Abstract: 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.

Abstract: Systems, devices, and methods are disclosed for a novel LDPC decoder. An architecture is described to implement a novel sequence of bit node processing (BNP) and check node processing (CNP) operations. More specifically, the BNP may be split into two parts: a BNP accumulator and a BNP extrinsic information calculator. This separation of processing modules may provide for fewer read and write operations to and from edge memory.

Abstract: Methods, systems, and devices are described for forward error correction for flash memory. Encoded data from flash memory may be used to generate a number of data streams. At each of a number of error detection sub-modules operating in parallel, a different one of the data streams is processed. Each error detection sub-module may detect whether a portion of the respective received stream contains an error, and forward the portion to an error correction module. The error correction module, physically separate from the error detection sub-modules, may correct the forwarded portions of the respective received streams containing an error. The age and error rate associated with the flash memory may be monitored, and a coding rate or other aspects may be dynamically adapted to account for these factors.

Abstract: 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.

Abstract: Polarization mode dispersion (PMD) in a dual-pole optical communications network is compensated for using an adaptive PMD equalizer. The PMD equalizer may include a number of substantially identical filter modules that provide partial outputs which may be combined to form a PMD compensated output. A constant modulus algorithm (CMA)-based equalizer may track PMD across both poles and generates an error signal. The CMA-based equalizer includes a filter bank, and uses an update algorithm and tap/output adjustments based on a difference between combined tap energies and an index, and feedback from a forward error correction code frame synchronizer.

Abstract: 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.

Abstract: Methods, systems, and devices are described for tap adjustment and reseeding in a digital filter. Filter and signal characteristics are measured and tap adjustments and reseeding of tap values may be performed based on the filter and signal characteristics. Filter characteristics that may be measured include a filter center of mass which may provide an indication that filter taps for a filter may be drifting toward a filter edge and thus reducing the dynamic range of the filter. Signal characteristics may include a timing offset between received input signals, and characteristics related to which of a particular input signal is present at a filter output. Filter taps, according to various embodiments, may be adjusted, and/or re-initialized responsive to one or more of the signal or filter characteristics.

Abstract: A soft-decision forward error correction scheme for received optical signals is described. Differential decoding may be performed, for example, in each polarization after coherent QPSK detection. Hard decisions may be made based on judging the most likely transition between each pair of received input symbols. Soft-input generation is also described, representing the reliability of the hard decisions. The soft-input information may be generated through simplified algorithms that utilize the most likely transitions to determine a reliability assignment.

Abstract: 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.

Abstract: Methods, systems, and devices are described for formatting of data streams to be transmitted over fiber optic channels, and for processing received optical signals. A data transmission device may include a digital coding and modulation module that encodes a digital data stream, inserts unique words into the digital data stream, and modulates the encoded data stream and unique words onto optical channels for transmission over an optical fiber. A demodulation and decoding device may include a unique word identification module that identifies the unique words inserted in each optical channel stream, determines one or more characteristics of the plurality of optical channels based on the unique words, and provides the one or more characteristics to one or more other modules in the demodulator and decoding device.

Abstract: 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.

Abstract: Soft bit metric generation computational complexity can be reduced by identifying and utilizing only the dominant terms in a reliability calculation such as a logarithmic likelihood ratio (LLR). The dominant terms are those terms for which the signs of the x and y components match those of channel outputs of the channel outputs. One technique for identifying the dominant terms is by determining the most likely transitions from two consecutive channel output samples Values for the dominant terms can be estimated by either the joint reliability of two consecutive samples of the in-phase component (x1,x2) or by the joint reliability of two consecutive samples of the quadrature components (y1,y2).

Abstract: Methods, systems, and devices are described for forward error correction for flash memory. Encoded data from flash memory may be used to generate a number of data streams. At each of a number of error detection sub-modules operating in parallel, a different one of the data streams is processed. Each error detection sub-module may detect whether a portion of the respective received stream contains an error, and forward the portion to an error correction module. The error correction module, physically separate from the error detection sub-modules, may correct the forwarded portions of the respective received streams containing an error. The age and error rate associated with the flash memory may be monitored, and a coding rate or other aspects may be dynamically adapted to account for these factors.

Abstract: Systems, devices, and methods are disclosed for a novel edge memory architecture. An architecture is described wherein the extrinsic information typically stored inside the edge memory is reformatted. Instead of storing the extrinsic information for every edge, the novel edge memory stores a set of possible extrinsic information values for a check node in a “value memory.” The edge memory also stores an index for each edge in a second, “index memory,” identifying which value stored in the value memory applies to each respective edge.

Abstract: Methods, systems, and devices are described for formatting of data streams to be transmitted over fiber optic channels, and for processing received optical signals. A data transmission device may include a digital coding and modulation module that encodes a digital data stream, inserts unique words into the digital data stream, and modulates the encoded data stream and unique words onto optical channels for transmission over an optical fiber. A demodulation and decoding device may include a unique word identification module that identifies the unique words inserted in each optical channel stream, determines one or more characteristics of the plurality of optical channels based on the unique words, and provides the one or more characteristics to one or more other modules in the demodulator and decoding device.

Abstract: Systems, devices, and methods are disclosed herein using a pre-interleaving process to be performed at the transmitter. Data is rearranged at the transmitter, and the rearranged data is transmitted over the communication channel in an order that is more suitable for parallel processing at the decoder. Because processing at the transmitter is bit-wise rather than the multi-bit, soft-decision information at the decoder, pre-interleaving may reduce use system resources when compared to a re-interleaving process at the decoder.

Abstract: Soft bit metric generation computational complexity can be reduced by identifying and utilizing only the dominant terms in a reliability calculation such as a logarithmic likelihood ratio (LLR). The dominant terms are those terms for which the signs of the x and y components match those of channel outputs of the channel outputs. One technique for identifying the dominant terms is by determining the most likely transitions from two consecutive channel output samples Values for the dominant terms can be estimated by either the joint reliability of two consecutive samples of the in-phase component (x1,x2) or by the joint reliability of two consecutive samples of the quadrature components (y1,y2).

Abstract: In an optical transmission system which utilizes polarization multiplexing, a receiver includes an adaptive equalizer which is adjusted at turn-up such that two polarization modes at the equalizer output are time aligned. The adaptive equalizer may be reset in a directed manner in response to an indication that one polarization mode is present at both the first and second outputs. Further, the dominant filters taps of the adaptive equalizer are maintained near a middle of a tap index range. The receiver may also include an interpolation function upstream of the adaptive equalizer and a symbol timing error estimation function that feeds a control signal back to the interpolation function, wherein the interpolation function causes the adaptive equalizer function and symbol timing error estimation function to receive an integer number of samples per symbol.

Abstract: 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.

Abstract: Methods, systems, and devices are described for formatting of data streams to be transmitted over fiber optic channels, and for processing received optical signals. A data transmission device may include a digital coding and modulation module that encodes a digital data stream, inserts unique words into the digital data stream, and modulates the encoded data stream and unique words onto optical channels for transmission over an optical fiber. A demodulation and decoding device may include a unique word identification module that identifies the unique words inserted in each optical channel stream, determines one or more characteristics of the plurality of optical channels based on the unique words, and provides the one or more characteristics to one or more other modules in the demodulator and decoding device.