This paper describes 950 GHz power performance of double-doped AlGaAs/InGaAs/AlGaAs heterojunction field-effect transistors (HJFET) operated at a drain bias voltage ranging from 2.5 to 3.5 V. The developed 1.0 µm gatelength HJFET exhibited a maximum drain current (Imax) of 500 mA/mm, a transconductance (gm) of 300 mS/mm, and a gate-to-drain breakdown voltage of 11 V. Operated at 3.0 V, a 17.5 mm gate periphery HJFET showed 1.4 W Pout and -50.3 dBc adjacent channel leakage power at a 50 kHz off-carrier frequency from 950 MHz with 50% PAE. Harmonic balance simulations revealed that the flat gm characteristics of the HJFET with respect to gate bias voltage are effective to suppress intermodulation distortion under large signal operation. The developed HJFET has great potential for small-sized digital cellular power applications operated at a low DC supply voltage.

This paper is concerned with the evaluation of the block error probability Pic of a block modulation code for closest coset decoding over an AWGN channel. In most cases, the conventional union bound on Pic for closest coset decoding is loose not only at low signal-to-noise ratios but at relatively high signal-to-noise ratios. In this paper, we introduce a new upper bound on the probability of union of events by using the graph theory and we derive an improved upper bound on Pic for some block modulation codes using closest coset decoding over an AWGN channel. We show that the new bound is better than the conventional union bound especially at relatively high signal-to-noise ratios.

In this paper we propose a two-stage address coding scheme to transmit two data symbols at once within a frame in a MFSK/FH-CDMA system. We compare it with the conventional system using single-stage address coding. Assumed that the address codes of all users are known in the receiver. A multiuser detection scheme is applied and the performance is evaluated by computer simulations to show the improvement in bit error rate (BER) compairing to the conventional system. We also investigate the performance of error-correcting coding and decoding in the two-stage address coded MFSK/FH-CDMA system. An erasure decoding scheme is modified for the two-stage address coded system and is utilized to improve spectral efficiency or to increase user capacity in the MFSK/FH-CDMA system. Finally, we investigate a hybrid scheme of combining the multi-user detection scheme and the error-correcting decoding scheme for the two-stage address coded MFSK/FH-CDMA system. The performance is evaluated by computer simulations.

Schnorr's identification scheme is the most efficient and simplest scheme based on the discrete logarithm problem. Unfortunately, Schnorr's scheme is not provably secure, i.e., the security has not been proven to be reducible to well defined intractable problems. Two works have already succeeded to construct provably secure variants of Schnorr's scheme. They have been constructed with a common approach, i.e., by modifying the formula to compute the public key so that each public key has multiple secret keys. These multiple secret keys seem to be essential for their provable security, but also give rise to a penalty in their efficiency. In this paper, we describe a new approach to constructing a provably secure variant, where we never modify the formula, and show that with our approach, we can construct a new efficient provably secure scheme.

This letter is concerned with the evaluation of the average computational complexity of the maximum likelihood decoding of a linear block code using its trellis diagram. Each section of the L-section minimal trellis diagram for a linear block code consists of parallel components which are structurally identical subgraphs without cross connection between them. A parallel component is also known to be decomposed into subgraphs, and a decoding algorithm by using the structure of the subgraphs of parallel components was proposed, and an upper bound on the worst case computational complexity was derived. In this letter, the average computational complexity of the decoding algorithm is evaluated by computer simulation. We evaluated the average numbers of additions and comparisons performed in the decoding algorithm for example codes, (64,45) extended and permuted binary primitive BCH code, the third order Reed-Muller (64,42) code and its (64,40) subcode. It is shown that the average numbers are much smaller than those for the worst case, and hence the decoding algorithm is efficient when the number of sections, L, is small, say 4 or 8, for the example codes. Especially, for the (64,45) extended binary primitive BCH code with L4, the average numbers of additions and comparisons in the decoding algorithm for finding the survivor's metric of each state after finding the smallest metric among parallel branches are about 1/50 and 17/100 of those in the conventional exhaustive search, respectively. The number of additions and comparisons by the conventional search for all the example codes is smallest when L is 4. As a result, the decoding algorithm with L4 gives the smallest number of operations among those decoding methods considered here.

