Theoretical prediction of propagation is required for the future urban mobile communications, in order to make possible precise and universal prediction for arbitrary conditions. The necessity and the fundamental concept of theoretical prediction are introduced, and the theoretical prediction of mean field strength in urban areas is reviewed and discussed. Theoretical method is important particularly in prediction of multipath delay characteristics, in relation to the prediction of error rates in digital mobile radio communications.

An optical On-Off Keyed (OOK) pulse is often stretched in dispersive channels, thus producing intersymbol interference (ISI) and degrading the performance. In this paper, error probability is presented for a convolutionally encoded optical OOK channels with ISI. Both ISI-matched and ISI-mismatched decoders are taken into account in the error probability analysis. The encoded optical OOK signal is received by Avalanche Photo Diode (APD) and the number of APD output photo-electrons is counted for soft decision Viterbi decoding. Error probability is derived for a 3-bit and an ideal soft decision schemes in ISI-mismatched decoder and for an ideal soft decision scheme in ISI-matched decoder. Numerical results demonstrate the effects of mismatching or 3-bit soft decision scheme. Some computer simulations are carried out to confirm the validity of the analysis.

Power-law decay of current for the application of step-function voltage observed for amorphous materials can be expressed by an admittance sa(0a1) of a linear diode using complex angular frequency s. It is shown that power-law decay can be interpreted as a superposition of exponential decays having fractally distributed relaxation times and simulated using RC networks. By use of a similar manner, admittance s-b (0b1) showing the relation of duality can be simulated using RL networks. According to these methods, we can synthesize the admittance involving non-integer exponents systematically.

Compared to multi-level signature file techniques, PSF (Partitioned Signature File) technique has less processing overhead by its characteristics of a simple file organization. In a multi-processor environment, the PSF technique also has an advantage that queries can be processed in parallel effectively by allocating one or more partitions to each processor. Main point of the PSF technique is a partitioning scheme based on a key selection. In this paper, an n-BFK (n-Bounded Floating Key) partitioning scheme is proposed, in which the number of segments for a key selection is bounded by n. The cost model is developed for the performance evaluation of the proposed scheme. By performance comparison with the existing schemes, the efficiencies of the proposed scheme are shown with respect to a disk access cost, a signature reduction ratio, and an uniformity of workload.

In this paper, we study the performance of convolutional coding using an error-and-erasure correction Viterbi decoder for π/4-shift QDPSK mobile radio transmission. The receiver uses received signal envelope as channel state information to erase unreliable symbols instead of making explicit decision before decoding. The performance study is carried out over frequency-selective fading channel with additive white Gaussian noise, co-channel interference and propagation delay spread. The results show that decoding with symbol erasure can significantly improve the system transmission performance compared to decoding without symbol erasure.

We propose a direct-sequence spread-spectrum multi-access (DS/SSMA) receiver that incorporates multipath diversity combining and multistage co-channel interference (CCI) cancellation. This receiver structure which is more resistant to the near/far problem essentially removes more and more of the CCI with each successive cancellation stage. With the assumption that perfect channel estimates have been obtained, we analyze the bit error rate (BER) performance of this system when received powers are unequal. Results show that the BER can approach that of a single-user case as the number of CCI cancellation stages increases.

This paper describes an automatic transistor model parameter generation technique for a circuit simulator which can take device geometry into account. An 'area factor' is used to generate model parameters for different transistor shapes; however, the conventional method could not reflect the actual geometry differences other than for the emitter area. This resulted in inaccurate model parameters and such parameters were not acceptable to accurately simulate circuits for RF ICs. The proposed technique uses actually measured parameters and process data for a reference transistor and generates the individual model parameters for different shape transistors. In this technique, the parasitic resistor values are calculated and fitted in place of directly extracting them from the measured data. This ensures a better estimate. The reference transistor is made sufficiently large to neglect measurement errors in generating the parasitic capacitors. Thus, the model parameters for a very small transistor can be generated accurately. The model generating procedure has been implemented as a pre-processor to SPICE. This technique enables a fast turn around for RF IC circuit design which uses various shape transistors.

The robust finite settling time stabilization problem is considered for a multivariable discrete time plant with structured uncertainties. Finite settling time (FST) stability of a feedback system is a notion introduced recently for discrete time systems as a generalization of the dead-beat response. The uncertain plant treated in this paper is described by (E0+ΣKi=1qiEi)x(t+1)(A0+ΣKi=1qiAi)x(t)+(B0+ΣKi=1qiBi)u(t), and y(t)=(C0+ΣKi=1qiCi)x(t) where Ei, Ai, Bi and Ci (0iK) are prescribed real matrices and qi (1iK) are uncertain parameters restricted to prescribed intervals [qi, i]. It is shown in this paper that a controller robustly FST stabilizes such an uncertain plant, if, the uncertain plant satisfies some conditions, and the controller simultaneously FST stabilizes a finite set of plants. The result leads to a testable necessary and sufficient condition of the existence of a solution to the robust FST stabilization problem, and a systematic method of designing a robust FST stable feedback system, in the case where the plant contains only one uncertain parameter.

