A multi-terminal serial optical link(MSOL) achieves very simple and cost effective radio cell configurations because only one pair of fibers is needed. In addition, low cost Fabry-Perot laser diodes(FP-LDs) can be employed. MSOL has a substantial problem in that the beat noise degrades the C/N in the up-link. To reduce this noise, we propose using an automatic wavelength-offset control(AWOC) circuit. The AWOC circuit offsets the LD wavelength by controlling the laser bias current to minimise the RF band beat noise which is inherent in MSOL systems, and enables high C/N optical-microwave transmission. An experimental MSOL consisting of 5 radio access stations, each equipped with AWOC, is constructed to estimate the noise free dynamic range for 800-MHz 20-carrier signal transmission. The up-link comprises a single mode fiber connecting five 1.3-µm FP-LDs operating at 0.2 mW. The down-link consists of a single mode fiber and one 1.3-µm Distributed Feedback type Laser Diode(DFB-LD) emitting at 4.0 mW. The experimental device achieves over 15 dB noise reduction compared to MSOL without AWOC in the temperature range of 0 to 40. By using the proposed AWOC, MSOL can achive low cost optical fiber RF microcell systems that are easy to install. Additionally, when we install MSOL in the radio base station, the links become more cost effective than coaxial cable links; they offer a wide dynamic range and higher transmission quality.

In this letter, we propose an adaptive multiuser receiver using a Hopfield network for code-division multiple-access communications and its performance is compared with that of the other types of multiuser receiver via computer simulation. The proposed adaptive receiver estimates both the signal amplitudes and spreading sequences for all the users using training data.

A miniature transceiver, including highly integrated MMIC front-end, for 1.9 GHz band personal handy phone system(PHS) has been developed. The terminal, adopting direct conversion transmitter and receiver technology, consists of four high-density RF circuit modules and a digital signal processing LSI with 2.7 V power supply. The four functional modules are a power amplifier, a transmitter,a receiver, and a frequency synthesizer. Each functional module includes one IC chip and passive LCR components connected with solder bumps on module substrate. The experimental miniature PHS handset has been fabricated to verify the design concepts of the miniature transceiver. The total volume of the developed PHS terminal is 60cc, including the 12cc front-end which comprises the four RF functional circuit modules. The air interface connection with the PHS base station simulator has been confirmed.

Rate-based congestion control is a promising scheme as data transfer service in ATM networks, and has been standardized in the ATM Forum. To migrate the existing upper layer protocols to ATM networks, however, further investigation is necessary. In particular, when ABR service class is applied to TCP (Transmission Control Protocol), duality of congestion control schemes in different protocol layers, i.e., conventional window-based congestion control in the Transport layer and ratebased congestion control in the ATM layer, may have a unexpected influence on performance. As an alternative approach for supporting TCP protocol, EPD (Early Packet Discard) has been recently proposed, which adds the function to the UBR (Unspecified Bit Rate) service. It does not have a "duality problem" since EPD only discards cells selectively to improve packet-level performance. In this paper, we exhibit performance of TCP protocol over ATM networks by using a simulation technique. We first compare rate-based control of ABR service and EPD applied to UBR service, and show that rate-control achieves better fairness and higher throughput in most circumstances. However, rate-based control requires careful tuning of control parameters to obtain its effectiveness and a duality problem leads to unexpected degradation of TCP-level performance. By the rate-based congestion control, temporal congestion at the switch is quickly relieved by the rate down of the source terminals. However, our simulation explores that if the parameter set of the rate-based congestion control is not appropriately used, the congestion is also recognized at TCP due to packet drops and TCP unnecessarily throttles its window size. To avoid this sort of the problem, we develop the appropriate parameter set suitable to TCP on ABR service, and point out that some modification of TCP may be necessary for further performance improvement.

This paper proposes a design technique for 3-D non-separable QMF banks with Face-Centered Cubic Sampling (FCCS) and Body-Centered Cubic Sampling (BCCS). In the proposed technique, 2-D McClellan transformation is applied to a suitably designed 2-D prototype QMF to obtain 3-D QMFs. The design examples given in this paper demonstrate advantages of the proposed method.

A 1.9GHz direct conversion receiver(DCR) chip which integrates an LNA, I/Q mixers(MIX), active lowpass filters(LDF) and variable gain amplifiers(VGA) was fabricated. Because the DCR for QPSK modulation systems is sensitive to the 2nd-order nonlinearity, linearization techniques are adopted in MIX and LPF. The DCR chip was fabricated using a BiCMOS process, and the die size is 5.1 mm by 5.1mm. The chip can operate from 2.7 V supply voltage and consumes 165mW when all the functions are activated. Suppression of local signal radiation and the 2nd-order distortion indicate the feasibility of Si-based DCR for QPSK modulation systems such as PHS.

