Abstract: A Doppler frequency searching method and correlator are disclosed. In the present invention, before Doppler frequency removal, a received signal is converted into digital form and the spreading code is removed. Then the signal is down-sampled to have a low sampling rate, which can be determined according to the maximum Doppler frequency to be searched. The Doppler frequency searching is done by stages. Each stage is in charge of a portion of the Doppler frequency to be removed. The sampling rate can be further reduced in each stage. Each stage can have a plurality of Doppler frequency removal units sharing the portion of Doppler frequency that the stage is to remove. Power consumption is reduced since Doppler frequency removal is executed with low sampling rate.

Abstract: A method and system for receiving a beacon signal includes a splitter that divides a beacon signal into a first beacon signal and a second beacon signal. The system includes a pair of downconverters down converting the beacon signals into down converted signals. A pair of beacon receivers receives the two downconverted signals and a controller communicates with the first beacon receiver and the second beacon receiver through a first connection and a second connection. Upon interruption of the first connection, the second connection is used for communicating the beacon signals.

Abstract: Methods and apparatus for processing of data from a network of GNSS reference stations are presented. An ionosphere-free, federated geometry filter is employed so that computation time increases only linearly with the increase in number of reference stations, significantly reducing processing time as compared to a centralized filter approach.

Abstract: A method for navigation processing in a satellite positioning system receiver is disclosed. A method in accordance with the present invention comprises separating the three SATPS satellites into a first pair and a second pair, constructing a primary solution and an alternate solution, wherein the primary solution and the alternate solution satisfy the measurement constraints, computing a Doppler difference estimate for the primary solution and a Doppler difference estimate for the alternate solution, computing Doppler difference residuals for the first pair and the second pair of SATPS satellites, and comparing the Doppler difference residuals for said primary and alternate solutions to determine a valid solution. Typically, the computing of a Doppler difference residuals comprises differencing a measured Doppler difference from an estimated Doppler difference for the first pair and the second pair of SATPS satellites.

Abstract: A method for substituting at least one high quality position measurement of an object taken before an interrupting event with a set of upgraded low quality position measurements of the object provided by the same source of measurements after the interrupting event.

Abstract: A method of GPS accuracy adjustment for an integrated INS/GPS navigation system which utilizes microelectro mechanical systems (MEMS) based inertial sensors to mitigate multipath problems arising when a vehicle is in an area with many high-rise buildings is disclosed. Even when GPS measurement output values are deviated from that expected, the INS/GPS navigation system uses as many measurement outliers as possible without discarding, unless they are obvious error values, thereby maintaining a practical level of accuracy. The measurement outliers typically occur when the integrated INS/GPS navigation system receives GPS signals which have transmitted through multipaths such as reflection by buildings, since the signal path lengths vary.

Abstract: A device can access scaled values and scaling factors, which are used to convert the scaled values into coefficients and residuals. The coefficients and residuals can in turn be used with time-dependent functions to reconstruct predicted ephemeris data, including clock correction data, for satellite navigation system satellites. Ephemeris data that is broadcast from any of the satellites can be used to update the calculated ephemeris data.

Abstract: A method and apparatus for determining long term orbit (LTO) models using variable time-horizons to improve the orbit and clock model accuracy. The method and apparatus use either historic ephemeris or historic measurements for at least one satellite to produce an orbit parameter prediction model (an LTO model). The parameter predicted by the model is compared to an orbit parameter of a current broadcast ephemeris. The result of the comparison (an indicia of accuracy for the model) is used to establish a time-horizon for the orbit parameter prediction model for that particular satellite. Such a time-horizon may be established in this manner for each satellite within a satellite constellation.

Abstract: A GNSS ultra-tight coupling (UTC) receiver architecture applicable to space borne orbit platforms is described. A receiver in accordance with this architecture retains the rotational motion sensors typically found in an inertial measurement unit (IMU) of a conventional UTC receiver, but replaces the IMU accelerometer sensors with precise orbital dynamics models to predict the translational motion of the platform center of gravity (CG). Drag and radiation pressure may be modeled as well. The various models can be implemented in software. The IMU rotational sensors are retained for compensation of the GNSS antenna lever arm effect due to platform rotation.

