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.

VP Network Designer, a software tool that automates the tasks involved in the transaction of service orders in VP leased line services, is introduced here in this paper. The tool is composed of two functions: VP Design Explorer which, given a request for VP establishment, determines a disjoint backup and target VP routes to support fault tolerance under VP-APS scheme; Network Resource Administrator which provides data administering functions, useful in maintaining a clear insight into the state of the network. The paper focuses on the implementation of VP Design Explorer. A scheme, proposed as disjoint VP routes search, is used to evaluate a pair of VP routes that guarantee duct level independence. The scheme is based on an integer programming modeling approach, and is proved to be effective for evaluating disjoint paths in a hierarchical network. VP Design Explorer is equipped with an additional feature where, under conditions of resource shortage, it presents a set of additional resources that are necessary to satisfy VP demand, together with the VP routes that become possible by the additions. Formulation of the problem is attained through an extension of the disjoint VP routes search scheme. A prototype of VP Network Designer is presented and its performance tested using computer simulations. The tool is found to achieve a computational time performance in the order of seconds and minutes, for evaluating disjoint VP routes search problems under real life ATM network conditions.

The proposed GCRA (Generic Cell Rate Algorithm) traffic shaper consists of a regulator and a scheduler. It can shape multiple incoming VBR (Variable Bit Rate) cell streams simultaneously to be strictly conforming according to the GCRA algorithm when the cells depart for the ATM output link. The impact of cell emission conflicts is considered and resolved by using an EDD (Earliest-Due-Date) scheduler and a feedback signal from the scheduler to the regulator. The call admission control condition and the cell delay bound are derived. Simulation results demonstrate that the output cell streams of the proposed GCRA traffic shaper do not contain any non-conforming cells and the scheduler queue size is significantly reduced. Meanwhile, the delay performance is almost not affected by the use of the feedback mechanism.

We propose a robust detection scheme by employing an order statistic filter as a preprocessor of the input signal. For ease of design, the variance of the order statistic filtered output is modeled by proposing an approximate upper bound. The detector is analytically designed using a fixed sample size (FSS) test scheme. The performance of the proposed detector is compared to that of other robust detectors in terms of the sample size required for given false alarm and miss detection probabilities. Finally, analytical results are verified by computer simulation.

This study presents a novel window-based token protocol which supports two priority levels of ATM-like bursty traffic. The proposed protocol ensures that packets arriving during a given window period are always transmitted prior to those arriving during subsequent window periods. During which periods, high priority (delay-sensitive) packets are served by a nonpreemptive priority service discipline. Under this window-based token protocol, the delay bounds for packets of both priority levels are derived when the traffic streams satisfy the traffic descriptors. Hence, a call admission control policy based on delay bounds can be employed to guarantee QoS parameters such as the packet delay and packet loss-free requirement for each traffic stream. The protocol proposed herein can achieve tighter delay bounds than the IEEE 802. 5 token protocol and the timed token protocol used in FDDI, particularly for high priority bursty traffic, thereby making it highly attractive for supporting not only real-time multimedia VBR or CBR services such as in ATM networks but also ATM encapsulation such as in Cells In Frames (CIF) protocol.

This paper describes key technologies for implementing ATM internode signalling. The reliability of a multimedia handling network can be improved by setting multiple virtual paths(VPs)between two nodes and setting signalling links over each internode VP. A software structure appropriate for handling the signalling protocol(MTP3b)within this framework is proposed. We also propose a cost-effective and reliable way to set a signalling route between a node and the service control point(SCP), based on the associate mode structure. Evaluation by implementing a node system shows that it requires only 15% more dynamic program steps for one sending/receiving sequence of the VP signalling than the existing method for circuit-related information. Thus, we could attain highly reliable and cost-effective signalling for ATM multimedia networks.

This paper proposes a frequency diversity transmission scheme that obtains a frequency diversity gain and does not degrade spectrum efficiency; it utilizes multiple carrier frequencies alternately, not simultaneously. This scheme improves the bit error rate (BER) of significant information bits by sacrificing that of insignificant bits in fading channels. Simulation results show that the error floor of significant information bits is reduced to less than 1/5 while that of insignificant bits is doubled. They also show that the proposed scheme improves the received 4-bit ADPCM voice signal-to-noise ratio (SNR) by approximately 4 dB even when the frequency correlation is 0. 5.

