Optical access networks will be key infrastructures to realize the multimedia society in the near future. Usually, in the case of trunk line, optical cables are installed under the ground. But optical fiber cables approach to offices and homes for optical access networks, the cables often take forms of aerial cables. Some issues must be considered in the optical cable splicing of aerial routes. This paper discusses some subjects; for example, a spare length of the fiber in a cable closure should be short and the splicer should be light weight and compact size to ensure easy operation in the aerial site. This paper also proposes two types of fusion splicers and a useful operation table for aerial optical cable splicing.

A Reed-Solomon coded Type-I Hybrid ARQ scheme based on a Selective-Repeat (SR) ARQ with multicopy retransmission is proposed for mobile/personal satellite communication systems of a transmitter and a receiver both with the finite buffer. The performance of the proposed scheme on fading channels is analyzed. The basic idea of the strategy is the use of two modes; the SR mode and the multicopy mode. In the latter mode, erroneous blocks stored in the transmitter buffer are alternatively retransmitted multiple times when ν consecutive retransmissions in the SR mode are received in error. Numerical and simulation results for ν1 show that the proposed scheme presents better performance than the conventional SR+ST scheme 2 of the 2N block buffer by Miller and Lin.

For designing the underwater transmission system using directly projected audible sound by underwater loudspeaker to prevent a diving accident and/or to give a working instrucion, it is important to estimate the transmission loss for a wall not onl for pure tones but also for wideband signal such as voice and noise. In this paper, two practical methods of evaluating the underwater insulation effect for a single wall are discussed. One is a reconfirmation that the mass law which is frequently used in air still explains the transmission loss in water. Because parameters such as surface density and sound velocity in the mass law are widely changeable depending on the depth in water, much complexity is involved in preparing a theoretical curve for every parameter. So to avoid such complexity, a unified parameter Φ(=ωm cos θ/2ρc) is introduced to describe the mass law. This newly presented curve as a function of Φ is in good agreement with all rearranged experimental data for every kind of plates. The other is a proposition of new evaluating method of insulation effect of a wall for a wideband signal, using an idea of (100-α) percentage point of the noise level probability destribution, Lα. Firstly proposed method is confirmed experimentally and secondly proposed method is confirmed by a simulation experiment.

A network with input and output buffer is proposed. It consists of several switching stages composed of 33 basic switching elements which are connected with perfect shuffle and horizontal connections. The proposed network reduces the required number of stages, and increases the fault tolerance due to its highly regular connection scheme. Its performance was evaluated with computer simulation under bursty traffic environment. For a 128128 switch with 11 switching stages, packet loss ratio of 10-6 was obtained when the input load is 0.8 and the burstiness is 10.

Two high output-resistance CMOS current mirrors suitable for a low-voltage operation and achieving a high output-swing are presented. They incorporate a modified regulated-cascode, which employs a current-mode amplifier. The main architecture concepts and their detailed schematic examples are discussed. SPICE simulation comparison is shown and the properties of each architecture are pointed out.

This paper proposes a new approach for distributing millimeter wave signals from a central location to micro-base-stations using optical fiber links. The links utilize two Mach-Zehnder external optical modulators (EOMs) to perform all optical down-conversion, eliminating the need for a local oscillator or laser diode in the micro-base-station. A simple model of the EOMs is developed to illustrate the principle of dual-EOM mixing. The characteristics of conversion loss and intermodulation are examined for two cases: where the EOMs are operated in the linear mode and where the local oscillator's EOM is biased as a frequency doubling modulator. Additionally, we examined the use of an optical amplifier to reduce conversion loss for these two cases. The measured conversion loss of the link was 82 dB, and we estimated this could be reduced to about 48 dB by employing an optical amplifier and a more efficient EOM for RF reception.

This paper presents fully digital high speed (17.6Mb/s) burst modem for Offset Quadrature Phase Shift Keying (OQPSK), which employs novel digital modem VLSICs. The modulator VLSIC directly generates modulated intermediate frequency (IF) signals in a fully digitalized manner. A newly proposed digital reverse-modulation and pre-filtered carrier filter-limiter scheme realizes low power consumption and stable operation in a low Eb/No condition. The demodulator VLSIC also achieves fast bit-timing acquisition in burst mode. Moreover, it supports stable initial burst acquisition by a novel automatic frequency control (AFC) acquisition detector and a digital burst detector. A digital burst automatic gain control (AGC) compensates burst-to-burst level differences without analog circutits. Performance evaluation results show that the new modem achieves satisfactory bit-error-rate performance in severe environments. The developed modem has been employed in a commercial portable earth station for ISDN services and reduces the hardware size to one third that of the conventional one.

A systematic procedure to configure faulttolerant systolic arrays based on Triplicated Triple Modular Redundancy is proposed. The design procedure consists of the triplication of the dependence graph which is formed from a target regular algorithm and the transformation onto physical time-processor domain. The resultant systolic arrays tolerate failures not only on processing elements but also on communication links. While it needs sophisticated connection scheme between processing elements to guarantee the fault-tolerance on communication links, the link complexity is possibly reduced by optimizing redundant operation scheme. Unconstrained and constrained link minimization problems are introduced, and the possibility and the constraints required for link complexity reduction are investigated.