Abstract: The invention relates to a data server (40) used in a system (10) for supplying complementary data, so-called augmentation data, for satellite navigation signals. The inventive server (40) is especially adapted to be used with elements that are compatible with those used in EGNOS technology (European Geostationary Navigation Overlay Service). Said system (10) for supplying augmentation data for the satellite navigation signals comprises at least one calculator (20) for the determination of said augmentation data, said augmentation data being determined from data transmitted by at least one receiving station (S01. . . SON) receiving navigation information sent by means of at least one satellite. Said server (40) comprises a first inlet (401) for receiving the augmentation data transmitted by the calculator (20), a first outlet (402) for transmitting the augmentation data towards at least one user (U01. . .

Abstract: Techniques to determine a position estimate for a wireless terminal. An accurate position estimate for the initially obtained (e.g., based on a first (accurate) position determination sub-system). For each of one or more transmitters (e.g., base stations) in a second (less accurate) position determination sub-system, an “expected” pseudo-range is computed based on the accurate position estimate for the terminal and the base station location, a “measured” pseudo-range is also obtained, and a pseudo-range residual is then determined based on the expected pseudo-range and the measured pseudo-range. Therefore, to determine an updated position estimate for the terminal, measured pseudo-ranges are obtained for a sufficient number of transmitters. The measured pseudo-range for each base station may be corrected based on the associated residual. The updated position estimate is then determined based on the corrected pseudo-ranges for these transmitters.

Abstract: A mobile communication device (202) and peer mobile communication devices (204, 206) are capable of direct voice and data communication. The mobile communication device has a reference oscillator (104) which is used for generating operating frequencies, and is subject to frequency errors resulting from manufacturing tolerances, heat, and other error sources. The mobile communication device receives a frequency correction message (506) from a peer mobile communication device that has calibrated its reference oscillator. The frequency correction message contain offset information which is used by the mobile communication device to determine its offset (316) from a nominal frequency (302).

Abstract: The dual mode positioning system comprises multiple wireless network devices, one of the multiple wireless network devices including a GPS receiver. DSS is coupled to the multiple wireless network devices and an operation mode switch is also coupled to the multiple wireless network devices including a GPS receiver. A satellite GPS receiver coupled to the operation mode switch. The satellite GPS receiver is operated in an indoor area confined by walls with wide FOV (field of view) glass window, the operation mode switch switching to GPS mode for the satellite GPS receiver receives signals from greater than 3 satellites. Moreover, the satellite GPS receiver is operated in an indoor area confined by concrete walls or walls with narrow FOV glass window, the operation mode switch switching to Joint GPS/WPS mode for the satellite GPS receiver cannot receive signals from greater than 3 satellites.

Abstract: The present disclosure relates to an arrangement and an electronic navigational control system for a self-propelling device (5), preferably a lawn-mowing robot. The system comprises at lease one navigational control system (3) connected to at least one signal generator (1) and a sensing unit arranged at the self-propelling device (5). The sensing unit senses at least one, in the air medium propagating, time and space varying magnetic field, at least transmitted via the navigational control station (3) and in turn retransmits at least one signal processed by the unit to at least one driving source which contributes to the device's movements across the surface. The system comprises structure by which the signal generator (1) sends a current through the navigational control station (3), the current generating the time and space varying magnetic field, whereby the sensing unit comprises structure by which the device (5) is maneuvered based on the properties of the sensed magnetic field.

Abstract: A method and a device for generating a modulated navigation signal which is intended to be used to position a downlink receiver. Four pseudorandom navigation codes of chip rhythms greater than 0.5 MHz are modulated onto a carrier of frequency greater than 500 MHz according to an 8-PSK modulation of constant amplitude with a modulation frequency fM such that: 8fc?fM where fc=Max(fci), and fci designates the chip rhythms.

Abstract: Systems, methods and devices for improving the performance of Global Navigation Satellite System (GNSS) receivers are disclosed. In particular, the improvement of the ability to calculate a satellite position or a receiver position where a receiver has degraded ability to receive broadcast ephemeris data directly from a GNSS satellite is disclosed. Correction terms can be applied to an approximate long-term satellite position model such as the broadcast almanac.

Abstract: Methods and apparatus for receiving an estimate of L1 iono delay and L1 iono delay rate, receiving GEO slant ionospheric delay, receiving user iono vertical error information for a GEO satellite, and computing a L1/L5 bias estimate from the estimate of L1 iono delay and L1 iono delay rate and GEO slant ionosperic delay. A wide area augmentation system (WAAS) includes L1/L5 bias estimation. The L1/L5 bias is the differential bias between the WAAS GEO satellite L1 and L5 signals. The data used in the L1/L5 bias estimation include the GEO L1 ionospheric delay estimated from a Kalman filter, and the GEO slant ionospheric delay calculated from the Ionospheric Grid Point (IGP) information in a WAAS message. The Sigma User Ionospheric Vertical Error (UIVE) is used as one of the conditions for performing the L1/L5 bias estimation.

