Acceleration techniques have been incorporated into the generalized method of characteristics (GMC) to perform transient analysis of uniform transmission lines, for the special case when the transmission lines are driven by digital signals. These techinques have been proved to improve the simulation speed to a great extent when the analysis is carried out using iterative waveform relaxation method. It has been identified that the load impedance connected to the transmission line has a bearing on the efficiency of one of these acceleration techniques. Examples of an RLCG line terminated with linear loads as well as nonlinear loads are given to illustrate the advantage of incorporating these acceleration techniques.

Subcarrier multiplexing uses the available fiber bandwidth in optical transmission, efficiently. Semiconductor lasers, which are used as optical sources in such systems, exhibit nonlinear characteristics. Nonlinearity degrades the performance of such transmission systems. For nonlinearity compensation, nonlinear predistortion may be incorporated prior to the laser. Characteristics of this nonlinear block invert those of the laser source. Performance of the radio subcarrier multiplexed system with and without predistortion is evaluated by harmonic and intermodulation distortions analyses. Nonlinear distortion level decreases significantly when predistortion is employed prior to the laser. This enhancement results in system requirements on carrier-to-noise ratio being met for FM, 4-level QAM and HDTV (Zenith proposal) radio subcarriers. This amount of increase in carrier-to-noise ratio is a function of the optical modulation index.

Reducing communication complexity is a viable approach to multilevel logic synthesis. A communication complexity based approach was proposed previously. In the previous works, only disjoint input decomposition was considered. However, for certain types of circuits, the circuit size can be reduced by using overlapped decomposition. In this paper, we consider overlapped decompositions. Some design issues for overlapped decompositions such as detecting globals" and deriving subfunctions are addressed. Moreover, the Decomposition Don't Cares (DDC) is considered for improving the decomposed results. By using these techniques together, the area and delay of circuits can be further minimized.

Fiber-optic passive double star (PDS) network is described as an access network for microcellular radio communication systems. The intrinsic characteristics of the PDS network, reduction in the optical fiber count and flexible access capability, are examined. A unit cell structure is introduced which enables the PDS network to be effectively incorporated into the access portion of microcellular radio communication systems. The reduced total fiber length in the unit cell structure based on the PDS network is discussed in comparison with the conventional architecture. Calculations show that there is an optimum splitting ratio that minimizes the total fiber length. When the microcell radius and service area radius are 100m and 10km, respectively, the total fiber length of the PDS network is reduced to only about 9% of that of the conventional single star (SS) network for a splitting ratio of 34. Resource sharing and handover between microcells in a unit cell are performed by using the dynamic channel allocation function of the PDS system. Substantial performance improvement for loaded traffic can be obtained by resource sharing. When the splitting ratio is 32, the available traffic of a base station (BS) increases from 0.9 [erl/BS] to 3.4 [erl/BS] by adopting dynamic channel allocation for the lost call probability of 0.01.

A new arithmetic multiple-valued algebra with functional completeness is introduced. The algebra is called Neuro-Algebra for it has very similar formula and architecture to neural networks. Two canonical forms of multiple-valued functions of this Neuro-Algebra are presented. Since the arithmetic operations of the Neuro-Aglebra are basically a weighted-sum and a piecewise linear operations, their implementations are very simple and straightforward. Furthermore, the multiple-valued networks based on the Neuro-Algebra can be trained by the traditional back-propagation learning algorithm directly.

This paper proposes a new subscriber distribution method called FTTA (Fiber To The Area), which uses millimeter-wave radio band to connect subscribers with base station and optical fiber to connect base station with control station in order to obtain broad-band transmission. Usually two main causes of signal degradation, i.e., rainfall attenuation on radio channel and intermodulation distortion on optical channel are considered in this system. Taking into considerations of these two factors, we analyze the available capacity of FTTA system for various 22nQAM modulation levels. The analysis clarifies that there exists an optimum modulation level that can maxize the available capacity, and AGC circuit in the base station is useful to compensate the rainfall attenuation. It is shown that 18.0Gbps is available under the optimum modulation method of the 64QAM with AGC and 12.0Gbps under the 16QAM without AGC when 20 carriers are used.

