Stanford Telecommunications, Inc.

Itt Manufacturing Enterprises, Inc.

The Mitre Corporation

Aaron Weinberg

Leonard Schuchman

Kenneth D Cunningham

Daniel Urban

Lloyd Engelbrecht

Marc A Harlacher

Scott Bierly

Ronald C Bruno

Alexandr Draganov

Robert Smarrelli

Joseph Smallcomb

Ray Allen Daniel

Walter C Scales

Matthew S Simmons

Martin W Tucker

Rudy Rihani

Joseph Ziegler

Paul M Ebert

Joseph J Fee

Laurence Mailaender

Feisal S Keblawi

Yaroslav Kaminsky

Gene Allan McLeod

Cunninghasm, Ken

Thomas Land

A method for determining beamforming weights used onboard a satellite and ground-based beamforming weights used in a ground-based station as part of a satellite communication system. This beamforming method is a two-stage beamforming process that requires a reduced downlink bandwidth between the satellite and the ground-based station yet achieves optimal signal-to-noise ratio for bandwidth allocated for the downlink. values for the fixed onboard beamforming weights are computed to yield a maximum, where the maximum is computed over all possible fixed weights A represented by an L&#xd7;M matrix, the minimum is computed over all possible positions of remote communication devices U, and the signal-to-noise ratio (S/N) is computed for the optimal set of ground-based beamforming weights W={hacek over (W)}.

Optimized beamforming for satellite communication

A transceiver employing a steerable phased-array antenna includes a modem architecture in which signals from each antenna element in the array are independently processed down to the individual baseband channel level, and digital beamforming is performed at baseband. The data rate reduction from IF to baseband permits parallel signal data from multiple antenna elements to be time multiplexed and serially processed at acceptable data rates at baseband with minimal modem hardware requirements. Both for transmit signal modulation and received signal demodulation, the computation of carrier tracking, automatic gain control (AGC)/power-control, and beamforming are shared by the same processing circuitry for all channels when performed at baseband. The resulting baseband circuitry is only incrementally larger than that required for carrier tracking and AGC alone, yet accomplishes independent beamforming for each antenna element on each user channel.

Integrated beamformer/modem architecture

A Spread Spectrum system acquires signals with frequency uncertainty. The present invention independently computes the number of frequency bands necessary to cover the carrier frequency uncertainty and the chip rate uncertainty and uses the largest of the two quantities in the acquisition process. A receiver cycles through pseudonoise code phases until a matched filter output exceeds a threshold. The local code is adjusted based on that code phase and the signal is processed for carrier acquisition, where an FFT estimates the carrier frequency. The code phase and nearest neighbors are used to determine the presence of a false alarm. When a false alarm is absent, the detection is examined for an alias or noise spur. If an alias is absent, the signal search is complete. Otherwise, processing continues to search for a pseudonoise code. The process continues by examining all code phases for each band until a signal is detected.

Communication system and method for acquiring pseudonoise codes or carrier signals under conditions of relatively large chip rate uncertainty

Positioning system for locating a mobile body comprising a plurality of earth based spread spectrum (SS) broadcasting stations arranged geographically in a cellular pattern. Each SS broadcasting station include a modulator providing a channel signal structure which is substantially orthogonal with respect to adjacent stations in the cellular pattern, each channel signal including navigation beacon data including a unique beacon identification, station latitude and longitude, time_slot and phase characterizations and selected parameters of adjacent stations. In one embodiment, each modulator provides a chirped SS signal in which the navigation beacon is a frequency tone that is repeatedly swept over a selected frequency band for each station. In a further embodiment, each modulator provides a GPS like direct sequence SS signal in which the navigation beacon is a PN coded broadcast. A receiver on the mobile body receives the SS signals from at least three of the SS broadcasting stations and determines the location thereof. A fourth SS broadcasting station provides altitude CPS satellite signals can be used for timing control.

Cellular positioning system (CPS)

A communications system operating in one or more frequency bands of various number of channels per band (for a total of N channels), and a novel transceiver for receiving these multiple bands of signals. The transceiver comprises an antenna and RF front end for each said band, a separate RF to IF downconverter for each said band. The IF for each band is centered at a succession of frequencies F such that the spectra for each band are non-overlapping, with the center frequencies. Analog-to-digital converter sampling rate is chosen such that one band is centered at baseband, and one or more other bands are centered at a specific relationship with the sampling rate such that each band is individually downconverted to baseband by appropriate selection of tap weight multiplying sequences (such as alternating &plus;/&minus; sequence for the case of F equal to one-fourth the sampling rate). An analog-to-digital converter converts analog signals to digital signals from the combiner. A digital downconverter converts the digital signals to baseband signals and a single digital processor sequentially time shared among all the bands and channels.

