Microcrystalline silicon embedded in silicon oxide has been prepared by means of a wet oxidation of porous silicon (PS) anodically produced from degenerate Si wafers in a HF solution. As the oxidation proceeded, optical absorptions of the PS specimen in the visible light region shifted obviously to the higher energy side. Visible light emission from the oxidized specimen was observed at room temperature with photoexcitation by a He-Cd laser while the as-prepared specimen emitted no visible lights. These results are discussed in relation to the quantum size effect of the microcrystalline silicon confined in the oxide matrix as well as visible emissions from as-prepared specimens produced from non-degenerate Si wafers.

The essential functions of the passive double star (PDS) system are clarified by comparing them to the functions of the single star (SS) and the active double star (ADS) system. A layered structure describing the functional characteristics of the PDS system is proposed for flexible transport capability. The functions of the optical network unit (ONU) on the customer premises are systematically partitioned into four layers. The functions of the optical subscriber unit (OSU) in the central office are described using five layers. Call by call activation and deactivation techniques are described on the basis of a layered architecture. The reduction of ONU power consumption by adopting activation and deactivation control is also discussed.

Optical fiber cable systems are being developed in many countries for subscriber loops as the infrastructure to realize B-ISDN (Broadband Integrated Services Digital Network). The present systems are DLC (Digital Loop Carrier) systems which provide leased lines, POTS (Plain Old Telephone Services), and N-ISDN (Narrowband ISDN) services. Before FTTH (Fiber To The Home) networks can be implemented, their construction cost must be lowered to the level of the current metallic network. The FTTH network must also be easy to operate and maintain. In this paper, we describe optical fiber cables, splicing, and testing technologies used in the NTT cable networks, and introduce the technologies being developed to construct FTTH networks.

Subscriber network opticalization is the key issue for the next generation network. Fiber-optic systems have been limited to mainly big business applications, so far. Massive opticalization including home and small business customers remains the ultimate goal. Opticalization of the subscriber network needs an enormous investment and a long construction period. In order to achieve smooth evolution towards B-ISDN, the subscriber network must be effectively opticalized well in advance of full B-ISDN deployment. This paper presents the development concept of optical subscriber network. It also describes the design concept and configuration of fiber-optic subscriber systems. Deployment strategies and the developing technologies for the future subscriber network are also addressed.

We will introduce W-trees of a W-graph which is a graph containing wild components. A wild component is an incompletely defined subgraph which is known to be a tree but what kind of the tree is unspecified. W-tree is defined as a set of edges and vertices of wild components obtained from a non-sigular major submatrix of a W-incidence matrix. The properties of a W-tree are useful for studying linear independent W-cutsets and so on in a W-graph.

In case of the system identification problem, such as an echo canceller, estimated impulse response obtained by the frequency-domain adaptive filter based on the circular convolution has estimation error because the unknown system is based on the linear convolution in the time domain. In this correspondence, we consider a sufficient condition to reduce the estimation error.

This letter proposes an active reflector for calibrating a synthetic aperture radar (SAR), in which the frequency of a received SAR signal is shifted by a certain amount and then it is retransmitted to the SAR. The frequency shift causes a shift of the reflector SAR image in an azimuth direction relative to its background. This function would allow to enhance a signal-to-clutter ratio of the reflector image by moving it onto a radiometrically dark background, and hence it would be of value for SAR calibration even in a narrow test site. The theory, design and development are described briefly.

Among the many fabrication methods for oxide superconductor films, metal organic chemical vapor deposition (MOCVD) is particularly suitable for industrial application because of its mass productivity and the low growth temperature. Therefore we have studied this technique using the horizontal cold wall furnace type MOCVD method to obtain high quality superconducting films. As the result, we have succeeded in fabricating YBa2Cu3Oy films which have high critical temperatures (over 80 K) under substrate temperatures as low as 700 without post-annealing. But, in the course of our experiments, it was found that the thicknesses of YBa2Cu3Oy films fabricated by MOCVD were not uniform. The cause of this non-uniformity is believed to be that the deposition rate exponentially falls off along the flow direction because of the decrease of the source gas concentration through the reaction. In this paper, this non-uniformity is analytically studied. It is shown that the deposition rate decrease can be controlled with a tapered inner tube, and that these theoretical results are in good agreement with the results of experiment. In addition, it is indicated that the superconducting property of the films has less dependence on substrate position as a result of the tapered inner tube.

