Abstract: Embodiments of the present invention provide a phase detection method and apparatus. The apparatus comprises a phase detector, the phase detector comprising a calculation unit configured to calculate a phase difference according to a product of receiving power at different moments, so as to perform clock recovery by using the phase difference; wherein the receiving power is that obtained in sampling input signals at a predefined sampling rate, the predefined sampling rate being 2 times of a symbol rate. With the method and apparatus of the embodiments of the present invention, the problem that in case of a relatively large frequency difference or line width, or the transmitted signals are Nyquist signals of spectral widths close to the symbol rate, a conventional phase detection method will be invalid, is solved by calculating a phase difference only according to a product of receiving power at different moments.

Abstract: Embodiments of the present invention provide a timing synchronization apparatus and method for multi-carrier modulation signals. Wherein the apparatus includes: a predicting unit configured to denoise delay of symbols received before a currently received symbol, and to predict delay of the currently received symbol or of a symbol received after the currently received symbol according to the denoised symbol delay and a sampling clock frequency offset; and a timing synchronization unit configured to perform timing synchronization according to a predicted value of the delay of the currently received symbol or of the symbol received after the currently received symbol. With the apparatus and method, a signal to noise ratio of multi-carrier modulation signals may be effectively improved, and an effect of a timing error on a communication system may be lowered, thereby improving performance of the communication system.

Abstract: The present invention relates to a butterfly filter coefficient setting method and device, a receiver, and a receiving method. The receiver is a DP-CO-OFDM receiver, comprising: a phase recovery device configured to perform a phase recovery of a received signal one OFDM symbol by one OFDM symbol, so as to obtain a phase-recovered first polarization signal and a phase-recovered second polarization signal; a butterfly filter configured to perform butterfly filtration of the phase-recovered first polarization signal and the phase-recovered second polarization signal one OFDM symbol by one OFDM symbol, so as to obtain a butterfly-filtered first polarization signal and a butterfly-filtered second polarization signal; a coefficient setting unit configured to set a filter coefficient used by the butterfly filter for the current OFDM symbol; and a data recovery device configured to recover data from the butterfly-filtered first polarization signal and the butterfly-filtered second polarization signal.

Abstract: The embodiments of the present invention provide a method and an apparatus for compensating nonlinear distortions in an intensity modulation-direct detection (IM-DD) system; wherein the method comprises: calculating, according to nonlinear coefficients and differences between values of an input signal at different time, nonlinear distortions of the input signal, so as to eliminate the nonlinearity distortions. By applying the method and the apparatus provided by the embodiments of the present invention, nonlinear cost of the IM-DD system can be effectively reduced, thereby improving the system capacity.

Abstract: A method, apparatus and system for estimating frequency offset that includes: a first calculating unit to calculate a correlation value of each of multiple sequences with different lengths according to a received signal containing the sequences with different lengths, where each of the sequences is repeatedly transmitted many times in the signal; a second calculating unit to calculate a decimal frequency according to the correlation value; a first determining unit to determine an integer frequency offset according to the decimal frequency offset to which each of the sequences corresponds; and a second determining unit to determine a total frequency offset according to the decimal frequency offset and the integer frequency offset.

Abstract: Embodiments of the present disclosure provide a calculating apparatus and method for nonlinear weighting coefficient. The calculating apparatus for nonlinear weighting coefficient includes: an approximation processing unit configured to use a rational function to perform approximation processing on a link loss/gain function in intra-channel nonlinear distortion estimation; and a coefficient calculating unit configured to calculate a nonlinear weighting coefficient in the nonlinear distortion estimation by using the approximated link loss/gain function and a large dispersion approximation, to obtain an analytical closed solution of the nonlinear weighting coefficient. With the embodiments of the present disclosure, a weighting coefficient of high precision may be obtained, thereby performing high-precision estimation on nonlinear distortion in case of loss.