To connect among many radio base stations by using optical fiber bus link in microcellular system, subcarrier multiplexing (SCM) is excellent in simplicity and flexibility. But performance degradation due to optical beat noises is severe problem. To solve this problems, this paper proposes a new type of intercell connection bus fiber-optic link (ICBL) using time division multiplexing, called TDM-ICBL. This paper also analyzes transmission performance of TDM-ICBL theoretically and compares with SCM-ICBL. The analysis clarifies that while the number of RBSs connected to SCM-ICBL is severely restricted by beat noises, TDM-ICBL is more useful than SCM-ICBL when there are many number of connected RBSs.

Optical switching networks to transport vast amounts of information are important for B-ISDN services. Wavelength division multiplexing (WDM) is emerging as the dominant technology for future optical networks. A large capacity photonic ATM switch architecture using WDM technology is proposed in this paper. The proposed switch is suitable for WDM optical ATM networks, that is, an input and an output of the switch are wavelength division multiplexed. The basic switch module of the proposed switch has a simple architecture, and reduces the amount of a buffer hardware by introducing the WDM concept.

Conceptual graph formalism is a knowledge representation language in AI based on a graphical form of logic. Although logic is the basis of the conceptual graph theory, there is a strongly felt absence of a formal treatment of conceptual graphs as a logic programming language. In this paper, we develop the notion of a conceptual graph program as a kind of graph-based order-sorted logic program. First, we define the syntax of the conceptual graph program by specifying its major syntactic elements. Then, we develop a kind of model theoretic semantics and fixpoint semantics of the conceptual graph program. Finally, we show that the two types of semantics coincide for the conceptual graph programs.

Intelligent Tutoring Systems (ITS) represents a wide class of computer based tutoring systems, designed with an extensive use of the technology of modern Artificial Intelligence. Successful applications of various expert systems and other knowledge based systems of AI gave rise to a new wave of interests to ITS. Yet, many authors conclude that practically valuable achievements of ITS are rather modest despite the relatively long history of attempts to use knowledge based systems for tutoring. It is advocated in this paper that some basic obstacles for designing really successful ITS are due to the lack of well understood and sound models of the education process. The paper proposes to overcome these problems by borrowing the required models from AI and adjacent fields. In particular, the concept of Learning Levels from AI might be very useful both for giving a valuable retrospective analysis of computer based tutoring and for suggestion of some perspective directions in the field of ITS.

We propose an algorithm for image decomposition based on Hadamard functions, realized by answer-in-weights neural network, which has simple architecture and is explored with steepest decent method. This scheme saves memory consumption and it converges fast. Simulations with least mean square (LMS) and absolute mean (AM) errors on a 128128 image converge within 30 training epochs.

In this paper face feature detection and tracking are discussed, using methods called edge pixel counting and deformable circular template matching. Instead of utilizing color or gray scale information of the facial image, the proposed edge pixel counting method utilizes the edge information to estimate the face feature positions such as eyes, nose and mouth, using a variable size face feature template, the initial size of which is predetermined by using a facial image database. The method is robust in the sense that the detection is possible with facial images with different skin color and different facial orientations. Subsequently, by using a deformable circular template matching two iris positions of the face are determined and are used in the edge pixel counting, to track the features in the next frame. Although feature tracking using gray scale template matching often fails when inter frame correlation around the feature areas are very low due to facial expression change (such as, talking, smiling, eye blinking etc.), feature tracking using edge pixel counting can track facial features reliably. Some experimental results are shown to demonstrate the effectiveness of the proposed method.

This paper proposes novel optical path accommodation design algorithms for networks wherein the number of wavelengths multiplexed into a fiber is restricted. This algorithm optimizes both optical path route and wavelength assignment in VWP/WP networks. It minimizes optical path cross-connect (OPXC) system scale in terms of incoming/outgoing fiber port numbers. A comparison in terms of required OPXC system scale between the WP and VWP schemes is demonstrated for the first time.

