We have proposed a digital beamforming (DBF) self-beam-steering array antenna which features maximal ratio combining enabling it to efficiently use the received power or to rapidly track the desired signal. The DBF self-beam-steering array antenna utilizes digital signal processing with an active array antenna configuration. ASIC implementation of the digital signal processor is inevitable for DBF antenna application in practical mobile communications environments. In this paper, we present a scheme for implementing a digital signal processor in ASICs using ten FPGAs (Field Programmable Gate Arrays) for the DBF self-beam-steering array antenna. Results of some experiments obtained in a large radio anechoic chamber are shown to confirm a basic function of the system.

The status of the plastic optical fiber (POF) for high-speed data communication is described. Very recently, the low-loss and high-bandwidth perfluorinated GI POF which has no serious absorption loss from visible to 1.3-µm wavelength was successfully prepared at Keio University. Since the core diameter (300-1000 µm) of the GI POF is much larger than that of the multimode silica fiber (62.5 µm), the serious modal noise in the conventional multimode silica fiber was virtually eliminated, resulting in stable giga bit order data transmission with inexpensive couplers and connectors.

Lower bounds on the size of shares |Vi| which are more tight than |Vi>| |S| is the size of the secret, are known only for some graphical access structures. This paper shows lower bounds on |Vi| greater than |S| for some non-graphical access structures Γ. We first prove that if {P1, Pi} Γ-for any Pi P^ = {P2, , Pn} and Γ ^= 2P^ Γ is the access structure of a (k, n-1) -threshold scheme on P^, thenmaxilog|Vi>| n+k-3/n-1 log|S|for Pi {P1, P2, , Pn}. Next, we show that maxilog |Vi| 1.5log |S| holds for a wider class of access structures.

This paper describes the design and performance of optical components for in-service fiber testing and monitoring in optical subscriber loops. As the number of test fibers increases, compact and cost-effective components are becoming more important. To meet this need, we have developed a highly-dense hybrid structure for optical couplers and filters, which both play key roles in testing systems. It was realized by utilizing a polyimide-base thin film filter and a waveguide-type wavelength insensitive coupler. This component operates by combining a signal and a test light with a ratio of 80/20% and isolating the test light with a value of 50 dB. The experimental samples were successfully fabricated with an excess loss of 1 dB, a return loss of 40 dB, a plolarization dependent loss (PDL) of 0.3 dB, and good environmental and mechanical stability. We successfully applied the samples to an optical branch module (OBM), and achieved a component density twice that of a conventional module. The optical characteristics of the OBM met our target values. The results we obtained for termination cords incorporating the polyimide-base filter were also satisfactory.

A simplified analysis is presented for the reverse link capacity of DS-CDMA mobile radio with transmit power control (TPC) based on measurement of signal-to-interference plus background noise (SIR) when users require different levels of quality. The link capacity is defined as the maximum achievable sum of the required SIRs, and the increase in transmit power due to SIR-based TPC is discussed. Also analyzed is the total link capacity when narrowband DS-CDMA systems share the radio spectrum of a wideband system. The capacity loss due to non-uniform use of the spectrum is discussed.

In this paper, we propose a clustering based linear ordering algorithm which consists of global ordering and local ordering. In the global ordering, the algorithm forms clusters from n given vertices and orders the clusters. In the local ordering, the elements in each cluster are linearly ordered. The linear order, thus produced, is used to obtain optimal κ-way partitioning based on scaled cost objective function. When the number of cluster is one, the proposed algorithm is exactly the same as MELO [2]. But the proposed algorithm has more global partitioning information than MELO by clustering. Experiment with 11 benchmark circuits for κ-way (2 κ 10) partitioning shows that the proposed algorithm yields an average of 10.6% improvement over MELO [2] for the κ-way scaled cost partitioning.

Asynchronous Transfer Mode (ATM) is considered to bo the key technology for realizing B-ISDN. This paper discusses current research on ATM switching nodes for high-speed communication networks. Although some ATM switching nodes have been deployed, much work continues for resolving problems as regards operations and maintainability, such as ATM layer performance evaluation including layered management scheme upon detection of line failure, function test methods regarding channel connectivity for multicasting, and real-time ATM traffic-monitoring mechanism with QoS control. To achieve sufficient ATM node maintainability, the ATM cell transfer quality on the VP and VC levels should be ensured both within the ATM nodes and between adjacent ATM nodes. Since ATM switching nods handle many kinds of virtual paths and virtual channels, each channel's connectivity must be confirmed. This paper proposes ATM layer performance evaluation concept, layered management scheme upon detection of line failure, function test methods for a multicast switch using test cells that periodically pass through pre-determined switching path routes. It also proposes the concept of test cell generation for simulating multiplexed ATM test cells taking ATM truffic characteristics into account. Furthermore, this paper describes a fault diagnosis scheme using test cells that can continually observe the entire ATM connection length in the system. A real-time traffic monitoring hardware configuration and an interface with software control are also discussed and it is clarified that the required functions can be realized by using commercially available DSPs.

