Nec Corporation

Nec Laboratories America, Inc.

Nec Coproration

Makoto Shibutani

Wataru Domon

Masaki Umayabashi

Atsushi Iwata

Youichi Hidaka

Nobuyuki Enomoto

Kazuo Takagi

Katsumi Emura

Ting Wang

Yuanqiu Luo

Junqiang Nochur Hu

Dayou Qian

Yoshihiko Suemura

Shuntaro Yamazaki

Junji Namiki

Toshihito Kanai

Satomi Shioiri

Akihiro Kanazawa

Toshiharu Yasugi

An interference cancellation device includes: an interference signal generation unit including a buffer circuit that accumulates a first digital signal, delays the first digital signal, and outputs the first digital signal as a second digital signal and a digital signal processing circuit that processes the second digital signal in such a way as to have the same optical characteristic change as a reflected light whose optical characteristic changes according to the characteristic of an optical fiber transmission path, wherein the reflected light is a light reflected at a reflection point of the path when a transmission signal light modulated by the first digital signal is transmitted through the path, and outputs the second digital signal as an interference signal; and a subtraction unit that subtracts the interference signal from a third digital signal obtained by converting a reception signal light into an electric signal and outputting the result.

Interference cancellation device and interference cancellation method

A coherent optical receiver according to an exemplary aspect of the invention includes a coherent optical receiving part performing coherent detection by inputting and mixing local oscillation light and main signal light received through a transmission line with a signal applied at a transmitting side, outputting the signal applied to the main signal light as an electric signal, and regenerating and outputting an original signal on the basis of the electric signal; and a local oscillation optical frequency control part receiving channel information on a transmission line adjacent to the main signal light, and outputting the local oscillation light after changing a frequency of the local oscillation light depending on the presence or absence of adjacent channel signal light of other signal light in an adjacent channel.

Coherent optical receiver and optical receiving method

An optical transmission systemincludes an optical transmitterand an optical receiver. The optical transmitterincludes, a multiplexed code sequence generation unitarranged to multiplex a code included in the transmission code sequence to be time shifted, and an optical transmission unitthat converts a multiplexed code sequence into a light signal and transmit it. The optical receiverincludes, an optical reception unitthat receives and converts the light signal transmitted from the optical transmitterinto a code sequence, and a transmission code sequence regeneration unitthat regenerates the transmission code sequence by identifying a code based on a value of a plurality of codes each corresponding to one another included in the code sequence.

Optical transmission system and optical transmission method

A coherent optical receiver according to an exemplary aspect of the present invention includes a coherent optical receiving unit, a first waveform equalizing circuit compensating waveform distortion caused by characteristics of the coherent optical receiving unit and compensating chromatic dispersion in a predetermined range to an input signal, a second waveform equalizing circuit compensating chromatic dispersion of the input signal, and a controller monitoring a chromatic dispersion amount of the input signal and controlling a compensation coefficient regarding the chromatic dispersion compensation performed by each of the first waveform equalizing circuit and the second waveform equalizing circuit depending on the chromatic dispersion amount to be compensated.

Coherent optical receiver and coherent optical receiving method

A network system and method include a wireless base station integrated at a central office of a service provider. The wireless base station is configured to provide portable and fixed services to customers. A passive optical network is coupled to the wireless base station at the central office to provide a link to extend an antenna for wireless operations of the wireless base station to a remote site such that a wireless signal from the wireless base station is transmitted in parallel with a passive fiber network signal through the link.

System and method for providing wireless over a passive optical network (PON)

A node that configures a spanning tree over a network to which a plurality of nodes are connected generates a tree after a cost change using another LAN while continuing to operate the tree that existed before the change, and switches the tree that is used for forwarding after the new tree has been stable.

Network system, spanning tree configuration method, spanning tree configuration node, and spanning tree configuration program

A node to relay the Ethernet frame provided with means to insert, in the relay process of the frame, two or more VLAN tags into the frame at a time and to remove the inserted VLAN tags wherein a TTL area to show the frame survival time is provided in the VLAN tag to be inserted to the frame so that whether the survival time has been elapsed or not is checked by the value in the TTL area and the frame after elapse of the survival time is discarded without being relayed.

