Abstract: Measurement corrections transmitted from reference stations at known positions are transmitted to differential Global Position System receivers for use in computation of position information relative to the receiver. In one embodiment, circuitry included in the receiver detects errors in transmissions of measurement correction data streams from the closest reference station and replaces erroneous portions of the data streams with corresponding portions received from a second reference station. Alternately, a plurality of measurement correction data streams received from a plurality of reference stations are combined to produce a combined measurement correction used to correct the position information received from satellites.

Abstract: A centimeter level survey system includes reference base station and rover GPS units connected by a radio data link. Each includes recorders for the storage of raw measurement information including range, phase, cycle counts and time information. The rover unit is typically moved to points of interest during a survey while the base remains over a fixed, and known location. Generally, the base antenna is located to optimize a clear view of the sky. The rover is subject to interruption of the radio data link from the primary reference station. During periods that the rover is initialized and in contact with the primary reference station base station over the radio data link, the rover provides real time centimeter level position solutions to a survey user, otherwise, the rover records its raw measurements in a file that begins with the last valid initialization information and that ends with any newly reestablished initialization information.

Abstract: In a dynamic communication system (90) wherein communication parameters vary appreciably between transmissions, subscriber units (200) are susceptible to link blockages resulting in a loss of successive feedback instructing subscriber units (200) of adjustments to communication parameters to be employed in a subsequent transmission on a communication link (105). A method and system are employed to predict subsequent communication parameters and employ these predictions during link blockages in an attempt to reestablish communications and upon the removal of a link blockage, a subscriber unit (200) employs the predicted communication parameters in resuming communications without requiring complex reallocation of an additional communication link.

Abstract: An aircraft local-area augmentation system that employs a differential global positioning system (GPS) to assist aircraft (102) landing is disclosed. One or more GPS ground stations (120), each including at least two GPS receivers (122) and a datalink transmitter (126), calculate and transmit GPS correction data to an aircraft (102). An aircraft (102) employs a GPS receiver (106) for receiving ranging signals (112) from GPS satellites (108), and a datalink receiver (116) for receiving GPS correction data and other information from a GPS ground station (120). The aircraft (102) further includes a data processor (110) for determining a global position of the aircraft (102) as a function of the aircraft GPS pseudorange data and the GPS correction data. The system minimizes the introduction of non-common errors by the use of double-differencing calculations using multiple combinations of satellite (108) and GPS ground station receiver (122).

Abstract: A satellite communication system has at least one satellite (1) with an antenna that generates a moving beam pattern on the surface of the earth. The beam pattern (3) is comprised of a plurality of sub-beams (4). A method of this invention determines an attitude correction signal for the satellite by the steps of: (a) providing at least one reference transmitter (10) at a known location on the surface of the earth; (b) transmitting at least one signal from the at least reference transmitter into at least one of the sub-beams; (c) receiving the at least one signal with the satellite antenna and transponding the received at least one signal to a ground station (8).

Abstract: Method and apparatus for compensating for the differences in time varying signals S(t;R;S) received and processed by two signal receivers (R.sub.2 and R.sub.3), located at the same site, from two signal sources (S.sub.2 and S.sub.3) that are spaced apart from the receivers. A receiver (R.sub.1) is chosen as a baseline, and two double difference signals DD(t;R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.2 ;S.sub.2)+S(t;R.sub.2 ;S.sub.3) and DD(t;R.sub.1 ;R.sub.3 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.3 ;S.sub.2)+S(t;R.sub.3 ;S.sub.3) are formed. Time averages of these two double difference signals are formed, using a time interval of length T lying in a preferred range, and are subtracted from the corresponding double difference signals to form first and second compensated signals.