An optical receiver for hybrid SCM video distribution systems that distribute AM, QAM (quadrature amplitude modulation) and FM TV signals simultaneously is investigated. We propose a novel receiver configuration called the Frequency Division type Receiver (FDR) with consists of a photo detector, filter, and multiple preamplifiers. The receiver is compared with existing receivers in terms of optical sensitivity, distortion characteristics, and configuration simplicity. We clarify that the newly developed FDR type receiver is most suitable for hybrid SCM video distribution systems.

This paper describes an overview of wireless communications based on fiber-radio technologies from the viewpoint of system applications, particularly in the area of microcell radio systems. Feasible fiber-radio networks design are detailed in order to increase system performance and cost effectiveness. The benefits of the evolving fiber-radio microcell system are discussed with a spectral delivery scheme to meet traffic demands. Foreseeable electronic and optic technologies are reviewed in light of the key parameters to optimize the overall system. This strategy will play a role in broadband and flexible networks.

This paper presents a potential FM double modulation technique for subcarrier optical transmission in order to improve the input dynamic range. The proposed theory of FM double modulation is presented. The BER performance and input dynamic range are shown theoretically and experimentally compared with conventional direct intensity modulation. It was found that the dynamic range could be experimentally improved by 20dB compared with the conventional method by using FM double modulation. The proposed technique achieved an input dynamic range of 60 dB even when using a commercial Fabri-Perot LD.

This paper describes the performance of AlGaAs/GaAs HBT's developed for power applications. Their applicability to power amplifiers used in digital mobile radio communications is examined through measurement and numerical simulation, considering both power capability and linearity. Power HBT's with carbon-doped base layers showed DC current gains over 90. A linear gain of 19.2 dB, a maximum output RF power of 32.5 dBm, and a power added efficiency of 56 percent were obtained at 950 MHz. Numerical simulations showed that the power efficiency of HBT amplifiers could be improved by using harmonic trap circuits. Intermodulation measurements showed that third-order distortions were at most 21 dBc level at the 1-dB gain compression point. RF spectrum simulations using π/4 shift QPSK modulation showed that side-band spectrum generation was less than 45 dBc level at points 50 kHz off of the carrier frequency. These properties indicate that the power handling capabilities and linearity of HBT amplifiers offer promising potentials for digital mobile radio communications.

Atmospheric optical communication (AOC) system using subcarrier PSK modulation is proposed and its superiority to OOK modulation in the presence of scintillation is discussed theoretically. An experimental AOC setup with a subcarrier modulated by 155.52(Mb/s) DPSK at light wave-length λ=0.83(µm) over an 1.8(km) outdoor path is employed to show the performance. Theoretical and experimental results are compared under scintillation in clear weather and a good agreement is observed. Finally, AOC systems using subcarrier M-ary PSK and multiple subcarriers are proposed and discussed.

This paper presents a delivery mechanism using a spectrum delivery switch (SDS) in a microcell system. In our fiber-optic microcell systems, modulators, demodulators and spectrum delivery switches are installed in a central station. A spectrum delivery switch controls provide flexible dynamic channel assignment and functions as a hand over algorithm. This control method employs a TDMA time slot switch and a MODEM connection switch. The relation between blocking probability and offered traffic are described and computer simulation results are shown. The results indicate an improvement in this blocking probability over conventional systems.

This paper analyses the amplification characteristics of a two-loop controlled switching power amplifier for a digital portable telephone and presents the amplifier which has a flat gain and small phase delay from dc to 100kHz. This amplifier is a modification of a switching regulator and it uses two-loop control to achieve a wideband amplification characteristic. Optimum amplification characteristics, however, can't be designed by using the conventional method for designing a switching regulator because a flat gain and small phase delay in an amplification characteristic has not been considered for most switching regulators. This paper analyses in detail the small-signal transfer functions of the switching power amplifier and shows the behaviour of zero and poles. It also shows the boundary condition of large-signal operation. A new design procedure of a switching power amplifier is presented, and the analytical results are verified by experiments.

