Abstract: A method of determining the location of an unknown source 10 transmitting a signal to satellite relays 14 and 16 comprises receiving replicas of the signal from the relays at receivers 18. The receivers 18 also transmit and receive reference signals via respective relays 14 and 16. All signals are downconverted, digitized and correlated with one another in pairs using a correlation function including a term which compensates for time varying differential frequency offset (DFO). Compensation for time varying differential time offset or time dilation is achieved by replicating or adding to signal samples and applying phase corrections. This procedure enables a correlation maximum and associated measurement results to be obtained despite the effects of relay satellite motion which mitigate against this. Results are used in a prior art geometrical technique to locate the unknown transmitter.

Abstract: A method and apparatus encompasses a technique for routing an information packet through a satellite communications system 20 from a source satellite 38 to a destination satellite 40. A path through the system 20 is chosen for the packet and an identifier identifying the path is appended to the packet. In addition, an identifier identifying the destination satellite 40 is appended to the packet. Satellites in the system 20 then use the identifiers in the packet to route the packet to the destination satellite 40. If the chosen path is not available, an alternate path can be taken by the packet. In one embodiment of the present invention, a centralized controller 36 is provided for controlling the routing of packets throughout the entire system 20.

Abstract: A system and method for providing remote viewing of satellite transponder plots. The system and method piovides for remote viewing of transponder plots derived from transponders located on a satellite that communicate with ground terminals having an antenna. The system comprises an antenna switch for receiving transponder signals from the antenna. A spectrum analyzer is coupled to the antenna switch for generating transponder plots. An equipment control computer is coupled to the antenna switch and the spectrum analyzer that selectively routes signals from the antenna switch to the spectrum analyzer and routes transponder plots generated by the spectrum analyzer. A server computer is coupled to the equipment control computer that stores the transponder plots generated by the spectrum analyzer that are routed by the equipment control computer.

Abstract: A method and system for determining a position of an object utilizes two-way ranging and polystatic techniques. A first communication transceiver at a first known location provides a bidirectional communication path between the first communication transceiver and the object wherein the first communication transceiver transmits a first ranging signal to the object and the object transmits a second ranging signal to the first communication transceiver in response to the first ranging signal. The first communication transceiver further provides a first unidirectional communication path between the first communication transceiver and the object wherein the first communication transceiver performs one of transmitting a third ranging signal to the object and receiving a fourth ranging signal from the object.

Abstract: A sole means global navigation apparatus adapted for use on an aircraft includes a GPS receiver to provide GPS measurement data and an inertial sensor system adapted to provide inertial translational and rotational data which during time periods is independent of the GPS position data. A navigation system coupled to both of the GPS receiver(s) and the inertial sensor system determines a navigation solution as a function of both the condition of the GPS satellite data and the uncertainty in the Inertial data. An augmentation system coupled to the navigation solution determining system is used to increase the accuracy and/or integrity of the GPS/inertial sensor, thereby achieving style means navigation requirements.

Abstract: A method and system for determining a position of an orbiting transceiver in a communications network includes at least a first and second transceiver at a first and second known location, respectively, on Earth. The first and second transceivers are adapted to transmit and receive communications signals to and from the orbiting transceiver. A processor coupled to one of the first and second transceivers determines a first and second range measurement between each of the first and second transceivers and the orbiting transceiver, respectively, as well as corresponding first and second range rates representative of a time rate of change of the first and second range measurements.

Abstract: A radio frequency (RF) sync pulse is transmitted throughout a building having a plurality of rooms to be traversed by a plurality of players during, for example, an assault training exercise. Ultra-sound pulses are transmitted from fixed piezoelectric transducers mounted at each corner of each room. The ultra-sound pulses with encoded room identity information are generated in a predetermined timed sequence by different ultra-sound transducers after each RF sync pulse. Each player carries an RF receiver for receiving the RF sync pulses. Each player also carries multiple microphones for receiving the ultra-sound pulses transmitted in a room in which the player is currently located. Timing circuitry carried by each player generates signals representative of the delays between each RF sync pulse and the receipt of each of the ultra-sound pulses sequentially received thereafter.