Abstract: The methods and apparatus of the present invention provides for determining accurate positions using a global positioning satellite system (GPS), either the United States Navstar or Russian Glonass, without the use of radio broadcast differential corrections. The method contemplates that selective availability (S/A) is either disabled or satellites with S/A active can be identified and not used. In one method, a GPS receiver is positioned at a reference location with a known position. The apparent position determined by the GPS receiver is then compared to the known position to determine an error correction. Preferably, the error correction is made to each satellite's pseudorange as a timing or range correction. When the GPS receiver moves, the error correction is applied to each satellite's pseudorange. The satellites used for position determination are chosen based on the "quality" of the satellite. Here, "quality" can mean the geometry of the satellite relative to the earth and the absence of SIA.

Abstract: Mobile stations correct their frequencies using a signal received from the moving relay station including correction of any Doppler shift caused by the satellite's movement. The mobile station includes a receiver for receiving a paging channel signal broadcast by the moving relay station and demodulators and decoders for decoding the information in the paging channel signal. Using the decoded information, the mobile station can determine an estimate of its position within the communication system. The mobile station can also determine a frequency error and a Doppler shift using the decoded information and the position estimate. A frequency controlling signal is determined using the determined frequency error and the Doppler shift. A controlled reference oscillator then uses the frequency correcting signal as a control input signal. Finally, the mobile station contains a transmitter for transmitting a signal using the voltage controlled oscillator as a reference.

Abstract: A method of automatically controlling and verifying telecommands in a satellite control system in which a satellite status analyzing/processing unit and a telecommand producing/executing unit are closely connected with each other to share a knowledge base with information regarding the telecommands. The present method comprises the steps of transmitting the telecommands to a satellite for the control thereof, receiving the resultant telemetry from the satellite, analyzing the received telemetry, inferring telemetry values corresponding to the transmitted telecommands from the information in the knowledge base, verifying a telecommand execution status of the satellite on the basis of the analyzed result and inferred telemetry values and producing a control command upon recognizing an abnormal status of the satellite in accordance with the verified result. According to the present invention, an operator needs not check data one by one to determine whether the telecommand execution is normal or not.

Abstract: A satellite communication system has at least one satellite (1) with an antenna that generates a moving beam pattern on the surface of the earth. The beam pattern (3) is comprised of a plurality of sub-beams (4). A method of this invention determines an attitude correction signal for the satellite by the steps of: (a) providing at least one reference transmitter (10) at a known location on the surface of the earth; (b) transmitting at least one signal from the at least reference transmitter into at least one of the sub-beams; (c) receiving the at least one signal with the satellite antenna and transponding the received at least one signal to a ground station (8).

Abstract: A relative speed of a vehicle with respect to a satellite is detected from a deviation of a tuning frequency caused by the Doppler effect, and a vehicle speed is determined from the relative speed. A piezoelectric oscillation gyro detects an angular speed of rotation of the vehicle, which is integrated to determine an azimuth. A travel is detected in terms of the vehicle speed and the azimuth, and the detected travel and information from available GPS satellites are substituted into a navigation equation to solve it for a solution. Alternatively, altitude information detected by an altitude sensor and the angular speed of rotation of the vehicle as detected by the piezoelectric oscillation gyro may be is inputted. The angular speed of rotation is integrated to determine the azimuth. Information from two GPS satellites and information representing azimuth .phi. and altitude .DELTA.z are substituted into the navigation equation to solve it for a solution. Kalman filter is employed.

Abstract: A satellite navigation receiver system for determining an accurate three dimensional position estimate of a movable object and initiating correction of the location of the movable object in response to the three dimensional estimate, utilizing a receiver for receiving range measurement signals from a satellite navigation system, a clock having a constant frequency drift rate for at least a predetermined period of time, and a processing scheme capable of computing clock bias estimates over a predetermined period of time including an instantaneous time, using the clock bias estimates in a quadratic function to adaptively derive a smoothed clock bias estimates over the predetermined period of time including the instantaneous time, computing a three dimensional position estimate of the movable object's position using the smoothed clock bias estimate at the instantaneous time, and determining if the three dimensional position estimates are of sufficient quality for a user's intended purpose, whereby depending on t

