Abstract: System and method embodiments are provided for improving reception of direct detection optical signals. In an embodiment, a method for optical transmission includes bit loading and power loading, with a digital signal processor (DSP), transmission bits of an orthogonal frequency-division multiplexing (OFDM) signal; calculating, with the DSP, a signal-signal beat interference (SSBI) component of the bit and power loaded OFDM signal by modulating each subcarrier with a symbol; and subtracting, with the DSP, the calculated SSBI component from the bit and power loaded OFDM signal.

Abstract: Embodiment reduced-state trellis equalization techniques compute accumulated path metrics (APMs) for a subset of candidate states for at least some stages in the trellis based on a neighborhood map of an ML state. This reduces the number of APMs that are computed and stored during trellis equalization. Other embodiments select a subset of candidate states for which APMs are transported to the next stage of the trellis based on the neighborhood map. This eliminates the need to sort the remaining APMs during reduced state trellis equalization. The neighborhood map identifies a subset of the highest probability neighbors for an ML state. The subset of candidate states identified as highest probability neighbors may be saved in a look-up table. The look-up table may be generated offline and/or generated/updated dynamically during run-time operation.

Abstract: A digital signal processing method and apparatus is described. The digital processing apparatus comprises a coarse carrier recovery module for performing a coarse carrier compensation of a received modulated signal; and a trellis-based equalization module selectable between a first mode for performing a trellis-based equalization to compensate a residual inter-symbol interference of the received modulated signal and a second mode for performing a trellis-based equalization to compensate a residual phase noise of the received modulated signal.

Abstract: System and method embodiments are provided for carrier-signal power ratio (CSPR) control in direct detection optical systems. In an embodiment, a method for CSPR control in a direct detection optical system includes receiving an electrical signal in a receiver (RX) digital signal processor (DSP), wherein the electrical signal is obtained from a corresponding optical signal via a direct detection component; estimating, a CSPR for the electrical signal; generating one of a control signal according to the CSPR; and transmitting the control signal to one of an optical filter and a laser, wherein the wavelength control signal controls causes a center wavelength (CW) of one of the optical filter and the laser to be adjusted such that an offset between the CW of the laser and the CW of the optical filter results in a desired CSPR.

Abstract: Provided is an apparatus and method for transmitting and receiving wireless signals. A transmitting apparatus has a signal processor and a transmitter. The signal processor is configured to generate a signal having a middle channel and at least one side channel. The transmitter is configured to wirelessly transmit the signal subject to a spectral mask that has shoulder regions. According to an embodiment of the invention, the signal processor generates the signal such that each side channel is positioned in one of the shoulder regions of the spectral mask. In this manner, bandwidth from the shoulder regions can be utilized by one or more side channels. Also provided is a receiving apparatus having a receiver configured to wirelessly receive the signal, and a signal processor configured to process the signal.

Abstract: An apparatus comprising a receiver configured to receive an optical signal that carries a multi-rate data signal associated with a first transmission data rate and a second transmission data rate. The apparatus further comprises a processor configured to convert the optical signal into a plurality of digital electrical signals, decode a first portion of the digital electrical signals according to a first modulation format associated with the first transmission data rate, detect a rate change signaling block in the digital electrical signals that indicates a rate change from the first transmission data rate to the second transmission data rate associated with a second modulation format, and decode a second portion of the digital electrical signals received after the rate change signaling block according to the second modulation format.

Abstract: Provided is an apparatus and method for transmitting and receiving wireless signals. A transmitting apparatus has a signal processor and a transmitter. The signal processor is configured to generate a signal having a middle channel and at least one side channel. The transmitter is configured to wirelessly transmit the signal subject to a spectral mask that has shoulder regions. According to an embodiment of the invention, the signal processor generates the signal such that each side channel is positioned in one of the shoulder regions of the spectral mask. In this manner, bandwidth from the shoulder regions can be utilized by one or more side channels. Also provided is a receiving apparatus having a receiver configured to wirelessly receive the signal, and a signal processor configured to process the signal.

Abstract: Quasi-reduced state trellis equalization techniques achieve low-latency inter-symbol interference (ISI) equalization by selecting a subset of accumulated path metrics (APMs) for a leading symbol to propagate over a trellis to candidate states of a trailing symbol. This simplifies the computation of APMs for candidate states of the trailing symbol. Thereafter, APMs for candidate states of the trailing symbol are computed based on the subset of APMs for the leading symbol that were propagated over the trellis. Propagating fewer than all APMs for the leading symbol to the trailing symbol reduces the complexity of APM computation at the trailing symbol.

Abstract: A method and apparatus for performing residual phase noise compensation is described. A coarse carrier compensation of a received modulated signal is performed to obtain a coarse carrier compensated signal and a trellis-based residual carrier recovery is performed to estimate a residual phase noise of the coarse carrier compensated signal. The coarse carrier compensated signal is compensated based on the estimated residual phase noise.

