A simulation model for natural convection was developed for determining the surface temperature distribution in base plates with rectangular vertical fins in communication equipment. An estimated velocity derived from the buoyancy and pressure drop equations in a duct was used for laminar forced convection cooling simulations in parallel plates. Temperature distributions in finned plates were calculated by numerical integration of the heat conduction equation. An experimental study was also performed, to check these simulation results, by changing the height of fins, the pitch of fins, and the heat generation conditions. Experimental results and analytical results were found to agree well. Also, this simulation method was extended to analyze natural convection cooling in vertical base plates with inclined parallel fins. We placed alternately on the plates the sections without fins and the sections with fins on the plates. Using the inclined fins, air flow rate between fins was large and fresh air flew into the fins from the side of the plates. The natural convective heat-transfer rate for inclined fins was found to be 14% higher than that for vertical fins.

The location of stations on the buses can not be ignored in the analysis of the DQDB protocol, especially when traffic load is heavy. In this paper, we propose a new method to model the DQDB (Distributed Queue Dual Bus) protocol by assuming that the request arrival process depends on both the value of the request counter and the location of a station on the buses. By taking these dependences, we can catch the real behavior of the DQDB stations, which is locationally dependent and unfair under heavy load traffic. Based on this model, we analyze the DQDB system with finite buffer by considering the request counter states and buffer states separately and obtain the throughput, mean packet delay and packet reject probability of individual stations. The throughput in individual stations matches that of simulation very well within the range of traffic up to the channel capacity. Also the delay and packet reject rate performance is good up to moderate traffic load. These numerical results reveal the properties of the location dependence and the unfairness of DQDB system under heavy load condition. The analytic results under heavy load traffic for a general DQDB system has not been reported till now. Therefore we conclude that our model and analysis are valid and effective.

This paper describes the fiber unit blowing length of an optical fiber distribution system for business buildings which employs pipe cable, fiber units and the fiber unit blowing technique. The relationship between the applied force and the length of a fiber unit blown into a straight pipe is investigated theoretically and experimentally and the fiber unit blowing length is estimated. Moreover, the pipe bending radius which has a small bending resistance force is clarified. Cables, fiber units and unit blowing equipment are manufactured based on the results and their transmission and mechanical characteristics are confirmed to be stable.

An adaptive array has been proposed as a canceller for both inter-symbol interference (ISI) and co-channel interference (CCI). However, it has no path-diversity gain since it selects just one signal correlated to the reference signal. In this paper, a novel interference canceller having sufficient path-diversity gain is proposed. The canceller is characterized by the combined configuration of an adaptive array and an equalizer. In the proposed system, a pre-selecting adaptive array is installed first. By employing a specific training sequence and sampling timing at the receiver during the training period, the perfect correlation between the "desired signal" and "short delayed" is achieved. Therefore, the pre-selecting adaptive array can extract the desired and ISI signals simultaneously, and the cascaded adaptive equalizer can provide the path-diversity gain without degradation by interference. The proposed system achieves a simple configuration and robustness against both ISI and CCI with a sufficient path diversity gain. In computer simulations, average BER characteristics of the proposed system were evaluated in a quasi-static Rayleigh fading channel. The simulation results showed that the system can reduce both long-delayed ISI and CCI efficiently, and that the expected path diversity gain is obtained even with strong CCI. They also showed that the degradation is not so serious when the number of antenna elements is less than that of incoming signals.

In this letter, we propose new methods for estimating frequency and phase of a complex sinusoid in complex white Gaussian noise. These new estimators use the cyclostationarity of the sinusoid which is a cyclostationary signal type. Only one component corresponding to a lag of zero of cyclic autocorrelations is used to reduce the computational load. The performances of our proposed estimators are compared to those of Kay estimator, Cramer-Rao bound (CRB) and maxim-likelihood estimator (MLE). Simulation results show that our proposed methods can estimate the frequency and phase correctly even in low signal-to-noise ratio (SNR).

This letter newly proposes the polarity-reversing type photonic receiving scheme based on bipolar correlation for optical CDMA signal in radio highway. The proposed scheme can more improve the limitation of the number of radio base stations connected to radio highway and more reduce the peak laser power at the radio base station than the conventional unipolar type receiving scheme using prime codes.

