Charalampos Konstantopoulos - Academia.edu (original) (raw)

Conference Papers by Charalampos Konstantopoulos

19th IEEE Symposium on Computers and Communications (ISCC 2014), Jun 24, 2014

A critical issue dealt with in Wireless Sensor and Actor Networks (WSANs) is the real time respon... more A critical issue dealt with in Wireless Sensor and Actor Networks (WSANs) is the real time response of actors to events occurring in the network area. The fast notification of actors from Sensor Nodes (SNs) about the events as well as the effective coordination of actors for prompt event handling is most important in these networks. In this paper, we introduce a distributed protocol for effective event handling in a WSAN. Existing approaches mainly favoring actors near the current event for handling it, may lead to highly ineffective solutions for certain worst-case scenarios. Through a randomized approach, our solution also selects distant actors for handling events, and guarantees fast average responsiveness to events and a balanced energy distribution among actors. In addition, it features efficient distributed algorithms for sensor to actor and actor to actor coordination which are of independent interest.

The investigation of mobile agent (MA) middleware as a technology for implementing efficient data... more The investigation of mobile agent (MA) middleware as a technology for implementing efficient data fusion schemes on wireless sensor networks (WSN) has been a subject of intense research in the past few years. Nevertheless, the itineraries followed by travelling MAs largely determine the overall performance of the data fusion applications. Along this line, this article introduces a novel algorithmic approach for efficient itinerary planning of MA objects engaged in data fusion tasks. Our algorithm adopts an iterated local search (ILS) approach in deriving the hop sequence of multiple travelling MAs over the deployed source nodes. Simulation results demonstrate the performance gain of our method against existing multiple MA itinerary planning methods.

6th International Conference on Ubiquitous and Future Networks (ICUFN 2014), Jul 9, 2014

Mobile agents (MAs) have been proposed as a distributed middleware approach suitable for autonomi... more Mobile agents (MAs) have been proposed as a distributed middleware approach suitable for autonomic data aggregation operations in Wireless Sensor Networks (WSN). Determining optimal itineraries for MAs traveling through WSN nodes is a non-trivial problem. Thus, several heuristics have been proposed to perform efficient itinerary planning for MAs. However, the evaluation of these heuristics is typically performed on the ground of different parameter spaces and assumptions about the underlying network and the capabilities of nodes. Herein, we implement, simulate and compare the most prominent itinerary planning algorithms upon a common parameter space, making realistic network-level assumptions.

Papers by Charalampos Konstantopoulos

The use of mobile agents for data fusion in wireless sensor networks has been recently proposed i... more The use of mobile agents for data fusion in wireless sensor networks has been recently proposed in the literature to answer the scalability problem of client/server model. In this article, we consider the problem of calculating a near-optimal route for a mobile agent that incrementally fuses the data as it visits the nodes in a distributed sensor network. The order of visited nodes affects not only the quality but also the overall cost of data fusion. We propose two heuristic algorithms that adapt methods usually applied in network design problems in the specific requirements of sensor networks. They suggest the proper number of MAs that minimizes the overall data fusion cost and construct near-optimal itineraries for each of them.

Abstract One of the most important features in image analysis and understanding,is shape. Mathema... more Abstract One of the most important features in image analysis and understanding,is shape. Mathematical,morphology,is the image,processing branch,that deals with shape analysis. The definition of all morphological,transformations is based on two primitive operations, i.e. dilation and erosion. Since many,applications require the solution of morphological problems in real time, researching time efficient algorithms for these two operations is crucial. In this paper, effi- cient parallel algorithms for the binary dilation and ero- sion are presented and evaluated for an advanced,associa- tive processor. Simulation results indicate that the achieved speedup is linear. Keywords: mathematical morphology, dilation, erosion, massively parallel processor, associative processor, hyper- cube

