Showing papers on "Efficient energy use published in 2003"

An adaptive energy-efficient MAC protocol for wireless sensor networks

Abstract: In this paper we describe T-MAC, a contention-based Medium Access Control protocol for wireless sensor networks. Applications for these networks have some characteristics (low message rate, insensitivity to latency) that can be exploited to reduce energy consumption by introducing an activesleep duty cycle. To handle load variations in time and location T-MAC introduces an adaptive duty cycle in a novel way: by dynamically ending the active part of it. This reduces the amount of energy wasted on idle listening, in which nodes wait for potentially incoming messages, while still maintaining a reasonable throughput.We discuss the design of T-MAC, and provide a head-to-head comparison with classic CSMA (no duty cycle) and S-MAC (fixed duty cycle) through extensive simulations. Under homogeneous load, T-MAC and S-MAC achieve similar reductions in energy consumption (up to 98%) compared to CSMA. In a sample scenario with variable load, however, T-MAC outperforms S-MAC by a factor of 5. Preliminary energy-consumption measurements provide insight into the internal workings of the T-MAC protocol.

An energy efficient hierarchical clustering algorithm for wireless sensor networks

Abstract: A wireless network consisting of a large number of small sensors with low-power transceivers can be an effective tool for gathering data in a variety of environments. The data collected by each sensor is communicated through the network to a single processing center that uses all reported data to determine characteristics of the environment or detect an event. The communication or message passing process must be designed to conserve the limited energy resources of the sensors. Clustering sensors into groups, so that sensors communicate information only to clusterheads and then the clusterheads communicate the aggregated information to the processing center, may save energy. In this paper, we propose a distributed, randomized clustering algorithm to organize the sensors in a wireless sensor network into clusters. We then extend this algorithm to generate a hierarchy of clusterheads and observe that the energy savings increase with the number of levels in the hierarchy. Results in stochastic geometry are used to derive solutions for the values of parameters of our algorithm that minimize the total energy spent in the network when all sensors report data through the clusterheads to the processing center.

Single-ISA heterogeneous multi-core architectures: the potential for processor power reduction

Abstract: This paper proposes and evaluates single-ISA heterogeneous multi-core architectures as a mechanism to reduce processor power dissipation. Our design incorporates heterogeneous cores representing different points in the power/performance design space; during an application's execution, system software dynamically chooses the most appropriate core to meet specific performance and power requirements. Our evaluation of this architecture shows significant energy benefits. For an objective function that optimizes for energy efficiency with a tight performance threshold, for 14 SPEC benchmarks, our results indicate a 39% average energy reduction while only sacrificing 3% in performance. An objective function that optimizes for energy-delay with looser performance bounds achieves, on average, nearly a factor of three improvements in energy-delay product while sacrificing only 22% in performance. Energy savings are substantially more than chip-wide voltage/frequency scaling.

Energy efficient schemes for wireless sensor networks with multiple mobile base stations

Abstract: One of the main design issues for a sensor network is conservation of the energy available at each sensor node We propose to deploy multiple, mobile base stations to prolong the lifetime of the sensor network We split the lifetime of the sensor network into equal periods of time known as rounds Base stations are relocated at the start of a round Our method uses an integer linear program to determine new locations for the base stations and a flow-based routing protocol to ensure energy efficient routing during each round We propose four metrics and evaluate our solution using these metrics Based on the simulation results we show that employing multiple, mobile base stations in accordance with the solution given by our schemes would significantly increase the lifetime of the sensor network

