We report the feasibility of forward error correction (FEC) and superimpose (SI) for improving transmission performance in subcarrier multiple access (SCMA) systems under optical beat interference (OBI). By combining SI and FEC, error rate floors near 10^<-4> could be eliminated in eight channel 14.6313 Mbit/s multiplexed upstream transmission in a passive double star (PDS) network.

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We came up with 500ch QAM signalsoptical transmission. 500 QAM signal are transmitted using a laser-diode and single fiber and 2000 video programs can be delivered to subscribers. The 500 QAM signal can be branched off using EDFA optical amplifier. Then it is one of promissing transmission method for a standerd FTTH network. We did 500 QAM signals transmission experiment, employing 16QAM for modulation method and SM fiber. Setting optical modulation index of 16QAM to 1.5%/ch., BER of 16QAM signal is shown less than 10^<-6> over all channels. We also evaluate branching optical signal. We clear that more than 10,000 branching can be realized using 3 stages EDFA amplifier.

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Future CATV services, such as Video On Demand(VOD), and hybrid transmission systems(AM/QAM and FM/PSK), have been proposed^<[1][2]>. Analog transmission equipment is preferable in view of simple transmission equipment constraction compared with digital transmission. This paper reports on a VSB-AM 150ch optical transmission equipment which is adaptable to the analog and digital transmission.

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The authors examined the SCM optical transmitter employing an MQW-EA external modulator having broadband and low chirp characteristics and the predistortion linearization circuit that compensates the nonliear distortion generated by the modulator. A 2.4 GHz AM/16QAM/FM hybrid SCM signal transmission and a 100 km-long 42 channel AM-SCM signal transmission were performed by means of the MQW-EA modulator, EDFAs and 1.3μm zero-dispersion single mode fibers. The experimental results show the feasibility of the modulator for broadband analog transmission systems and for suppressing the signal distortion caused by the combined action of laser chirp and fiber dispersion. Furthermore, the authors verify that applying the electrical circuit that compensates the third order nonlinear distortion is effective for the modulator.

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In general, informational transmission systems from a terminal to the other terminal are applied to standard optical communication. However, an informational injection on the fiber way, besides no cutting fiber cables, is being needed more and more. We produce characteristics and designs of some methods based on following principles : (1) faraday effect (2) bending loss, (3) elastic vibration. In this paper, we propose bi-directional communication systems needless all terminal LDs to carry information from end-users, which can be simply composed. For the application, we assumed optical fiber CATV systems requested from end-users, and mentioned the realization of the systems.

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For the statistical study of scintillation fading of 100GHz band, the propagation experiment has been carried out through the 390m path in Nagoya from April 1988 to March 1991. In this paper, statistical analysis for the origin of the scintillation fading in the short range path has been discussed. Large scale scintillation fadings where the receiving power changes before and after the scintillation fadings are clearly attributable to the difference of the water vapour densities due to the difference of the wind directions. Other scintillation fadings are more or less caused by southern wind and there are many scintillation fadings when water vapour densities are of 7-21g/m^2 before and after the scintillation fadings.

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The multimedia communication services commence in near future. In order to prepare for new media society, Fiber optic cables for a broadband ISDN or Super high way are now expected to be installed in the subscriber loop areas. In our city, there are already many kind of useful facilities, the cityscape, especially traditional scenerys, however, suffered from damage with almost all of them. They are poles, aerial lines for telephone, electric power, and so on. The authors propose that system engineers contribute widely not only to the convenience and the high efficiency, but also the sight and the safety of the cities.

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Feasibility of Subcarrier Multiple Access (SCMA) networks for multimedia transmission platforms has been investigated. SCMA is quite suitable for the platforms of various "personal" and "consumer" communication applications because of its flexibility and simple configuration. In this paper, the techniques to avoid or reduce beat noise which degrades the SCMA network performance are discussed. Furthermore, design examples of several system applications such as "Live on Demand" and distributed antenna systems for radio systems are presented.

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To meet the increase the number of base stations in the fiber optic microcell radio systems, less expensive fiber optic transmission method are now being studied. In this paper we propose a novel transmission architecture. In this system the signals of three sectors are frequency converted and frequency division multiplexed to one signal stream, which is then transmitted through one optical fiber. Using this technique with wavelength division multiplexing(WDM), the number of optical fiber lines is reduced to 2 for nine signals of three sectors. The optical link performance is discussed form the viewpoint of 3rd order distortion and CNR for system design. It is clear that the use of this system will be very effective in constructing microcell radio systems.

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Recently, microcell radio systems using subcarrier multiplexed (SCM) fiber optic links and the associated technologies have been extensively studied. In the fiber optic link for microcell radio systems, very low distortion characteristics to meet the wide dynamic range and cost-effectiveness is indispensabel. This paper describes predistortion technique using IM2 generated by a simple nonlinear circuit which can reduce the distortion of LD by more than 10dB. 1.9GHz SCM fiber optic link with a Fabry-Perot LD, whose dynamic range is more than 55dB after 10km of fiber, has been realized by employing the predistortion technique.

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