Multi-band, multi-function integrated transceiver

A parallel digital matched filter is constructed which performs numerous simultaneous correlations of a received spread spectrum signal against various replica offsets of its spreading sequence. This allows for the rapid acquisition of the received signal code phase, and subsequent handoff to tracking for a multi-channel receiver. A novel matched filter computational architecture is utilized, in which common digital arithmetic elements are used for both acquisition and tracking purposes. As each channel is sequentially acquired by the parallel matched filter, a subset of the arithmetic elements are then dedicated to the subsequent tracking of that channel. This process is repeated, with the remaining available arithmetic elements accelerating the acquisition of the next channel, and so on, until all resources are allocated as tracking channels. Additionally, multiple data inputs and delay lines are present in this architecture, and are available for processing at each arithmetic element. In this way, multiple signal bands and user channels may be integrated within a common receiver framework.

Sequential-acquisition, multi-band, multi-channel, matched filter

A spread-spectrum demodulator architecture is presented which utilizes parallel processing to accomplish rapid signal acquisition with simultaneous tracking of multiple channels, while implementing an integrated multi-element adaptive beamformer, Rake combiner, and multi-user detector (MUD). A matched filter computational architecture is utilized, in which common digital arithmetic elements are used for both acquisition and tracking purposes. As each channel is sequentially acquired by the parallel matched filter, a subset of the arithmetic elements are then dedicated to the subsequent tracking of that channel. Additionally, multiple data inputs and delay lines are present, connecting the sampled baseband data streams of numerous RF bands and antenna elements with the arithmetic elements. The matched filter/despreader processing is virtually independent of channel origin or utilization; e.g., CDMA users, RF bands, beamformer elements, or Rake Fingers. Integration of the beamformer weighting computation with the demodulator results in substantial savings by sharing the existing circuitry performing carrier tracking and AGC. An optimal demodulator solution can be achieved through unified &ldquo;space/time&rdquo; processing, by providing all observables (element snapshots, Rake Fingers, carrier/symbol SNR/phase, etc.), for multiple channels, to a single adaptive algorithm processor that can beamform, Rake, and perform joint detection (MUD).

Integrated beamforming/rake/mud CDMA receiver architecture

A digital positioning system using digital AM and FM radio stations for use in the environment of a plurality of digital AM and FM (AM/FM) radio stations which comprises a customer service center and a reference station which regularly and passively receives signals from all local digital AM/FM stations and measures variations in key parameters of frequency and wavelength thereof and provides AM/FM correctional data signals corresponding to each AM/FM station frequency and wavelength variation to the customer service center. The customer service center is adapted to provide the AM/FM correctional data signals to each of the digital AM/FM radio stations for insertion into ancillary digital data broadcast from each digital AM/FM radio station. A plurality of mobile receivers in the environment of AM/FM radio stations, each of the mobile receivers receiving and processing three or more digital AM and/or FM signals and estimating and updating its position at periodic intervals and sending the results thereof to the customer service center via cellular or other network.

Digital AM/FM positioning system (DAFPS)&mdash;an international positioning system

Positioning system for locating a mobile body comprising a plurality of earth based spread spectrum (SS) broadcasting stations arranged geographically in a cellular pattern. Each SS broadcasting station include a modulator providing a channel signal structure which is substantially orthogonal with respect to adjacent stations in the cellular pattern, each channel signal including navigation beacon data including a unique beacon identification, station latitude and longitude, time.sub.-- slot and phase characterizations and selected parameters of adjacent stations. In one embodiment, each modulator provides a chirped SS signal in which the navigation beacon is a frequency tone that is repeatedly swept over a selected frequency band for each station. In a further embodiment, each modulator provides a GPS like direct sequence SS signal in which the navigation beacon is a PN coded broadcast. A receiver on the mobile body receives the SS signals from at least three of the SS broadcasting stations and determines the location thereof. A fourth SS broadcasting station provides altitude. CPS satellite signals can be used for timing control.

