System for adjusting a reference constellation for demodulating an optical signal include a coherent electro-optical receiver configured to convert a received optical signal to a plurality of electrical signals, an array of analog-to-digital convertors configured to digitize the plurality of electrical signals, and processor logic. The processor logic is configured to process the digitized plurality of electrical signals using a reference constellation to yield a plurality of decoded signals and a signal quality measurement. The reference constellation includes an inphase component equal to an ideal inphase component plus an inphase offset and a quadrature component equal to an ideal quadrature component plus a quadrature offset. The processor logic is configured to determine an optimal inphase offset and optimal quadrature offset. The processor logic is configured to update the reference constellation using the optimal inphase offset and the optimal quadrature offset.

A method of providing wireless communications in a wireless network can include wirelessly receiving a chirp spread-spectrum modulated signal at a first gateway device, the chirp spread-spectrum modulated signal being transmitted by a remote client device. The chirp spread-spectrum modulated signal can be demodulated at the first gateway device to provide demodulated data at the first gateway device. The demodulated data can be processed to provide an indication that a decode of a packet including the demodulated data failed. Time adjacent chirps included in the demodulated data can be combined to provide combined data at the first gateway device. A message can be transmitted from the first gateway device to a remote server responsive to an amplitude of the combined data exceeding a threshold value and the indication that the decode of the packet including the demodulated data failed.

A coherent optical reception device includes a local oscillation laser that supplies laser light, a coherent optical reception front-end unit that receives a multi-level modulated optical signal, demodulates the optical signal on the basis of the laser light, and converts a demodulated optical signal into an electrical analog signal, an analog-to-digital converter that converts the analog signal into a digital signal, a compensation unit that compensates for an influence of dispersion due to a wavelength or a polarized wave of the optical signal and recovers a carrier phase of the digital signal, a constellation distortion compensation unit that compensates for constellation distortion of the multi-level modulation included in the digital signal in which an influence of dispersion is compensated for by the compensation unit, and an error correction decoding unit that performs error correction of the digital signal in which the constellation distortion is compensated for.

Method and apparatus for signal detection in dynamic channels with high carrier frequency offset are provided. A coherent detector and a non-coherent detector are operated in parallel on a block of samples of an input signal to determine respective time offset candidates of the input signal. The time offset candidate obtained from the non-coherent detector is used to determine a frequency offset candidate of the input signal.

Blind polarization demultiplexing algorithms based on complex independent component analysis (ICA) by negentropy maximization for quadrature amplitude modulation (QAM) coherent optical systems are disclosed. The polarization demultiplexing is achieved by maximizing the signal's non-Gaussianity measured by the information theoretic quantity of negentropy. An adaptive gradient optimization algorithm and a Quasi-Newton algorithm with accelerated convergence are employed to maximize the negentropy. Certain approximate nonlinear functions can be substitutes for the negentropy which is strictly derived from the probability density function (PDF) of the received noisy QAM signal with phase noise, and this reduces the computational complexity. The numerical simulation and experimental results of polarization division multiplexing (PDM)-quadrature phase shift keying (QPSK) and PDM-16QAM reveal that the ICA demultiplexing algorithms are feasible and effective in coherent systems and the simplified ones can also achieve equivalent performance.

A receiving method for receiving a plurality of carriers and generating one or a plurality of streams. The method includes a first demodulating step of processing a first transmission signal and generating a first demodulation output; a second demodulating step of processing a second transmission signal different from the first transmission signal and generating a second demodulation output; a combining step of generating one stream based on the first demodulation output and the second demodulation output; a selecting step of selecting one among the first demodulation output and the one stream, and generating a selected stream; and a back-end processing step of generating an output for a display from the selected stream and the second demodulation output. In the selecting step, the first demodulation output is selected in a receiving mode in single channel transmission, and the one stream is selected in a receiving mode in multiple channel transmission.

Phase noise is corrected in a communication system including a modulated signal having a constellation including multiple constellation points. The system and methods include a coarse phase recovery followed by a fine phase recovery. Coarse phase corrected points can be generated using an M.sup.th power operation. Fine phase corrected points can be generated by rotating each coarse phase corrected point by an angle that is determined by the location of that coarse phase corrected point in the constellation, and applying a phase offset function to each transformed point. A phase noise mitigated constellation can be generated by derotating the fine phase corrected points.

A frequency difference compensation unit (510) generates a carrier recovery signal by compensating for a frequency difference between a local light beam and an optical signal in a plurality of digital signals. A first symbol determination unit (521) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with the signal arrangement of multi-value modulation. A second symbol determination unit (522) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced. A loop filter unit (540) and a compensation signal generation unit (550) temporarily generates a compensation signal using a determination result of the second symbol determination unit (522), and then regularly generates the compensation signal using a determination result of the first symbol determination unit (521).

A receiving system of the present disclosure includes: a plurality of demodulators; an add-on generating one stream based on an output from each of the demodulators; a selector selecting and outputting one among an output from one of the demodulators, namely the demodulator, and the one stream from the add-on; and a back-end processor generating an output for a display based on an output from the selector and the other demodulators, namely the demodulators. The selector selects an output from the demodulator in a single channel transmission mode, and selects the stream from the add-on in a multiple channel transmission mode.

Provided are a preamble symbol generation method and receiving method, and a relevant frequency-domain symbol generation method and a relevant device, characterized in that the method comprises: generating a cyclic prefix according to a partial time-domain main body signal truncated from a time-domain main body signal; generating a modulation signal based on a portion or the entirety of the partial time-domain main body signal; and generating time-domain symbols based on at least one of the cyclic prefix, the time-domain main body signal and the modulation signal, wherein the preamble symbol contains at least one of the time-domain symbols. Therefore, using the entirety or a portion of a certain length of a time-domain main body signal as a prefix, it is possible to implement coherent detection, which solves the issues of performance degradation with non-coherent detection and differential decoding failure under complex frequency selective fading channels; and generating a modulation signal as a postfix based on the entirety or a portion of the above truncated time-domain main body signal enables the generated preamble symbol to have sound fractional frequency offset estimation performance and timing synchronization performance.