In the ITS (Intelligent Transport Systems), it is an essential condition (mixed environment) that vehicles that have communication equipment and vehicles that do not have it simultaneously run in the same road. In this paper, a vehicular driving assistant system that is applicable to the mixed environment is proposed. The proposed system uses spread spectrum techniques and consists of several new systems such as a PN code assignment system, new vehicle position systems, and a vehicle map update system. In the proposed system, the wireless broadcast CDMA is used for inter-vehicle communications. This paper also shows preexaminations of the proposed system by using an autonomous traffic flow simulator including inter-vehicle communications. It is shown that the traffic safety can be improved by using inter-vehicle communications.

This paper describes code assignment and the multicode sense scheme for an inter-vehicle CDMA communication network. When considering an inter-vehicle broadcasting CDMA communication network, spreading code assignment and notification problems arise. In such a CDMA network, the use of common codes is a solution. Then an objective function of common code assignment in an IVCN is formulated as a combinatorial optimization problem. In addition, a multicode sense (MCS)/CDMA system is proposed as a simple code assignment scheme. Computer simulations show that the MCS/CDMA system can autonomously perform spatial rearrangement of the common codes using only local information that each vehicle can obtain by sensing the code channels.

M-ary/SS systems are compared with DS/SS systems applied the multicarrier systems and the RAKE receiver in the presence of AWGN, frequency selective Rayleigh fading and partial-band interference. In particular, the BER performance and SSMA capability are evaluated. Consequently, the M-ary/SSMA system using the multicarrier techniques is subject to the M-ary/SSMA system with the RAKE receiver in the presence of partial-band interference. The BER performance of the M-ary/SSMA system is better than that of the DS/SSMA system when the number of users is smaller than 20. And the spectral efficiency of the multicarrier M-ary/SSMA system is best in the four systems when JSR=20 [dB] and BER=10-3.

In this paper, the bit error rate (BER) performance of the Spread Spectrum communication with Constrained Spreading Code system is studied under the synchronous CDMA system. Particularly, BER considering the tracking error is derived by theoretical analysis. The synchronizing spreading sequence is employed to track the signals in the receiver. As the result, the BER performance is degraded by increasing the number of users. However, the BER performance can be improved by canceling the co-channel interference and by suppressing the cross-correlation value between the information spreading sequence and the synchronizing spreading sequence.

Wideband wireless access based on DS-CDMA (W-CDMA) is a promising access technique for the 3rd generation mobile communication systems using 2 GHz carrier frequencies. In this paper, several promising techniques to enhance significantly the link performance or capacity are identified. They are (a) interference reduction techniques: interference cancellation and adaptive antenna array (b) required E b/I0 reduction techniques: channel coding and adaptive transmit power control (TPC). For the last decade, many theoretical studies have been done on interference cancellation and adaptive antenna array techniques. Now, it is time to implement real hardware to demonstrate their capabilities under real mobile radio propagation channels. In mobile radio, because of the well-known near/far problem and the adverse effect of fading, fast TPC is indispensable. Currently, a simple closed-loop fast TPC is adopted. The use of a more sophisticated adaptive fast TPC algorithm, which can adapt its power up/down step size according to the variations in channel conditions, may reduce the power control error, resulting in reduced interference to other users. Fast TPC and channel coding work complementarily against fading. Channel coding is another interesting area of research. Turbo coding is the most promising technique. In this paper, the above mentioned techniques are introduced. Preliminary experimental results of interference cancellation and adaptive antenna array techniques are also presented.

DQRUMA (Distributed-Queueing Request Update Multiple Access) protocol has been proposed as an access protocol for the wireless ATM Local Area Networks. DQRUMA protocol is useful to transmit fixed-length packets (e. g. ATM cells). However, it cannot be applied to multimedia environment because it does not include any access control policy for multimedia traffic. In the paper, we propose a slot assignment scheme of DQRUMA protocol in wireless ATM LAN which supports integrated multimedia traffic with different service requirements. In this scheme we can allocate network resources according to the service requirements of each medium because the base station assigns Transmit-Permission flexibly according to the features of each medium.

