Now showing 1 - 10 of 50
  • Publication
    Compression in wireless sensor networks: A survey and comparative evaluation
    (Association for Computing Machinery, 2013-11-01) ; ;
    Wireless sensor networks (WSNs) are highly resource constrained in terms of power supply, memory capacity, communication bandwidth, and processor performance. Compression of sampling, sensor data, and communications can significantly improve the efficiency of utilization of three of these resources, namely, power supply, memory and bandwidth. Recently, there have been a large number of proposals describing compression algorithms for WSNs. These proposals are diverse and involve different compression approaches. It is high time that these individual efforts are put into perspective and a more holistic view taken. In this article, we take a step in that direction by presenting a survey of the literature in the area of compression and compression frameworks in WSNs. A comparative study of the various approaches is also provided. In addition, open research issues, challenges and future research directions are highlighted.
    Scopus© Citations 151  949
  • Publication
    Recovery From a First-Time Lateral Ankle Sprain and the Predictors of Chronic Ankle Instability: A Prospective Cohort Analysis
    Background: Impairments in motor control may predicate the paradigm of chronic ankle instability (CAI) that can develop in the year after an acute lateral ankle sprain (LAS) injury. No prospective analysis is currently available identifying the mechanisms by which these impairments develop and contribute to long-term outcome after LAS. Purpose: To identify the motor control deficits predicating CAI outcome after a first-time LAS injury. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: Eighty-two individuals were recruited after sustaining a first-time LAS injury. Several biomechanical analyses were performed for these individuals, who completed 5 movement tasks at 3 time points: (1) 2 weeks, (2) 6 months, and (3) 12 months after LAS occurrence. A logistic regression analysis of several "salient" biomechanical parameters identified from the movement tasks, in addition to scores from the Cumberland Ankle Instability Tool and the Foot and Ankle Ability Measure (FAAM) recorded at the 2-week and 6-month time points, were used as predictors of 12-month outcome. Results: At the 2-week time point, an inability to complete 2 of the movement tasks (a single-leg drop landing and a drop vertical jump) was predictive of CAI outcome and correctly classified 67.6% of cases (sensitivity, 83%; specificity, 55%; P = .004). At the 6-month time point, several deficits exhibited by the CAI group during 1 of the movement tasks (reach distances and sagittal plane joint positions at the hip, knee and ankle during the posterior reach directions of the Star Excursion Balance Test) and their scores on the activities of daily living subscale of the FAAM were predictive of outcome and correctly classified 84.8% of cases (sensitivity, 75%; specificity, 91%; P < .001). Conclusion: An inability to complete jumping and landing tasks within 2 weeks of a first-time LAS and poorer dynamic postural control and lower self-reported function 6 months after a first-time LAS were predictive of eventual CAI outcome.
    Scopus© Citations 255  2496
  • Publication
    Postural control strategies during single limb stance following acute lateral ankle sprain
    Single-limb stance is maintained via the integration of visual, vestibular and somatosensory afferents. Musculoskeletal injury challenges the somatosensory system to reweight distorted sensory afferents. This investigation supplements kinetic analysis of eyes-open and eyes-closed single-limb stance tasks with a kinematic profile of lower limb postural orientation in an acute lateral ankle sprain group to assess the adaptive capacity of the sensorimotor system to injury. Sixty-six participants with first-time acute lateral ankle sprain completed a 20-second eyes-open single-limb stance task on their injured and non-injured limbs (task 1). Twenty-three of these participants successfully completed the same 20-second single-limb stance task with their eyes closed (task 2). A non-injured control group of 19 participants completed task 1, with 16 completing task 2. 3-dimensional kinematics of the hip, knee and ankle joints, as well as associated fractal dimension of the center-of-pressure path were determined for each limb during these tasks. Between trial analyses revealed significant differences in stance limb kinematics and fractal dimension of the center-of-pressure path for task 2 only. The control group bilaterally assumed a position of greater hip flexion compared to injured participants on their side-matched “involved”(7.41 [6.1°] vs 1.44 [4.8]°; η2 = .34) and “uninvolved” (9.59 [8.5°] vs 2.16 [5.6°]; η2 = .31) limbs, with a greater fractal dimension of the center-of-pressure path (involved limb = 1.39 [0.16°] vs 1.25 [0.14°]; uninvolved limb = 1.37 [0.21°] vs 1.23 [0.14°]). Bilateral impairment in postural control strategies present following a first time acute lateral ankle sprain.