Vehicular speed response phase locked loop (VSR-PLL) is a novel circuit to remove a steady-state frequency offset which arises in the receiver with directive antenna. In this paper, the circuit is applied to Ricean fading environment. For the application of VSR-PLL to Ricean statistics channel, the Doppler shift information of direct wave must be obtained because the self-oscillation frequency of VCO is controlled by using the information. This paper describes an estimation method for the Doppler shift of the direct wave, and shows the several results of the performance analysis for the estimation method and proposed VSR-PLL with the method. As a result, we found that the proposed VSR-PLL could reduce the irreducible bit-error rate for QPSK system from about 10-2 to 10-3 on several conditions.

Per-Virtual Connection (VC) queueing allows an ATM switch to schedule cells to be transmitted on a link based on their VC. This alternative to the traditional First-In-First-Out(FIFO)queueing, in which cells from different VCs of the same priority are stored in a common queue, is implemented by some switch manufacturers. This paper assesses the merits of per-VC scheduling in regards to capacity, traffic shaping, and interworking with traffic management mechanisms such as connection admission control (CAC) and use of queue thresholds. The paper also discusses the conditions which favor the use of per-VC scheduling.

While active researches have been continuously made on the ATM switch architectures and the QoS service guarantees, most of them have been treated independently in the past. In this paper, we first explain the architectural requirement on the ATM switches to implement the mechanism of QoS guarantees in the context of ATM congestion control. Then we discuss how a vital link between two should be built, and remaining problems are pointed out.

This paper introduces and studies the performance of an NN space-division, single-stage ATM switch with dual input-queueing. Each input port has two separate FIFO queues, an "odd" and an "even" queue. An incoming cell is stored at the input at either of two FIFOs according its output port destination (output ports are also labeled as "odd" or "even"). Hence we call this scheme the Odd-Even switch. We compare the Odd-Even switch to the ordinary input-buffered switch and we find that it can achieve a remarkably higher performance, in terms of throughput, mean delay and cell loss. This is due to the fact that the Head-of-Line effect becomes less problematic under the Odd-Even switch. Our results are based on various traffic models. Finally, we compare the Odd-Even scheme to the Look-ahead (input "window") policy.

We demonstrate an electrooptic synthesis technique for generating arbitrarily shaped short optical pulses from a CW narrow linewidth laser. For the optical pulse shaping, a large-amplitude electrooptic phase modulator is specially fabricated by employing the quasi-velocity-matching. The phase modulated light having sidebands as wide as 1 THz is separated and phase-only-controlled spatially by a liquid crystal modulator array. After composing the light by using a grating, nearly 1. 2 ps of Fourier-transform-limited optical pulses is obtained.

Requirements engineering refers to activities of gathering and organizing customer requirements and system specifications, making explicit representations of them, and making sure that they are valid and accounted for during the course of the design lifecycle of software. One very popular software development practice is the incremental development practice. The incremental development refers to practices that allow a program, or similarly specifications, to be developed, validated, and delivered in stages. The incremental practice is characterized by its depth-first process where focuses are given to small parts of the system in sequence to fair amounts of detail. In this paper, we present a development and validation of specifications in such an incremental style using a tool called ASADAL, a comprehensive CASE tool for real-time systems. ASADAL supports incremental and hierarchical refinements of specifications using multiple representational constructs and the evolving incomplete specifications can be formally tested with respect to critical real time properties or be simulated to determine whether the specifications capture the intended system behavior. In particular, we highlight features of ASADAL's specification simulator, called ASADAL/SIM, that plays a critical role in the incremental validation and helps users gain insights into the validity of evolving specifications. Such features include the multiple and mixed level simulation, real-value simulation, presentation and analysis of simulation data, and variety of flexible simulation control schemes. We illustrate the overall process using an example of an incremental specification development of an elevator control system.

This paper discusses an ATM based access system for a broadband access network that provides flexible and cost effective multimedia services for mass consumption including households. The access system proposed herein uses ATM-PDS subscriber transmission technologies, thus enabling multiple users to share a single fiber resource while transmitting or receiving multimedia information within the broadband network. The system also has virtual channel concentration function by using the bearer connection control protocol being studied for VB5. 2 interface in the ITU-T. We show that the virtual channel concentration function reduces the access cost per user. We also discuss multiple QoS control methods in the system to provide multiple services efficiently. This paper evaluates two methods to handle ABR class and UBR class traffic: shared bandwidth with preferred ABR method, and guaranteed bandwidth with overriding method. The result indicates that when using the shared bandwidth with preferred ABR method for the access system, ABR throughput and UBR throughput per VC depend on the proportion of the number of ABR-VC connections to the total active VCs and on the each buffer size in the access system. And it is difficult to control ABR-VC and UBR-VC throughputs in the access network by using the shared bandwidth with preferred ABR method, which simple mechanism. With the guaranteed bandwidth with overriding method, while ABR-VC throughput and UBR-VC throughput also depend on the proportion of ABR-VCs to the total VCs and on the buffer size, it can offer the minimum guaranteed throughput to the UBR traffic. The result shows the method is effective for easy service provisioning.

