This paper describes theoretical analyses of a new CRV (Code Rule Violation) collision detection method applicable to an optical CSMA/CD LANs. The new method is based on the ideas combining a partial response (1,0, --1) circuit with the basic CRV collision detection method; the ideas are proposed in IEEE 802.3 committee. The circuit configuration of the new method, however, is different from that proposed in IEEE 802.3 committee. First, the paper outlines the basic CRV collision detection method and shows the problem that it can't detect a collision when identical bits are continuously received. Secondly, a practical circuit configuration of the new method is introduced. To realize large optical dynamic range and stability in collision detection, the circuit is designed not to detect CRVs on noisy zero level signals caused by signal negation with partial response circuits. The calculation formulae are then derived for the basic and the new method to determine the CRV rate with and without signal collision. At a bit rate of 10Mb/s, the CRV rate with and without signal collision is then calculated for the basic and the new method. Finally, the calculation results are compared with each other, and it is clarified that the new method is an effective method to increase CRV rate when signal collision occurs.

Polyvinyl alcohol gel (PVA gel) has been applied in various fields as a biomedical material in Japan since the mechanical and the electrical characteristics are very similar to the human body. In this paper, the electrical characteristics of the electrode coated with PVA gel containing saline solution are described. The electrode has been applied to a stimulation electrode in an extracochlear prosthesis. It is expected that the coated electrode can stick to the round window membrane without scarring it. From the experimental results, is was found that the electrical impedance of a stimulation electrode coated with PVA gel exhibited good stability and the effective double-layer capacitance of the coated electrode was less dependent on the current than the capacitance of the Pt-Ir electrode. The electrical characteristics of the PVA electrode were proved to be very stable for long term use in-vivo. The coated electrode was ascertained to be able stimulate reliably the auditory nerves of a guinea pig.

It is known that the moments of the cepstrum of a mixed phase signal sequence can be calculated without directly calculating the cepstrum, avoiding the phase unwrapping algorithm and the aliasing error etc. Using this, moments of cepstrum of the minimum phase sequence are calculated from the linear phase sequence without actually calculating the minimum phase sequence.

UM codes, which are block-oriented convolutional codes with branches as long as a block code, are known to possess large minimum distances compared to the ordinary convolutional codes, but optimal decoding of UM codes is generally quite difficult since the number of decoder states is an exponential function of the branch length. In this paper, a class of UM codes which are partially decodable with block decoders, termed the PBD-UM code, is investigated and shown to be effective. Such a code, for example, can be constructed from the BCH code and decoded by a decoder consisting of a number of BCH decoders. Since the BCH code is easy to decode, the PBD-UM code constructed in this manner, is also relatively easy to decode. As a specific example, a decoding scheme based on Tanaka's step-by-step soft-decision decoding algorithm is proposed and investigated through simulation.

This paper analyzes the delay performance of 1-persistent CSMA/CD LANs with bus topology and a finite number of heterogeneous stations, each possessing an infinite buffer. The mean waiting time at each individual station is obtained under a light-traffic assumption that the channel is occupied only by successful transmission periods. It is shown that the stations near the heavy-traffic stations gain better performance among light stations and the extent to which the individual delays differ depends on the network configuration as well as the protocol parameters.

Corporate information communication systems are recently orienting the integration of various kinds of communication services. A PBX and a LAN have been indispensable in the realization of these systems. Some PBXs are orienting towards distributed switching architecture, and LAN systems are increasing their scale. Both requirements can be realized by means of a high speed loop optical fiber network. An integrated LAN should satisfy the required performance as a multimedia LAN and should be provided self-healing functions which heal failures automatically, to enable continuous operation of the entire system. This paper introduces a multimedia LAN, which attaches importance to the self-healing functions, called SHM-LAN. Its system architecture and its characteristics, such as efficient channel allocation are presented. This paper also deals with the self-healing functions and some applications.

This paper describes the implementation types of private networks from the viewpoint of equipment and users, and utilization trends from low to high-speed services. Technology trends of private networks from the viewpoint of high-speed and broadband communication, multimedia communication, media access methods and intelligent communication are also examined. A concept for implementing future private networks in the Broadband ISDN (B-ISDN) age, and the major technology and the future efforts to achieve this implementation are discussed. Asynchronous Transfer Mode (ATM) is shown to be the key technology for integrating both various and heavy traffic media communication.

This paper is a discussion of the utilization of a campus network at Shinshu University called S-net. S-net was constructed and put into use in 1985, and a total of 48,734 persons made use of S-net in 1990. The structure of S-net is explained and then a description of its current layout is presented. The transmission capabilities of S-net are investigated and the state of utilization of the network is described. The number of S-net users by hour forms a distribution which peaks at 4:00 p.m. and again at 10:00 p.m. Furthermore, a questionnaire survey among S-net users was conducted and the requests and requirements expressed pertaining to the campus network are presented. From these results it can be seen that the demands on the campus network are great. And it was revealed that although a strong desire was voiced on one hand for improvements in the present user environment, requests concerning multi-media networks or connections to off-campus networks exist as well. Finally, the points of improvement of future S-nets based on the opinions and suggestions of the users and six years of actual operating experience with S-net are discussed.

