7,466,778 Memory Efficient OFDM Channel Estimation and Frequency Domain Diversity Processing
A frequency domain diversity DVB receiver device includes multiple antenna ports for receiving radio signals, and radio signal processing circuits connected to the antenna ports that convert the received radio signals into digital samples. The digital samples from the different antenna ports time-share a front-end processor which processes the digital samples to provide time-domain symbols. The time-domain symbols are stored in time-domain symbol buffers according to which of the antenna ports the time-domain symbols are received. A fast fourier transform circuit then retrieves the time-domain symbols and converts them frequency-domain symbols, which are then stored one or more frequency-domain symbol buffers according to the antenna ports the corresponding radio signals are received. A diversity processor which combines the frequency-domain symbols from the frequency-domain symbol buffers.
7,432,810 Radio Frequency Tags For Use in a Motion Tracking System
Small radio frequency tags for use in a motion capture system include a power source, circuitry for generating radio frequency identification signals, an antenna for transmitting the signals, and means for automatically activating the tags so that the tags begin transmitting the signals including a tag identification code when a cover is removed. The activation means may include a release strip that, when removed, opens or closes an electrical circuit that activates the tag and also exposes an adhesive covered surface of the tag so that the tag can then be adhered to a clothed or unclothed human body or other object to be tracked. The activation means can also include an optical sensor, an oxygen sensor, or other sensors. The battery and the antenna may be printed or constructed of film, thus allowing the tag to be small, thin, and flexible.
7,423,602 Multiple-Point to Multiple-Point Communication System
Methods and apparatus for a high speed wireless communication system are disclosed. The high speed wireless links are accomplished using relatively narrow beams (<1.degree.). These beams are produced using rotational motion at a base station in the center of a cell. In one embodiment of the invention, a radio and an antenna are mounted on a rotating element attached to a vertical mast. In another embodiment, a rotating mirror is employed to produce reflected beams. The present invention may be implemented using the 71-76 GHz, 81-86 GHz, and/or 92-95 GHz frequency bands.
7,009,561 Radio Frequency Motion Tracking System and Method
A radio frequency (RF) motion capture system includes stationary sensor receivers, one or more transmitter marker tags on one or more objects to be tracked within a capture zone, at least one stationary reference tag transmitter, and a processing system for processing the received signals. The individual tags transmit burst of spread-spectrum RF signals. The transmitted signals include a common sync code, and a tag identification code that is unique to each tag. By computing double differences of pseudoranges, clock terms are cancelled out allowing the processing system to precisely determine the location of each tag as it moves through the capture zone without the need to synchronize clocks between sensors and tags. The system can be used for RF match moving.
A scalable satellite data communication system that provides incremental global broadband services using Earth-fixed cells may begin with a limited satellite deployment that initially serves a limited number of Earth-fixed cells. The system has the flexibility to incrementally increase the number of Earth-fixed cells that are served, with minimal constraints on the relative locations of the cells on the Earth, by adding satellites of potentially greater complexity to the system. Backward compatibility with existing user terminals is achieved by maintaining the same satellite communication interface as with the already-deployed satellite constellation. Continuous and/or non-continuous service may be provided to selected Earth-fixed cells. Scheduled non-continuous service is particularly advantageous for bulk data transport services. Satellites may use simple mechanically-steered antennas. Communication links may be handed from one satellite to another when one satellite moves out of range and is no longer able to cover a selected Earth-fixed cell.
6,665,296 Network Access Communication System
A communication system is disclosed which provides two-way communications access to a wide area network (WAN) for a very large number of subscribers. It offers an inexpensive "last-mile" hookup from a subscriber terminal to a communications hub. The hub is connected to a WAN such as the Internet. The system comprises service areas, 0.7 to 1.5 km radius, wherein the hub and subscribers are located. Subscribers are connected to a subscriber terminal, directly or through a local area network (LAN). Each terminal communicates with the hub by a SHF radio link. Distributed routing of signals provides subscribers with no-waiting, transmission of information at speeds about ten Mbps. Availability of a communication path approximates a fiber optic cable. The LAN may be a local public switched telephone network. Each service area is divided into one to forty sectors. Eight sectors can support approximately 1,600 subscribers. Service areas may be arranged to cover larger areas. Overlapping service areas permit subscribers to be within line-of-sight of a hub. Service area arrangement is readily adapted to terrain, existing structure and number of subscribers.