An existing TDRSS satellite communication system is incorporated, together with low-power ground-based remote transceivers of special design, and additional beamforming and steering elements at the ground terminals, to make possible digital communication between low power field transceivers and satellite ground terminals. The satellite communication system transmits to its ground terminals a composite signal, comprising amplified, phase-coherent signals received by an array of broad-coverage antennas on the satellite. The field transceiver transmits a pseudonoise coded signal spread across all or a portion of the satellite's receive bandwidth. At the ground terminals, the downlinked composite signal is processed by a beamformer to define a narrow, high-gain beam between the satellite and low-power transceiver. Signal processing gain and beamformer gain in combination serve to elevate the received, demodulated signals well above the noise level at the receiver. Through this invention, a large multiplicity of non-interfering reverse-link (remote-to-central) communication channels may be supported by a host satellite communication system of the nature described. By the introduction of forward link signal channels into the satellite ground terminal, and scheduling of forward link transmissions to the set of low-power remote transceivers along with normal transmit activities, highly useful two-way communication can be extended to a class of users not initially served by the satellite communication system.

Satellite for increasing the utility of satellite communication systems

An information broadcast system having a broadband broadcast system selected from cable and satellite for broadcasting requested information from a selected information source, including the Internet, to one or more selected subscriber stations includes an independent backhaul channel for communicating information request signals from a subscriber station to one or more central processing stations. The system includes a data broadcast station for transmitting requested data from the selected data source and central station via the data broadcast station to the one or more selected subscriber stations. The high-data rate broadcast station forwards requested data from a data source to the data broadcast station. A backhaul satellite communication system, independent of the broadband broadcast system, has a backhaul satellite ground terminal for coupling information request signals from backhaul satellite communication system to high data broadcast station terminal. Each subscriber station has a broadband broadcast receiver for receiving requested information broadcast by the high data rate broadcast and a satellite antenna for transmitting backhaul request signals to the backhaul satellite.

Wireless request channel for use with information broadcast system

The satellite radio communication system of this invention provides communication between one or more service centers and an ensemble of fixed and mobile user terminals. One or more earth orbiting satellites are provided with each satellite having transmitter forming a down-link channel which is slow frequency hopped, and a multi-beam antenna system with a single channel per beam to time division multiple broadcast signals to all user terminals covered by each said beam, respectively. Each user terminal includes a transceiver for receiving a down-link channel broadcast from the one of said beams in whose path it lies, and a return link comprised of a dedicated narrow band broadcast channel with slow frequency hopping of down-link channel. There is a fixed set of frequencies through which the frequency hopping is carried out, with the plurality of fixed and mobile user terminals using the same set of frequency hopping frequencies. Mutually synchronized transmissions from each user is such that while the ensemble of users display the same set of frequency hopping frequencies, each user in said ensemble of fixed and mobile user terminals employs a unique frequency at each instant of time.

Multi-beam satellite communication system with user terminal frequencies

A scrambled analog signalling system having a source of analog signals to be sent to a receiving device is comprised of a multiple stage charge coupled device (66) having analog signal input terminals connected to receive analog signal samples from said source of analog signals. The multiple stage charge coupled device having N stages, corresponding stage taps, and an input clock signal. A shuffling circuit (68) having a first input connected to the N stage taps for receiving the analog signal samples and second input for receiving a random seed (67) signal to cause a random reordering of incoming analog signal samples, a source of random seed signals connected to the second input, and an output device (72) connected to receive a stream of the analog signal samples which have been shuffled according to a mapping code carried by the random seed signal. A filter for reconstructing the analog signal in its scrambled format, and a transmission system for conveying the analog signal in its scrambled format to the receiving device.

Charge-coupled-device based all-analog wave form scrambling with

A satellite communication system including one or more satellites in geosynchronous orbit and inclined at a predetermined angle greater than 0.degree. relative to earth, a preferred angle being about 28.5.degree. for full earth coverage, there is a constellation of satellites. Each satellite has a multi-element phased array antenna and transmit and receive circuits selectively connected to said multi-element phased array antenna for providing spatially discriminated spot radiation beams on the earth's surface, and a steerable spaced/ground antenna and transmitter-receiver circuitry connected thereto. At least one gateway ground terminal having means for performing all spacecraft command and control, including uplink phasing of said phased array antenna for directive satellite transmissions to desired user locations. Tracking the moving satellites via combination of range and doppler tracking, steering said space/ground antenna in accordance with satellite motion, performing all ground-beamforming associated with user inbound transmissions, performing all user signal modulation and demodulation, providing the necessary ground interfaces with the external cellular and terrestrial networks. A plurality of earth-based low power transceivers are provided for one and two-way communications via selected elements of said phased array antenna.

Growing community of inventors

Potomac, MD, United States of America

Aaron Weinberg