The 2-vertex-connectivity augmentation problem for a specified set of vertices of a graph with degree constraints, 2VCA-SV-DC, is defined as follows: "Given an undirected graph G = (V,E), a specified set of vertices S ⊆V with |S|3 and a function g:V→Z+∪{∞}, find a smallest set E' of edges such that (V,E ∪E') has at least two internally-disjoint paths between any pair of vertices in S and such that vertex-degree increase of each v ∈V by the addition of E' to G is at most g(v), where Z+ is the set of nonnegative integers." This paper shows a linear time algorithm for 2VCA-SV-DC.

Admission control is becoming an essential technique for IP networks to provide full-fledged multimedia streaming services. Although signaling-based schemes are utilized to achieve this, these are difficult to deploy and can hardly achieve strict admission control taking the properties of packet arrival into consideration. In this paper, we propose a novel admission control strategy called the Tentative Accommodating and Congestion Confirming Strategy (TACCS). The main idea is to accommodate incoming flows tentatively and confirm congestion after a certain period. Since tentative accommodating enables us to generate the same situation as where incoming flows have been accommodated, TACCS makes it possible to control admission considering the properties of packet arrival after they have been accommodated, without collecting resource information in advance. From the results of mathematical analysis, we confirmed that TACCS enabled a domain to control admission without a centralized management agent and we provided guidelines for configuring parameters of TACCS.

A chordal graph is a graph which contains no chordless cycle of at least four edges as an induced subgraph. The class of chordal graphs contains many famous graph classes such as trees, interval graphs, and split graphs, and is also a subclass of perfect graphs. In this paper, we address the problem of enumerating all labeled chordal graphs included in a given graph. We think of some variations of this problem. First we introduce an algorithm to enumerate all connected labeled chordal graphs in a complete graph of n vertices. Next, we extend the algorithm to an algorithm to enumerate all labeled chordal graphs in a n-vertices complete graph. Then, we show that we can use, with small changes, these algorithms to generate all (connected or not necessarily connected) labeled chordal graphs in arbitrary graph. All our algorithms are based on reverse search method, and time complexities to generate a chordal graph are O(1), and also O(1) delay. Additionally, we present an algorithm to generate every clique of a given chordal graph in constant time. Using these algorithms we obtain combinatorial Gray code like sequences for these graph structures in which the differences between two consecutive graphs are bounded by a constant size.

We propose a real-time measurement method, DPDC (Detection of Packet-Delay Correlation), which models both available bandwidth and the averaging time scale. In this method, measurement periods are short and constant, while the theoretical measurement error is reduced. DPDC is established based on the discussion of the systematic error of the packet pair/train measurement. We evaluate through simulations its accuracy and robustness against the multihop effect. We also verify the feasibility of real-time measurements through testbed experiments using a tool called Linear that implements DPDC. Efficiency is demonstrated through simulations and testbed experiments by analyzing accidental and systematic errors. Finally, we discuss the available bandwidth variation in an Internet path using real-time data produced by Linear measurements and passive monitoring.

In this paper by using an exactly analytic approach the clock jitter in the feedback path of the continuous time Delta Sigma modulators (CT DSM) is modeled as an additive jitter noise, providing a time invariant model for a jittery CT DSM. Then for various DAC waveforms the power spectral density (psd) of the clock jitter at the output of DAC is derived and by using an approximation the in-band power of the clock jitter at the output of the modulator is extracted. The simplicity and generality of the proposed approach are the main advantages of this paper. The MATALB and HSPICE simulation results confirm the validity of the proposed formulas.

This paper proposes a new approach for analog portion testing, which can meet requirements for high-speed and high-accuracy testing simultaneously with reasonable cost. The key concept of the new method is cooperation of an LSI tester and some circuitry built in a target SoC device. We will explain the operation principle of the proposed method. The proposed method can be one of the methods to overcome today's expensive production test of analog portion on SoC (System on Chip) devices which heavily depends on LSI tester capability and will become harder in near future.

Packet loss and delay cause degradation in the quality of real-time, interactive applications such as video conferencing. Forward error correction (FEC) schemes have been proposed to make the applications more resilient to packet loss, because the time required to recover the lost packets is shorter than that required to retransmit the lost packets. On the other hand, the codec generally used in real-time applications like MPEG4 has the feature that the sending bit rate and the packet size of the traffic vary significantly according to the motion of an object in a video. If the traditional FEC coding, which is calculated on the basis of a fixed-size block, is applied to such applications, a waste of bandwidth and a delay variation are caused and the quality is degraded. In this paper, we propose suitable FEC schemes for visual communication systems using variable bit-rate (VBR) codec and evaluate the effectiveness of these schemes using our prototype implementation and experimental network.