This paper clarified fundamental aspects of both triboelectric processes and electrostatic discharge (ESD) phenomena to the electronic systems. A chance for ESD can occur if a charged metal object (steel piped chair, for example) contacts or collides with another metal objects at moderate speed. At metal-metal ESD event, the metal objects act as a radiation antenna in a very short time (some 100ps, for example) which emanates impulsive electromagnetic fields with unipolarity into the surrounding space. Because of ESD at low-voltage (3kV or less) conditions, the direction of electrons movement at the spark gap is always unidirectional and fixed. The spark gap works as a momentary switch and also as a "diode." The dominant fields radiated from the metal objects are impulsive electric fields or impulsive magnetic fields which depend on the metal object's electrical and geometric conditions. This impulsive electromagnetic fields penetrate electronic systems, causing electromagnetic interference (EMI) such as malfunctions or circuit upset. The difference between EMI actions in high-voltage ESD and low-voltage ESD is experimentally analyzed in terms of energy conversion/consumption. A series of experiments revealed that EMI actions due to the metal-metal ESD are not proportional to the charge voltage nor the discharge current. In order to capture single shot impulsive electromagnetic fields very close to the ESD point (wave source), a short monopole antenna as an ultra broad-band field sensor was devised. As for signal transmissions between the short monopole antenna and the instrument (receiver), micro/millimeter wave techniques were applied. The transmission line's minimum band width DC-18.5GHz is required for time domain measurements of low-voltage ESD.

The local moment functions for discrete Wigner trispectrum are examined in ambiguity and in time-frequency domain. A concept of multiple and multidimensional circular convolution in frequency domain is introduced into the discrete Wigner higher order time-frequency signal representation of any order. It is shown that this concept based on the 1st order spectra of the signal offers an insight into the properties of inconsistent local moment functions and their representation both in ambiguity and time-frequency domain. It allows to prove that midfrequency crossterms of a multicomponent signal can not be removed by any generalized 4th order ambiguity function which employ kernel function in the ambiguity domain. It is shown, that the concept of multiple convolution in frequency domain can lead to the crossterm-reduced discete time-frequency representations of any order

A decision circuit with a function of detecting the phase difference between input data and clock signal is presented. Direct coupled FET logic (DCFL) was used for basic gates. The circuit architecture was chosen to be suitable for DCFL. Novel circuit technologies were adopted to the phase detectors. In GaAs/AlGaAs pseudomorphic inverted HEMT's were used for fabrication. The decision circuit showed a wide phase margin of 288 degrees and small decision ambiguity of 27 mVpp up to 10 Gb/s. Linear and wide-range phase detection was achieved as well as an ability to compensate the variation of transition density, input bias and temperature.

A directed graph G = (V,E) is called the n-rotator graph if V = {a1a2an|a1a2an is a permutation of 1,2,,n} and E = {(a1a2an,b1b2bn)| for some 2 i n, b1b2bn = a2aia1ai+1an}. We show that for any pair of distinct nodes in the n-rotator graph, we can construct n - 1 disjoint paths, each length < 2n, connecting the two nodes. We propose a nonadaptive fault-tolerant file transmission algorithm which uses these disjoint paths. Then the probabilistic analysis of its reliability is given.

This paper proposes a mutual exclusion method that is unified for the parallel and distributed systems. The method partially serializes requests into partial queues of requests, which are next totally serialized into a main queue. A request in the main queue is authorized to enter the critical section (CS) when the request receives the privilege token from the previous request in the queue. In the distributed system of N sites that each is a parallel system, mutual exclusion is performed by cooperation of two algorithms based on the same method. The algorithm for the distributed system works on a logical network (that is a directed tree) of S ( N) sites. The algorithm for each site produces a local-main queue of requests. The chunk of requests in the local queue is concatenated at a time to the partial queue of the distributed system. The the cost of mutual exclusion -- the number of intersite messages required per CS entry -- is reduced to O(1) (between 0 and 3).