Abstract: A method and system of forming communication links in a satellite communications system. The satellite communications system includes a plurality of transmitter groups, a satellite and a plurality of downlink receivers. Each transmitter is associated with only one transmitter group. At least two transmitters of two separate transmitter groups are disposed geographically adjacent to each other. Each transmitter of a transmitter group transmits an uplink communications signal that is a CDMA signal having a predetermined code that is selected from a code set assigned to the group of transmitters with which the transmitter is associated. Each respective code set is different from other code sets associated with selected groups of transmitters and forms a code set pattern that repeats.

Abstract: A method and system for determining a position of an orbiting transceiver in a communications network includes at least a first and second transceiver at a first and second known location, respectively, on Earth. The first and second transceivers are adapted to transmit and receive communications signals to and from the orbiting transceiver. A processor coupled to one of the first and second transceivers determines a first and second range measurement between each of the first and second transceivers and the orbiting transceiver, respectively, as well as corresponding first and second range rates representative of a time rate of change of the first and second range measurements.

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: In a code division switch in a satellite communication system each of a plurality of uplink CDMA modulated RF beams, each including a plurality of uplink traffic channels, are down converted to IF and overspread with a new orthogonal code having a spreading rate N times that of the spreading code of the uplink CDMA modulated RF beam. All of the overspread beams are combined into a single combined IF stream. The individual traffic channels are extracted from the combined IF stream by de-overspreading the stream with orthogonal codes and despreading with beam and traffic channel specific orthogonal codes. All traffic channels are respread with downlink beam codes and downlink orthogonal traffic channel codes and joined onto selected ones of downlink CDMA modulated IF beams having common destinations with the included traffic channels. Downlink CDMA modulated IF beams are up converted to RF frequency and transmitted to selected destinations.

Abstract: A design of equally loaded, under varying traffic load conditions, high efficiency power amplifiers for a multibeam communication system is presented. Output beam contains signals of only one beam corresponding to its input beam. Signals arriving at the feed elements for an input beam "b", of the 1 to N beams, corresponding to an input beam "b", arrive in phase and add together, while signals arriving at said feed elements for the output beam "b" corresponding to the remaining input beams arrive in antiphase and cancel one another by appropriate selection of two set of fixed input and output phase shifters. The output beams are shaped to produce a small reduction of power at the crossover point of adjacent beams. MMIC and high Tc superconducting designs, including the design of high Tc superconducting reflector antenna, are presented.

Abstract: A method and apparatus for handing off communications between a primary satellite system (500) and an alternate satellite system (550) determines (602) when a hand-off condition for the primary satellite system (500) exists. An alternate satellite (552) is determined (604, 904) which has a coverage area (554) which is positioned such that the alternate satellite (552) can provide an alternate communication link (556). A hand-off between the primary satellite system (500) and the alternate satellite system (550) is then performed (606). When the hand-off condition is alleviated (610), a hand-off back to the primary satellite system (550) is performed and normal operations are resumed (600).

Abstract: A satellite repeater system (10) provides a connection from satellites (12) to user terminals (14) that are located within a building. The satellite cellular repeater system receives satellite signals on a satellite receive antenna (18) and retransmits the received signal within a building using amplifiers (30) and indoor antennas (32). The system also receives signals from a user terminal, amplifies the signals, and retransmits the user terminal signals with an outdoor satellite antenna (20) back to a satellite. For a multi-story building each floor may be provided with a local transmit antenna (32), transmit amplifier (30), receive antenna (34), and receive amplifier (36) for conducting bidirectional communications with satellite telephones or user terminals that are present on that floor.

Abstract: The encoding/transmission of information in an OFDM system is enhanced by using complementary codes and different patterns of amplitude modulation representing respective data words. The complementary codes, more particularly, are converted into phase vectors and modulated by the selected pattern. The result is then used to modulate respective carrier signals. The modulated result is then transmitted to a receiver which decodes the received signals to recover the encoded information.

Abstract: An improved multi-beam bent-pipe communications satellite system and method includes a subchannel switching processor for extracting and switching subchannels of information to and from a plurality of uplink and downlink beams and an intersatellite link for routing certain of the extracted subchannels to another satellite in the system. The subchannel switching processor preferably employs a partial subchannelization processor that combines a coaxial switching network for switching some of the uplink channels at the channel level with an analog or digital transparent subchannel switching network connected to a portion of the uplink channels for extracting and switching at the subchannel level. The switched subchannels are combined to form channels, and then routed to either the downlink beams (where they are combined with other switched channels), or to the intersatellite link for transmission to another satellite.

