In most of the methods proposed so far to design approximately linear phase IIR digital filters (IIR DFs), the design takes place only in the time or in the frequency domain. However, when both magnitude and phase responses are considered, IIR DFs with better frequency responses can be obtained if their characteristics in both domains are taken into account. This paper proposes a design method for approximately linear phase IIR DFs, which is based on parameter estimation techniques in the time domain followed by a nonlinear optimization algorithm in the frequency domain. Several examples are presented, illustrating the proposed method.

This article proposes, given an independently-and-identically distributed binary source, an arithmetic code-like variable-to-variable length source code whose compression efficiency achieves nearly the rate function in a range of small distortion. Inheriting advantages of arithmetic codes, the proposed code requires neither large memory capacity nor large computation time for management of messages and codewords. The Elias code, which can be regarded as an antecedent of arithmetic codes, is defined originally in terms of the first-in-first-out (FIFO) coding form. The proposed code corresponds to an extension from the Elias code refined in terms of the last-in-first-out (LIFO) coding form into one considered a fidelity criterion.

The a-Si films deposited on quartz substrates were crystallized by lateral sweep annealing in steep temperature gradient using a gas burner. Random nucleation in amorphous region was effectively suppressed in the temperature gradient, so lateral solid phase epitaxial growth from crystallites generated at the initial stage of lateral sweep annealing spread over 100 µm. Their crystallographic orientations were mostly (100).

After the intrinsic pulsed light illumination, a transient negative photoconductivity (TRANP) was observed in silicon doped with gold. The ambient temperature dependence of the TRANP-current was measured and compared with the simulated results obtained by solving rate equations. The temperature dependence of the peak value of the TRANP-current was in agreement with the simulated result. The activation energy of gold acceptor level obtained from the time constant in the recovery process was also consistent with the simulation. It was cleared from this result that the recovery process is dominated by the electron re-emission from gold acceptor level to the conduction band. It was concluded that the occurrence of the TRANP is well explained by using our model proposed before.

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.

It often occurs in the acoustic environment that a specific signal is contaminated by the additional noise of non-Gaussian distribution type. In order to extract exactly the various statistical information of only specific signal from the observed noisy data, a stochastic signal processing by use of digital computer is essential. In this study, a stochastic method for estimating the probability function of the specific signal embedded in the additional noise is first theoretically proposed in a suitable form for the quantized level observation. Then, the effectiveness of the proposed method is experimentally confirmed by applying it to the observed data in the acoustic environment.

In the maximum-likelihood decoding under a non-Gaussian noise, the decoding region is bounded by complex curves instead of a perpendicular bisector corresponding to the Gaussian noise. Therefore, the error rate is not evaluated by the Euclidean distance. The Bhattacharyya distance is adopted since it can evaluate the error performance for a noise with an arbitrary distribution. Upper bound formulae of a bit error rate and an event error rate are obtained based on the error-weight-profile method proposed by Zehavi and Wolf. The method is modified for a non-Gaussian channel by using the Bhattacharyya distance instead of the Euclidean distance. To determine the optimum code for an impulsive noise channel, the upper bound of the bit error rate is calculated for each code having an encoder with given shift-register lehgth. The best code is selected as that having the minimum upper bound of the bit error rate. This method needs much computation time especially for a code with a long shift-register. To lighten the computation burden, a suboptimum search is also attempted. For an impulsive noise, modeled from an observation in digital subscriber loops, an optimum or suboptimum code is searched for among codes having encoders with a shift-register of up to 4 bits. By using a code with a 4-bit encoder, a coding gain of 20 dB is obtained at the bit error rate 10-5. It is 11 dB more than that obtained by Ungerboeck's code.

A new image restoration filter based upon a physical model of an image degradation is constructed. By means of this filter, signal dependent noise and blur can be suppressed. In particular, image degradation noise can be modeled in generalized form. Noise suppression and deblurring are performed separately. This filter has additional applications when used in conjunction with the degradation model, such as real photographic images and photoelectronic images. Simulation results show that this filter gives a superior performance in restoring an image degraded by signal dependent noise and blur.

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.

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.

Surface damage to n-type silicon wafers induced by Reactive Ion Etching (RIE) with CF4 gas was evaluated using X-ray photoelectron spectroscopy (XPS) and the current-voltage (I-V) characteristics of Au/n-Si Schottky diodes fabricated on the damaged surface. The reaction products (SiF, SiF2, and SiF3) in the damaged layer were detected by XPS. Assuming the surface damage on a silicon wafer induced by RIE acts as a donor, the donor density was found to be about 21019 cm-3. The distribution of SiF3 and the donor density in the depth direction were almost equal. The thickness of the damaged layer was about 15 nm. These findings suggest that the donor in the damaged layer on a silicon surface induced by RIE may be SiF3.

This paper first discusses the software reusability-based development process in a lifecycle and reusable objects modification process called differentiation. Next, the supporting environment is described. Both the method and the environment allow developers to carry out requirement definitions, specification and implementation in a reusable way. Some quantitative evaluations are given about how productivity and quality have been improved by using this method and environment, based on a number of case studies made on development projects. Reusability has been largely improved by differential specification, and adjustment method and a direct transformation capability.

A specification formalism for business application software is presented. Our approach is to investigate specification documents which are actually used in development projects of business applications in banking, insurance, and government systems. Since the specification documents are prepared mainly for users' review for the developing software, the representation of the documents is designed to be easy to understand for users, only in business terminology without losing a certain level of formality. Also, to avoid redundancy of the specification, there are some implicit assumptions in the specification. We have analyzed some commonality of these assumptions hidden in specification documents and are trying to construct a language by formalizing the underlying system model.