The Fourier series expansion method is applied to the problem of EM waves guided by a dielectric grating with periodic surface-relief. The periodic structures of dielectric gratings are divided into two types: (1) surface-relief type and (2) modulated refractive index type. For the modulated dielectric grating, the rigorous solution is obtained using the space-harmonics expansion method, but the usual method cannot be applied to the grating whose dielectric constant distribution has discontinuities. Previously, we pointed out this issue and gave an improved method which can be applied to those problems. This method can also be applied to the surface-relief grating by approximating it as an assembly of stratified thin modulated dielectric gratings. In this paper, numerical analysis is given for gratings with sinusoidal surface and triangular surface for both perpendicular polarization (TE waves) and parallel polarization (TM waves). The validity of our method has been checked by increasing the number of modal expansion terms and the number of multilayers. The results are compared with those obtained by other numerical methods. The differences in the propagation characteristics between the surface-relief grating and the modulated dielectric grating in Bragg region are also discussed.

This paper proposes a new service scheme which multiplexes several independent sub-documents onto the main document in a conventional facsimile broadcasting system. These multiplexed facsimile signals are moreover unified besides the voice channels in television system. The scheme does not increase the amount of facsimile signals, thus, it can save the frequency resources and communication channels. In this system, the main facsimile document is open for common subscribers, but the multiplexed sub-documents are delivered only for the special subscribers who are registered to the broadcasting station for each channel.

This letter deals with the problem of assigning tasks to the processors of a distributed computing system such that the sum of execution and communication costs is minimized. If the number of processors is two, this problem can be solved efficiently using the network flow approach pioneered by Stone. This problem is, however, known to be NP-complete in the general case, and thus intractable for systems with a large number of processors. Recently, an optimal algorithm with the time complexity of O(n2m3 log n) has been suggested for the problem of assigning m interacting tasks to a linear array of n processors. They solved the problem by using the two-terminal network flow approach. In this letter, we propose a multiterminal network flow approach for the task assignment problem in homogeneous linear array networks. The task assignment problem for a homogeneous linear array network of n processors is first transformed into (n-1) two-terminal network flow problems, and then solved in time no worse than O(nm3) by applying the Goldberg-Tarjan's network flow algorithm for each two-terminal network flow problem.

Tunable fiber lasers with ring resonator structure were reported in this paper. A tunable fiber directional coupler links the rear-earth-doped single-mode fiber to from a ring resonator. Laser oscillation should occur in the fiber ring cavity when the rear-earth ions in the fiber are excited by a pumping light. The losses of the directional coupler and rear-earth-doped fiber are very small so that the fiber ring laser has low threshold and high slope efficiency. In this fiber ring laser, the directional coupler plays three functions of transmitting pumping light, coupling lasing oscillation and tuning laser wavelength. We have used both Nd3+-doped and Er3+-doped single-mode fiber to fabricate the tunable fiber ring lasers. An argon ion laser was used as the pump source. For the Nd3+-doped fiber ring lasers with cavity lengths of 3 meters and 5 meters, the lasing threshold were 0.8 mW and 4.9 mW respectively at the lasing wavelength of 1.088 nm. The highest slope efficiency was about 30%. The laser wavelength could be tuned continuously in the Nd3+ fluorescent spectrum and the tunning range is greater than 60 nm. The Er3+-doped fiber ring lasers had the cavity lengths of 1 meter and 8 meters, lasing at 1550 nm with a tuning range of about 70 nm, the thresholds were 1.9 mW and 14.2 mW and the slope efficiencies were 6.1% and 10.2% respectively. A novel fiber ring laser with single-longitudinal-mode output was demonstrated. This fiber laser has a composite resonator which is composed of two subrings. Longitudinal mode is selected in the subrings coupled each other. A laser linewidth less than 40 MHz was got from the Nd3+-doped fiber ring laser.

The diffraction of a plane electromagnetic wave by a perfectly-conducting finite sinusoidal grating is analyzed using the Wiener-Hopf technique combined with the perturbation method. Assuming the depth of the grating to be small compared with the wavelength and approximating the boundary condition on the grating surface, the problem is reduced to that of the diffraction by a flat strip with a certain mixed boundary condition. Introducing a perturbation expansion for the unknown scattered field under the small-depth approximation, the problem is formulated in terms of the zero order and the first order Wiener-Hopf equations, which are solved exactly in a formal sense by a factorization and decomposition procedure. Applying a rigorous asymptotics, explicit high-frequency asymptotic solutions are further obtained for the width of the grating large compared with the wavelength. Scattered far field expressions are derived by taking the inverse Fourier transform are applying the saddle point method. Representative numerical examples of the far field patterns are given for various physical parameters, and the scattering characteristics of the grating are discussed.

