A numerical scheme to analyze a three-dimensional perfectly conducting body that has edges and corners is presented. The geometry of the body can be arbitrary. A new formulation using boundary element method has been developed. This formulation allows that a scatterer has edges and corners, where the behavior of the electromagnetic fields become singular.

The main purpose of this paper is to give a new representation method of the convergence characteristics of the LMS algorithm using tap-input vectors. The described representation method is an extended version of the interpretation method based on the orthogonal projection. Using this new representation, we can express the convergence characteristics in terms of tap-input vectors instead of the eigenvalues of the input signal. From this representation, we consider a general method for improving the convergence speed.

We believe that virtual world communication will subsume BBS and visual communication. Accordingly, we proposed the networked virtual world "Interspace" for visual communication. If we are to achieve education and training in this world, techniques to receive and transmit information without any special training are necessary. The traditional "easy" ways of transmitting information are talking and drawing. In Interspace, users can already talk each other. In this paper we focus on drawing. In daily life we communicate through drawings in various situations. At this time it is important to recognize who is drawing and where the participants are watching. It is difficult to realize these functions using conventional media, but it is possible to realize them in virtual space. In virtual space, the system can clearly represent who is drawing and where participants are watching; expressing topics in virtual space frees us from many physical restrictions. In this paper we discuss the process of drawing when many participants share topics in virtual space; the necessary conditions for our system are considered. We design a system that offers functions to make drawing sheets, to display the view fields of participants, and to share visual fields. Furthermore, we propose the mode of InterSheet called "InterMirror" which shows mirror images of partners and their drawings. We make a prototype and evaluate it. The results indicate the synergistic effect of drawing with voice and the usefulness of drawing for communication in virtual space.

A data-base for data compression is universal if in its construction no prior knowledge of the source distribution is assumed and is optimal if, when we encode the reference index of the data-base, its encoding rate achieves the optimal encoding rate for any given source: in the noiseless case the entropy rate and in the semifaithful case the rate-distortion function of the source. In the present paper, we construct a universal data-base for all stationary ergodic sources, and prove the optimality of the thus constructed data-base for two typical methods of referring to the data-base: one is a block-shift type reference and the other is a single-shift type reference.

We have developed a 15-Gbit/s 96-gate Si-bipolar gate array using 0.5-µm Si-bipolar technology, a sophisticated internal cell design, an I/O buffer design suitable for high-speed operation and high-frequency package technology. The decision circuit and 4 : 1 multiplexer fabricated on the gate array operate up to 15-Gbit/s and above 10-Gbit/s respectively. The data input sensitivity and the phase margin of the decision circuit are 53 mVpp and 288 at 10-Gbit/s operation. This gate array promises to be useful in shortening the development period and lowering cost of 10-Gbit/s class IC's.

The use of existing metallic local line facilities is being studied for providing "video on demand (VOD)" services to residential subscribers across asymmetric digital subscriber lines (ADSL). ADSL carries a high-rate channel in the downstream direction from a central office (CO) to the subscriber, and a low-rate channel in both directions on an existing 2-wire pair. Audio and video signals are compressed by the moving picture experts group's standardized algorithms (MPEG 1 and MPEG 2), and delivered to the subscriber in the high-rate channel. Control (demand and response) signals are transceived in the low-rate channel. This paper presents the line length coverage of ADSL systems given the environment of NTT's local networks. The bit rates in the downstream and upstream directions are assumed to be 1.6-9.2Mbit/s and 24kbit/s, respectively. Two types of ADSL systems are considered: transceiving ADSL signals using the plain old telephone service (POTS) line or the basic rate access (BRA; 320 kbaud ping-pong transmission system) line on the same 2-wire pair. 16-QAM, 32-QAM and 64-QAM are compared as transmission schemes. Intra-system crosstalk interference (interference between identical transmission systems) and inter-system crosstalk interference (interference between different transmission systems) with the existing digital subscriber lines (DSL) are estimated. It is shown that the inter-system crosstalk interference with BRA is most stringent, and ADSL with 16-QAM yields the best performance in NTT's local networks. This paper concludes that realizing ADSL with 16-QAM can achieve channel capacities of up to 9.2Mbit/s for fiber-in-the-feeder (FITF) access systems, but the possibility of applying ADSL to direct access systems is remote except for a restricted short haul use. Some comparisons regarding American local networks are also described.

