In this paper, we argue that the lag size of half a moving horizon of the minimum variance finite impulse response (MVFIR) smoother is not generally best in the sense of the estimation error variance even though it has been believed to be optimal for a simple input/output (I/O) model with correlated data. For a more general analysis, a state space model is considered in this paper. It is shown via numerical example that the dependency of the lag size on the minimum estimation error variance is asymmetric around half a moving horizon and varies with model parameters. In the case of a scalar system, the best lag size is represented in a closed-form. Some hints on a numerical method are presented for a more general vector system. Considering the lag size as well as the estimation error, we also propose a new performance criterion that puts a penalty on the large lag size while making the estimation error small.

This letter proposes robust finite impulse response (FIR) filters for linear continuous-time statespace models with bounded uncertainties. A set of all reachable current states under bounded uncertainties is determined from inputs and outputs on a recent finite time interval. If some condition is met, this set is shown to be represented in an ellipsoidal form. The derivation procedure is much simplified by utilizing the result on the optimal tracking control with an indefinite cost function. In order to minimize the maximum estimation error due to uncertainties, the center of the reachable ellipsoidal set is chosen as an estimated state. It is shown through simulation that the proposed robust FIR filter achieves a more robust performance than existing robust infinite impulse response (IIR) filters.

Coexistent heterogenous wireless networks may interfere with each other and result in significant performance degradation when devices are collocated in the same environment. Understanding the impacts of interference among different wireless networks is one of critical issues for designing and implementing network system with multiple wireless technologies. The main goal of this paper is to provide a general framework to evaluate the interfering effects of one network to another network system. As a measure of performance, packet error rate (PER) is evaluated, where the PER is obtained from bit error rate (BER) and collision time. Analytic results are validated by simulations using OPNET.

In this paper, a new clear channel assessment (CCA) method: cascaded-CCA, is proposed that is apropos for next generation cognitive radios. The primary motivation for the proposed approach is to integrate the respective advantages of two 'standard' CCA mechanisms (energy detection and preamble detection) to arrive at a new dual-threshold CCA family that can provide greater flexibility towards tuning MAC performance. The performance of cascaded-CCA is explored via MATLAB simulations that implement the CCA modules and medium access control (MAC) protocol for IEEE 802.11 and IEEE 802.15.4 as representative examples.

In this paper, a new duty-cycle adaptation algorithm is proposed for IEEE 802.15.4 beacon-enabled networks. We modify the reserved frame control field in the MAC layer header to deliver the end device's buffer occupancy and queueing delay. A MAC status index is proposed to represent the queue occupancy and queueing delay. Based on the proposed MAC status index, the coordinator estimates the number of packets in the end devices and control duty-cycle adaptively. Simulation results show that the proposed algorithm decreases the packet drop and increases energy efficiency

In IEEE 802.15.4 beacon-enabled networks, the length of active periods should be configured appropriately in order to save energy and accommodate traffic. This paper proposes ECAP, a bursty traffic adaptation algorithm for IEEE 802.15.4 beacon-enabled networks. To accommodate bursty traffic, the proposed algorithm is designed to extend the active periods dynamically based on the requests from devices. The simulation results show the performance enhancement in terms of end-to-end delay and energy consumption per packet transmission

In this letter, we propose a fixed-lag finite impulse response (FIR) smoother for a class of continuous-time state space signal models. The proposed fixed-lag FIR smoother is linear with respect to outputs on the recent finite time interval and has a kernel function depending only on given system parameters. It is optimal in the sense that the variance of the estimation error is minimized with the unbiased constraint. The fixed-lag minimum variance FIR (MVF) smoother has a closed-form solution and can be easily extended to an FIR filter by setting the lag size to zero. A simulation example is presented to illustrate the performance of the proposed MVF smoother by comparing with a conventional fixed-lag Kalman infinite impulse response (IIR) smoother.

We propose a fixed-lag finite-impulse-response (FIR) smoother for a discrete-time state space model. The proposed FIR smoother estimates the state at the fixed-lag time using measured output samples on the recent finite time horizon so that the variance of the estimation error is minimized. The minimum variance FIR (MVFIR) smoother is unbiased and independent of any a priori information of the state on the horizon. A numerical example shows that the proposed MVFIR smoother has better performance than the fixed-lag Kalman smoother based on the infinite impulse response structure when transitory modeling uncertainties exist.