Abstract: Embodiments provide an apparatus for monitoring an optical signal to noise ratio (OSNR), a transmitter and a communication system. The apparatus for monitoring optical signal to noise ratio includes: a signal extracting unit and a signal processing unit. The signal extracting unit is configured to extract pilot signals and non-pilot signals at two polarization states from received signals, frequencies of the pilot signals at the two polarization states being different, and the polarization states being differentiated by the frequencies of the pilot signals; and the signal processing unit is configured to obtain OSNRs at the two polarization states by using the pilot signals and the non-pilot signals extracted by the signal extracting unit. With the embodiments of the present disclosure, by making the frequencies of the pilot signals at different polarization states be different, OSNRs at different polarization states may be obtained more accurately.

Abstract: The embodiments relate to a method and an apparatus for compensating nonlinear damage. The method and apparatus being used in a dual-polarization communication system, the method comprising: calculating, according to input time-domain signals, a plurality of multiplicative parameters indicative of nonlinear damages to the input signals; constructing a plurality of multiplicators by using the plurality of multiplicative parameters; and compensating the input time-domain signals by using the plurality of multiplicators.

Abstract: A method and apparatus for adaptive nonlinear equalization, comprising: a horizontal polarization component compensation unit configured to calculate a linear damage value of an input signal, a nonlinear damage value of a horizontal component of the input signal, and a crosstalk value caused by a vertical component to the horizontal component, and compensate the horizontal component according to the linear damage value, the nonlinear damage value and the crosstalk value; and, a vertical polarization component compensation unit configured to calculate a linear damage value of the input signal, a nonlinear damage value of a vertical component of the input signal, and a crosstalk value caused by a horizontal component to the vertical component, and compensate the vertical component according to the linear damage value, the nonlinear damage value and the crosstalk value.

Abstract: A bias monitoring method and apparatus and a transmitter, the bias monitoring apparatus being used for monitoring deviation of a direct current bias point of an optoelectronic modulator and including: a first signal processing unit configured to perform first signal processing on an electric driving signal inputted into the optoelectronic modulator, so as to output a reference signal; a second signal processing unit configured to perform second signal processing on an electric output signal obtained based on an optical signal outputted by the optoelectronic modulator, so as to output a monitoring signal; and a monitoring signal calculating unit configured to calculate correlation between the reference signal and the monitoring signal, and output a calculation result of the correlation as a bias monitoring signal. The sensitivity of the bias monitoring apparatus may be improved, and complexity of hardware may be lowered.

Abstract: Embodiments of the present disclosure provide an estimation apparatus and method for nonlinear distortion and a receiver. The estimation method for nonlinear distortion includes: sampling a band-limited analog signal to obtain a sampling sequence; calculating a nonlinear perturbation coefficient in nonlinear distortion estimation based on a Nyquist pulse; calculating a nonlinear perturbation term superimposed on a signal by using the nonlinear perturbation coefficient and the sampling sequence; and calculating a nonlinear distortion waveform by using the nonlinear perturbation term. With the embodiments of the present disclosure, not only any modulation formats are compatible, but also advantages of high precision and good adaptability may be achieved.

Abstract: An apparatus and method for estimating intra-channel nonlinear damage, including: a first determining unit configured to determine a nonlinear phase shift weighting dispersion distribution function of an optical fiber transmission link according to a parameter of the optical fiber transmission link; a segmenting unit configured to segment the nonlinear phase shift weighting dispersion distribution function of the optical fiber transmission link into at least one rectangle; a calculating unit configured to respectively calculate a nonlinear perturbation coefficient of each rectangle in the at least one rectangle, and perform summation on the nonlinear perturbation coefficients of all the rectangles, so as to obtain a nonlinear perturbation coefficient of the optical fiber transmission link; and a second determining unit configured to determine intra-channel nonlinear damage of the optical fiber transmission link according to the nonlinear perturbation coefficient of the optical fiber transmission link.

Abstract: The present invention provides a nonlinear compensating apparatus and method and a transmitter. The nonlinear compensating apparatus includes: an information sequence acquiring unit, configured to acquire a symbol information sequence of the pulse signal; a perturbation quantity acquiring unit, configured to calculate, by pre-obtained weighting coefficients to which each item corresponds, the weighted sum of interaction items of pulses on one or more moments relative to the current moment; a perturbation quantity processing unit, configured to combine the items of the perturbation quantity based on the weighting coefficients; and an information compensating unit, configured to calculate a difference between the symbol information sequence and the processed perturbation quantity to obtain a compensated symbol information sequence. With the embodiments of the present invention, the complexity of calculation may be further lowered, and requirements on hardware may also be lowered.