6,157,642 Coding System And Method For Low-Earth Orbit Satellite Data Communication
A data communication system for a constellation of low-Earth orbit (LEO) satellites that employ Earth-fixed cellular beam management technology is disclosed. The data to be communicated is formed into data packets by a transmitting ground terminal. Each data packet includes a header and a payload. The header contains address and other control information and the payload contains the data to be communicated. The header and payload databits are separated and outer forward error correction (FEC) encoded with an outer error correction code. The symbols of the outer encoded header and payload codewords are interleaved, first separately and then together. The outer encoded, interleaved header and payload codewords are inner encoded by an inner FEC encoder. Upon receipt by an uplink satellite, the inner error correction code is removed and the resulting codeword symbols are de-interleaved. The outer error correction code of the header portion is then removed to recover the header of the original signal. The information contained in the header is used to route the data packets through the satellite constellation to the appropriate downlink satellite. The downlink satellite re-outer encodes the header and the symbols of the re-outer encoded header and the still outer encoded payload codewords are separately interleaved and then interleaved together. The interleaved re-outer encoded header and outer encoded payload databits are re-inner encoded. Upon receipt by a receiving ground terminal, the data packets are inner decoded to remove the inner error correction code and the symbols of the header and payload codewords are de-interleaved. Then the header and payload codewords are outer decoded to remove the outer error correction codes and recover the header and payload. Preferably a payload filter is included to eliminate the need to outer decode payload codewords not destined for the receiving ground terminal.
6,157,621 Satellite Communication System
The Satellite Communication System disclosed in the specification is a dynamic constellation of satellites. The present invention is capable of offering continuous voice, data and video service to customers across the globe on the land, on the sea, or in the air. The preferred embodiment of the invention comprises a low Earth orbit satellite system that includes 40 spacecraft traveling in each of 21 orbital planes at an altitude of 700 km (435 miles). This relatively large number of satellites employed by the preferred embodiment was selected to provide continuous coverage of the Earth's surface at a high minimum mask angle of forty degrees. Each of the individual 840 spacecraft functions as an independent sovereign switch of equal rank which knows the position of its neighbors, and independently handles traffic without ground control. The satellites are capable of transporting calls to millions of customers using portable, mobile and fixed residential and business terminals, and gateways to public phone networks. The constellation uses the 20 and 30 GHz frequency bands for communications between Earth and the constellation, and the 60 GHz band for communicating among the satellites. The present invention is designed to support in excess of 2,000,000 simultaneous connections, representing over 20,000,000 users at typical business usage levels, and over 350 billion minutes of use per year. Only a system such as the preferred embodiment, which utilizes 840 satellites at a preferred minimum mask angle of forty degrees, can accomplish these challenging objectives
6,127,967 Low-Earth Orbit Satellite Acquisition and Synchronization System Using a Beacon Signal
A system for acquiring the beacon of a satellite and synchronizing data transmission between the satellite and a ground terminal is disclosed. The ground terminal conducts a search for a satellite to be acquired. The search may be based on previously developed information from which the location of the satellite can be predicted and, thus, limited to a small area of the sky, or cover a large area of the sky in accordance with a search routine. After the beacon of a satellite is acquired, the geographic area served by the satellite is determined. If the satellite does not serve the cell within which the ground terminal is located, a further satellite search is conducted, which may be based in part on information contained in the beacon of the acquired satellite. After the satellite serving the cell containing the ground terminal is acquired, a test is made to determine how long the satellite will continue to cover the cell. If the time period is short, communication waits until the next satellite to cover the cell is acquired. If the time period is long, communication is allowed to begin. The beacon is also used by the ground terminal to: (i) accurately time uplink data transmissions; (ii) estimate uplink Doppler, Doppler rate, and Doppler rate derivative and use this information to pre-compensate the carrier frequency of the uplink data transmissions for Doppler variations; and (iii) estimate the carrier frequency of downlink data transmission(s) by continuously tracking the beacon carrier frequency and scaling the result by a suitable scaling factor.
