Matsushita Electric Industrial Co., Ltd.

Panasonic Corporation

Nippon Telegraph and Telephone Corporation

Other

Kuniaki Utsumi

Hiroaki Yamamoto

Masaru Fuse

Kazuki Maeda

Hiroyuki Sasai

Katsuyuki Fujito

Satoshi Furusawa

Susumu Morikura

Mariko Nakaso

Kouichi Masuda

Tsutomu Niiho

Hiroaki Nakata

Manabu Tanabe

Yasushi Matsui

Hideaki Takechi

Katsumi Iwatsuki

Mitsuhiro Teshima

Yoshikazu Ishii

Shigeru Kuwano

Shigeru Yamane

Hiroaki Asano

Toru Shiozaki

Kazuo Tanaka

Koji Kikushima

Seiichiro Kawashima

Hitoshi Uematsu

Yutaka Fuke

A SW () receives an Ethernet&#xae; signal from an outside of areas E and F. The SW () selects and outputs the obtained Ethernet&#xae; signal to any one of APs (to) in accordance with a network structure managed by the SW (). The AP (to) converts the Ethernet&#xae; signal to an electrical signal type wireless LAN signal, which is in turn output to a main station (). The main station () frequency-multiplexes the signal output from each of the APs (to), and converts the signal to an optical signal, which is in turn output to sub-stations (and). The sub-station (and) transmits the signal transmitted from the main station () to a terminal in the form of a wireless radio wave. Thereby, when a plurality of communication areas are present, the accommodation capacity of an AP can be effectively utilized in each communication area.

Method and system for extending coverage of WLAN access points via optically multiplexed connection of access points to sub-stations

A wireless communication system capable of keeping a level of a wireless signal received by a relay apparatus within a predetermined dynamic range. In a control apparatus, a transmitting section converts a downstream electric signal into a downstream optical signal and transmits the downstream optical signal to the relay apparatus via an optical transmission path. The relay apparatus converts the received downstream optical signal into a downstream electric signal and transmits the downstream electric signal as a wireless signal to a wireless communication terminal from a transmitting/receiving antenna section. In the relay apparatus, a level adjustment section adjusts the level of the wireless signal transmitted by the relay apparatus such that the receiving level of the wireless signal received by the relay apparatus is kept within a predetermined range.

Wireless communication system

This invention discloses an optical burst transmission system in which an optical generator generates Type 1 lightwaves having different wavelengths corresponding to transmission lines and having undergone intensity modulation with obtained data; a broad spectrum optical generator generates, by incorporating Type 2 lightwaves, a Type 3 lightwave using a fewer light emitting devices than the number of the Type 1 lightwaves, each Type 2 lightwaves having a corresponding wavelength apart from Type 1 lightwave's wavelength with an FSR interval and having undergone the intensity modulation with clock signals; an optical multiplexer multiplexes the Type 1 and Type 3 lightwaves to output the combination to each transmission line; and an optical routing unit extracts, from the combination, pairs of one Type 1 lightwave and one Type 2 lightwave having the corresponding wavelength, and guides pairs to each transmission line corresponding to the Type 1 lightwave's wavelength in each pair.

Low-cost optical burst transmission system, apparatus, and method

A branch portionbranches an inputted electrical signal into an in-phase signal and an opposite phase signal which have an opposite relation as to a phase. A first FM laserconverts the in-phase signal into an optical frequency-modulated signal (a first optical signal) having a center wavelength &#x3bb;and then outputs the resultant signal. A second FM laserconverts the opposite phase signal into an optical frequency-modulated signal (a second signal) having a center wavelength &#x3bb;and then outputs the resultant signal. The two optical signals are combined and then inputted into an optical-electrical converting portion. The optical-electrical converting portionsubjects the inputted optical signals to optical heterodyne detection by its square-law detection characteristic, and outputs a beat signal between the two optical signals which is a wide-band FM signal at a frequency corresponding to a wavelength difference &#x394;&#x3bb;(=|&#x3bb;|) between the first optical signal and the second optical signal. It is thus possible to increase frequency deviation of the outputted FM signal and thus greatly improve a CNR.

FM modulator

A branch portion branches an inputted electrical signal into an in-phase signal and an opposite phase signal which have an opposite relation as to a phase. A first FM laser converts the in-phase signal into an optical frequency-modulated signal (a first optical signal) having a center wavelength &lgr;1 and then outputs the resultant signal. A second FM laser converts the opposite phase signal into an optical frequency-modulated signal (a second signal) having a center wavelength &lgr;2 and then outputs the resultant signal. The two optical signals are combined and then inputted into an optical-electrical converting portion . The optical-electrical converting portion subjects the inputted optical signals to optical heterodyne detection by its square-law detection characteristic, and outputs a beat signal between the two optical signals which is a wide-band FM signal at a frequency corresponding to a wavelength difference &Dgr;&lgr;(&equals;&verbar;&lgr;1&minus;&lgr;2&verbar;) between the first optical signal and the second optical signal. It is thus possible to increase frequency deviation of the outputted FM signal and thus greatly improve a CNR.

