This paper proposes a new class of error locating codes which corrects random single-bit errors and indicates a location of an erroneous b-bit byte which includes e-bit errors, where 2 e b, called SECSe/bEL codes. This type of codes is very suitable for an application to memory systems constructed from byte-organized memory chips because this corrects random single-bit errors induced by soft-errors and also indicates the position of the faulty memory chips. This paper also gives a construction method of the proposed codes using tensor product of the two codes, i.e., the single b-bit byte error correcting codes and the single-bit error correcting and e-bit error detecting codes. This clarifies lower bounds and error control capabilities of the proposed codes.

The periodic correlation properties of M sequences coded by channel codes are discussed. As for the channel codes, the Manchester code and the eight DC free codes in the FM family codes, which include the conventional FM code and the differential Manchester code, are adopted. The M sequences coded by the DC free codes in the FM family codes are referred to as FM coded M sequences. The periodic correlation properties of all combinations of the FM coded M sequences are checked, and the combinations which can provide almost the same or better properties as compared with those of the preferred pairs of M sequences are described. An example of code design using the FM coded M sequences for asynchronous direct sequence/spread spectrum multiple access systems is also discussed.

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.

When bit error probability of a trellis-coded modulation (TCM) scheme becomes very small, it is almost impossible to evaluate it by an ordinary Monte-Carlo simulation method. Importance sampling is a technique of reducing the number of simulation samples required. The reduction is attained by modifying the noise to produce more errors. The low error rate can be effectively estimated by applying importance sampling. Each simulation run simulates a single error event, and importance sampling is used to make the error events more frequent. The previous design method of the probability density function in importance sampling is not suitable for the TCM scheme on an additive non-Gaussian noise channel. The main problem is how to design the probability density function of the noise used in the simulation. We propose a new design method of the simulation probability density function related to the Bhattacharyya bound. It is reduced to the same simulation probability density function of the old method when the noise is additive white Gaussian. By using the proposed method for an additive non-Gaussian noise, the reduction of simulation time is about 1/170 at bit error rate of 106 if the overhead of the calculation of the Bhattacharyya bound is ignored. Under the same condition, the reduction of the simulation time by the proposed method is 1/65 of the ordinary Monte-Carlo method even if we take the overhead for importance sampling into account.

This paper investigates the effect of crosstalk in multichannel coherent optical ASK systems. A closed-form signal-to-noise ratio (SNR) expression as a function of number of channels, channel separation, laser phase noise, intermediate frequency (IF) filter bandwidth expansion factor (α), system bit rate (Rb=1/T), and additive shot noise is presented. When the desired channel is between two channels in the electrical domain, the minimum permissible electrical domain channel spacing for a 1dB sensitivity penalty due to crosstalk is found to be 4.85Rb when α is optimum; and 8Rb when α=5 for νT=0.30 at BER=10-9. A fairly good agreement is found between the results of this work and those of a previous study.

With a view to applying to the active matrix displays, micromechanical electrostatic switches having Si-N both-ends-fixed beam of size 1.4 µm by 23 µm grown with LP-CVD on Si wafer were studied about its kinetic switching characteristics, especially its switching speed and hysteresis behavior. Electrostatic beam sticking problems were improved with the additional inverse polarity and short duration pulse following on the turn-on signal. The switching beam deflection of 0.16 µm with the switching time of less than 100 nsec. was measured by tightly focused laser interferometric method. Observed turn-on threshold voltages were more than 30 V, and the on/off hysteresis widths were from one third to two thirds of its threshold voltage. The memory function was experimented for the 2 msec. long holding period with the hold voltage of 25 V following on the writing pulse with the duration of 2 µsec. and the amplitude of 32 V. Now, planarization process has been considered to imtroduce the contact electrodes that were not built-in for these experiments. Although conductive actual switches were not tested, with the obtained results, it seems that the micromechanical electrostatic switch has the large potentials as an active matrix element in display panel especially in electro-luminescent devices or field-emission devices.

In this paper, we discuss computational methods for obtaining the bifurcation points and the branch directions at branching points of solution curves for the nonlinear resistive circuits. There are many kinds of the bifurcation points such as limit point, branch point and isolated point. At these points, the Jacobian matrix of circuit equation becomes singular so that we cannot directly apply the usual numerical techniques such as Newton-Raphson method. Therefore, we propose a simple modification technique such that the Newton-Raphson method can be also applied to the modified equations. On the other hand, a curve tracing algorithm can continuously trace the solution curves having the limit points and/or branching points. In this case, we can see whether the curve has passed through a bifurcation point or not by checking the sign of determinant of the Jacobian matrix. We also propose two different methods for calculating the directions of branches at branching point. Combining these algorithms, complicated solution curves will be easily traced by the curve tracing method. We show the example of a Hopfield network in Sect.5.

