Nec Corporation

Nec C Orporation

Toshiharu Ito

Manabu Arikawa

Seigo Takahashi

Kohei Hosokawa

Yoshimasa Ono

Takashi Ishikawa

Emmanuel Le Taillandier De Gabory

Kiyoshi Fukuchi

Akihiro Tanaka

Hitoshi Takeshita

Yasunori Futatsugi

Satomi Shioiri

Yoshihisa Inada

Daisaku Ogasahara

Yohei Hasegawa

A communication system includes: a transmitting-side terminal; a transmitting-side communication apparatus configured to receive data transmitted by the transmitting-side terminal and transmit the received data by radio transmission to a receiving-side communication apparatus; and the receiving-side communication apparatus configured to transmit the data received by radio transmission from the transmitting-side communication apparatus to a receiving-side terminal. The transmitting-side terminal includes a control unit configured to control a transmission speed of the data addressed to the receiving-side terminal based on a first error rate that is an error rate of radio transmission from the transmitting-side communication apparatus to the receiving-side communication apparatus and a second error rate that is an error rate of transmission from the transmitting-side terminal to the receiving-side terminal.

Communication system, terminal, control method, and nontransitory computer-readable medium storing program

Tracking control of a light beam is achieved at high speed and with good precision, without requiring preparation of an optical system that causes high signal loss when coupling a reception light beam with an optical fiber. A reception device for optical space communication comprises: fibers having a plurality of propagation modes with spatially different characteristics; an optical coupling system for coupling the reception light beam to the fibers; and a mode separator that separates the coupled light into a plurality of propagation modes, the adjustment axes of the optical coupling system for coupling the reception light beam to one end of the fibers being controlled on the basis of the total coupling strength to all of the modes, and the priority of control of the axes being adjusted on the basis of information about the coupling strength ratio for each mode.

Reception device for optical space communication, optical space communication system, and method for controlling optical space communication device

A receiving optical system control device according to the present invention has: a light intensity calculation means for calculating, from a reception signal acquired by receiving, for each of plurality of mode light beams which are of the incident optical beams and which have been coupled to a plurality of propagation modes of the optical transmission medium by an optical system provided with a variable mechanism, the light intensity of each of the mode light beams; an optical phase calculation means for calculating the optical phase of each of the mode light beams from the reception signal; a relative phase calculation means for calculating the relative phase between the plurality of mode light beams from the optical phases; and a control amount calculation means for calculating the control amount of the variable mechanism from the light intensity and the relative phase.

Receiving optical system control device and receiving optical system control method

It is difficult in related communication apparatuses to avoid degradation of communication quality due to fading and achieve sufficient throughput performance; therefore, a communication apparatus according to an exemplary aspect of the present invention includes fade avoidance rate calculation means for calculating, from a time variation in communication quality information and a transmission pattern in transmitting a communication packet repeatedly, a fade avoidance rate of a probability that the communication packet lies outside a fade duration, with respect to each transmission pattern; throughput calculation means for calculating, from the transmission pattern and the fade avoidance rate, a throughput of the communication packet with respect to each transmission pattern; and transmission pattern determination means for determining an optimum transmission pattern, of the transmission pattern, by which the throughput is maximized.

Communication apparatus and communication method

An optical reception terminal includes a plurality of matrix filters () respectively provided for a plurality of modes and configured to perform polarization separation and equalization on a coherently received signal in a corresponding mode, and two combining filters () respectively provided for two polarizations and configured to combine signals in corresponding polarization among signals output from the plurality of matrix filters () after weighting the signals. Filter coefficients of the plurality of matrix filters () and weighting coefficients of the two combining filters () are controlled based on a deviation from a desired state of both signals in two polarizations after combining by the two combining filters (), so as to minimize a sum of deviations.

Optical space communication system, optical reception device, optical reception method, and non-transitory computer readable medium

A signal processing device combines a plurality of received signals, and includes: a phase reference signal selection means for selecting a signal serving as a phase reference from among the plurality of received signals on the basis of the quality of the plurality of received signals; a relative phase calculation means for obtaining information about the relative phases of the plurality of received signals before the combining; a phase compensation means for performing relative phase compensation on each of the plurality of received signals on the basis of the relative phases; and a phase correction means for calculating a phase correction amount based on the relative phase information and performing phase correction on the received signals, wherein when switching occurs in the selected phase reference signal, the phase correction amount is changed by as much as the relative phase difference between the phase reference signals before and after the switching.

Signal processing device and signal processing method

The signal combining device includes: a plurality of first filters to subject each of a plurality of reception signals to processing with first filter coefficients, the plurality of reception signals being generated by subjecting optical signals to coherent detection; a plurality of second filters to subject outputs of the first filters to processing with second filter coefficients; a combiner to output combined signals acquired by combining outputs of the second filters; and a controller to perform adaptive control for each of the first filter coefficients and each of the second filter coefficients with different step sizes in each other, so that the combined signals are in a predetermined state, based on the reception signals input to the first filters and the combined signals, and to switch an update state of a filter coefficient of each of the first filters, based on magnitudes of the second filter coefficients.

Signal combining device and signal combining method

The objective of the present invention is to reduce the size of a receiving device circuit in an optical space communication system while maintaining communication stability. A data receiving device which decodes one item of data from a plurality of input signals includes: two or more digital signal processing means for subjecting the plurality of input signals to signal processing; a first recording means for temporarily recording the plurality of input signals; a SN ratio estimating means for estimating S/N ratios of each of the plurality of input signals and determining the number of the plurality of input signals to be combined, and the signals to be combined; and a scheduling means for carrying out overall control on the basis of the results from the SN ratio estimating means.

