Research Papers - Department of Electrical and Electronic Engineering

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Open Access
Robustness of digital filters with respect to limit-cycle behavior under coefficient perturbations
(International Society for Optics and Photonics, 1996-06-07) Kulasekere, E. C; Premaratne, K; Bauer, P. H
A digital filter which has been designed to be limit cycle free may exhibit limit cycles at the implementation stage. This is due to the inability to implement filter coefficients exactly in hardware when they are quantized to satisfy available wordlength requirements. Given a digital filter which is limit cycle free under zero input conditions, the work below presents an algorithm which finds a region in the coefficient space, about the nominal filter coefficient values, where in the filter remains limit cycle free. Furthermore the results of the algorithm will also indicate the availability of other machine representable numbers for the coefficients that fall within this robustness region. Hence one may even choose shorter wordlength registers for coefficient storage if the corresponding grid falls within the constructed robustness region.
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An exhaustive search algorithm for checking limit cycle behavior of digital filters
(IEEE, 1996-10) Premaratne, K; Kulasekere, E. C; Bauer, P. H; Leclerc, L. J
The presence of limit cycles that may arise in fixed-point arithmetic implementation of a digital filter can significantly impair its performance. This paper presents an algorithm to determine the presence/absence of such limit cycles. For generality, the filter is taken to be in its state-space formulation. The algorithm is applicable independent of filter order, type of quantization nonlinearity, and whether the accumulator is single or double length. It may be utilized to construct limit cycle free regions in filter coefficient space. Once a filter is determined to be limit cycle free, a technique that provides a robustness region in coefficient space where all filters remain limit cycle free is also presented.
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Optimal placement of actuators and sensors for floor vibration control
(American Society of Civil Engineers, 2000-12) Hanagan, L. M; Kulasekere, E. C; Walgama, K. S; Premaratne, K
Lightweight floor systems are susceptible to excessive levels of vibration caused by occupant activities such as walking, dancing, and aerobics. Ongoing research utilizes active control to reduce vibration. Placement of multiple actuators and sensors for effective vibration control of flexible systems such as floors is a challenging task. The method proposed in this paper simultaneously determines optimal placements for multiple actuators, sensors, and appropriate output feedback gains of the controller. Instead of carrying out the controller design in the analog domain and then applying a transformation to arrive at a digital implementation, the proposed algorithm provides a digital controller directly. This allows lower sampling rates to be used at the implementation stage. To obtain faster settling times in the presence of external disturbances, a performance index that penalizes system states exponentially is utilized. The nonlinearities associated with actuator saturation due to force/stroke limitations is considered explicitly in the optimization. The proposed algorithm uses an interpolation scheme in case only partial knowledge of the mode shape is available. Hence it is applicable to a wider class of 2D structures that do not possess closed-form expressions for modal shapes and for which one has to resort to finite-element or experimental modal analysis.
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Resource management of task oriented distributed sensor networks
(IEEE, 2001-05-06) Zhang, J; Kulasekere, E. C; Premaratne, K; Bauer, P. H
In this paper we provide a foundation for a unified analysis of both the decision fusion and congestion avoidance aspects of a task-oriented distributed sensor network (DSN). Such a framework allows network resource management to be carried out in a manner that is sensitive to the overall objectives of the DSN rather than decoupling them via perhaps simple fairness strategies. The proposed approach associates importance measures related to the degradation and relevance of incoming data lines at each network node. These are then used to carry out intelligent resource management and avoid congestion in a manner which is implicitly related to the decision objectives of the DSN and explicitly related to the resource availability. To achieve this, we propose a 'per-flow' technique that decouples data flow among nodes at different hierarchical levels of the DSN. The resulting framework allows seamless integration of the importance measures providing resource management decisions that are sensitive to the overall DSN objectives.
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Simulation of a transformer winding for partial discharge propagation studies
(IEEE, 2002-01-27) Hettiwatte, S. N; Crossley, P. A; Wang, Z. D; Darwin, A; Edwards, G
A simulation model of a continuous disc type 6.6 kV transformer winding was used to study the propagation behaviour of partial discharge (PD) pulses. The model based on multi-conductor transmission line theory uses a single turn as a circuit element with the capacitance, inductance, and losses calculated as distributed parameters. Transfer functions that describe how the location of the PD source affects the current signals measured at the terminals of the winding were calculated. The paper shows how the position of the zeros in the frequency response of the measured current signals can be used to locate the source of the discharge. Sensitivity studies on the parameters of the model were used to investigate the effect of inaccuracies in the model on the position of the zeros and hence the location of the discharge.
