The authors propose a waveguide π-junction with an inductive wall. Galerkin's method of moments is applied to analyze it and small reflection and desired power division ratio is realized. Good agreement between the calculated result and the measured one verifies the design of a unit π-junction. The characteristics of aπ-junction with a wall are almost the same as those of a conventional π-junction with a post. Important advantage of the new π-junction with a wall is that it can be manufactured in the die-cast process of the waveguide while a post in the conventional one must be attached in an additional process. A 16-way power divider consisting of 8 π-junctions is designed at 11.85 GHz and the characteristics are predicted.

This paper presents a 15-GHz MMIC direct optical injection-locked oscillator (MMIC OILO) with very-wide locking range that uses photosensitive HBTs. The MMIC OILO consists of an HBT and a positive feedback circuit including a Q-damping variable resistor. By utilizing the high-fT/fmax photosensitive HBT, we realize both high-frequency oscillation of 15 GHz and increased equivalent electrical injection power. In addition to increasing the RF injection power, the Q-damping variable resistor effectively reduces the quality-factor of the oscillator, thus realizing the very wide locking range (f) of 567 MHz (f/fosc3.8%). The locking bandwidth of 3.8% is over 10 times wider than that of any yet reported microwave direct OILO. Furthermore, it is shown that the MMIC OILO can also work as a high-gain Q-variable filter photoreceiver by increasing a Q-damping variable resistance over the self-oscillation suppression range.

In this paper it is pointed out that although an elegant differential-like approach is developed, Coppersmith' attacking method on NIKS-TAS cannot succeed to forge a shared key of legitimate entities especially when p-1 contains highly composite divisors, as well as decomposibility-hard divisors. This is mainly due to a severe reduction of modulo size. Computer simulation results confirm this assertion. The ambiguity in the solutions to the collusion equations in the first phase can be analyzed by the elementary divisor theory. Moreover, two basis vectors, qi,ri in the second phase, are found to be inadequate to represent the space spanned by xi-yi and ui-vi(i=1,...,N), because qi,ri exist frequently over the space with small modulo size. Then, the erroneous values of αi,βi,...,εi(i=1,...,N) are derived from the inadequate basis vectors, qi,ri. Also, when the degeneracy in modulo size happens, the solutions to αi,βi,...,εi(i=1,...,N) cannot be solved even by means of the exhaustive search over the small prime divisors of p-1.

In this paper, we propose to use graded-index multimode fibers (GI-MMFs) with Fabry-Perot laser diodes (FP-LDs) for short-span and low-cost feeders. The multimode fiber feeders can be applied to wireless personal communication systems where the required feeder length is within several hundred meters, such as distributed antenna networks for microcellular systems or wireless LANs. The use of multimode fibers makes fiber coupling and connection easier, and has the potential to greatly reduce total system cost. Three types of GI-MMFs are considered as transmission media, (1) silica-based glass optical fiber (GI-GOF),(2) silica-core plastic-clad fiber (GI-PCF), and (3) all-plastic optical fiber (GI-POF). It is shown that GI-GOF and GI-PCF are suitable for use as feeders in the microcells of CDMA cellular and wireless LAN systems within 300m in length. GI-POF is estimated to be suitable for use as feeders in wireless LANs within 100m in length. A multimode fiber feeder with FP-LDs and GI-PCF of 300 m is developed in order to demonstrate its applicability to a wireless LAN system operating in the 2.4 GHz ISM band.

External modulators, which have smaller chirping characteristics than laser diode direct modulation, are desired for high-speed and long-distance optical fiber communication systems. This paper reviews semiconductor and Ti:LiNbO3 guided-wave high-speed optical modulators. Since several effects exist for semiconductor materials, various kinds of semiconductor optical modulators have been investigated. Among these, absorption type intensity modulators based on Franz-Keldysh effect in bulk materials and quantum confined stark effect in multiple quantum well materials, are promising because of compactness, low drive voltage nature and integration ease with DFB lasers. Recent progress on semiconductor absorption modulators and DFB-LD integrated semiconductor modulators is discussed with emphasis on a novel fabrication method using selective area growth by MOVPE (Metal Organic Vapor Phase Epitaxy). The Ti:LiNbO3 optical modulators are also important, due to the advantage of superior chirping characteristics and wide bandwidth. Since the Ti:LiNbO3 optical modulator has low propagation loss and low conductor loss natures for optical waves and microwaves, respectively, the traveling-wave electrode configuration is suitable for high-speed operation. Here, broadband Ti:LiNbO3 optical modulators are discussed with emphasis on traveling-wave electrode design.