Abstract: A system and method are provided for detecting local interference in GPS signals. A plurality of remotely located GPS receivers are capable of receiving GPS signals and producing GPS related data. A monitoring station is capable of storing at least one expected GPS parameter for each of the plurality of GPS receivers. A first processor at the monitoring station is programmed to determine, for each of the GPS receivers, whether said GPS related data deviates from any of the at least one GPS parameter by more than a predetermined range of error, and for issuing a warning in response thereto.

Abstract: An anti-jam system for use with a normal L1 Only Global Positioning System (GPS) receiver. The anti-jam system includes a switchable L1/L2 RF downconverter for receiving L1 and L2 RF signals from an RF signal source and converting a selected one of the L1 or L2 RF signals to a low frequency analog signal. An analog-to-digital converter (ADC) converts the low frequency analog signal to a digital signal. A digital anti-jam processor processes the digital signal to enhance anti-jam performance. A digital-to-analog converter (DAC) converts the processed digital signal to an enhanced analog signal. An RF upconverter converts the enhanced analog signal to an L1-based RF signal for use by a normal L1 Only GPS receiver.

Abstract: A horizontal navigation system aided by a carrier phase differential Global Positioning System (GPS) receiver and a Laser-Scanner (LS) for an Autonomous Ground Vehicle (AGV). The high accuracy vehicle navigation system is highly demanded for advanced AGVs. Although high positioning accuracy is achievable by a high performance RTK-GPS receiver, the performance should be considerably degraded in a high-blockage environment due to tall buildings and other obstacles. The present navigation system is to provide decimeter-level positioning accuracy in such a severe environment for precise GPS positioning. The horizontal navigation system is composed of a low cost Fiber Optic Gyro (FOG) and a precise odometer. The navigation errors are estimated using a tightly coupled Extended Kalman Filter (EKF). The measurements of the EKF are double differenced code and carrier phase from a dual frequency GPS receiver and relative positions derived from laser scanner measurements.

Abstract: According to one embodiment of the invention, a stationkeeping method for a geostationary satellite includes determining a gravitational force of the sun on the satellite at a beginning of a stationkeeping operation and a gravitational force of the moon on the satellite at the beginning of the stationkeeping operation. An initial inclination vector of the satellite is determined at the beginning of the stationkeeping operation that accounts for a first set of one or more perturbations affecting the orbit of the satellite. A maneuver strategy is determined to correct for a second set of one or more perturbations affecting the orbit of the satellite without accounting for the first set of one or more perturbations affecting the orbit of the satellite. Finally, a maneuver is performed on the satellite according to the maneuver strategy.

Abstract: A method, apparatus for reducing errors in a plurality of beacon beams is disclosed. The method comprises the steps of computing quantized channel weights {tilde over (W)}c from channel weights Wc for at least some of the channels; estimating the quantization error ?Ba for each of the beacon beams from a difference between the channel weights Wc and the computed quantized channel weights {tilde over (W)}c; and adding the estimated quantization error ?Ba to the beacon beams. Similarly, a beacon biases equivalent to the beacon asymmetry error can be computed by the ground beacon beam forming software and uploaded to the on-board software for error compensation. The apparatus comprises one or more means, such as a processor communicatively coupled to a memory storing instructions for performing these operations.

Abstract: Navigation signal group delay calibration methods and systems are described. In an embodiment, a code signal generated in a navigation system platform can be measured where the code signal includes timing delay(s). An additional code signal generated in the navigation system platform can be measured where the additional code signal is designated as a timing reference signal. A differential group delay between the code signal and the timing reference signal can the be mathematically estimated in the navigation system platform to correct for an inaccurate position estimation that would result from the timing delay(s).

Abstract: A navigation satellite receiver accepts satellite-position table messages comprising truncated GPS ephemeris parameters. In particular, at least one of the two harmonic corrections to inclination angle, Cic and Cis, are not communicated and not used in the solution of navigation receiver position. In a first method embodiment of the present invention, both the two harmonic corrections to inclination angle, Cic and Cis, are omitted from the computation. In a second method embodiment of the present invention, only one of the two harmonic corrections to inclination angle, Cic and Cis, are omitted from the computation, depending on Min(Cis sin(2?k), Cis cos(2?k)).

