Cross-layer design through joint routing and link allocation in wireless sensor networks

Both energy and bandwidth are scarce resources in sensor networks. In the past, the energy efficient routing problem has been extensively studied in efforts to maximize sensor network lifetimes, but the link bandwidth has been optimistically assumed to be abundant. Because energy constraint affects how data should be routed, link bandwidth affects not only the routing topology, but also the allowed data rate on each link, which in turn affects the lifetime. Previous research that focus on energy efficient operations in sensor networks with the sole objective of maximizing network lifetime only consider the energy constraint ignoring the bandwidth constraint. This thesis shows how infeasible these solutions can be when bandwidth does present a constraint. It provides a new mathematical model that address both energy and bandwidth constraints and proposes two efficient heuristics for routing and rate allocation. Simulation results show that these heuristics provide more feasible routing solutions than previous work, and significantly improve throughput. A method of assigning the time slot based on the given link rates is presented. The cross layer design approach improves channel utility significantly and completely solves the hidden terminal and exposed terminal problems --Abstract, page iii

Minimum-power multicast routing in static ad hoc wireless networks

(broadcasting incremental power). Wan et al. (2001) proved that SPT has an approximation ratio of at least ( 2) where is the total number of nodes, and both MST and BIP have constant approximation ratios. Based on the approach of pruning, Wieselthier et al. also proposed three greedy heuristics for Min-Power Asymmetric Multicast Routing: P-SPT (pruned shortest-path tree), P-MST (pruned minimum spanning tree), and P-BIP (pruned broadcasting incremental power). In this paper, we first prove that the approximation ratios of these three heuristics are at least ( 1 2) 1, and 2 (1), respectively. We then present constant-approxiation algorithms for Min-Power Asymmetric Multicast Routing. We show that any-approximation Steiner tree algorithm gives rise to a-approximation heuristic for Min-Power Asymmetric Multicast Routing, where is a constant between 6 and 12. In particular, the Takahashi-Matsuyama Steiner tree heuristic leads to a heuristic called SPF (shortest-path first), which has an approximation ratio of at most 2. We also present another heuristic, called MIPF (minimum incremental path first), for Min-Power Asymmetric Multicast Routing and show that its approximation ratio is between (13 3) and 2. Both SPF and MIPF can be regarded as an adaptation of MST and BIP, respectively, in a different manner than pruning. Finally, we prove that any-approximation Steiner tree algorithm also gives rise to a 2-approximation algorithm for Min-Power Symmetric Multicast Routing. Index Terms—Approximation algorithms, multicast routing, power control. I

Modular Energy Efficient Protocols for Lower Layers of Wireless Sensor Networks

Wireless sensor networks (WSNs) emerged as one of the compelling research areas in recent years. It has produced promising solutions for several potential applications such as intrusion detection, target detection, industrial automation, environmental monitoring, surveillance and military systems, medical diagnosing systems, tactical systems, etc. WSNs consist of small size of sensor nodes that are disseminated in a targeted area to monitor the events for collecting the data of interest. Meanwhile, WSNs face many challenging problems such as high energy consumption, network scalability and mobility. These problems profoundly affect the lifetime of the network, limit the access to several WSN application areas, and the Quality of Service (QoS) provision parameters including throughput, latency, bandwidth, data buffering, resource constraints, data redundancy, and medium reliability. Although, there has been significant research conducted in WSNs over the last few years to maintain a high standard of communication, especially coverage, challenges of high power consumption, mobility and scalability to name a few. The major problem with WSNs at the low layers are the excessive energy consumption by the sensor’s transceiver. Other related challenges are mobility and scalability that limit the QoS provision. To handle these issues, novel modular energy efficient protocols are proposed for lower layers of WSNs. These modular based protocols improve the energy consumption, providing cross-layering support to handle mobility, scalability and data redundancy. In addition, there is a protocol that automates handling the idle listening process. Other protocols optimize data frame format for faster channel access, data frame transfer, managing acknowledgement time and retry transmission, check the capability of sensing the nature of environment to decide to use either active or passive mode that help save energy, determine shortest efficient path, packet generation rate, automatic active and sleep mode, smart queuing, data aggregation and dynamically selection of the cluster head node. All these features ensure the QoS provision and resolve many problems introduced by mobility and scalability for multiple application areas especially disaster recovery, hospital monitoring system, remotely handling the static and mobile objects and battlefield surveillance systems. Finally, modular energy efficient protocols are simulated, and results demonstrate the validity and compatibility of the proposed approaches for multiple WSNs application areas