The local wiring structure which is known as a technique for reducing junction capacitance due to the area reduction of the Source/Drain junction by the "on-field" contact scheme was constructed. Its effect on speed/power improvement was evaluated with a ring oscillator. A speed improvement of 15% and a 17% reduction in power dissipation was obtained as compared with conventional non-local wiring structures. This technique was applied to a practical device application, that is, a 0.35 µm embedded dual port SRAM used as a buffer memory in an asynchronous transfer mode switch (ATM-SW) LSI. In order to suppress the coupling noise between the write and read bitlines with the small cell realized by the local wiring scheme, a new divided layer 'bitline architecture was developed. As a result, reduction of SRAM macro size of 31% was attained by also applying the local wiring scheme to peripheral circuits, such as decoder, sense amplifier, and driver. A detailed analysis on this embedded dual port SRAM revealed a 15.2% reduction of write port power at 3.3 V. It is also shown that the local wiring technique is more effective with low power supply voltages to allow for further power reduction.

For reversal complexity on an off-line Turing machine, which is a Turing machine with a read-only two-way input tape except work-tapes, we can consider two kinds of definition; the first one is a definition in which the number of reversals over the input tape is not counted, and the second one is a definition in which it is counted. Unlike time and space complexities, whether or not there is any difference between these two definitions does not seem to be trivial. In this paper, we will show the following results: (1) let S(n) be any function, and R(n) be an (R(n), S(n)) reversal-space constructible function. Then, DRESPk(R(n), S(n)) IDRESPk+2(R(n) + log(nS(n)), n2R(n)S(n)), (2) let R(n) and S(n) be any functions. Then, NRESPk(R(n), S(n)) INRESPk+1(R(n), n2S(n)), and ARESPk(R(n), S(n)) = IARESPk(R(n), S(n)), where DRESP denotes a deterministic reversal- and space-bounded class under the definition disregarding reversals over the input tape, and IDRESP denotes a deterministic reversal- and space-bounded class under the definition counting it. The suffix k denotes the number of work-tapes. The classes NRESP, INRESP, ARESP and IARESP are also defined similarly for NTMs and ATMs.

This letter proposes a map-matching method for automotive navigation systems. The proposed method utilizes the innovation of the Kalman filter algorithm and can achieve more accurate positioning than the correlation method which is generally used for the navigation systems. In this letter, the performance of the proposed algorithm is verified by some simulations.

The direct measurement of sidewall roughness on a ridge-type GaAs waveguide was performed using an atomic force microscope (AFM) combined with a scanning electron microscope (SEM). The ridge sidewall of a GaAs waveguide formed by wet-etching and the ridge sidewall formed after regrowth of a 2.45-µm GaAs/AlGaAs epitaxial layer on the same waveguide were observed using introducing the technique for sample slanting. The observed power spectral density was used to determine the scattering loss caused by the sidewall roughness. It was found that the ridge-type GaAs waveguide for light wave transmission had a scattering loss of 0.029 dB/cm in the as-etched ridge state and a scattering loss of 0.17 dB/cm after regrowing the cover GaAs/AlGaAs epitaxial layer. A leaky GaAs/AlGaAs waveguide for polariton-quantum-wave trans-mission had a scattering loss of 1.3l0-5 dB/cm, which means that the scattering loss is negligible. Furthermore, it was found that a periodical surface fluctuation (spatial frequency 2.2 µm-1) along the waveguide appeared after the regrowth of the epitaxial layer. Thus, this method is useful for direct observation of sidewall roughness and can be used to quantitatively determine the sidewall scattering loss.

We studied the application of precursor solutions that can be fired into oxides to form a protective layer for AC-type Plasma Display Panel (AC-PDP). Our study of alkoxide and metallic soap as MgO precursors revealed that the crystallinity of MgO films depends on the starting substance. Since the electric discharge characteristics of a panel and the lamination effect of the protective layer depend on precursors, it was confirmed that binders having higher crystallinity provide better characteristics. Our study revealed that a compound-oxide film has high crystallinity. The application of a Ba0.6Sr0.4Gd2O4 formation solution to a binder and the application of a Sr0.6Mg0.4Gd2O4 formation solution to a protective layer both are seemed promising We also found that a double-layer film, made by forming a protective layer of fine MgO powder and a Ba0.6Sr0.4Gd2O4 binder, on top of a protective layer made of fine MgO powder and a MgO binder, provides a luminous efficiency 5.3 times higher than that of sputtered MgO film which is one of candidates for the large panel, and the conventional electron beam evaporation is not suitable for the large panel. We further found that a triple-layer protective film made by forming a thin film of Sr0.6Mg0.4Gd2O4 provides low voltages of 1 V in firing voltage (Vf) and 35 V in sustaining voltage (Vs) compared to the double-layer film and provides a luminous efficiency 5.5 times higher than that of sputtered MgO film. A life test revealed the triple-layer film in particular providing a useful life of more than 10,000 hours. From these findings, we concluded that the compound-oxides which is composed of alkaline-earth-metal and rare-earth-element could be applied effectively to a protective layer for AC-PDP.