This letter proposes a new retransmission control scheme for slow-frequency-hopped communication systems, in which the number of (re)transmitted packets is adaptively decreased in a certain period. Performance of the proposed scheme is analyzed and compared with that of the conventional scheme in terms of the normalized throughput and the 98% packet transmission delay. The numerical results show the superiority of the proposed scheme.

Array redistribution is required very often in programs on distributed memory parallel computers. It is essential to use efficient algorithms for redistribution, otherwise the performance of programs may degrade considerably. In this paper, we focus on automatic generation of communication routines for multi-dimensional redistribution. The principal advantage of this work is to gain the ability to handle redistribution between arbitrary source and destination processor sets and between arbitrary source and destination distribution schemes. We have implemented these algorithms using Parallelware communication library. Some experimental results show the efficiency and flexibility of our techniques compared to the other redistribution works.

Exception handling is not only useful for increasing program readability, but also provides an effective means to check and locate errors, so it increases productivity in large-scale program development. Some typical and frequent program errors, such as out-of-range indexing, null dereferencing, and narrowing violations, cause exceptions that are otherwise unlikely to be caught. Moreover, the absence of a catcher for exceptions thrown by API procedures also causes uncaught exceptions. This paper discusses how the exception handling mechanism should be supported by the compiler together with the operating system and debugging facilities. This mechanism is implemented in the compiler by inserting inline check code and accompanying propagation code. One drawback to this approach is the runtime overhead imposed by the inline check code, which should therefore be optimized. However, there has been little discussion of appropriate optimization techniques and efficiency in the literature. Therefore, a new solution is proposed that formulates the optimization problem as a common assertion elimination (CAE). Assertions consist of check code and useful branch conditions. The latter are effective to remove redundant check code. The redundancy can be checked and removed precisely with a forward iterative data flow analysis. Even in performance-sensitive applications such as telecommunications software, figures obtained by a CHILL optimizing compiler indicate that CAE optimizes the code well enough to be competitive with check suppressed code.

Privacy, voter uncoercibility, collision freedom, verifiability, and tally correctness are essential properties of modern electronic election systems. None of the single-authority election systems proposed in the literatures achieves all the above five properties. In this paper we propose a universal single-authority election system that satisfies the five properties. In particular, the privacy of each voter is protected against the authority and other voters, and no voter can coerce any other voter into changing the value of his vote in our proposed system. We also show that it is impossible for a collision-free single-authority election system to possess the voter uncoercibility and authority uncoercibility at the same time.

We report the state of the art of superconducting network switching circuits and system technology. Mainly, we describe our switching core circuits and challenges to demonstrate superconducting prototype systems. And also, we review other approach to perform the superconducting digital communication briefly. In our switching core circuits, a ring-pipeline architecture has been proposed and the component circuits of the prototype chips have been fabricated and tested successfully. It is very important to demonstrate the prototype system in order to estimate the total performance of the system with superconducting devices. We have designed a multi-processor system with a superconducting network as a prototype system to demonstrate an interprocessor network system.

This paper proposes and investigates a coding and decoding scheme to achieve adaptive unequal error protection (UEP) using several convolutional codes which have different error-correcting capabilities. An appropriate encoder is selected to unequally protect each frame of information sequence according to the importance of the frame. Since the supplemental information of selected encoder is not sent for the sake of reducing redundancy, we assume that the decoder does not know which encoder was used, and the decoder has to estimate the used encoder. In order to estimate which encoder was used, the method using biased metric in Viterbi decoding is proposed. In decoding, however, there is a problem of Decoder-Selection-Error (DSE), which is an error that the decoder selected in a receiver does not correspond to the encoder used in a transmitter. An upper bound of DSE rate in decoding is derived. The proposed decoding scheme using the biased metric in a trellis can improve DSE rate and BER performance, because transition probability of encoders is taken into account in calculating likelihood by means of making branch or path metric biased. Computer simulation is employed to evaluate the BER performance and DSE rate of the proposed scheme. The performance is compared with a conventional equal error protection scheme and a UEP with the supplemental information on the used encoder. It is found that the proposed scheme can achieve better performance than them in case N=2.