Abstract: Embodiments of the present invention provide a coefficient determining apparatus, equalizer, receiver and transmitter. The coefficient determining apparatus comprises: a synchronizer configured to find a position of a training sequence from signals containing the training sequence received by a transmitter; and a first processor configured to set an initial tap coefficient of an equalizer according to the received signals and the training sequence; wherein in each polarization state, the training sequence comprises n pairs of training symbols, in the n pairs of training symbols, the training symbols of the same pair being identical, the training symbols of the different pair being different, a cyclic prefix and a cyclic postfix being respectively inserted before and after each pair of training symbols, and n being an integer greater than 1.

Abstract: Embodiments of the present invention provide a timing synchronization apparatus and method for multi-carrier modulation signals. Wherein the apparatus includes: a predicting unit configured to denoise delay of symbols received before a currently received symbol, and to predict delay of the currently received symbol or of a symbol received after the currently received symbol according to the denoised symbol delay and a sampling clock frequency offset; and a timing synchronization unit configured to perform timing synchronization according to a predicted value of the delay of the currently received symbol or of the symbol received after the currently received symbol. With the apparatus and method, a signal to noise ratio of multi-carrier modulation signals may be effectively improved, and an effect of a timing error on a communication system may be lowered, thereby improving performance of the communication system.

Abstract: A compensation apparatus and method for inter-channel nonlinear damage are disclosed where the apparatus includes: an iteration parameter determining unit configured to determine an iteration step of cross-phase modulation damage compensation performed in each channel in a multichannel optical fiber transmission link; an estimating unit configured to divide an optical fiber transmission link in each iteration step of each channel into one or more optical fiber segments, and perform cross-phase modulation damage estimation at a position in each optical fiber segment where the nonlinear damage is maximal; and a first compensating unit configured to perform cross-phase modulation damage compensation according to the result of the cross-phase modulation damage estimation.

Abstract: The embodiments provide an inverse channel apparatus and transmitter, receiver and system containing the apparatus; wherein the inverse channel apparatus comprises: an inverse nonlinear calculating unit configured to perform nonlinear additive calculation and nonlinear multiplicative calculation on input signals, so as to obtain signals containing nonlinear damage of the input signals on at least one polarization state; and an inverse linear calculating unit configured to calculate signals containing nonlinear damage and linear damage of the input signals on at least one polarization state according to the signals containing nonlinear damage of the input signals on at least one polarization state and a linear function of a channel.

Abstract: Embodiments of the present invention provide a receiver and a receiving method. The receiver comprises: a branch forming unit a plurality of signal branches; each of the signal branches comprising a joint processing unit; and the joint processing unit being used to eliminate an inter-carrier interference of the subcarrier signal in a present signal branch and the subcarrier signals in other signal branches adjacent to the present signal branch. With the embodiments of the present invention, the inter-carrier interference may be eliminated and the performance of the system may be improved; and the sampling rate of the analog digital converter may also be lowered.

Abstract: The embodiments provide an automatic bias control method and apparatus for an optical transmitter. The apparatus includes: a detecting unit configured to monitor output optical power of an I/Q modulator of the optical transmitter; a calculating unit configured to calculate bias voltage indicating values of the I modulator, Q modulator and phase modulator of the I/Q modulator according to the output optical power and known modulation data; and an adjusting unit configured to adjust respectively Direct-Current (DC) bias voltages of the I modulator, Q modulator and phase modulator according to the bias voltage indicating values of the I modulator, Q modulator and phase modulator. With the embodiments, known modulation data are used to realize automatic bias control by monitoring the evenness of distribution of the power of output optical signals of the transmitter in the four quadrants of an I/Q plane.

Abstract: A method and apparatus for compensating nonlinear damage are disclosed. The method for compensating nonlinear damage, including: determining an additive parameter indicating an amount of nonlinear damage based on a plurality of sampled signal sets among which a sampling time of an input signal varies according to different time; and subtracting the additive parameter from the input signal.