Hughes Electronics Corporation

The Boeing Company

Hughes Aircraft Company

The Directv Group, Inc.

Andrew L Strodtbeck

Jennifer L Vollbrecht

Harold A Rosen

Robert R Hayes

Victor S Reinhardt

Susan E Bach

David A Langsam

Cecilia Y Cheng

Todd G Ellenberger

Parthasarathy Ramanujam

Lauriston Chin Wah

Ronald W Burch

Gregory C Busche

Gustave Solomon

Denise A Uyeda

Paul Y Sako

A communication system employing site diversity combing to increase link availability includes at least two receivers at receive sites within a single downlink beam separated by enough distance to provide decorrelation of weather phenomena&#x2014;such as rain fade outages. A signal transmits digital symbols to all the receivers and may use bandwidth efficient modulation with forward error correction coding. Sampled symbol values for each codeword are produced at each receiver, which are connected by one or more ground links so that all data can be collected at one site. At least two different soft-decision computation modules translate the sampled symbol values from the different receivers into different sets of soft-decision values&#x2014;which may be log-likelihood-ratio (LLR) values reflecting the probability value for each bit of the codeword&#x2014;that are digitally synchronized and combined for use by a decoder. The technique thus avoids disadvantages of either coherent waveform combining or BER-based digital switching.

Efficient diversity combining for wideband downlink

An optical communication terminal transmits data via an optical signal with a transmit mirror positioned to direct the optical signal. The optical communication terminal includes a processor configured to develop a control signal for a mirror controller to establish an optimal position of the transmit mirror. The optical communication terminal further includes a modulator coupled to the processor that modulates the optical signal in accordance with a position of the transmit mirror during transmission of the optical signal. The optimal position of the transmit mirror may be established by a scanning routine that adjusts the position of the transmit mirror to a plurality of predetermined offset positions during transmission of the optical signal. The intensity of the optical signal as received by a further optical communication terminal is then determined and provided via modulation of a further optical signal transmitted back to the first-named optical communication terminal. The predetermined offset positions and the corresponding received intensities may then be utilized to determine the optimal position of the transmit mirror.

Alignment system and method for optical satellite communication

The present invention discloses a predistortion modulation system for use in satellite systems. A typical apparatus of the invention includes a predistortion processor for predistorting a digital data source signal to reduce transmission distortion and an adaptive algorithm processor for controlling the predistortion processor according to a received a feedback signal derived from the transmitted data source signal. In further embodiments, the non-linear and linear predistortion is adaptively controlled. The invention is particularly useful in a digital cinema satellite system.

Predistorted modulation system for bandwidth efficient satellite links

An adaptive quadrature amplitude modulation (&ldquo;QAM&rdquo;) decoding system for use in, for example, high speed, bandwidth efficient QAM communication systems includes a circuit that adaptively adjusts gain and voltage bias and provides adaptive equalization feedback based on the same signal used to decode the QAM symbols.

Adaptive quadrature amplitude modulation decoding system

An apparatus for estimating an error rate in a digital communication system is provided. A satellite ground station or a user satellite transmits a digital data stream to a relay satellite. The relay satellite calculates an error rate associated with the data stream by sanding one or more bits of the data to an error rate estimator. Each bit sent to the error rate estimator is delayed, inverted, and exclusive-ored (XOR) with the next bit in the data sequence. By averaging the output of the exclusive-or an analog representation (i.e., a moving average) of the error rate is produced. The analog estimate may then be converted to a digital signal. The error rate estimate may be returned to an equalizer within the relay's demodulator, thereby allowing the on-board equalizer to tune the demodulator for a minimum error rate. The error rate estimate may also be multiplexed into the spacecraft telemetry system. Once received by a receiver station, the telemetered error rate information can be used to monitor link quality or to tune distortion mitigation systems on the relay or at the transmit site.

Method and apparatus for estimating an error rate in a digital communication system

A soft decision decodable short binary block coding arrangement is provided for use as an inner code with a Reed-Solomon outer code in a concatenated coding scheme. The inner code is a (n,k) short block code having a message length k&times;i, where i is a small integer selected to eliminate any need for interleaving between the inner and outer codes. Eliminating interleaving mitigates inner code decoder burst errors. The inner code is preferably formed as a punctured (15,11) Hamming code modified to form a (12,8) code sequence.

Short block code for concatenated coding system

A method for uplink power control and time synchronization in a satellite communications system that is achieved using satellite-based measurements of the uplink signal power and signal arrival time. Uplink signals transmitted from an originating terminal are received by a communications satellite which measures the received signal power and arrival time. The satellite transmits a downlink signal to the originating terminal containing information of the measured uplink signal power and arrival time. The originating terminal receives the downlink signal and transmits subsequent uplink signals with an uplink signal power and transmission timing based on the information transmitted by the satellite.

Satellite-based measurement for uplink power control and time synchronization

A circuit for canceling cross polarization interference has a first signal input and a second signal input. An adjustable cancellation network circuit is coupled to the first input and the second input. The adjustable cancellation network circuit has a first programmable vector modulator having a first weight and a second programmable vector modulator having a second weight. The first weight is correlated to the first input signal to obtain a first output signal. The second weight is correlated with the second input signal to obtain a second output signal. A performance measurement circuit is coupled to the cancellation network circuit and receives the first output signal and the second output signal. The performance measurement circuit generates a first correlated signal corresponding to the amount of interference in the first correlated signal and a second correlated signal corresponding to the amount of interference in the second correlation signal. A controller is coupled to the cancellation network and performance measurement circuit. The controller receives the first correlated signal and the second correlated signal. The controller calculates an updated first weight and second weight in response to the first correlated signal and the second correlated signal.