Abstract: A system (10) and method delivers geolocation or other signals (26, 28) to a communication unit (24) located within an area (20) (e.g., a building) where an obstruction exists between the signal transmitter (12, 18) and the communication unit (24). The system (10) uses an infrastructure transceiver apparatus (14, 16, 22) to receive (204, 304, 604) the signals (26, 28) and retransmit (208, 310, 610) them within the area (20). A communication unit (24) calculates responsive data, such as its approximate position, from the retransmitted signals and reports (406, 704) the responsive data to a host system via the infrastructure transceiver apparatus (14, 16, 22).

Abstract: A satellite communication system (100) includes a satellite (102) in a predefined orbit projecting a plurality of beams (1-48) designating a coverage area (115). The satellite (102) has a communication device (200), a frequency synthesizer (222) for setting a frequency of the communication device for communicating via a beam of the plurality of beams (1-48) and a controller (216) coupled to the frequency synthesizer (222) for compensating for a Doppler frequency shift associated with the beam.

Abstract: A system and method are disclosed for bidirectionally coupling a first satellite communication system to a second satellite communication system, wherein the first and second systems operate with different protocols. In a presently preferred embodiment of this invention the first system uses a spread spectrum (SS), code division multiple access (CDMA) technique wherein the satellites serve as simple `bent pipe` repeaters for relaying communications between a user and a gateway. The second satellite communication system may be any other type of system having at least one characteristic that precludes direct communication between the first and the second systems. In an exemplary embodiment the second system uses a time division multiple access (TDMA) technique, and furthermore enables direct satellite-to-satellite communication links.

Abstract: The present invention provides a combined ground and satellite system for global aircraft surveillance, navigation, landing guidance and collision avoidance which comprises a satellite subsystem consisting of both a satellite constellation and associated ground stations, and a ground subsystem consisting of a network of ground stations, together with an airborne subsystem comprised of a transponder unit located in each of the aircraft using the system. A high speed two-way data link is provided between each of the subsystems using spread spectrum technology to permit overlaying and operation of the system in an existing band of narrow channels with minimum mutual interference. The system of the invention is reliable because of the redundant subsystems, and is not subject to failure. Also, the system provides for computations to be made on the ground, rather than in the aircraft, thereby reducing the size and complexity of the airborne equipment.

Abstract: A paging/messaging system using the L3 transmission channel of a constellation of GPS satellites orbiting the earth, is comprised of an earth-based injection terminal having a source of paging/messaging signals and a radio transmitter for broadcasting paging/messaging on the L3 transmission channel to in-view ones of the constellation of GPS satellites. A plurality of earth-based mobile receiving stations, each mobile receiving station having an omnidirectional receiving antenna and an L3 transmission channel receiver for receiving the L3 transmission channel broadcasts from the in-view ones of the constellation of GPS satellites and demodulating and decoding to recover the paging/messaging signals, a display as used to present the paging/messaging signals to a designated user the recovered paging/messaging signals.

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: A communication system (10), and a method executed by same, for allocating communications traffic through a plurality of satellites (12) of a constellation of low earth orbit satellites. Each of the plurality of satellites is oriented, at any given time when in view of a ground station (18), at a particular elevation angle. The method comprises the steps of: (a) providing each of the plurality of satellites with a receiver for receiving communication links from the ground station and a transmitter for transmitting communication links to user terminals; (b) in response to a request for service, determining if a highest elevation angle satellite can be assigned a new communications link; (c) if yes, assigning a new communication link to the highest elevation angle satellite; (d) if no, determining if a second highest elevation angle satellite can be assigned a new communications link; and (e) if yes, assigning a new communication link to the second highest elevation angle satellite.