Abstract: Methods for transmitting and receiving radiated energy (15a, 15b, 15c) from and to a satellite (12) which moves with respect to the Earth's surface are disclosed. The invention pertains to any satellite (12) which is not in an equatorial orbit at geosynchronous altitude. The present invention reduces hand-off overhead in systems that utilize satellite-fixed cells, augments frequency re-use, and enhances the communications and sensing capacity of the satellite. In accordance with the methods of the invention, satellite footprints (16a, 16b, 16c) are partitioned into linear spanning cells (18) and multiple linear segments (22). The linear spanning cells (18) resemble long strips that extend across an entire footprint (16a, 16b, 16c). Multiple linear segments (22) are smaller contiguous areas that lie within the linear spanning cells (18). The alignment of the linear spanning cells (18) across a footprint (16a, 16b, 16c) is determined by a correction angle .phi.

Abstract: A GPS reference system and corresponding method utilizing a network of reference stations and a master station. Each reference station receives GPS signals from GPS satellites it observes and computes in response a pseudo-range residual for each GPS satellite it observes. The master station is in communication with the reference stations to receive the computed pseudo-range residuals and comprises a pseudo-range residual synchronizer, an ephemeris and clock correction estimator for each GPS satellite observed by the reference stations, and a transmitter. The pseudo-range residual synchronizer is responsive to the received pseudo-range residuals in order to compute clock differences between the reference stations and remove the clock differences from the received pseudo-range residuals so as to synchronize them.

Abstract: A calibration system utilizing existing location techniques for a global radio telecommunication system 10 autonomously calibrates the communication system's location system by routing precision location data through system 10. Calibration reduces system errors by allowing time slots to remain narrow. The precision data is carried by existing commands throughout the system to measure location errors inserted by satellites 12. A gateway 16 compiles and evaluates received calibration data and determines when to update all gateways 16 with new satellite variance data tables 435. The calibration system provides early warning of degradation of system components and long-term analysis of system performance.

Abstract: In a satellite mobile communication system in which at least one mobile earth station communicates with a land earth station which is coupled with a network, through a satellite, the land earth station measures frequency offset in a request signal and/or a response signal in a received signal from the mobile earth station due to frequency offset by a transponder in the satellite and/or a local oscillator of said mobile earth station, and doppler shift due to movement of the satellite. The measured frequency offset is forwarded to the mobile earth station through a singalling channel or a communication channel through a satellite. The mobile earth station compensates frequency offset by adjusting oscillation frequency of a local oscillator in the mobile station based upon the measured frequency offset sent from the land earth station.

Abstract: A differential ground station repeater in which a plurality of transmitters are utilized to relay information to an aircraft from a single ground station situated to receive satellite information and to transmit the satellite and other information to the plurality of correction transmitters in which the transmitters utilize a single frequency but transmit at different described sub-time slots so that the aircraft may utilize the signal of any of the transmitters it may be receiving signals.

Abstract: A method and apparatus for computing a precise position estimate for a receiver at or near the surface of the Earth uses a inertial reference unit associated with the receiver and a satellite-based navigation system. The satellite-based navigation system is used to determine a position estimate for the receiver at consecutive positions along its path of motion. The inertial reference unit is used to determine velocity vectors for the receiver. Each velocity vector corresponds to travel of the receiver between the consecutive positions. The velocity vectors from the inertial reference unit are used to refine the position estimates of the satellite-based navigation system to obtain precise position estimates.

Abstract: In a method and system for locating an unknown transmitter which emits an interfering signal, multiple signals, including a phase-calibrating signal and the interfering signal, are simultaneously observed within a passband. These signals are then simultaneously cross-correlated. The phase-calibrating signal is then isolated from the cross-correlated signals and processed to determine an amount of offset to compensate for frequency fluctuations between local oscillators in satellites, which receive and retransmit the phase-calibrating signal and the interfering signal.

