Abstract: Systems and methods are disclosed and include a method that includes adding a training symbol prefix to an OFDM symbol frame, the prefix including a plurality of training symbols, each including N sub-symbol fields. N/2 of the sub-symbol fields are zero valued, and N/2 of the sub-symbol fields carry corresponding symbols of a N/2 sub-symbol pseudo random training symbol. A first half of the pseudo random training symbol is symmetrical to a second half of the pseudo random training symbol. An OFDM N-sub-carrier transmission carries the prefix as signal power on a first N/2 of its N sub-carriers and suppresses signal power on a second N/2 of the sub-carriers. The first N/2 and second N/2 sub-carriers alternate in the frequency domain.

Abstract: Systems and methods are disclosed and include a method that includes adding a training symbol prefix to an OFDM symbol frame, the prefix including a plurality of training symbols, each including N sub-symbol fields. N/2 of the sub-symbol fields are zero valued, and N/2 of the sub-symbol fields carry corresponding symbols of a N/2 sub-symbol pseudo random training symbol. A first half of the pseudo random training symbol is symmetrical to a second half of the pseudo random training symbol. An OFDM N-sub-carrier transmission carries the prefix as signal power on a first N/2 of its N sub-carriers and suppresses signal power on a second N/2 of the sub-carriers. The first N/2 and second N/2 sub-carriers alternate in the frequency domain.

Abstract: Systems and methods are disclosed and include a method that includes adding a training symbol prefix to an OFDM symbol frame, the prefix including a plurality of training symbols, each including N sub-symbol fields. N/2 of the sub-symbol fields are zero valued, and N/2 of the sub-symbol fields carry corresponding symbols of a N/2 sub-symbol pseudo random training symbol. A first half of the pseudo random training symbol is symmetrical to a second half of the pseudo random training symbol. An OFDM N-sub-carrier transmission carries the prefix as signal power on a first N/2 of its N sub-carriers and suppresses signal power on a second N/2 of the sub-carriers. The first N/2 and second N/2 sub-carriers alternate in the frequency domain.

Abstract: Systems and methods are disclosed and include a method that includes adding a training symbol prefix to an OFDM symbol frame, the prefix including a plurality of training symbols, each including N sub-symbol fields. N/2 of the sub-symbol fields are zero valued, and N/2 of the sub-symbol fields carry corresponding symbols of a N/2 sub-symbol pseudo random training symbol. A first half of the pseudo random training symbol is symmetrical to a second half of the pseudo random training symbol. An OFDM N-sub-carrier transmission carries the prefix as signal power on a first N/2 of its N sub-carriers and suppresses signal power on a second N/2 of the sub-carriers. The first N/2 and second N/2 sub-carriers alternate in the frequency domain.

Abstract: Disclosed methods include transmitting an OFDM signal including a succession of frames spaced apart by a set of training symbols that are symmetric in time and each formed by a plurality of even-frequency sub-carriers, spaced by odd frequency zeros. The OFDM signal is received and sampled and timing metrics are determined. Local maximums, or peaks of the timing metrics are detected, and from the peaks a coarse time offset is determined. A correlation metric, at sample indexes within a region determined by the coarse time offset, is applied and, based on a peak, an estimated time offset is generated. A correlation metric of the estimated time offset is determined and, based on the correlation metric, an estimated frequency offset is generated.

Abstract: Disclosed methods include transmitting an OFDM signal including a succession of frames spaced apart by a set of training symbols that are symmetric in time and each formed by a plurality of even-frequency sub-carriers, spaced by odd frequency zeros. The OFDM signal is received and sampled and timing metrics are determined. Local maximums, or peaks of the timing metrics are detected, and from the peaks a coarse time offset is determined. A correlation metric, at sample indexes within a region determined by the coarse time offset, is applied and, based on a peak, an estimated time offset is generated. A correlation metric of the estimated time offset is determined and, based on the correlation metric, an estimated frequency offset is generated.

Abstract: An approach for increasing transmission throughput of a non-linear wireless channel, and efficient decoding of the transmitted signal via a simplified receiver, is provided. A signal reflects a source signal, and includes linear inter-symbol interference based on a faster-than-Nyquist signaling rate and a tight frequency roll-off, and non-linear interference based on high-power amplification for transmission over the wireless channel. The signal is received over a non-linear wireless channel, and is processed via a plurality of decoding iterations. A set of soft information of a current decoding iteration is generated based on a current estimate of the source signal and a final set of soft information from a previous decoding iteration. The current estimate of the source signal is based on an estimate of the linear ISI and the non-linear interference, which is based on the final set of soft information from the previous decoding iteration.