Surface construction is known as a way to visualize volume data. Although currently used algorithms such as marching cubes have good enough quality for volume visualization, they do not ensure adequate surface topology. These algorithms work well when the surface is rather simple. While when complicated, the surface does not separate the internal and external spaces, that is, there exist some holes on the surface, or exist redundant overlaps or self-intersection. Actually, adequate surface topology is important not only for visualization but for laser stereolithography, which creates real 3D plastic objects. In the present paper, we propose a new method that produces a set of triangular patches from a given volume data. The fact that the set of patches has no holes, no redundancy, no self-intersection, and has orientable closed surface topology is shown.

The problem of two-dimensional scattering of electromagnetic waves by a grating with several strips arbitrarily oriented in one period is analyzed by means of the Wiener-Hopf technique together with the formulation using the concept of the mutual field. A formulation for the analysis of multiple scattering from the grating is based on the representation of the scattered field by a grating composed of one strip in one period. The Wiener-Hopf equations and a representation of the scattered wave are obtained. The characteristic of the sampling function is used to expand the unknown function associated with the field on the strip into a series, and then the Wiener-Hopf equations are reduced to a set of simultaneous equations. For evaluation of the convergence and the errors in the numerical results, the relative error with respect to the extrapolated value and the square error for satisfaction of the boundary condition are computed. From numerical comparison of the present method with other various methods, it is found that the present method provides us accurate results. Some numerical examples of the reflection coefficients are presented for the reflection grating and transmission gratings.

This paper describes design considerations for high frequency active BPFs up to 100 MHz. The major design issues for high frequency active filters are the excess phase shift in the integrators and high power consumption of the integrators. Typical bipolar transistor based transconductors such as the Gilbert gain cell and the linearized transconductor with two asymmetric emitter-coupled pairs have been analyzed and compared. It has been clarified that the power consumption of the linearized transconductor can be much smaller than that of the Gilbert gain cell because of its high transconductance to working current ratio while maintaining a signal to noise ratio of the same order. A simple high-speed fully differential linearized transconductor cell is proposed with emitter follower buffers and resistive loads for excess phase compensation. A novel gyrator based transformation for the LC ladder BPF has been introduced. This transformation has resulted in a structure with simple capacitor-coupled active resonators which exactly preserves the original transfer function. A fourth order 10.7 MHz BPF IC was designed using the proposed transconductors. It was fabricated and has demonstrated the usefulness of the proposed approach. In addition, an experimental 100 MHz second order BPF IC with Q=14 has been successfully implemented indicating the potential of the proposed approach.

In general, the work on developing an expert system has relied on domain experts to provide all domain-specific knowledge. The method for acquiring knowledge directly from experts is inadequate in oriental medicine because it is hard to find an appropriate expert and the development cost becomes too high. Therefore, we have developed two effective methods for acquiring knowledge indirectly from sample cases. One is to refine a constructed knowledge base by using sample cases. The other is to train a neural network by using sample cases. To demonstrate the effectiveness of our methods, we have implemented two prototype systems; the Oriental Medicine Expert System (OMES) and the Oriental Medicine Neural Network (OMNN). These systems have been compared with the system with the knowledge base built directly by domain experts (OLDS). Among these systems, OMES are considered to be superior to other systems in terms of performances, development costs, and practicalness. In this paper, we present our methods, and describe our experimental and comparison results.

A multicarrier modulation is considered as an effective technique in high speed digital transmission under the multipath fading. In this paper, we theoretically analyze the bit error rate (BER) performance of the multicarrier modulation/differential detection scheme, and show the trade-offs between the BERs and the number of carriers or the guard period to clarify the optimum values to minimize the BER in the number of carriers and the guard period.

An integrator is quite a suitable active element for high-speed filters. The effect of its excess phase shifts, however, is severe in the case of high-Q filter realization. The deterioration due to the excess phase shifts cannot be avoided when only integrators are used as frequency-dependent elements like in leapfrog realization. This paper describes a design of second-order high-speed and high-Q filters with low sensitivity to excess phase shifts of integrators by adding a passive RC circuit. The proposed method can drastically reduce the effect due to the undesirable pole of an integrator, which is the cause of the excess phase shifts, compared to conventional filters using only integrators. As an example, a fourth-order bandpass filter with 5-MHz center frequency and Q=25 is implemented by the proposed method on a monolithic chip. The results obtained here show quite good agreement with the theoretical values. This demonstrates effectiveness of the proposed method and feasibility of high-speed and high-Q filters on a monolithic chip.