Energy-efficient operation of rail vehicles

Abstract: This paper describes an analytical process that computes the optimal operating successions of a rail vehicle to minimize energy consumption. Rising energy prices and environmental concerns have made energy conservation a high priority for transportation operations. The cost of energy consumption makes up a large portion of the Operation and Maintenance (O&M) costs of transit especially rail transit systems. Energy conservation or reduction in energy cost may be one of the effective ways to reduce transit operating cost, therefore improve the efficiency of transit operations. From a theoretical point of view, the problem of energy efficient train control can be formulated as one of the functions of Optimal Control Theory. However, the classic numerical optimization methods such as discrete method of optimum programming are too slow to be used in an on-board computer even with the much improved computation power, today. The contribution of this particular research is the analytical solution that gives the sequence of optimal controls and equations to find the control change points. As a result, a calculation algorithm and a computer program for energy efficient train control has been developed. This program is also capable of developing energy efficient operating schedules by optimizing distributions of running time for an entire route or any part of rail systems. We see the major application of the proposed algorithms in fully or partially automated Train Control Systems. The modern train control systems, often referred as “positive” train control (PTC), have collected a large amount of information to ensure safety of train operations. The same data can be utilized to compute the optimum controls on-board to minimize energy consumption based on the algorithms proposed in this paper. Most of the input data, such as track plan, track profile, traction and braking characteristics, speed limits and required trip time are located in an on-board database and/or they can be transmitted via radio link to be processed by the proposed algorithm and program.

Energy efficiency based packet size optimization in wireless sensor networks

Abstract: This paper addresses the question of optimal packet size for data communication in energy constrained wireless sensor networks. Unlike previous work on packet length optimization in other wired and wireless networks, energy efficiency is chosen as the optimization metric. The use of fixed size packets is proposed in light of the limited resources and management costs in sensor networks. The optimal fixed packet size is then determined for a set of radio and channel parameters by maximizing the energy efficiency metric. Further, the effect of error control on packet size optimization and energy efficiency is examined. While retransmission schemes are found to be energy inefficient, it is shown that forward error correction can improve the energy efficiency eventhough it introduces additional parity bits and encoding/decoding energy consumptions. In this regard, binary BCH codes are found to be 15% more energy efficient than the best performing convolutional codes, which have thus far been considered for error control in sensor networks.

A protocol for tracking mobile targets using sensor networks

Abstract: With recent advances in device fabrication technology, economical deployment of large scale sensor networks, capable of pervasive monitoring and control of physical systems have become possible. Scalability, low overhead anti distributed functionality are some of the key requirements for any protocol designed for such large scale sensor networks. In this paper, we present a protocol, Distributed Predictive Tracking, for one of the most likely applications for sensor networks: tracking moving targets. The protocol uses a clustering based approach for scalability and a prediction based tracking mechanism to provide a distributed and energy efficient solution. The protocol is robust against node or prediction failures which may result in temporary loss of the target and recovers from such scenarios quickly and with very little additional energy use. Using simulations we show that the proposed architecture is able to accurately track targets with random movement patterns with accuracy over a wide range of target speeds.

Analyzing the energy consumption of security protocols

Abstract: Security is critical to a wide range of wireless data applications and services. While several security mechanisms and protocols have been developed in the context of the wired Internet, many new challenges arise due to the unique characteristics of battery powered embedded systems. In this work, we focus on an important constraint of such devices -- battery life -- and examine how it is impacted by the use of security protocols.We present a comprehensive analysis of the energy requirements of a wide range of cryptographic algorithms that are used as building blocks in security protocols. Furthermore, we study the energy consumption requirements of the most popular transport-layer security protocol SSL (Secure Sockets Layer). To our knowledge, this is the first comprehensive analysis of the energy requirements of SSL. For our studies, we have developed a measurement-based experimental testbed that consists of an iPAQ PDA connected to a wireless LAN and running Linux, a PC-based data acquisition system for real-time current measurement, the OpenSSL implementation of the SSL protocol, and parametrizable SSL client and server test programs. We investigate the impact of various parameters at the protocol level (such as cipher suites, authentication mechanisms, and transaction sizes, etc.) and the cryptographic algorithm level (cipher modes, strength) on overall energy consumption for secure data transactions.Based on our results, we discuss various opportunities for realizing energy-efficient implementations of security protocols. We believe such investigations to be an important first step towards addressing the challenges of energy efficient security for battery-constrained systems.

