Viasat, Inc.

Visat, Inc.

Matthew D Nimon

William H Thesling

Fan Mo

Donald Wesley Becker

Sameep Dave

Mark Vanderaar

Richard T Gedney

Methods, systems, and devices are described for modulating and demodulating data on optical signals. During modulation, at least one stream of symbol mapped bits is filtered with at least one pulse shaping filter to reduce a bandwidth of the stream of bits and to pre-compensate for at least one identified non-ideal transmission condition. The filtered bits are modulated onto a waveform in the digital domain, and the modulated filtered bits are transmitted to digital-to-analog converter. The output of the digital-to-analog converter is converted to an optical signal. During demodulation, a received optical signal is sampled at a first sampling rate at an ADC, downsampled to a lower sampling rate for filtering, filtered with at least one discrete pulse-shaping filter, upsampled for equalization and demodulation, and then equalized and demodulated.

DAC-based optical modulator and demodulator

Systems, devices, processors, and methods are described which may be used for the reception of a wireless broadband signal at a user terminal from a gateway via a satellite. A wireless signal may include a series of physical layer frames, each frame including a physical layer header and payload. The received signal is digitized and processed using various novel physical layer headers and related techniques to synchronize the physical layer frames and recover data from physical layer headers for purposes of demodulation and decoding.

False lock detection for physical layer frame synchronization

Symbol timing acquisition is described for a wireless broadband signal received at a user terminal from a gateway via a satellite. In-phase and quadrature channels of the wireless signal may each be sampled at a rate of one sample per symbol. The samples may be interpolated to generate an early interpolation and a late interpolation for each of the samples. A difference measurement is obtained between the early interpolation and the late interpolation for a set of the samples. A number of the difference measurements may be averaged, and symbol timing may be modified based on the average. This process may be continued on an iterative basis to acquire symbol timing.

Symbol timing acquisition using early-late interpolation

Methods, systems, and devices are described for a digital demodulator device for processing received optical signals. The device may include a quadrature error filter that receives a digitized version of an optical signal, and removes quadrature errors to generate a filtered series of data samples. The device may also include a frequency offset removal module for performing frequency rotation on the filtered series of data samples. The device may include a chromatic dispersion compensation module which removes chromatic dispersion from horizontal and vertical polarization channels. The device may include a polarization mode dispersion (PMD)/polarization dependent loss (PDL) compensation module which compensates for interference caused by PMD and PDL. The device may also include a phase recovery module configured to track and correct phase.

Digital demodulator architecture

Systems, devices, processors, and methods are described which may be used for the reception of a wireless broadband signal at a user terminal from a gateway via satellite. A physical layer header may be identified, the header including a number of subcode blocks. A phase may be estimated for each of the subcode blocks, and intra-header phase differences may be calculated. The intra-header phase differences may be used to calculate a frequency error, which may be corrected. Frequency errors may be monitored and, when such errors fall below a threshold level, an alternative inter-frame frequency error tracking method may be used.

Delta-theta frequency estimation

Methods, systems, and devices are described for a low complexity interpolator for use in optical transmission systems. An input receives a digitized version of an optical signal, and provides samples of the received signal to a filter module. The filter module filters the input samples according to a set of filter coefficients provided by a memory. The set of filter coefficients are provided based on the output of a numerically controlled oscillator that provides an output corresponding to an accumulation of partial periods of the first sample rate. Filtered data samples are output to a sample block assembler that receives the data samples, removes filtered data samples where it is indicated that the sample is not valid, and outputs valid filtered data samples at the second sample rate and at a fixed number of samples power output period.

Interpolator for high-rate optical communications

Methods, systems, and devices are described for compensating for a coarse frequency offset between a received optical signal and a local oscillator at a demodulator. Multiple samples are received of an output of a discrete Fourier transform performed on the received optical signal. A magnitude of each sample is determined, and the determined magnitudes may be filtered by a digital domain filter. A difference is computed between the determined magnitudes for a first set of the samples and the determined magnitudes for a second set of the samples, and a local oscillator correction factor is generated based on at least the computed difference.

Coarse frequency offset estimation and correction for high-speed optical communications

Start of frame correlation for physical layer header synchronization

Physical layer header structure for decoding and synchronization

Cross-polar interference cancellation in a dual-polarization system is described. A terminal in a satellite communication system may receive a first communication signal in a first polarization and a second communication signal in a second polarization substantially orthogonal to the first polarization. The terminal may correlate in-phase or quadrature components of the first communication signal with in-phase or quadrature components of the second communication signal to generate one or more correlation measurements. Correction terms may be generated, using the correlation measurements, to remove at least some of the cross-polar interference.

Digital cross-polar interference cancellation

An architecture for the dynamic assignment of links in a multi-user communication system. A plurality of information channels are provided in a forward communication link of the communication system for carrying channel information of the plurality of information channels from a transmitter to a plurality of corresponding receiving devices. The channel information in corresponding select ones of the plurality of information channels is varied dynamically in response to link conditions of the associated receiving devices to more efficiently utilize the channel bandwidth.

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Fairview Park, OH, United States of America

Matthew D Nimon