Free-space optical communication receiving device and method of controlling the same

An optical space communication device includes first and second optical antennas that transmit first and second transmission light and receive first and second reception light, first and second delay circuits that provide a delay to transmission data included in the first and second transmission light, third and fourth delay circuits that provide a delay to reception data included in the first and second reception light, and a receiver that sets a delay of at least one of the first delay circuit and the second delay circuit and sets a delay of at least one of the third delay circuit and the fourth delay circuit, based on delays between the first and third delay circuits and the first optical antenna, delays between the second and fourth delay circuits and a fourth optical antenna, and delays between a communication destination and the third and fourth delay circuits.

Optical space communication device and delay adjustment method

An appropriate synthesized signal cannot be obtained by only correcting relative phase errors of a plurality of received signals; therefore, a received signal processor according to an exemplary aspect of the present invention includes a plurality of signal-to-noise ratio estimation means for estimating respective signal-to-noise ratios of a plurality of digital signal sequences in which relative phase errors of a plurality of received signal sequences having been corrected; a plurality of temporary decision means for performing symbol decisions of the plurality of digital signal sequences and outputting symbol signal sequences; symbol-map-rotation determination means for determining respective phase rotation amounts of the plurality of digital signal sequences from the plurality of symbol signal sequences and the respective signal-to-noise ratios of the plurality of digital signal sequences; and a plurality of phase rotation means for rotating phases of the plurality of digital signal sequences respectively based on the phase rotation amounts.

Received signal processor and method for processing received signal

It is difficult in a free space optical transmitter to transmit a beacon beam stably at low cost, and that it is impossible to maintain stable tracking; therefore, a free space optical transmitter according to an exemplary aspect of the present invention includes a laser beam transmitting means for transmitting a plurality of laser beams capable of interfering with each other and differing in one of an optical frequency and a time variation in a phase difference; and a wavefront control beam transmitting means for transmitting, to a free space, a plurality of wavefront control beams obtained by making each of the plurality of laser beams have a different wavefront.

Free space optical transmitter and free space optical communication method

In order to increase a compensation range for Doppler shift compensation, this digital signal processing circuit is provided with a Doppler shift compensation unit which, on the basis of a sample sequence signal which is oversampled at N (where N is an integer at least equal to 2) times a symbol rate and includes a central sample corresponding to the timing at a symbol center, and a transition sample corresponding to the timing of a symbol transition, finds a Doppler shift amount included in the sample sequence signal and performs Doppler shift compensation. The Doppler shift compensation unit includes a symbol determining unit which performs a symbol determination with respect to the central sample and a determination with respect to the transition sample. The Doppler shift compensation unit switches between these determinations for each corresponding sample and performs said determinations in order to obtain a phase difference and thereby detect the Doppler shift amount.

Digital signal processing circuit and optical space communication system

A receiving-side splitterthat constitutes part of an optical communication devicesplits a receiving-side signal light into a plurality of lights at a splitting ratio according to the intensity distribution of mutually different propagation modes included in the receiving-side signal light passed through a transmission medium. A transmission-side splittersplits a transmission-side signal light into a plurality of-lights. A signal processing devicedetects the light intensity and/or the phase of the receiving-side signal light, and sets a control target value for the light intensity and/or the phase of the transmission-side signal light to a value according to the result of the detection. A modulatoradjusts the light intensity or the phase of a the transmission-side signal light so that the light intensity or phase equals the set value. A multiplexermultiplexes the plurality of transmission-side signal lights.

Optical communication device, optical communication system, and optical communication method

In the optical transmission system to transmit optical signals using a plurality of adjacent paths, it is difficult to detect a delay difference between a plurality of paths and chromatic dispersion with a high degree of accuracy due to a crosstalk; therefore, a method for detecting optical signal information according to an exemplary aspect of the present invention includes generating a plurality of data signal sequences corresponding to a plurality of paths multiplexed spatially, each of the plurality of data signal sequences obtained by inserting periodically a training signal with a plurality of frequency components in a data signal, in the plurality of data signal sequences, the training signals respectively included in the data signal sequences to be propagated through adjacent paths at least having different frequency components from each other at the same timing, each of a plurality of the training signals included in one of the data signal sequences having the plurality of frequency components whose frequency difference differing depending on a position to be inserted; and calculating a propagation delay difference between the plurality of paths and chromatic dispersion amounts in the plurality of paths from the plurality of frequency components included in the training signals having been propagated through the plurality of paths by optical signals.

Optical transmission system, optical receiver, and method for detecting optical signal information

It is difficult in a free space optical receiver to satisfy both of the stable receiving and the highly sensitive receiving; therefore, a free space optical receiver according to an exemplary aspect of the present invention includes a light collecting means for collecting laser light having propagated through a free space transmission path; a multimode light generating means for receiving input of the laser light collected by the light collecting means, exciting multimode light, and outputting multimode propagation light including a plurality of propagation mode light beams with a number smaller than a number of multimode light beams possible to be excited; and a mode separating means for separating the multimode propagation light into the plurality of propagation mode light beams and outputting the plurality of propagation mode light beams.

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Tokyo, Japan

Toshiharu Ito