This paper describes a new, low power 16-bit Digital Signal Processor (DSP). The DSP has a double-speed MAC mechanism, an accelerator for Viterbi decoding, and a block floating section which contribute to lower power consumption. The double-speed MAC can perform two multiply and accumulate operations in one instruction cycle. Since MAC operations are so common in digital signal processing, this mechanism can reduce the average clock frequency of the DSP resulting in lower power consumption. The Viterbi accelerator and block floating circuitry also reduce the clock frequency by minimizing the number of required cycles needed to be executed. The DSP was fabricated using a 0.8 µm CMOS 2-aluminum layer process technology to integrate 644 K transistors on a 9.30 mm9.09 mm die. It can realize an 11.2 kbps VSELP speech CODEC while consuming only 70 mW at 3.5 V Vdd.

This paper proposes a protocol verification tool where protocols are described in an extended Petri net and Horn clauses. The extended net model contributes to reduce state space in verification with hierarchical description. The model also includes timed and colored net. Horn clause enables protocol designers to grasp a protocol by the declarative semantics. They can describe non critical but mandatory portion of a protocol like error processing or abortion with Horn clauses. Protocols are verified through simulation. Protocol verification includes two methods, all-in-one and hierarchical methods. By the all-in-one method all description is translated into Prolong clause and simulated exhaustively, whereas by the hierarchical verification, simulation begins with the lowest layer and deduces sufficient conditions that give liveness and safeness of the net model. Then the layer is replaced by a simpler net model that is incorporated into the higher layer. The scheme is applied to an illustrative example of the Alternating Bit protocol to discuss its effectiveness.

This paper discusses a coding-based selection approach to a communication aid for the severely motor disabled. Several approaches including row-column scanning are briefly described, then we propose a new selection scheme based on the theory of adaptive coding. They are compared each other with respect to average switch activations in generating some text samples.

This paper addresses approaches to enhancement of performance of the CMA (Constant Modulus Algorithm) adaptive array antenna in multipath environments that characterize the mobile radio communications. The cost function of the CMA reveals that it has an AGC (Automatic Gain Control) procedure of holding the array output voltage at a constant value. Therefore, if the output voltage by the initial weights is different from the object value, then the CMA may suffer from slow convergence because suppression of the multipath waves is delayed by the AGC behavior. Our objective is to improve the convergence characteristics by adopting the differential CMA for the adaptive array algorithm. First, the basic performance of the differential CMA is clarified via computer simulation. Next, the differential CMA is incorporated into the eigen-beamspace system in which the eigenvectors of the correlation matrix of array inputs are used in the BFN (Beam Forming Network). This BFN creates the optimum orthogonal multibeams for radio environments and works helpfully as a preprocessor of the differential CMA. The computer simulation results have demonstrated that the differential CMA with the eigen-beamspace system has much better convergence characteristics than the conventional CMA with the element space system. Furthermore, a modified algorithm is introduced which gives the stable array output voltages after convergence, and it is confirmed that the algorithm can carry out more successful adaptation even if the radio environments are changed abruptly.

Secure communications via chaotic synchronization is experimentally demonstrated using 3-pieces of commercial integrated circuit phase-locked loops, MC14046. Different from the conventional chaotic synchronization secure communication systems where one channel is used, our system uses two channels to send one signal to be concealed. Namely, one channel is used to send a synchronizing chaotic signal. The other channel is used to send the informational signal superimposed on the chaotic masking signal at transmitter side. The synchronizing chaotic signal is applied as a common input to two identical PLL's located at both transmitter and receiver sides. It has been shown previously by us that the VCO inputs of almost identical two PLL's driven by a common chaotic signal become chaotic, and synchronized with each other. This synchronization is only possible for those who knows exact internal configuration and exact parameter values of the PLL at transmitter side. Therefore, we can use the synchronized VCO input signal as a masking signal which can be used as a key for secure communications. The advantage of this method compared to the previous one channel method is that informational signal frequency range does not affect the quality of recovered signal. Our experiments demonstrate good masking and recovery characteristics for sinusoidal, triangular, and square waves.

