In this paper, we study unequal error protection (UEP) capabilities of punctured convolutional codes. For constructing the good UEP convolutional codes, the conditional weight distributions of UEP convolutional codes are defined and evaluated. The conditional weight distributions are computed by using the transfer functions of time-varying trellis structures of punctured convolutional codes. The best UEP convolutional codes from the viewpoint of the weight distributions are listed.

A key distribution system is a system in which users securely generate a common key. One kind of identity-based key distribution system was proposed by E. Okamoto. Its security depends on the difficulty of factoring a composite number of two large primes like RSA public-key cryptosystem. Another kind of identity-based key distribution system was proposed by K. Nyberg, R. A. Rueppel. Its security depends on the difficulty of the discrete logarithm problem. On the other hand, Koblitz and Miller described how a group of points on an elliptic curve over a finite field can be used to construct a public key cryptosystem. In 1997, we proposed an ID-based key distribution system over an elliptic curve, as well as those over the ring Z/nZ. Its security depends on the difficulty of factoring a composite number of two large primes. We showed that this system over an elliptic curve is more suitable for the implementation than those over the ring Z/nZ. In this paper, we apply the Nyberg-Rueppel ID-based key distribution system to an elliptic curve. It provides relatively small block size and high security. This public key distribution system can be efficiently implemented. However the Nyberg-Rueppel's scheme requires relatively large data transmission. As a solution to this problem, we improve the scheme. This improved scheme is very efficient since data transferred for the common key generation is reduced to half of those in the Nyberg-Rueppel's scheme.

Recently, Garcia and Stichtenoth proposed sequences of algebraic function fields with finite constant fields such that their sequences attain the Drinfeld-Vl bound. In the sequences, the third algebraic function fields are Artin-Schreier extensions of Hermitian function fields. On the other hand, Miura presented powerful tools to construct one-point algebraic geometric (AG) codes from algebraic function fields. In this paper, we clarify rational functions of the third algebraic function fields which correspond to generators of semigroup of nongaps at a specific place of degree one. Consequently, we show generator matrices of the one-point AG codes with respect to the third algebraic function fields for any dimension by using rational functions of monomial type and rational points.

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.

We propose a method of reducing laser-clipping-induced distortion in a subcarrier multiplexed (SCM) optical-cable TV system. This scheme reduces amplitude peaks of the SCM signal by controlling the phases of video carriers to prevent the clipping which occurs when these peaks fall below the threshold of a laser-diode. It is experimentally shown that using this method reduces the bit error rate in an AM-VSB / QAM hybrid optical-transmission system.

In general, the performance of partial response maximum-likelihood (PRML) system is degraded by nonlinear distortion and high frequency noise in high-density digital magnetic recording. Conventional PRML system for single-track recording improves the performance when high order PRML systems and high rate codes are adopted. But, in general it is difficult to realize LSI circuits for high order PRML system and high rate code. In this paper, a trellis coded class four partial response maximum-likelihood (TC-PR4ML) system for high density two-track digital magnetic recording is proposed. Our two-track recording method can increase the coding rate over 1, which contributes to a decrease in both degradation effects from partial erasure, one of nonlinear distortions, and high frequency noise in high density recording. The error rate performance of the proposed system is obtained by computer simulation taking account of the partial erasure and it is compared with that of a conventional NRZ coded class four partial response maximum-likelihood (NRZ-PR4ML) system. The results show that the proposed system is hardly affected by partial erasure and keeps good performance in high density recording.

A structure and an iterative decoding algorithm of a turbo trellis-coded modulation system, proposed by Robertson and et al. , are improved. For the encoder, removal of the odd-even constraint of an interleaver is discussed and a structure which removes a serial connection of an interleaver and a deinterleaver is proposed. The latter makes encoding delay nearly half. A decoding algorithm which is a natural extension of the standard decoding algorithm to TCM is proposed. In the proposed algorithm, logarithm of an a posteriori probability ratio is divided into three component values: an a priori value, a channel value and an extrinsic information. The extrinsic information is transferred to the next decoding stage as an a priori value. The proposed algorithm is easier to understand than the Robertson's algorithm in which a combination of the channel value and the extrinsic information is transferred to the next stage. Simulation results show the proposed algorithm realizes equivalent or better performance than the Robertson's algorithm. The removal of the odd-even constraint gives a little better performance than that with odd-even constraint in some conditions. By this improvement, bit error rate of 10-5 is obtained at Eb/N0 0. 4 dB from the Shannon limit for 2 bit/symbol transmission with 8-PSK modulation.

Millimeter- and submillimeter-wave low-noise superconducting receivers, such as superconductor-insulator-superconductor (SIS) mixers, hot-electron bolometer (HEB) mixers, and superconducting direct detectors, are addressed in this paper. Some general topics on the development of SIS mixers, including SIS junction and integrated tuning circuitry, mixing circuitry, and mixer-performance simulation, are extensively discussed. A tuneless waveguide SIS mixer developed at Nobeyama Radio Observatory (NRO) and its performance are presented. The fundamental mechanisms of diffusion- and phonon-cooled HEB mixers and recent advances in HEB mixers are briefly reviewed. Finally, incoherent detectors with superconducting tunnel junctions are discussed. Results for a direct detecting experiment at 500 GHz are given.

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.