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

Abstract: An array antenna system (40) has a plurality of radiators (44) for generating a set of beams (48), wherein axes of the beams are spaced apart from each other allowing the respective beams to illuminate separate areas of the earth or other receiving region. A sequence of positional offsets (52) is applied to the set of beams by either mechanically (108) moving the radiators to redirect the beams, or by introducing a phase or time-delay taper (84) to the phase shifters (80) or delay lines of a beam former (38) for each of the beams. The succession of positional offsets redirects the beams along a path offset from a central location (50) of each beam, and passing between the sites of adjacent beams. This provides for improved uniformity of illumination of the receiving region.

Abstract: A design of equally loaded, under varying traffic load conditions, power amplifiers for a multibeam satellite is presented. Each output beam contains signals of only one beam corresponding to its input beam. The output beams are shaped to produce a small reduction of power at the crossover point of adjacent beams. MMIC and high Tc superconducting designs, including the design of high Tc superconducting reflector antenna, are presented.

Abstract: A satellite communications scheme for enhancing the communications system with existing satellites is disclosed. The existing satellites include a transponder having a phase locked loop phase demodulator at the front end thereof. The present invention discloses a technique wherein the phase demodulator is locked by transmitting a relatively high-power carrier from the ground to the satellite transponder. Once the demodulator has been locked, remote ground terminals operating at much lower power levels can access the satellite transponder by transmitting at carrier frequencies spaced apart from the primary high-power carrier. These are down-converted by the transponder phase demodulator and then typically amplitude and frequency limited before being remodulated and retransmitted.

Abstract: A system for measuring the relative positions of first and second units includes a re-transmitting apparatus at the first unit and a receiver at the second unit capable of making simultaneous real-time comparisons of phase and frequency information contained in first signals received directly from the satellites by the second unit and second signals received from the satellites by the first unit and immediately retransmitted to the second unit in their entirety without processing before retransmission.

Abstract: A communications satellite payload provides for efficient communications between user devices, such as hand held cellular telephones, and terrestrial gateways that may be connected to world-wide public telephone and telegraph (PTTs) networks. The satellite payload simultaneously supports a plurality of independent antenna beams, for example 12 or 16 beams, on both the uplink and downlink for user devices employing full duplex communications. The satellite payload furthermore supports an identical number of full duplex channels between a terrestrial gateway and the satellite. The communications satellite payload is carried by one satellite of a plurality of such satellites in a low earth orbit (LEO) constellation to provide worldwide communications. Downlink beam forming occurs prior to final amplification of transmitted signals, thereby reducing losses within the beam forming equipment.

Abstract: A transponder demodulates a phase modulated ranging signal transmitted by an earth station. The transponder converts the analog ranging signal to digital form. The digital ranging signal is demodulated into its I and Q phase components. Next the demodulated ranging signal is re-modulated and digitally combined with a selected transmit frequency. Then the re-modulated ranging signal is converted from digital to analog form. The ranging signal is transmitted to the earth station.

Abstract: Improved automatic gain control for an amplifier is obtained by controlling the size of a null zone in a drive signal for the amplifier. The size of the null zone is controlled by estimating strength of an interference signal, and dynamically varying the size of the null zone based on the estimated strength of the interference signal. As a result, the amplifier rarely saturates, regardless of signal strength. The invention is useful to reduce the harmful effects of jamming or interference.

Abstract: In a space-division multiplex communication method of executing multiplex communication according to this invention, a plurality of radio beams a--a' to d--d' radiated at same frequency in different directions and rotated at same rotational angular speed .omega. are independently received in synchronism with the rotational angular speed .omega. by a plurality of communication terminals R1 to R3 arranged at arbitrary positions in a space where the radio beams can be received, thereby realizing unidirectional multiplex communication using the same frequency. Interstation bidirectional multiplex communication is performed by introducing a frequency-division system to the communication terminals R1 to R3 of the unidirectional multiplex communication. The space-division multiplex communication method can effectively use a frequency by a multiplex communication system of space-dividing a radio beam.

Abstract: A system and method for determining the position of an airborne object, using a fixed station and a pair of earth orbit satellites whose positions are known. Separate periodic signals are transmitted from the fixed station via the first and second satellites to the object whose position is to be determined. The phase offset in periodic characteristics of the periodic signals as received from the first and second satellites is measured at the object. The phase offset corresponds to a realtive time difference in propagation of the signals traveling two different paths to the object. The object transmits via the first satellite a return signal indicative of the measured relative time difference. This return signal is activated some time in the future according to the object local time, which is slaved to receipt of the periodic signal sent through the first satellite. This future time is the start of the particular time period as decided by the fixed station's schedule.