Method and apparatus for canceling cross polarization interference

A method and system for controlling uplink power for signal transmission in a satellite communication system employing on-board demodulation and remodulation and having a plurality of user terminals that are linked by and that communicate with each other by way of a satellite relay system. A downlink error rate of the data in a downlink data stream is determined based on known data bits. An end-to-end error rate of the uplink data stream and the downlink data stream is determined. An error rate of the signal transmission is then determined based on the downlink error rate and the end-to-end error rate. The signal transmission is then controlled based on the error rate of the signal transmission.

Method and system for controlling uplink power in a high data rate

A satellite-based communication system providing high rate transfer of data between linked terminals. The system comprises a plurality of user terminals (VSAT's) that are linked by and that communicate with each other by way of a satellite-based relay system. A network control center provides configuration signals that control the satellite relay system and coordinate linking of terminals to each other. Frequency division multiplexing uplinks are used from the terminals and the network control center to the satellite relay system. Time division multiplexing are used on downlinks from the satellite relay system to the terminals and the network control center. Each user terminal comprises a data compression and decompression circuit, a transceiver, and an antenna for transmitting and receiving data to and from the satellite relay system. The satellite relay system comprises a satellite, a wide area antenna, a plurality of receive antennas, a plurality of transmit antennas, and a signal processor. The wide area antenna is provided for communicating control signals between the user terminals and the network control center. The plurality of receive antennas operate in a first frequency band and produce a first plurality of beams that cover a service area. The plurality of receive antennas receive time domain modulated data from the user terminals. The plurality of transmit antennas operate in a second frequency band and produce a second plurality of beams that cover the service area. The plurality of transmit antennas transmit frequency domain modulated data to the user terminals. The signal processor demodulates the time domain modulated data received from a user terminal, routes the demodulated data so that it is transmitted to a second user terminal, remodulates the data to provide frequency domain modulated data, and transmits the frequency domain modulated data to the second user terminal. Video cameras and monitors are coupled to the user terminals to provide for video teleconferencing.

High data rate satellite communication system

A communication protocol or method that provides for terminal access, data flow, call monitoring and terminal polling, and call termination between user terminals connected to a high data rate satellite communication system. An 'Aloha' random access channel that forms part of a bent-pipe architecture is used in conjunction with orderwire uplink and downlink channels to permit the system to cleanly and simply establish its data links and thus provide terminal access. A network control center is used to assign a source user terminal to uplink and downlink channels. After the communication link is established, uplinked data is demodulated, and routed to every downlink beam where it is multiplexed with other data channels, then remodulated and downlinked to every user terminal. The orderwire uplink is only from the network control center to the satellite relay system, and uses the channel without demodulation and remodulation. The orderwire downlink is only from the satellite relay system to the user terminals, and uses the channels with demodulation and remodulation. Each user terminal monitors its orderwire downlink channel to recognize and extract messages addressed to it. Data flow, call monitoring and terminal polling is performed once the source and destination user terminals have been assigned their beams and frequency and time slots. Thereafter, data transfer between terminals is generally independent of the network control center. Input data generated at a source user terminal is multiplexed and transmitted to the satellite relay system. The satellite relay system demodulates the data, routes it so that it is retransmitted on a beam that communicates with the destination user terminal, remultiplexes and remodulates the data, and then transmits the multiplexed data to the destination user terminal. The network control center monitors the link so that system resources are not unnecessarily tied up if a connection is lost. This is achieved by causing both terminals to send periodic messages to the network control center indicating that they are active on the network, or the network control center may periodically poll each terminal and terminate a call if either terminal is unresponsive or provides a signal indicating that it has hung up. Several call termination procedures are also provided.

Communication protocol for a high data rate satellite communication

Frequency reuse and data coding methods for use in a high data rate satellite communication system. The frequency reuse method provides for dual polarization and spatial reuse of transmit and receive beams to provide for a twelve-fold increase in the effective bandwidth and number of users that may be supported by the system. Transmit and receive antennas provide multiple, interleaved transmit and receive antenna beams. Digital input data at a source user terminal is coded and transmitted from a source user terminal on one of the plurality of receive antenna beams. The received data is demodulated and is routed so that it may be transmitted to a destination user terminal. The data is then remodulated, multiplexed, and transmitted to the destination user terminal on one of the plurality of transmit beams. The transmitted data is decoded at the destination user terminal to produce the output data. The input and output data processed by the system is digital, and the coding (concatenated coding forward error correction processing) is employed to reduce the sensitivity of communicated data to interference. The presently preferred encoding method comprises Reed-Solomon encoding input data, interleaving the encoded data, and convolutionally encoding the interleaved data and then time division multiplexing and modulating the data. The presently preferred decoding method comprises demodulating and demultiplexing received time division multiplexed data, Viterbi decoding the demultiplexed data, deinterleaving the Viterbi decoded data, and Reed-Solomon decoding the deinterleaved data to produce the output data. Other multiplexing schemes may alternatively be employed. The demodulating and remodulating steps regenerates a high quality digital data stream on the satellite that is communicated to the destination terminal to reduce the effects of uplink interference upon the downlink data stream.

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Marina Del Rey, CA, United States of America

Andrew L Strodtbeck