In this paper, we consider conventional signaling link fault tolerance and error correction mechanisms to provide reliable services of mobile multimedia telecommunication network based on ATM (Asynchronous Transfer Mode) technology. Also, we propose an efficient signaling protocol interworking architecture and a reliable distributed interworking network architecture between SS7 based FPLMTS and ATM networks. Besides, we evaluate the performance of proposed method through computer simulation. According to the results, proposed signaling architecture shows efficient and fast fault restoration characteristics than conventional MTP-3/3b based network. Functional signaling protocol stack and network architecture of proposed fast rerouting mechanism provide reliable and efficient restoration performance in view of interworking between SS7 based FPLMTS and ATM networks.

Distributed multimedia applications are often sensitive to the Quality of Service (QoS) provided by the communication network. They usually require guaranteed QoS service, so that real-time communication is possible. However, searching a route with multiple QoS constraints is known to be a NP-complete problem. In this paper, we propose a new simple and efficient distributed QoS routing algorithm, called "DQoSR," for supporting real-time communication in high-speed networks. It searches a route that could guarantee bandwidth, delay, and delay jitter requirements. Routing decision is based only on the modified cost, hop and delay vectors stored in the routing table at each node and its directly connected neighbors. Moreover, DQoSR is proved to construct loop-free routes. Its worst case message complexity is O(|V|2), where |V| is the number of nodes in the network. Thus DQoSR is fast and scales well to large networks. Finally, extensive simulations show that average rate of establishing successful connection of DQoSR is very near to optimum (the difference is less than 0.4%).

A hybrid mo-demodulation approach, fully insensitive to the phase noise induced by the sources, is described for CDMA applications at optical frequencies. It is analytically demonstrated that, using bipolar codes in conjunction with polarisation modulation, the considered system can improve the performance of coherent schemes with not negligible laser linewidths, as well as the performance of more conventional noncoherent schemes based on intensity modulation and unipolar codes.

This paper presents an FPGA architecture for high-speed systems, such as next-generation B-ISDN telecommunications systems. Such a system requires an LSI in which an over-10K-gate circuit can be implemented and that has a clock cycle rate of 80MHz. So far, the FPGA architecture has only been discussed in terms of its circuit structure. In contrast we consider the circuit structure of the FPGA along with the performance of its dedicated CAD system. We evaluate several FPGA logic-element structures with a technology mapping method. From these experiments, a multiplexor-based logic-element is found to be suitable for implementing such a high-speed circuit using the BDD-based technology mapping method. In addition, we examine how to best utilize the characteristics of the selected logic-cell structure in designing the wiring structure. It is found that the multiplexor-based cell can be connected efficiently in a clustered wiring structure.

New THz radiation devices made of high-Tc superconductors are fabricated and their characteristics are studied in detail. Ultrashort electromagnetic pulses with 0.5 ps width have been radiated into free space from current biased devices made of superconducting YBa2Cu3O7 (YBCO) films by exciting with femtosecond laser pulses. The Fourier spectrum of them extends up to 3 THz. The radiation mechanism is ascribed to the ultrafast supercurrent modulation by the optical pulses. The THz waveform is analyzed using rate equations describing the relaxation of photoexcited quasiparticles. By the improvement of the device structure and the collecting optics, the radiation power can be increased up to 0.5 µW. A new type THz radiation from YBCO films under an external magnetic field without a transport current is also reported.

Optical transmission systems with large capacity employing wavelength-division multiplexing (WDM) techniques are now widely under development. Optical amplifiers, especially Erbium-Doped Fiber Amplifiers (EDFA's), are vital components for such transmission systems. Optical amplifiers in WDM systems are employed as common amplifiers for all WDM'ed optical carriers, therefore, change in power of a specific carrier gives rise to gain fluctuation of the remaining carriers. In this paper, we discuss about automatic gain control (AGC) of EDFA for WDM'ed optical carriers under transient gain saturation. Two methods have been reported to perform AGC, i.e., pump feedback control method and compensation light feedback control method. Theory and experimental results have been already reported on pump feedback control method. Here, theory has been generalized to be applicable for compensation light feedback method including schematics with amplified spontaneous emission (ASE) as a probe light to measure the gain of EDFA. Experimental results have confirmed the analysis. Good performance has been obtained for both methods with simple electronic circuits and ASE has been found to work as an excellent probe light source.

The dipole-dipole interaction among excitons is shown to give rise to an intrinsic nonlinearity, which yields a localized mode in a forbidden band, providing a coherent state for quantum computation. Employing this mode, a quantum XOR (exclusive OR) gate is proposed. A block structure of quantum dot arrays is also proposed, to implement quantum circuits comprising the quantum XOR gates for computation.