Abstract: Methods for secure communication of location and other information by two spaced apart receivers in a location determination (LD) system, such as GPS, GLONASS and LORAN-C, that use pseudorange corrections to enhance the accuracy of the computed present location of an LD receiver. A pseudorange correction signal PRC(t;i;j), presenting a correction of a pseudorange measurement made at time t at an LD receiver number i from an LD signal issued by an LD signal source number j, is transmitted at a consecutive sequence of times t=t.sub.0, t.sub.1, t.sub.2, . . . , t.sub.n. The pseudorange correction signal PRC(t.sub.n ;i;j), or a message sent in a time interval t.sub.n-1 <t.ltoreq.t.sub.n, is encrypted, using an encryption key that is a function of and depends non-trivially upon one or more of the preceding pseudorange correction values PRC(t.sub.k ;i;j) (k.ltoreq.n-1). This encryption key varies from one time interval t.sub.n-1 <t.ltoreq.t.sub.

Abstract: Method and apparatus for reducing the contributions of receiver noise signal error and multipath signal error from signals received in a Satellite Positioning System (SATPS) from one or more SATPS satellites by formation and appropriate filtering of differences of signals DD that are differences of SATPS signals received by the SATPS receiver/processor. A difference signal DD of code-phase-derived delta range signals and carrier-phase-derived delta range signals is formed, and this difference signal is passed through a first statistical processing filter with an associated time constant .tau.1 in the approximate range 50-[500] 100 sec, to produce smoothed or filtered signal with the estimated receiver noise error reduced or removed. The difference signal DD is passed through second and third statistical processing filters having associated time constants .tau.2=5-20 sec and .tau.

Abstract: A multi-loop control system for a gimballed antenna that employs devices for measuring both absolute line-of-sight (an autotrack receiver or beacon tracker) and relative angular position (a resolver). The control system uses both signals simultaneously, thereby increasing the performance and pointing accuracy capability. Two control loops operate simultaneously to provide for optimum performance. The first loop is an inner high-bandwidth control loop that uses the relative gimbal angle measurement to control pointing of the antenna along a precommanded profile. The inner loop may run alone to provide for coarse pointing. When available, the line-of sight measurement is used in a low-bandwidth outer loop to provide corrections to the command profile of the inner loop. Control logic is provided that allows switching between several control modes.

Abstract: A method for compensating for the differences in time varying signals S(t;R;S) received and processed by two signal receiver/processors (R.sub.2 and R.sub.3), located at the same site, from two signal sources (S.sub.2 and S.sub.3) that are spaced apart from the receiver/processors. A receiver/processor (R.sub.1) is chosen as a baseline, and double difference signals DD(t;R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.2 ;S.sub.2)+S(t;R.sub.2 ;S.sub.3) and DD(t;R.sub.1 ;R.sub.3 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.3 ;S.sub.2)+S(t;R.sub.3 ;S.sub.3) are formed. The respective time averages DD(R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3).sub.avg and DD(R.sub.1 ;R.sub.3 ;S.sub.2 ;S.sub.3).sub.avg of these two double difference signals are formed, using a time interval of length T lying in a preferred range given by 120 sec.ltoreq.T.ltoreq.1800 sec. First difference signals, DDC(t;R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3)=DD(t;R.sub.1 ;R.sub.2 ;S.sub.

Abstract: A system and method for maintaining a precise time standard among a system of orbiting satellites is disclosed. In an illustrative embodiment, atomic clock data is circulated among the satellites via RF crosslinks. Each satellite uses the received data as input to a Kalman process which acts to minimize the mean squared error among the satellite clocks to form a set of "ensemble clocks". The resulting ensemble clock values are then transmitted to an earth station where an offset between the ensemble clocks and Universal Time is computed. The offset is transmitted from the earth station to the satellites where it is used by the satellites to lock their on-board clocks to Universal Time, thereby creating a corrected system time. The corrected system time is transmitted, via RF crosslinks, to satellites not having operational on-board clocks. The satellites without atomic clocks employ phase locked loops to anchor their clocks to the corrected system time as it is received over the crosslinks.

