Abstract: 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—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—which may be log-likelihood-ratio (LLR) values reflecting the probability value for each bit of the codeword—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.

Abstract: 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—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—which may be log-likelihood-ratio (LLR) values reflecting the probability value for each bit of the codeword—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.

Abstract: 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—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—which may be log-likelihood-ratio (LLR) values reflecting the probability value for each bit of the codeword—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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: An adaptive quadrature amplitude modulation (“QAM”) 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.

Abstract: 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.

Abstract: A router circuit has an electrical-to-optical converter for changing the plurality of electrical input signals into a plurality of optical input signals. A mixing circuit is coupled to the electrical-to-optical converter. The mixing circuit generates a plurality of substantially identical composite signals corresponding to the plurality of optical inputs. The composite signals comprise at least a portion of each of the plurality of optical signals. A plurality of optical bandpass filters is coupled, respectively, to each of said plurality of composite signals. The bandpass filters pass a portion of the composite optical signals to form a plurality of filtered signals. An optical-to-electrical converter is coupled to the plurality of bandpass filters. The optical-to-electrical converter converts the plurality of filtered optical signals into a respective plurality of electrical output signals.

Abstract: 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.

Abstract: 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.

Abstract: 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×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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.