An analytic equation was derived for the time jitter of digital NRZ signals due to inter-symbol interference in the PCB transmission lines loaded by DRAM chips which are located in uniform spacing. The inter-symbol interference is caused by a low-pass filtering effect of the loaded transmission line. Good agreements were observed between the equation and measurements with an average error of 17.5%.

A password-based mechanism is the most widely used method of authentication in distributed environments. However, because people are used to choosing easy-to-remember passwords, so-called "weak-passwords," dictionary attacks on them can succeed. The techniques used to prevent dictionary attacks lead to a heavy computational load. Indeed, forcing people to use well-chosen passwords, so-called "strong passwords," with the assistance of tamper-resistant hardware devices can be regarded as another fine authentication solution. In this paper, we examine a recent solution, the SAS protocol, and demonstrate that it is vulnerable to replay and denial of service attacks. We also propose an Optimal Strong-Password Authentication (OSPA) protocol that is secure against stolen-verifier, replay, and denial of service attacks, and minimizes computation, storage, and transmission overheads.

This paper presents a multimedia architecture extension design for a 200-MHz, 1.6-GOPS embedded RISC processor. The datapath architecture of the processor which realizes parallel execution of data transfer and SIMD (single instruction stream multiple data stream) parallel arithmetic operations is designed. Four SIMD parallel 16-bit MAC (multiply-accumulation) instructions are introduced with a symmetric rounding scheme which maximizes the accuracy of the 16-bit accumulation. This parallel 16-bit MAC on a 64-bit datapath is shown to be efficiently utilized for DSP applications such as the correlation and the matrix-vector multiplications in the multimedia RISC processor. By using the parallel MAC instruction with the symmetric rounding scheme, a 2D-IDCT which satisfies the IEEE1180 can be implemented in 202 cycles.

This paper proposes new recursive fixed-point smoother and filter using covariance information in linear continuous-time stochastic systems. To be able to treat the stochastic signal estimation problem, a performance criterion, extended from the criterion in the H filtering problem by introducing the stochastic expectation, is newly introduced in this paper. The criterion is transformed equivalently into a min-max principle in game theory, and an observation equation in the Krein spaces is obtained as a result. For γ2<, the estimation accuracies of the fixed-point smoother and the filter are superior to the recursive least-squares (RLS) Wiener estimators previously designed in the transient estimation state. Here, γ represents a parameter in the proposed criterion. This paper also presents the fixed-point smoother and the filter using the state-space parameters from the devised estimators using the covariance information.

A general tracking control problem for mobile robots is proposed and solved using the backstepping technique. A global result is given for the kinematic steering system to make the tracking error approaching to zero asymptotically. Based on our efforts, the proposed controller can solve both the tracking problem and the regulation problem of mobile robots. In particular, mobile robots can now globally follow any differentiable with bounded velocities path such as a straight line, a circle and the path approaching to the origin using the proposed controller. Moreover, the problem of back-into-garage parking is also solved by our approach. Some interesting simulation results are given to illustrate the effectiveness of the proposed tracking control laws.

Scattering responses from a dielectric sphere are analyzed in the time-frequency domain by using two types of wavelet transform in order to reveal the scattering mechanisms. In the resulting time-frequency displays, various scattering processes including reflection, refraction, and diffraction can be clearly resolved and identified. The delay time of each scattering process agrees well with that obtained by the ray theory. Furthermore, the natural frequencies that are not easy to extract by the conventional Fourier analysis can be extracted.

Web caching has become an important problem when addressing the performance issues in Web applications. The expiration time of the Web data item is useful a piece of information for performance enhancement in Web caching. In this paper, we introduce the notion of the effective reference probability that incorporates the effect of expiration time for Web caching. For a formal approach, we propose the continuous independent reference model extending the existing independent reference model. Based on this model, we define formally the effective reference probability and derive it theoretically. By simply replacing the reference probability in the existing cache replacement algorithms with the effective reference probability, we can take the effect of expiration time into account. The results of performance experiments show that the replacement algorithms using the effective reference probability always outperform existing ones. In particular, when the cache fraction is 0.05 and data update is comparatively frequent (i.e., the update frequency is more than 1/10 of the reference frequency), the performance is enhanced by more than 30% in LRU-2 and 13% in Aggarwal's method. The results show that the effective reference probability significantly enhances the performance of Web caching when the expiration time is given.