A field trial was conducted to evaluate the technical performance of land mobile message communication in different environments. The OmniTRACS system and the Ku-band JCSAT satellite were utilized as the mobile communications system and the satellite, respectively. The trial took place in September 1990 at different areas in Japan. Data collected correspond to about 65 hours of operation, during which a large number of messages were sent via the satellite. Two land mobile terminals operated simultaneously, each terminal having a function of generating messages automatically which simulates a large volume of traffic corresponding to about 50 terminals. Thus, the system was evaluated under the condition that 100 mobile terminals were in operation. Obtained data have been analyzed with a particular focus on the message transmission correlating with actual environments. The analysis was done by classifying environments into five categories: overall condition, type of roads, terrain, areas and weather conditions. The average transmission count per message experienced under all conditions is equal to 1.432 for forward messages transmitted from the hub station to mobiles, and 1.157 for return messages transmitted from mobiles to the hub station. With respect to the classification by the type of roads, for enample it becomes obvious that the performance is generally good except along roads of North-South orientation through dense urban areas. It is concluded that the message communications from/to mobiles are feasible in a wide range of environments, with the performance of success essentially depending on the visibility of satellite.

This paper analyzes the performance of the capacity controlled radio system under a frequency selective fading environment. This system controls the number of modulation levels according to the number of active subscribers. In the analysis, we consider the capacity controlled system either with or without adaptive equalizer. As the results of analysis, it is clarified that the system is superior to the conventional fixed capacity system, and can be considered as a good countermeasure for multi-path fading. And it is found that there exists a synergistic effect due to capacity controlling and adaptive equalizing.

This paper proposes the laser diode receiving mixer which utilizes the laser diode nonlinearity. The laser diode receiving mixer can make the bidirectional fiber optic link simple and cost-effective. These laser diodes are applied to configure the LD-LD MIX link which consists of two laser diodes, two local oscillators, two microwave switches and one fiber cable. The LD-LD MIX link configuration is extended to introduce novel two fiber optic links, i.e. the local suppression link and the image cancellation link. These links utilize the combination of microwave circuits and optical devices. These configurations are experimentally investigated at microwave frequencies and the QPSK signal transmission is successfully demonstrated.

Reactive gases such air pollution agents as H2S or SO2 usually corrode the electrical contact surfaces. Since corrosion products formed on the surface increase contact resistance, they harmfully degrades contact reliability. To prevent the corrosion of the surface, oil coating on it may be effective. The oil film acts basically as a barrier for reaction between the corrosive gas and the surface. For thin film coating, the corrosion inhibition can not be expected. However, effect of film thickness on the corrosion property has not been clarified. In the present study, in order to clarify the corrosion inhibition of the oil coating for the contacts, the stearic acid coating on Ag (silver) contact surface was studied from view-point of the relationship between the thickness of the coating film and the contact resistance. As results, the effect of the stearic acid coating on corrosion inhibition in the atmosphere contained with H2S 3 ppm was found. However, the corrosion of the surface coated with thin stearic acid film occurred at microscopically scattered thin patiches in the specific pattern of the film. Existing of the optimum thickness of the stearic acid coating which gives both minimum contact resistance and effective corrosion inhibition was found. In the intermediate film thickness, this optimum thickness was induced by the increased contact resistance due to corrosion of the thin film region and insulation property of the stearic acid in the thick film region. Moreovr,it was found that this optimum thickness was affected by corrosion time. At the early stage of corrosion, the optimum thickness was about 200 . However, the corrosion time becomes longer as 700 min, this optimum thickness changed to thick as 1000 . With this increase in the thickness, the contact resistance in the optimum thickness rised to high level. Furthermore, the contact resistance in the optimum thickness decreased with increase in the contact load. However, dependence of the contact load on the optimum thickness was not recognized under a certain corrosion time.

We apply Fahlman and Lebiere's (FL) algorithm to network synthesis and incremental learning by making use of already-trained networks, each performing a specified task, to design a system that performs a global or extended task without destroying the information gained by the previously trained nets. Investigation shows that the synthesized or expanded FL networks have generalization ability superior to Back propagation (BP) networks in which the number of newly added hidden units must be pre-specified.

For a method to control the microwave coupled lines with optically induced plasma effectively, we propose the selective mode-control method, which restricts controlled modes to a selected one. We analyzed the basic characteristics of coupled microstrip lines theoretically by using the spectral domain technique and indicated the effectiveness of this method with the aid of numerical results. Further, we designed an optically controlled change-over switch as an application of this method.