This paper considers the problem of finding a largest common subgraph of graphs, which is an important problem in chemical synthesis. It is known that the problem is NP-hard even if graphs are restricted to planar graphs of vertex degree at most three. By the way, a graph is called an almost tree if E(B)V(B)+ K holds for every block B where K is a constant. In this paper, a polynomial time algorithm for finding a largest common subgraph of two graphs which are connected, almost trees and of bounded vertex degree. The algorithm is an extension of a subtree isomorphism algorithm which is based on dynamic programming. Moreover, it is shown that the degree bound is essential. That is, the problem of finding a largest common subgraph of two connected almost trees is proved to be NP-hard for any K0 if degree is not bounded. The three dimensional matching problem, a well known NP-complete problem, is reduced to the problem.

In this paper, we investigate various technology aspects in fiber-to-the-microcell systems. Background studies on radio propagation environment and system operations are provided first. The fundamental linearity characteristics of a directly and externally modulated optical links are analyzed next. An overall comparison between the two types of optical links, and system requirements among all types of wireless systems (from macrocells to picocells) are presented. Future research and development directions are also suggested.

This paper reports performance improvement in an optical fiber feeder for microcellular mobile radio systems. A low noise optical receiver using a transformer resonant circuit is described. With this receiver, CNR degradation due to receiver noise is suppressed to less than 0.9dB. Furthermore, two novel techniques, the use of a multiple-LD transmitter and automatic LD input level control, are proposed. The multiple-LD transmitter increases transmitter output power and reduces the transmitter noise. With a dual-LD transmitter, it is possible to increase the optical loss margin by 3.1dB, which corresponds to transmission length expansion of 6.2km, or to improve the received CNR by 2.8dB, which enables communication range expansion. Automatic LD input level control, which optimizes LD input level according to the received radio power, can expand the actual dynamic range of the up link.

In this study, an expression of the regression relationship with less information loss is concretely derived in the form suitable to the existence of amplitude constraint of the observed data and the prediction of response probability distribution. The effectiveness of the proposed method is confirmed experimentally by applying it to the actual acoustic data.

A new method by which images are coded with predictable and controllable subjective picture quality in the minimum cost of bit rate is developed. By using wavelet transform, the original image is decomposed into a set of subimages with different frequency channels and resolutions. By utilizing human contrast sensitivity, each decomposed subimage is treated according to its contribution to the total visual quality and to the bit rate. A relationship between physical errors (mainly quantization errors) incurred in the orthonormal wavelet image coding system and the subjective picture quality quantified as the mean opinion score (MOS) is established. Instred of using the traditional optimum bit allocation scheme which minimizes a distortion cost function under the constraint of a given bit rate, we develop an "optimum visually weighted noise power allocation" (OVNA) scheme which emphasizes the satisfying of a desired subjective picture quality in the minumum cost of bit rate. The proposed method enables us to predict and control the picture quality before the reconstruction and to compress images with desired subjective picture quality in the minimum bit rate.

This paper describes the hierarchical behavioral description language celled SFL and its processing system. This integrated CAD system called PARTHENON is used for designs of the leading ASICs in the NTT Systems Labs. This paper shows, therefore, the effectiveness of PARTHENON as a practical high-lelel synthesis system through real design experience. SFL was developed to aid in the design of the hardware functions and behaviors of ASICs composed solely of clocksynchronized circuits. The main features of SFL are as follows: (1) It is not mixed with connection description, but employs only behavioral description (like procedual description in program language), and it provides hierarchical expression of behavioral description. (2) It permits the description of parallel processing operations by adopting a new hardware task concept. And, (3) it is linked with the behavioral simulator, logic synthesizer, and other components of the processing system. After describing SFL in some detail, a brief explanation of its synthesizer and other processing components is provided, along with its application results in the real design of some leading ASICs at the NTT Systems Laboratories.