A numerical method is presented for calculating transverse and non-transverse (or tangent) types of homoclinic points of a two-dimensional noninvertible map having an invariant set that reduces to a one-dimensional noninvertible map. To illustrate bifurcation diagrams of homoclinic points and transitions of chaotic states near the bifurcation parameter values, three systems including coupled chaotic maps are studied.

For the solutions of linear systems of equations with unsymmetric coefficient matrices, we propose an improved version of the quasi-minimal residual (IQMR) method by using the Lanczos process as a major component combining elements of numerical stability and parallel algorithm design. For Lanczos process, stability is obtained by a coupled two-term procedure that generates Lanczos vectors scaled to unit length. The algorithm is derived such that all inner products and matrixvector multiplications of a single iteration step are independent and communication time required for inner product can be overlapped efficiently with computation time. Therefore, the cost of global communication on parallel distributed memory computers can be significantly reduced. The resulting IQMR algorithm maintains the favorable properties of the Lanczos process while not increasing computational costs. The efficiency of this method is demonstrated by numerical experimental results carried out on a massively parallel distributed memory computer, the Parsytec GC/PowerPlus.

This paper proposes an FFT (Fast Fourier Transform) interference detection for interference suppression which combines notch filtering and FEC (forward error correction) to improve the Pe (probability of error) performance degradation due to co-channel interference in digital satellite communication systems. The proposed FFT interference detection scheme can determine the co-channel interference carrier frequency, power, and bandwidth precisely by using the power detection threshold suitable for the desired signal power spectrum, and the notch filter characteristic can be set according to the results. The interference suppression with the proposed scheme achieves the degradation in required Eb/No to only 1.0 dB at a Pe of 10-4 compared to that with the optimum notch filter (ideal detection) in unknown CW (continuous wave) and FM (frequency modulation) co-channel interference environments. Moreover, the proposed scheme improves the required Eb/No by 6.5 dB compared to that without a notch filter in an FM interference environment with interference carrier frequency offset normalized by the desired signal clock rate of 0.52, desired to undesired (interference) signal power ratio of 3 dB and interference bandwidth at 10 dB down power point from the peak normalized by the desired signal clock rate of 0.25.

A multicast (point-to-multipoint) protocol of a satellite broadcast channel by a source and many destinations is presented and its performance characteristics are analyzed. We propose a new time-domain multicast scheme for packet satellite channels, retransmission via collisions protocol (called RVCP). RVCP is classified to the automatic repeat request (ARQ) of the multi-selective-repeat scheme and does not require individual channels for each receiving station to request for broadcast packets that have been received incorrectly. Our analytical models show that RVCP performs considerably better than the other protocols, particularly in the situation that packet error rate is less than 10-4 or there are a large number of destinations. It is an excellent characteristic of RVCP that the equipment of the source station need not increase in proportion to the number of destinations, too. And since RVCP is a relatively simple protocol, it is easy to be implemented.

This paper describes the performance of a video communication system over mobile radio channels. Mobile channel quality changes rapidly due to various factors. When compressed video data is transmitted through these channels, it is indispensable to employ an error control scheme because reconstructed video quality is seriously degraded by channel error. To control this error, an automatic repeat request (ARQ) scheme is often employed, however, this incurs a cost. The benefit of a non-degraded reconstructed video sequence is offset by the transmission delay due to ARQ retransmission. We apply to a video communication system a selective-repeat ARQ which is combined with the coding control scheme to reduce the transmission delay. We evaluate the quality of the reconstructed video sequence and transmission delay using computer simulations and make clear its applicability over Rayleigh and Nakagami-Rican fading channels and intersymbol interference.

A new Neural Network Equalizer (NNE), employing multilayer feedforward neural network, is proposed as a compensation method for nonlinear and multipath distortion that arises from FTTA (Fiber To The Air) system. If a signal in a channel is affected by nonlinear distortion, the conventional Decision Feedback Equalizer (DFE) finds difficulty in perfect compensation of it. To compensate for nonlinear distortion as well as multipath distortion, an equalizer, employing neural network, is investigated. A new neural network equalizer, yielding a cubic function as unit output function, is proposed in order to compensate the nonlinear distortion effectively. We also propose an initial weights of neural network for preventing from local minimum. Computer simulation results show that the compensation performance of the new NNE is superior to the conventional DFE and the conventional NNE.