We have proposed a connection-based optical wavelength division multiplexing network architecture. For the networks such as inter-office LANs, the guarantee of the bandwidths of connection-oriented calls is necessary. Notable features of the network are that multicast can be executed without copying the same data, and that time slots are rearrangeable to increase the throughput. The topology is passive star and a network controller (NWC) is connected to manage the time slot assignment. Each station's transmitting wavelength is fixed and is different from that of other stations. Each receiver changes the receiving wavelength slot by slot. Stations reserve time slots with permission of the NWC. Once a time slot is reserved the station can use the slot in every frame until the reservation is cancelled. This feature guarantees the bandwidths of connection-oriented calls. Upon receiving a time slot request, the NWC searches for a not-in-use slot common to the source station's transmitter (Tx) and the destination station's receiver (Rx). If there is no common empty slot and both the Tx and the Rx have empty slots, the NWC rearranges the already allocated time slots to create a new common empty slot. Simulations were performed to estimate the blocking rates for various cases of call bandwidth including multi-bitrate (the case in which various bandwidth calls are generated in a network) and multicast call, the calculation load of the NWC when it assigns a time slot including rearrangement, and the success rate of rearrangement. It was found that the blocking rate with the rearrangement is greatly reduced (1/10) compared with the case without rearrangement of the same throughput when the number of slots in a frame is more than 120, the number of stations in the network is 60 and the blocking rate without the rearrangement is less than 10-2. Over 100 Gbps throughput can be achieved when the number of slots in a frame is 120-240, the number of stations is 60, the bitrate of a transmitter is 2.5Gbps and the blocking rate is about 10-2. The rearrangement is especially effective in the case of multi-bitrate in which the blocking rate can be reduced to 1/100 that of the case without rearrangement at some point. It is also shown that a slot assignment including rearrangement can be executed sufficiently quickly (5s). These results indicate that practical realization of this access control architecture is possible.

Information systems to support cooperative work among people should be first designed to help humam communication. However, there are few systems based on the analysis of human communication. Standing on this situation, we propose a meeting support system for the participants' understandings by indicating the suitable information about the topic of the scene". Our system provides only useful information by monitoring each statement without complex methods. To show something useful multi-media information for members, we propose the following structure of the meeting on the basis of the analysis of communication. Each statement is classified into two levels, either; a statement about the progress" of the meeting (context-level utterances) or, a statement about objects" (content-level utterances). Further, content-level utterances are classified into two types, position utterances and argument utterances. Using this classification of statements, the proceeding of the meeting is represented as the tree model which is called a context-tree". If the structure of meetings is fixed, it is possible to select only useful information from all shared information for members by analyzing each content-level utterance. The system introduced in this paper shows appropriate multi-media information about the topic of the scene" by using the above model. We have implemented a prototype system based on the above ideas. Moreover, we have mode some experiments to show the effectiveness of this system. Those results show that our method is effective to improve the productivity" of meetings.

This paper establishes a general relation between the two-dimensional Least Mean Square (2-D LMS) algorithm and 2-D discrete orthogonal transforms. It is shown that the 2-D LMS algorithm can be used to compute the forward as well as the inverse 2-D orthogonal transforms in general for any input by suitable choice of the adaptation speed. Simulations are presented to verify the general relationship results.

A quasi-synchronous (QS) code division multiple access (CDMA) system is proposed for mobile communications. In the proposed method, which uses the time division duplex (TDD) mode of transmission, a mobile receiver can measure propagation delay changes. It then accordingly adjusts its transmission time so its signal can arrive at base station synchronously with other mobile units. A simple control unit is used at the mobile unit in order to reduce any error due to the propagation delay changes. The system operates as follows. At the start of a call, a mobile unit is quasi-synchronised through feedback control from the base station. The mobile unit then maintains synchronous status without any further base station feedback. The degree of the quasi-synchronous accuracy is determined by a clock in mobile units. This paper shows performance results based on using a clock rate of ten times faster than the spreading rate. Orthogonal codes are used for spreading the signals. The results demonstrate that the reverse link CDMA multiuser interference is to a great degree removed.

