Jamal N. Al-Karaki

Routing techniques in wireless sensor networks: a survey

Wireless sensor networks consist of small nodes with sensing, computation, and wireless communications capabilities. Many routing, power management, and data dissemination protocols have been specifically designed for WSNs where energy awareness is an essential design issue. Routing protocols in WSNs might differ depending on the application and network architecture. In this article we present a survey of state-of-the-art routing techniques in WSNs. We first outline the design challenges for routing protocols in WSNs followed by a comprehensive survey of routing techniques. Overall, the routing techniques are classified into three categories based on the underlying network structure: flit, hierarchical, and location-based routing. Furthermore, these protocols can be classified into multipath-based, query-based, negotiation-based, QoS-based, and coherent-based depending on the protocol operation. We study the design trade-offs between energy and communication overhead savings in every routing paradigm. We also highlight the advantages and performance issues of each routing technique. The article concludes with possible future research areas.

Data aggregation in wireless sensor networks - exact and approximate algorithms

A fundamental challenge in the design of wireless sensor networks (WSNs) is to maximize their lifetimes. Data aggregation has emerged as a basic approach in WSNs in order to reduce the number of transmissions of sensor nodes, and hence minimizing the overall power consumption in the network. We study optimal data aggregation in WSNs. Data aggregation is affected by several factors, such as the placement of aggregation points, the aggregation function, and the density of sensors in the network. The determination of an optimal selection of aggregation points is thus extremely important. We present exact and approximate algorithms to find the minimum number of aggregation points in order to maximize the network lifetime. Our algorithms use a fixed virtual wireless backbone that is built on top of the physical topology. We also study the tradeoffs between energy savings and the potential delay involved in the data aggregation process. Numerical results show that our approach provides substantial energy savings.

Wireless Multimedia Sensor Networks: Current Trends and Future Directions

Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. In this paper, we outline the design challenges of WMSNs, give a comprehensive discussion of the proposed architectures, algorithms and protocols for the different layers of the communication protocol stack for WMSNs, and evaluate the existing WMSN hardware and testbeds. The paper will give the reader a clear view of the state of the art at all aspects of this research area, and shed the light on its main current challenges and future trends. We also hope it will foster discussions and new research ideas among its researchers.

Data aggregation and routing in Wireless Sensor Networks: Optimal and heuristic algorithms

A fundamental challenge in the design of Wireless Sensor Networks (WSNs) is to maximize their lifetimes especially when they have a limited and non-replenishable energy supply. To extend the network lifetime, power management and energy-efficient communication techniques at all layers become necessary. In this paper, we present solutions for the data gathering and routing problem with in-network aggregation in WSNs. Our objective is to maximize the network lifetime by utilizing data aggregation and in-network processing techniques. We particularly focus on the joint problem of optimal data routing with data aggregation en route such that the above mentioned objective is achieved. We present Grid-based Routing and Aggregator Selection Scheme (GRASS), a scheme for WSNs that can achieve low energy dissipation and low latency without sacrificing quality. GRASS embodies optimal (exact) as well as heuristic approaches to find the minimum number of aggregation points while routing data to the Base-Station (BS) such that the network lifetime is maximized. Our results show that, when compared to other schemes, GRASS improves system lifetime with acceptable levels of latency in data aggregation and without sacrificing data quality.

On the optimal clustering in mobile ad hoc networks

A mobile ad hoc network (MANET) can be represented by a set of logical clusters with clusterheads (CHs) acting like virtual base-stations, hence forming a wireless virtual backbone. The role of clusterhead is a temporary one, which changes dynamically as the topology or other factors affecting it change. Finding the minimal set of CHs is an NP-complete problem. We study the performance tradeoffs between two clustering approaches. The first one is a simple clustering strategy, called virtual grid architecture (VGA), which is based on a fixed rectilinear virtual topology, while the second one is an optimal clustering strategy. We consider homogeneous as well as heterogeneous networks. First, for homogeneous MANETs with a large number of users and under the VGA clustering approach, we derive expressions for the number of CHs, worst case path length, and average case path length. We also derive expressions for the communication overhead. Second, we develop an integer linear program (ILP) that finds the optimal number of connected CHs in small to medium sized heterogeneous MANETs. Analytical and simulation results show that our proposed clustering algorithm (VGA), although being simple, is close to optimal.

