Optimal On-Line Scheduling of Multiple Control Tasks: A Case Study

We study the problem of dynamically scheduling a set of state-feedback control tasks controlling a set of linear plants. We consider an on-line non-preemptive scheduling policy that is optimal in the sense that it minimizes a quadratic performance criterion for the overall system. The optimal scheduling decision at each point in time is a function of the states of the controlled plants. To be able to solve the scheduling problem for realistic examples, we use the technique of relaxed dynamic programming to compute suboptimal solutions with error bounds. The approach is compared to earlier approaches in a case study involving simultaneous control of one ball-and-beam process and two DC-servo processes. We also show how the scheduling policy can be modified to allow for background tasks to execute when the need for control is small. 1

Sub-optimal sensor scheduling with error bounds

Abstract: In this paper the problem of sub-optimal sensor scheduling with a guaranteed distance to optimality is considered. Optimal in the sense that the sequence that minimizes the estimation error covariance matrix for a given time horizon is found. The search is done using relaxed dynamic programming. The algorithm is then applied to one simple second order system and one sixth order model of a fixed mounted model lab helicopter. Copyright c○2005 IFA

State Estimation for Distributed and Hybrid Systems

This thesis deals with two aspects of recursive state estimation: distributed estimation and estimation for hybrid systems. In the first part, an approximate distributed Kalman filter is developed. Nodes update their state estimates by linearly combining local measurements and estimates from their neighbors. This scheme allows nodes to save energy, thus prolonging their lifetime, compared to centralized information processing. The algorithm is evaluated experimentally as part of an ultrasound based positioning system. The first part also contains an example of a sensor-actuator network, where a mobile robot navigates using both local sensors and information from a sensor network. This system was implemented using a component-based framework. The second part develops, a recursive joint maximum a posteriori state estimation scheme for Markov jump linear systems. The estimation problem is reformulated as dynamic programming and then approximated using so called relaxed dynamic programming. This allows the otherwise exponential complexity to be kept at manageable levels. Approximate dynamic programming is also used to develop a sensor scheduling algorithm for linear systems. The algorithm produces an offline schedule that when used together with a Kalman filter minimizes the estimation error covariance

Automatic Gain Control in High speed WCDMA Terminals

In this study, it is investigated how different parameters influence 16QAM modulation. The focus is on how different parameters in the Automatic Gain Control algorithm influence raw bit error rates, but other parameters such as frequency error and misplaced decision levels are also investigated. The goal is not to develop optimal parameter configurations, but to gain some understanding on what parameters that are of great importance. The simulations are made with several types of fading multi path channels as well as Additive White Gaussian Noise (AWGN) channels. The investigations are carried out through simulations in a simulation environment implemented in Matlab. From the simulations the conclusion is drawn that 16QAM is more sensitive to frequency errors than QPSK and that an important parameter in the AGC is the DC blocker bandwidths. The optimal AGC design with repsect to bit error rate depends on the type of channel model used, but it seems that a slower AGC design is preferred when compared to a faster one. The step resonse simulations indicate that there is no problem with using a fast AGC. The AGC seems to be more important at high signal to noise ratios because the fading become more visible in that case

Valuing improvements in the water rights system in South Africa : a contingent ranking approach

In the context of increasing water scarcity, understanding is growing that irrigation water rights are important and that a lack of effective water rights systems constitute a major reason for inefficient water management. This study carried out a contingent ranking experiment to study how smallholder irrigators in South Africa would value potential changes in water rights. Three specific dimensions of water rights, relevant for the South African case, are considered: duration, quality of title and transferability. Results indicate that smallholder irrigators are prepared to pay considerably higher water prices if improvements are made in the water rights system. This implies that the proposed interventions in the water rights system would improve the efficiency and productivity of the small-scale irrigation sector. The increased willingness to pay could furthermore also assist South African government to reach the objective of increased cost recovery

