Separating movement and gravity components in an acceleration signal and implications for the assessment of human daily physical activity.

INTRODUCTION: Human body acceleration is often used as an indicator of daily physical activity in epidemiological research. Raw acceleration signals contain three basic components: movement, gravity, and noise. Separation of these becomes increasingly difficult during rotational movements. We aimed to evaluate five different methods (metrics) of processing acceleration signals on their ability to remove the gravitational component of acceleration during standardised mechanical movements and the implications for human daily physical activity assessment. METHODS: An industrial robot rotated accelerometers in the vertical plane. Radius, frequency, and angular range of motion were systematically varied. Three metrics (Euclidian norm minus one [ENMO], Euclidian norm of the high-pass filtered signals [HFEN], and HFEN plus Euclidean norm of low-pass filtered signals minus 1 g [HFEN+]) were derived for each experimental condition and compared against the reference acceleration (forward kinematics) of the robot arm. We then compared metrics derived from human acceleration signals from the wrist and hip in 97 adults (22-65 yr), and wrist in 63 women (20-35 yr) in whom daily activity-related energy expenditure (PAEE) was available. RESULTS: In the robot experiment, HFEN+ had lowest error during (vertical plane) rotations at an oscillating frequency higher than the filter cut-off frequency while for lower frequencies ENMO performed better. In the human experiments, metrics HFEN and ENMO on hip were most discrepant (within- and between-individual explained variance of 0.90 and 0.46, respectively). ENMO, HFEN and HFEN+ explained 34%, 30% and 36% of the variance in daily PAEE, respectively, compared to 26% for a metric which did not attempt to remove the gravitational component (metric EN). CONCLUSION: In conclusion, none of the metrics as evaluated systematically outperformed all other metrics across a wide range of standardised kinematic conditions. However, choice of metric explains different degrees of variance in daily human physical activity

An Infrastructure for End Customer Metering of Networked Services

The Internet today is driven by business relations between customers and service providers. An increasing number of services offered in this context require guaranteed quality, specified as part of a contract. The challenge is then to guarantee Quality of Service (QoS) in a best effort network, such as the Internet. Existing standards (IETF DiffServ/Intserv) provide means to offer this QoS. How these services ought to be charged is another important aspect, as it gives the provider incentives to recover its costs and make a stream of revenue. It is argued that before any real deployment of QoS and charging mechanisms takes place, other developments have to occur. Services provided to end-customers need to be measured according to the terms stated in the contract. Such terms specify the acceptable performance level in the service level agreement (SLA), in addition to a tariff used to charge for the service. Thus, a metering system to report and store resource usage information is necessary to (a) dynamically assert whether a service delivered conforms to its SLA, and (b) charge for the service based on the tariff. Metering in this business scenario, however, poses issues that need to be addressed. Security is an important one, as there will be incentives for customers or providers to cheat. Also, the metering system has to be instructed to measure whatever parameters the service contract relies on, therefore requiring its automatic configuration and management. Finding the limitations of a measurement system in terms of performance is another relevant aspect, so as to help the understanding of its operation in heterogeneous host environments. The thesis of this work is that an infrastructure tailored for end-customer metering of networked services is necessary to address the above issues. The main contributions of this dissertation can be summarised as follows: (a) The EdgeMeter system is proposed to facilitate the metering of services in a general business context. It supports safe transport and storage of measurement data, as well as flexible configuration of metering points based on SLA/Tariffs automatically distributed by service providers; (b) A modular approach allows extensibility and flexibility of this infrastructure. Measurement modules can be stored and located in the network. A scalable network location framework. Lighthouse, is proposed and evaluated. It is shown that this framework computes more accurate network locations, when compared to other related techniques; (c) A security framework based on a trustworthy third-party component, the Meter Inspection Authority (MIA), is proposed to tackle security issues. MIA endorses the accuracy and safety of metering systems; (d) To assess the performance of metering systems, experimental work is carried out using a prototype implementation of EdgeMeter. It is found that the performance of such systems has strong influence on accuracy. Under certain loads, in which the normal behaviour of the system is degraded (poor performance), the metering service may be inaccurate

Service level agreement and tariff related control of Internet metering

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On the accuracy of embeddings for Internet coordinate systems

Internet coordinate systems embed Round-Trip-Times (RTTs) between Internet nodes into some geometric space so that unmeasured RTTs can be estimated using distance computation in that space. If accurate, such techniques would allow us to predict Internet RTTs without extensive measurements. The published techniques appear to work very well when accuracy is measured using metrics such as absolute relative error. Our main observation is that absolute relative error tells us very little about the quality of an embedding as experienced by a user. We define several new accuracy metrics that attempt to quantify various aspects of user-oriented quality. Evaluation of current Internet coordinate systems using our new metrics indicates that their quality is not as high as that suggested by the use of absolute relative error.