This letter proposes a robust finite impulse response (FIR) filter for a class of linear discrete-time systems with quadratic bounded uncertainties. A set of all reachable current states under uncertainties is obtained from inputs and outputs measured on a recent finite time interval, which is represented in an ellipsoidal form. To minimize the maximum estimation error due to uncertainties, the center of the ellipsoid is chosen as an estimated state and the corresponding estimation error is obtained from the major axis of the ellipsoid. It is shown by simulation that the proposed robust FIR filter has a more robust performance than both robust infinite impulse response (IIR) filters and nominal FIR filters.

In this paper, the performance of IEEE 802.15.4 ZigBee under the interference of IEEE 802.11b wireless local area network (WLAN) and/or Bluetooth is evaluated using an analytic model for the coexistence among ZigBee, WLAN, and Bluetooth. The packet error rate (PER) is evaluated, where the PER is obtained from the bit error rate (BER) and the collision time. The BER is obtained from the signal-to-interference-plus-noise ratio (SINR). Finally, the analytic results are validated by simulations.

The number of channels specified for IEEE 802.15.4 low-rate wireless personal area networks (LR-WPANs) is too few to operate many applications of WPANs in the same area. To overcome this limit, we introduce virtual channel, a novel concept to increase the number of available channels when various WPAN applications coexist. A virtual channel is basically created via superframe scheduling within the inactive periods in a logical channel preoccupied by other WPANs. To maximize the coexistence capability of WPANs using virtual channels, we propose (1) least collision superframe scheduler (LC-scheduler), (2) less complex heuristics, and (3) virtual channel selector (VCS) to efficiently manage multiple available logical channels. In addition, a simple but practical synchronization method is developed to compensate different time drifts among coexisting WPANs. The simulation results demonstrate that a remarkable improvement on the coexistence capability of the 802.15.4 can be achieved through the proposed schemes.

This paper proposes and evaluates a new aggregation algorithm in wireless sensor networks with time constraint. In the proposed algorithm, each aggregation node controls its aggregation time in order to aggregate and transfer data from child nodes within a given deadline of the sink node. The objective of the algorithm is to deliver the time constrained data within time bound while reducing the energy consumption resulted from the number of transmissions. Based on the aggregation tree, the proposed algorithm considers the number of the child nodes to determine the aggregation time. The performance of the proposed algorithm is evaluated using both the miss ratio and the aggregation gain

In this paper, an energy-efficient contention-based MAC protocol (ECM) for wireless ad hoc networks is proposed. The ECM is the combined protocol of the power management scheme and the collision avoidance scheme of the IEEE 802.11 DCF to reduce the energy consumption of a node. The proposed ECM enhances power saving effects of the legacy IEEE 802.11 DCF, provides longer network lifetime, and delivers more packets than the power management scheme of the legacy IEEE 802.11 DCF. These results are shown throughout the simulation

This paper presents an interference model of IEEE 802.11b wireless local area network (WLAN) affected by IEEE 802.15.4 wireless personal area network (WPAN). The packet error rate (PER) of the IEEE 802.11b under the interference of the IEEE 802.15.4 is analyzed, and is obtained by the bit error rate (BER) and the collision time. The safe distance ratio can be obtained from the PER. Further, this paper suggests a packet length to reduce the effect of the IEEE 802.15.4 interference and obtain a maximum throughput of the IEEE 802.11b. The analytic results are validated using the simulation

In this letter, we propose a new Hscrinfinfilter (HF) with a finite impulse response (FIR) structure for linear continuous-time state-space systems. This filter is called the HscrinfinFIR filter (HFF). The upper bound for an Hscrinfinperformance criterion is derived and then minimized among the filters with linearity, FIR structure, and quasideadbeat property. The HFF is obtained by solving the differential Riccati equation. We show through simulations that the HFF is more robust against temporary uncertainties and is faster in convergence than a conventional HF

Disseminating data generated by sensors to users is one of useful functions of sensor networks. In probable real-time applications of sensor networks, multiple mobile users should receive data within their end-to-end delay constraint. In this paper, we propose a dynamic DElay-constrained minimum-Energy Dissemination (DEED) scheme. A dissemination tree (d-tree) is updated in a distributed way without regenerating the tree from scratch, such that energy consumption of the tree is minimized while satisfying end-to-end delay constraints. The d-tree is adjusted using delay estimation based on geometric distance. DEED increases the probability that packets arrive at users within an upper-bound end-to-end delay (UBED) and minimizes energy consumption in both building the d-tree and disseminating data to mobile sinks. Evaluation results show that DEED makes each node consume small energy resources and maintains fewer UBED misses when compared to Directed Diffusion and other baselines for sensor networks.

