Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Ntt Innovative Devices Corporation

Mitsuteru Yoshida

Etsushi Yamazaki

Yoshiaki Kisaka

Masahito Tomizawa

Tomohiro Takamuku

Kengo Horikoshi

Katsuichi Oyama

Seiji Okamoto

Yasuharu Onuma

Tsutomu Takeya

Masanori Nakamura

Kazuhito Takei

Koichi Ishihara

Tomoyoshi Kataoka

Takayuki Kobayashi

Kazushige Yonenaga

Yasuyuki Endoh

Masayuki Ikeda

Tomoharu Semboku

Hiroyuki Nouchi

Naoki Fujiwara

Masahiro Suzuki

Yoshiaki Yamada

Akira Hirano

Hiroyuki Uzawa

Yuki Yoshida

Takuya Ohara

Naoki Miura

Fukutaro Hamaoka

Koki Shibahara

Osamu Ishida

Asuka Matsushita

Kohki Shibahara

Masahiro Tachibana

Sadayuki Yasuda

Yasuyuki Endo

Eiichi Hosoya

Atsushi Suenaga

Tomoharu Senboku

An adaptive equalizer () according to this invention includes an adaptive equalization filter () configured to adaptively compensate for a waveform distortion caused by a polarization fluctuation of a received signal () by updating a tap coefficient, a first tap coefficient updater () configured to calculate the tap coefficient according to the polarization fluctuation of the received signal () using a variable step size and update the tap coefficient of the adaptive equalization filter (), a second tap coefficient updater () configured to calculate the tap coefficient according to the polarization fluctuation of the received signal () using a fixed step size μ, a polarization state estimator () configured to estimate a polarization state of the received signal () using the tap coefficient calculated by the second tap coefficient updater (), and a step size updater () configured to obtain the step size corresponding to the polarization state estimated by the polarization state estimator () and update the variable step size. According to this invention, it is possible to provide an adaptive equalizer that always implements stable followability to various SOP fluctuations.

Adaptive equalizer, adaptive equalization method, and optical communication system

A tap-coefficient control circuit sets the tap coefficient converged by the second tap coefficient updater as an initial value of the tap coefficient in the first digital filter which is to be updated by the first tap coefficient updater, arranges the tap coefficients converged by the second tap coefficient updater in descending order of contribution degree to the convergence operation of tap coefficient update in the first tap coefficient updater, judges the tap coefficient not less than upper specified number to be valid and the tap coefficient less than the specified number to be invalid, and sets the tap coefficient of the first digital filter corresponding to the tap coefficient judged to be invalid to zero not to be used in a calculation of the first tap coefficient updater until a next judgment result is made.

Adaptive equalizer, equalization method, and optical communication system

First compensation circuitry includes a first digital filter compensating a phase difference between a phase of a symbol of a received signal and a sampling timing, and first filter coefficient calculation circuitry calculating a filter coefficient of the first digital filter as a first filter coefficient. Second filter coefficient calculation circuitry calculates, as a second filter coefficient, a filter coefficient for adaptive equalization that compensates distortion due to temporally changing polarization dispersion, based on an output of the first digital filter. Coefficient combination circuitry combines the first filter coefficient and the second filter coefficient. Second compensation circuitry includes a second digital filter which uses a filter coefficient combined by the coefficient combination circuitry and performs a compensation of the phase difference between the phase of the symbol of the received signal and the sampling timing, and a process of the adaptive equalization at the same time.

Adaptive equalization device, adaptive equalization method, and communication device

A frame synchronization apparatus () according to this invention includes a multiplication unit () configured to multiply a received signal by an inverse complex number of a predetermined synchronization pattern with respect to a predetermined signal point on a complex space diagram for each of a plurality of symbols of the received signal, an addition average unit () configured to perform addition averaging of outputs from the multiplication unit for the plurality of symbols of the received signal, and a synchronization determination unit () configured to perform coincidence determination of whether an output from the addition average unit () falls within a predetermined coincidence determination range of the predetermined signal point, and determine a synchronization state of the frame synchronization based on a result of the coincidence determination. According to this invention, it is possible to provide a frame synchronization apparatus that correctly determines a synchronization state even if an error rate of received symbols is high.

Frame synchronization apparatus, optical communication apparatus, and frame synchronization method

A known pattern comparison type phase difference detection unit () detects a phase difference between a known pattern extracted from a received signal and a true value of the known pattern as a first phase difference. M indicates the number of modulation phases in a phase modulation method of the received signal. An M-th power type phase difference detection unit () removes a modulation component by raising the received signal to M-th power, and detects phase variation from a modulation phase point used for mapping on a transmission side, as a second phase difference. A phase compensation unit () compensates phase variation of the received signal based on an addition result of the first phase difference and the second phase difference.