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 method is proposed for locating large gas leaks in subscriber cable networks composed of different type cables and/or branch cables that uses pressures periodically measured at several points. Theoretical pressure curves corresponding to these measured pressure curves are calculated using a model representing the actual cable network. These curves are called the calculated pressure curves. The position of the leak is varied in the calculation model and where the measured and calculated pressure curves coincide the most, the leak position in the calculation model indicates the estimated leak position. The calculated pressure curves are based on the Laplace transform and an analogy between the pneumatic characteristics in cable networks and the electrical characteristics in electrical transmission networks. An experiment using a cable network about 910m long resulted in a location error of less than 30m.

It is important to analyze a tracking or synchronizing process in Spread Spectrum (SS) receiving system. The most common SS tracking system considered here consists of pseudorandom (PN) generator, Lowpass Filter (LPE) and Voltage Controlled Oscillator (VCO). The SS receiver is to track or synchronize its local PN generator to the received PN waveform by VCO. The fundamental equation of the system is known by a second order nonlinear differential equation in terms of phase difference between local PN generator and received PN waveform. The differential equation is nonautonoumous due to PN function of time t with period T. Picking up the gain of VCO as the main parameter in the system we show that the system has bifurcation from the normal oscillation through subharmonic oscillation to finally chaos. In the final case, chaos is confirmed by investigating maximum Liapunov number and both stable and unstable manifolds.

Empirical studies confirm that the received radio signals in certain cellular systems are well modelled by Nakagami statistics. Therefore, performing relevant systems studies can be potentially useful to a system designer. A very useful statistical measure for characterizing the performance of a mobile radio system is the probability of outage, which describes the fraction of time that the signal-to-interference ratio (SIR) drops below some threshold. A more refined criterion for the outage is the failure to simultaneously obtain a sufficient SIR and a minimum power level for the desired signal. Thus, we derive new expressions for the probability of outage where a mobile unit receives a Nakagami desired signal and multiple, independent, cochannel Nakagami interferers. A salient feature of our results is that, unlike some previous studies, the outage expressions do not restrict the Nakagami fading parameter, m, to strictly integer values. Furthermore, since the received signals in mobile radio also experience log-normal shadowing, we analyze the case where the received signals are modelled by a composite of Nakagami and log-normal distributions. Outage probabilities are computed and graphically presented for several cases. The effect of specifying a minimum signal requirement for adequate reception is found to introduce a floor on the outage probability. It is also found that shadowing in macrocellular systems severely degrades the desired quality of service by increasing the reuse distance necessary for a given outage level.

The rapid progress in semiconductor technology and chip mounting technology has made it possible to produce portable computes with high performance, such as notebook computers and PDAs. Portable computes can be used anytime and anywhere. By using the features of mobility, some cooperative works anywhere with multiple portable computers have been realized. However, present networks such as a wireless LAN or a public wireless network are too limited to permit portable computers to cooperate with each other. As the result, a new networking technology for portable computers has been highly requested. In this paper, we propose a novel network technology suitable for face-to-face communication, which we call "Wireless DAN" (Desk Area Network). Here, face-to-face communication is a communication between people who can directly see faces and hear voices with each other. In Wireless DAN, computers independently recognize the network configuration around them. Although present computer networks assume permanence and all computers must be registered before the system can be used, Wireless DAN enables a computer to communicate with computers nearby at any place the user goes without any complicated procedures or dedicated network equipment such as a base station. We also present a new support system for face-to-face cooperative work, which makes it possible to join or leave a meeting while it is in progress. We have developed an experimental system of Wireless DAN and the support system, which is comprised of notebook personal computers with an existing peer-to-peer infrared LAN card. The support system has been implemented using the functions provided by Wireless DAN and thus the system has been simplified. With the experimental system, we confirmed that Wireless DAN operates effectively for face-to-face communication.

The concept of a new visual communication environment is proposed. The proposed system is a shared and interactive multi-user virtual space that consists of a CG-based virtual space structure and video-based objects. Human interface design issues are discussed from the view point of creating a new reality for enhanced communication.

In this paper, a new switched-current auto-tuning filter is proposed. Switched-current (SI) is a current-mode analog sampled-data circuit technique. An SI circuit can be realized using only standard digital CMOS technologies, and is capable of realizing high frequency circuits. The proposed filter is composed of SI-OTA (operational transconductance amplifier) integrators. The gain of an SI-OTA integrator can be electronically controlled by the bias current. The proposed filter is a current controlled filter (CCF) and a PLL technique was used as its tuning method. A 2nd-order SI auto-tuning low-pass filter with 100kHz cutoff frequency was designed assuming a 2µm CMOS process. The characteristics of this SI filter and its tuning characteristics were confirmed by SPICE simulations.