We have fabricated superconducting microwave passive components such as resonators, bandpass filters and delay lines with YBCO thin film conductors deposited on MgO substrates. Considerably high unloaded Q values of 12000 at 5.5 GHz was obtained with the YBCO microstrip resonator at 77 K, which indicated that the surface resistance of the YBCO thin film was 0.79 mΩ at that frequency and temperature. Excellent microwave properties were also demonstrated with the bandpass filter and the delay line. Considerably low insertion loss of about 1 dB was obtained with the 10 GHz YBCO bandpass filters at 77 K which have a various bandwidth from 0.5% to 10%. Also excellent microwave propagation was obtained with a 1.3 nsec YBCO coplanar delay line. Its insertion loss was less than 1 dB for the frequencies up to 4 GHz.

The authors design a simple feed system for a planar slotted waveguide array. A waveguide π-junction with negligible reflection is cascaded to compose a multiple-way power divider. The frequency characteristics of the power divided to each port and the reflection at the feed point are discussed and high performances are predicted. The maximum number of cascaded junctions in this system can be determined in terms of a desired frequency bandwidth and allowable deviation in divided power.

This paper proposes a high resolution and fast frequency settling PLL synthesizer for frequency hopping radio communication equipment. The proposed synthesizer enables the carrier frequency to be changed within the duration of a burst signal and yields higher frequency resolution than the reference signal frequency. To reduce frequency settling time without degradation of frequency resolution and phase noise, this paper proposes a new phase and frequency preset (PEP) PLL synthesizer which employs a digital phase accumulator to generate high resolution reference signal. Experimental results show that the settling time of a prototype synthesizer is less than 300µs while spurious signals are suppressed by more than 55 dB. In comparison with conventional PLL synthesizers, the frequency settling time is reduced by 80%. Furthermore, the higher frequency resolution than the reference signal is successfully demonstrated. Therefore, the proposed PFP PLL synthesizer with the digital reference signal can achieve the output signal with high frequency resolution less than 1Hz.

The DSD (Double Soft Decision) concatenated forward error correction scheme is proposed to realize a higher-coding-gain forward error correction system with simple hardware. The novel scheme soft decision decodes inner codes as well as outer codes. In this scheme, likelihood information from an inner Viterbi decoder is used for the decoding of outer codes. Path memory circuit status 1,0 ratio is newly proposed as a measure of likelihood information and it is shown that this method is the most reliable even though it has the simplest hardware among the alternative likelihood information extracting methods. Computer simulation clarifies that the proposed DSD scheme improves Pe performance to one-third that of the conventional hard decision outer decoding.

This paper proposes a next-generation narrow-band ISDN (N-ISDN), including a suitable network and network node architecture. The proposed N-ISDN allows every subscriber to use H0/HI-class calls as easily as present telephone calls, and could rapidly expand ISDN services to all the subscribers of a public network. The present status of ISDN is first analyzed then the need for popularization of H0/HI-call services is discussed. The proposed key technologies to popularize HO/HI services are (1) on-chip integration of ISDN switching systems, (2) distribution of small on-chip switching systems over the subscriber switching area, (3) H0-based trunk circuit networks using H0 on-chip switching systems and (4) efficient and flexible call management for 64-kb/s basic-class calls. An estimation of hardware volume of switching nodes is used to show that the proposed architecture is more economical than other possible alternatives, i.e. conventional ISDN and B-ISDN.

The transmission of 8-bit µ-law PCM signals using 16-level weighted QAM over Gaussian channels is examined. The weighting process modifies the positions of the QAM constellation points so that the overall distortion in the recovered information-bearing source signal is reduced. The PCM bits are mapped to the weighted QAM points such that the most significant bits have a lower probability of being in error than the least significant bits. The weighted QAM systems have been optimized for the same energy signal energy per transmitted symbol as for unweighted QAM. Also, the erasure zone is established at the detector, such that if the output falls into the erasure zone, the regenerated sample is replaced by interpolation. The theoretical results indicates that 16-level weighted QAM have a gain of 5dB over unweighted QAM.