In this paper, we propose an interference canceller for asynchronous DS-CDMA. The principle is based on parallel cancellation using soft decision(PCSD), however, we propose to add an operation to suppress the strength of interfering signals replica on PCSD. We show here that this operation plays a very important theoretical role in PCSD, and that the performance of our proposed scheme approaches that of a perfect decorrelating detector under certain conditions. With this theoretical background in mind, we named this scheme the "Near-Decorrelating Multistage Detector"(NDMD). To demonstrate NDMD performance, we performed two kinds of computer simulations. In the first kind of simulation, simple conditions are assumed in order to evaluate basic cancelling performance. In the other kind of simulation, essential techniques for CDMA cellular systems such as FEC, transmission power control(TPC), and base band filtering were implemented while taking into account NDMD as applied to such systems. These simulations numerically demonstrate that NDMD is very efficient in cancelling out interference and that it improves asynchronous DS-CDMA performance.

This paper studies a congestion control scheme in integrated variable bit-rate video, audio and data (e. g. , image or text) communications, where each video stream is synchronized with the corresponding audio stream. When the audio and video streams are output, media synchronization control is performed. To avoid congestion, we employ a dynamic video resolution control scheme which dynamically changes the video encoding rate according to the network loads. By simulation, the paper evaluates the performance of the scheme in terms of throughput, loss rate, average delay, and mean square error of synchronization. Numerical results show the effectiveness of the scheme.

Conventional fast block-matching algorithms, such as TSS and DSWA/IS, are widely used for motion estimation in the low-bit-rate video coding. These algorithms are based on the assumption that when searching in the previous frame for the block that best matches a block in the current frame, the difference between them increases monotonically when a matching block moves away from the optimal solution. Unfortunately, this assumption of global monotonicity is often not valid, which can lead to a high possibility for the matching block to be trapped to local minima. On the other hand, monotonicity does exist in localized areas. In this paper, we proposed a new algorithm called Peano-Hilbert scanning search algorithm (PHSSA). With the Peano-Hilbert image representation, the assumption of global monotonicity is not necessary, while local monotonicity can be effectively explored with binary search. PHSSA selects multiple winners at each search stage, minimizing the possibility of the result being trapped to local minima. The algorithm allows selection of three parameters to meet different search accuracy and process speed: (1) the number of initial candidate intervals, (2) a threshold to remove the unpromising candidate intervals at each stage, and (3) a threshold to control when interval subdivision stops. With proper parameters, the multiple-candidate PHSSA converges to the optimal result faster and with better accuracy than the conventional block matching algorithms.

Repeaterless transmission system design employing remote pumping in a single fiber is clarified. The design is aimed to realize cost effective submarine transmission systems with easy maintenance. Remote pumping in a single fiber can extend repeaterless transmission distance without decreasing the system capacity per cable. It is applicable for high-count-fiber cable such as the 100-fiber submarine cable already developed. A simple but effective system configuration is presented that uses remote pumping from receiver end; both remote-pre erbium-doped fiber (EDF) amplification and backward pumping Raman amplification are employed. Stable transmission can be obtained without optical isolators, therefore the optical time domain reflectometry (OTDR) method is supported by this system. Three fiber configurations, which consist of dispersion shifted fiber (DSF), pure silica core fiber (PSCF) and a combination of DSF and PSCF, are examined to compare system performance. Remote-pre EDF is optimized in terms of length and location from receiver end by optical SNR (OSNR) calculations. Maximum signal output power is also determined through a waveform simulation based on the split-step Fourier method, in order to avoid waveform distortion caused by the combined effect of self-phase modulation (SPM) and group velocity dispersion (GVD). Through these calculations and simulations, we confirm the proposed repeaterless transmission system performance of 600Mbit/s-451 km with PSCF, 2. 5 Gbit/s-407 km with DSF + PSCF, and 10 Gbit/s-376 km with DSF+PSCF, which include system margin.

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.

This paper discusses a power save management method appropriate for the features of the fiber-optic access network based on Passive Double Star (PDS) topology, where PDS termination processing LSIs for the Optical Network Unit (ONU) operate intermittently and the usage rate is low at the residential customer. We developed PDS termination processing LSIs for the ONU, performed power management, and evaluated the degree of consumed power.

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.