We have previously reported studies [3], [4] of the steady state system throughput in a slotted ring network. In this paper, we analyze the transient state of packet transmission and derive several characteristics of the network.

The printed dipole on a semi-infinite substrate is investigated. The solution is based on the moment method in the Fourier transform domain. We analyze far-field and near-field radiation patterns for a printed dipole. Therefore, we make radiation fields clear.

This paper is concerned with a point-oriented finite volume time domain (FVTD) method in the Cartesian coordinate system and its application to the analysis of electro-magnetic wave propagation in a bended waveguide as well as radiation from and receiving by a horn antenna with a flange of arbitrary angle. The perfectly matched layer (PML) is used for the absorbing boundary conditions (ABC's). The boundary conditions for a perfect conductor not well suited to the Cartesian coordinate system are also proposed. According to this algorithm, the boundary conditions are satisfied in an average fashion at the conductor surface without changing the computational scheme. In this sense, numerical computations based on the present method are simple but flexible. Numerical results show good convergence.

Petri net is a graphical and mathematical modeling tool for discrete event systems. This paper treats analysis problems for Petri nets under the earliest firing rule. Under this firing rule, transitions must fire as soon as they are enabled. Marked Petri nets under the earliest firing rule are called earliest firing systems, for short. First, some relations in analysis problems between the earliest and the normal firing systems are discussed. These problems include deadlock freedom, boundedness, persistency and liveness. Then, relations among three types of reachability are considered from the viewpoint of the earliest firing rule. Since earliest firing systems can simulate register machines, they have equivalent modeling powers to Turing machines. It suggests, however, that most of the analysis problems of earliest firing systems with general net structures are undecidable. In this paper, net structures are restricted to a subclass called dissynchronous choice (DC) nets. It is shown that the reachability problem from an initial marking to dead markings (markings where no transition can fire) in earliest firing DC systems is equivalent to the usual reachability problem of the same systems under the normal firing rule. Then, the result is applied to reachability problems of controlled DC systems in which some transitions in the net have external control input places. It is shown that for systems where every transition in the net has an external control input place, one type of reachability problem is decidable. Lastly, the liveness problem of earliest firing DC systems is considered and it is shown that this problem is equivalent to that of the underlying DC system under the normal firing rule. It is also shown that this liveness problem is decidable.

There has been an increasing interest in multiple scattering phenomena in recent years. This is primarily due to the discovery of new multiple scattering phenomena and an increasing awareness that a common thread underlies the work of many researchers in such diverse fields as atmospheric optics, ocean acoustics, radio physics, astrophysics, condensed matter physics, plasma physics, geophysics, bioengineering, etc. In addition, waves in random media is one of the most challenging problems to theoreticians. Thus the field of wave propagation and scattering encompasses the most practical as well as the most theoretical questions. The strong interest in this subject is reflected in the launch of a new journal, Waves in Random Media, by the Institute of Physics, United Kingdom in 1991. This paper reviews some of the most recent developments and discoveries in the field of wave propagation and scattering in turbulence and volume and surface scattering. Included are new discoveries of backscattering enhancement and memory effects which may be applicable to tissue optics, ultrasound imaging, ocean acoustics and geophysical remote sensing. Also indicated are recent developments of numerical Monte-Carlo techniques and experimental studies on this subject.

Spread-spectrum (SS) sharing with comb spectrum structure in a microcell/macrocell cellular architecture in order to increase spectral efficiency is proposed. Such method employs a filter in the code division multiple access (CDMA) transmitter to feature comb spectrum structure, and suppress interference with a narrowband time division multiple access (TDMA) system in using together in SS sharing. The relationship between microcellular capacity and macrocellular capacity of the system is explored and compared to those of conventional SS sharing and orthogonal sharing. To be concrete, we investigate two cases, i.e., using no power control and ideal power control in the TDMA system. In both cases, the proposed SS sharing gives better capacity results than the conventional SS sharing and in the comparison when ideal power control is used in th. TDMA system, it even has the property to oppose the orthogonal sharing in ideal condition without interference.

This paper deals with the scattering of a plane wave from a two-dimensional random thin film. For a Gaussian random disorder, a first order solution is derived explicitly by a probabilistic method. It is then found that ripples appear in angular distributions of the incoherent scattering. Furthermore, the incoherent scattering is enhanced in the directions of backscattering and specular reflection. Physical processes that yield such an enhanced scattering are discussed. Numerical examples of the coherent and incoherent scattering are illustrated in figures.

The two variational principles, the Maupertuis' and the Hamilton's principle, are discussed in conjunction with the Fermat's principle. These two principles are shown to describe two different aspects of waves, thus resulting in the different geometry of wave propagation, the treatment of which is thus called the stationary optics or the dynamical optics, respectively. Comparisons for the results obtained from these geometrical optics are given. Another new variational principle valid for the dynamical waves reflected/refracted at the inter-faces, which has not yet been discovered so far, is also derived.