions including at least a unique TAG ID. In a high resolution embodiment, object location is accomplished by time-of-arrival (TOA) differentiation, with each receiver (FIG. 2b) including a TOA trigger circuit (64) for triggering on arrival of a TAG transmission, and a time base latching circuit (65) for latching the TOA count from an 800 MHz time base counter. In a low resolution embodiment, each receiver of the array is assigned a specific location-area, and receives TAG transmissions almost exclusively from TAGs located in that area, thereby eliminating the need for any time-of-arrival circuitry.