Abstract: A system of making satellite-to-ground range measurements, carrying out communications between a ground station and a constellation of autonavigating satellites, and using these range measurements to improve navigation accuracy is disclosed. The system comprises an anchor that is in a fixed position relative to the earth. The anchor implements a filtering algorithm to arrive at solutions for the satellites' positions based on measured satellite positions and predicted satellite positions. Each time a new measurement is received by the anchor an update is generated. In this manner the system is capable of updating satellite positions at a greater rate than similar prior art systems, thereby, decreasing the transient response associated with satellite delta-v maneuvers and decreasing the quantity of data that must be exchanged by the anchor and the satellites.

Abstract: The present invention relates to a device for correcting a frequency shift due to the Doppler effect in a transmission system. The device for correcting a frequency shift due to the Doppler effect is applicable to a transmission system in which a signal is transmitted in a transmission lobe between a transmitter and a receiver that are in relative motion. The frequency shift which is the difference between the frequency of the transmitted signal as measured at the receiver and as measured at the transmitter is presented as the sum of a center frequency characteristic of the transmission lobe plus a position frequency which is a function of the position of the receiver in the transmission lobe. The device includes means for tuning the receiver which has a tuning frequency such that said tuning frequency is equal to the sum of the transmitted frequency plus the center frequency.

Abstract: An orbiting satellite-based telecommunication system for providing store and forwarding service by having a ground station, in response to an instruction from an orbiting satellite over a specific communication channel of the down link, supply transmit data to the orbiting satellite through an unused one of a plurality of communication channels of the up link in accordance with a packet protocol, and having the ground station in response to another instruction from the orbiting satellite through the down link, receive the transmit data from the orbiting satellite through an unused one of said plurality of communication channels in accordance with the protocol wherein said orbiting satellite is provided with a divider for dividing the frequency band of the up link into a plurality of subchannels on the basis of the Doppler shift amount due to variations in the distance between a terminal and the orbiting satellite; a demodulator for demodulating the transmit data on a subchannel-by-subchannel basis; and data p

Abstract: Method and apparatus for reducing the contributions of receiver noise signal error and multipath signal error from signals received in a Satellite Positioning System (SATPS) from one or more SATPS satellites by formation and appropriate filtering of differences of signals DD that are differences of SATPS signals received by the SATPS receiver/processor. A difference signal DD of code-phase-derived delta range signals and carder-phase-derived delta range signals is formed, and this difference signal is passed through a first statistical processing filter with an associated time constant .tau.1 in the approximate range 50-500 sec, to produce smoothed or filtered signal with the estimated receiver noise error reduced or removed. The difference signal DD is passed through second and third statistical processing filters having associated time constants .tau.2=5-20 sec and .tau.

Abstract: The present invention relates to a no outage GPS/AM position finding system wherein a GPS system having a plurality of satellites transmits time and location data over radio frequency signals to enable a mobile GPS receiver station on the ground to determine its position, and a cellular telephone is carried with the mobile GPS receiver, traveling in range of a plurality of conventional ground based amplitude modulated (AM) transmitters for transmitting AM signals. Each mobile GPS receiver station includes phase detection means for simultaneously receiving a predetermined number of the AM signals, and measuring the changes in phase of each of the AM signals as the mobile GPS receiver travels, and deriving therefrom an AM position signal. A reference station for receiving the GPS and AM signals provides correction signals via a cellular telephone network which receives and transmits the correction signals to the mobile GPS receiver station.

Abstract: A method for fast acquisition of Satellite Positioning System (SATPS) signals from a satellite-based positioning system, such as GPS or GLONASS, that does not require permanent storage of satellite almanac information at an SATPS ground station. This SATPS signal acquisition method can be used whenever the "new" station initially powers up or has lost lock on one or more SATPS signals that must be reacquired. A nearby reference SATPS station, whose location coordinates are known with high accuracy, provides the new SATPS station with differential positioning SATPS information, and, optionally, with SATPS satellite ephemeride information on each SATPS satellite visible from the reference station. The new station then uses this differential SATPS information to establish channels to search for (only) the SATPS satellites that are visible from the reference station.