To improve the emission properties of blue-emitting phosphor layer, SrS:Ce, we evaluated CeN instead of conventional CeCl3 as a starting material. We evaluated the composition and the crystallinity of the thin films using RBS and XRD methods. We also evaluated luminescent properties of EL devices using SrS:Ce phosphor layer. From the results of RBS and XRD measurements, we found that the concentration of the oxygen impurity in SrS:Ce thin films was decreased and the crystallinity of SrS:Ce thin films was improved when CeN is used. These results mean that the degradation of SrS:Ce thin films can be prevented by the use CeN. The evaluation of luminescent properties, shows that the luminance of SrS:Ce EL device is increased by the use of CeN.

Recently, the number of users utilizing mobile communication services has increased greatly in many information and communication fields. In the future, the number of mobile communication system users will increase even faster, until the rate of diffusion ultimately reaches that of telephones. The day that each person has his own portable mobile terminal is not so far off. Moreover, the systems will not only be used as telephones but also as mobile computing for multimedia information. Digitalization technologies of mobile communication systems needed to realize such mobile computing will be introduced in this paper.

This paper proposes a differentially-coded-quadrature-phase-shift-keying (DQPSK) coherent demodulator using a new simultaneous carrier and bit-timing recovery scheme (SCBR). The new DQPSK SCBR (DSCBR) scheme works with a frequently used preamble, whose baseband signal alternates between two diagonal decision points, for example, a repeated bit-series of "1001." With the DSCBR scheme, the proposed demodulator achieves a significantly agile carrier and bit-timing recovery using an open-loop approach with a one-part preamble. To illustrate this, a preamble of 8 symbols is applicable with the Eb/No degradation from the theory over AWGN of 0.2 dB. It is also shown that the proposed demodulator achieves an improvement in the required Eb/No of more than 2 dB over differential detection over Ricean fading communication channels. The channels are modeled for wireless broadband communication systems with directional antennas or line of sight (LOS) paths. This paper concludes that the proposed demodulator is a strong candidate for receivers in wireles broadband communication systems.

Given the tremendous growth in the cellular phone system and the Personal Hadny-phone System (PHS), it is to be expected that demands for mobile computing using those wireless infrastructures, that is mobile computer access, will dramatically increase. This paper describes high-quality and high-speed data transmission technology for PHS mobile computing and current PHS data transmission standardization activities. Furthermore, wireless agent communication and a service example are presented together with the concept of background communication for the coming wireless multimedia services.

This paper proposes the use, in integrated wireless systems, of the Reserved Idle Signal Multiple Access with Collision Resolution (R-ISMA/CR) protocol for applications in future multimedia mobile communications. It is applied to the integrated voice and data wireless system. Moreover, the consideration is made of the integrated voice and the low-bit video wireless system in R-ISMA/CR. To integrate video we employed not only a packed discard for video packets when the video packet delay is more than a threshold value, but also the connection packet (CP) technique for improving the channel utilization. Finally the integration of voice, data, and low-bit-video wireless system in R-ISMA/CR is considered. The performance are evaluated mainly by simulations.

Applying ARQ to real time video communication can significantly increase transmission delay due its retransmission operations. We analyze this delay and propose an adaptive error control scheme that uses acknowledgment from the receiver to reduce the delay. We evaluate this scheme using a computer simulation and show that the proposed scheme can reduce the delay by controlling the amount of video data by changing the quantization step size and video frame skipping. It also offers acceptable video quality as confirmed by a subjective evaluation test.

We propose a new bit timing recovery (BTR) scheme, what we call Step Sampled BTR (SSBTR), that can lower the sampling clock frequency and shorten the clock phase convergence time, for burst signals in high bit rate wireless access systems. The SSBTR scheme has the following characteristics. A sine wave resulting from the BTR code passing through a Nyquist Transmission System is always used, the sampling clock has a lower frequency than the system clock, and the clock phase of Intermediate Frequency (IF) signal input can be estimated from as few as 3 sampled data. The SSBTR scheme corrects the clock phase only once in a burst signal. Therefore, in some wireless access systems, some kind of operation must be performed after the SSBTR, in order to deal with long burst signals, instability of the system clock, and so on. In other wireless access systems that do not have these problems, clock phase can be fixed by the SSBTR scheme alone. The preformance of the SSBTR scheme with respect to additive white Gaussian noise (AWGN) was examined by computer simulation. In addition, when SSBTR is implemented in hardware, there are imperfections in the circuitry that lead to phase estimation error and thus deterioration, so we studied the effects of several such imperfections by computer simulation. The results of these simulations clarify the performance of the SSBTR scheme.