Distributed Kalman Filtering Using Weighted Averaging

This paper addresses the problem of distributed Kalman filtering, with focus on limiting the required communication bandwidth. By distributed we refer to a scenario when all nodes in the network desire an estimate of the full state of the observed system and there is no centralized computation center. Communication only takes place between neighbors and only a fixed number of times each sample. To reduce bandwidth requirements of individual nodes, estimates instead of measurements are communicated. A new estimate is then formed as a weighted average of the neighbouring estimates. The weights are optimized to yield a small estimation error covariance in stationarity. The minimization can be done off line thus allowing only estimates to be communicated. The advantage of communicating estimates instead of measurements becomes more evident when the number of nodes exceeds the size of the state vector to be estimated. The algorithm is applied to one simple second order system and temperature sensing network

Depressive Symptomatology And Suicide Attempts In Adolescents With Mobility Limitations

Adolescents with mobility limitations may be at increased risk of certain adverse outcomes because of unique or exacerbated pre-existing challenges. The current study examined the relationships among mobility limitations, depressive symptomatology, and suicidal behaviors. Moreover, it was examined if pain and perceived social support mod-erated the relationships between severity of mobility limitations and the three outcome variables, and whether depressive symptomatology mediated the relationships between mobility limitations and suicidal behaviors. Secondary analyses of the AddHealth data set were performed. The sample was 49.18% female, 16.02% African-American, 65.46% Caucasian, 12.20% Hispanic, and 6.33% coded as Other. The mean age was 15.96 (SE = 0.11). In all, 4.35% reported mobility limitations; 22.49% had scores indicative of de-pressive symptomatology, 12.91% indicated suicidal ideation, and 3.62% had attempted suicide in the past year. Adolescents with mobility limitations were significantly more likely to be in the depressive symptomatology (OR = 1.64, 95% CI = 1.15-2.35), suicidal ideation (OR = 1.91, 95% CI = 1.35-2.72), and suicide attempt (OR = 2.53, 95% CI = 1.45-4.40) groups compared to adolescents without mobility limitations after controlling for age, gender, race, family income, and community residence. Severity of mobility limitations was not significantly associated with any of the three outcome variables. Pain was significantly associated with depressive symptomatology with an R2 change = 0.11, B = 1.29 (95% CI = 1.16-1.41), Wald F (1, 131) = 402.83, p \u3c .0001. Adding perceived ii social support in the next step resulted in an R2 = 0.27 (Wald F (16, 131) = 783.04, p \u3c .0001). Perceived social support was significantly associated with depressive symptoma-tology with an R2 change = 0.10, B = -0.70 (95% CI = -0.78 to -0.61), Wald F (1, 131) = 276.86, p \u3c .0001. However, pain and perceived social support did not significantly mod-erate the relationships between severity of mobility limitations and depressive symptoma-tology and suicidal behaviors. Depressive symptomatology partially mediated the rela-tionships between mobility limitations and suicidal ideation and suicide attempt (12-14% respectively). Based on these results, experiencing mobility limitations in adolescence should be considered a potential risk factor for depressive symptomatology and suicidal behaviors

Model Based Information Fusion in Sensor Networks

In this paper, a model based sensor fusion algorithm for sensor networks is presented. The algorithm, referred to as distributed Kalman filtering is based on a previously presented algorithm with the same name. The weight selection process has been improved yielding performance improvements of several times for the examples studied. Also, solutions to both optimization problems involved in the iterative off-line weight selection process are given as closed form expressions. The algorithm is also demonstrated on a typical signal tracking application

Automatic Gain Control In WCDMA Terminals

This article gives a presentation of the Automatic Gain Control algorithm used in WCDMA (3rd generation mobile networks). The focus is on how the controller bandwidth influences settling times and modulation distortion. This will be investigated through simulation for two different channel cases

Hästen, den bästa terapeuten? En kvalitativ studie om hästens betydelse för socialt arbete

The aim of this study was to examine businesses which use horses in various kinds of social work, and the opinions and experiences of the professional practitioners of these operations. I used semistructured interview to answer my questions, and I ended up interviewing eight people from seven different operations. Everyone was working in some kind of business which used horses as either an aid for the social work, or as a leisure activity for their clients. The clients had difficulties such as mental illness or some kind of disability. I found that my interviewees had experienced various forms of positive effects when their clients spent time with the animal. The professional practioners could see that their clients's motivation, trust and awareness had approved after spending time with the horse, and clients with psysical disabilties also gained from horsebackridning. But I also found that it is a theme which need more research and structure, and it needs people that's willing to fight for the cause