Phase variation compensation device, phase variation compensation method and communication device

A plurality of error correction circuits corrects errors of the data transmitted through the plurality of transmission lines. A combining portion combines the plurality of transmission lines to the plurality of error correction circuits. The plurality of transmission lines includes a first transmission line, and a second transmission line having a lower transmission characteristic than the first transmission line. The plurality of error correction circuits includes a first and a second error correction circuit having lower error correction capability and power consumption than the first error correction circuit. The combining portion uses a function to combine a plurality of error correction circuits with one transmission path, combines the first transmission line with the second error correction circuit at a higher rate than the first error correction circuit, and combines the second transmission line with the first error correction circuit at a higher rate than the second error correction circuit.

Error correction device, error correction method, and communication device

A band division timing adjustment unit aligns timings of a plurality of signals, which are generated by dividing a received signal according to a plurality of frequency bands, in a time domain and combines the plurality of signals for which the timings have been aligned. A chromatic dispersion compensation unit compensates chromatic dispersion of an output signal of the band division timing adjustment unit for each of the plurality of frequency bands.

Chromatic dispersion compensation device, chromatic dispersion compensation method, and communication device

A signal-to-noise ratio (SNR) estimation method includes an optical signal transmission step of inserting at least one pair of signal sequences into transmission data and transmitting the transmission data into which the at least one pair of signal sequences is inserted, a signal sequence extraction step of extracting the at least one pair of signal sequences from a received signal obtained by receiving the transmitted transmission data, an inner product calculation step of calculating an inner product value of the extracted at least one pair of signal sequences, a reception power calculation step of calculating reception power of the extracted at least one pair of signal sequences, and an SNR calculation step of calculating an SNR of the at least one pair of signal sequences on the basis of the calculated inner product value and the calculated reception power.

Signal-to-noise ratio estimation method, optical transmission apparatus, and optical transmission system

An optical receiver includes: a first calculation unit that obtains a log likelihood ratio for each M-dimension (M is a natural number), based on a received signal; and a second calculation unit that obtains a log likelihood ratio of an N dimensional symbol (N is a natural number), based on the log likelihood ratio for each M-dimension.

Optical receiver, optical transmission device, and method for optical receiver

An optical transmitter of an optical data transmission system transmitting data through an optical fiber transmission path includes a main signal generator that converts first transmission data into a predetermined signal format to generate a first signal, a DCSK modulator that DCSK-modulates second transmission data to generate a second signal, a signal-multiplexer that performs time-division multiplexing of the first signal and the second signal, and an electro-optical converter that converts a multiplexed signal obtained by the time-division multiplexing of the signal-multiplexer from an electric signal into an optical signal, and outputs the optical signal to the optical fiber transmission path.

Optical transmitter, optical receiver, optical data transmission system, optical transmission method, and optical reception method

A reception circuit includes a first adaptive compensator compensating distortion of a received signal. An adaptive compensation coefficient calculator includes a known-signal detector detecting first and second known-signals from the received signal, a second adaptive compensator compensating distortion of the received signal, a tap coefficient initial value calculator calculating an initial value of a tap coefficient of the second adaptive compensator by comparing the first known-signal with its true value, a first phase shift compensator compensating phase shift of an output of the second adaptive compensator using the second known-signal, and a tap coefficient calculator calculating tap coefficients of the first and second adaptive compensators by comparing at least one of the first and second known-signals compensated by the second adaptive compensator and the first phase shift compensator with its true value.

Transmission characteristic compensation apparatus, transmission characteristic compensation method, and communication apparatus

Fourier transform is performed on a reception signal to obtain a first calculation value. Fourier transform is performed on a known signal to obtain a second calculation value. The first calculation value is divided by the second calculation value to obtain a third calculation value. Inverse Fourier transform is performed on the third calculation value to obtain a fourth calculation value. A maximum value of an amplitude of the fourth calculation value and a sample point at which the maximum value is obtained are detected. The position of the known signal in the reception signal is detected from the sample point at which the maximum value is obtained.

Known signal detection method

A Fourier-transformer performs Fourier transform on a filter coefficient output from an adaptive equalizer which comprises a finite impulse response filter of N taps (N represents an integer of 2 or more) in a time direction. An eigenvalue sum calculator integrates a frequency-differentiation result of the Fourier-transformed filter coefficient and a complex conjugate of the Fourier-transformed filter coefficient to calculate a matrix, and calculates a sum of two eigenvalues of the matrix. A proportionality factor calculator calculates a proportionality factor for frequency from the sum of the two eigenvalues.

Chromatic dispersion estimating circuit, optical reception device and chromatic dispersion amount estimating method

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.

Coherent optical reception device

Growing community of inventors

Kanagawa, Japan

Mitsuteru Yoshida