Abstract: An approach for increasing transmission throughput of a non-linear wireless channel, and efficient decoding of the transmitted signal via a simplified receiver, is provided. A signal reflects a source signal, and includes linear inter-symbol interference based on a faster-than-Nyquist signaling rate and a tight frequency roll-off, and non-linear interference based on high-power amplification for transmission over the wireless channel. The signal is received over a non-linear wireless channel, and is processed via a plurality of decoding iterations. A set of soft information of a current decoding iteration is generated based on a current estimate of the source signal and a final set of soft information from a previous decoding iteration. The current estimate of the source signal is based on an estimate of the linear ISI and the non-linear interference, which is based on the final set of soft information from the previous decoding iteration.

Abstract: An approach is provided for increasing transmission throughput rates for a source signal transmitted over a wireless channel, applying faster-than-Nyquist (FTN) signaling rates combined with tight frequency roll-off to the a source signal. A receiver is provided that compensates for ISI effects induced by the FTN rate and tight frequency roll-off, where the complexity of the receiver grows only linearly with the interference memory. The receiver comprises an equalizer configured to compensate for the ISI effects, and a decoder configured to decode the output of the equalizer to determine and regenerate the source signal. The receiver processes the received signal via a plurality of processing iterations. For one processing iteration, the decoder generates a set of a posteriori soft information based on the output of the equalizer, and the equalizer uses the a posteriori soft information as a priori soft information for a subsequent processing iteration.

Abstract: An approach for improved compensation for nonlinear distortion in multicarrier satellite systems is provided. Source reflecting encoded and modulated sequences of source data symbols are received. Each source signal is predistorted, and a transmit filter is applied to each predistorted source signal. Each filtered signal is translated to a carrier frequency, and the translated signals are combined into a composite signal for transmission via a multicarrier transponder. The final predistorted version of each source signal is generated via an iterative process of a number of stages, wherein, for a given stage and for each source signal, the process comprises: receiving a prior predistorted version of each source signal from a preceding stage; processing each prior predistorted source signal based on all of the received prior predistorted source signals, wherein the processing is performed based on a characterization of one or more characteristics of the multicarrier satellite transponder.

Abstract: A signal transmission approach comprises encoding a source signal (comprising source symbols) to generate a corresponding encoded signal. The encoded signal is modulated by mapping each source symbol to a respective signal constellation point of an applied signal constellation to generate a modulated signal. The modulated signal is pre-distorted based on a distortion estimate to generate a pre-distorted signal. The pre-distorted signal is filtered to generate a filtered signal. The filtered signal is frequency translated and amplified to generate a transmission signal for transmission via an uplink channel of a satellite communications system. To increase throughput, the source signal is processed through the apparatus and the resulting transmission signal is generated at a Faster-than-Nyquist (FTN) symbol rate and with a tight frequency roll-off. The modulated signal is pre-distorted based on a distortion estimate relating to the nonlinearity and the filters applied before and/or after the pre-distorter.

Abstract: An approach is provided for increasing transmission throughput rates for a source signal transmitted over a wireless channel, applying faster-than-Nyquist (FTN) signaling rates combined with tight frequency roll-off to the a source signal. A receiver is provided that compensates for ISI effects induced by the FTN rate and tight frequency roll-off, where the complexity of the receiver grows only linearly with the interference memory. The receiver comprises an equalizer configured to compensate for the ISI effects, and a decoder configured to decode the output of the equalizer to determine and regenerate the source signal. The receiver processes the received signal via a plurality of processing iterations. For one processing iteration, the decoder generates a set of a posteriori soft information based on the output of the equalizer, and the equalizer uses the a posteriori soft information as a priori soft information for a subsequent processing iteration.

Abstract: A signal transmission approach comprises encoding a source signal (comprising a plurality of source symbols) to generate a corresponding encoded signal. The encoded signal is modulated by mapping each source symbol to a respective signal constellation point of an applied signal constellation to generate a modulated signal. The modulated signal is pre-distorted based on a distortion estimate to generate a pre-distorted signal. The pre-distorted signal is filtered to generate a filtered signal. The filtered signal is frequency translated and amplified to generate a transmission signal for transmission via an uplink channel of a satellite communications system. To increase throughput, the source signal is processed through the apparatus and the resulting transmission signal is generated at a Faster-than-Nyquist (FTN) symbol rate and with a tight frequency roll-off.