Block matching motion estimation algorithms are widely used in video coding schemes. In this pape... more Block matching motion estimation algorithms are widely used in video coding schemes. In this paper, we design an efficient hierarchical block matching motion estimation (HBMME) algorithm on a hypercube multiprocessor. Unlike systolic array designs, this solution is not tied down to specific values of algorithm parameters and thus offers increased flexibility. Moreover, the hypercube network can efficiently handle the non regular data flow of the HBMME algorithm. Our techniques nearly eliminate the occurrence of "difficult" communication patterns, namely many-to-many personalized communication, by replacing them with simple shift operations. These operations have an efficient implementation on most of interconnection networks and thus our techniques can be adapted to other networks as well. With regard to the employed multiprocessor we make no specific assumption about the amount of local memory residing in each processor. Instead, we introduce a free parameter S and assume that each processor has Θ(S) local memory. By doing so, we handle all the cases of modern multiprocessors, that is fine-grained, medium-grained and coarse-grained multiprocessors and thus our design is quite general. approach, we study the softwarebased realization of the HBMME algorithm on a hypercube-based multiprocessor. We also present an efficient full search block matching motion estimation (FSBMME) algorithm which is used as a subroutine in the HBMME algorithm. A basic point in our study is the amount of local memory at each processor. Specifically, we assume that there is Θ(S) local memory at each processor where S is a free parameter. Most programmable architectures used in video coding are coarse-grained multiprocessors where each processor has enough memory to keep all data it will need throughout algorithm execution. Thus interprocessor communication is almost eliminated and processors can operate independently. In our study, by including the amount of local memory at each processor as a free parameter, we consider all classes of modern multiprocessors, that is fine-grained, medium-grained as well as coarsegrained parallel machines. As will become evident later, the smaller the value of the parameter S is, the harder it is to design an efficient algorithm. This is because interprocessor communication becomes inevitable when processors have limited local memory. In order to keep communication overhead low, we need to carefully arrange the necessary communication operations. In addition, the use of a powerful network such as the hypercube for the implementation of the HBMME algorithm is well justified, because this algorithm has a non regular data flow and its inherent communication is not local. Thus it cannot be easily implemented on systolic arrays. Dedicated hardware designs for the HBMME algorithm 11, 12, 13] require high external memory bandwidth or relieve these requirements by using large on chip memory.

Organization, scalability and routing have been identified as key problems hindering viability an... more Organization, scalability and routing have been identified as key problems hindering viability and commercial success of mobile ad hoc networks. Clustering of mobile nodes among separate domains has been proposed as an efficient approach to address those issues. In this work, we introduce an efficient distributed clustering algorithm that uses both location and energy metrics for stable cluster formation. Unlike existing active clustering methods, out algorithm relieves the network from the unnecessary burden of control messages broadcasting. This is achieved through adapting broadcast period according to mobile nodes mobility pattern. For relative static network topologies, broadcast period is lengthened. In contrast, broadcast period is shortened to meet the requirements of highly dynamic networks for consistent cluster configurations.

In this paper we present efficient, scalable and portable parallel algorithms written in the Coar... more In this paper we present efficient, scalable and portable parallel algorithms written in the Coarse-Grained Multicomputer (CGM) and the Bulk Synchronous Parallel (BSP) models for the off-line clustering, the on-line retrieval and the update phases of the text retrieval problem based on the vector space model and using clustering to organize and handle a dynamic document collection. To the best of our knowledge, our parallel retrieval algorithms are the first ones analyzed under specific parallel models, which capture within a few parameters the characteristics of the parallel machine.

Mobile ad hoc networks comprise a collection of wireless nodes that dynamically create a network ... more Mobile ad hoc networks comprise a collection of wireless nodes that dynamically create a network among themselves without using any pre-existing infrastructure. Clustering of mobile nodes among separate domains has been proposed as an efficient approach to answer the organization, scalability and routing problems of mobile ad hoc networks. In this work, we propose an efficient distributed clustering algorithm that uses both location and energy metrics for stable cluster formation. Unlike existing active clustering methods, out algorithm relieves the network from the unnecessary burden of control messages broadcasting. This is achieved through adapting broadcast period according to mobile nodes mobility pattern. For relative static network topologies, broadcast period is lengthened. In contrast, broadcast period is shortened to meet the requirements of highly dynamic networks for consistent cluster configurations.