As the size and complexity of network increases, the distributed systems management (DSM) will be vital in order to improve the availability of network management, to reduce the complexity of network operations, and to provide the high reliability. In this paper, we (1) describe general requirements required for systems management in distributed environment, (2) introduce the basic structure of distributed network management system (DNMS) for efficient network management, and also especially illustrate the concrete design of system management application process which is an important element among them, (3) propose the connectionless CMIP to accomplish for effectively managing the distributed management system, and indicate its efficiency; this protocol is available to manage dynamically changing DSM environment, to negotiate among the managing systems, to handle the dynamic informations etc. Finally, (4) the behavior and software structure of a suggested management system during negotiation to execute the received request for implementation are presented.

This paper analyzes the performance of an ATM cell multiplexer with a two level MMPP input on a discrete-time basis. We approximated the input process as a simple MMPP model. We developed an MMPP/D/1/K queueing model for the ATM cell multiplexer, and employed an analytic approach for the evaluation of cell loss probability. We verified the accuracy of the results using computer simulation. We applied the above analytic method to connection admission control (CAC) of the ATM network. The resulting connection admission control scheme employs the concept of the "effective bandwidth" and table-look-up procedure. We confirmed through a computer simulation that the proposed connection admission control scheme outperforms the peak bandwidth allocation scheme with respect to link utilization.

This paper describes the structure and properties of superconductive small antennas with thin-film matching circuits. These circuits make it possible to realize small antennas, 38 mm20 mm16 mm in size. This is one quarter the length of our previously reported ceramic antennas. The actual gain of this antennas was -4.5 dBi at 470 MHz. This value is 5.5 dB higher than that of Cu antennas with exactly the same structure.

The inherent simplicity of the LMS (Least Mean Square) Algorithm has lead to its wide usage. However, it is well known that high speed convergence and low final misadjustment cannot be realized simultaneously by the conventional LMS method. To overcome this trade-off problem, a new adaptive algorithm using Multiple ADF's (Adaptive Digital Filters) is proposed. The proposed algorithm modifies coefficients using multiple gradient vectors of the squared error, which are computed at different points on the performance surface. First, the proposed algorithm using 2 ADF's is discussed. Simulation results show that both high speed convergence and low final misadjustment can be realized. The computation time of this proposed algorithm is nearly as much as that of LMS if parallel processing techniques are used. Moreover, the proposed algorithm using more than 2 ADF's is discussed. It is understood that if more than 2 ADF's are used, further improvement in the convergence speed in not realized, but a reduction of the final misadjustment and an improvement in the stability are realized. Finally, a method which can improve the convergence property in the presence of correlated input is discussed. It is indicated that using priori knowledge and matrix transformation, the convergence property is quite improved even when a strongly correlated signal input is applied.

Generalized telegraphist's equations for waveguides are frequently used for analyzing fields in tapered rectangular waveguides. However, the telegraphist's equations do not give exact fields in E-plane tapers of the rectangular waveguides. In this letter, the new telegraphist's equations are shown, and the equations give the fields which exactly satisfy Maxwell's equations and the boundary conditions for the E-plane taper of the waveguide.

Thin-film YBCO Josephson junctions were successfully fabricated by a pulsed excimer laser ablation, and the mixing experiments in the microwave region (820 GHz) were carried out at the temperature of 77 K. The IF output maximum was obtained at the bias voltage midway between the zero and the first Shapiro steps for the fundamental mixing. For the 2nd harmocic mixing, the IF output maximum was obtained at a zero bias voltage, and the conversion efficiency was -14 dB at the microwave frequency of 18 GHz. These results strongly suggest that the fabricated thin-film Josephson junctions work well at the temperature of 77 K as detectors and mixers in the microwave regions (820 GHz).