      799Scopus© Citations 40
  • Publication
    TrickleTree: A Gossiping Approach To Fast And Collision Free Staggered Scheduling
    (International Academy, Research, and Industry Association (IARIA), 2011-09) ; ;
    In recent years, data gathering has received significant attention as an application of Wireless Sensor Networks (WSNs). Staggered data tree based protocols have been shown to be successful in reducing energy consumption in data gathering scenarios. An important part of staggered protocols is the process of schedule construction. In order to minimize energy consumption, this process must be fast. In this paper, we present TrickleTree, a fast distributed protocol for establishing staggered and collision free communication schedule. TrickleTree has three functions: to establish routes, i.e., construct a data gathering tree, to establish a staggered communication schedule, i.e, assign time slots to links, and to disseminate the maximal tree depth in the network. To minimize network setup time, TrickleTree combines neighborhood discovery and schedule construction into one step. To ensure that good neighbors are discovered before a node joins the network, TrickleTree uses a rating mechanism. Collisions during node association are reduced by using association slots. To increase the message delivery rate with small message overhead, TrickleTree uses adaptive gossiping. We provide a formal analysis of the protocol properties i.e., collision free scheduling and termination. The behavior of the proposed approach is evaluated in simulation. The results show up to 90% in a reduction in schedule setup time and a 50% reduction of duty cycle compared to a flooding approach.
      150
  • Publication
    Low-Complexity Concurrent Error Detection for Convolution with Fast Fourier Transforms
    In this paper, a novel low-complexity Concurrent Error Detection (CED) technique for Fast Fourier Transform-based convolution is proposed. The technique is based on checking the equivalence of the results of time and frequency domain calculations of the first sample of the circular convolution of the two convolution input blocks and of two consecutive output blocks. The approach provides low computational complexity since it re-uses the results of the convolution computation for CED checking. Hence, the number of extra calculations needed purely for CED is significantly reduced. When compared with a conventional Sum Of Squares - Dual Modular Redundancy technique, the proposal provides similar error coverage for isolated soft errors at significantly reduced computational complexity. For an input sequence consisting of complex numbers, the proposal reduces the number of real multiplications required for CED in adaptive and fixed filters by 60% and 45%, respectively. For input sequences consisting of real numbers, the reductions are 66% and 54%, respectively.
      371
  • Publication
    Reliability Analysis of Memories Protected with BICS and a per-Word Parity Bit
    (Association for Computing Machinery (ACM), 2010-02) ; ;
    This paper presents an analysis of the reliability of memories protected with Built-in Current Sensors (BICS) and a per-word parity bit when exposed to Single Event Upsets (SEUs). Reliability is characterized by Mean Time to Failure (MTTF) for which two analytic models are proposed. A simple model, similar to the one traditionally used for memories protected with scrubbing, is proposed for the low error rate case. A more complex Markov model is proposed for the high error rate case. The accuracy of the models is checked using a wide set of simulations. The results presented in this paper allow fast estimation of MTTF enabling design of optimal memory configurations to meet specified MTTF goals at minimum cost. Additionally the power consumption of memories protected with BICS is compared to that of memories using scrubbing in terms of the number of read cycles needed in both configurations.