Thin Si films grown on anodized porous silicon have been characterized using a high-energy ion scattering technique with related simulations of MeV ions in solids. It turned out that the simulations are necessary and very usuful for quantitative and nondestractive analysis of thin films with thicknesses less than 100 nm. In the case of the epitaxial Si films examined, it is often insufficient for the characterization of crystalline quality to measure only the channeling minimum yield, and therefore, it is emphasized that angular scans over the critical angle in the vicinity of a channeling direction must be performed for the analysis of possible imperfections in thin films. The possible imperfections observed in the epitaxial specimen are treated quantitatively.

In this paper, a new M-estimation technique for the linear prediction analysis of speech is proposed. Since in the conventional linear prediction (CLP) method the obtained estimates are very much affected by the large amplitude residual parts, in the proposed method we use a loss function which assigns large weighting factor for small amplitude residuals and small weighting factor for large amplitude residuals which is for instance caused by the pitch excitations. The loss function is based on the assumption that the residual signal has an independent and identical t-distribution t(α) with α degrees of freedom. The efficiency of this new estimator depends on α. When α=, we get the CLP method. When the proposed method with small α is applied to the problems of estimating the formant frequencies and bandwidths of the synthetic speech by finding the roots of the prediction polynomial, we can achieve a more accurate and a smaller standard deviation (SD) estimate than that with large α. When the signal is very spiky, the proposed method can ahieve more efficient and accurate estimates than that with robust linear prediction (RBLP) method. The loss function is modified in the similar manner as the autocorrelation method. The solution is calculated by the Newton-Raphson iteration technique. The simulation results show that only few iterations are needed to reach a stationary point, the stationary point is always a local minimum and the obtained prediction filter is always minimum phase. Preliminary experiments on the human speech data indicate that the obtained results are insensitive to the placement of the analysis window and a higher spectral resolution than the CLP and RBLP method can be achieved.

A Ge/Si structure grown by chemical vapor deposition (CVD) is angle-lapped and characterized by the micro-Raman spectroscopy. Near the interface, the phonon mode due to the Si-Ge bond is clearly observed, which indicates that a SiGe alloy is formed by the solid-phase interdiffusion at the interface. The thickness of the interfacial alloy layer is about 0.2 µm. Amount of residual strain is estimated by comparing the measured phonon frequencies with those predicted from the composition profie, but the shift due to the residual strain is not appreciable. Both the interdiffusion at the interface and the nearly complete relaxation of the lattice mismatch are attributed to the high growth temperature of the CVD sample.

The quality of polycrystalline silicon films and electrical characteristics of polycrystalline silicon gate metal-oxide-semiconductor (MOS) capacitors were investigated under various processing conditions, including phosphorus doping. The stresses observed in Si films deposited in the amorphous phase show complex behavior during thermal treatment. The stresses in as-deposited Si films are compressive. They change to tensile with annealing at 800, and to compressive after an additional annealing at 900. The kind of charges trapped in the SiO2 film during the negative constant current stress in Polycrystalline silicon gate MOS capacitors differ with the maximum process temperature. The trapped charges of samples annealed at 800 were negative, while those of samples annealed at 900 were positive.

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.

Silicon nitride (SiNx) films have been deposited at lower substrate temperatures (500) by direct (without mercury-sensitization) photo-chemical vapor deposition (photo-CVD) using SiH4 and NH3 with a low-pressure mercury lamp. Films deposited at around 350 have a polymeric structure such as (Si(NH)2)n. Films deposited at 500 were close to stoichiometric Si3N4 with a slight amount of hydrogen. The refractive index and the dielectric constant of films deposited at 500 became almost equal to the values of thermally synthesized Si3N4. The resistivity was as high as 51016 Ωcm. The minimum density of interface states in Al/SiNx/Si MIS (metal-insulator-semiconductor) diodes was estimated to be 91010 cm-2eV-1 by a quasi-static capacitance-voltage measurement. For SiNx films deposited at 300, the density of interface states, which was in the order of 1011 cm-2eV-1 as deposited, decreased by a rapid thermal anneal after the deposition. For Al/SiNx/InP MIS diodes, it was 31011 cm-2eV-1 by high-frequency capacitance-voltage measurements. Direct photo-CVD for SiNx films is promising for low-temperature formation of a gate insulator.

Diffusion of phosphorus impurities from a polycrystalline silicon films into a silicon substrate was investigated as a function of the mean concentration of phosphorus in a polycrystalline silicon film at the first diffusion stage. We presented that good control of the redistribution of implanted phosphorus impurities was possible by optimizing the normalized dose, which is the value: [the total dose of phosphorus impurities]/[the polycrystalline silicon film thickness], in the case of samples both with and without an arsenic doped layers. In the range where the normalized dose was less than 1.52.51020 cm-3, deeper junctions were formed in samples with an arsenic doped layer. In the range where the normalized dose was more than 1.52.51020 cm-3, however, deeper junctions were formed in samples without any arsenic doped layer rather than in samples with an arsenic doped layer. These results mean that formation of the junction in the device structure where a high concentration phosphorus doped polysilicon layer is stacked on to the high concentration arsenic layer embeded at the surface of the substrate can be restricted by optimizing the normalized dose. Moreover, a trade-off relationship between suppressing phosphorus diffusion and maintaining low contact resistance against normalized doses was also observed.