Abstract: A precision antenna pointing system and methods are disclosed. Antenna pointing error is determined by detecting RF signal phases at locations along the edge of an antenna reflector. A set of signal phase reference harnesses are used to compensate for harness induced errors. Furthermore, multiplexing is used to minimize electronics induced phase errors.

Abstract: A system and a method for augmentation of satellite positioning systems wherein a monitoring ground station (MGS) is connected to a computer center in charge of determining the level of error of a satellite (NS) broadcasting positioning signals, and transmitting navigation correction data to a mobile user. The transmission is performed using a digital satellite system using at least one digital satellite (DS) capable of broadcasting multiplexed data in down-link transmission to a user station (U). The user station (U) de-multiplexes and retrieves the navigation correction data from said digital satellite down-link transmission by way of a frame adapter (7) connected to a satellite receiver (6). Specific data such as time or GNSS almanacs are replicated under specific format and put into specific parts of a signaling channel to enable time broadcast to standard receivers of a DS system, and to speed-up acquisition of GNSS satellite signal by standard GNSS receivers possibly in use in the U station.

Abstract: An Assisted Global Positioning System (AGPS) module time synchronization method and device using system time information in a mobile terminal that perform time synchronization using system frame information and a GPS module operation period in a process of searching for the position of a terminal using the AGPS module in an asynchronous mobile communication system. Accordingly, the GPS module operation period is set to be greater than the system frame period so that GPS system time can be immediately seen when an arbitrary GPS tick interrupt is operated.

Abstract: A communication system has a high altitude communication device that has an antenna for directing beams to a fixed cell pattern with a polarity of cells. A specific pattern of cells having the same communication resource is provided. Preferably, cells having the same resource are separated. The antenna is shaped to suppress interference with locations having the same resource. The areas not having the same resource are not suppressed to allow the system to have maximum capacity and allow a smaller antenna aperture.

Abstract: A system and method are provided for detecting local interference in GPS signals. A GPS receiver is capable of determining its GPS coordinates. A memory is capable of storing an initial location of the GPS receiver and a user-defined range of error. A processor is programmed to determine whether GPS coordinates from the GPS receiver differ from the initial location by more than a range of error, and for issuing a warning in response thereto.

Abstract: A method of GPS accuracy adjustment for an integrated INS/GPS navigation system which utilizes microelectro mechanical systems (MEMS) based inertial sensors to mitigate multipath problems arising when a vehicle is in an area with many high-rise buildings is disclosed. Even when GPS measurement output values are deviated from that expected, the INS/GPS navigation system uses as many measurement outliers as possible without discarding, unless they are obvious error values. The measurement outliers occur when the integrated INS/GPS navigation system receives GPS signals which have transmitted through multipaths such as reflection by buildings, since the signal path lengths vary. Even in such a condition, rather than simply discarding such measurement outliers, the method utilizes the measurement outliers while adjusting the accuracy thereof depending on the degree of deviation.

Abstract: An apparatus for providing a telematics service including an AGPS function. An initial position measuring time of a telematics system is shortened due to the AGPS function of the telematics service, so the telematics service is rapidly provided to a user. Because the telematics system utilizes satellite ephemeris information and user position information, a reception sensitivity of a GPS signal is improved in a downtown area, in which the GPS signal is attenuated. The telematics system includes an AGPS information processing module for rapidly providing the telematics service to the user.

Abstract: A mobile terminal generates an estimate of GPS time. The mobile terminal includes a cellular receiver, a GPS receiver, and a processor. The cellular receiver is configured to receive communication signals from cells in a wireless communication system. The GPS receiver receives GPS signals and determines a GPS time reference therefrom. The processor estimates a cell time reference from the received communication signals, and generates cell-to-GPS timing data that represents a time offset between the cell time reference and the GPS time reference. The processor then estimates GPS time based on a time indicator portion of a received communication signal and the cell-to-GPS timing data. The estimated GPS time may be used by the GPS receiver to acquire GPS signals.

Abstract: The invention provides a system and method for activating an in-vehicle wireless communication device. A mobile identification number associated with the wireless communication device is provided. A broadcast signal containing the mobile identification number and a satellite radio subscriber identifier is received at an in-vehicle satellite radio receiver. The mobile identification number is stored in the wireless communication device based on the satellite radio subscriber identifier.

