Abstract: An optical communication system for optically transmitting transmission data from a transmitting station to a transmitting device includes an adder for adding an intermediate frequency subcarrier signal modulated with data to be transmitted to a pilot carrier signal as a sinusoidal wave, and an electro-optical converter for electro-optically converting the above sum signal to an optical signal by directly modulating a semiconductor laser element having a resonant frequency fr in accordance with the sum signal and transmitting the signal to an optical fiber for a down link. The frequency fIF of the intermediate frequency subcarrier signal and the frequency fLO of the pilot carrier signal satisfy fLO?fIF?1[GHz], 2×fIF<fLO<(?)×fr, fIF<1[GHz], and 2 [GHz]<fLO.

Abstract: An orthogonal frequency division multiplexing (OFDM) signal transmission apparatus which transmits OFDM signals by using a plurality of transmission antennas includes a subcarrier setting device which sets signals for subcarriers so as to use some of the subcarriers of the OFDM signals as pilot subcarriers to transmit pilot signals and use the remaining subcarriers as data subcarriers to transmit data signals, the subcarrier setting device changing polarities of signals for the pilot subcarriers for each transmission antenna.

Abstract: In a wireless transmitting device which performs transmission by an OFDM using a plurality of subcarriers orthogonal to each other, a plurality of preambles to which a plurality of different subcarrier groups selected from a plurality of subcarriers within an OFDM signal band are allocated are transmitted by using a plurality of transmit antennas, and data is transmitted by using the antennas after the preambles are transmitted.

Abstract: A radio receiver comprises a first amplifier to amplify a received radio signal; a quadrature demodulator to demodulate the radio signal amplified by said first amplifier and thereby generate a baseband signal; a second amplifier to amplify the baseband signal; a demodulator to demodulate the baseband signal amplified by said second amplifier; and a gain controller to control timing of a change in a gain of said second amplifier, in case that changing the gain of said first amplifier and the gain of said second amplifier, on the basis of a gain of said first amplifier before and after the change.

Abstract: A mobile communications terminal includes positional information generator configured to generate positional information indicating a current position of the terminal, receiver which receives identification information sent from the base station of the second mobile communication network, notification information generator configured to generate notification information including the identification information and the positional information generated at the time of receiving the identification information, and transmitter which transmits the notification information to the service area calculation apparatus via the first mobile communication network to derive the information concerning the service area.

Abstract: The present invention is intended to provide a mobile communication terminal permitting a user to obtain location information of wireless base station which provides contents data in certain areas. The terminal accumulates identification information of wireless base stations when wireless services are received. The invention has functions of interrelating the identification information with location information of the terminal when the services are received and of storing both kinds of information. Wireless LAN service areas are displayed together with map information.

Abstract: An optical communication system for optically transmitting transmission data from a transmitting station to a transmitting device includes an adder for adding an intermediate frequency subcarrier signal modulated with data to be transmitted to a pilot carrier signal as a sinusoidal wave, and an electro-optical converter for electro-optically converting the above sum signal to an optical signal by directly modulating a semiconductor laser element having a resonant frequency fr in accordance with the sum signal and transmitting the signal to an optical fiber for a down link.

Abstract: A laying method for laying communication cables (16) is provided which allows to lay optical fiber cables (20) in an underground pipeline such as a sewage pipe neither placing direct tension nor allowing slack on them, and for a main pipe in which a plurality of optical fiber cables (20) are to be laid, the method also allows to lay optical fiber cables (20) in the upper space of inside the pipeline and to obviate the need of an expensive robot for the laying operation. In the proposed laying method, a high-strength low-elongation tension member is disposed to be slidable in the lengthwise direction along each optical fiber cable (20, 21, 22), and the tension members (25, 26, 27) are drawn into the underground pipeline (1) to tension the trunk tension member (25) thereby stretching the trunk tension member (25) substantially straight in the underground pipeline (1), and thus the optical fiber cables (20, 21, 22) are laid in the upper space of inside the underground pipeline (1).

Abstract: An optical communication system for optically transmitting transmission data from a transmitting station to a transmitting device includes an adder for adding an intermediate frequency subcarrier signal modulated with data to be transmitted to a pilot carrier signal as a sinusoidal wave, and an electro-optical converter for electro-optically converting the above sum signal to an optical signal by directly modulating a semiconductor laser element having a resonant frequency fr in accordance with the sum signal and transmitting the signal to an optical fiber for a down link. The frequency fIF of the intermediate frequency subcarrier signal and the frequency fLO of the pilot carrier signal satisfy fLO−fIF≧1 [GHz], 2×fIF<fLO<(2/3)×fr, fIF<1 [GHz], and 2 [GHz]<fLO.

Abstract: The present invention provides a light transfer system comprising a plurality of slave stations each equipped with a light transmitter for outputting an optical signal corresponding to an information signal and a master station for receiving an optical multiplex signal obtained by optically multiplexing the optical signals sent from the plurality of slave stations, wherein the plurality of slave stations adjusts an amount of heat radiated from an exothermic-effect-only heat source of the optical transmitter to thereby control a wavelength of the optical signal output from a laser diode of the light transmitter.

Abstract: In this invention, there is provided an optical communication system comprising a plurality of sub-stations and a main station connected to the plurality of sub-stations via an optical transmission path. The plurality of sub-stations respectively comprise modulation section for modulating a wavelength of an optical signal which is transmitted from the respective sub-station to the main station via the transmission path containing information signals by using a control signal having a unique frequency allocated to the sub-station, arbitrary pairs of control signals having different frequency differences.

Abstract: A system for transmitting, over an optical transmission path using an optical fiber, wavelength-multiplex signals of a plurality of channels to which different wavelengths are assigned, the system comprising an optical transmission terminal station for transmitting the wavelength-multiplex signals to the optical transmission path, an optical reception terminal station for receiving the wavelength-multiplex signals from the optical transmission path, and at least one of ADD/Drop-Multiplexer nodes each including at least a demultiplexer unit for demultiplexing a plurality of channels to a channel in accordance with a given wavelength and a multiplexer unit for multiplexing a plurality of channels in accordance with a given wavelength, wherein optical pulses having pulse waveforms with an equal full-width at half-maximum are applied to the optical signals.