Proceedings of the 1st ACM international conference on PErvasive Technologies Related to Assistive Environments - PETRA '08, 2008

Abstract Wireless Sensor Networks (WSNs) has been identified as a promising technology for suppor... more Abstract Wireless Sensor Networks (WSNs) has been identified as a promising technology for supporting assistive environments. This article introduces PROTECT, a system that employs autonomous software objects referred to as Mobile Agents (MAs) able of locating and informing visually impaired persons for potential risks. PROTECT utilizes a 3-tier architecture where the first tier comprises a Base Station (BS), the second tier mobile sinks (carried by blinds on their sticks) and the third tier stationary sensor nodes. This WSN is ...

2008 IEEE Symposium on Computers and Communications, 2008

Mobile Agent (MA) technology has been recently proposed in Wireless Sensors Networks (WSNs) liter... more Mobile Agent (MA) technology has been recently proposed in Wireless Sensors Networks (WSNs) literature to answer the scalability problem of client/server model in data fusion applications. Herein, we present CBID (Clone-Based Itinerary Design), a novel algorithm that calculates near-optimal routes for MAs that incrementally fuse the data as they visit the nodes while enabling a fast update of designed itineraries which is especially important for highly dynamic topologies. The order of visited nodes highly affects the quality and the overall cost of data fusion. The key MAs characteristic exploited by CBID to reduce energy consumption and response time is their cloning capability. Parallel dispatched MAs sequentially visit sensor nodes arranged in tree structures and upon visiting a node with two or more child nodes, the MAs (master MAs) clone of themselves with each clone (slave MA) visiting a tree branch. When all slave MAs return to that node, report their data to the master MA and are self-destroyed. This results in highly reduced energy consumption and response time since many MAs work in parallel. Simulation results prove the high effectiveness of CBID in data fusion tasks compared to other alternative algorithms.

Proceedings of the 12th ACM international symposium on Mobility management and wireless access - MobiWac '14, 2014

Lecture Notes in Computer Science, 2006

The main objective of clustering in mobile ad-hoc network environments is to identify suitable no... more The main objective of clustering in mobile ad-hoc network environments is to identify suitable node representatives, i.e. cluster heads (CHs) to store routing and topology information; CHs should be elected so as to maximize clusters stability, that is to prevent frequent cluster re-structuring. A popular clustering algorithm (LID) suggests CH election based on node IDs (nodes with locally lowest ID value become CHs). Although fast and simple, this method is biased against nodes with low IDs, which are likely to serve as CHs for long periods and are therefore prone to rapid battery exhaustion. Herein, we propose LIDAR, a novel clustering method which represents a major improvement over traditional LID algorithm: node IDs are periodically re-assigned so that nodes with low mobility rate and high energy capacity are assigned low ID values and, therefore, are likely to serve as CHs. Our protocol also greatly reduces control traffic volume of existing algorithms during clustering maintenance phase, while not risking the energy availability of CHs. Simulation results demonstrate the efficiency, scalability and stability of our protocol against alternative approaches.

Distributed Computing and …, Jan 1, 2006

Clustering for mobile ad-hoc networks (MANETs) has attracted the interest of many researchers as ... more Clustering for mobile ad-hoc networks (MANETs) has attracted the interest of many researchers as it offers enhanced scalability and performance improvement. The main challenge of the clustering algorithms is the formation of stable clusters despite the topological changes due to the host mobility. In this paper, we present a novel clustering algorithm, which first predicts the future host mobility and then uses this information to build a stable clustering structure over hosts that will probably exhibit low mobility in the future. In this way, long lifetime for the clustering structure is guaranteed, thereby eliminating the need for frequent reclustering. For predicting the future host mobility, we use provably good information theoretic techniques, which allow on-line learning of a reliable probabilistic model for future mobility.