Abstract: The present invention relates to a GPS/dead-reckoning combination system and an operation method of the same. The GPS/dead-reckoning combination system includes a GPS receiver that receives an absolute position data of a moving unit from a GPS; an inertia sensor that measures a displacement of the moving unit based on a dead-reckoning method; a forward and backward movement judging unit that judges a state data concerning a forward or backward movement of the moving unit; a dead-reckoning processor that measures a running distance and a position of the moving unit based on a dead-reckoning method in reference with the data provided from the inertia sensor and the forward and backward movement judging unit; and a computation unit that estimates the current position of the moving unit in reference with the data from the GPS receiver and the dead-reckoning processor.

Abstract: A system for standard positioning service (SPS) and precise positioning service (PPS) cooperative operation is disclosed. In one embodiment, a PPS receiver is utilized to process a PPS data portion of a positioning signal. In addition, an SPS receiver is utilized to process an SPS data portion of the positioning signal. Furthermore, the PPS receiver and the SPS receiver are communicatively coupled such that the PPS data portion from the PPS receiver is cross-validated with the SPS data portion from the SPS receiver thereby corroborating the accuracy of the positioning signal.

Abstract: A plurality of satellites are placed into a virtually geosynchronous orbit, in which a first part of the orbit, that is near apogee, has a similar movement to the rotation of the earth, and therefore the orbit appears virtually stationary relative to the earth. Different satellites in the orbit are caused to have specified standardized parameters, and also defined according to an orbital position at a date certain. The different satellites and therefore be assigned to different owners according to these parameters.

Abstract: A method and apparatus for calibrating such a spot beam antenna by use of scanned spot beam signal characteristics measured by a plurality of ground based navigation receivers is disclosed.

Abstract: A horizontal navigation system aided by a carrier phase differential Global Positioning System (GPS) receiver and a Laser-Scanner (LS) for an Autonomous Ground Vehicle (AGV). The high accuracy vehicle navigation system is highly demanded for advanced AGVs. Although high positioning accuracy is achievable by a high performance RTK-GPS receiver, the performance should be considerably degraded in a high-blockage environment due to tall buildings and other obstacles. The present navigation system is to provide decimetre-level positioning accuracy in such a severe environment for precise GPS positioning. The horizontal navigation system is composed of a low cost Fiber Optic Gyro (FOG) and a precise odometer. The navigation errors are estimated using a tightly coupled Extended Kalman Filter (EKF). The measurements of the EKF are double differenced code and carrier phase from a dual frequency GPS receiver and relative positions derived from laser scanner measurements.

Abstract: A method and apparatus for estimating a lever arm correction between the wide beam antenna and the spot beam antenna in a navigational satellite system is disclosed. A prescribed satellite maneuver is used to increase the accuracy of the predicted satellite attitude in determining the lever arm, and lever arm corrections are provided to navigation receivers using curve fit coefficients to permit long range estimates and to minimize data transmission requirements.

Abstract: A method and apparatus for estimating a lever arm correction between the wide beam antenna and the spot beam antenna in a navigational satellite system is disclosed. A prescribed satellite maneuver is used to increase the accuracy of the predicted satellite attitude in determining the lever arm, and lever arm corrections are provided from a ground segment to navigation receivers using curve fit coefficients to permit long range estimates and to minimize data transmission requirements.

Abstract: A positioning satellite for a constellation of satellites of a radio navigation satellite system includes transmitter adapted to transmit operational signals intended to enable the determination of positions of radio navigation receivers, receiver adapted to receive at least some of the operational signals transmitted by positioning satellites of the constellation that are in view and processor adapted to interrupt transmission of the operational signals by the transmitter at selected times for a selected duration and to analyze during each transmission interruption at least some of the operational signals received by the receiver during at least a portion of the selected duration, for example to verify the waveform thereof and/or to determine pseudodistances.

Abstract: A satellite navigation method determined the position of the receiver (1) by determining the signal travel time between the satellites (3, 4) and the receiver (1). Either the times of reception by the receiver (1) of the signals from the satellites are determined, both by means of an accurate time reference, in the receiver (1), and based on the signals from the satellites, then compared with each other, or at least two position solutions are determined based on the reception times, by the receiver (1) of signals from the satellites, determined by means of an accurate time reference of the receiver (1) and of at least one signal from the different satellites respectively, then compared with each other.

