Connectivity, Coverage and Placement in Wireless Sensor Networks

Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes

WISE Abstraction Framework for Wireless Networks

Current wireless networks commonly consist of nodes with different capabilities (e.g., laptops and PDAs). Link quality such as link error rate and data transmit rate can differ widely. For efficient operation, the design of wireless networks must take into account such heterogeneity among nodes and wireless links. We present systematic approaches to overcome problems due to heterogeneous node capability and link quality in wireless networks. We first present a general framework called WISE (Wireless Integration Sublayer Extension) that abstracts specific details of low-level wireless communication technologies (e.g., modulation or backoff scheme). WISE provides a set of common primitives, based on which upper-level protocols can operate efficiently without knowing the underlying details. We also present a number of protocol extensions that employ the WISE framework to enhance the performance of specific upper-level protocols while hiding lower-level heterogeneity (e.g., link error rate). Our multihop WLAN architecture improves system performance by allowing client nodes to use multihop paths via other clients to reach an AP. Our geographic routing extension considers both location and link quality in the next hop selection, which leads to optimal paths under certain conditions. To address heterogeneity in node capability, we consider virtual routing backbone construction in two settings: cooperative and selfish. In the cooperative setting, we present a protocol extension that constructs an optimal backbone composed of a small number of high-capability nodes, which can be generalized to a more resilient backbone. For the selfish case, we use game theory and design an incentive-compatible backbone construction scheme. We evaluate our work from multiple perspectives. We use theoretical analysis to prove that our extensions lead to optimal solutions. We use simulations to experiment with our schemes in various scenarios and real-world implementation to understand the performance in practice. Our experiment results show that our schemes significantly outperform existing schemes

Extensions to the IEEE 802.11 TSF for Efficient and Reliable Network Synchronization in Large Scale MANETs

Designing new protocols for Mobile Ad hoc Networks (MANETs) is a great challenge due to their distributed and self organized nature. Though, aspects of approved algorithms for hierarchical topographies may be carried over to these flat networks. The IEEE 802.11 protocol supports ad hoc networks in small scale applications, but its performance in large scale environments is still under investigation. Besides the Distributed Coordination Function (DCF), the Timer Synchronization Function (TSF) can be significantly improved in order to increase the performance in large scale multihop networks. This article presents systematic extensions to the TSF that allow increasing the overall reliability and disburdening the network at the same time. The presented scheme may be tailored to specific applications and even supports mobile stations and herewith MANETs

Broadcast Scheduling in Interference Environment

Broadcast is a fundamental operation in wireless networks, and nai¨ve flooding is not practical, because it cannot deal with interference. Scheduling is a good way of avoiding interference, but previous studies on broadcast scheduling algorithms all assume highly theoretical models such as the unit disk graph model. In this work, we reinvestigate this problem by using the 2-Disk and the signal-to-interference-plus-noise-ratio (SINR) models. We first design a constant approximation algorithm for the 2-Disk model and then extend it to the SINR model. This result, to the best of our knowledge, is the first result on broadcast scheduling algorithms in the SINR model

Neighbour coverage: a dynamic probabilistic route discovery for mobile ad hoc networks

Blind flooding is extensively use in ad hoc routing protocols for on-demand route discovery, where a mobile node blindly rebroadcasts received route request (RREQ) packets until a route to a particular destination is established. This can potentially lead to high channel contention, causing redundant retransmissions and thus excessive packet collisions in the network. Such a phenomenon induces what is known as broadcast storm problem, which has been shown to greatly increase the network communication overhead and end-to-end delay. In this paper, we show that the deleterious impact of such a problem can be reduced if measures are taken during the dissemination of RREQ packets. We propose a generic probabilistic method for route discovery, that is simple to implement and can significantly reduce the overhead associated with the dissemination of RREQs. Our analysis reveals that equipping AODV with probabilistic route discovery can result in significant reduction of routing control overhead while achieving good throughput

Channel Allocation in An Overlaid Mesh Network

In spite of recent advancement of Wireless Mesh Technology, a lot of research challenges remained to be solved to extract the full capacity of this modern technology. As 802.11a/b/g standards make available the use of multi radio multi channel in a wireless node, a lot of research activities are going on to efficiently allocate the channel of a Mesh Network to boost its overall performances. In this research, the prospect of dividing the total network area into two non-overlapping channels of a given Mesh Network is investigated and analyzed numerically. It is found that the throughput is doubled as well as the fairness improves considerably if we deploy two channels instead of single channel backbone. An extensive simulation study has been carried out to find the optimum coverage area between two channels. The study shows that at a particular point of allocation, the network gives the optimum response.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format