Operations Research and Computing: Algorithms and Software for Analytics, 2015

2007 IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications, 2007

In this article, we consider the problem of calculating an appropriate number of near-optimal (su... more In this article, we consider the problem of calculating an appropriate number of near-optimal (subject to a certain routing objective) routes for mobile agents (MAs) that incrementally fuse the data as they visit the nodes in a distributed sensor network. We propose an improved heuristic algorithm which computes an approximate solution to the problem by suggesting an appropriate number of MAs and constructing near-optimal itineraries for each of them. The performance gain of our algorithm over alternative approaches both in terms of cost and task completion latency is demonstrated by a quantitative evaluation and also in simulated environments through a Java-based tool.

19th IEEE Symposium on Computers and Communications (ISCC 2014), Jun 24, 2014

A critical issue dealt with in Wireless Sensor and Actor Networks (WSANs) is the real time respon... more A critical issue dealt with in Wireless Sensor and Actor Networks (WSANs) is the real time response of actors to events occurring in the network area. The fast notification of actors from Sensor Nodes (SNs) about the events as well as the effective coordination of actors for prompt event handling is most important in these networks. In this paper, we introduce a distributed protocol for effective event handling in a WSAN. Existing approaches mainly favoring actors near the current event for handling it, may lead to highly ineffective solutions for certain worst-case scenarios. Through a randomized approach, our solution also selects distant actors for handling events, and guarantees fast average responsiveness to events and a balanced energy distribution among actors. In addition, it features efficient distributed algorithms for sensor to actor and actor to actor coordination which are of independent interest.

The investigation of mobile agent (MA) middleware as a technology for implementing efficient data... more The investigation of mobile agent (MA) middleware as a technology for implementing efficient data fusion schemes on wireless sensor networks (WSN) has been a subject of intense research in the past few years. Nevertheless, the itineraries followed by travelling MAs largely determine the overall performance of the data fusion applications. Along this line, this article introduces a novel algorithmic approach for efficient itinerary planning of MA objects engaged in data fusion tasks. Our algorithm adopts an iterated local search (ILS) approach in deriving the hop sequence of multiple travelling MAs over the deployed source nodes. Simulation results demonstrate the performance gain of our method against existing multiple MA itinerary planning methods.

6th International Conference on Ubiquitous and Future Networks (ICUFN 2014), Jul 9, 2014

Mobile agents (MAs) have been proposed as a distributed middleware approach suitable for autonomi... more Mobile agents (MAs) have been proposed as a distributed middleware approach suitable for autonomic data aggregation operations in Wireless Sensor Networks (WSN). Determining optimal itineraries for MAs traveling through WSN nodes is a non-trivial problem. Thus, several heuristics have been proposed to perform efficient itinerary planning for MAs. However, the evaluation of these heuristics is typically performed on the ground of different parameter spaces and assumptions about the underlying network and the capabilities of nodes. Herein, we implement, simulate and compare the most prominent itinerary planning algorithms upon a common parameter space, making realistic network-level assumptions.

The use of mobile agents for data fusion in wireless sensor networks has been recently proposed i... more The use of mobile agents for data fusion in wireless sensor networks has been recently proposed in the literature to answer the scalability problem of client/server model. In this article, we consider the problem of calculating a near-optimal route for a mobile agent that incrementally fuses the data as it visits the nodes in a distributed sensor network. The order of visited nodes affects not only the quality but also the overall cost of data fusion. We propose two heuristic algorithms that adapt methods usually applied in network design problems in the specific requirements of sensor networks. They suggest the proper number of MAs that minimizes the overall data fusion cost and construct near-optimal itineraries for each of them.