This paper discusses crystal-growth and device-design issues associated with the development of high-performance InP/InGaAs heretostructure bipolar transistors (HBTs). It is shown that a highly Si-doped n+-subcollector in the HBT structure causes anomalous Zn redistribution during metalorganic vapor phase epitaxial (MOVPE) growth. A thermodynamical model of and a useful solution to this big problem are presented. A novel hybrid structure consisting of an abrupt emitter-base heterojunction and a compositionally-graded base is shown to enhance nonequilibrium base transport and thereby increase current gain and cutoff frequency fT. A double-heterostructure bipolar transistor (DHBT) with a step-graded InGaAsP collector can improve collector breakdown behavior without any speed penalty. We also elucidate the effect of emitter size shrinkage on high-frequency performance. Maximum oscillation frequency fmax in excess of 250 GHz is reported.

This letter presents SAM, a multiplexer for ATM's circuit emulation services that can precisely control the cell clumping at the connection-level. Compared with a FIFO (First In First Out) multiplexer, it also improves the connection-level diffusion and CDV (Cell Delay Variation) performance. SAM can therefore significantly increase the number of connections accepted by CAC (Call Admission Control) procedures in the subsequent multiplexer.

This paper describes the multiple access performance of parallel combinatory spread spectrum (PC/SS) communication systems in nonfading and Rayleigh fading multipath channels. The PC/SS systems can provide the high-speed data transmission capability by transmitting multiple pseudo-noise sequences out of a pre-assigned sequence set. The performance is evaluated in terms of average bit error rate (BER) by numerical computation. In nonfading white gaussian channel, the PC/SS systems are superior to conventional direct sequence spread spectrum (DS/SS) systems under the identical spreading factor condition. In Rayleigh fading channel, the performance of the PC/SS system without diversity is poorer than that of the DS/SS system. By including the explicit and implicit diversity, the performance of the PC/SS system becomes better than that of conventional DS/SS systems. A longer spreading sequence is assignable to a PC/SS system having the spreading factor equal to that in the conventional DS/SS system. Hence, the error control coding is easily. It is found that the PC/SS systems including diversity and Reed-Solomon coding improves the multiple access performance.

In this paper, we propose two parallel processing methods for multidimensional (MD) sampling lattice alteration. The use of our proposed methods enables us to alter the sampling lattice of a given MD signal sequence in parallel without any redundancy caused by up- and down-sampling, even if the alteration is rational and non-separable. Our proposed methods are provided by extending two conventional block processing techniques for FIR filtering: the overlap-add method and the overlap-save method. In these proposed methods, firstly a given signal sequence is segmented into some blocks, secondly sampling lattice alteration is implemented for each block data individually, and finally the results are fitted together to obtain the output sequence which is identical to the sequence obtained from the direct sampling lattice alteration. Besides, we provide their efficient implementation: the DFT-domain approach, and give some comments on the computational complexity in order to show the effectiveness of our proposed methods.

A deterministic pushdown automaton (dpda) having just one stack symbol is called a deterministic restricted one-counter automaton (droca). A deterministic one-counter automaton (doca) is a dpda having only one stack symbol, with the exception of a bottom-of-stack marker. The class of languages accepted by droca's which accept by final state is a proper subclass of the class of languages accepted by doca's. Valiant has proved the decidability of the equivalence problem for doca's and the undecidability of the inclusion problem for doca's. Hence the decidability of the equivalence problem for droca's is obvious. In this paper, we evaluate the upper bound of the length of the shortest input string (witness) that disproves the inclusion for a pair of real-time droca's which accept by final state, and present a new direct branching algorithm for checking the inclusion for a pair of languages accepted by these droca's. Then we show that the worst-case time complexity of our algorithm is polynomial in the size of these droca's.