    Scopus© Citations 6  288
  • Publication
    Low-Power TinyOS Tuned Processor Platform for Wireless Sensor Network Motes
    (Association for Computing Machinery (ACM), 2010-05-03) ; ;
    In this article we describe a low power processor platform for use in Wireless Sensor Network (WSN) nodes (motes). WSN motes are small, battery-powered devices comprised of a processor, sensors, and a Radio Frequency transceiver. It is expected that WSNs consisting of large numbers of motes will offer long-term, distributed monitoring, and control of real-world equipment and phenomena. A key requirement for these applications is long battery life. We investigate a processor platform architecture based on an application-specific programmable processor core, System-On-Chip bus, and a hardware accelerator. The architecture improves on the energy consumption of a conventional microprocessor design by tuning the architecture for a suite of TinyOS based WSN applications. The tuning method used minimizes changes to the Instruction Set Architecture facilitating rapid software migration to the new platform. The processor platform was implemented and validated in an FPGA-based WSN mote. The benefits of the approach in terms of energy consumption are estimated to be a reduction of 48% for ASIC implementation relative to a conventional programmable processor for a typical TinyOS application suite without use of voltage scaling.
    Scopus© Citations 4  534
  • Publication
    Improved patient specific seizure detection during pre-surgical evaluation
    Objective: There is considerable interest in improved off-line automated seizure detection methods that will decrease the workload of EEG monitoring units. Subject-specific approaches have been demonstrated to perform better than subject-independent ones. However, for pre-surgical diagnostics, the traditional method of obtaining a priori data to train subject-specific classifiers is not practical. We present an alternative method that works by adapting the threshold of a subject-independent to a specific subject based on feedback from the user. Methods: A subject-independent quadratic discriminant classifier incorporating modified features based partially on the Gotman algorithm was first built. It was then used to derive subject-specific classifiers by determining subject-specific posterior probability thresholds via user interaction. The two schemes were tested on 529 h of intracranial EEG containing 63 seizures from 15 subjects undergoing pre-surgical evaluation. To provide comparison, the standard Gotman algorithm was implemented and optimised for this dataset by tuning the detection thresholds. Results: Compared to the tuned Gotman algorithm, the subject-independent scheme reduced the false positive rate by 51% (0.23 to 0.11 h−1) while increasing sensitivity from 53% to 62%. The subject-specific scheme further improved sensitivity to 78%, but with a small increase in false positive rate to 0.18 h−1. Conclusions: The results suggest that a subject-independent classifier scheme with modified features is useful for reducing false positive rate, while subject adaptation further enhances performance by improving sensitivity. The results also suggest that the proposed subject-adapted classifier scheme approximates the performance of the subject-specific Gotman algorithm. Significance: The proposed method could potentially increase the productivity of offline EEG analysis. The approach could also be generalised to enhance the performance of other subject independent algorithms.
    Scopus© Citations 32  489
  • Publication
    Single-leg drop landing movement strategies in participants with chronic ankle instability compared with lateral ankle sprain 'copers'
    Individuals with CAI display alterations in hip joint kinematics and energetics during a unipodal landing task compared to LAS 'copers'. These alterations may be responsible for the increased risk of injury experienced by individuals with CAI during landing manoeuvres. Thus, clinicians must recognise the potential for joints proximal to the affected ankle to contribute to impaired function following an acute lateral ankle sprain injury and to develop rehabilitation protocols accordingly.
    Scopus© Citations 46  1161
  • Publication
    Phase-Difference Ambiguity Resolution for a Single-Frequency Signal in the Near-Field Using a Receiver Triplet
    The problem of ambiguity in the phase-difference of a signal received by widely-spaced receivers is considered. It is shown that a collinear receiver triplet with a specific configuration combined with a proposed algorithm can be utilized for phase-difference disambiguation. The identifiability condition is that the difference of the two smaller inter-receiver spacings is not greater than a half-wavelength of the impinging signal and is greater than zero. The effect of the emitter location relative to the receiver array and the effect of noise are studied. Analytic formulae for the MSE (mean squared error) under Gaussian white noise are obtained and are used to directly determine performance versus SNR (signal-to-noise ratio) given the emitter location and the receiver configuration. Performance is found to exhibit an SNR threshold effect that depends on the emitter location and the sensor configuration. The analytic performance predictions are found to be close to the performance obtained in simulation.
    Scopus© Citations 20  430