Recently the mobile communication systems including cellular systems have become popular and wide spread in our life. Especially in the most urban areas many subscribers have become to use the mobile communications. Therefore, it is required to analyze the wave propagation in the urban area to provide a stable service to users through the mobile communications network. For this purpose, we simulate the electric field distribution of urban areas in which a wave source is surrounded by buildings. As for the simulation method, we use the 3 dimensinal ray tracing and the uniform geometrical theory of diffraction (UTD). Also we compare the numerical result with the experimental one which is achieved from the miniature model of real buildings.
According to the rapid development of technologies and wide spread of users in the mobile telecommunications area, the needs for a small and bradband antenna become indispensable. Also a phased array technology is one of bases for antennas for wireless telecommunications such as the smart antenna which is necessary to provide the seamless and high quality service to as many users as possible. As a first step for the broadband phased array, some characteristics of two element array of a small and broadband MS-LPDA antenna are presented in this report. The mutual coupling and the element pattern are investigated through single-fed equi-E and equi-H-plane arrays. The beam scanning pattern is also studied through two basic structures of the phased array, and it is shown that the side lobe level changes according to the distance between array elements and the frequencies.
We propose a passive optical network (PON) system, based on a wavelength-division multiplexing router, with modulators at the optical network units (ONUs) instead of lasers. In order to make up for optical power deficiency at upstream signal sources, we use optical amplifiers that were located at ONUs. We evaluate transmission characteristics of the system, especially an influence of amplified spontaneous emission (ASE). We discuss suppressions of ASE and indicate a possibility that the system can be operated at high bit rate.
We propose the CATV video and IP multiplexing transmission system. The wavelengths of WWDM(Wide passband wavelength division multiplexing) are assigned to CATV video and IP services. The influence of the crosstalk is evaluated by carrier noise ratio(CNR), composite second order (CSO) and composite triple beat (CTB) for video signal, and packet loss for IP traffic from the viewpoint of the transmission quality. The design of the service multiplexing system of video and IP is clarified.
On recent optical fiber communication system, chromatic dispersion of the fiber limits the transmission distance. The optical single sideband modulation (optical SSB) is one of candidates to overcome the effect of it. SSB modulation has many advantages such as small bandwidth of a channel, low optical power of the transmitter and so on. In this paper, we simulated the eye opening characteristics in suppressed carrier SSB (SSB-SC) format and studies the signal distortion of chromatic dispersion effects. As a result, we find that SSB-SC format using electrical dispersion equalizer has the good eye opening characteristics that is independent of the transmission distance.
40 Gbit/s-based WDM transmission using the dispersion flattened transmission span, which consisted of positive and negative dispersion fiber, was experimentally investigated. In the SMF-based transmission line, which has large dispersion, the penalty due to nonlinear crosstalk between WDM channels was found to be small. The effectiveness of distributed Raman amplification and low-nonlinear fiber to suppress the intra-channel nonlinear crosstalk was also investigated. By using optimum dispersion map on low-nonlinear fiber span, transmission distance over 2000 km was achieved in 16 x 40 Gbit/s WDM transmission experiment.
For WDM transmission systems, Optical Fiber Amplifiers employing novel High-speed AGC and Tone-Signal ALC functions are proposed. Based on a both wavelength and time resolved simulation technique, the amplifier repeater is designed and fabricated. The AGC/ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels (32ch - 1ch) less than 0.45dB and keep output power constant over 9dB input power range.
We have developed a radio wave transmitting system using optical modulator for a Digital TV broadcasting relay station. The features of this newly developed system, with optical fiber cable is used as transmission line, are no use of electrical power line at the receiving point and multi-carrier waves transmission. Therefore, transmitting and receiving point are easly separated, so the system is effective for SFN.
This paper proposes a novel WDM hypercube network (WDM-HCN) architecture. The proposed network uses cyclic-frequency arrayed waveguide grating routers (AWGs), wavelength-band multiplexier/demultiplexiers, and TDM-WDM converters to form a hierarchical network configuration. The network enables us to realize a large scale HCN with small AWGs as building blocks and a small number of wavelengths. The paper shows a 12 dimensional WDM-HCN with 4, 096 nodes is achievable using the currently available technology such as 16-port AWGs and 32 wavelength WDM.