Energy-smart home system

Abstract: An “Energy-Smart” Home System is described where the existing proliferation of electrical junction boxes in the typical home or building are used for a unique combination of purposes, supporting diverse functionalities that heretofore have not been combined, and enabling ease of installation with no new wiring. Typically, this system relies on powerline communication and uses electrical wiring for energy distribution, monitoring, and control as well as security, audio/video communications and entertainment, and general network communications such as file transfers and Internet connectivity. An underlying theme in this “Energy-Smart” Home System allows energy-related information to be gathered by way of EMAC (Energy Monitoring And Control) points typically installed at convenient locations such as electrical junction boxes used for power plug receptacles and wall switches. In addition to being visually displayed at the point of energy use or measurement, energy-related information—electrical and thermal—is typically communicated through a powerline data link to a centrally located intelligent device such as a PC, Residential Gateway or Smart Thermostat where it may be monitored, analyzed, profiled, viewed, and also used to enable energy-related control functions. Energy consumption can be alternately displayed in terms of cost-per-time. Energy monitoring is also added to the electrical breaker box, offering an easy way to supplement distributed EMAC points. In general, this Energy-Smart Home System creates a form of “Bio-Feedback for Home Energy”, making the consumer far more aware, enabling more effective and efficient energy usage, while at the same time creating an electrical power distribution and communications infrastructure that enables significant advancements in security, communications, and comfort, in addition to enhanced energy control and conservation.

A node scheduling scheme for energy conservation in large wireless sensor networks

Abstract: In wireless sensor networks that consist of a large number of low-power, short-lived, unreliable sensors, one of the main design challenges is to obtain long system lifetime without sacrificing system original performances (sensing coverage and sensing reliability). In this paper, we propose a node-scheduling scheme, which can reduce system overall energy consumption, therefore increasing system lifetime, by identifying redundant nodes in respect of sensing coverage and then assigning them an off-duty operation mode that has lower energy consumption than the normal on-duty one. Our scheme aims to completely preserve original sensing coverage theoretically. Practically, sensing coverage degradation caused by location error, packet loss and node failure is very limited, not more than 1% as shown by our experimental results. In addition, the experimental results illustrate that certain redundancy is still guaranteed after node-scheduling, which we believe can provide enough sensing reliability in many applications. We implement the proposed scheme in NS-2 as an extension of the LEACH protocol and compare its energy consumption with the original LEACH. Simulation results exhibit noticeably longer system lifetime after introducing our scheme than before. Copyright © 2003 John Wiley & Sons, Ltd.

Carbon trading in the policy mix

Abstract: The Kyoto Protocol is stimulating the development of emissions-trading schemes at the national and international levels. These are being introduced alongside existing policy instruments such as carbon taxes and negotiated agreements, leading to complex problems of policy interaction. But the topic of policy interaction remains under-researched. This paper aims to improve understanding of such interactions by examining the conditions under which a cap-and-trade scheme for carbon-dioxide emissions may usefully coexist with carbon/energy taxes, support mechanisms for renewable electricity, and policies to promote energy efficiency. The paper argues that each of these instrument combinations may be acceptable, provided they contribute to either improving the static or dynamic efficiency of the trading scheme, or delivering other valued policy objectives. But, since the coexisting instruments may raise overall abatement costs while contributing nothing further to emission reductions, the objectives and trade-offs within the policy mix must be explicit.

Energy management for battery-powered embedded systems

Abstract: Portable embedded computing systems require energy autonomy. This is achieved by batteries serving as a dedicated energy source. The requirement of portability places severe restrictions on size and weight, which in turn limits the amount of energy that is continuously available to maintain system operability. For these reasons, efficient energy utilization has become one of the key challenges to the designer of battery-powered embedded computing systems.In this paper, we first present a novel analytical battery model, which can be used for the battery lifetime estimation. The high quality of the proposed model is demonstrated with measurements and simulations. Using this battery model, we introduce a new "battery-aware" cost function, which will be used for optimizing the lifetime of the battery. This cost function generalizes the traditional minimization metric, namely the energy consumption of the system. We formulate the problem of battery-aware task scheduling on a single processor with multiple voltages. Then, we prove several important mathematical properties of the cost function. Based on these properties, we propose several algorithms for task ordering and voltage assignment, including optimal idle period insertion to exercise charge recovery.This paper presents the first effort toward a formal treatment of battery-aware task scheduling and voltage scaling, based on an accurate analytical model of the battery behavior.