Abstract One of the most important features in image analysis and understanding,is shape. Mathema... more Abstract One of the most important features in image analysis and understanding,is shape. Mathematical,morphology,is the image,processing branch,that deals with shape analysis. The definition of all morphological,transformations is based on two primitive operations, i.e. dilation and erosion. Since many,applications require the solution of morphological problems in real time, researching time efficient algorithms for these two operations is crucial. In this paper, effi- cient parallel algorithms for the binary dilation and ero- sion are presented and evaluated for an advanced,associa- tive processor. Simulation results indicate that the achieved speedup is linear. Keywords: mathematical morphology, dilation, erosion, massively parallel processor, associative processor, hyper- cube

Block matching motion estimation algorithms are widely used in video coding schemes. In this pape... more Block matching motion estimation algorithms are widely used in video coding schemes. In this paper, we design an efficient hierarchical block matching motion estimation (HBMME) algorithm on a hypercube multiprocessor. Unlike systolic array designs, this solution is not tied down to specific values of algorithm parameters and thus offers increased flexibility. Moreover, the hypercube network can efficiently handle the non regular data flow of the HBMME algorithm. Our techniques nearly eliminate the occurrence of "difficult" communication patterns, namely many-to-many personalized communication, by replacing them with simple shift operations. These operations have an efficient implementation on most of interconnection networks and thus our techniques can be adapted to other networks as well. With regard to the employed multiprocessor we make no specific assumption about the amount of local memory residing in each processor. Instead, we introduce a free parameter S and assume that each processor has Θ(S) local memory. By doing so, we handle all the cases of modern multiprocessors, that is fine-grained, medium-grained and coarse-grained multiprocessors and thus our design is quite general. approach, we study the softwarebased realization of the HBMME algorithm on a hypercube-based multiprocessor. We also present an efficient full search block matching motion estimation (FSBMME) algorithm which is used as a subroutine in the HBMME algorithm. A basic point in our study is the amount of local memory at each processor. Specifically, we assume that there is Θ(S) local memory at each processor where S is a free parameter. Most programmable architectures used in video coding are coarse-grained multiprocessors where each processor has enough memory to keep all data it will need throughout algorithm execution. Thus interprocessor communication is almost eliminated and processors can operate independently. In our study, by including the amount of local memory at each processor as a free parameter, we consider all classes of modern multiprocessors, that is fine-grained, medium-grained as well as coarsegrained parallel machines. As will become evident later, the smaller the value of the parameter S is, the harder it is to design an efficient algorithm. This is because interprocessor communication becomes inevitable when processors have limited local memory. In order to keep communication overhead low, we need to carefully arrange the necessary communication operations. In addition, the use of a powerful network such as the hypercube for the implementation of the HBMME algorithm is well justified, because this algorithm has a non regular data flow and its inherent communication is not local. Thus it cannot be easily implemented on systolic arrays. Dedicated hardware designs for the HBMME algorithm 11, 12, 13] require high external memory bandwidth or relieve these requirements by using large on chip memory.

Organization, scalability and routing have been identified as key problems hindering viability an... more Organization, scalability and routing have been identified as key problems hindering viability and commercial success of mobile ad hoc networks. Clustering of mobile nodes among separate domains has been proposed as an efficient approach to address those issues. In this work, we introduce an efficient distributed clustering algorithm that uses both location and energy metrics for stable cluster formation. Unlike existing active clustering methods, out algorithm relieves the network from the unnecessary burden of control messages broadcasting. This is achieved through adapting broadcast period according to mobile nodes mobility pattern. For relative static network topologies, broadcast period is lengthened. In contrast, broadcast period is shortened to meet the requirements of highly dynamic networks for consistent cluster configurations.

In this paper we present efficient, scalable and portable parallel algorithms written in the Coar... more In this paper we present efficient, scalable and portable parallel algorithms written in the Coarse-Grained Multicomputer (CGM) and the Bulk Synchronous Parallel (BSP) models for the off-line clustering, the on-line retrieval and the update phases of the text retrieval problem based on the vector space model and using clustering to organize and handle a dynamic document collection. To the best of our knowledge, our parallel retrieval algorithms are the first ones analyzed under specific parallel models, which capture within a few parameters the characteristics of the parallel machine.

