Catálogo de publicaciones - libros

Wireless sensor networks (WSNs) are comprised of energy constrained nodes. This limitation has led to the crucial need for energy-aware protocols to produce an efficient network. The concept of heterogeneity has been introduced in a WSN by deploying a large number of low power sensor nodes and a small number of more powerful nodes to serve as cluster heads (CHs). We propose a sleep scheduling scheme for balancing energy consumption rates in low power sensor nodes based on Analytical Hierarchy Process (AHP). We consider three factors contributing to the optimal nodes scheduling decision and they are the distance to CH, residual energy, and sensing coverage overlapping, respectively. We evaluate the efficiency of our proposed scheme in terms of important network parameters and compare with traditional random sleep scheduling in heterogeneous sensor networks. The proposed scheme is observed to improve network lifetime and conserve energy without compromising desired coverage.

Energy efficiency is a primary issue for the performance of a wireless sensor network. This paper works on both communication and transmission to reduce unnecessary energy waste, i.e., to conserve energy consumption, for a wireless sensor network. To improve idle listening, for example, we allow sensor nodes to activate or sleep periodically; to improve collision and overhearing, we use an algorithm to alternate the wakeup time of neighboring sensor nodes and thus reduce transmission latency.

Energy consumption estimation in sensor network is a critical process for network lifetime estimation before actual deployment. Energy consumption can be estimated by simulating the sensor network with a power model. Power model is the key component for the accurate estimation. However, the power model is not publicly accessible and it is not easy to generate accurate fine-grain power model. In this paper we proposed a simplified but yet accurate power model for AVR-based sensor nodes. Also, we developed an automated power model generation tool. The tool generates an instruction-level power model that can be connected to sensor network simulators. We model the current consumption of ATmega128 instruction set which is the most widely used processor in sensor node. Loading, execution, and control of the measurement framework are managed by the tool. Using the tool, we can generate power models of various sensor nodes using ATmega128 as their processor. Experimental result shows that our tool successfully generated accurate power models of various sensor nodes including Mica2.

Conventional mission-critical systems cannot prevent mission failure in dynamic battlefield environments in which the execution situations or missions change abruptly. To solve this problem, self-adaptive systems have been proposed in the literature. However, the previous studies do not offer specifics on how to identify changes in a system situation or to transform situation information into the actions the systems must take in dynamic environments. This paper proposes a situation-awareness based self-adaptive system architecture (SASA) to support more efficient adaptation and, hence, achieve more accurate and successful missions, even in dynamic execution environments. A case study for air defense systems (ADS) using tests in a HLA/TRI-based real-time distributed simulation environment was implemented.

In this paper, we propose a fast handoff algorithm for micromobility management enhancement in HMIPv6 networks, which eliminates the DAD procedure involved in the regular HMIPv6 in order to decrease handoff latency and increase the resource utilization efficiency. In the proposed scheme, the MAP is designed to guarantee the uniqueness of MN’s interface identifier within a MAP domain as long as the MN moves in a MAP domain, so that the MN configures the new address without the DAD procedure resulting in the decreased handoff latency significantly. When the MN resides in a subnet, MIPv6 is used adaptively as a mobility management protocol, which is to reduce bandwidth waste from the IP packet header overhead of IP-in-IP tunneling from the regular HMIPv6. Thru various computer simulation results, we verified the superior performance of the proposed scheme by comparing with the results of other schemes, MIPv6 and HMIPv6.

In this paper, we address a power-aware scheduling algorithm for mixed real-time tasks. A mixed-task system consists of periodic and sporadic tasks, each of which is characterized by its worst-case execution requirements and a deadline. We propose a dynamic voltage scaling algorithm called DVSMT, which dynamically scales down the supplying voltage (and thus the operating frequency) using on-line slack distribution when jobs complete earlier while still meeting their deadlines. Simulation results show that DVSMT saves up to 60% more than the existing algorithms both in the periodic and mixed task systems.

In recent years, fieldbuses have been more widely used in real-time distributed control systems. There are many international fieldbus protocol standards, but they are not interoperable among themselves. This paper proposes an integrated fieldbus network architecture based on a switched Ethernet which provides real-time communication features to the nodes in different fieldbuses. This paper also analyzes the schedulability conditions for real-time periodic messages on the switched Ethernet and an EDF (Earliest Deadline First)-based scheduling algorithm to support the real-time communication requirements of the periodic messages without any change in the principles of the switch.

We consider the problem of scheduling exception handlers in real-time systems that operate under run-time uncertainties including those on execution times, activity arrivals, and failure occurrences. The application/scheduling model includes activities and their exception handlers that are subject to time/utility function (TUF) time constraints and an utility accrual (UA) optimality criterion. A key underpinning of the TUF/UA scheduling paradigm is the notion of “best-effort” where high importance activities are always favored over low importance ones, irrespective of activity urgency. (This is in contrast to classical admission control models which favor feasible completion of admitted activities over admitting new ones, irrespective of activity importance.) We consider a transactional style activity execution paradigm, where handlers that are released when their activities fail (e.g., due to time constraint violations) abort the failed activities after performing recovery actions. We present a scheduling algorithm called Handler-assured Utility accrual Algorithm (or HUA) for scheduling activities and their handlers. We show that HUA’s properties include bounded-time completion for handlers and bounded loss of the best-effort property. Our implementation on a Real-Time Java Virtual Machine demonstrates the algorithm’s effectiveness.

This paper proposes a Path-oriented Real-time Medium Access Control (PR-MAC) protocol for sensor networks to guarantee the bounded delay of data transmission. PR-MAC removes sleep delay with a Bidirectional Pipelining Schedule (BPS) algorithm, and reduces communication delay caused by contention with a multi-channel communication mechanism. BPS enables a node to wake twice during a work cycle so as to support bidirectional data transmission. In either direction, the nodes along a path wake up sequentially. The multi-channel mechanism allocates a special channel for each communication path so that multiple simultaneous events will not interfere with one another. The data delay and energy consumption of PR-MAC is compared with those of S-MAC and DMAC. We implement the prototype of PR-MAC on the ns-2 simulator. Experiments showed PR-MAC performs better than S-MAC in reducing the transmission delay of both data and control message.

In this paper, we consider a new packet scheduling algorithm for real time traffic in the high speed downlink packet access system that has been introduced for WCDMA system to providing high transmission rates. The objective of the design is to meet the maximum tolerable delay and consider the channel assigning based on the received SIR for real-time traffic users. The proposed scheduling algorithm shows that the users are ranked by the ratios of the bits in the buffer to the residual time for transmission, the ranked users are assigned channels based on the SIR value table and get service one by one. The simulation results show that the proposed algorithm can provide the lower packet drop rate for real time quality of service (QoS) requirement.