We consider a bisimilarity control problem for transition systems. For this control problem, a necessary and sufficient condition for its solvability and a method for synthesizing a state feedback controller have been presented in the literature. However, the state of the system to be controlled is not necessarily observable. In this paper, we synthesize an observer-based output feedback controller for the bisimilarity control problem under a certain condition, and show that this output feedback controller is a solution to the control problem.

A simple robust finite-time convergent observer is presented in the presence of unknown input disturbance and measurement noise. In order to achieve the robust estimation and ensure the finite-time convergence, the proposed observer is constructed by using a multiple integral observer scheme in a hybrid system framework. Comparative computer simulations and laboratory experiments have been performed to test the effectiveness of the proposed observer.

This paper proposes an updating state dependent disturbance observer (USDDOB) to reject position dependent disturbances when parameters vary slowly, and input and output are time-delayed. To reject the effects of resultant slowly-varying position dependent disturbances, the USDDOB uses the control method of the state dependent disturbance observer (SDDOB) and time-invariance approximation. The USDDOB and a main proportional integral (PI) controller constitute a robust controller. Simulations and experiments using a 1-degree-of-freedom (1-DOF) tilted planar robot show the effectiveness of the proposed method.

Since the conventional cascade controller for electric motor drives requires accurate information about the system parameters and load conditions to achieve a desired performance, this paper presents a new practical control structure to improve the robust performance against parameter uncertainties. Two first-order disturbance observers (DOB) are incorporated with the cascade structure, to preserve the nominal performance. The analysis of the robust performance of the DOB is presented by using the singular perturbation theory. Simulation results suggest that the proposed controller can be used effectively as an additional compensator to the conventional cascade scheme.

Secure authentication of low cost Radio Frequency Identification (RFID) tag with limited resources is a big challenge, especially when we simultaneously consider anonymity, un-traceability, and forward secrecy. The popularity of Internet of Things (IoT) further amplifies this challenge, as we should authenticate these mobile tags in the partial-distributed-server environments. In this paper, we propose an RFID authentication scheme in the partial-distributed-server environments. The proposed scheme owns excellent performance in terms of computational complexity and scalability as well as security properties.

In order to improve the motion control performance, a new friction determination method, using the LuGre model, is proposed. The model parameters are determined by performing two-step closed-loop experiments using a proportional-integral observer (PIO). The PIO is also used to develop a robust motion controller to deal with additional uncertainties including the effect of the inaccurate estimation of the friction. The experimental results reveal improved performance compared to that of a single-PIO-based controller.

As the quantity of mobile application traffic keeps increasing, operators are facing the scalability limits of VoIP protocols. Higher queuing delays at the Session Initiation Protocol (SIP) server create significantly more retransmissions in the network. When the message arrival rate including retransmissions exceeds the message serving capacity of a SIP server, the queue size increases and eventually the SIP server can crash. Our analysis demonstrates that server crash can be prevented if the buffer size of the SIP server is limited. However, having smaller buffer sizes yields side effects such as lower successful transaction ratio for bursty traffic. In this paper, we propose a new SIP server scheduling mechanism in which the original incoming SIP requests have strict priority over the retransmitted requests. The priority based scheduling mechanism provides network administrator with the ability to configure the buffer size of a SIP server to a moderately high value. We implement the proposed priority-based scheduling mechanism in the JAIN-SIP stack and confirm that the implementation requires minimal changes to the SIP standard. Numerical experiments show that the proposed scheduling mechanism provides significantly and consistently better scalability at high buffer sizes compared to the heavily used first-in-first-out scheduling, thus enabling us to avoid server overloads.

This paper studies an adaptive high gain observer design for nonlinear systems which have lower triangular nonlinearity with Lipschitz coefficient, depending on the control input. Because the gain of the proposed observer is tuned automatically by a simple update law, our design approach doesn't need any information about the Lipschitz constant. Also, it is shown that under some assumptions, the dynamic gain of the proposed observer is bounded and its estimation error converges to zero asymptotically. Finally, a numerical example is given to verify the effectiveness of our design approach.