Abstract: A system and methods that accommodate for nonlinear interference in a multi-carrier communications system are provided. A first signal is received by a receiver. The first signal comprises a source signal transmitted on a carrier over a communications channel. The first signal reflects a source symbol mapped to one of a plurality of signal constellation points, and each signal constellation point is associated with a different one of a plurality of signal clusters. A received representation of the source signal with respect to the source symbol is acquired from the first signal. A plurality of likelihood metrics are determined, where each likelihood metric is based on the received representation of the source signal with respect to the source symbol and a different one of a plurality of core parameters, wherein each core parameter is based on a centroid estimate with respect to a different one of the signal clusters.

Abstract: A receiver is provided that can receive a first signal transmitted on a first carrier and a second signal transmitted on a second carrier. The receiver includes a channel estimation portion, a multicarrier nonlinear equalizer, a first log likelihood computing portion and a second log likelihood computing portion. The channel estimation portion can output a first estimation. The multicarrier nonlinear equalizer can output a first equalized signal and a second equalized signal. The first log likelihood ratio computing portion can output a first log likelihood ratio signal based on the first equalized signal. The second log likelihood ratio computing portion can output a second log likelihood ratio signal based on the second equalized signal. The multicarrier nonlinear equalizer can further output a third equalized signal and a fourth equalized signal. The third equalized signal is based on the first signal, the second signal and the first estimation.

Abstract: A communications system includes a base station that is configured to transmit a signal that is modulated according to a predetermined modulation scheme and an orthogonal frequency division multiplexing scheme, wherein the signal is encoded using space-frequency coding. The base station includes a plurality of multiple-input multiple-output (MIMO) transceivers. The system includes a terminal that is configured to receive the modulated signal. The above arrangement is particularly applicable to providing multichannel multipoint distribution services (MMDS) over a radio communications system.

Abstract: The present invention provides a communication system for use with a first source signal and a second source signal. The first source signal is on a first channel and includes M symbols, where M is an integer greater than 1. The second source signal is on a second channel and includes X symbols, where X is an integer greater than 1. The first channel is different from the second channel. The communication system includes a first modulator unit, a second modulator unit and an adder. The first modulator unit can generate a first modulated signal based on the first source signal and includes a first inter-symbol distortion estimating unit and a first stage predistortion unit. The second modulator unit can generate a second modulated signal based on the second source signal and includes a second inter-symbol distortion estimating unit and a predistortion unit. The adder can generate an added signal based on the first modulated signal and the second modulated signal.

Abstract: An aspect of the present invention is drawn to a receiver operable to receive a first signal transmitted on a first carrier and to receive a second signal transmitted on a second carrier. The receiver includes a first filter, a second filter and a nonlinear compensator. The first filter is arranged to receive the first signal and to generate a first filtered signal. The second filter is arranged to receive the second signal and to generate a second filtered signal. The nonlinear compensator is arranged to output a first compensating signal based on the first filtered signal and the second filtered signal and to output a second compensating signal based on the first filtered signal and the second filtered signal. Further, the nonlinear compensator can reduce one of nonlinear interference within the first filtered signal and nonlinear interference between the first filtered signal and the second filtered signal.

Abstract: The present invention provides a communication system for use with a first source signal and a second source signal. The first source signal is on a first channel and includes M symbols, where M is an integer greater than 1. The second source signal is on a second channel and includes X symbols, where X is an integer greater than 1. The first channel is different from the second channel. The communication system includes a first modulator unit, a second modulator unit and an adder. The first modulator unit can generate a first modulated signal based on the first source signal and includes a first inter-symbol distortion estimating unit and a first stage predistortion unit. The second modulator unit can generate a second modulated signal based on the second source signal and includes a second inter-symbol distortion estimating unit and a predistortion unit. The adder can generate an added signal based on the first modulated signal and the second modulated signal.

Abstract: A communications system includes a base station that is configured to transmit a signal that is modulated according to a predetermined modulation scheme and an orthogonal frequency division multiplexing scheme, wherein the signal is encoded using space-frequency coding. The base station includes a plurality of multiple-input multiple-output (MIMO) transceivers. The system includes a terminal that is configured to receive the modulated signal. The above arrangement is particularly applicable to providing multichannel multipoint distribution services (MMDS) over a radio communications system.