A branch portion branches an inputted electrical signal into an in-phase signal and an opposite phase signal which have an opposite relation as to a phase. A first FM laser converts the in-phase signal into an optical frequency-modulated signal (a first optical signal) having a center wavelength &lgr; and then outputs the resultant signal. A second FM laser converts the opposite phase signal into an optical frequency-modulated signal (a second signal) having a center wavelength &lgr; and then outputs the resultant signal. The two optical signals are combined and then inputted into an optical-electrical converting portion . The optical-electrical converting portion subjects the inputted optical signals to optical heterodyne detection by its square-law detection characteristic, and outputs a beat signal between the two optical signals which is a wide-band FM signal at a frequency corresponding to a wavelength difference &Dgr;&lgr;(&equals;&verbar;&lgr; ) between the first optical signal and the second optical signal. It is thus possible to increase frequency deviation of the outputted FM signal and thus greatly improve a CNR.

A modulated electrical signal Smod produced upon amplitude-modulating a subcarrier having a high frequency (for example, a millimeter-wave band) by a baseband signal SBB to be transmitted and a main carrier MC outputted from a light source are inputted to an external optical modulating portion in an optical transmitter. The external optical modulating portion amplitude-modulates the main carrier MC by the modulated electrical signal Smod, to output a double-modulated optical signal OSdmod to an optical filter portion. The optical filter portion passes only a component of one of sidebands included in the double-modulated optical signal OSdmod, and outputs the component to an optical fiber as an optical signal OS. An optical/electrical converting portion in an optical receiver optical/electrical-converts the optical signal OS transmitted through the optical fiber, to directly obtain a baseband signal SBB. Consequently, the optical receiver is constructed simply and at low cost without requiring a wideband optical/electrical converting element for optical/electrical-converting a high-frequency electrical signal and a high-frequency electrical component (a frequency converter, a demodulator, a semirigid cable or a waveguide) which is very high in cost or is difficult to process.

Optical transmitter-receiver

An oscillator outputs an additional signal with a frequency which is higher than a frequency corresponding to a bandwidth of a frequency band allotted to an electrical signal to be transmitted and lower than a half of a lowest frequency of a frequency band allotted to the electrical signal to be transmitted. Thereby, if a second order intermodulation distortion between the additional signal and the electrical signal to be transmitted occurs, a frequency where distortion occurs is outside all of the frequency bands allotted to the electrical signal to be transmitted, and the occurring second order intermodulation distortion does not affect the electrical signal to be transmitted. Further, if the second order intermodulation distortion of the additional signal occurs, the frequency where distortion occurs is outside all of the frequency bands allotted to the electrical signal to be transmitted, and the occurring second order intermodulation distortion does not affect the electrical signal to be transmitted. Not only noise and distortions caused by reflected optical signal but also OBI noise can be reduced by using the additional signal.

Optical transmission device and system

In FIG. 5, a plurality of signal sources 21.sub.1 to 21.sub.N each generate a carrier with different frequencies. A pulse signal generating portion 23 generates a pulse signal with the same period and time width as those of a horizontal synchronizing signal in NTSC system color television broadcasting. Delay devices 32.sub.1 to 32.sub.N delay timing of the pulse signal for a randomly predetermined delay amount. Level adjuster 52.sub.1 to 52.sub.N generate a modulating signal by adjusting each pulse base of the delayed pulse signal for a level within a range between 12.5% and 74.375% with respect to a pulse top. Modulators 42.sub.1 to 42.sub.N output a signal obtained by modulating the carrier with the modulating signal. A multiplex portion 24 multiplexes the modulated signals to output a resultant signal as a test signal. The error rate of a QAM signal is evaluated with the test signal. It is therefore possible to evaluate the error rate of the QAM signal in a signal state approximate at the maximum to a state of an actual AM video signal (that is, analogous distribution characteristics of the multiplex signal amplitude). In the error rate evaluation method according to an embodiment of the present invention, it is thus possible to accurately evaluate the error rate of the QAM signal under the strictest conditions, which may occur in the actual, AM video signal, thereby ensuring the reliability of the entire CATV system.