6,011,951 Technique for Sharing Radio Frequency Spectrum in Multiple Satellite Communication Systems
A technique for sharing radio frequency spectrum between multiple satellite communication systems. A first and a second satellite communication system each contain a plurality of satellites in a plurality of non-geostationary (non-GSO) Earth orbits. Each of the plurality of non- GSOs has a predefined orbital plane. Within each orbital plane, satellites of the first and second satellite communication systems are alternating, such that each orbital plane contains satellites from each of the satellite systems. In this manner, it is possible to achieve satisfactory discrimination between satellites and Earth-based stations. The Earth-based station of each communication system will communicate with the closest satellite of its respective communication system. In an alternative technique that is particularly useful when an Earthbased station in the first communication system is able to communicate with more than one satellite, a satellite is selected based on the topocentric separation of the satellite from satellites in the second system. The system can also combine alternating satellites within an orbital plane with alternating orbital planes with satellites of each respective communication system.
5,995,841 Technique for Sharing Radio Frequency Spectrum in Multiple Satellite Communication Systems
A technique for sharing radio frequency spectrum in a multiple communication satellite system with a plurality of satellites in each of a plurality of non-geostationary (non-GSO) Earth orbits. A first satellite communication system uses a plurality of predefined non-GSO Earth orbits and a second satellite communication system uses a plurality of predefined orbits that are interleaved with the orbital planes of the first satellite communication system. In this manner, it is possible to achieve satisfactory discrimination between satellites and Earth-based stations. With near polar orbits, the topocentric separation between satellites decreases as the latitude of the Earth based stations increases due to the convergence of orbital planes near the poles. To compensate for the decreased topocentric separation, the system utilizes one or more mitigation techniques to select one of a plurality of possible satellites to communicate with the Earth-based station in order to effectively increase topocentric separation.
5,936,570 Low-Earth Orbit Satellite Acquisition and Synchronization System Using a Beacon Signal
A system for acquiring the beacon of a satellite and synchronizing data transmission between the satellite and a ground terminal is disclosed. The ground terminal conducts a search for a satellite to be acquired. The search may be based on previously developed information from which the location of the satellite can be predicted and, thus, limited to a small area of the sky, or cover a large area of the sky in accordance with a search routine. After the beacon of a satellite is acquired, the geographic area served by the satellite is determined. If the satellite does not serve the cell within which the ground terminal is located, a further satellite search is conducted, which may be based in part on information contained in the beacon of the acquired satellite. After the satellite serving the cell containing the ground terminal is acquired, a test is made to determine how long the satellite will continue to cover the cell. If the time period is short, communication waits until the next satellite to cover the cell is acquired. If the time period is long, communication is allowed to begin. The beacon is also used by the ground terminal to: (i) accurately time uplink data transmissions; (ii) estimate uplink Doppler, Doppler rate, and Doppler rate derivative and use this information to pre-compensate the carrier frequency of the uplink data transmissions for Doppler variations; and (iii) estimate the carrier frequency of downlink data transmission(s) by continuously tracking the beacon carrier frequency and scaling the result by a suitable scaling factor.
5,822,680 Frequency Sharing for Satellite Communication System
A communication system and methods for sharing a common communication frequency, without interfering with a second communication system which has a plurality of satellites operating in geostationary orbits (GO) and ground stations (GS) which communicate with the satellites (GEO) on the common communication frequency, is disclosed. Conventional geostationary satellites broadcast in C and K(u) bands. Ground stations (GS) which receive these signals must have their antennas pointed toward the plane of the Equator (EQ). Satellites which occupy inclined orbits (LO) and communicate with terrestrial terminals propagate beams of energy that do not intersect the plane of the Earth's Equator. Terrestrial terminals in the northern hemisphere communicate with a satellite only when the sub-satellite point of the satellite is at a latitude more northerly than the terrestrial terminal. Terrestrial terminals in the southern hemisphere communicate with a satellite only when the sub-satellite point of the satellite is at a latitude more southerly than the terrestrial terminal. The spatial isolation of signals achieved by this novel pointing method insures that both the geostationary and inclined orbit satellite systems do not interfere with each other.