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An electrical PD location method applied to a continuous disc type transformer winding
(IEEE, 2003-06-01) Hettiwatte, S. N; Wang, Z. D; Crossley, P. A; Jarman, P; Edwards, G; Darwin, A
A 6.6 kV continuous disc type winding of a distribution transformer is used to investigate the propagation of partial discharges (PD) with the aim of location. The winding was modelled, as multiconductor transmission lines with each turn represented by a transmission line. This approach results in the model being valid up to a few MHz in frequency. The validity of the model was confirmed by impedance measurements on the winding. The transfer functions calculated between probable PD source locations to winding terminals showed that the troughs (or zeros) change in frequency with the location of PD source and hence can be used for the location of PD. Transfer functions obtained experimentally using a discharge calibrator as the PD source, showed very good agreement with the calculations.
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Conditioning and updating evidence
(Elsevier, 2004-04-01) Kulasekere, E. C; Premaratne, K; Dewasurendra, D. A; Shyu, M. L; Bauer, P. H
A new interpretation of Dempster–Shafer conditional notions based directly upon the mass assignments is provided. The masses of those propositions that may imply the complement of the conditioning proposition are shown to be completely annulled by the conditioning operation; conditioning may then be construed as a re-distribution of the masses of some of these propositions to those that definitely imply the conditioning proposition. A complete characterization of the propositions whose masses are annulled without re-distribution, annulled with re-distribution and enhanced by the re-distribution of masses is provided. A new evidence updating strategy that is composed of a linear combination of the available evidence and the conditional evidence is also proposed. It enables one to account for the integrity’ and inertia’ of the available evidence and its flexibility’ to updating by appropriate selection of the linear combination weights. Several such strategies, including one that has a probabilistic interpretation, are also provided. 2003 Elsevier Inc. All rights reserved.
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A measurements-based discharge location algorithm for plain disc winding power transformers
(IEEE, 2005-06-20) Wang, Z. D; Hettiwatte, S. N; Crossley, P. A
A measurements-based electrical method for locating partial discharges (PD) in transformers is described in the paper. This location method relies on the series resonance frequencies of the signals produced at the transformer terminals by a discharge on the winding. Based on the equivalent circuit of plain disc type winding which consists of series inductance (L), series capacitance (K) and shunt capacitance to earth (C) of the winding, an analytical location algorithm is derived which gives the relationship between the location of a discharge and its terminal response's series resonance frequencies. LKC parameters of the equivalent circuit can be estimated using the series resonance frequencies of a calibration signal measured at the bushing tap during PD calibration. The PD location algorithm was tested on 11 kV transformer winding using signals produced by a discharge simulator and real discharges, and the results confirm its validity with a location accuracy of better than 10% of the winding length. However, blind area where this location algorithm is not applicable does exist near the neutral of the winding and far away from the measuring terminal. Since this location algorithm uses the series resonance frequencies below 500 kHz, it can be implemented with conventional PD measuring circuitry and instruments to detect and locate discharges in power transformers.
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Free route air traffic flow manager
(IEEE, 2005-12-11) Abeysooriya, M; Kulasekere, E. C
As the world moves towards the era of globalization and as the business world continues to revolutionize, meeting the expectations of a timely and safe air transportation system has become major challenge to the field of aviation. Most of the existing air traffic control systems primarily focus on generating pre-defined routes for aircrafts based on the 'fixed route model'. But with the advancement of technologies in the field of aviation an effective and practical mechanism called 'free route modeling' has been introduced. The few test beds that exist worldwide based on this concept, have been implemented for certain specific airspaces eliminating the possibility of using this strategy at any location worldwide. This paper presents the design and implementation of the 'free route air traffic flow manager' project which proposes a framework which can be used as a generic tool to over come this limitation. This tool will allow the user to dynamically create a free route modeling system for a certain airspace by configuring a 3D airspace according to the given requirements for that airspace. The dynamically developed free route modeling system will facilitate the functionalities of generating the initial free route for an aircraft & provide dynamic re- planning for the configured air space when a conflicting scenario is reported.
Open Access
An algorithm for energy driven cluster head rotation in a distributed wireless sensor network
(Colombo, 2005-12-15) Gamwarige, S; Kulasekere, E. C
Wireless sensor networks (WSNs) consists of large number of inexpensive, low-power, sensors that can be placed in an ad hoc fashion to form a communication network. Efficient techniques for inter sensor communication and information gathering is critical for prolonging the lifetime of the sensor network. Clustering provides an effective way for extending the lifetime of a sensor network. In this paper we propose a distributed and energy driven clustering algorithm where the cluster heads are selected based on relative residual energy level of sensors. Furthermore the cluster head candidacy selection phase, and the cluster head candidacy rotation among phases is triggered only when any of cluster heads energy drops below a dynamic threshold computed by the algorithm. As a result, the overheads in the inter sensor communications will be reduced and thereby the proposed algorithm will favor more powerful nodes over the weaker ones to prolong the lifetime of the entire sensor network in both homogeneous and heterogeneous sensor networks. The results have shown that the the proposed algorithm performs better when compared to existing algorithms such as LEACH, SEP, HEED and ANTCLUST based on the Percentage Node Alive (PNA) and the First Node Dies (FND) metrics.