Optical transmission method, error rate evaluation method applied in

In a system for simultaneously optically transmitting a plurality of digital modulation signals using an analog SCM transmission technique, the degree of degradation of the waveform of a transmission signal or the magnitude of distortion thereof differs depending on bands, whereby there arises a difference in transmission quality among channels. Therefore, an analog signal to be transmitted is converted into a digital signal by an analog-to-digital converting portion, after which the digital signal is divided, by a hierarchy separating portion, into a plurality of groups of digital information depending on degrees of importance in constructing the original analog signal. A modulating portion digitally modulates carriers having different frequencies which are respectively assigned to the groups of digital information. A multiplexing portion frequency-multiplexes and simultaneously optically transmits all the digital modulation signals. In this case, the carrier corresponding to the digital information having a higher degree of importance is set on a lower frequency side, and the carrier corresponding to the digital information having a lower degree of importance is set on a higher frequency side. Consequently, it is possible to minimize the effect of the degradation and the distortion caused in the transmission on received and reproduced data, whereby high-quality transmission is possible.

Optical transmitter and optical transmission system using the same

A branch portion 107 branches a modulating signal into two signals in opposite phases. One of them is inputted to an FM laser element 102. The other one is adjusted in propagation delay and in amplitude and then is inputted to an IM suppressing laser element 110. The FM laser element 102 outputs an optical-frequency-modulated signal around a wavelength .lambda.1, whose optical intensity is also modulated. A local light source 104 outputs light at a wavelength .lambda.0, which is different from the oscillation wavelength .lambda.1 of the FM laser element 102 by .DELTA..lambda.. The IM suppressing laser element 110 outputs an optical-intensity-modulated signal. The three lights are combined and inputted to a photodetection portion 106. The photodetection portion 106 applies a heterodyne detection to inputted lights to output an FM modulated signal corresponding to a beat signal of the outputted optical signal from the FM laser element 102 and the outputted light from the local light source 104 at frequency corresponding to the difference .DELTA..lambda. between the original two wavelengths, and also cancels the average-value variation component in the FM modulated signal with an electrical signal produced by square-law detecting the optical-intensity-modulated signal from the IM suppressing laser element 110, thereby producing an ideal FM modulated signal.

FM modulation device

A center station 1 generates an all-channel signal 2 obtained by multiplexing signals on all channels, and transmits the signals to a selective distribution station 10 through 1 wire transmission line such as an optical fiber. Subscribers' transmitting devices 40.sub.1 to 40.sub.N transmit requests for channels to be received by corresponding subscribers' receiving devices 30.sub.1 to 30.sub.N to the selective distribution station 10 in a radio transmission system. The selective distribution station 10 selects the signals on the channels requested from the all-channel signal 2 in response to requests to receive channels serving as up-signals transmitted in a radio transmission system from the subscribers' transmitting devices 40.sub.1 to 40.sub.N, and distributes and transmits the selected signals to the subscribers' receiving devices 30.sub.1 to 30.sub.N as down-signals.

Catv system in which chanel selection signal is transmitted from the

A signal for which the amplitude of envelope becomes substantially 0 only for a certain period of time within the time of a period T, and a measured signal having a certain amplitude are synthesized, and the synthesized signal is optically transmitted. When a plurality of reflection points are present on a light transmission line, there is an increase in harmonic distortion or intermodulation distortion as well as in cross modulation distortion after receiving. This increase in cross modulation distortion causes an increase in variation of amplitude of the measured signal. In such a case, it is possible to calculate the distance between, and/or reflectance of, reflection points present on end faces of optical elements and/or connecting points of optical fibers on the light transmission line by investigating first periodical characteristics of variation of the transmitted measured signal during transmission relative to the change in central light frequency of the signal light, or investigating second periodical characteristics of variation of the transmitted measured signal during transmission corresponding to the change in the frequency of the measured signal.

Method for measuring distance between reflection points along light

The present invention provides an optical disc comprising a main-image signal recording area holding a signal of a main image for a display, and a sub-image signal recording area holding a signal of a sub image to be displayed including an image of a time counted down in accordance with a progress of a sub-image signal reproduction. Furthermore it provides an image signal transmitting apparatus for repeatedly transmitting a main-image signal and a sub-image signal one after the other by utilizing such optical disc, the image signal transmitting apparatus comprising a image signal reproduction device for reproducing the main-image signal and the sub-image signal, a cycle time memory for memorizing a main-image signal transmission cycle, and a control device for obtaining a time difference between the cycle and time required for the main-image signal reproduction as well as control the image signal reproduction device.

Image signal transmission apparatus for repeatedly reproducing and

A picture image distributing apparatus provided within a passenger moving vehicle, consists of: a head end portion for multichannel FDM picture image signals; an electrical optical for converting the FDM picture image signals into optical signals; an optical amplifier for optically amplifying the optical outputs; one optical fiber transmission path connected to optical taps of unequal distribution for branching halfway on one portion of the optical power except for the branching at a final point, an optical/electrical converter for receiving optical signals branched at the final point or halfway so as to convert them into electrical signals; and a passenger seat picture image receiving terminal connected to the optical/electrical converter so as to receive the electrical signals.

Growing community of inventors

Sanda, Japan

Kuniaki Utsumi