This paper proposes a novel optical modulator for a millimeter wave (MMW) subcarrier optic link. The modulator enables the bi-phase modulation of MMW subcarriers. It simplifies the optic link by unifying such functions as IF modulation, up-convertion to MMW, and optical modulation, which are separately equipped in a conventional system. A simple model of a Mach-Zehnder external optical modulator (EOM) is used to illustrate how bi-phase modulation of millimeter wave (MMW) subcarriers can be accomplished by switching the EOM bias with a binary data signal. Experimental results are presented to confirm predictions. A wideband communications test system employing the EOM as a bi-phase modulator and utilizing spread spectrum modulation (1.3 µm optical wavelength, 40 GHz subcarrier, 100 MHz chip rate, 10MHz data rate) was developed. Bit error rate (BER) characteristics of an optical link that includes the proposed modulator are presented and compared with ideal performance and simulated predictions. Degradation of the BER characteristics from the simulation was less than 1 dB at a BER of 10-6. A frequency doubling subcarrier bi-phase modulator is also described.

We describe the design, fabrication, and characteristics of a push-pull type ridged Ti:LiNbO3 optical modulator with two electrodes. The structure keeps microwave propagation loss low and enables a large interaction between microwaves and optical waves under the condition of velocity and impedance matching, resulting in a large modulation bandwidth and low driving voltage. Using this structure, we have developed an optical intensity modulator with an optical 3-dB bandwidth of 45 GHz (an electrical 3-dB bandwidth of 30 GHz) and a half-wave voltage of 3.9 V in single-electdoe operation (a half-wave voltage of 1.95 V in push-pull operation)at a wavelength of 1.55µm.

This paper reviews an application of optical techniques to Microwave Signal Processing (MSP), such as frequency multiplexing using external optical modulators (EOMs), and microwave frequency add-drop multiplexing and mixing using semisconductor optical amplifiers (SOAs), as well as microwave phase control in the optical domain. The cascaded EOM links can be applied to microwave and millimeter-wave signal distribution networks. The add-drop links using SOAs can make it possible to realize a compact and cost-effective radio repeater for radio signal distribution. The several SOA mixing link configurations are also described.

The present paper is concerned with an algorithm for the minimization of multiple-valued input, binary-valued output functions. The algorithm is an extension to muitiple-valued logic of an algorithm for the minimization of ordinary single-output Boolean functions. It is based on a local covering approach. Basically, it uses a "divide and conquer" technique, consisting of two steps called expansion and selection. The present algorithm preserves two important features of the original one. First, a lower bound on the number of prime implicants in the minimum cover of the given function is furnished as a by-product of the minimization. Second, all the essential primes of the function are identified and selected during the expansion process. That usually improves efficiency when handling functions with many essential primes. Results of a comparison of the proposed algorithm with the program ESPRESSO-IIC developed at Berkeley are presented.

This article considers a hybrid data backup model for a file system, which combines both conventional magnetic disk (MD) and write-once, read-many optical disk (OD). Since OD recently is a lower cost medium as well as a longer life medium than the ordinary MD, this kind of backup configuration is just recognized to be important. We mathematically formulate the hybrid data backup model and obtain the closed-form average cost rate when the system failure time and the recovery time follow exponential distributions. Numerical calculations are carried out to obtain the optimal backup policy, which is composed of two kinds of backup sizes from the main memory to MD and from MD to OD and minimizes the average cost rate. In numerical examples, the dependence of the optimal backup policy on the failure and the recovery mechanism is examined.

This paper describes the performance of a predistorter implementation to a superluminescent diode (SLD) in fiber-optic wireless systems under the optical reflection. SLD intensity noise and 3rd-order intermodulation distortion (IM3) are experimentally compared with those of DFB-and FP-LD. It is observed that the IM3 of SLD has ideal 3rd characteristics and output noise remains unchanged against the number of optical connectors. It is also found that the predistorter reduces IM3 by 8 dB. Receiver sensitivity of the system is discussed from the view point of overall design. the BER performance of an SLD with predistorter using a π/4-QPSK signal as a subcarrier is also described theoretically and experimentally.

In this paper, we propose a new method of dialogue data collection which can be used to evaluate modules of a spoken dialogue system. To evaluate the module, it is necessary to use suitable data. Human-human dialogue data have not been appropriate to module evaluation, because spontaneous data usually include too much specific phenomena such as fillers, restarts, pauses, and hesitations. Human-machine dialogue data have not been appropriate to module evaluation, because the dialogue was unnatural and the available vocabularies were limited. Here, we propose 'Hybrid method' for the collection of spoken dialogue data. The merit is that, the collected data can be used as test data for the evaluation of a spoken dialogue system without any modification. In our method a human takes the role of some modules of the system and the system, also, works as the other part of the system together. For example, humans works as the speech recognition module and the dialogue management and a machine does the other part, response generation module. The collected data are good for the evaluation of the speech recognition and the dialogue management modules. The reasons are as follows. (1) Lexicon: The lexicon was composed of limited words and dependent on the task. (2) Grammar: The intention expressed by the subjects were concise and clear. (3) Topics: There were few utterances outside the task domain. The collected data can be used test data for the evaluation of a spoken dialogue system without any modification.