We design a full-order observer for discrete-time linear time-invariant systems with constant output delays. The observer design is based on the output delay model expressed by a two-dimensional state variable, with discrete-time and space independent variables. Employing a discrete-time state transformation, we construct an explicit strict Lyapunov function that enables us to prove the global exponential stability of the full-order observer error system with an explicit estimate of the exponential decay rate. The numerical example demonstrates the design of the full-order observer and illustrates the validity of the exponential stability.

This paper proposes the state observer design for feedforward nonlinear systems with delayed output. It is shown that by using the Lyapunov-Krasovskii functional, the proposed design method ensures the asymptotic stability of estimation error for an arbitrarily large output delay. Finally, an illustrative example is given in order to show the effectiveness of our design method.

This paper proposes a session state migration architecture for flexible server consolidation. One of technical challenges is how to split a session state from a connection and bind the session state to another connection in any servers. A conventional server and client application assumes that a session state is statically bound to a connection once the connection has been established. The proposed architecture reduces the migration latency, compared to an existing study by splitting the session state from the connection. This paper classifies common procedures of session state migration for various services. The session state migration architecture enables service providers to conduct server maintenance at their own convenience, and to conserve energy consumption at servers by consolidating them. A simulation to evaluate server consolidation reveals that the session state migration reduces the number of servers for accommdating users, compared to virtual machine migration. This paper also shows implementation of the session state migration architecture. Experimental results reveal that the impact caused by the proposed architecture on real-time applications is small.

We propose a motor speed ripple elimination method using a state dependent disturbance observer (SDDOB). The SDDOB eliminates the state dependent disturbance in the system regardless of the operation frequency, input time delay and output time delay. The SDDOB and a main proportional integral (PI) controller constitute a robust motor speed controller. Experimental results show the effectiveness of the proposed method.

Recently, Shao et al. [M. Shao and Y. Chin, A privacy-preserving dynamic id-based remote user authentication scheme with access control for multi-server environment, IEICE Transactions on Information and Systems, vol.E95-D, no.1, pp.161–168, 2012] proposed a dynamic ID-based remote user authentication scheme with access control for multi-server environments. They claimed that their scheme could withstand various attacks and provide anonymity. However, in this letter, we will point out that Shao et al.'s scheme has practical pitfalls and is not feasible for real-life implementation. We identify that their scheme is vulnerable to two kinds of attacks and cannot provide anonymity.

In order to reduce cost and improve efficiency, many data centers adopt virtualization solutions. The advent of virtualization allows multiple virtual machines hosted on a single physical server. However, this poses new challenges for resource management. Web workloads which are dominant in data centers are known to vary dynamically with time. In order to meet application's service level agreement (SLA), how to allocate resources for virtual machines has become an important challenge in virtualized server environments, especially when dealing with fluctuating workloads and complex server applications. User experience is an important manifestation of SLA and attracts more attention. In this paper, the SLA is defined by server-side response time. Traditional resource allocation based on resource utilization has some drawbacks. We argue that dynamic resource allocation directly based on real-time user experience is more reasonable and also has practical significance. To address the problem, we propose a system architecture that combines response time measurements and analysis of user experience for resource allocation. An optimization model is introduced to dynamically allocate the resources among virtual machines. When resources are insufficient, we provide service differentiation and firstly guarantee resource requirements of applications that have higher priorities. We evaluate our proposal using TPC-W and Webbench. The experimental results show that our system can judiciously allocate system resources. The system helps stabilize applications' user experience. It can reduce the mean deviation of user experience from desired targets.