Data dissemination from sources to sinks is one of the main functions in sensor networks. In this paper, we propose SEAD, a Scalable Energy-efficient Asynchronous Dissemination protocol, to minimize energy consumption in both building the dissemination tree and disseminating data to mobile sinks. SEAD considers the distance and the packet traffic rate among nodes to create near-optimal dissemination trees. The sinks can move without reporting their location to the tree while receiving data updates successfully. Our evaluation results illustrate that SEAD consumes less energy on building and maintaining a dissemination tree to multiple mobile sinks compared to other approaches such as directed diffusion, TTDD, and mobile ad hoc multicast.

In this paper, a new communication network with high safety, maintainability, and user convenience for digital I and C systems of nuclear power plants are proposed based on integrated design concepts, such as simple structure, standardized protocol, hard real-time property, high-speed data rate, fault-tolerance, verification and validation, hierarchical architecture, data transfer control using data gateway, and enhanced network management. Components of the proposed communication network are three level networks such as a field network, a control network, and an information network, a data gateway between the control network and the information network, and data gateway between control divisions. A new data flow concept for enhancing independence and user convenience in the data gateway between the control network and the information network is proposed. The architectures of three level networks and both gateways are proposed.

In this paper, an unified approach is proposed to solve forbidden state problems in a general class of controlled Petri nets (CPNs). A new subnet called the step-aligned subnet, which can describe various kinds of PN structures such as marked graphs, state machines and asymmetric nets, is introduced. The step-evaluation method is developed to efficiently investigate the reachable marking problem in step-aligned subnets instead of the full search of reachability graph. The crucial idea of the method is to decompose a large reachable marking problem into a number of smaller subproblems. This paper derives a necessary and sufficient condition in order to find maximally permissive controls in the context of step-aligned subnets. Theoretic results are applied to modeling and control of a flexible assembly cell.

We concentrate on some important timing characteristics of elevator group control (EGC) systems. The main discussion and calculations should be considered as a further development of the three passages concept. To achieve better global performance of the EGC system, especially to reduce hall call waiting time, a calculation methodology of car kinematics is presented. The importance of detailed kinematics considerations is demonstrated with data taken from a real high-speed EGC system in 63-floor building in Seoul, Korea.

In this paper, a study on modeling, analysis and optimal control problems for a class of hybrid manufacturing systems is investigated. In this framework, the discrete entities have a state characterized by a temporal component whose evolution is described by event-driven dynamics and a physical component whose evolution is described by continuous time-driven dynamics, thus it is a typical hybrid system. Not only the optimal control for a manufacturing process but also the optimal entrance time for each job's entry into the production line is considered in this paper. The whole problem is solved by a two-level optimization method: in the inner level, for any given arrival time sequence of the jobs, the optimal control for manufacturing process is considered, which includes the properties of the optimal control as well as solving method etc, while in the outer level, we use an improved evolutionary programming algorithm to decide the optimal entering time to production line for each job. Finally, some examples are given to illustrate the validity of our algorithm.

A study on modeling, scheduling and optimal control problems for a class of hybrid manufacturing systems is investigated. In this framework, the discrete entities have a state characterized by a temporal component whose evolution is described by event-driven dynamics and a physical component whose evolution is described by continuous time-driven dynamics, thus it is a typical hybrid system. Not only the optimal control for manufacturing processes like that discussed in many references but also the optimal machining sequence are considered. The whole problem is solved by a two-level optimization method: in the inner level, for any given machining sequence of the jobs, the optimal control for the manufacturing process is considered, which is a nonsmooth, nonconvex optimization problem in the general case; while at the outer level, we use an improved genetic algorithm to decide the optimal machining sequence of a batch of jobs to be processed. Finally, some examples are given to illustrate the validity of our algorithm.

A geometric kinematics modeling of a three wheeled autonomous mobile robot is proposed. Three types of basic motions are proposed for the path generation of the developed mobile robot. All paths of the mobile robot are achieved by the combination of proposed basic motions. The proposed scheme is verified through computer simulations and a practical model.

In this paper, a new approach is proposed to control elevator group systems. Hall call waiting times (HWTs) are estimated by a statistic approximation of traffic data, which are reasonably accurate under different kinds of real traffic situations. Two assignment policies are proposed to satisfy the passengers' demands and to handle exceptional situations. In addition, these policies are extended in order to reduce the variance of HWTs and long HWTs. The performance of the elevator system employing the proposed policies are compared with each others in terms of several performance indices by computer simulation.

