Catálogo de publicaciones - libros

The construction of backbone is a fundamental problem in sensor networks. As being critical to routing, data fusion and query broadcasting, the backbone should contain as fewer nodes as possible. Meanwhile, it also should be power-efficient in order to prolong its lifetime. In this paper, we propose a novel design of backbone for sensor networks by minimizing its total transmission cost. We term this kind of backbone (simply ). The construction of MWB is proved to be NP-Complete. Two heuristic algorithms (one is centralized and the other is distributed) are developed for constructing such backbone. The centralized algorithm, executed at the base station, is to find an optimal backbone by using the information of all nodes and links in the network. The distributed algorithm run at each node, however, uses the information of its neighbors and two-hop neighbors to determine whether it should be included in the backbone. Simulated experiments are conducted to evaluate the novel backbone, and performance comparisons are also done with the existing schemes.

Energy is one of the most important factors in the design of routing protocols in wireless sensor networks. This paper first analyzes the energy consumption in typical clustering protocols and finds that the consumption is not evenly distributed among nodes. Thus some nodes die quickly with the reduction of the network lifetime. Then a new energy-balanced strategy is introduced in clustering protocols. The strategy assigns the head communication load to base station by detecting the energy consumption in the cluster heads. The evenly distributed energy among the nodes is realized by controlling the head consumption. Simulation results show that the lifetime of the network is significantly prolonged with the new energy-balanced strategy.

This paper discusses the energy efficient QoS topology control problem in ad hoc wireless networks. Given a set of nodes in a plane, end-to-end traffic demands and delay bounds between node pairs, the problem is to find a network topology that can meet the QoS requirements and the total transmission power of nodes is minimized. We consider two cases of the problem: 1) the traffic demands are not splittable, and 2) the traffic demands are splittable. The first case is formulated as an integer linear programming problem. The latter case is formulated as a mixed integer linear programming problem. A greedy algorithm and an approximation algorithm with ratio n are proposed to solve the problem, where n is the number of nodes. Extensive simulations are conducted to evaluate the performance of proposed algorithms.

One of the key problems for Wireless Sensor Networks (WSNs) is the design of Medium Access Control (MAC) protocol. MAC protocol controls the activity of wireless communication module of sensor nodes, which is the major consumer of sensor energy. The energy efficiency of MAC protocol makes a strong impact on the network performance. TDMA-based MAC protocol is inherently collision free, and can rule out idle listening since nodes know when to transmit. In this paper, we present ED-TDMA, an energy efficient protocol for event driven applications in wireless sensor network. ED-TDMA improves channel utility by changing the length of TDMA frame according to the number of source nodes and saves energy with bitmap-assisted TDMA schedule. In addition, ED-TDMA employs intra-cluster coverage to prolong network lifetime and to improve system scalability. Simulation results show that ED-TDMA performs better for wireless sensor network with high-density deployment and under low traffic.

Sensor networks have attracted much attention in the recent years for its wide applications in biology, medicine, security and battlefield, etc. Data gathering is one of the most important operations in wireless sensor networks. In this paper, we present an energy-delay efficient data gathering protocol, SODG, for sensor networks while taking the transmission interference into considerations. The significance of this proposal is that it is fully localized and distributed, and only depends on the one-hop neighbors’ information. To minimize the delay, the parallel transmissions are permitted with interference- free guaranteed. The experimental simulations show that our protocol is energy- delay efficient. Especially, SODG protocol improves about 64% over PEGASIS on energy consumption, and about 80% over chain-based protocols on delay.

Wireless sensor networks have been widely used for civilian and military applications, such as environmental monitoring and vehicle tracking. In these applications, continuous query processing is often required and their efficient evaluation is a critical requirement to be met. Due to the limited power supply for sensor nodes, energy efficiency is a major performance measure in such query evaluation. In this paper, we focus on continuous NN query processing. We observe that the centralized data storage and monitoring schemes do not favor energy efficiency. We therefore propose a localized scheme to monitor long running nearest neighbor queries in sensor networks. The key idea is to establish a monitoring area for each query so that only the updates relevant to the query are collected. Experimental results show that our scheme outperforms the centralized scheme in terms of energy efficiency and network lifetime.

Sensor networks generate a large amount of data during monitoring process. These data must be sparingly exacted to conserve energy. There are two methods to obtain data: “push” and “pull”. When the sensory data satisfied a preset condition, they are “push”ed towards the base station. The “pull” method is to actively query the sensor networks for any interesting sensory data. The problem is how to plan the query and save the energy. When a query has been executed, there are some hints that can be kept to optimize the subsequent query processing. Energy consumption can be reduced by not contacting nodes whose values either can be predicted or are unlikely to be used. In this paper, we propose a history-sensitive based method to optimize top-k query processing in sensor networks. The top-k query looks for and utilizes the historical data in each sensor node. Subsequent top-k queries are guided by these historical data, therefore, to improve the entire query process. Simulation results show that the number of query hops can be reduced and the delays in response are improved.

Data replication is suitable to improve the response time, the global traffic, and the sharing of data since even in the case of disconnection of a server. The nodes can continue to have access to replicas of data. On an Ad hoc mobile network, the frequent partition of the network and the lack of fixed infrastructures complicate the data access and the sharing task.

In this paper, we propose a method of data replication in a mobile ad hoc network. The method is composed of two main phases. The first phase aims at creating replicas from new data in the network and at realizing the first distribution of these replicas. The second phase is devoted to the redistribution of replicas in order to overcome the impact of dynamic changes of topology and to satisfy the evolution of users’ needs.

Accessing remote data is a challenging task in mobile ad hoc networks (MANETs). A common technique used to improve the performance of data access is replication, which improves the performance of data access in distributed systems at the cost of increased storage space and communication overhead. Due to strict resource constraint, node mobility and impairments of wireless transmission, applying replication schemes developed for distributed systems to MANETs directly leads to poor performance. In this paper, we develop a zone-based replication scheme for MANETs. In this scheme, every node proactively maintains replica distributing information within its replicating zone, which leads to the access from requesting node to the requested data item (including its replicas) distributed in its replicating zone can be satisfied directly. If requested data item is outside the replicating zone, reactive lookup process is invoked to find the node hosting the requested data item and the route to this node at the same time. Opportunistic data replicating is performed spontaneously with data transferring, and corresponding replica is allocated to nodes located in the replicating zone of the requesting node. Using cross-layer design, we illustrate how the hybrid adaptive routing technique, zone routing protocol, assists data lookup and replication to achieve high performance of data access. Simulation results have shown that our design is successful in a dynamic MANET.

We consider duty cycling in sensor networks for time-critical monitoring, where sensors monitor events and send the information to a data collection node (called ). Latency is considered as the delay elapsed between the time when and the time when . Such networks are different from general purpose ad hoc networks, where latency is defined as the delay elapsed between the time when initiates a packet and the time when receives the packet. We aim to prolong network lifetime by scheduling periodic sensors’ duty cycles while preserving small latency from to the . In our duty cycle schemes, sensors are grouped into sets; the collaboration between different sets is designed to enable the availability of event reports at active sensors before they reach the sink. Our ideas are simple and achieve desirable properties: the network lifetime is proportional to the number of sets and the performance is comparable to that of non-duty-cycled networks with the same number of active sensors, as shown in our analyses and simulations.