Winston Khoon Guan Seah

A flexible quality of service model for mobile ad-hoc networks

Quality of service (QoS) support in mobile ad-hoc networks (MANETs) is a challenging task. Most of the proposals in the literature only address certain aspects of the QoS support, e.g., QoS routing, QoS medium access control (MAC) and resource reservation. However, none of them proposes a QoS model for MANETs. Meanwhile, two QoS models have been proposed for the Internet, viz., the integrated services (IntServ) model and the differentiated services (DiffServ) model, but these models are aimed for wired networks. In this paper, we propose a flexible QoS model for MANETs (FQMM) which considers the characteristics of MANETs and combines the high quality QoS of IntServ and service differentiation of Diff-Serv. Salient features of FQMM include: dynamics roles of nodes, hybrid provisioning and adaptive conditioning. Preliminary simulation results show that FQMM achieves better performance in terms of throughput and service differentiation than the best-effort model.

Localization in underwater sensor networks: survey and challenges

In underwater sensor networks (UWSNs), determining the location of every sensor is important and the process of estimating the location of each node in a sensor network is known as localization. While various localization algorithms have been proposed for terrestrial sensor networks, there are relatively few localization schemes for UWSNs. The characteristics of underwater sensor networks are fundamentally different from that of terrestrial networks. Underwater acoustic channels are characterized by harsh physical layer environments with stringent bandwidth limitations. The variable speed of sound and the long propagation delays under water pose a unique set of challenges for localization in UWSN. This paper explores the different localization algorithms that are relevant to underwater sensor networks, and the challenges in meeting the requirements posed by emerging applications for such networks, e.g. offshore engineering.

Wireless sensor networks powered by ambient energy harvesting (WSN-HEAP) - Survey and challenges

Wireless sensor networks (WSNs) research has pre-dominantly assumed the use of a portable and limited energy source, viz. batteries, to power sensors. Without energy, a sensor is essentially useless and cannot contribute to the utility of the network as a whole. Consequently, substantial research efforts have been spent on designing energy-efficient networking protocols to maximize the lifetime of WSNs. However, there are emerging WSN applications where sensors are required to operate for much longer durations (like years or even decades) after they are deployed. Examples include in-situ environmental/habitat monitoring and structural health monitoring of critical infrastructures and buildings, where batteries are hard (or impossible) to replace/recharge. Lately, an alternative to powering WSNs is being actively studied, which is to convert the ambient energy from the environment into electricity to power the sensor nodes. While renewable energy technology is not new (e.g., solar and wind) the systems in use are far too large for WSNs. Those small enough for use in wireless sensors are most likely able to provide only enough energy to power sensors sporadically and not continuously. Sensor nodes need to exploit the sporadic availability of energy to quickly sense and transmit the data. This paper surveys related research and discusses the challenges of designing networking protocols for such WSNs powered by ambient energy harvesting.

Cooperative packet caching and shortest multipath routing in mobile ad hoc networks

A mobile ad hoc network is an autonomous system of infrastructureless, multihop wireless mobile nodes. Reactive routing protocols perform well in such an environment due to their ability to cope quickly against topological changes. In this paper, we propose a new routing protocol called Caching and Multipath (CHAMP) Routing Protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route breakdowns. Simulation results reveal that by using a five-packet data cache, CHAMP exhibits excellent improvement in packet delivery, outperforming AODV and DSR by at most 30% in stressful scenarios. Furthermore, end-to-end delay is significantly reduced while routing overhead is lower at high mobility rates.

Mobility-based d-hop clustering algorithm for mobile ad hoc networks

This paper presents a mobility-based d-hop clustering algorithm (MobDHop), which forms variable-diameter clusters based on node mobility pattern in MANETs. We introduce a new metric to measure the variation of distance between nodes over time in order to estimate the relative mobility of two nodes. We also estimate the stability of clusters based on relative mobility of cluster members. Unlike other clustering algorithms, the diameter of clusters is not restricted to two hops. Instead, the diameter of clusters is flexible and determined by the stability of clusters. Nodes which have similar moving pattern are grouped into one cluster. The simulation results show that MobDHop has stable performance in randomly generated scenarios. It forms lesser clusters than Lowest-ID and MOBIC algorithm in the same scenario. In conclusion, MobDHop can be used to provide an underlying hierarchical routing structure to address the scalability of routing protocol in large MANETs.