Abstract: A satellite communication system in which a satellite receives a signal on a uplink carrier frequency, frequency translates it, and transmits the signal at a downlink carrier frequency. The downlink carrier frequency differs from the uplink carrier frequency by a standard frequency offset and a frequency offset error. A terminal earth station transmits to the satellite an inbound signal on the uplink carrier frequency. A hub earth station continually transmits to the satellite an outbound signal on an uplink carrier frequency and receives from the satellite the outbound signal at the downlink carrier frequency. The hub strips the outbound signal from the downlink carrier frequency and compares the stripped downlink carrier frequency to the reference carrier. A frequency offset error signal corresponding to the frequency offset error is generated.

Abstract: The accuracy of a vehicle position estimate generated using a satellite-based navigation system is improved by accounting for non-linear errors in the vehicle position computations. The standard navigation equation is modified to include the error coefficients .alpha., .beta., .gamma. and .delta.. .alpha. is used to model errors in the x dimension. .beta. is used to model errors in the y dimension. .gamma. is used to model errors in the z dimension. .delta. is used to model errors in the pseudoranges. The error coefficients may be computed using an open-ended GPS system or a differential GPS system. The error coefficients may be computed in real time or may be computed once and used for a period thereafter. Once computed, the error coefficients are factored into the computation of a vehicle position estimate for increased precision.

Abstract: A satellite communications system includes a feed array and reflector receiving antenna coupled to a dual-mode network, for generating two channels, with independent signals representing two beams, one for each channel. Each output channel of the dual-mode network contains redundant information relating to a plurality of information channels. In the absence of an interfering signal or intrusion, the combined signals are amplified and block frequency-converted, then de-multiplexed into separate channels, which are each applied through selection switches to a transmitter multiplexer for retransmission. An alternate signal is tapped from each of the two received signal channels, phase controlled, and combined, to produce a combined signal representing a receive antenna beam with a null controllable in position in response to phase. The combined signal is demultiplexed into separate information channels.

Abstract: An embodiment of the present invention relates to a worldwide network of differential GPS reference stations (NDGPS) that continually track the entire GPS satellite constellation and provide interpolations of reference station corrections tailored for particular user locations between the reference stations Each reference station takes real-time ionospheric measurements with codeless cross-correlating dual-frequency carrier GPS receivers and computes real-time orbit ephemerides independently. An absolute pseudorange correction (PRC) is defined for each satellite as a function of a particular user's location. A map of the function is constructed, with "iso-PRC" contours. The network measures the PRCs at a few points, so-called reference stations and constructs an iso-PRC map for each satellite. Corrections are interpolated for each user's site on a subscription basis.

Abstract: The accuracy of the performance of an inertial navigation system is validated by comparing data measured by a fourth gyro and accelerometer to an analytic equivalent constructed from measurements made by a primary gyro/accelerometer orthogonal triad.

Abstract: A satellite orientation detection system disposed to detect the pointing orientation of a geosynchronous satellite (10) relative to a reference location on the earth. The present invention is also capable of ascertaining the angular orientation of a longitudinal axis of the satellite (10) relative to a defined axis on the surface of the earth. A ground station (20) is included for transmitting a first linearly polarized and a second circularly polarized electromagnetic reference beam. The present system also includes a receive antenna (28) coupled to the satellite (10) for receiving the first and second reference beams and for generating an antenna-beam pattern P1 and P2 disposed to rotate about a reference axis A. A rotating polarizer arrangement (44), aligned with the receive antenna (28), periodically varies the portion of the linearly polarized energy within the first reference beam transmitted thereby.

Abstract: A method for tracking a satellite in a land mobile satellite communications system is disclosed. A rate gyro is provided for use in the event that an automatic satellite tracking is prevented. The satellite is automatically tracked using a receive signal level if the receive signal level equals or exceeds a threshold. An output of the rate gyro is constantly compensated while automatically tracking the satellite. When the receive signal level falls below the threshold and the automatic satellite tracking becomes unable, the satellite is tracked using the compensated output of the rate gyro.