Earth-fixed cell beam management methods which may be employed to allocate beams generated by a constellation of low Earth orbit satellites flying in orbits below geosynchronous altitudes are disclosed. These beams are electronically steered so that they illuminate "Earthfixed cells" as opposed to "satellite-fixed cells." Beam steering apparatus using a spherical dielectric lens is disclosed. In a system that employs satellite-fixed cells, the "footprint" of the beams propagated by a spacecraft defines the zone on the ground called a "cell" which is illuminated by the spacecraft. This satellite-fixed cell moves constantly as the spacecraft moves around the globe. In sharp contrast, an "Earth-fixed cell" is a stationary region mapped onto the surface of the Earth that has permanent fixed boundaries, just like a city or a state. Although the rapidly moving satellites still shine their beams over the ground in rapidly moving footprints, the locations of the footprints at any given time do not determine the location of the unchanging Earth-fixed cells. The great advantage provided by using cells having boundaries that are fixed to an Earth-fixed grid is realized when a subscriber being served by one satellite must switch to another beam in the same satellite or to a second satellite because the first is moving out of range below the local horizon. With satellite-fixed cells, this "hand-off" involves the assignment to the terminal of a new communication channel within the new beam or new satellite. This assignment process takes time and consumes processing capacity at both the terminal and the satellite. It is also subject to blocking, call interruption, and call dropping if there is not an idle communication channel in the next serving beam or satellite. The Earth-fixed cell method avoids these problems by allocating communication channels (frequency, code, and/or time slot) on an Earth-fixed cell basis rather than on a satellite-fixed cell basis. Regardless of which satellite/ beam is currently serving a particular cell, the terminal maintains the same channel assignment, thus ameliorating the "hand-off" problem.
5,678,175 Satellite System Using Equatorial and Polar Orbit Relays
A satellite communications system is disclosed. One of the embodiments of the present invention includes six to fourteen satellites which operate in a single Equatorial orbit. These satellites are capable of providing communications services to locations on the Eart which are within thirty degrees of the Equator. Another embodiment of the invention utilizes both the single Equatorial orbit plane in combination with other satellites moving in polar or inclined orbits. The embodiment that combines satellites in Equatorial, polar and inclined orbits will provide a wide variety of data services to virtually any point on the globe. In the preferred embodiments, the satellites are designed to operate in a circular low Earth orbit at an altitude of from 800 to 1852 kilometers. Although the preferred embodiments utilize this specific range of altitudes, the satellites are designed to fly in any orbit that is not a geosynchronous orbit. The satellites are also capable of speeding packetized messages around the globe either by working in combination with relay stations on the ground, by transferring message payloads across different orbits via the relay stations or by conveying packetized payloads through the use of inter-satellite links.
5,548,294 Dielectric Lens Focused Scanning Beam Antenna for Satellite Communication System
A method and apparatus for providing a plurality of beams transmitted and received from positions in low Earth orbit for communicating directly with a plurality of portable, mobile and fixed terminals and gateways is disclosed. A plurality of scanning beam antennas is deployed on each satellite within a constellation of satellites placed in low Earth orbit. Each one of said plurality of scanning beam antennas simultaneously receives and transmits a plurality of beams, each of which beams illuminates cell in an Earth-fixed grid. The beams are formed by each scanning beam antenna and are focused on the cell by a dielectric lens. A preferred embodiment uses a Luneberg spherical lens. Each beam is electronically shaped and steered to keep the cell of the Earth-fixed grid within the beam footprint.
5,408,237 Earth-Fixed Cell Beam Management for Satellite Communication System
Earth-fixed cell beam management methods which may be employed to allocate beams generated by a constellation of low Earth orbit satellites flying in orbits below geosynchronous altitudes are disclosed. These beams are electronically steered so that they illuminate "Earthfixed cells" as opposed to "satellite-fixed cells." In a system that employs satellite-fixed cells, the "footprint" of the beams propagated by a spacecraft defines the zone on the ground called a "cell" which is illuminated by the spacecraft. This satellite-fixed cell moves constantly as the spacecraft moves around the globe. In sharp contrast, an "Earth-fixed cell" is a stationary region mapped onto the surface of the Earth that has permanent fixed boundaries, just like a city or a state. Although the rapidly moving satellites still shine their beams over the ground in rapidly moving footprints, the locations of the footprints at any given time do not determine the location of the unchanging Earth-fixed cells. The great advantage provided by using cells having boundaries that are fixed to an Earth-fixed grid is realized when a subscriber being served by one satellite must switch to another beam in the same satellite or to a second satellite because the first is moving out of range below the local horizon. With satellite-fixed cells, this "hand-off" involves the assignment to the terminal of a new communication channel within the new beam or new satellite. This assignment process takes time and consumes processing capacity at both the terminal and the satellite. It is also subject to blocking, call interruption, and call dropping if there is not an idle communication channel in the next serving beam or satellite. The Earth-fixed cell method avoids these problems by allocating communication channels (frequency, code, and/ or time slot) on an Earth-fixed cell basis rather than on a satellite-fixed cell basis. Regardless of which satellite/beam is currently serving a particular cell, the terminal maintains the same channel assignment, thus ameliorating the "hand-off" problem.