Mobile ad hoc networks comprise a collection of wireless nodes that dynamically create a network ... more Mobile ad hoc networks comprise a collection of wireless nodes that dynamically create a network among themselves without using any pre-existing infrastructure. Clustering of mobile nodes among separate domains has been proposed as an efficient approach to answer the organization, scalability and routing problems of mobile ad hoc networks. In this work, we propose an efficient distributed clustering algorithm that uses both location and energy metrics for stable cluster formation. Unlike existing active clustering methods, out algorithm relieves the network from the unnecessary burden of control messages broadcasting. This is achieved through adapting broadcast period according to mobile nodes mobility pattern. For relative static network topologies, broadcast period is lengthened. In contrast, broadcast period is shortened to meet the requirements of highly dynamic networks for consistent cluster configurations.

Proceedings of the 1st ACM international conference on PErvasive Technologies Related to Assistive Environments - PETRA '08, 2008

Abstract Wireless Sensor Networks (WSNs) has been identified as a promising technology for suppor... more Abstract Wireless Sensor Networks (WSNs) has been identified as a promising technology for supporting assistive environments. This article introduces PROTECT, a system that employs autonomous software objects referred to as Mobile Agents (MAs) able of locating and informing visually impaired persons for potential risks. PROTECT utilizes a 3-tier architecture where the first tier comprises a Base Station (BS), the second tier mobile sinks (carried by blinds on their sticks) and the third tier stationary sensor nodes. This WSN is ...

2008 IEEE Symposium on Computers and Communications, 2008

Mobile Agent (MA) technology has been recently proposed in Wireless Sensors Networks (WSNs) liter... more Mobile Agent (MA) technology has been recently proposed in Wireless Sensors Networks (WSNs) literature to answer the scalability problem of client/server model in data fusion applications. Herein, we present CBID (Clone-Based Itinerary Design), a novel algorithm that calculates near-optimal routes for MAs that incrementally fuse the data as they visit the nodes while enabling a fast update of designed itineraries which is especially important for highly dynamic topologies. The order of visited nodes highly affects the quality and the overall cost of data fusion. The key MAs characteristic exploited by CBID to reduce energy consumption and response time is their cloning capability. Parallel dispatched MAs sequentially visit sensor nodes arranged in tree structures and upon visiting a node with two or more child nodes, the MAs (master MAs) clone of themselves with each clone (slave MA) visiting a tree branch. When all slave MAs return to that node, report their data to the master MA and are self-destroyed. This results in highly reduced energy consumption and response time since many MAs work in parallel. Simulation results prove the high effectiveness of CBID in data fusion tasks compared to other alternative algorithms.

Proceedings of the 12th ACM international symposium on Mobility management and wireless access - MobiWac '14, 2014

Lecture Notes in Computer Science, 2006

The main objective of clustering in mobile ad-hoc network environments is to identify suitable no... more The main objective of clustering in mobile ad-hoc network environments is to identify suitable node representatives, i.e. cluster heads (CHs) to store routing and topology information; CHs should be elected so as to maximize clusters stability, that is to prevent frequent cluster re-structuring. A popular clustering algorithm (LID) suggests CH election based on node IDs (nodes with locally lowest ID value become CHs). Although fast and simple, this method is biased against nodes with low IDs, which are likely to serve as CHs for long periods and are therefore prone to rapid battery exhaustion. Herein, we propose LIDAR, a novel clustering method which represents a major improvement over traditional LID algorithm: node IDs are periodically re-assigned so that nodes with low mobility rate and high energy capacity are assigned low ID values and, therefore, are likely to serve as CHs. Our protocol also greatly reduces control traffic volume of existing algorithms during clustering maintenance phase, while not risking the energy availability of CHs. Simulation results demonstrate the efficiency, scalability and stability of our protocol against alternative approaches.

Distributed Computing and …, Jan 1, 2006

Clustering for mobile ad-hoc networks (MANETs) has attracted the interest of many researchers as ... more Clustering for mobile ad-hoc networks (MANETs) has attracted the interest of many researchers as it offers enhanced scalability and performance improvement. The main challenge of the clustering algorithms is the formation of stable clusters despite the topological changes due to the host mobility. In this paper, we present a novel clustering algorithm, which first predicts the future host mobility and then uses this information to build a stable clustering structure over hosts that will probably exhibit low mobility in the future. In this way, long lifetime for the clustering structure is guaranteed, thereby eliminating the need for frequent reclustering. For predicting the future host mobility, we use provably good information theoretic techniques, which allow on-line learning of a reliable probabilistic model for future mobility.