Abstract: An inertial navigation system with automatic redundancy and dynamically calculated gyroscopic drift compensation utilizes three, two-degree of freedom gyroscopes arranged whereby any two of the gyroscopes form an orthogonal triad of measurement sensitive axes. The input axes of the three gyroscopes form three pairs of parallel input axes, each pair of parallel input axes corresponding to one axis of the orthogonal triad of axes. The three gyroscopes are operated in a plurality of preselected combinations of both clockwise and counter clockwise directions, thus changing the direction of the angular momentum vector by 180.degree.. Parity equations are formed from each pair of gyroscope outputs whose measurement sensitive axes are parallel. The parity equations include combinations of gyroscope pairs that have been operated in both the clockwise and counterclockwise directions.

Abstract: An improved system and method for determining a position fix in space and time using the Global Positioning System (GPS) satellite network signals. The system comprises at least three fixed base stations each having a satellite receiver operating in conjunction with a highly accurate (atomic-standard) clock. Each base station's position is known with great accuracy. GPS satellite signals are collected over statistically significant periods of time at each base station and fitted to determine with the clock offset and drift of the station clocks, thus establishing a "network" of base station clocks that in the aggregate is of great accuracy and precision. An arbitrary number of mobile receiver stations similarly collect data for working periods of statistically significant duration; these data are used in conjunction with the base station data to compute position fixes for the mobile stations.

Abstract: A method and apparatus is disclosed for automatic elimination of frequency instabilities in a receiver frequency converter. Such instabilities result from temperature variations and mechanical vibrations of the local oscillator of a first stage converter. A marker signal is introduced into the first stage down converter mixer and is subjected to the same variations in frequency conversion as is the received signal from an antenna. Intermediate down converted received signals and an intermediate down converted marker signal are received by a second stage converter where such signals are applied to a mixer, the output of which is free of frequency variations introduced by the local oscillator of the first stage converter.

Abstract: A precision satellite tracking system incorporating a novel smoothing processor. The satellite tracking system estimates an angle between an antenna boresight and a desired line of sight to a moving satellite. The smoothing processor receives a sequence of pointing error measurements and using a Taylor series mathematical model of the satellite motion, the processor utilizes the sequence of measurements to generate the coefficients of the Taylor series model. The processor then executes a sequential, discounted least mean square algorithm to estimate the satellite's angular position, velocity, and acceleration as a function of time. Based on these estimates, the processor determines incremental adjustments to azimuth and elevation pointing angles of the antenna to maintain the center of an antenna beam on the moving satellite. The information is used in a program track mode to continually update the pointing of the antenna beam during the measurement process.

Abstract: A method of assigning communicaton links in a dynamic communication network, such as a network of earth orbiting satellites arranged, for example in three constellations. The assignments are made in phases, with the first phases assigning high priority link classes. Subsequent phases assign lower priority link classes. A set of constraints is established, and a high priority subset of these constraints can be assured by requiring that any assignment set to be accepted results in a network topology satisfying that subset of constraints even if existing links must be intentionally broken. Other constraints are met only if existing links need not be broken.

Abstract: An improvement in a coprocessor system for correcting for drifts in directions of navigation gyros, by means of satellite navigation information from global positioning satellites. Values of gyro navigation information from the gyros are interpolated to values that are valid at a cycle time. A cycle time is a time when the satellite navigation information is valid. The interpolated gyro navigation information is coprocessed with the satellite navigation information to arrive at accurate gyro drift terms. The gyro drift terms are used in correcting for the drifts in the navigation gyros.

Abstract: A method is disclosed for determining the heading of an aircraft which is equipped with both an inertial navigation system and a device capable of receiving navigation satellite signals and computing the aircraft's position, speed and acceleration therefrom. While the aircraft is still on the ground and before flight operations begin, an initial alignment of the inertial navigation system with an earth-fixed coordinate system is performed, and during this alignment, data corresponding to the initial attitude of an aircraft-fixed coordinate system relative to the earth-fixed coordinate system is also determined and stored. Thereafter, during flight operations, the acceleration vector of the aircraft relative to the aircraft-fixed coordinate system is measured by the inertial navigation system and then transposed into a coordinate system which has been horizontally aligned with the earth-fixed system using the initial attitude data.