One of the functions that should be provided in ATM LANs is multicast communication. For multicast communication on ATM LANs, the architecture of switch fabric and protocols for signaling have been studied. However, when data communication using a multicast connection such as LAN emulation service is provided, ABR service on a multicast connection (Multicast ABR) is also required. ABR service has been actively discussed in the ATM forum. Unfortunately, the study on flow control mechanism for Multicast ABR is not enough. This paper discusses the suitable flow control mechanism for Multicast ABR and shows its performance.

In this paper, a simple frame synchronization system for M-ary/SS communication systems is proposed, and synchronization performance and the resulting bit error rate performance are analyzed. The frame synchronization system uses racing counters and framing chips which are added to spreading sequences. M-ary/SS communication systems can improve bit error rate performance under the condition in which there is an additive white gaussian noise. Synchronization of M-ary/SS communication systems is difficult, however, because M-ary/SS communication systems have several spreading sequences. The authors proposed the simple frame synchronization system which uses only one chip in the spreading sequence as a framing signal. This system needs a long time for initial acquisition as the frame length is longer. The proposed system in this paper can make initial acquisition time short by increasing the number of framing chips. The proposed system corresponds to the conventional system when the number of framing chips is l. As the result, it is shown that several framing chips contribute to decrease the initial acquisition time. Moreover, the frame synchronization system can be applied to asynchronous M-ary/SSMA system when different framing chip pattern is assigned to each user.

In this paper, a multiuser receiver using a Hopfield network (Hopfield network receiver) for asynchronous codedivision multiple-access systems is proposed. We derive a novel likelihood function for the optimum demodulation of a data subsequence whose length is far shorter than that of the entire transmitted data sequence. It is shown that a novel Hopfield network receiver can be derived by exploiting the likelihood function, and the derived receiver leads to a low complexity receiver. The structure of the proposed receiver consists of a bank of correlators and a Hopfield network where the number of units is proportional to both the number of users and the length of a data sequence demodulated at a time. Computer simulation results are presented to compare the performance of the proposed receiver with those of the conventional multiuser detectors. It is shown that the proposed receiver significantly outperforms the correlation receiver, decorrelating detector and multistage detector, and provides suboptimum performnace.

In this paper, we describe effects of oddcorrelation functions and band-limitation filters for direct-wave reception systems using broadband spread-spectrum (B-SS) techniques. The receiver of this system is synchronized to the direct-wave. First, the effects of odd-correlation functions are investigated by using M-sequences and random sequences. The effects of even-correlation functions for those sequences can be easily obtained by using results of effects of odd-correlation functions for random sequences. Here we derive a novel function of odd-correlation variance for M-sequence, which is obtained theoretically. Consequently, we show the advantage of M-sequence which is used as spreading sequence. As a reason, in the odd-correlation function of M-sequence, small values are taken near the synchronous phase where harmful scattered-waves exist, strongly. Next, the effects of both odd-correlation function and band-limitation filter are studied by using several kinds of filters. Here we discuss the difference of characteristics in case that despreading sequence of bandlimited pulse or that of rectangular pulse is used in the correlator of the receiver. The technique despreading by rectangular pulse can be achieved a high speed signal processing and equipment miniaturizing because of utilization of switching circuit. We show the advantage of despreading sequence of rectangular pulse, when the limitation bandwidth of transmitting signal takes a small value. Because the characteristics of the correlation function between transmitting sequence of bandlimited pulse and despreading sequence of rectangular pulse can be kept better than that between the transmitting sequence and despreading sequence of bandlimited pulse. As these results, in severe bandlimited direct-wave reception systems using B-SS techniques, M-sequence of rectangular pulse as despreading sequence is most suitable.

This paper gives an overview of the research and development trends in millimeter-wave short-range application systems, such as communication systems and sensing systems, in Japan and other countries. Frequency management trends are also described. Major research and development efforts in Japan have currently been concentrated on the 59-64 GHz band. The first major achievement resulting from those efforts was the allocation of the 60-61 GHz band to the automotive radar systems. Test productions of automotive radars in this band have already started. Further technological developments to reduce the cost and size of radar products are, however, required in order for such radar systems to be widely used. Development of broadband wireless LAN systems has also been intensively made in the 60 GHz band. In addition, technical issues related to standardization of millimeter-wave wireless LAN systems in the 60 GHz band have been examined at the Association of Radio Industries and Businesses. The application areas of millimeter-waves in the future are expected to become more diverse. Research and development trends of future application systems, such as broadband mobile communication systems and imaging radar systems, are also described. These systems require more advanced millimeter-wave technologies, such as smart antennas, low power-consumption devices, and more sensitive detectors. Efforts to develop these technologies must be strengthened.