This paper describes the design of a high-speed 4-2 compressor for fast multipliers. Through the survey of the six kinds of representative conventional 4-2 compressor (RBA 1-3 and NBA 1-3) in both the redundant binary (RB) and the normal binary (NB) scheme, we extracted two problems that degrades the operating speed. The first is the use of multi-input complex gates and the second is the existence of transmission gates (TG) at the input and/or output stages. To solve these problems, we propose high-speed 4-2 compressors using the RB scheme, which we call the high-speed redundant binary adders (HSRBAs). Six kinds of HSRBAs, HSRBA 1-6, were derived by making the Boolean equations suitable for high-speed CMOS circuits. Among them, HSRBA2, HSRBA4 and HSRBA6 have no multi-input complex gate and input/output TG, and perform at a delay time of 0.89 ns which is the fastest of all 4-2 compressors. We investigated the logical relation between HSRBAs and conventional 4-2 compressors by analyzing the Boolean equations for each circuit. This investigation shows that all the conventional redundant binary adders RBA1-3 have the same logic structures as HSRBA2. We also showed the conventional normal binary adders NBA1-3 have the same logic structures as HSRBA1, HSRBA3 and HSRBA5, respectively. This implies all 4-2 compressors can be derived from the same equation regardless of RB or NB. We applied the HSRBA2 to a 5454-bit multiplier using 0.5-µm CMOS technology. The multiplication time at the supply voltage of 3.3 V was 8.8 ns. This is the fastest 5454-bit multiplier with 0.5-µm CMOS so far, and 83% of the speed improvement is due to the high speed 4-2 compressor.

An ordered binary decision diagram (OBDD) is a directed acyclic graph for representing a Boolean function. OBDDs are widely used in various areas which require Boolean function manipulation, since they can represent efficiently many practical Boolean functions and have other desirable properties. However, there is very little theoretical research on the complexity of constructing an OBDD. In this paper, we prove that the optimal variable ordering problem of a shared BDD is NP-complete, and briefly discuss the approximation hardness of this problem and related OBDD problems.

Recently applications of Hilbert curves are studied in the area of image processing, image compression, computer hologram, etc. We have proposed a fast Hilbert scanning algorithm using lookup tables in N dimensional space. However, this scan is different from the one of previously proposed scanning algorithms. Making the lookup tables is a problem for the generation of several Hilbert scans. In this note, we describe a method of making lookup tables from a given Hilbert scan which is obtained by other scanning methods.

In this paper, we study three-dimensional motion estimation using optical flow. We construct a weighted quotient-form objective function that provides an unbiased estimator. Using this objective function with a certain projection operator as a weight drastically reduces the computational cost for estimation compared with using the maximum likelihood estimator. To reduce the variance of the estimator, we examine the weight, and we show by theoretical evaluations and simulations that, with an appropriate projection function, and when the noise variance is not too small, this objective function provides an estimator whose variance is smaller than that of the maximum likelihood estimator. The use of this projection is based on the knowledge that the depth function has a positive value (i. e., the object is in front of the camera) and that it is generally smooth.

This paper overviews fiber-oriented wireless communication systems, particularly in the area of microcell systems. The benefits of fiber-oriented wireless systems are discussed focusing on an application board scheme to facilitate new service deployment in light of intelligent networks. Dynamic range improvement technologies to remove interference are highlighted. Overall system performance is calculated for an economical FP-LD. Furthermore, effective modem use and a potential diversity technique are introduced. This strategy will play a role in realizing flexible fiber-optic subscriber networks.

Several papers have been shown equalization in the reception side. However, equalization in transmission side that is partial response signaling (PRS) or precoding is also possible in a two-way interactive communication such as time or frequency division duplex (TDD of FDD). This paper proposes and investigates a system which includes a transmission equalization and reception equalization based on an array antenna. This system is the extension in spatial and temporal domains. The channel capacity can be improved in the super channel which includes the transmitter and receiver array antenna.

This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. During good channel conditions, the modulation parameters are selected to increase the transmission rate as much as possible with satisfying a certain transmission quality. As channel conditions become worse, lower rate modulation parameters are applied or transmission is stopped. The performances in fading environments are evaluated theoretically and by computer simulations. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

We have developed a complete chromium oxide (Cr2O3) passivated gas tubing system by introducing ferritic stainless steel instead of conventional austenitic stainless steel (SUS316L). 100% Cr2O3 passivation film can be formed on electropolished ferritic stainless steel surface because the diffusion coefficient of Cr in ferritic stainless steel is 104 times larger than in austenitic stainless steel. In ferritic stainless steel, moreover, welded bead surface is covered by 100% Cr2O3 pas-sivated film by an introduction of advanced welding technology.

Air interfaces of the future mobile communication are widely spreading, because of the multimedia service demands, technology trends and radio propagation conditions. Radio-Highway Networks are expected to realize the universal, seamless and multi-air-interface capability for mobile access networks, and play an important role in the future multimedia radio communications. For the radio-highway networks, this paper newly proposes natural bandpass sampling - asynchronous time division multiple access (NBS-ATDMA) method, where radio signals are natural bandpass sampled at the radio base station and are asynchronously multiplexed on the optic fiber bus link and intelligently transmitted to its desired radio control station. We theoretically analyze the loss probability of the radio signal due to collision in the network and the carrier-to-noise power ratio of received radio signals at the radio control station. Moreover, in order to reduce the loss probability, two access control methods, carrier sense and pulse width control, are proposed, and it is clarified that these improve the number of base station connected to radio highway networks.