To support international medical collaboration activities carried out among Japan, Sri Lanka and other countries in Asia, we have been developing a collaboration system, which incorporates synchronous and asynchronous collaboration paradigms through network-effective persistent information sharing. The designed system facilitates synchronous collaborative work on maxillo-facial cases through real-time high-quality image delivery and by bringing the system database objects to a shared-workspace. The asynchronous activities are supported through a web based collaborative environment that enables both activity-centric and object-centric navigation of collaboration contents incorporated with email notifications of the system updates. Multimedia records of synchronous sessions are posted to the system database for later reviewing. Geographically dispersed groups experiencing different scales of network heterogeneities are served by a distributed application level multicast overlay and an adaptive multimedia delivery mechanism. The designed collaboration system also features several useful collaboration tools, user friendly GUI and ubiquitous connectivity.

In this letter, we focus on rearranged pilot patterns for channel estimation in a mobile communication system using Orthogonal Frequency Division Multiplexing (OFDM). The conventional pilot patterns for channel estimation in OFDM systems do not have robust characteristics in time-varying channels. In order to overcome this weakness of the conventional pilot patterns, we propose the pilot patterns with robust mobility for OFDM systems, which can achieve a good error performance in time-varying multi-path fading channels. Simulation results show that the bit error rate (BER) performances of the proposed pilot patterns are better than those of the conventional pilot patterns in fast time-varying fading channels under the same pilot density and data rate.

Space-frequency transmit diversity (SFTD) and space-code transmit diversity (SCTD), which are both based on space-time block codes (STBC), were applied to time-direction spreading and two-dimensional spreading orthogonal frequency-division multiplexing code-division multiplexing (OFDM-CDM) systems, and the transmission performances were compared by computer simulation. SFTD is designed for space and two adjacent subcarriers whereas SCTD is designed for space and two distinct Walsh-Hadamard (WH) codes. The simulation results show that SCTD applied to time-direction spreading OFDM-CDM was superior to SFTD because frequency selectivity distorted STBC's orthogonality between sub-carriers in SFTD. In contrast, when they were applied to two-dimensional spreading OFDM-CDM, SFTD was superior to SCTD when the number of WH codes belonging to the same mother-code group is small because the frequency diversity provided by SFTD surpassed that provided by SCTD. In addition, both SFTD and SCTD provide high tolerance to large Doppler spread. It can be therefore concluded that both SCTD and SFTD can be used in the same frame by code-multiplexing according to their suitability to physical channels. SCTD is suitable for transmitting high-rate data via time-direction spreading, whereas SFTD is suitable for transmitting control data via two-dimensional spreading.

In this paper, Constrained Interpolation Profile (CIP) method is applied to Maxwell's equation including complex permittivity and permeability and the validity of CIP method applied to the equation is confirmed compared with the FDTD method. And the dependency on CFL (Courant-Friedrich-Lewy) condition, cell size and estimates of , and of the absorbing characteristics of one-layer EM-absorber are calculated using CIP method and compared with that by FDTD method. As a result, it is confirmed that the characteristics obtained by CIP method is different from that by FDTD method.

This letter describes four-branch open-loop transmit diversity schemes that are based on group-coherent codes using space-time block codes (STBC-GCC), for orthogonal frequency-division multiplexing and code-division multiplexing (OFDM-CDM) systems. Open-loop STBC-GCC is designed for transmitting control data by two-dimensional spreading, which is achieved by applying two distinct Walsh-Hadamard (WH) codes within the same mother-code group to two different groups of transmit antennas. The simulation results demonstrated that open-loop STBC-GCC applied to two-dimensional spreading provides space diversity gains and frequency diversity gains. It can therefore be concluded that open-loop STBC-GCC is suitable for transmitting common control data or broadcast data via two-dimensional spreading OFDM-CDM.