Operations Research and Computing: Algorithms and Software for Analytics, 2015

2007 IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications, 2007

In this article, we consider the problem of calculating an appropriate number of near-optimal (su... more In this article, we consider the problem of calculating an appropriate number of near-optimal (subject to a certain routing objective) routes for mobile agents (MAs) that incrementally fuse the data as they visit the nodes in a distributed sensor network. We propose an improved heuristic algorithm which computes an approximate solution to the problem by suggesting an appropriate number of MAs and constructing near-optimal itineraries for each of them. The performance gain of our algorithm over alternative approaches both in terms of cost and task completion latency is demonstrated by a quantitative evaluation and also in simulated environments through a Java-based tool.

Lecture Notes in Computer Science, 2012

ABSTRACT This paper presents a clustering protocol combined with a mobile sink (MS) solution for ... more ABSTRACT This paper presents a clustering protocol combined with a mobile sink (MS) solution for efficient data gathering in wireless sensor networks (WSNs). The main insight for the cluster creation method is drawn from image processing field and namely from the watershed transformation which is widely used for image segmentation. The proposed algorithm creates multi-hop clusters whose clusterheads (CHs) as well as all cluster members near the CHs have high energy reserves. As these are exactly the nodes most burdened with relaying of data from other cluster members, the higher levels of available energy at these nodes prolong the network lifetime eventually. After cluster creation, a MS periodically visits each CH and collects the data from cluster members already gathered at the CH. Simulation results show the higher performance of the proposed scheme in comparison to other competent approaches from the literature.

Artificial Intelligence …, Jan 1, 2006

{pantziou, v m a m a l i s } Q t e i a t h .

Wireless Networks, 2014

ABSTRACT This paper presents a gradient-based multi-hop clustering protocol combined with a mobil... more ABSTRACT This paper presents a gradient-based multi-hop clustering protocol combined with a mobile sink (MS) solution for efficient data gathering in wireless sensor networks. The main insight for the clustering algorithm is drawn from image processing field and namely from the watershed transform, widely used for image segmentation. The proposed algorithm creates multi-hop clusters whose cluster heads (CHs) as well as cluster members near the CHs have high energy reserves. Specifically, the energy of the sensors in a cluster increases progressively as getting closer to the CH. As the nodes closer to the CH are most burdened with relaying of data from other cluster members, the higher levels of available energy at these nodes prolong the network lifetime eventually. After cluster formation, a MS periodically visits each CH and collects the data from cluster members already gathered at the CH. Simulation results show the higher performance of the proposed scheme in comparison to other competent approaches in the literature.

Mobile agent (MA)-based middleware has been thoroughly investigated in the past few years as a me... more Mobile agent (MA)-based middleware has been thoroughly investigated in the past few years as a means to address the efficiency, scalability, and reliability issues of data fusion applications on wireless sensor networks. Deriving an efficient itinerary for each MA to follow is of high importance, because itineraries determine to a large extent the overall performance of data fusion tasks. In this article, we present a novel algorithmic approach for efficient itinerary planning of MA objects undertaking data fusion tasks. We adopt a method based on iterated local search to construct the itineraries (ie, visiting sequences of source nodes) assigned to multiple traveling MAs. We apply alternative optimization criteria which aim either at minimizing the overall energy expenditure over all derived MA itineraries or prolonging the network lifetime. Furthermore, we propose algorithmic solutions for 2 realistic settings which have not been investigated in the past: firstly, the employment of multiple sinks that share the responsibility of MA-based data fusion tasks across the sensor field, and secondly, the consideration of heterogeneous sensor networks comprising nodes powerful enough to host the runtime environment required to execute MA code as well as "ordinary" nodes which lack these resources. Simulation tests verify the performance gain attained by our algorithmic methods against alternative itinerary planning approaches which involve multiple MAs.