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Performance analysis of the edcr algorithm in a distributed wireless sensor network
(IEEE, 2006-04-11) Gamwarige, S; Kulasekere, E. C
The energy driven cluster-head rotation (EDCR) algorithm proposed in S. Gamwarige and E. Kulasekere (2005) has been shown to out performed existing clustering algorithms such as LEACH (W.B. Heinzelman et al., 2002), HEED (O. Younis and S. Fahmy, 2004), ANTCLUST based (J. Kamimura et al., 2004) and SEP (G. Smaragdakis et al., 2004) in terms of END and PNA (95%) lifetime metrics in a distributed wireless sensor network (WSN). In this paper we present theoretical analysis of the performance parameters such as the optimum transmission range (R opt ) and the clustering trigger threshold value (lambda i ) of EDCR in terms correctness and complexity of the algorithm. Further we explain how to find the optimal values for such parameters in order to maximize the network lifetime
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Application of the edcr algorithm in a cluster based multi-hop wireless sensor network
(IEEE, 2006-10-18) Gamwarige, S; Kulasekere, E. C
The energy driven cluster head rotation algorithm proposed in (Gamwarige, S and Kulasekere, E, 2005) and analyzed in (Gamwarige, S and Kulasekere, E, 2006) is based on a single hop communication model where the data messages from each cluster head (CH) node is sent directly to the base station (BS). As a result when the wireless sensor network (WSN) dimensions are large, the nodes located far away from the BS die much faster. In this paper a method of extending the lifetime of the WSN based on a multihop communication model applied to the EDCR algorithm is proposed. The modified EDCR (EDCR-MH) relays all CH to BS messages via other CH nodes by computing a shortest path based on local heuristic information. Further, the EDCR-MH also has provisions to minimize the burden due to excessive data relay on nodes closer to the BS. The results indicate that the proposed algorithm out performs algorithms like under similar conditions
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Distributed Wireless CSMA/CA based Unified Navigation Solution
(IEEE, 2006-12-15) Samarakoon, S. M. D. D; Silva, A. P. M; Samaraweera, S. M. D. W; Fernando, T. G. A; Kulasekere, E. C
This research proposes a multiple access protocol known as the Distributed Wireless CSMA/CA (DWCC). This protocol is optimized for a distributed wireless communication network where the node availability and behavior are both uncertain and unpredictable. An application based on a distributed communication network formed using inter vessels communication at deep sea is used to illustrate the salient features of the proposed protocol. A method is outlined on how the proposed new protocol can be applied to extend radar vision at each vessel in the presence of radar jamming and/or communication node failure at mid sea. That is, the DWCC protocol is used to gather information from all vessels to construct a cumulative radar map at any node and thus extending the radar vision beyond the display capability of a single node.
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MIMO LMMSE transceiver design with imperfect CSI at both ends
(IEEE, 2007-06-24) Blostein, S. D; Ding, M
This paper presents a new result on minimum total mean squared error (MSE) joint transceiver design for multiple-input multiple-output (MIMO) systems, with imperfect channel state information (CSI) at both ends and subject to a total power constraint. The channel knowledge here is the channel mean and transmit correlation information. The joint design is formulated into an optimization problem, to which the closed-form optimum solution is found. The optimum precoder consists of a linear filter, a matrix which collects effective channel eigenmodes, and a diagonal power allocation matrix. The linear filter balances the suppression of channel noise and the additional noise induced by channel estimation error. Given the precoder, the optimum decoder is simply a linear minimum MSE (LMMSE) data estimator. The performance degradations due to imperfect channel estimation and/or transmit correlation are demonstrated by simulation results. The relation between the minimum total MSE design and the maximum mutual information design is determined as well, under the above mentioned imperfect CSI.
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Optimization of cluster head rotation in energy constrained wireless sensor networks
(IEEE, 2007-07-02) Gamwarige, S; Kulasekere, E. C
The performance of energy driven cluster head (CH) rotation algorithms have been shown to be far more superior to time driven CH rotation algorithms when it comes to maximizing the sensor bed lifetime. The sensor bed life time is improved by selecting the proper points at which a CH role is relinquished to higher energy nodes via a CH rotation phase. However no formal analytical method is available to find the optimal point at which the CH rotation should be carried out. This research proposes an analytical iterative method to obtain the optimal points at which the CH rotation can be carried out. The method proposes an optimal value c opt for the energy threshold at which this rotation could occur. The values obtained via the analytical method is shown to be optimal via simulations using the EDCR and EDCR-MH algorithms. The analytical method proposed can be used in any energy driven algorithm to find the optimal point for CH rotations avoiding any ad hoc simulation based methods to maximize the lifetime of the sensor bed.