Particulate media composed of very small particles were studied to determine high-density recording performance and thermal stability. Studied media included metal particulate media with mean particle length of 71, 102 and 148 nm, and Ba ferrite particulate media with mean diameter of 22, 28 and 50 nm. Using a loss-term simulation program, taking into account gap-loss, spacing-loss and particle length loss, the recording capability (D20 of 265 kFRPI for MP and 290 kFRPI for Ba ferrite media) was estimated. Thermal stability was evaluated from magnetization time decay measurements. It was found that MP media with large Ku values and 71 nm particles were satisfactorily stable, and the particle volume is still large enough in respect of thermal stability. However, 22-nm Ba ferrite media were less stable, primarily because of small Ku values and particle volume. It was also clarified that positive inter-particle interaction accelerates magnetization time decay, in the presence of a large reverse field.

Several subband array methods have been proposed as useful means to perform joint spatio-temporal equalization in digital mobile communications. These methods can be applied to mitigate problems caused by the inter-symbol interference (ISI) and co-channel interference (CCI). The subband array methods proposed so far can be classified into two major schemes: (1) a centralized feedback scheme and (2) a localized feedback scheme. In this paper, we propose subband arrays with partial feedback scheme, which generalize the above two feedback schemes. The main contribution of this paper is to derive the steady-state mean square error (MSE) performance of subband arrays implementing these three different feedback schemes. Unlike the centralized feedback scheme which can be designed to provide the optimum equalization performance, the subband arrays with localized and partial feedback schemes are in general suboptimal. The performance of these two suboptimal feedback schemes depends on the channel characteristics, the filter banks employed, and the number of subbands.

The Active HYpermedia Delivery System (AHYDS) facilitates the access to multimedia information over a large-scale network and wide spectrum of media. We developed intelligent access facilities that build on the access paradigms supported by current web applications. This facility generalizes not only different kinds of logical data models (relational, object, hyperlink), but also access mechanisms of multimedia applications to make them customizable and scalable. This paper proposed the distributed management mechanism of the AHYDS platform. The major contribution of this paper is the mechanism for distributed multimedia delivery management over large-scale network and heterogeneous environment. We also propose the mechanism to manage huge multimedia data.

The (cinema) caption processing that adds descriptive text on a sequence of frames is an important video manipulation function that a video editor should support. This paper proposes an efficient MC-DCT compressed domain approach to insert the caption into the MPEG compressed video stream. It basically adds the DCT blocks of the caption image to the corresponding DCT blocks of the input frames one by one in the MC-DCT domain as in [6]. However, the strength of the caption image is adjusted in the DCT domain to prevent the resulting DCT coefficients from exceeding the maximum value allowed in MPEG. In order to adjust the strength of the caption image adaptively we need to know the exact pixel value of the input image. This is a difficult task in DCT domain. We propose an approximation scheme for the pixel values in which the DC value of a block is used as the expected pixel value for all pixels in that block. Although this approximation may lead to some errors in the caption area, it still provides a relatively high image quality in the non-caption area, whereas the processing time is about 4.9 times faster than the decode-captioning-reencode method.

In the future Internet, various kinds of services will rapidly increase its volume and require different qualities. Thus, it is main technical problem to guarantee various QoS to each connection. However, in the current IP networks where most applications use TCP as transport protocol, most typical packet discarding scheme, RED (Random Early Detection), causes unfairness such as the difference of bandwidth sharing among flows traversing the same router. To dissolve this problem, we consider that two viewpoints are important associated with flow-base fairness. One is instantaneous flow condition and the other is historical flow condition. In this paper, we propose the packet discarding scheme considering both instantaneous and historical use of network resources for the purpose of dissolving unfairness of each flow and improving the flow-base QoS. We call this proposal method "Random Early Drop with Dual-fairness metrics (DRED). " DRED can improve whole throughput and transfer completion time of information such as a file, etc.

This paper provides a new robust guaranteed cost controller design method for discrete parameter uncertain time delay systems. The result shows much tighter bound of guaranteed cost than that of existing paper. In order to get the optimal (minimum) value of guaranteed cost, an optimization problem is given by linear matrix inequality (LMI) technique. Also, the parameter uncertain systems with time delays in both state and control input are considered.

This paper proposes a measure of coefficient quantization errors for linear discrete-time state-space systems. The proposed measure of state-space systems agrees with the actual output error variance since it is derived from the exact evaluation of the output error variance due to coefficient deviation. The measure in this paper is represented by the controllability and the observability gramians and the state covariance matrix of the system. When the variance of coefficient variations is very small, the proposed measure is identical to the conventional statistical sensitivity of state-space systems. This paper also proposes a method of synthesizing minimum measure structures. Numerical examples show that the proposed measure is in very good agreement with the actual output error variance, and that minimum measure structures have a very small degradation of the frequency characteristic due to coefficient quantization.