With the increase of commercial multimedia applications using digital video, the security of video data becomes more and more important. Although several techniques have been proposed in order to protect these video data, they provide limited security or introduce significant overhead. This paper proposes a video security scheme for MPEG video compression standard, which includes two methods: DCEA (DC Coefficient Encryption Algorithm) and "Event Shuffle." DCEA is aim to encrypt group of codewords of DC coefficients. The feature of this method is the usage of data permutation to scatter the ciphertexts of additional codes in DC codewords. These additional codes are encrypted by block cipher previously. With the combination of these algorithms, the method provides enough security for important DC component of MPEG video data. "Event Shuffle" is aim to encrypt the AC coefficients. The prominent feature of this method is a shuffling of AC events generated after DCT transformation and quantization stages. Experimental results show that these methods introduce no bit overhead to MPEG bit stream while achieving low processing overhead to MPEG codec.

This letter investigates a distinct set of complex unitary matrices for differential space time coding by using QPSK modulation. The numerical results show that the properly selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate (BER) performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

During devastating natural disasters, numerous people want to make calls to check on their families and friends in the stricken areas, but many call attempts on mobile cellular systems are blocked due to limited radio frequency resources. To reduce call blocking and enable as many people as possible to access mobile cellular systems, placing a limit on the holding time for each call has been studied [1],[2]. However, during a catastrophe, emergency calls, e.g., calls to fire, ambulance, or police services are also highly likely to increase and it is important that the holding time for these calls is not limited. A method of limiting call holding time to make provision for emergency calls while considering the needs of ordinary callers is proposed. In this method, called the HTL-E method, all calls are classified as emergency calls or other according to the numbers that are dialed or the terminal numbers that are given in advance to the particular terminals making emergency calls, and only the holding time of other calls is limited. The performance characteristics of the HTL-E method were evaluated using computer simulations. The results showed that it reduced the rates of blocking and forced call termination at handover considerably, without reducing the holding time for emergency calls. The blocking rate was almost equal for emergency and other calls. In addition, the HTL-E method handles fluctuations in the demand for emergency calls flexibly. A simple method of estimating the holding-time limit for other calls, which reduces the blocking rate for emergency and other calls to the normal rate for periods of increased call demand is also presented. The calculated results produced by this method agreed well with the simulation results.

In recent years, considerable attention has been devoted to continuously running software systems whose performance characteristics are smoothly degrading in time. Software aging often affects the performance of a software system and eventually causes it to fail. A novel approach to handle transient software failures due to software aging is called software rejuvenation, which can be regarded as a preventive and proactive solution that is particularly useful for counteracting the aging phenomenon. In this paper, we focus on a high assurance software system with fault-tolerance and preventive rejuvenation, and analyze the stochastic behavior of such a highly critical software system. More precisely, we consider a fault-tolerant software system with two-version redundant structure and random rejuvenation schedule, and evaluate quantitatively some dependability measures like the steady-state system availability and MTTF based on the familiar Markovian analysis. In numerical examples, we examine the dependence of two fault tolerant techniques; design and environment diversity techniques, on the system dependability measures.

Current TCP-friendly congestion control mechanisms adjust the packet rate in order to adapt to wired network conditions and obtain a throughput not exceeding that of a TCP connection operating under the same conditions. However, these mechanisms can not be directly applicable to wireless network because there is no way to distinguish congestion losses from wireless channel losses. In this letter, a new loss differentiation algorithm for wired-to-wireless streaming service is described. The approach does not only adjust the sending rate according to the network status, but also provide the useful feedback to the video encoder.

In this paper a straight-forward approach to extract the equivalent loop-gain of a continuous time Delta-Sigma modulator with an arbitrary DAC waveform in z-domain is presented. In this approach the arbitrary DAC waveform is approximated by the infinite number of rectangular pulse shapes. Then simply using the transformations available in literatures for a rectangular DAC pulse shape and applying superposition on each rectangular pulse shape, the loop-gain of the system is derived in z-domain.

We consider the chains of integrators with nonlinear terms which allow state and input delays. We provide an output feedback controller which globally asymptotically stabilizes the given system under certain sufficient conditions. It turns out that the obtained result includes several existing results as particular cases. This point is shown through two applications of the main result. Also, industrial processes are presented to illustrate the practicability of our result.

This paper discusses clock skew due to manufacturing variability and environmental change. In clock tree design, transition time constraint is an important design parameter that controls clock skew and power dissipation. In this paper, we evaluate clock skew under several variability models, and demonstrate relationship among clock skew, transition time constraint and power dissipation. Experimental results show that constraint of small transition time reduces clock skew under manufacturing and supply voltage variabilities, whereas there is an optimum constraint value for temperature gradient. Our experiments in a 0.18 µm technology indicate that clock skew is minimized when clock buffer is sized such that the ratio of output and input capacitance is four.