This paper proposes a translation method for programmable logic controllers (PLCs) used in most automation systems. It describes detailed steps of the method that converts from a ladder diagram directly to a native code. A general-purpose DSP (digital signal processor) based PLC with the translation method is implemented. A benchmark test in an automotive manufacturing process shows that the proposed translation method fairly speeds up the execution in comparison with existing interpretation methods.

An algorithm for the real time detection of the direction error in the heading of a mobile robot is proposed. The proposed algorithm is designed for an omnidirectional image sensor. For the omnidirectional image sensor, a hemispherical mirror, one CCD camera, and a vision board are used. This configuration has low cost and efficiency in collecting omnidirectional data with one image compared with other types of image sensors. The proposed algorithm is verified through computer simulations and a practical mobile robot.

An optimal group control for elevator systems is proposed with a timed Petri net based approach. The elevator system is modeled by timed Petri nets and hall call waiting times are estimated with a moment generating function method, which is applicable to real traffic patterns. Two assignment policies are proposed to satisfy the demands of passengers (i.e. hall/car calls) and to handle exceptional situations. The performances of the elevator system employing the proposed policies are compared with each others by several performance indices.

In redundancy optimization problems related to cooperating manipulators, constraints should be considered for physical limits of the manipulators. The constraints have been imposed mostly in the form of linear inequality constraints, which lead to polyhedric feasible regions. We propose quadratic inequality constraints (QICs) which lead to ellipsoidal feasible regions to solve the optimization problem faster and to directly handle constraints on quadratic quantities. We investigate the effect of the use of QICs from the points of view of problem size and change of the feasible region. In order to efficiently deal with QICs, we utilize the dual quadratically constrained quadratic programming (QCQP) method. The proposed scheme and another well-known quadratic programming method are applied to numerical examples and compared with each other. The results show that the use of QICs makes it possible to make trade-off between optimality and fast computation capability and implements faster computation than the existing method.

We consider the problem of assigning reels of components to slots on feeder racks of a surface mounting machine which is used to populate printed circuit boards with surface mount technology. This reel assignment problem (RAP) is one of a series of optimization problems that should be addressed to improve the production rate. We preprocess RAP to facilitate the application of dynamic programming and then formulate it as an integer programming problem. We solve the problem by using a heuristic algorithm based on dynamic programming. We implement the algorithm as a computer program and perform computer simulations. The simulation results are compared to those of the Effective Algorithm previously proposed.

A method is proposed for solving the forbidden state problem in a general class of non-ordinary controlled Petri nets (NCPNs). A concept of step-aligned subnets is introduced to handle the behavior of reachable markings in NCPNs. In addition, the step-alignment algorithm is developed to transform any loop-free subnets into step-aligned subnets. New procedures called the step-evaluation method and the forbidden condition reduction algorithm (FCRA) are developed to efficiently check admissible/boundary conditions given forbidden conditions and to reduce the computational complexity.

A recursive square root algorithm for Receding Horizon Tracking Control (RHTC) based on state-space model which the original sequential algorithm exhibits O(Nn/sup 2/) complexity is derived and its systolic implementation method is also shown. The parallel processing algorithm needs O(Nn) computations for an n-th order plant and N-step prediction horizon on O(n/sup 2/+nN) processor array.

This paper deals with the supervisory control of a discrete event system which is modeled by a state machine of which the states and the structure have their own physical meanings related to the real system. The control objective is specified by a desired transition trajectory set to consider the internal behavior as well as the output behavior, which is represented by a generated language. A supervisory control problem to get a desired internal behavior is defined, and a minimally restrictive solution is provided. Using the relation between the internal behavior and the output behavior, the control problem is reduced to a control problem to get a generated language corresponding to the internal behavior.

In this paper manufacturing systems are modeled by a cyclic place-timed controlled marked graph (PTCMG), which is a special class of timed controlled Petri nets. The control problem of manufacturing systems which can be formulated as a forbidden state problem of a discrete event system is considered. A maximally permissive state feedback control is synthesized in a PTCMG to guarantee a more enlarged admissible marking set for most of forbidden state problems than a cyclic controlled marked graph. A practical application is illustrated for an automated guided vehicle (AGV) coordination problem in a flexible manufacturing facility.