The background concepts and methodologies of the knowledge-based program understander ALPUS is discussed. ALPUS understands user's buggy Pascal programs using four kinds of programming knowledge: the knowledge on algorithms, programming techniques, the Pascal language, and logical bugs. The knowledge on algorithms, the key knowledge, is represented in a form of hierarchical data structure called Hierarchical Procedure Graph (HPG). In HPG each node represents a chunk of operations called process," which is consisted of sub-processes. The other knowledge is maintained as independent knowledge bases and linked to associated processes of the HPG. The knowledge about bugs acquired by cognitive experiment is grouped into three categories: bugs on algorithms, programming techniques, and the Pascal language, and connected to associated elements of programming knowledge respectively. ALPUS tries to understand user's buggy programs, detects logical bugs, infers user's intentions, and gives advices for fixing bugs. Program understanding is achieved by three steps: normalization, variable identification, and process and technique identification. Normalization results in improving flexibility of understanding. Variable, process and technique identifications are achieved by knowledge-based pattern matching. Intentions are inferred by means of information attached to buggy patterns. The result of comprehension is reported to a user (i.e., student). Experimental results using Quicksort programs written by students show that the HPG formalism is quite powerful in understanding algorithm-oriented programs. The ALPUS's way of program comprehension is useful in the situation of programming education in an intermediate class of an engineering school. The ALPUS system is a subsystem of the intelligent programming environment INTELLITUTOR for learning programming, which was implemented in the frame-based knowledge engineering environment ZERO on a UNIX workstation.

A photonic/video hybrid system for optical information processing by synthesis of the coherence function is proposed. Optical coherence function can be synthesized to have delta-function-like shape or notch shape by using direct frequency modulation of a laser diode with an appropriate waveform. Therefore, by choosing only the interference component in the interferometer, information processing functions can be obtained. The photonic/video hybrid system proposed provides a novel way to choose the interference component, which can improve the spatial resolution compared with our previous system with holographic technique. Selective extraction two-dimensional (2-D) information from a three-dimensional (3-D) object is successfully performed in basic experiments.

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.

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.

Slepian, Wolf and Wyner proved famous source coding theorems for correlated i.i.d. sources. On the other hand recently Han and Verdú have shown the source and channel coding theorems on general sources and channels whose statistics can be arbitrary, that is, no assumption such as stationarity or ergodicity is imposed. We prove source coding theorems on correlated general sources by using the method which Han and Verdú developed to prove their theorems. Also, through an example, we show some new results which are essentially different from those already obtained for the i.i.d. source cases.

We consider the identification of a class of systems which are both time-varying and nonlinear. Time-varying nonlinear systems are often encountered in practice, but tend to be avoided due to the difficulties that arise in modelling and estimation. We study a particular time-varying polynomial model, which is a member of the class of time-varying Wiener models. The model can characterise both time-variation and nonlinearity in a straightforward manner, without requiring an excessively large number of coefficients. We formulate a procedure to find least-squares estimates of the model coefficients. An advantage of the approach is that systems with rapidly changing dynamics can be characterised. In addition, we do not require that the input is stationary or Gaussian. The approach is validated with an application to an automobile modelling problem, where a time-varying nonlinear model is seen to more accurately characterise the system than a time-invariant nonlinear one.

This paper proposes a novel phase ambiguity resolver with combining a very low power Viterbi decoder employing a scarce state transition scheme to realize cost effective receivers for the PCM sound broadcasting satellite service. The theoretical analyses on phase decision performance show that the proposed resolver achieves the symbol-by-symbol phase detection and decides correctly phases of the demodulated data even if the bit error probability of 710-2. The resolver also reduces the phase decision time to below 1/1000 of that of the conventional resolver. Furthermore, experimental results of the power consumption estimate that the prototype Viterbi decoder consumes only 60mW at the data rate of 24.576Mbit/s.

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.

We propose an accurate FET model for microwave nonlinear circuit simulation, which has been modified from the Statz model. We have greatly enhanced the accuracy of both dc and capacitance expressions, especially in the knee voltage region where Ids begins to saturate. In the expression of dc characteristics, our model improves the accuracy by incorporating the drain-source voltage dependence of pinch-off voltage, the gate-source voltage dependence of knee voltage, and the non-square dependence of drain current against the gate-source voltage. The non-square-root voltage dependence of gate capacitances is considered as well. All modifications are simple and the parameter extraction is kept as simple as that of the Statz model. By using this model, good agreement has been obtained between simulated and measured characteristics of a GaAs FET. For the dc characteristics and the S-parameters, each of estimated error is within 5% and 10%. The model accuracy has been verified by comparison of simulated and measured results of power amplifier performances over a wide range of operating conditions.

Tracing solution curves of nonlinear equations is an important problem in circuit simulation. In this paper, simple techniques are proposed for improving the computational efficiency of the spherical method, which is a method for tracing solution curves. These techniques are very effective in circuit simulation where solution curves often turn very rapidly. Moreover, they can be easily performed with little computational effort.

This paper presents an analytical study and computer-based model of radio wave polarization propagating through a microcell. It covers the following topics: the influence of random orientation of a handset terminal on the performance of communication systems using either a linearly or circularly polarized base-station antenna; an analysis of the computer-based simulation of the power response on different polarizations in a street-canyon microcell.

The distributed measurement-based quasi-fixed frequency assignment (also known as quasi-static adaptive frequency assignment-QSAFA) methodology is a practical solution for frequency assignment in the emerging TDMA personal communications networks (PCN/PCS). Five different QSAFA algorithms are studied in this paper under different interference threshold settings. It is found that a simple aggressive algorithm without using a threshold (LIA-Least Interference Algorithm) performs the best under the conditions studied. The performance of this algorithm is also justified by the theoretical proof presented at the end of this paper.