Abstract: The present applies to digital wavelength converters that convert, independently of the format in which optical data may be encoded, an input waveform at a first wavelength to an output waveform at a second wavelength. When operating in an environment where an input waveform has a pilot tone associated thereto, the method and system of the present disclosure allows for the removal of the pilot tone from the input waveform, and also allows for the addition of another pilot to the output waveform.

Abstract: A method for wavelength conversion comprising receiving an input optical signal with a first wavelength, converting the input optical signal to a plurality of input analog signals, generating a plurality of digital signals based on the input analog signals, compensating for waveform distortions by at least filtering one or more of the digital signals to generate one or more compensated digital signals, converting the compensated digital signals to output analog signals via digital-to-analog (DA) conversion, generating an output optical signal with a second wavelength different from the first wavelength based on the output analog signals, and transmitting the output optical signal.

Abstract: An apparatus comprising a processing unit configured to encode a data sequence in a plurality of modulation formats to produce a multi-rate data stream, wherein a first of the modulation formats provides a first transmission data rate, and wherein a second of the modulation formats provides a second transmission data rate different from the first transmission data rate, and insert a rate change signaling block into the multi-rate data stream to indicate a rate change from the first transmission data rate to the second transmission data rate, and a frontend coupled to the processing unit and configured to convert the multi-rate data stream into an optical signal, and transmit the converted optical signal towards a remote optical receiver via an optical network.

Abstract: It is possible to compress log likelihood ratios (LLRs) by exploiting the mapping symmetry between bits in the same symbol. For example, two LLRs corresponding to the same dimension of a square Quadrature Amplitude Modulation (QAM) symbol can be compressed into a single compressed LLR that excludes the magnitude bits of one of the LLRs because the magnitude component of LLRs for bits corresponding to the same dimension of a square QAM symbol exhibit a piecewise linear relationship with one another. Similar techniques can be used to exploit piecewise linear relationships between a subset of constellation points in a non-square QAM constellation.

Abstract: The present disclosure provides a method and system for fine estimation of a local oscillator frequency offset of a received signal at a coherent receiver, by evaluating the probability mass function (PMF) of the signal phase of output symbols at different frequencies. At frequencies other than the actual frequency offset, the signal phase is uniformly distributed in [??,?] such that the summation of a function of PMF values where the function is convex or concave between 0 and 1 can be utilized to determine an a frequency offset to be used by the coherent receiver.

Abstract: An optical circuit switching matrix includes a plurality of optical ports, each optical port being optically coupled to a respective one of a plurality of user nodes and an optical coupler having at least one input port optically coupled to the plurality of optical ports, and an output port. The optical circuit switching matrix also includes a wavelength demultiplexer having an input optically coupled to the output port of the optical coupler, and a plurality of output ports, each output port being optically coupled to a respective one of the plurality of optical ports.

Abstract: An apparatus comprising a digital signal processor (DSP) configured to code a plurality of data sub-streams using a plurality of modulation formats to generate a plurality of coded data symbols, wherein each modulation format leads to a unique bit rate for coded data symbols associated with a modulation format, transform the coded data symbols into a frequency domain by applying Fourier transform on each coded data symbol, map the frequency-transformed data symbols onto a plurality of subcarrier signals associated with a plurality of frequency tones, wherein at least two of the subcarrier signals correspond to different modulation formats, and generate an electrical signal in a time domain based on the subcarrier signals.

Abstract: The present applies to digital wavelength converters that convert, independently of the format in which optical data may be encoded, an input waveform at a first wavelength to an output waveform at a second wavelength. When operating in an environment where an input waveform has a pilot tone associated thereto, the method and system of the present disclosure allows for the removal of the pilot tone from the input waveform, and also allows for the addition of another pilot to the output waveform.

Abstract: An optical circuit switching matrix includes a plurality of optical ports, each optical port being optically coupled to a respective one of a plurality of user nodes and an optical coupler having at least one input port optically coupled to the plurality of optical ports, and an output port. The optical circuit switching matrix also includes a wavelength demultiplexer having an input optically coupled to the output port of the optical coupler, and a plurality of output ports, each output port being optically coupled to a respective one of the plurality of optical ports.

Abstract: A method of optical communication comprising encoding four modulated symbols to generate four encoded symbols in two orthogonal polarizations and transmitting the four encoded symbols in two successive time slots. An optical communication apparatus comprising a processor configured to receive two sequences of digital symbols in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital symbol per polarization is received in each of the plurality of time slots, divide each of the two sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital symbols received in two consecutive time slots, and adaptively equalize the four digital symbols of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors.

Abstract: It is possible to perform ISI estimation for quasi-static band-limited communication channels using a minimal number of discontinuous pilots communicated across different time intervals. In one example, at least two frames are received in different time intervals, and noise vectors are extracted from pilots carried in the respective frames. Spectral estimation is performed on the noise vectors, collectively, to obtain a set of tap coefficients, which are then used to perform ISI equalization on at least one of the frames. In this way, ISI equalization is performed on a frame communicated in one time interval using at least some pilots communicated in another time interval. Using discontinuous pilots to perform channel estimation may enable lower pilot densities in next-generation communication systems.