Energy use and energy access in relation to poverty

Abstract: This paper looks at how access and use of energy are related to poverty. Different approaches to how energy poverty might be measured are presented. One approach involves the estimation of basic energy needs of a household based on engineering calculations and certain normative assumptions. The second looks at poverty in relation to access to different energy sources. An alternative approach is then provided that combines the elements of access and consumption of energy in order to examine how these relate to the well being of households. Examining well being in terms of both these dimensions – access to clean and efficient energy sources; and sufficiency in terms of the quantity of energy consumed, could be an important complementary measure of poverty. The consumption dimension includes non-commercial consumption and thus includes self-produced and bartered products. The access dimension can serve as an indicator of the extent of market integration, or more specifically, as an indicator of the opportunity to join the modern market economy.

Energy aware lossless data compression

Abstract: Wireless transmission of a bit can require over 1000 times more energy than a single 32-bit computation. It would therefore seem desirable to perform significant computation to reduce the number of bits transmitted. If the energy required to compress data is less than the energy required to send it, there is a net energy savings and consequently, a longer battery life for portable computers. This paper reports on the energy of lossless data compressors as measured on a StrongARM SA-110 system. We show that with several typical compression tools, there is a net energy increase when compression is applied before transmission. Reasons for this increase are explained, and hardware-aware programming optimizations are demonstrated. When applied to Unix compress, these optimizations improve energy efficiency by 51%. We also explore the fact that, for many usage models, compression and decompression need not be performed by the same algorithm. By choosing the lowest-energy compressor and decompressor on the test platform, rather than using default levels of compression, overall energy to send compressible web data can be reduced 31%. Energy to send harder-to-compress English text can be reduced 57%. Compared with a system using a single optimized application for both compression and decompression, the asymmetric scheme saves 11% or 12% of the total energy depending on the dataset.

Minimum energy disjoint path routing in wireless ad-hoc networks

Abstract: We develop algorithms for finding minimum energy disjoint paths in an all-wireless network, for both the node and link-disjoint cases. Our major results include a novel polynomial time algorithm that optimally solves the minimum energy 2 link-disjoint paths problem, as well as a polynomial time algorithm for the minimum energy k node-disjoint paths problem. In addition, we present efficient heuristic algorithms for both problems. Our results show that link-disjoint paths consume substantially less energy than node-disjoint paths. We also found that the incremental energy of additional link-disjoint paths is decreasing. This finding is somewhat surprising due to the fact that in general networks additional paths are typically longer than the shortest path. However, in a wireless network, additional paths can be obtained at lower energy due to the broadcast nature of the wireless medium. Finally, we discuss issues regarding distributed implementation and present distributed versions of the optimal centralized algorithms presented in the paper.

On evaluating request-distribution schemes for saving energy in server clusters

Abstract: Power-performance optimization is a relatively new problem area particularly in the context of server clusters. Power-aware request distribution is a method of scheduling service requests among servers in a cluster so that energy consumption is minimized, while maintaining a particular level of performance. Energy efficiency is obtained by powering-down some servers when the desired quality of service can be met with fewer servers. We have found that it is critical to take into account the system and workload factors during both the design and the evaluation of such request distribution schemes. We identify the key system and workload factors that impact such policies and their effectiveness in saving energy. We measure a web cluster running an industry-standard commercial web workload to demonstrate that understanding this system-workload context is critical to performing valid evaluations and even for improving the energy-saving schemes.

Gas-Fired Distributed Energy Resource Technology Characterizations

Abstract: The U. S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) is directing substantial programs in the development and encouragement of new energy technologies. Among them are renewable energy and distributed energy resource technologies. As part of its ongoing effort to document the status and potential of these technologies, DOE EERE directed the National Renewable Energy Laboratory to lead an effort to develop and publish Distributed Energy Technology Characterizations (TCs) that would provide both the department and energy community with a consistent and objective set of cost and performance data in prospective electric-power generation applications in the United States. Toward that goal, DOE/EERE - joined by the Electric Power Research Institute (EPRI) - published the Renewable Energy Technology Characterizations in December 1997.As a follow-up, DOE EERE - joined by the Gas Research Institute - is now publishing this document, Gas-Fired Distributed Energy Resource Technology Characterizations.