The formulation of the process of analog system design has been done on the basis of the control theory application. This approach generalizes the design process and produces different design trajectories inside the same optimization procedure. The problem of the optimal design algorithm construction is defined as the minimal-time problem of the control theory. The main equations for the proposed design methodology were elaborated. These equations include the special control functions that are introduced artificially to generalize the design problem. Optimal dependencies of the control functions give the possibility to reduce the total computer design time. This idea was tested with different optimization algorithms of the design process. Numerical results of some simple electronic circuit design demonstrate the efficiency of the proposed approach. These examples show that the traditional design strategy is not time-optimal and the potential computer time gain of the optimal design strategy increases when the size and complexity of the system increase.

This letter focuses on the design of a unified estimator for scheduled control in nonlinear systems with unknown parameter. An estimation law with a finite convergence time is formulated to compute the unknown scheduling parameter that drives a scheduled controller. This estimator can also be extended to the types of scheduled controllers addressed in the literature.

In this paper, we present a new transmit diversity scheme with power control by using two transmit antennas in which the power control unit is added to adaptively suit the channel fading variation. Compared to the transmit diversity scheme (STD, one space time coding scheme) proposed by Alamouti and the traditional maximal ratio combining (MRC) diversity scheme employed at the receiver, simulation results indicate that the new scheme has considerable performance gain. We also discuss the effects of the imperfect channel parameter estimation on the performance of the system. Simulation results show that the new system is more robust to the estimation error of channel fading parameters than the STD. As the signal to noise ratio is relatively high, the diversity scheme with power control is more sensitive to the channel estimation error compared to the MRC. But when the channel estimation accuracy is relatively high, the diversity scheme with power control still has better performance than the ideal MRC as the BER is about 1 10-3.

This paper proposes a novel adaptive array configuration that reduces high-power co-channel interference (CCI) by utilizing the difference in arrival times between CCI and the desired signal in asynchronous TDD systems. The proposed adaptive array extracts only the CCI and employs pre-null steering for only the CCI by utilizing the fact that only the CCI arrives during the guard time in asynchronous TDD systems. Since the proposed adaptive array enables us to apply the Minimum Mean Square Error (MMSE) algorithm through synchronization with the desired signal using the output signal obtained by pre-null steering, high quality transmission can be achieved even in the presence of high-power CCI. Moreover, based on measurements using a fading simulator and field data, an adaptive array testbed exemplifying the proposed configuration is presented to show the reduction in the high-power CCI.

Emerging multimedia technologies introduce the prevalent multicast transmission, and the multicast tree is determined using the time-invariant network parameters. This paper addresses the time-varying multicast tree problem and presents path selection heuristics for multicast routing to determine an alternative path for real-time applications. A network is partitioned into the optimal region, the disjoint region, and the edge cutset if a branch of the multicast tree meets the un-guaranteed QoS condition. The path selection heuristics operate during the multicast session phase to efficiently select an alternative routing path containing an edge in the edge cutset to connect the multicast tree again. The source-based heuristics PS-SPT finds the path for minimal source-to-destination delay and the sharing-based heuristics PS-DDMC for minimal total cost. These path selection heuristics can efficiently provide solutions to keep the multicast transmission reliable. Simulation results also show that the proposed heuristics can provide effective good solutions for real-time multicast transmission. PS-SPT can select a path with optimal source-to-destination delay and PS-DDMC can select a path with optimal total cost.

Wireless LANs have been used for realizing fully-distributed users in a multimedia environment that has the ability to provide real-time bursty traffic (such as voice or video) and data traffic. In this paper, we present a new realistic and detailed system model and a new effective analysis for the performance of wireless LANs which support multimedia communication with non-persistent carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this CSMA/CA model, a user with a packet ready to transmit initially sends some pulse signals with random intervals within a collision avoidance period before transmitting the packet to verify a clear channel. The system model consists of a finite number of users to efficiently share a common channel. Each user can be a source of both voice traffic and data traffic. The time axis is slotted, and a frame has a large number of slots and includes two parts: the collision avoidance period and the packet transmission period. A discrete-time Markov process is used to model the system operation. The number of slots in a frame can be arbitrary, dependent on the chosen lengths of the collision avoidance period and packet transmission period. Numerical results are shown in terms of channel utilization and average packet delay for different packet generation rates. They indicate that the network performance can be improved by adequate choice of ratios between the collision avoidance period and transmission period, and the pulse transmission probability.