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A cluster based energy balancing strategy to improve Wireless Sensor Networks lifetime
(IEEE, 2007-08-09) Gamwarige, S; Kulasekere, E. C
Wireless Sensor Networks (WSNs) have been of interest due to its many areas of application. The lifetime of the sensor bed is of crucial importance for the successful deployment of such networks. Many algorithms have been proposed based on clustering and cluster head (CH) rotation to improve the lifetime of WSNs. EDCR [1] and EDCR-MH [2] are two such algorithms that have shown promising results. The lifetime of the entire sensor bed can be significantly improved if the energy associated with a sensor node is depleted at the same rate irrespective of its location with respect to the Base Station (BS). This research proposes a new algorithm for CH selection and rotation that incorporates the desirable features of both EDCR and EDCRMH together with a modified minimum distance communication between CH and BS. The algorithm is capable of balancing the energy depletion rate of sensor nodes across the entire sensor bed irrespective of their node locations. Unlike previous algorithms, the proposed algorithm can be applied to significantly larger sensor beds while maintaining the lifetime performance. Analytical models are presented to identify salient parameters of the proposed algorithm. Simulation results are provided to illustrate the applicability of the algorithm. The results indicate that the lifetime of the entire sensor bed is improved over existing algorithms.
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Uplink-downlink duality in normalized MSE or SINR under imperfect channel knowledge
(IEEE, 2007-11-26) Ding, M; Blostein, S. D
Duality between the multi-antenna multi-user uplink and the downlink has been discovered in terms of sum rate, capacity region, signal-to-interference-plus-noise-ratio (SINR) region or normalized mean-squared error (MSE) region. Previous work on duality has assumed perfect channel knowledge. However, channel estimation is never perfect in practice. In this paper, channel estimation error as well as antenna correlation at the base station (BS) is taken into account. A multi-user system with multiple antennas at the BS and with single-antenna users is studied. Joint detection and transmission are used in the uplink and the downlink, respectively. It is analytically shown that with imperfect channel state information (CSI), under the same sum power constraint, the achievable SINR regions or the normalized MSE regions in both links are the same, as in the case with perfect CSI. Monte Carlo simulation results and discussions are also provided to complement the analysis.
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Relation between joint optimizations for multiuser MIMO uplink and downlink with imperfect CSI
(IEEE, 2008-03-31) Ding, M; Blostein, S. D
Joint linear minimum sum mean-squared error (referred to as MSMSE) transmitter and receiver (transceiver) optimization problems are formulated for multiuser MIMO systems under a sum power constraint assuming imperfect channel state information (CSI). Both the uplink and the dual downlink are considered. Based on the Karush-Kuhn-Tucker (KKT) conditions associated with both problems, a relation between the two problems is discovered, which is termed the uplinkdownlink duality in sum MSE under imperfect CSI. As a result, the MSMSEs in both links are the same and any admissible uplink design satisfying the KKT conditions can be translated for application to the downlink, and vice versa. Simulation results are provided to demonstrate the duality and show the impact of imperfect CSI.
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Enhancing flexibility of belief representations
(IEEE, 2008-04-06) Senaratne, D; Kulasekere, E. C
Several attempts have been made to enhance the flexibility of belief representation in the Shafer model. This paper questions their ability to retain the intuitiveness. A method of enhancing the flexibility of belief representations, without compromising the intuitiveness is proposed. In it we relax the Shafer's exclusivity constraint by disregarding the formalism: 'subsets as propositions' and expressing support as functions of propositions. A compact and intuitive notation for propositions, termed N-of, is introduced. This notation simplifies the formulation of propositions from the statements humans make.
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Joint optimization for multiuser MIMO uplink systems with imperfect CSI
(IEEE, 2008-05-24) Ding, M; Blostein, S. D
In this paper, a joint linear minimum sum meansquared error transceiver optimization problem is formulated for multiuser MIMO uplink systems under a sum power constraint assuming imperfect channel state information (CSI). Two methods are proposed to solve this problem. One is based on the associated Karush-Kuhn-Tucker conditions. The other is to solve an equivalent problem, approaching the solution by solving a sequence of semi-definite programming problems. After obtaining the solution to the optimization problem, we investigate the effects of channel estimation errors and antenna correlation at the base station on system performance. Simulation results are provided.