Recently, Lee et al. [Y. Lee, E. Kim, S. Seok, and M. Jung, A smartcard-based user authentication scheme to ensure the PFS in multi-server environments, IEICE Transactions on Communications, vol.E95-B, no.2, pp.619–622, 2012] proposed a smartcard-based user authentication scheme for multi-server environments. They claimed that their scheme could withstand various attacks and provide the perfect forward secrecy (PFS). However, in this letter, we will point out that their scheme is vulnerable to three kinds of attacks and cannot provide the PFS.

Virtualization technologies are widely deployed in data centers to improve system utilization. However, they increase the workload for operators, who have to manage the structure of virtual networks in data centers. A virtual-network management system which automates the integration of the configurations of the virtual networks is provided. The proposed system collects the configurations from server virtualization platforms and VLAN-supported switches, and integrates these configurations according to a newly developed XML-based management information model for virtual-network configurations. Preliminary evaluations show that the proposed system helps operators by reducing the time to acquire the configurations from devices and correct the inconsistency of operators' configuration management database by about 40 percent. Further, they also show that the proposed system has excellent scalability; the system takes less than 20 minutes to acquire the virtual-network configurations from a large scale network that includes 300 virtual machines. These results imply that the proposed system is effective for improving the configuration management process for virtual networks in data centers.

This paper examines the robust performance of a load torque observer for the position control of a surface-mounted permanent magnet synchronous motor (PMSM) under parameter uncertainties. The load torque observer has been widely employed to compensate for unknown slow-varying disturbances without explicit analysis on the robustness against parameter uncertainties. By using the singular perturbation theory this paper presents an analysis on the robust performance of the load torque observer based on the reduced-order estimator. As the observer poles are placed sufficiently left of the complex plane, the feedforward compensation with estimation can recover nominal system performance without parameter uncertainties and load torque disturbance. An example shows the performance of the load torque observer.

Nowadays, a user authentication is very important in network environments. For safe authentication, they came up with six essential conditions in earlier studies. And a variety of mechanisms is presented by research scientists. However, they could not achieve the PFS. Because, though all these schemes are assumed that the communication between a smart card and a host is safe, actually it is not. Therefore, in this paper, we will point out what the communication between a smart card and a host is not safe, and propose a new user authentication mechanism that can reach to the PFS. And also, an encryption algorithm is used about 45% less than earlier studies in our proposed scheme. Thus, we can say that enhance the efficiency.

The IEEE 802.15.4 protocol is considered a promising technology for low-cost low-power wireless personal area networks. Researchers have discussed the feasibility of voice communications over IEEE 802.15.4 networks. To this end, the personal area network (PAN) coordinator allocates guaranteed time slots (GTSs) for voice communications in the beacon-enabled mode of IEEE 802.15.4. Although IEEE 802.15.4 is capable of supporting voice communications by GTS allocation, it is impossible to accommodate voice transmission beyond two hops due to the excessive transmission delay. In this paper, we propose a GTS allocation scheme for bidirectional voice traffic in IEEE 802.15.4 multihop networks. The goal of our proposed scheme is to achieve low end-to-end delay and packet drop ratio without a complex allocation algorithm. Thus, the proposed scheme allocates GTSs to devices for successful completion of voice transmission in a superframe duration. The proposed scheme also considers transceiver switching delay. This is relatively large compared to a time slot due to the low-cost and low-gain antenna designs. We analyze and validate the proposed scheme in terms of average end-to-end delay and packet drop ratio. Our scheme has lower end-to-end delay and packet drop ratio than the basic IEEE 802.15.4 GTS allocation scheme.

We propose an adaptive coding algorithm for digital hologram transmission based on server-client interaction. A client can visualize various images of 3D objects from a digital hologram, which are reconstructed on different depth planes. The client's requests for reconstruction depths are sent to the server. The server adaptively encodes and transmits the same object image as the client's reconstructed image. When the client changes the reconstruction depth, only the prediction error of the new image is transmitted. Experimental results show that, in some cases, the proposed algorithm reduces more than half of the distortion at the same bitrate compared with the conventional coding technique.