End-to-end support for statistical quality of service in heterogeneous mobile ad hoc networks

In heterogeneous mobile ad hoc networks (MANETs), different types of mobile devices with diverse capabilities may coexist in the same network. The heterogeneity of MANETs makes end-to-end support for quality of service (QoS) guarantees more difficult than in other types of networks, not to mention the limited bandwidth and frequent topology changes of these networks. Since QoS routing is the first step toward achieving end-to-end QoS guarantees in heterogeneous MANETs, we propose a QoS routing protocol for heterogeneous MANETs. The proposed protocol, called virtual grid architecture protocol (VGAP), uses a cross-layer approach in order to provide end-to-end statistical QoS guarantees. VGAP operates on a fixed virtual rectilinear architecture (virtual grid), which is obtained using location information obtained from global positioning system (GPS). The virtual grid consists of a few, but possibly more powerful, mobile nodes known as ClusterHeads (CHs) that are elected periodically. CHs discover multiple QoS routes on the virtual grid using an extended version of the open shortest path first (OSPF) routing protocol and an extended version of WFQ scheduling policy that takes into account the wireless channel state. Moreover, VGAP utilizes a simple power control algorithm at the physical layer that provides efficient energy savings in this heterogeneous setting. Simulation experiments show that VGAP has a good performance in terms of packet delivery ratio, end-to-end packet delay, call blocking probability, and network scalability.

Efficient virtual-backbone routing in mobile ad hoc networks

Since the physical topology of mobile ad hoc networks (MANETs) is generally unstable, an appealing approach is the construction of a stable and robust virtual topology or backbone. A virtual backbone can play important roles related to routing and connectivity management. In this paper, the problem of providing such a virtual backbone with low overhead is investigated. In particular, we propose an approach, called virtual grid architecture (VGA), that can be applied to both homogeneous and heterogeneous MANETs. We study the performance tradeoffs between the VGA clustering approach and an optimal clustering based on an integer linear program (ILP) formulation. Many properties of the VGA clustering approach, e.g., VGA size, route length over VGA, and clustering overhead are also studied and quantified. Analytical as well as simulation results show that average route length over VGA and VGA cardinality tend to be close to optimal. The results also show that the overhead of creating and maintaining VGA is greatly reduced, and thus the routing performance is improved significantly. To illustrate, two hierarchical routing techniques that operate on top of VGA are presented and evaluated. Performance evaluation shows that VGA clustering approach, albeit simple, is able to provide more stable (long lifetime) routes, deliver more packets, and accept more calls.

Stimulating Node Cooperation in Mobile Ad hoc Networks

Mobile Ad hoc Networks (MANETs) rely on the cooperation of nodes for packet routing and forwarding. Much of the existing work in MANETs assume that mobile nodes (possibly owned by selfish users) will follow prescribed protocols without deviation. However, a user may misbehave due to several advantages resulting from noncooperation, the most obvious being power saving. As such, the network availability is severely endangered. Hence, enforcing the cooperation among nodes becomes a very important issue. Several different approaches have been developed to detect non-cooperative nodes or deal with the non-cooperative behavior of mobile nodes in MANETs. These protocols are first surveyed in details in this paper. It is found that the proposed approaches have several concerns that prevent them from really enforcing the node cooperation in MANETs. Thus, a new scheme that can stimulate and also enforce nodes to cooperate in a selfish ad hoc environment is presented. We also present a mechanism to detect and exclude potential threats of selfish mobile nodes. The simulation results indicate that by using the proposed scheme, MANETs can be robust against nodes’ misbehaving and the performance of the network is enhanced many folds when compared to other existing schemes.

SENSORIA: A New Simulation Platform for Wireless Sensor Networks

This paper considers the simulation of Wireless Sensor Networks (WSNs) using new approach. We present Sensoria, a fully fledged simulator for WSNs that has considerable differences to all other existing simulators. Sensoria is very powerful in simulating a range of small to large scale WSNs based on a simple and complete Graphical User Interface (GUI). Sensorias GUI allows users to design various simulation scenarios and display the simulation results graphically with many formats. Sensoria is a component-based simulator and it can be easily reconfigured to adapt to different levels of simulation details and accuracy. We demonstrate the usage of Sensoria via studying many performance metrics of a set of simple and flat routing protocols that are customized by Sensoria. The paper concludes with evidence that, albeit being simple and ease-of-use, Sensoria proves to be efficient and effective tool for WSN research purposes.

Analysis of routing security-energy trade-offs in wireless sensor networks

Wireless Sensor Networks (WSNs) are expected to be deployed on a large scale in the near future. WSNs play a key role in gathering information about various environmental phenomena. When sensor nodes are deployed in hostile environments or in some security-sensitive applications, some security measures such as confidentiality and integrity are highly required. Although, a significant number of researchers have put effort on developing sensor network structure and routing protocols, very less emphasis was given to the security issues. For example, many routing protocols for WSNs have been proposed, but most of them have been designed without security in mind. In this paper, security challenges and problems in WSNs are first analysed and summarised. An overview of the current solutions on secure routing in WSNs is then briefly described. Finally, a secure routing protocol for large scale WSNs, called Secure and Energy Efficient Protocol (SEEP) is presented. SEEP operates on a clustered network and provides security at both intra- and inter-cluster levels. The strength of SEEP stems from its ability to meet conflicting goals of providing high-level security while maximising energy efficiency. Performance evaluation of the proposed protocol show that SEEP can achieve a better level of security with less computational and communication overhead when compared to other schemes.