A novel joint timing/frequency synchronization scheme based on Radon-Wigner transform of LFM signals in CO-OFDM systems

An optical chip comprises an input edge coupler having at least one input waveguide and configured to receive light on two orthogonal modes of same polarization, a demultiplexer configured to divide the two orthogonal modes into a mode carried on a first intermediate waveguide and a mode carried on a second intermediate waveguide independent from the first intermediate waveguide, a polarization multiplexer configured to recombine the modes carried on the intermediate waveguides into two polarization-orthogonal modes carried on one output waveguide.

Optical chip and method for coupling light

The high speed rotation of state of polarization (RSOP) is a key issue for 16 quadrature amplitude modulation (QAM) coherent optical polarization division multiplexing (PDM) communication systems in strong lightning weather. To reduce the bit error rate (BER) caused by the high speed of RSOP, the historical information is first proposed to correct the demodulation process in coherent optical communication systems. By adding the time reverse error term into the cost function, a new equalization algorithm is proposed for coherent optical communication systems. Compared with the conventional Multi-modulus Algorithm (MMA), simulation results show that the average BER and steady-state error (SSE) of the new algorithm is reduced by 33.47% and 4.08%, respectively. Moreover, the average tolerance of RSOP of the new algorithm is increased by 28.57% compared with the MMA in 16 QAM coherent optical PDM communication systems.

/pdf/time-reverse-equalization-algorithm-for-16-qam-coherent-2tiijum1hh.pdf

Time Reverse Equalization Algorithm for 16 QAM Coherent Optical Communication Systems

The invention discloses a depolarization multiplexing method based on a momentum factor, and belongs to the technical field of coherent light communication. The method comprises the following steps: firstly, initializing a demultiplexing matrix A (n), wherein the demultiplexing matrix is a 2 * 2 matrix; inputting the two paths of polarization state signals X '(n) and Y' (n) into A (n) to obtain ademultiplexed signal; finding out constellation points X # (n) and Y # (n) closest to X # '(n) and Y #' (n), and calculating an initial error epsilon1 (n); inputting the constellation points X # (n) and Y # (n) into an inverse matrix A-1 (n) to obtain pseudo observation signals X ''(n) and Y ''(n), and calculating a reverse observation error epsilon2 (n); then constructing a momentum factor omega(n) by the gradient information of the matrix A (n); updating the multiplexing matrix A (n) by using a gradient descent method; and finally repeating the above steps, solving to obtain a demultiplexingsignal, and updating the demultiplexing matrix A (n). The invention also discloses a depolarization multiplexing system based on the momentum factor, and the convergence speed of the depolarization multiplexing algorithm is further improved by introducing the new dimension of the momentum factor. Therefore, the technical problem of polarization state tracking in a lightning environment is solved.

Depolarization multiplexing method and system based on momentum factor

The invention relates to a carrier frequency synchronization method for a UFMC system based on an FPGA, and belongs to the field of wireless communication. According to the method, a UFMC symbol is used as a training sequence, and the training sequence contains the same symbols of m parts, wherein m is not less than 2; the whole frequency offset estimation process is completed through a decimal frequency offset and an integer frequency offset; and the decimal frequency offset is obtained through self-correlation of the two same data parts before and after the training sequence, and training sequence estimation after decimal frequency offset compensation is multiplied by a local training sequence and FFT is made to obtain the integer frequency offset. According to the method, the estimationprecision can be guaranteed through the decimal frequency offset estimation, and the system requirements can be met; through the integer frequency offset estimation, the overall estimation range is greatly increased. A system frequency offset value is effectively estimated, a bit error rate of the system is reduced, and the communication quality is improved.

Carrier frequency synchronization method for UFMC system based on FPGA

In this paper, we propose a joint method of frequency offset estimation based on training symbol and virtual subcarriers for coherent optical orthogonal frequency division multiplexing(CO-OFDM) system. In the proposed method, the integer frequency offset is estimated through subtraction between the mode got form the first data subcarriers' position in OFDM symbols and the number of virtual subcarriers inserted in each side of the OFDM symbol, in which the first subcarrier's position can be found at the maximum slope of the fitting curve to virtual subcarriers; While the fractional frequency offset is estimated by periodic characteristic of the training symbol. Theoretical analysis and simulation results show that the estimation accuracy is improved by the proposed method in the additive white Gaussian noise(AWGN) and the dispersive channel. Simultaneously, estimation range of the proposed algorithm is about [−5GHz, +5GHz], satisfying the practical application requirement, and when the optical signal-to-noise ratio(OSNR) is low, it can still operate properly.

A joint frequency offset estimation algorithm based on training symbol and virtual subcarriers for CO-OFDM systems

A twice fixed point real number de-multiplexing algorithm used for polarization division multiplex multiplexing system de-multiplexing of the invention relates to the field of communication transmission. The steps are as follows: QPSK modulation of data of two paths of a QPSK-CO-PDM transmission system, conversion of an optical signal expression, calculation of four components output by a polarization diversity coherent receiver of a QPSK-CO-PDM transmission system receiving end and crosstalk elimination separately carried out between cophase components and between quadrature components to recover original signals and to raise transmission reliability of the system. According to the invention, with lower calculating complexity, de-multiplexing is carried out on complex signals, which is in a higher-order quadrature modulation format and between which crosstalk is caused by PMD, PDL and polarization mode coupling, to realize a purpose of source signal separating. Defects of high calculating complexity, impossibility of highly efficiently eliminating crosstalk between twp complex signals and low system transmission quality of existing de-multiplexing algorithms targeted at complex signal separating are overcome.

A twice fixed point real number de-multiplexing algorithm used for polarization division multiplexing system de-multiplexing

Twice real-valued FastICA (TR-FastICA) algorithm is proposed in this paper to eliminate crosstalk between the two polarization multiplexed complex-valued higher-order quadrature modulation format such as QPSK signals induced by polarization mode coupling with polarization mode dispersion (PMD) and polarization dependent loss (PDL) for the coherent optical polarization division multiplexing (CO-PDM) system. The proposed algorithm has much lower computation complexity meaning simpler hardware implementation compared with algorithm based on complex maximization of non-Gaussianity (CMN). Simulation results show that the proposed TR-FastICA algorithm can eliminate crosstalk between the two polarization signals effectively and improve the transmission performance.

Polarization de-multiplexing algorithm based on twice real-valued FastICA (invited)

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A joint frequency offset estimation algorithm based on training symbol and virtual subcarriers for CO-OFDM systems

A twice fixed point real number de-multiplexing algorithm used for polarization division multiplexing system de-multiplexing

Polarization de-multiplexing algorithm based on twice real-valued FastICA (invited)