Uthman Baroudi

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.

Bypass AODV: improving performance of ad hoc on-demand distance vector (AODV) routing protocol in wireless ad hoc networks

Bypass-AODV, a local recovery protocol, is proposed to enhance the performance of AODV routing protocol by overcoming several inherited problems such as unnecessary error recovery invocations, newly non-optimal reconstructed routes, high packet drop ratios, and high routing overheads. Bypass-AODV uses cross-layer MAC-notification to identify mobility-related link break, and then setup a bypass between the broken-link end nodes via an alternative node while keeps on the rest of the route. Therefore, Bypass-AODV enhances resource utilization by avoiding unnecessary error recovery cycles and consequently increases the network throughput. On the other hand, Bypass-AODV enhances route reliability; it avoids dropping packets by transmitting them over the constructed bypass. The simulation results show that when running 1-TCP connection, Bypass-AODV performs better than AODV. In particular, this behavior is rapidly changed with increasing the physical distance between the TCP connection end nodes beyond 2 hops. For example, when number of hops is equal to 6, goodput is enhanced by more than 100% compared to AODV for a 1-TCP connection and about 24% for multiple TCP connections. Further, the ratio of packet drop is reduced from 16% to 2%. Moreover, considering the hop count, the Bypass-AODV shows less sensitivity to the ongoing number of TCP connections.

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.

Optimal node repositioning for tolerating node failure in wireless sensor actor network

Wireless sensor and actor networks (WSANs) usually operate in harsh environment and thus become susceptible to breakage in connectivity due to the failure of one or multiple actor nodes. The positions of some of these actors are critical to the sustainability of inter-node communications. Specifically, some node failures may cause the network to partition into disjoint segments. Given that WSANS are deployed in remote areas, restoring connectivity through self reconfiguring the network topology becomes the most preferred solution. This paper investigates the optimal actor repositioning for restoring connectivity after one or multiple node fail. In particular, the problem is formulated as an integer linear program such that every node can reach every other node in the network while maximizing network coverage and minimizing the distance that an actor ought to travel.

Efficient monitoring approach for reputation system-based trust-aware routing in wireless sensor networks

Trust-aware routing in wireless sensor networks (WSNs) is a crucial problem that has drawn the attention of researchers. The motivation for tackling this problem arises directly from the highly constrained nature of a WSN and its easy exposure to insecure conditions. In this regard, reputation-based solutions are used to provide trust-aware routing. However, this approach requires that a node needs to continuously monitor its environment to detect misbehaviour events. This is considered to be a costly operation for WSN nodes because of its resource scarcity. Here, the authors propose a reputation system-based solution for trust-aware routing, which implements a new monitoring strategy called an efficient monitoring procedure in a reputation system (EMPIRE). EMPIRE is a probabilistic and distributed monitoring methodology that tries to reduce the monitoring activities per node while maintaining the ability to detect attacks at a satisfactory level. The proposed procedure has been evaluated using the Monte Carlo simulation. New evaluation methodologies are introduced to test and explore the efficiency of our proposed procedure. Simulation results of the reputation system show that reducing monitoring activities with EMPIRE does not have a significant impact on system performance in terms of security.

Least Distance Movement Recovery approach for large scale Wireless sensor and actor networks

In most applications of Wireless sensor and actor network it is important to sustain connectivity among all actors at all times. When an actor fails the inter-actor topology may get partitions into disjoint blocks and the application may be negatively impacted. Tolerating the actor failure and restoring the lost connectivity need to be performed while imposing the least overhead on the individual actors. In this paper a Least Distance Movement Recovery (LDMR) algorithm is proposed. LDMR is a distributed approach that exploits non cut-vertices actors in the recovery process. The idea is for a set of direct neighbours of the failed node to move toward the position of the failed node while its original position is replaced with the nearest non cut-vertex actor. The recovery process starts with the search phase where each neighbour broadcasts a message containing the failed node ID, neighbour node ID and, Time-To-Live (TTL). When a neighbour receives responses, it chooses the best candidate based on a certain criteria (e.g. distance). We compare our approach with Recovery through Inward Motion (RIM) which depends only on cascaded movements. Extensive simulation experiments are carried out to validate the performance.

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.

Random and realistic mobility models impact on the performance of bypass-AODV routing protocol

Due to lack of mass deployment of wireless ad hoc networks, simulation is the main tool to evaluate and compare different routing protocol proposals. Previous studies have shown that a certain routing protocol behaves differently under different presumed mobility patterns. Bypass-AODV is a new optimization of the AODV routing protocol for mobile ad-hoc networks. It is proposed as a local recovery mechanism to enhance the performance of AODV routing protocol. It shows outstanding performance under random waypoint mobility model compared with AODV. However, random waypoint is a simple model that may be applicable to some scenarios but it is not sufficient to capture some important mobility characteristics of scenarios where MANETs deployed. In this work, we would like to investigate the performance of Bypass-AODV under wide range of mobility models including other random mobility models, group mobility models and vehicular mobility models. Ns-2 simulation results show that bypass-AODV is insensitive to the selected random mobility model and it has a clear performance improvement compared to AODV. It shows a comparable performance under group mobility model compared to AODV. But, for vehicular mobility models, bypass-AODV is suffering from performance degradation at high speed conditions.

Radio Frequency Energy Harvesting Characterization: An Experimental Study

This paper presents the outcomes of experiments performed to acquire data and to evaluate various parameters to: (1) assess the feasibility of harvesting the energy from the ambient RF power to energize wireless sensor nodes, and, (2) characterize commercially available PowerCastTM energy harvester. The parameters of interest are: (1) Ambient RF power along several bands, (2) Time, Tc, taken by PowerCastTM energy harvester for charging, and (3), The received signal strength indicator (RSSI) captured by PowerCast™ energy harvester. The former measurements are taken at different locations inside King Fahd University campus. The latter two quantities were computed from data acquired at various coordinates of the harvester relative to the transmitter and the source of energy. The data is acquired in indoor and outdoor scenarios. The acquired data was processed in MATLAB and it was concluded that: (1) The ambient RF power in not sufficient to energize the commercially available PowerCast™ RF power harvester which has a specified requirement of at least -10dBm power to successfully harvest RF energy. (2) The outdoor experiments suggested that Tc is directly, while RSSI is inversely proportional to the radial distance from the power transmitter. The two quantities are also significantly affected by the variation of azimuth and elevation of harvester w.r.t. the transmitter. (3) It is observed in the indoor experiments that trends of Tc and RSSI are not as regular as those in the case of outdoor experiments. Experimental procedure and all of the analyses are documented in detail so that it can be a useful reference for researchers working in this area.

Optimal placement of heterogeneous wireless sensor and relay nodes

Oil and Gas industry shows great interest in deploying wireless sensor network for monitoring smart wells. The deployed sensors are very expensive and it is important to minimize the deployment cost while satisfying the coverage and connectivity requirements. In this work, we present a coverage-connectivity model for optimal deployment of sensors and relays. The monitored field is presented as a grid of 2D bounded space. We develop an Integer Linear Program (ILP) for minimizing the total cost of the sensors and relays for complete coverage of predetermined critical points in the monitored field and maintain and connectivity of the sensors with a central processing unit. The proposed model lends itself easily to a wide range of industrial applications. A numerical example is presented.