A mode-matching method in the sense of least squares is applied for analyzing grating couplers having various groove shapes. These couplers are formed on surfaces of core regions of the thin-film waveguides and their periodic parts extend finitely. The grating couplers are analyzed for the plane wave incidence when the Bragg condition is satisfied. The discussion is developed about the grating coupler which is formed on the asymmetric waveguide and has arbitrary triangular grooves. However various couplers, which have triangular, rectangular and sinusoidal grooves and are formed on asymmetric and symmetric waveguides, are analyzed and results for them are presented in this paper. The approximate scattered fields of each region of the coupler are described by the superpositions of the plane waves with band-limited spectra, respectively. These approximate wave functions are determined by the minimization of the mean-square boundary residual. This method results in the simultaneous Fredholm type integral equations of the second kind for these spectra. Results of analyses based on the first order approximate solutions are presented. The comparison between each coupling efficiency derived by the present method for couplers having sinusoidal, triangular and rectangular grooves is presented in this paper.

This paper discusses an efficient numerical calculation technique for scattering from three dimensional bodies of perfect conductors and dielectric materials. The key of this method is to express the scattering fields by the field generated by the distributed hypothetical dipoles (or the equivalent sources). Since the scattered field should be analytic in each homogeneous sub-domain of general scattering bodies, the equivalent sources to be used for expressing the scattered field in one of those sub-domains should be distributed outside of this space domain. Unknown vector currents of equivalent dipoles are solved by the generalized mode-matching method. Example scatterers discussed here are finite conducting and dielectric cylinders with rotationary symmetry. The results are discussed with comparative data obtained by other numerical method and also with experiments that we took.

An analytical theory of the quasi LP-modes in anisotropic optical fibres with a homogeneous circular core and homogeneous cladding is developed. Analytical expressions for the quasi LP-mode fields are obtained by the separated variable method and by the perturbation method under the following conditions. The Cartesian permittivity tensors of the core and cladding are diagonal and have the same orientation in the crosssection of the fibre. The longitudinal components of these permittivity tensors are equal, and the differences between the transversal and longitudinal components of these tensors are sufficiently small. The transversal components of the quasi LP-mode fields are derived from Maxwell's equations in the linear approximation on these differences. Solutions of the mode characteristic equation for the quasi LP-modes are reduced to the known solutions of the characteristic equation for the LP-modes in the isotropic optical fibre.

A design method to realize the large modal birefringence and the low dispersion (within 2 ps/km/nm) over the spectral range 1.30-1.55µm is investigated for the polarization-maintaining optical fibers with the crescent or circular hollow pits. When the low dispersion is satisfied for the HE11o mode, one of two orthogonally polarized HE11 modes, it is found that (1) the crescent pits type has a larger modal birefringence than the circular pits type for Δ11.21% (Δ1: the relative index difference), and (2) the maximum modal birefringence of the crescent pits type is nearly equal to that of the circular pits type for Δ11.21%.

Generally speaking, a field generated by a current located on any surface depends on the shape of the surface and the current value and its distribution. The main idea discussed below is based on the existence of such surfaces for which a certain property of fields generated by currents distributed on these surfaces does not depend on the currents and is fully and soley determined by the surfaces. This is such a property that any complete system of functions generates an incomplete system of fields. This means that it is impossible not only to realize but even to approximate any given field by the generated field if the given field does not satisfy this condition. In this case, the corresponding inverse problem of the approximate current synthesis is not solvable. Practical results have been received for the horn construction, the determination of the scattering body shape and so on.

Codes having order-K spectral density nulls, i.e., codes such that the power spectral density of the encoded sequences and its first 2K-1 derivatives vanish at rational submultiples f of the symbol frequency are investigated. Several necessary and sufficient conditions for a code to have an order-K spectral density null at f are given. A lower bound on the minimum Euclidean distance of a code with an integer alphabet and with an order-K spectral density null also is derived. Canonical diagrams for higher order spectral density nulls and nonzero spectral lines are introduced.

This paper proposes () an algorithm that dynamically constructs an asymptotically-balanced binary tree to store successively-given keys without knowledge of the distribution of key occurence, and () another algorithm for quick key search over the constructed tree such that: If the tree has in memory at least a key that is inside the Δ-neighbor (in a Hamming space) of a reference key, then the algorithm can find one of such Δ-neighbor keys almost with probability 1. The memory capacity required to describe a tree in the tree construction algorithm is of order being proportional to the number l of keys already processed. For an independently and idenically distributed binary source of generating keys, the mean computation time required to update a tree for every key input can be of an order being a little higher than (log2l)2log2(log2l), and that required to search a Δ-neighbor key can be of an order being a little higher than (log2l)3.