Abstract: A method and system for determining the position of an object using a fixed station and a plurality of earth orbit satellites whose positions are known. Separate periodic signals are transmitted from the fixed station via first and second satellites to the object whose postion is to be determined. The phase offset in periodic characteristics of the periodic signals as received from the first and second satellites is measured at the object. The phase offset corresponds to a relative time difference in propagation of the signals traveling two different paths to the object. The object transmits via the first satellite a return signal indicative of the measured relative time difference. This return signal is activated some time in the future according to the object local time, which is slaved to receipt of the periodic signal sent through the first satellite. This future time is the start of the particular time period as decided by the fixed station's schedule.

Abstract: A multiple beam space antenna system for facilitating communications between a satellite switch and a plurality of earth-based stations is shown. The antenna is deployed after the satellite is in orbit by inflation of a raft-type supporting structure which contains a number of antenna horns. These antenna horns are oriented in substantially concentric circular groups about a centrally located antenna horn. Each of the antenna beams projects an area on the earth. Each of the areas of the beams are contiguous. As a result, one large area is subdivided into many smaller areas to facilitate communications. In addition, a lens may be employed to focus the beams of the horn antennas.

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: In a satellite communications system, a rotatable 90.degree. phase shifter and a rotatable 180.degree. phase shifter introduce variable phase shifts to a single pilot signal, which is transmitted to the satellite. Downlink cross-polarization interference cancelling control signals are derived from a beacon signal received from the satellite. A pulse sequence is generated to modulate the amplitude of a carrier to produce an ASK signal as the pilot signal. A correlation calculator provides coarse mode interference cancellation by estimating uplink cross-polarization interference components from the downlink cross-polarization cancelling control signals and adjusting the angle settings of the 90.degree. and 180.degree. phase shifters with the estimated components. The pilot signal is transmitted back to the earth and synchronously detected with the pulse sequence to derive a DC signal which represents an uplink cross-polarization interference.

Abstract: A satellite communication system is disclosed that would allow for communication between mobile and fixed terminals. The communications system includes a plurality of mobile users, a satellite in geosynchronous orbit for providing frequency addressable uplink and downlink signals to the mobile terminals, a base station for receiving siganls from and transmitting signals to the satellite and a plurality of fixed users coupled to the base station. The system provides the advantage of frequency reusability and frequency addressability in the uplink and downlink transmissions of the mobile users.

Abstract: A locating system employs a single-point device employing unique scanning patterns for generating peak signal data which can be used to calculate the position of a signal source within a scanned region. One preferred embodiment utilizes a satellite in high earth geosynchronous orbit and a simultaneous yaw and roll pattern to scan a substantial portion of the earth's surface. The point source being located may be virtually any form of transmitter of radiant energy such as infrared, electromagnetic, light or acoustical energy. The scanning device may also be positioned in a low earth orbit satellite, an aircraft, a missile or a helicopter. The single-point device re-radiates the signal source transmission to a computer command center which correlates single-point device scanning position data with received transmissions to accurately compute the location of the signal source. Beacons placed at precisely known locations may be used to interpret scan data.

Abstract: An audio satellite communication system is provided using the ranging mode of a telemetry tracking and control (TT&C) system. The audio is placed on one of the ranging tone subcarriers of a TT&C ground station and received via the ranging tone subcarrier at other TT&C ground stations within the coverage area of the satellite omni-directional antenna.

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 satellite communications system and method of communication which results in increased frequency-reusage within assigned frequency bands and allows for a reduction in satellite transponder requirements per unit of bandwidth employed. The disclosed system employs a satellite in a geostationary orbit having transponders and one or more large-aperture, high-gain antennas that provide a broad-area beam for a relatively wide service area and for transmitting to and receiving signals from N narrow-area beams for N respective sub-areas, the sub-areas corresponding to the high-traffic nodes. Both beam types operate in the same allocated frequency bands but with opposite linear or opposite handed circular polarizations, or, alternatively, with arbitrarily determined portions of the allocated frequency band pairs with dual polarization so that the allocated frequency spectrum is used at least N+1 times.