Abstract: In a time division multiple access satellite communications system having a master station and one or more remote stations, frequency offset through the translation oscillator in the satellite is corrected by transmitting a pilot frequency signal, reference to a high precision oscillator, through the satellite, so as to subject the pilot frequency signal to a frequency translation and monitoring the frequency translation of the pilot frequency signal as received at the master station subsequent to its transmission through the satellite. Signals to be transmitted over the satellite communications link from the master station to remote stations are subjected to a frequency translation that is effectively complementary to the monitored frequency translation.

Abstract: In a TVRO earth station having an antenna for receiving incoming satellite signals and polarizing means associated with the antenna for adjusting the relative alignment of the antenna orientation and the polarization of the incoming signals, an automatic polarization control system comprising means for producing an electrical control signal for controlling the polarizing means to adjust the relative alignment, means for detecting the noise level in the satellite signals received by the antenna, and means responsive to the detected noise level for adjusting the control signal, and thereby adjusting the polarizing means, to minimize the detected noise level.

Abstract: Undesired signals from interfering satellites are separated from desired signals from a target satellite by using a sum beam and a difference beam as in a monopulse radar. Both desired and undesired signals are received by an antenna and separated by different mode couplers from a waveguide. The fundamental mode of the waveguide provides the desired signals along with components from the interfering signals. Both desired and undesired signals are picked up from the waveguide through a fundamental mode coupler. The higher order modes of the waveguide provide the interfering signals alone, representing the difference beam which will be aligned along the boresight. In a circular waveguide, the TM.sub.01.sup.o will yield a difference pattern for vertical polarization in any plane, and a TE.sub.21.sup.o or TE.sub.01.sup.o mode will result in a difference pattern for horizontal polarization. A square or a rectangular waveguide could be used instead of a circular waveguide to achieve the same result.

Abstract: A transmitting power control system is disclosed wherein a master earth station sends a pilot signal to a satellite which retransmits it to the master station as well as to slave earth stations. A beacon signal is also sent from the satellite to the master station which compares it with the received pilot signal and controls its own transmission power level according to the result of the comparison so that the power level of retransmitted pilot signal is maintained constant. A warning signal is sent from the master station to all the slave stations when the received pilot signal decreases below a prescribed value corresponding to a predetermined precipitation. Each slave station receives the pilot signal from the satellite and controls its own transmission power level according to the received pilot signal.

Abstract: A closed loop system reduces pointing errors in one or more spacecraft instruments. Associated with each instrument is a electronics package (3) for commanding motion in that instrument and a pointing control system (5) for imparting motion in that instrument in response to a command (4) from the commanding package (3). Spacecraft motion compensation logic (25) compensates for instrument pointing errors caused by instrument-motion-induced spacecraft motion. Any finite number of instruments can be so compensated, by providing each pointing control system (5) and each commanding package (3), for the instruments desired to be compensated, with a link to the spacecraft motion compensation logic (25). The spacecraft motion compensation logic (25) is an electronic manifestation of the algebraic negative of a model of the dynamics of motion of the spacecraft. An example of a suitable model, and computer-simulated results, are presented.

Abstract: A NAVSTAR receiver in which the received signals are processed to produce digitized quadrature signals at zero i.f. Baseband phasor rotation to effect Doppler tracking in the receiver loop is accomplished by deriving digital signals representing sin .omega.T and cos .omega.T for the required rotation angle .omega.T, multiplying the quadrature signals separately and summing the outputs according to the algorithm I.sup.1 =I cos .omega.T+Q sin .omega.T and Q.sup.1 =Q cos .omega.T-I sin .omega.T, where I & Q are the digitized quadrature signals.