Abstract: A communication satellite cellular coverage pointing correction using uplink beacon signal is provided. A ground-based beacon transmits a monopulse tracking signal or a Traveling Wave Coupler (TWC) tracking signal to a specialized tracking feed section located within each uplink and downlink antennae of a satellite. From the monopulse or TWC tracking signal, a pointing correction is determined for each reflector, for example, the angle off boresight and the angle between the present beam direction and the target direction. Each reflector is then gimbaled to re-point the reflector to the target area. In this way, both uplink and downlink antennae are provided with closed-loop control over antenna pointing.

Abstract: The present invention relates to terrain navigation wherein an earth-reflected satellite signal is received from at least one reference signal source whose position is known (120), for example a navigation satellite. Based on information contained in the received signal a measured estimate of a shortest reflection distance (d1(tb)) to the satellite (120) is derived. A relative spatial movement (?x, ?y, ?h) of a relevant craft (110) since a previous positioning instance (ta) is registered onboard the craft (110). Moreover, stored surface information is retrieved pertaining to an elevation (h1b) of the earth surface (130) in relation to the mean sea level (z0) at at least one geographical position (X1b, Y1b). Based on the relative spatial movement (?x, ?y, ?h) and the retrieved surface information at least one calculated estimate of the shortest reflection distance (d1(tb)) to the satellite (120) is derived.

Abstract: A system for determining estimated navigation signal error information. Several error models are used by the evaluation unit, and, as a function of at least one defined selection standard, one of the several error models is selected. In determining the estimated navigation signal error information, the selected error model is applied to the received navigation signals, and the determined error information is transmitted to the radio navigation system and/or to user terminals.

Abstract: A method and apparatus for computing a lever arm correction between a wide beam coverage antenna and a steerable spot beam antenna of a navigational satellite is disclosed. A navigation receiver computes the lever arm correction using information from the navigational satellite that allows both the position of the navigational satellite and the navigational receiver to be determined using a known geometry of the steerable spot beam antenna and a prescribed satellite attitude maneuver profile.

Abstract: Systems, devices and methods are provided for determining the appropriate or desired geographical correction source for SBAS corrections. One aspect provided herein is a method. According to one method embodiment, a Space Based Augmentation System (SBAS) correction message is received from a selected SBAS satellite. It is determined whether at least one criterion is satisfied for using the selected SBAS satellite as a correction source and then processing the correction message received therefrom. A second SBAS satellite is selected from which to receive SBAS correction messages upon determining that at least one criterion is not satisfied for using the selected SBAS satellite as a correction source. One example of SBAS is the Wide Area Augmentation System (WAAS) used in North America. Other aspects and embodiments are provided herein.

Abstract: A method of steering a vehicle along a predetermined, or real time path by using a steering control algorithm. The vehicle includes a navigation system and a navigation antenna. The navigation antenna is mounted on the vehicle at an optimum antenna position, whereas the steering control algorithm assumes a nominal antenna position at a predetermined reference point. The method comprises the following steps: (A) obtaining a set of positioning data of the vehicle by using the navigation system and by using the navigation antenna mounted at the optimum antenna position; (B) modifying the set of positioning data of the vehicle; (C) measuring a steering angle(s) of the front wheels of the vehicle relative to a predetermined reference direction(s); (D) calculating a correction(s) to the measured steering angle(s); and (E) performing a steering action by using the correction(s) to the measured steering angle(s) to move the vehicle along the predetermined, or real time path.

Abstract: A method and system for knowing positioning system standard time at a mobile unit with respect to a system, such as the Global Positioning System, when normal, direct measurement may be impracticable owing to low signal-to noise ratio, by calibrating the timing signal of an available communication network, such as a cellular telephone transmission network (610, 615). A time reference is set for the communication network with respect to the positioning system at a time when an adequate signal-to-noise ratio prevails and the offset of a timing event in the communication network control signal measured by means of the mobile unit's internal clock may be determined (620, 625). Subsequent times are measured with respect to this time reference by using the internal clock to measure time intervals therefrom.

Abstract: A GPS information service system for providing supplemental GPS correction and signal acquisition information to subscribers. A GPS information server broadcasts GPS aiding information encrypted with subscription keys. A remote GPS subscription unit receives the key enablers for the subscription keys in service activation (SAM) messages for the services for which they have subscribed and then uses the subscription keys to decrypt the GPS aiding information. In order to prevent unauthorized access to the information, unsymmetrical signature generation and authentication algorithms are used for generating and authenticating signatures for the SAM messages.