Adrian Andronache

WACA: A Hierarchical Weighted Clustering Algorithm Optimized for Mobile Hybrid Networks

Clustering techniques create hierarchal network structures, called clusters, on an otherwise flat network. In a dynamic environment-in terms of node mobility as well as in terms of steadily changing device parameters-the clusterhead election process has to be re-invoked according to a suitable update policy. Cluster re-organization causes additional message exchanges and computational complexity and it execution has to be optimized. Our investigations focus on the problem of minimizing clusterhead re-elections by considering stability criteria. These criteria are based on topological characteristics as well as on device parameters. This paper presents a weighted clustering algorithm optimized to avoid needless clusterhead re- elections for stable clusters in mobile ad-hoc networks. The proposed localized algorithm deals with mobility, but does not require geographical, speed or distances information.

Multimedia content distribution in hybrid wireless networks using weighted clustering

Fixed infrastructured networks naturally support centralized approaches for group management and information provisioning. Contrary to infrastructured networks, in multi-hop ad-hoc networks each node acts as a router as well as sender and receiver. Some applications, however, requires hierarchical arrangements that¿for practical reasons¿has to be done locally and self-organized. An additional challenge is to deal with mobility that causes permanent network partitioning and reorganizations. Technically, these problems can be tackled by providing additional uplinks to a backbone network, which can be used to access resources in the Internet as well as to inter-link multiple ad-hoc network partitions, creating a hybrid wireless network. In this paper, we present a prototypically implemented hybrid wireless network system optimized for multimedia content distribution. To efficiently manage the ad-hoc communicating devices a weighted clustering algorithm is introduced. The proposed localized algorithm deals with mobility, but does not require geographical information or distances

Topology-based Clusterhead Candidate Selection in Wireless Ad-hoc and Sensor Networks

Clustering techniques create hierarchal network structures, called clusters, on an otherwise flat network. Neighboring devices elect one appropriate device as clusterhead. Due to the dynamic environment, clusterhead selection becomes an important issue. We consider the problem of appropriate clusterhead selection in wireless ad-hoc networks and sensor networks. This work presents topological criteria for robust clusterhead candidate selection, resilient to sporadic node mobility and failure as well as for efficient information dissemination. One of the main ideas of our approach is to avoid selecting nodes located close to the network partition border as such nodes are more likely to move out of the partition, thus causing a clusterhead re-election. We conducted experiments both for static topologies as well as for cases in the presence of node mobility. Our results showed that the frequency of clusterhead re-election and average shortest path length from the clusterhead decrease when considering topological criteria. Additionally, the clusters tend to be robust to clusterhead failure. The presented mechanisms rely on local topological information only and do not require geographical data.

NLWCA Node and Link Weighted Clustering Algorithm for Backbone-Assisted Mobile Ad Hoc Networks

This paper introduces a clustering algorithm for applications running in backbone-assisted mobile ad hoc networks. The algorithm assigns weights both to the network nodes and to the communication links in order to elect local leaders, so called clusterheads.

Hycast- podcast discovery in mobile networks

Podcasts are a popular way to provide multimedia information about certain topics. A multitude of podcast servers exist in the Internet, allowing people to subscribe to them. Typically, podcasts are downloaded onto desktop computers and copied on mobile devices to be played while being on the move. In this paper, we extend the idea of podcasts, making them available in mobile network environments. In particular, HyCast does not rely on central podcast directories. Instead, HyCast also allows discovering, subscribing to, and downloading podcasts and episodes in the local neighborhood. For the dissemination of podcast information, we introduce and evaluate two different strategies. One is based on peer-to-peer communication between one-hop neighbors. The second one employs clustering to reduce the overhead of the podcast information dissemination.

HyTrace Backbone-Assisted Path Discovery in Hybrid Networks

HyTrace is a hybrid system providing stable paths between mobile ad hoc nodes. The ad hoc network thereby is organized in clusters where the cluster heads maintain uplinks to a backbone network. The backbone keeps track of available clusters and stable connection between them. The backbone also inter-links different network partitions thus increasing the reliability of the whole system. The underlying Weighted Cluster Path Discovery algorithm still keeps working in settings where no backbone network is available. Broadcasting as well as message exchange between arbitrary nodes is used to further motivate the usefulness of the system.

Ad Hoc Collaborative Filtering for Mobile Networks

This work introduces a recommender system designed to augment the information discovery and dissemination in mobile networks. We use the system to optimize the podcast providing mechanism of the HyCast application. The presented recommender system is based on collaborative filtering and provides two different algorithms to determine similar network neighbors, which are used to incrementally build up a locally stored model for the final prediction calculation.

OLSR and WCPD as Basis for Service Discovery in MANETs

Service discovery is one of the most fundamental building blocks of self-organization. While mature approaches exist in the realm of fixed networks, they are not directly applicable in the context of MANETs. We investigate and compare two different protocols as basis for service discovery, namely OLSR and WCPD. OLSR is a proactive routing protocol while WCPD is a path discovery protocol integrating node and link stability criteria. Two conflicting objectives of service discovery are the coverage of service queries together with the required bandwidth. Simulations are performed based on a setting in a city center with human mobility. We show that OLSR outperforms WCPD in terms of coverage. Due to its proactive nature, however, bandwidth consumption is high. WCPD on the other hand is much more bandwidth efficient, but at the cost of lower coverage.Finally, we motivate employing OLSR on top of an overlay topology maintained by WCPD. This fosters stability while reducing overhead and keeping coverage high.

Node Stability in Dynamic Communication Networks

Clustering techniques create hierarchal network structures, called clusters, on an otherwise flat network. Neighboring devices elect one appropriate device as clusterhead. Due to the dynamic environment, clusterhead selection becomes an important issue. We consider the problem of appropriate clusterhead selection in wireless ad-hoc networks and sensor networks. This work analyzes synchronous as well as asynchronous heuristics for discovering nodes with prolonged topological stability. These nodes appear more appropriate to be elected as clusterheads, since the frequency of clusterhead re-election and re-clustering can be decreased. The heuristics described rely on 2-hop topological information and avoid any use of geographical data

HyMN-injection-based multimedia content distribution in hybrid wireless networks

Infrastructured networks typically employ centralized approaches for group management and information provisioning. In contrast to that, in multi-hop ad hoc networks each node acts as a router as well as sender and receiver. In pure ad hoc networks, no Internet access is available. An additional challenge is to deal with mobility that causes network partitioning and re-organizations. Technically, these problems can be tackled by providing additional uplinks to a backbone network. Those can be used to access resources in the Internet as well as to inter-link multiple ad hoc network partitions, creating a hybrid wireless network. In this paper, we present HyMN, a prototypically implemented hybrid wireless network system optimized for multimedia content providing. Within the ad hoc network, adequate devices are elected to maintain uplinks to a backbone, which can provide for instance multimedia news from certain sports events like Football Championships, Olympic Games and alike. In order to efficiently manage the ad hoc communicating devices, a weighted clustering algorithm is employed.