The renewable energy response to climate change

Abstract: The environmental impacts from fossil fuel use particularly climate change, security of future energy supplies and energy poverty, are the key drivers for further development and deployment of renewable energy technologies and distributed energy systems. High capital investment is required to achieve this, though this would be partly offset by savings in the cost of constructing new large power stations and the infrastructure necessary to transmit gas and electricity over large distances. Many proposed renewable energy projects have relatively low investment costs in terms of $/tonne of carbon avoided but the development of further policies and mechanisms by governments is required to enable renewables to compete more fairly with traditional fossil fuels and nuclear power, often carrying high subsidies in various forms. Valuing the cost of emitting carbon into the atmosphere is one such approach. Recent developments resulting in improvements in performance and the lowering of costs of renewable energy technologies and systems has led to their rapid growth, particularly of wind and solar. However many scenarios of future global energy use still show them providing less than 4% of the world's primary energy supply by 2030. If mitigation of climate change is to prove successful and occur in time to minimize the costs of adaptation, then a more rapid uptake of renewable energy will be required. Greater investment now to drive the cost of renewables further down their experience curves will lead to less risk from climate change and lower investment costs in the longer term.

Energy Efficient Routing Protocols for Mobile Ad Hoc Networks

Abstract: Summary Although establishing correct and efficient routes is an important design issue in mobile ad hoc networks (MANETs), a more challenging goal is to provide energy efficient routes because mobile nodes’ operation time is the most critical limiting factor. This article surveys and classifies the energy-aware routing protocols proposed for MANETs. They minimize either the active communication energy required to transmit or receive packets or the inactive energy consumed when a mobile node stays idle but listens to the wireless medium for any possible communication requests from other nodes. Transmission power control approach and load distribution approach belong to the former category, and sleep/power-down mode approach belongs to the latter category. While it is not clear whether any particular algorithm or a class of algorithms is the best for all scenarios, each protocol has definite advantages/disadvantages and is well suited for certain situations. The purpose of this paper is to facilitate the research efforts in combining the existing solutions to offer a more energy efficient routing mechanism. Copyright # 2003 John Wiley & Sons, Ltd.

Dynamically tuning processor resources with adaptive processing

Abstract: By using adaptive processing to dynamically tune major microprocessor resources, developers can achieve greater energy efficiency with reasonable hardware and software overhead while avoiding undue performance loss. Adaptive processors require few additional transistors. Further, because adaptation occurs only in response to infrequent trigger events, the decision logic can be placed into a low-leakage state until such events occur.

A survey of techniques for energy efficient on-chip communication

Abstract: Interconnects have been shown to be a dominant source of energy consumption in modern day System-on-Chip (SoC) designs. With a large (and growing) number of electronic systems being designed with battery considerations in mind, minimizing the energy consumed in on-chip interconnects becomes crucial. Further, the use of nanometer technologies is making it increasingly important to consider reliability issues during the design of SoC communication architectures. Continued supply voltage scaling has led to decreased noise margins, making interconnects more susceptible to noise sources such as crosstalk, power supply noise, radiation induced defects, etc. The resulting transient faults cause the interconnect to behave as an unreliable transport medium for data signals. Therefore, fault tolerant communication mechanism, such as Automatic Repeat Request (ARQ), Forward Error Correction (FEC), etc., which have been widely used in the networking community, are likely to percolate to the SoC domain. This paper presents a survey of techniques for energy efficient on-chip communication. Techniques operating at different levels of the communication design hierarchy are described, including circuit-level techniques, such as low voltage signaling, architecture-level techniques, such as communication architecture selection and bus isolation, system-level techniques, such as communication based power management and dynamic voltage scaling for interconnects, and network-level techniques, such as error resilient encoding for packetized on-chip communication. Emerging technologies, such as Code Division Multiple Access (CDMA) based buses, and wireless interconnects are also surveyed.