A low cost tracking system employing satellites of the global positioning system (GPS) is suitable for applications involving radiosondes, sonobuoys, and other objects. The tracking system includes a sensor mounted on each object which digitally samples the GPS satellite signals and records them in a data buffer. The digital samples are then transmitted, at a rate lower than that at which the GPS satellite signals were sampled, over a data telemetry link, interleaved with other telemetry data from the object. The GPS data is processed in a data processing workstation where the position and velocity of the sensor, at the time the data was sampled, is computed. The data buffer in the sensor is periodically refreshed, and the workstation periodically computes the new position and velocity of the sensor. Differential corrections are also provided at the workstation to aid in signal acquisition and to increase the precision of the position fix.
5,225,842 Vehicle Tracking System Employing Global Positioning System (GPS) Satellites
A tracking system employing global positioning system (GPS) satellites provides extremely accurate position, velocity, and time information for vehicles or any other animate or inanimate object within any mobile radio communication system or information system, including those operating in high rise urban areas. The tracking system includes a sensor mounted on each object, a communication link, a workstation, and a GPS reference receiver. The sensor operates autonomously following initialization by an external network management facility to sequence through the visible GPS satellites, making pseudo range and delta range or time difference and frequency difference measurements. No navigation functions are performed by the sensor, thereby permitting significant reductions in the cost thereof. The raw satellite measurements, with relevant timing and status information, are provided to the communication link to be relayed periodically back to the workstation. Differential corrections may also be provided at the workstation to increase the accuracy of the object location determination. In normal operation, three satellite measurements are required to compute the location of the object, but for a short time period a minimum of two satellite measurements are acceptable with time, altitude, and map aiding information being provided by the workstation.
4,862,178 Digital System for Codeless Phase Measurement
A codeless digital method and apparatus for obtaining measured phase from a plurality of L2 signal transmissions. An intermediate frequency signal is derived by mixing the L2 transmissions with a local oscillator. That signal is hardlimited and employed to terminate the count of a divide-by-32 counter that is clocked by the local oscillator signal and initiated by a signal in synchronization therewith whose frequency is a fraction of the local oscillator. The state of the counter is applied to a four bit latch. The state of the latch, which effectively discards the most significant bit of the count, provides the measured phase of the L2 transmissions from which position can be obtained by reference to the satellite phase and delta range values derived therefrom.
4,849,961 Fast Sequencing Demodulation Method and Apparatus
A fast sequencing method and apparatus for use in a radio navigation system of the GPS type. Satellite-coded signals are simultaneously received from a plurality of sources. The signals are decoded in a single channel by multiple samplings of each signal per each signal modulating period. By taking multiple signal samplings per data period, broadband receiver operation is realized, enhancing the suitability of such apparatus for navigation of medium and high g performance vehicles and the like.
A method and apparatus for detecting and identifying Doppler frequency and phase information contained within a signal of the direct sequence spread spectrum type. An incoming signal is split by a circuit and component parts mixed with first and second local oscillator signals, the frequency of the first local oscillator being less than that of the carrier and the second being greater than that of the carrier by the same amount, plus an amount equal to twice the maximum Doppler frequency shift. The heterodyned signals are then low pass filtered, mixed with each other to form a heterodyned output that is then low pass filtered. The resultant signal retains Doppler phase and frequency information and is independent of carrier frequency and modulating PN-code thereby providing an easily demodulated signal whose Doppler information may be readily identified.
4,642,647 Signal Generator for Radio Navigation System
An improved signal generator and method for radio navigation in accordance with systems of the type in which location is determined in accordance with radio fixings with respect to multiple points of reference, each of such points providing a coded transmission. Multiple coded bit sequences are stored in an addressable read only memory. Phantom signals comprising a plurality of coded sequences are generated by addressing the memory in accordance with preselected sequences. Further, predetermined phase shifts are applied to the coded sequences to facilitate signal detection and associated computational processes.
4,584,652 Apparatus and Method for Determining In-phase and Quardraturephase Components
A digital method and a digital processor for determining the in-phase and quadrature-phase components of a phase error of a detected signal. An incoming carrier signal is sampled directly, then combined with estimated phase data (derived in the computer) in the digital processor to derive in-phase and quadrature-phase components of phase error that are provided to the computer for derivation of a subsequent estimate of carrier phase data.