For quasi millimeter-wave and millimeter-wave high-speed wireless communications over wireless LANs and wireless ATMs, narrow beam antennas have been shown to provide high transmission quality by suppressing the troublesome multipath effect. However, the diameter of sector antennas needed to create the narrow beams rapidly increases with the sector number. In addition, the cylindrical shape of typical sector antennas does not suit portable terminals. This paper shows a methodology for designing planar sector antennas that overcomes these problems. The proposed antenna uses two kinds of beams and the antenna gains are equalized in all sectors. The antenna is developed as a 4-beam subarray fed by a planar Butler matrix circuit. The design method of the subarray and an evaluation of its characteristics in the 20 GHz band are discussed.

In this contribution an algorithm for joint detection in fast frequency hopping/multiple frequency shift keying (FFH/MFSK) multiple access (MA) systems is presented. The new algorithm - referred to as REC algorithm - evaluates ambiguities which occur during the decision process and iteratively reduces the number of candidate symbols. The REC algorithm is of low complexity, suitable for every addressing scheme, and effective for both an interference-only channel and a fading channel. For the interference-only channel the REC algorithm enables maximum likelihood (ML) joint detection with low computational effort.

In the envisaged Universal Mobile Telecommunications System (UMTS), the satellite component will have to provide services to mobile or, in some cases, hand held terminals with a required grade of user co-operation and link availability in various communication environments. This may require the capability of the satellite link to cope with more severe multipath environments than those for which mobile satellite links are most frequently designed (maritime or open rural applications); unfortunately, when the mobile radio channel is affected by multipath and a coherent demodulation is chosen, the phase synchronisation can be a critical issue. To satisfactorily deal with the arising difficulties, a dual channel demodulation is a viable and efficient strategy for the forward link, since only one common pilot channel is needed in this case. If the same dual channel demodulation is considered for the return link, an unacceptable capacity reduction may result. In this paper, some synchronisation strategies are analysed and an efficient dual channel demodulation scheme is proposed for the return link of a satellite DS-CDMA mobile communication system; furthermore, the impact on the overall system performance or capacity is analysed.

In this paper, the bit error rate (BER) performance of the Spread Spectrum communication system with Constrained Spreading Codes (SS-CSC) is analyzed. The BER of the SS-CSC system is the same as that of the Bi-orthogonal system. Moreover, the frequency utilization efficiency of the SS-CSC system is better than that of the Bi-orthogonal system when K 10 and N = 3.

This paper proposes a novel Doppler frequency shift compensation technique to achieve terrestrial and low earth orbit (LEO) satellite dual mode DS/CDMA terminals robust to high Doppler shift and multipath fading. In order to satisfy the requirements of wide dynamic range and high accuracy simultaneously, the proposed scheme employs two stage compensation scheme, i.e., coarse compensation to keep dynamic range of about 100 kHz and fine compensation to satisfy its resolution of about 30 Hz, using block demodulation technique. Computer simulation results show that the proposed scheme can sufficiently compensate for the offset frequency up to the range of about 100 kHz at the terrestrial and LEO satellite combined mobile communication systems.

A subclass of context-free languages, called pure context-free languages, which is generated by context-free grammar with only one type of symbol (i.e., terminals and nonterminals are not distinguished), is introduced and the problem of identifying from positive data a restricted class of monogenic pure context-free languages (mono-PCF languages, in short) is investigated. The class of mono-PCF languages is incomparable to the class of regular languages. In this paper we show that the class of mono-PCF languages is polynomial time identifiable from positive data. That is, there is an algorithm that, given a mono-PCF language L, identifies from positive data, a grammar generating L, called a monogenic pure context-free grammar (mono-PCF grammar, in short) satisfying the property that the time for updating a conjecture is bounded by O(N3), where N is the sum of lengths of all positive data provided. This is in contrast with another result in this paper that the class of PCF languages is not identifiable in the limit from positive data.

A circularly polarized omnidirectional antenna consisting of a vertical sleeve dipole and three pairs of titled parasitic elements set around it is proposed. The antenna is useful to mobile communication because the use of circular polarization allows us to suppress the effect of multi-path reflection waves (inverse rotation) caused by building walls and surface of the ground. The antenna with an omnidirectional pattern has a simple structure without a feeding network for radiating circular polarization. To understand the radiation characteristics of the proposed antenna, an approximation theory using the induced electromotive force method is introduced. As an example, using a fixed spacing of a quarter wave-length between the vertical dipole and the parasitic elements, the possibility of generation of circular polarization is examined. Then the computational results of the axial ratio and the input impedance are compared with the results of the numerical analysis using the moment method and the experimental result. The radiation characteristics of the antenna can be understood by using the approximation theory introduced here. As a summary of the study, the contour map of the axial ratio of circular polarization is depicted using the moment method. For practical design of this antenna, a small correction factor should be multiplied to the calculated results. From the experimental results, the proposed antenna has a gain of 2 dBi and 3 dB band-width with an axial ratio of about 8%.