Time-frequency representations (TFRs) have been developed as tools for analysis of non-stationary signals. Signal dependent TFRs are known to perform well for a much wider range of signals than any fixed (signal independent) TFR. This paper describes customised and sequential versions of the signal dependent TFR proposed in [1]. The method, which is based on the use of the Radon transform at distance zero in the ambiguity domain, is simple and effective in dealing with both simulated and real data. The use of the described method for time-scale analysis is also presented. In addition, the paper investigates a simple technique for detection of noisy chirp signals using the Radon transfrom in the ambiguity domain.

In this paper, a description of the Hopfield/Tank model used for the telecommunication network routing problem is given at first. And then through the "static" (i.e. the eigenvalue and the eigenspace of the connection matrix) and the dynamic analysis of the model, it has been found that the model has the faster rate to converge to the optimal or sub-optimal solutions from an initial value. Therefore the quality of the final solutions can be guaranteed. The influence of the initial value to the final solutions is also concerned in this paper. The simulation results are given at the end of this paper.

The organization of the proposed file and algorithms for search and maintenance of the file are simpler than those of a similar key search file based on B+-tree. An experiment using 230,188 keys with length 1-16 shows the good performance of the file. The storage utilization of the file is about 68%.

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.

Object-oriented programming requires different skills from those of traditional structured programming. Thus, a good interactive environment for beginners of object-oriented programming should be provided. We have designed and implemented a visual environment of object-oriented programming for beginners. If a programmer draws a diagram of the tree of the hierarchy of classes visually by using our tool, the relationship between superclasses and subclasses are automatically established. Moreover, in order to prevent careless mistakes to override methods, the prototype environment in the Smalltalk language checks written methods. We conducted an experiment with our tool and evaluated its usefulness.

In this paper, we study the following node-to-node fault tolerant routing problem: In the presence of up to n-1 faulty nodes, find a fault-free path which connects any two non-faulty nodes s and t in an n-connected graph. For node-to-node fault tolerant routing in n-dimensional hypercubes Hn, we give an algorithm which finds a fault-free path s t of length at most in O(n) time, where d(s, t) is the distance between s and t. We also show that a fault-free path s t in Hn of length at most d(s, t)2i, 1i, can be found in time. For node-to-node fault tolerant routing in n-dimensional star graphs Gn, we give an algorithm which finds a fault-free path s t of length at most min{d(Gn)3, d(s, t)6} in O(n) time, where is the diameter of Gn. It is previously known that, in Hn, a fault-free path s t of length at most d(s, t) for d(s, t)n and at most d(s, t)2 for d(s, t)n can be found in O(d(s, t)n) time, and in Gn, a fault-free path s t of length at most min{d(Gn)1, d(s, t)4}can be found in O(d(s, t)n) time. When the time efficiency of finding the routing path is more important than the length of the path, the algorithms in this paper are better than the previous ones.

This paper discusses linear cryptanalysis of LOKI89, LOKI91 and s2DES. Our computer program based on Matsui's search algorithm has completely determined their best linear approximate equations, which tell us applicability of linear cryptanalysis to each cryptosystem. As a result, LOKI89 and LOKI91 are resistant to linear cryptanalysis from the viewpoint of the best linear approximate probability, whereas s2DES is breakable by a known-plaintext attack faster than an exhaustive key search. Moreover, our search program, which is also applicable to differential cryptanalysis, has derived their best differential characteristics as well. These values give a complete proof that characteristics found by Knudsen are actully best.

A high efficiency and low voltage operation GaAs power amplifier module has been developed for the application to 1.5 GHz Japanese digital cellular phones. This paper summarizes the design method to increase efficiency and to reduce adjacent channel leakage power. Operated at a low drain bias voltage of 4.6 V, the power amplifier module delivers an output power of 1.5 W with 46% power-added efficiency and -52 dBs adjacent channel leakage power.