The development of saturation diving in civil and defense applications has enabled man to work in the sea at great depths and for long periods of time. This advance has resulted, in part, as a consequence of the substitution of helium for nitrogen in breathing gas mixtures. However, utilization of HeO2 breathing mixture at high ambient pressures has caused problems in speech communication; in turn, helium speech enhancement systems have been developed to improve diver communication. These speech unscramblers attempt to process variously the grossly unintelligible speech resulting from the effect of breathing mixtures and ambient pressure, and to reconstruct such signals in order to provide adequate voice communication. It is known that the glottal excitation is quasi-periodic and the vocal tract filter is quasi-stationary. Hence, it is possible to use an auto regressive modelisation to restore speech intelligibility in hyperbaric conditions. Corrections are made on the vocal tract transfer function, either in the frequency domain, or directly on the autocorrelation function. A spectral subtraction or noise reduction may be added to improve speech quality. A new VAD enhanced helium speech unscrambler is proposed for use in adverse conditions or in speech recognition. This system, implementable on single chip DSP of current technology, is capable to work in real time.

We present two types of ICF (INHIBIT Controlled by Fluxon) gates as the basic circuits of the phase-mode logic family, and fabricate an adder circuit. The experimental result demonstrates that the carry operation followed up to 99 GHz input pulses. The performance of Josephson devices is improved by the use of junctions with high current density (Jc). We may use the high-Jc junctions without external resistive shunt in the phase-mode logic circuits because of reduction of the junction hysteresis. One of the ways to overcome the large area occupancy for geometric inductance is to utilize the effective inductance of a Josephson junction itself. We investigate a circuit construction with high-Jc inductor junctions, intrinsically overdumped junctions and junction-type resistors for the compactness of circuit integration, and discuss various aspects of the circuit construction.

As a data transmission rate must be increased as required to support the future high-speed wireless communication systems under multipath fading, the conventional DS-CDMA scheme suffers considerably from an intensive processing requirement for the increased spreading rate to combat the inter-chip interference (ICI) and furthermore, from the intersymbol interference (ISI) as the symbol duration becomes less than the channel delay spread. In this paper, a multi-carrier parallel combinatory DS-CDMA (MC-PC-CDMA) scheme is considered as one possible variant access scheme to realize a bandwidth efficient transmission for high transmission rate while maintaining the beneficial features of the DS-CDMA scheme. This scheme combines the parallel combinatory signaling feature of the existing parallel combinatory CDMA (PC-CDMA) scheme with the orthogonal carrier multiplexing feature of multi-carrier modulation so as to improve the bandwidth efficiency and to reduce the self-interference among the parallel spreading sequences of each user, respectively. This particular system configuration also treats the previously proposed multi-carrier DS-CDMA systems as a special case. Our analysis of the bit error rate for the asynchronous CDMA system investigates the performance characteristics of the proposed system on varying design parameters, and shows the performance comparison with other types of multi-carrier DS-CDMA systems.

In this paper, we show that two-dimensional billiards with point interactions inside exhibit a chaotic nature in the microscopic world, although their classical counterpart is non-chaotic. After deriving the transition matrix of the system by using the self-adjoint extension theory of functional analysis, we deduce the general condition for the appearance of chaos. The prediction is confirmed by numerically examining the statistical properties of energy spectrum of rectangular billiards with multiple point interactions inside. The dependence of the level statistics on the strength as well as the number of the scatterers is displayed.

