Ameer Ahmed Abbasi

A survey on clustering algorithms for wireless sensor networks

The past few years have witnessed increased interest in the potential use of wireless sensor networks (WSNs) in applications such as disaster management, combat field reconnaissance, border protection and security surveillance. Sensors in these applications are expected to be remotely deployed in large numbers and to operate autonomously in unattended environments. To support scalability, nodes are often grouped into disjoint and mostly non-overlapping clusters. In this paper, we present a taxonomy and general classification of published clustering schemes. We survey different clustering algorithms for WSNs; highlighting their objectives, features, complexity, etc. We also compare of these clustering algorithms based on metrics such as convergence rate, cluster stability, cluster overlapping, location-awareness and support for node mobility.

Recovering From a Node Failure in Wireless Sensor-Actor Networks With Minimal Topology Changes

In wireless sensor-actor networks, sensors probe their surroundings and forward their data to actor nodes. Actors collaboratively respond to achieve predefined application mission. Since actors have to coordinate their operation, it is necessary to maintain a strongly connected network topology at all times. Moreover, the length of the inter-actor communication paths may be constrained to meet latency requirements. However, a failure of an actor may cause the network to partition into disjoint blocks and would, thus, violate such a connectivity goal. One of the effective recovery methodologies is to autonomously reposition a subset of the actor nodes to restore connectivity. Contemporary recovery schemes either impose high node relocation overhead or extend some of the inter-actor data paths. This paper overcomes these shortcomings and presents a Least-Disruptive topology Repair (LeDiR) algorithm. LeDiR relies on the local view of a node about the network to devise a recovery plan that relocates the least number of nodes and ensures that no path between any pair of nodes is extended. LeDiR is a localized and distributed algorithm that leverages existing route discovery activities in the network and imposes no additional prefailure communication overhead. The performance of LeDiR is analyzed mathematically and validated via extensive simulation experiments.

A Localized Algorithm for Restoring Internode Connectivity in Networks of Moveable Sensors

Recent years have witnessed a growing interest in the applications of wireless sensor networks (WSNs). In some of these applications, such as search and rescue and battlefield reconnaissance, a set of mobile nodes is deployed in order to collectively survey an area of interest and/or perform specific surveillance tasks. Such collaboration among the sensors requires internode interaction and thus maintaining network connectivity is critical to the effectiveness of WSNs. While connectivity can be provisioned at startup time and then sustained through careful coordination when nodes move, a sudden failure of a node poses a challenge since the network may get partitioned. This paper presents RIM; a distributed algorithm for Recovery through Inward Motion. RIM strives to efficiently restore the network connectivity after a node failure. Instead of performing a networkwide analysis to assess the impact of the node failure and orchestrate a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. In addition to minimizing the messaging overhead, RIM opts to reduce the distance that the individual nodes have to travel during the recovery. The correctness of the RIM algorithm is proven and the incurred overhead is analyzed. The performance of RIM is validated through simulation experiments.

Restoring Connectivity in Wireless Sensor-Actor Networks with Minimal Topology Changes

In Wireless Sensor-Actor Networks (WSANs), actors collect sensor readings and respond collaboratively to achieve an application mission. Since actors coordinate their operation, a strongly connected network topology would be required at all time. In addition, the path between actors may have to be capped in order to meet latency constraints. However, a failure of an actor may cause the network to partition into disjoint blocks and would thus violate such connectivity goal. One of the effective recovery methodologies is to autonomously reposition a subset of the actor nodes to restore connectivity. Contemporary schemes rely on maintaining 1 or 2-hop neighbor lists and predetermine criteria for nodes involvement in the recovery. However, 1-hop based schemes often impose high node relocation overhead. In addition, the repaired inter-actor topology using 2-hop schemes often differs significantly from its pre-failure status and some inter-actor data paths may get extended. This paper presents a Least-Disruptive topology Repair (LeDiR) algorithm. LeDiR relies on the local view of a node about the network in order to devise a recovery plan that relocates the least number of nodes and ensures that no path between any pair of nodes is extended. LeDiR is a localized and distributed algorithm that leverages existing path discovery activities and imposes no additional pre-failure communication overhead. LeDiR is validated through simulation and is shown to outperform existing schemes.

C 2 AM: an algorithm for application-aware movement-assisted recovery in wireless sensor and actor networks

In Wireless Sensor and Actor Networks (WSANs) a connected interactor topology is desirable in order for the deployed actors to work collaboratively. If a critical actor fails causing the inter-actor network to get partitioned into disjoint segments, the other actors close to the faulty node often exploit their mobility to autonomously restore the lost inter-actor connectivity. However, such a solution focuses on resource efficiency and assumes no constraints on the mobility of actors which can be impractical in the real scenarios. In addition, since actors need to carry out tasks to meet the application level requirements, unconstrained movement of actor(s) to restore interactor connectivity can cause a major failure at the application level. This paper presents C2AM; a recovery algorithm that factors in application level constraints on actors mobility while restoring the network connectivity. In addition to considering physical level requirements, C2AM accounts for application level concerns as well in order to avoid major disruptions to ongoing missions. Simulation results have validated the effectiveness of the algorithm in maintaining both objectives.

Immersive Environment: An Emerging Future of Telecommunications

This article surveys immersive communication environments and focuses on high-level issues and applications. The authors classify the immersive computing environments into three major categories: entertainment, business and society, and simulated learning and education.