This paper presents the performance of optically controlled MESFETs as photodetectors. The optical performance characteristics such as optic-to-electric responsivity, and BER for a π/4-QPSK signal are experimentally investigated. Measurements are performed by using MMIC compatible MESFETs. Experimental results are also evaluated in comparison with calculated PIN-PD limit. Optic-to-electric responsivity has high gain at lower received optical powers. It is shown experimentally that MESFET photodetectors improve the permissible optical power by 6 dB compared to the PIN-PD limit. Optically controlled MESFETs will provide a novel receivers for fiber-optic systems.

This paper proposes fiber-optic radio highway network using code division multiple access (CDMA) method which is universally applicable for various type of personal radio services and radio air interfaces. The proposed system can asynchronously open the radio-free space among any microcells. The outage probability and the number of connectable radio base stations are theoretically analyzed and compared with these in using conventional subcarrier multiplexing (SCM) method. Analysis results show that the reduction effect of the optical signal beat noise, due to spread spectrum of optical signal, improves the number of the active RBSs in CDMA radio highway network.

A new configuration is proposed for an optoelectronic network (OEN) using microwave frequency mixing and multiplexing. The mn OEN consists of m optical sources, m-parallel n-stage cascaded optical intensity modulators, and m-photodetectors. The mn OEN matrix is theoretically discussed, and 12, 22 and 33 OENs are analyzed in detail. The 22 OEN, which mixes and multiplexes microwaves, is further investigated and the theoretical prediction derived from OEN equations is experimentally confirmed.

Exploitation of air interfaces for mobile communications is rapidly increasing because of diversified service demands, technology trends and radio propagation conditions. This paper summarizes the radio and optic interaction devices and systems that can solve the future problems resulting from spreading demands in mobile multimedia communications. The concept of the Virtual Free Space Network (Radio Highway Network) is proposed for universal mobile access networks that can support any mobile service or radio air-interface. As one example of the proposed network, the optical TDMA network for radio is analyzed and results of some theoretical calculations are shown.

As an optically controlled array antenna, a "two-laser type" using two laser diodes whose frequency difference is set to the desired microwave frequency has been proposed. In this paper, we confirm experimentally that the beamforming network of the two-laser type array antenna has very broadband characteristics by measuring the amplitude and phase of microwave signals at 1.5 GHz, 10 GHz and 20 GHz. Using the optically controlled beam forming network, the radiation pattern of a 4-element linear array antenna was measured at 1.5 GHz.

This paper proposes a new block coded quadrature amplitude modulation (BC-QAM) scheme, which is designed by an optimization technique based on simulated annealing. Simulated annealing is an effective nonlinear optimization technique and can be applied to both the discrete and the continuous optimization problems. In this paper, the simulated annealing technique is used to design the optimum BC-QAM signal, which minimizes the upper bound on the bit error rate (BER) in a Rayleigh fading channel. The computer simulation shows that the proposed BC-QAM can improve the BER performance. This paper also proposes a simplified design method to reduce the number of variables to be optimized. The proposed simplified method optimizes the in-phase and quadrature components of the BC-QAM signal separately. The computer simulation also shows that the BC-QAM designed by the simplified method gives little degradation on the BER performance, although the simplified method can significantly reduce the number of optimization variables.

The SAR distributions over a homogeneous human model exposed to a near field of a short electric dipole in the resonant frequency region were calculated with the spatial resolution of 1cm3 which approximated 1g tissue by using the FDTD method with the expansion technique. The dependences of the SAR distribution on the distance between the model and the source and on frequency were investigated. It was shown that the large local SAR appeared in the parts of the body nearest to the source when the source was located at 20cm from the body, whereas the local SAR were largest in the narrow sections such as the neck and legs when the source was farther than 80cm from the model. It was also shown that, for the near-field exposure in the resonant frequency region, the profile of the layer averaged SAR distribution along the main axis of the body of the human model depended little on frequency, and that the SAR distribution in the section perpendicular to the main axis of the human body depended on frequency. The maximum local SAR per gram tissue over the whole body model was also determined, showing that the ratios of the maximum local SAR to the whole-body averaged SAR for the near-field exposure were at most several times as large as the corresponding ratio for the far-field exposure, when the small source located farther than 20cm from the surface of the human model.

A goal of a broadband ISDN network is to provide integrated transport for a wide range of applications such as teleconferencing, entertainment video, and file distribution. These require multipoint communications in addition to conventional point-to-point connections. The essential component to provide multipoint communications is a multicast packet switch. In this paper, we propose and analyze a new parallel multicast packet switch which easily approaches a maximum throughput of 100% as the number of fanout and multicast rate are increased. The proposed switch consists of a simple ring network and a point-to-point switch network in parallel. The ring network provides both replication and routing of multicast packets. The point-to-point switch network is responsible for delivering only unicast packets. The ring network provided in this switch overcomes the problems of clock synchronization and unfairness of access in the slotted ring by synchronizing the ring to the time slot used in the point-to-point switch and providing small amount of speed-up. Moreover, the significant drawbacks of the basic cascaded multicast fabric design are removed in this parallel switch which can separate the unicast and multicast packets before entering the switch fabric. The performance analysis shows that this switch with the small size of input/output buffers achieves good performance in delay and throughput, and the packet loss probability less than 10-9.