Frame transfer method and node in Ethernet

In a communication system in which a plurality of communication terminals sequentially transfer data to a server during the respective transmission permissible periods assigned to the respective communication terminals, the communication terminal transfers a preamble for synchronization to the server at a time of starting the transmission permissible period, converts a data frame for every 8 bits into every 10 bit-code, and transmits to the server, the signal string with a code indicating the head added there, during the transmission permissible period, and turns a communication to the server into a zero signal state, during a period other than the transmission permissible period, while the server establishes a synchronization by reading the preamble for synchronization inserted into the signal string received from each of the communication terminals, converts a portion of the zero signal state of the signal string into a predetermined special code string, and inversely transforms the received signal string into the data frame before the coding.

Communication system including several communication terminals and server, its communication terminal, its server and data transfer control program

A communication system includes a server and a plurality of terminals. The server repeatedly assigns transmission periods to the terminals in a regular order, each of the terminals being permitted as a current terminal to transmit data stored in a buffer thereof to the server during an assigned transmission period assigned thereto by the server as a current transmission period. The communication system includes: a transmission controller provided in each of the terminals for transmitting a release request notification to the server in a case where the terminal finishes data transmission before the end of the assigned transmission period assigned to the terminal, and a transmission period assigning portion provided in the server for assigning a next transmission period following the current transmission period to a next terminal different from the current terminal, in response to the release request notification.

Communication system capable of efficiently transmitting data from terminals to server

Disclosed is an optical network which has a plurality of subordinate optical networks, each of which being connected with a plurality of optical terminals which function as a transmitter and a receiver of a signal light, wherein multiplexing of transmission signals and demultiplexing of reception signals at the optical terminals are carried out in the subcarrier multiplexing manner; and a main optical network which is connected with the subordinate optical networks, wherein multiplexing of signal lights transmitted from the subordinate optical networks is carried out in the wavelength division multiplexing manner.

Optical network

An optical transmission system of an N : 1 or an N:N type is provided, in which there is no deterioration caused by beat noise between signals. A plurality of optical modulators are cascaded in an optical fiber transmission path having a light source and a plurality of light receivers connected to two respective ends of the optical fiber transmission path, and carrier waves having frequencies respectively different are applied to the optical modulators. This enables the light receivers to receive a radio frequency signal in which the carrier waves are frequency-multiplexed. The light receivers receive only the signal beam so that there is no occurrence of beat noise. In another arrangement, at the optical network terminal, a part of a signal beam is split and the split beam is intensity-modulated responsively to carrier waves by an optical modulator and, thereafter, is combined again to a passing beam. It is possible to obtain at the signal beam receiver a received signal in which carrier waves from respective optical network terminals are frequency-multiplexed. This prevents occurrence of inter-modulation distortion in the cascaded optical modulators.

Optical transmission system and optical network terminals used therein

The subcarrier frequency multiplexed optical transmission system disclosed is one in which a plurality of analog subcarrier signals and at least one digital subcarrier signal is optically transmitted by frequency multiplexing. The system includes an amplitude limiter, a filter, a multiplexer and a semiconductor laser. Portions of the analog subcarrier signals which are lower in level than the threshold value of the semiconductor laser are eliminated by the amplitude limiter, and further impulse distortions generated due to clipping in the frequency band of the digital subcarrier signal are eliminated by the filter. Then, the analog and digital subcarrier signals are frequency multiplexed to be inputted to the semiconductor laser. The system enables to reduce the transmission quality deterioration of digital subcarrier signal caused by clipping.

Optical transmitter for subcarrier frequency multiplexed optical

An optical module for use in a subcarrier multiplexed (SCM) optical transmission system and capable of reducing the distortion of a signal light due to multiple reflections. A distortion reducing device is implemented by an optical fiber cable longer than the coherence length of the signal light and is located at each of signal input and output portions or each portion where optical devices are jointed together within the module.

Growing community of inventors

Tokyo, Japan

Makoto Shibutani