An experimental study on propagation characteristics in a room of a modern office building using a 57.5 GHz carrier is described. The objective of the study is to provide initial information about the path-loss and fading characteristics for millimeter-wave wireless indoor communication systems. The area of the floor of the room is about 90 m2 and the room was almost empty with no furniture except the experimental apparatus. A wide-beam scalar feed horn transmission antenna and an omnidirectional receiving antenna were used and set to be with the same height. The measured area was divided into many "squares" to characterize the propagation. The variation of square transmission loss was calculated, and the regions where the maximum square transmission loss was observed were pointed out. It became clear that the distance power law for square transmission loss was approximately of the order d-2 along the direct path. Rician distributions for fast fading were derived in almost all squares of this room. The spectra for the fast fading envelope were also derived. From the propagation point of view, the results show that no extreme difficulty seems to exist in developing wireless communication systems in the 60 GHz band.

In case of object recognition using 3-D configuration data, the scale and poses of the object are important factors. If they are not known, we can not compare the object with the models in the database. Hence we propose a strategy for object recognition independently of its scale and poses, which is based on Hopfield neural network. And we also propose a strategy for estimation of the camera motion to reconstruct 3-D configuration of the object. In this strategy, the camera motion is estimated only with the sequential images taken by a moving camera. Consequently, the 3-D configuration of the object is reconstructed only with the sequential images. And we adopt the multiple regression analysis for estimation of the camera motion parameters so as to reduce the errors of them.

A new three-dimensional MMIC structure and an ultra-wideband miniature MMIC balun are proposed. The MMIC is a combined structure of multilayer MMICs and U-shaped micro-wires. This technology effectively reduces chip size and enhances MMIC performance. The proposed balun is constructed with three narrow conductors located side by side. The U-shaped micro-wire technology is employed to reduce the insertion loss and chip size. 1.51 dB insertion loss over 10 to 30 GHz, and 2 dB and 5 degrees of amplitude and phase balances over 5 to 35 GHz have been obtained. The intrinsic area of the balun is only 450800 µm, about 1/5 to 1/3 the area of recently reported miniaturized MMIC baluns.

A transmission power control technique on a TDD-CDMA/TDMA system for wireless multimedia networks is proposed. The assumed network connects mobile terminals to a node of an ATM based high speed LAN through a radio central unit. Only human interface facilities are implemented into the terminal so that users access integrated services through the node of the network. The uplink (from a mobile terminal to a radio central unit) employs a CDMA scheme to transmit human interface signals (2.4kbit/s) and the downlink employs a TDMA scheme to transmit display interface signals (24 Mbit/s). Both the CDMA and the TDMA signals occupy the same frequency band. To mitigate bit error rate degradation due to the fading, the radio central unit estimates the impulse response of the channel from the received CDMA signals and controls the transmission power of the TDMA signals to compensate the fading attenuation. The bit error rate performance of the downlink with the proposed transmission power control is theoretically analyzed under several fading conditions. Numerical results using the Nakagami-m fading model and recent propagation measurements show that the proposed power control technique compensates the fading attenuation and improves the bit error rate performances. The bit error rate of the downlink is reduced from 10-2 to 10-5 at the symbol SNR of 20dB by employing the proposed transmission power control, which is less sensitive to the severity of the fading. Furthermore, the proposed transmission power control is implemented without increasing the terminal complexity because all the processing on the power control of the downlink is carried out only in the radio central unit.

This work is concerned with a dynamic analysis of complex uniplanar guide-wave structures for MMICs at millimeter-wave frequencies. The enhanced spectral domain approach is effectively used to model such uniplanar structures with trapezoidal conducting strips involving microshielding enclosures. A wide range of line propagation and impedance characteristics is obtained for slotline and coplanar waveguide (CPW). The effect of different conductor profiles on line characteristics is discussed in detail. Results show an excellent agreement with other works. A class of dispersion-related curves are presented for design consideration.