Methods and systems for communication with a modified constellation are provided. One of the methods includes coding, by a transmitter in the user equipment, an input data stream into a constellation of symbols having at least two neighboring symbols therein which differ by more than one bit and which are separated by a modified Euclidean distance to increase a Gaussian white noise resiliency of the at least two neighboring symbols with respect to remaining symbols, the remaining symbols being separated by the Euclidean distance of exactly one bit. The method further includes modulating, by the transmitter, the symbol stream into a transmission stream.

Techniques are described for determining pre-compensation parameters to compensate for signal integrity degradation along a signal path. A processor generates a first digital signal and receives a second digital signal. The second digital signal is generated from an optical-to-electrical conversion of a feedback optical signal that is generated from an electrical-to-optical conversion of an electrical signal by an optical module. The processor determines the pre-compensation parameters based on the first and second digital signals.

A high speed satellite-based laser communications system and method for communications between a satellite-based transmitter system and a ground-based receiver over a free space optical link. The satellite-based transmitter system includes an encoder to encode data, a polarization modulator to linearly polarize the encoded data, one or at least two transmitters to transmit the laser beam, and a quarter-wave optical wave plate to circularly polarize the signal to be transmitted. The ground-based receiver includes an automatic gain control to apply AGC to the received data before the polarizations are reversed and the data is decoded. The system enables an increased data throughput and reduces or eliminates the effects of signal fading.

An apparatus having input and output ports using a plurality of optical connector adapters, wherein the fiber connections can follow a specific mesh pattern has a plurality of fibers inside the apparatus. The fibers pass through at least one mandrel and are designed to produce a leakage in the transmitted light from each fiber of least −30 dBm, wherein the fiber buffer of fibers around the mandrel are partially stripped in at least one section. The apparatus also has an imaging system consisting of at least a lens, camera sensor and an optical filter are placed in proximity to the fiber striped section wherein the optical filter has spectral properties tuned or partially tuned to the operational wavelength of the network and the optical filter is placed in the light path before the camera sensor.

A method, system, and apparatus enabled to selectively choose a baud rate for communication of optical data using a modem enabled to operate with an optical signal modulated at plurality of finely tuned baud rates.

In a method and system for decoding a differential M-ary phase or quadrature amplitude modulated signal, the incoming signal is decoded according to a plurality of different decoding rules, wherein said plurality of decoding rules correspond to different values of a resulting frequency difference or mismatch between a signal frequency and a local oscillator reference frequency. The invention allows to increase a tolerance window for the maximal allowable frequency offset, and thus helps to speed up an initial locking process or to allow for equipment which has a lower tuning granularity.

Techniques for transmitting a data signal through an optical communications system. An encoder is configured to encode the data signal to generate symbols to be modulated onto an optical carrier. Each symbol encodes multiple bits of data and includes a first portion selected from a first constellation and a second portion selected from a second constellation. The first and second constellations have respective different average amplitudes. Each of the first and second constellations have a cardinality of at least two and the cardinality of the first constellation is greater than the cardinality of the second constellation. A modulator is configured to modulate a first frame of the optical signal using the first portion and modulate a second frame of the optical signal using the second portion. A selection of one frame of the optical signal to be used as the first frame encodes at least 1 bit of data.

A free-space optical communication system is provided. The free-space optical communication system includes a transmitter configured to optically transmit data in a plurality of subcarrier signals over a free-space scattering medium. The free-space optical communication system includes a coherent receiver configured to receive the plurality of subcarrier signals and extract the transmitted data from the plurality of subcarrier signals after traversal over the free-space scattering medium.

Disclosed are a chromatic dispersion estimation method and device in optical coherent communication, wherein, the method includes: performing a fast Fourier transform on IQ-imbalance compensated data to obtain frequency-domain data in two polarization directions; calculating autocorrelation sequences of the frequency-domain data and performing an inverse fast Fourier transform on the values of the autocorrelation sequences; calculating modulus squares of the results of the inverse fast Fourier transform, and adding the results in the two polarization directions to obtain; determining a mean value of s of a plurality of data sets; calculating an index of the maximum value of, and estimating a dispersion value of the optical fiber link according to the index of the maximum value of. The abovementioned technical solution allows a significantly accurate and rapid estimation of dispersion values.

A system and method involve receiving, at a processor, a phase modulated signal such as an optical or electromagnetic signal, using one or more samples of an in-phase component I(t) and a quadrature component Q(t) of the received phase modulated signal to generate, at the processor, a processed signal using the equation [A−B×I(t)]×Q(t), where A and B are numerical parameters, and inputting the processed signal into a receiver operatively connected to the processor. The processed signal may be filtered prior to being input into the receiver. Parameters A and B may be selected to vary complexity and performance of the receiver while controlling distortion for different modulation indices.