In order to demodulate a Differential Chaos Shift Keying (DCSK) signal, the energy carried by the received chaotic signal must be determined. Since a chaotic signal is not periodic, the energy per bit carried by the chaotic signal can only be estimated, even in the noise-free case. This estimation has a non-zero variance that limits the attainable data rate. In this paper the DCSK technique is combined with frequency modulation in order to overcome the estimation problem and to improve the data rate of DCSK modulation.

In this paper, experimental results of evaluating dialogue strategies of confirmation with a noisy channel are presented. First, the types of errors in task-oriented dialogues are investigated and classified as communication, dialogue, knowledge, problem solving, or objective errors. Since the errors are of different levels, the methods for recovering from errors must be examined separately. We have investigated that the dialogue and knowledge errors generated by communication errors can be recovered through system confirmation with the user. In addition, we examined that the manner in which a system initiates dialogue, namely, dialogue strategies, might influence the cooperativity of their interactions depending on the frequency of confirmations and the amount of information conveyed. Furthermore, the choice of dialogue strategies will be influenced by the rate of occurrence of communication errors in a communication channel and related to the properties of the task, for example, the difficulty in achieving a goal or the frequency of the movement of initiatives. To verify these hypotheses, we prepared a testbed task, the Group Scheduling Task, and examined it through a computer-to-computer dialogue simulation in which one system took the part of a scheduling system and the other system acted as a user. In this simulation, erroneous input for the scheduling system was also developed. The user system was designed to act randomly so that it could simulate a real human user, while the scheduling system was devised to strictly follow a particular dialogue strategy of confirmation. The experimental results showed that a certain amount of confirmation was required to overcome errors when the rate of occurrence of communication errors was high, but that excessive confirmation did not serve to resolve errors, depending on the task involved.

In this paper, dependence of storage capacity of an analogue associative memory model using nonmonotonic neurons on static synaptic noise and static threshold noise is shown. This dependence is analytically calculated by means of the self-consistent signal-to-noise analysis (SCSNA) proposed by Shiino and Fukai. It is known that the storage capacity of an associative memory model can be improved markedly by replacing the usual sigmoid neurons with nonmonotonic ones, and the Hopfield model has theoretically been shown to be fairly robust against introducing the static synaptic noise. In this paper, it is shown that when the monotonicity of neuron is high, the storage capacity decreases rapidly according to an increase of the static synaptic noise. It is also shown that the reduction of the storage capacity is more sensitive to an increase in the static threshold noise than to the increase in the static synaptic noise.

Wavelength-division multiplexing (WDM) transmission systems have been intensely researched in order to increase the transmission capacity. One of the most important key devices for this use is erbium-doped fiber amplifiers (EDFAs) which feature a flattened gain, a high pumping efficiency and a low noise figure (NF), simultaneously. To fulfill these requirements, hybrid silica-based EDFAs (EDSFAs) composed of Al codoped and P/Al codoped EDSFs have been proposed so far. They are also attractive from the viewpoint of productivity, reliability, and cost-effectiveness. On the other hand, the optical bandwidth has been around 15 nm at most. In this paper, we have proposed newly designed hybrid EDSFAs for more than 25 nm optical bandwidth. The gain peak around 1. 53 µm can be suppressed through the saturation degree control in both EDSFs. The remaining obstacle is the diparound 1. 54 µm, which results in the relative gain non-uniformity of 10. 7% over the wavelength range from 1535 to 1560 nm. Owing to the glass composition optimization, the relative gain non-uniformity has been reduced to 5.8% without gain equalizers(GEQs), which is comparable to that of EDFFAs. As another solution, the hybrid EDSFA including two-stage Fabry Perot etalons as the GEQ has been proposed. In this configuration, the hybrid EDSFA has been designed to exhibit the gain profile similar to the summation of two sinusoidal curves, and the relative gain non-uniformity has been reduced to 3. 7%, which is almost equal to that of the hybrid EDFAs composed of EDSF and EDFF. Moreover, it has been demonstrated that newly developed hybrid EDSFAs exhibit a higher pumping efficiency and a lower NF than EDFFAs and hybrid EDSF/EDFFAs.