Design and performance analysis of MAC schemes for Wireless Sensor Networks Powered by Ambient Energy Harvesting

Energy consumption is a perennial issue in the design of wireless sensor networks (WSNs) which typically rely on portable sources like batteries for power. Recent advances in ambient energy harvesting technology have made it a potential and promising alternative source of energy for powering WSNs. By using energy harvesters with supercapacitors, WSNs are able to operate perpetually until hardware failure and in places where batteries are hard or impossible to replace. In this paper, we study the performance of different medium access control (MAC) schemes based on CSMA and polling techniques for WSNs which are solely powered by ambient energy harvesting using energy harvesters. We base the study on (i) network throughput (S), which is the rate of sensor data received by the sink, (ii) fairness index (F), which determines whether the bandwidth is allocated to each sensor node equally and (iii) inter-arrival time (@c) which measures the average time difference between two packets from a source node. For CSMA, we compare both the slotted and unslotted variants. For polling, we first consider identity polling. Then we design a probabilistic polling protocol that takes into account the unpredictability of the energy harvesting process to achieve good performance. Finally, we present an optimal polling MAC protocol to determine the theoretical maximum performance. We validate the analytical models using extensive simulations incorporating experimental results from the characterization of different types of energy harvesters. The performance results show that probabilistic polling achieves high throughput and fairness as well as low inter-arrival times.

Multipath Virtual Sink Architecture for Underwater Sensor Networks

The salient features of acoustic communications render many schemes that have been designed for terrestrial sensor networks unusable underwater. We therefore propose a novel virtual sink architecture for underwater sensor networks that aims to achieve robustness and energy efficiency under harsh underwater channel conditions. To overcome the long propagation delay and adverse link conditions in such environments, we make use of multipath data delivery. While conventional multipath routing tends to lead to contention near the sink, we avoid this caveat with the virtual sink design involving a group of spatially diverse physical sinks. Hence, we are able to exploit the reliability achieved from redundancy provided by multipath data delivery while mitigating the contention between the nodes.

Opportunistic routing in wireless sensor networks powered by ambient energy harvesting

Energy consumption is an important issue in the design of wireless sensor networks (WSNs) which typically rely on portable energy sources like batteries for power. Recent advances in ambient energy harvesting technologies have made it possible for sensor nodes to be powered by ambient energy entirely without the use of batteries. However, since the energy harvesting process is stochastic, exact sleep-and-wakeup schedules cannot be determined in WSNs Powered solely using Ambient Energy Harvesters (WSN-HEAP). Therefore, many existing WSN routing protocols cannot be used in WSN-HEAP. In this paper, we design an opportunistic routing protocol (EHOR) for multi-hop WSN-HEAP. Unlike traditional opportunistic routing protocols like ExOR or MORE, EHOR takes into account energy constraints because nodes have to shut down to recharge once their energy are depleted. Furthermore, since the rate of charging is dependent on environmental factors, the exact identities of nodes that are awake cannot be determined in advance. Therefore, choosing an optimal forwarder is another challenge in EHOR. We use a regioning approach to achieve this goal. Using extensive simulations incorporating experimental results from the characterization of different types of energy harvesters, we evaluate EHOR and the results show that EHOR increases goodput and efficiency compared to traditional opportunistic routing protocols and other non-opportunistic routing protocols suited for WSN-HEAP.

Review: Security threats and solutions in MANETs: A case study using AODV and SAODV

Mobile ad hoc network (MANET) security has become the focus of prolific research efforts. Driven by the unique and considerable difficulties of providing security arising from the dynamic nature of MANETs, many security schemes have been proposed. Rather than trying to encompass the entire field of MANET security, this paper focuses on networks using the popular Ad-hoc On-demand Distance Vector (AODV) protocol and a secure extension to AODV, the Secure AODV (SAODV) protocol. SAODV is representative of a number of secure versions of the AODV protocol in that it relies upon the use of cryptographic mechanisms to protect the routing control messages of AODV from being forged and/or altered by attackers. We conduct a vulnerability analysis of SAODV to identify unresolved threats to the algorithm, such as medium access control layer misbehaviour, resources depletion, blackholes, wormholes, jellyfish and rushing attacks. We then compare this vulnerability analysis to schemes that have been proposed to combat the identified threats. These proposals include multipath routing, incentive schemes, directional antennae, packet leashes, randomized route requests, localized self-healing communities and a reactive intrusion detection node blacklisting scheme.

TCP HACK: TCP header checksum option to improve performance over lossy links

Wireless networks have become increasingly common and an increasing number of devices are communicating with each other over lossy links. Unfortunately, TCP performs poorly over lossy links as it is unable to differentiate the loss due to packet corruption from that due to congestion. We present an extension to TCP which enables TCP to distinguish packet corruption from congestion in lossy environments resulting in improved performance. We refer to this extension as the HeAder ChecKsum option (HACK). We implemented our algorithm in the Linux kernel and performed various tests to determine its effectiveness. Our results have shown that HACK performs substantially better than both SACK and NewReno in cases where burst corruptions are frequent. We also found that HACK can co-exist very nicely with SACK and performs even better with SACK enabled.