This paper deals with an orthogonal functional expansion of a non-linear stochastic functional of a stationary binary sequence taking 1 with unequal probability. Several mathematical formulas, such as multivariate orthogonal polynomials, recurrence formula and generating function, are given in explicit form. A formula of an orthogonal functional expansion for a stochastic functional is presented; the completeness of expansion is discussed in Appendix.

We extend the use of a saturable Bragg reflector to modelock a NaCl:OH- color center laser, producing pulses adjustable from 200 fs to 2 ps, and tunable from 1. 499 µm to 1. 535 µm, with the minimum pulsewidth near 1. 51 µm. The laser is self-starting, requires no dedicated dispersion compensating optics, and maintains a highly stable, nearly transform limited output pulse train with up to 150 mW average output power.

Optimization of InGaAs/InAlAs multiple quantum well structures for high-speed and low-driving modulation, as well as polarization insensitivity and low chirp, was investigated as a function of well thickness and strain magnitude. As a result, very short optical pulses with 4-6 ps was obtained using a low driving-voltage (<2. 0 Vpp) electroabsorption modulator module operating at a 40-GHz large signal modulation. Small chirp operation for low insertion loss (<8 dB from fiber-to-fiber) with prebias was also demonstrated and the product of the pulse width and the spectral width was estimated to be 0. 39 for a 5 ps pulse width that is nearly transform-limited.

Input and output queueing two stage ATM switch model which is effective under variable hot-spot traffic is proposed. In order to prevent the degradation of performance due to hot-spot traffic, the hot-spot route is added in which cells destined to the hot-spot port bypass. The switch applies the backpressure mode basically. When the switch judges that the hot-spot port exists, it routes cells destined there to the hot-spot route and applies the queue loss mode on them. We evaluate both the cell loss probability and the mean system delay under the nonuniform traffic with variable hot-spot port by computer simulation. As the results, it is shown that our proposed switch can achieve better switching performance than those of conventional switches under variable traffic condition.

The symbol basis side information generated by Viterbi's ratio threshold test technique is proposed to improve the performance of the asynchronous slow-frequency-hopped multiple access system with BFSK signaling in the frequency non-selective fading channel. By properly setting the ratio threshold to produce erasure decisions for the received symbols, the system performances are optimized. The relationship among the hit symbols in a hop duration is exploited by this symbol basis side information to greatly reduce the packet error probability. This packet error rate improvement can be as large as two order of magnitude, compared with perfect hop basis side information systems.

Asynchronous Transfer Mode (ATM) networks are expected to support a diverse mix of traffic sources requiring different Quality Of Service (QOS) guarantees. This paper initially examines several existing scheduling disciplines which offer delay guarantees in ATM switches. Among them, the Earliest-Due-Date (EDD) discipline has been regarded as one of the most promising scheduling disciplines. The EDD discipline schedules the departure of a cell belonging to a call based on the delay priority assigned for that call during the call set-up. Supporting n delay-based service classes through the use of n respective urgency numbers D0 to Dn-1 (D0D1 Dn-1), EDD allows a class-i cell to precede any class-j (j>i) cell arriving not prior to (Dj-Di)-slot time. The main goal of the paper is to determine the urgency numbers (Dis), based on an in-depth queueing analysis, in an attempt to offer ninety-nine percentile delay guarantees for higher priority calls under various traffic loads. In the analysis, we derive system-time distributions for both high- and low-priority cells based on a discrete-time, single-server queueing model assuming renewal and non-renewal arrival processes. The validity of the analysis is justified via simulation. With the urgency numbers (Dis) determined, we further propose a feasible efficient VLSI implementation architecture for the EDD scheduling discipline, furnishing the realization of QOS guarantees in ATM switches.

We study buffer access policies which provide different loss priorities between two types of services, namely, real-time and nonreal-time services in ATM networks. Real-time services, such as video and voice, require the cell transmission with bounded delay. For these services, their available buffer sizes are limited by the delay bounds. We compare the performance of several buffering policies with bounded delay constraints of real-time services. Numerical results indicate that a simple buffering policy, called limited partial buffer sharing (LPBS) proposed in this paper, has a good performance for efficient use of ATM networks.