A folded short in parallel-plate waveguide is investigated using the Fourier transform and the mode-matching. A fast-converging series solution for scattering from the folded short is obtained and its characteristics are presented. Our solution for the E-plane short agrees well with measurements and is numerically more efficient than the existing moment-method solution. The presented scattering characteristics are useful for the design of the E- and H -plane shorts in rectangular waveguide.

The complex refractive indices n-jχ of typical magnetic fluids were evaluated for the sake of utilizing them as optical materials. Transmission and reflection spectra were measured in the wavelength range of 0.6-1.6 µm by using monochromators. Magnetic fluids were put into glass cells of 2.5-14-µm thickness for transmission measurement. Due to the absorption by magnetic fluids, the transmittance decreased notably with the increase of the sample thickness. The extinction coefficient χ was evaluated from the dependence of the transmittance on the sample thickness. χ was found to vary between 0.003 and 0.03 depending upon wavelength. The refractive index n was evaluated by fitting theoretical curves to the reflectances that were measured for various incident angles. n was found to vary between 1.6 and 1.7 depending slightly on wavelength. Since a magnetic fluid is a composite of ferrite particles and a solvent, the refractive index can be calculated by using the effective medium theory. The calculated value agreed well with the experimental value. Preliminary experiment of optical switching was also demonstrated by utilizing the mobility of a magnetic fluid.

Portable terminals have the potential of providing information and communication services not only to computer experts at their offices but also to many users being in a variety of daily life situations. The current user interfaces (UIs) of portable terminals are not suitable for a novice user of computers; they require some knowledge on computers from a user. To overcome this problem, the authors tried to implement their knowledge on the daily life in the design of a UI for novice users. As a result, two UI mechanisms, called Novice Interface and Graphical Metaphor Interface, which provide operations, expressions, and data structures in a way similar to those usually used in daily life are proposed. Novice Interface is to provide easy to use environment. It adopts a direct manipulation device with three buttons and a model of data structures, called Small World Model, that limits the number of functions and the depth of hierarchical menu. Graphical Metaphor Interface, being an extension of Novice Interface, is to provide services with a display screen that makes them well-understandable for any user. The proposed UI mechanisms were implemented in a prototype terminal and its software platform. The former offers several applications of the information services (like teleshopping, home banking, or database retrieval) and the communication services (like pen-based image mail, software fax, or telewriting); the latter enables those application programs to provide a consistent UI.

Realizing an effective channel connection scheme and a useful human-machine interface is important for popularizing the audio-visual communication services that should become significant in the near future. This paper describes a terminal design that is applicable to various audio-visual communication services. First, future audio-visual services are classified into three types: Videophone, Tele-monitoring and Video On Demand(VOD). The requirements for these services are discussed in detail. Second, a channel connection scheme is specified taking into consideration for the requirements and characteristics of various networks such as N-ISDN and LANs. Terminals based on these specifications are developed as prototypes and demonstrated to confirm the validity of these specifications.

The throughput performance of the non-persistent carrier sense spread spectrum with overload detection (NP-CSSS/OD) protocol is analysed and compared with that of the conventional non-persistent and one-persistent carrier sense multiple access with collision detection (NP-CSMA/CD and 1P-CSMA/CD) and the one-persistent carrier sense spread spectrum with overload detection (1P-CSSS/OD) protocols. We also introduced utilization measurements and did some performance comparisons between these protocols. At high offered loads, the NP-CSSS/OD protocol is found to offer the best throughput and utilization performances amongst them.

In this paper we present a system for secure communications based on chaos synchronization. Unlike the existing systems for communication via chaotic synchronization, our system extracts the information at the receiver without error. A possibility for secure communications using Lorenz system is given. A practical algorithm for secret-key cryptography is suggested and is evaluated through statistical tests that have not shown any weakness. Furthermore, the algorithm is extremely simple for implementation in a program.

Device figure-of-merits for digital ICs are derived from analytical delay expressions for emitter-coupled logic and source-coupled FET logic inverters and are compared with the operating speeds of D-F/Fs reported in previous studies. We show that device figure-of-merits for baseband amplifiers are equivalent to those for digital ICs. The validity of device figure-of-merits are confirmed by measuring the bandwidth of the baseband amplifiers fabricated with AlGaAs/GaAs LBCTs.

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.