YBa2Cu3Ox films were grown on MgO(100) substrates by liquid phase epitaxy. Their structural and electrical properties were examined. From TEM plan-view images, it is found that the film consists of large grains whose misorientation angles are less than 1. Although the DC critical current density values decrease with increasing the film thickness, the critical current density value of 9. 3105 A/cm2 at 77 K is obtained for a 7 µm-thick film. A microstrip resonator at 10. 8 GHz with a YBCO ground plane shows Q0 values of 14200 at 77 K and 23300 at 40 K, which correspond to surface resistance values of 650 and 400 µΩ, respectively. By using a microstrip line resonator with a Ti/Au ground plane, the critical field of the film at 77 K and 10. 8 GHz is estimated to be 30 Oe. The third-order intercept of the resonator with the Ti/Au ground plane is the input power of +43 dBm and the output power of +30 dBm at 77 K.

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.

The Finite-Difference Time-Domain (FDTD) method is applied to the analysis of electromagnetic fields in a reverberation chamber. The chamber is used for radiated susceptibility/immunity measurement of electromagnetic compatibility (EMC) test and measurement of the radiated power of radio transmitters. The analytical results defined the distribution of the electric field in the reverberation chamber and clarified the effect on field uniformity of the size of the chamber and the number, size, and position of stirrers.

A fuzzy Kohonen clustering network was proposed which integrates the Fuzzy c-means (FCM) model into the learning rate and updating strategies of the Kohonen network. This yields an optimization problem related to FCM, and the numerical results show improved convergence as well as reduced labeling error. However, the clusters may be either hyperspherical-shaped or hyperellipsoidal-shaped, we use a generalized objective function involving a collection of linear varieties. In this way the model is distributed and consists of a series of `local' linear-type models (based on the revealed clusters). We propose a method to generalize the fuzzy Kohonen clustering networks. Anderson's IRIS data and the artificial data set are used to illustrate this method; and results are compared with the standard Kohonen approach and the fuzzy Kohonen clustering networks.

This paper presents a new approach to computing symbol error probability of fast frequency-hopped M-ary frequency shift keying (FFH/MFSK) systems with majority vote under multitone jamming. For illustrating the applications, we first consider the case in which the source data rate is fixed and the hopping rate is allowed to vary. In this case, the optimum orders of diversity for several values of M are examined. Results show that M=4 outperforms other values. Then, we treat another case in which the hopping rate is fixed and the data rate is adjusted so as to obtain maximum throughput under a given constraint of error probability. In addition to the case of diversity alone, we also evaluate the performances of the fixed hopping rate case with channel coding using convolutional code and BCH code.

This paper describes IDDQ testability for bridging faults in a variety of flip-flops. The flip-flop is a basic element of the sequential circuit and there are various structures even for the same type. In this paper, we use five kinds of master-slave D-type flip-flops as the circuit under test. Target faults are two-line resistive bridging faults extracted from a circuit layout. A flip-flop with a deliberately introduced bridging fault is simulated by the SPICE simulator. Simulation results show that IDDQ testing cannot detect faults existing at specific points in some flip-flops, and this problem depends on the flip-flop structure. However, IDDQ testing has high fault coverage ( 98%) compared with traditional logic testing. We also examine performances of fully IDDQ testable flip-flops.

A new or future system of mobile telecommunication is built by new digital technologies to provide an improved and more consistent quality of service for the customers. These digital systems can provide greater number of transmission channel allocation for their subscribers and security. On the digital communication system, distortion of transmitted signal should be eliminated as much as possible for high communication quality. However, the need to both minimize distortion of signal amplifiers and continue to provide good filtering protection can become difficult to achieve with conventional high power amplifiers and filters. In this paper, the application of high-Tc superconducting (HTS) power filters on such digital communication systems and recent progress of filter device developments for those are discussed.

We discuss the security of the improved knapsack cryptosystem that Kobayashi and Kimura have proposed. Two attacking methods for their cryptosystem are proposed; one is the method for obtaining secret keys from public keys by using the continued fraction, and the other is for decrypting the ciphertext without knowing secret keys. We show that their cryptosystem is not secure against these attacks.

The stability of slotted ALOHA systems with various types of capture phenomena and multiple packet reception capability is discussed in conjunction with the cusp catastrophe. The slotted ALOHA systems considered are classified into; 1) single packet reception with geometric capture, 2) independent multiple packet reception with geometric capture, 3) single packet reception with M-out-of-N capture (M N), 4) multiple packet reception with M-out-of-N capture, and 5) single packet reception with perfect capture. First, general expressions for the cusp points and the bifurcation sets are derived. Then, we present explicit formula for the stability of slotted ALOHA systems for the five types of capture and multi-packet reception capability and demonstrate how the bistable behavior is mitigated due to capture effect and multi-packet reception capability.

A multicarrier modulation called orthogonal frequency division multiplex (OFDM) is attracting attention as a transmission scheme which is robust against multipath propagation. A major disadvantage of OFDM is that it is sensitive to nonlinear distortion due to its wide transmission amplitude range. The scope of this study is to cope with the nonlinear problem. We propose a nonlinear distortion compensation scheme using an iterative method which has been applied to an image signal restoration.

CDMA unslotted ALOHA system with finite size of queueing buffers is discussed in this paper. We introduce an analytical model in which the system is divided into two Markov chains; one is in the user part, and the other is in the channel part. In the user part, we can model the queueing behavior of the user station as an M/G/1/B queue. In the channel part, we can consider the number of simultaneously transmitted packets as an M1 + M2/D///K queue. We analyze the queueing system by using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, the rejection probability and the average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.