This paper introduces a new analytic method that uses modified state equations to evaluate the performance of PCSD (Packet Channel Sharing protocol for DCA systems) with the goal of increasing the spectrum efficiency of DCA systems by realizing channel sharing between circuit-switched calls and packets. The results of this analysis show that PCSD is more suitable for microcellular systems than cellular systems, and that PCSD system performance improves as the average holding time of circuit-switched calls increases. Moreover, this paper proposes a novel scheme to determine the optimum release delay time of packet channels in order to achieve high throughput for packets as well as high channel capacity for circuit-switched calls. The proposed scheme shows that the optimum release delay time for PHS (Personal Handy-phone System) is greater than 60 frames and less than 100 frames.

In this paper, a new variable length code transmission technique utilizing multicode DS/SS is proposed. A common problem associated with the use of variable length codes over wireless channels is loss of synchronization due to bit inversion caused by channel noise. The loss of synchronization produces burst errors in the received source symbols. The proposed system assigns multiple spreading codes to a single user to transmit variable length codes. The number of the spreading codes is equal to the maximum bit length of the codewords. All the bits of the codeword are spread and transmitted at one time by utilizing the assigned multiple spreading codes. Therefore no synchronization of the codeword is required. This paper evaluates the performance of the proposed technique over an AWGN channel and a Rayleigh fading channel. Our results show that the proposed technique improves the symbol error rate (SER) performance by 2-3 dB on the AWGN channel and 10-20 dB on the Rayleigh fading channel as compared with a conventional transmission technique. The source-channel coding suitable for the proposed technique improves the performance by another 15 dB on the Rayleigh fading channel. The proposed transmission technique works even in a low Es/No region.

In the multipath mobile channel, the received signal suffers from both the fluctuation in the received field intensity caused by fading and waveform distortion caused by the echo. Diversity reception using multiple spaced antennas is an effective method to compensate for fading, while echo cancellation with an adaptive array is good at compensating for waveform distortion. In this paper, an adaptive switching echo cancellation/diversity reception method to compensate for both waveform distortion and fading is proposed. The proposed switching reception monitors the impacts of channel conditions on received signal and then one of an echo canceller and a diversity receiver is selected accordingly to compensate the channel. The compensation performance of the proposed switching reception in terms of both average DUR (Desired to Undesired signal Ratio) and the probability of DUR below a threshold value is investigated with computer simulation. The results show that the adaptive switching echo cancellation/diversity reception has realized the advantages of both adaptive echo cancellation and diversity reception.

In this paper, we propose a teletraffic model and evaluate the performance in the terrestrial/satellite integrated mobile communication networks having hierarchical structure consisting of terrestrial microcell and satellite spot beam. In the proposed teletraffic model, both the subscriber terminal mobility in the terrestrial microcell and the satellite mobility in the LEO satellite spot beam are considered. The overflow traffic from microcell can be accommodated by the satellite spot beam and is analyzed by IPP (Interrupted Poisson Process) which is often used to analyze non-random overflow traffic. Various reservation channels for handoff calls in terrestrial microcell and satellite spot beam are considered. New calls initially directed to the satellite spot beam are also considered for reservation channels. Carried traffic, blocking, forced termination and non-completion probabilities are evaluated for the overall integrated networks.

A more judicious choice of trial functions to implement the Improved Circuit Theory (ICT) application to multi-element antennas is achieved. These new trial functions, based on Tai's modified variational implementation for single element antennas, leads to an ICT implementation applicable to much longer co-planar dipole arrays. The accuracy of the generalized impedance formulas is in good agreement with the method of moments. Moreover, all these generalized formulas including the radiation pattern expressions are all in closed-form. This leads to an ICT implementation which still requires much shorter CPU time and lesser computer storage compared to method of moments. Thus, for co-planar dipole arrays, the proposed implementation presents a relatively very efficient method and would therefore be found useful in applications such as CAD/CAE systems.

The characteristics of circular polarization from a slot with a parasitic dipole are investigated analytically. It is derived that its phase is linearly dependent upon the angle of the dipole and is independent of that of slot. This interesting behavior is also confirmed by experiments.

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.

This paper describes a realtime cell-loss ratio evaluation algorithm for ATM connection admission control. This algorithm gives an efficient evaluation of cell-loss ratio from traffic descriptors such as peak cell rate, sustainable cell rate, and maximum burst size for each VC. The most remarkable characteristics of this algorithm are that it terminates within a millisecond and that its time is independent of both the number of VCs and the capacity of a cell buffer.

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).