Energy-efficient routing over coordinated sleep scheduling in wireless ad hoc networks

In this paper, we study how energy-efficient routing at the network layer can be coordinated with sleep scheduling at the link layer to increase network-wide energy efficiency in wireless ad hoc networks. We identify a trade-off between the reduced transmit power at senders with multi-receiver diversity and the increased receive power at forwarders with coordinated sleep scheduling. Moreover, we provide a comprehensive study of how coordinated sleep scheduling affects the energy-efficient routing performance based on a 2-D gird topology and time division multiple access (TDMA) medium access control (MAC). Simulation results demonstrate the effectiveness of the integrated routing and sleep scheduling, significant impact of coordinated sleep scheduling on the energy-efficient routing performance, and relationship between networking conditions (in terms of the traffic load and node density) and overall system performance achieved by different energy-efficient routing protocols.     

A new integrated energy-saving scheme in green Fiber-Wireless（FiWi） access network

Energy savings in Internet have been regarded as a significant technical issue for academic and industrial community.Particularly,access network accounts for more than 70%of the total energy consumption of Internet.As a promising access technique,Fiber-Wireless(FiWi)network not only enables the cost-effective broadband access,but also provides more opportunities for energy savings.Previous works mostly focused on the energy savings in the optical back-end of FiWi.Generally,they extended the Optical Network Unit(ONU)sleep mechanisms initially designed for Passive Optical Network(PON)to FiWi by combining with the wireless rerouting.However,most of these works left the energy savings in the wireless front-end untouched.In fact,when one or more ONUs in the network is/are sleeping,many wireless components remain idle or underutilized which cause a lot of energy waste.Motivated by this,we propose a new integrated Wireless-Optical Energy Savings(WOES)scheme for the comprehensive energy savings in FiWi.The WOES scheme consists of two interactive modules,Energy-Efficient ONU Management(EEOM)and Energy-Aware Topology Configuration(EATC).EEOM aims at the energy savings in the optical back-end by putting the low-load ONUs into sleep state.A pair of thresholds is introduced into EEOM to maintain the states of ONUs.As soon as ONUs states change,EATC will reconfigure the wireless topology by putting the idle Radio Interfaces(RIs)into standby state,thus minimizing the energy consumption of the wireless front-end.Simulation results show that the WOES scheme can reduce the energy consumption significantly with just a little performance degradation in network throughput and end-to-end delay.     

Sleep-aware mode assignment in wireless embedded systems

Minimizing energy consumption is a key issue in designing wireless embedded systems. While a lot of work has been done to manage energy consumption on single processor real-time systems, little work has been done in network-wide energy consumption management for real-time tasks. Existing work on network-wide energy minimization assumes that the underlying network is always connected, which is not consistent with the practice in which wireless nodes often turn off their network interfaces in a sleep schedule to reduce energy consumption. Moreover, existing sleep scheduling techniques are unaware of computation status and often lead to unnecessary wakeup overheads. In this paper, we propose solutions to minimize network-wide energy consumption for real-time tasks with precedence constraints executing on wireless embedded systems. Our solutions jointly consider the radio sleep scheduling of wireless nodes and the execution modes of processors. Based on different wireless network topologies, we propose energy management schemes to minimize energy consumption while guaranteeing the timing constraint and precedence constraint. When the precedence graph is a tree, our solution gives optimal result on energy management. The experiments show that our approach significantly reduces total energy consumption compared with previous works.     

基于IEEE 802.16e的睡眠模式的研究

IEEE 802.16e介绍了两种睡眠模式来达到能量的有效利用,分别是睡眠模式Ⅰ和睡眠模式Ⅱ,睡眠模式Ⅰ使用二进制指数增长的睡眠周期大小,睡眠模式Ⅱ使用固定的睡眠周期大小。首先对两种睡眠模式的能量消耗和时延性能进行分析,然后引入马尔可夫判定过程,给出一种睡眠模式的选择算法,以满足对于能量消耗和时延的要求,从而达到一种在不同性能要求下的权衡,仿真结果给出了这种选择算法的性能特点。     

多个无线传感器网络中节能MAC协议设计

在无线传感器网络中,媒体访问控制(MAC)层协议影响着整个网络的性能。根据无线传感器网络对节点能耗和时延的要求,本文提出了一种基于跨层设计的节能MAC协议。利用物理层、MAC层和路由层之间的信息交互,在保证可靠通信的基础上,实现在一个监听/睡眠周期内数据多跳传输,缩短数据传输时延,并且有效控制网络数据传输的冗余度,降低冗余节点能量消耗。性能分析和仿真结果表明,节能MAC协议能够有效地降低网络时延并且减少节点能耗。     

Top-k query evaluation in sensor networks under query response time constraint

Top-k query in a wireless sensor network is to find the k sensor nodes with the highest sensing values. To evaluate the top-k query in such an energy-constrained network poses great challenges, due to the unique characteristics imposed on its sensors. Existing solutions for top-k query in the literature mainly focused on energy efficiency but little attention has been paid to the query response time and its effect on the network lifetime. In this paper we address the query response time and its effect on the network lifetime through the study of the top-k query problem in sensor networks with the response time constraint. We aim at finding an energy-efficient routing tree and evaluating top-k queries on the tree such that the network lifetime is significantly prolonged, provided that the query response time constraint is met too. To do so, we first present a cost model of energy consumption for answering top-k queries and introduce the query response time definition. We then propose a novel joint query optimization framework, which consists of finding a routing tree in the network and devising a filter-based evaluation algorithm for top-k query evaluation on the tree. We finally conduct extensive experiments by simulation to evaluate the performance of the proposed algorithms, in terms of the total energy consumption, the maximum energy consumption among nodes, the query response time, and the network lifetime. The experimental results showed that there is a non-trivial tradeoff between the query response time and the network lifetime, and the joint query optimization framework can prolong the network lifetime significantly under a specified query response time constraint.     

密集型传感器网络中移动sink的路径选择机制

针对密集型无线传感器网络,以最大化网络寿命为优化目标,将网络转换成相应的网络流图,利用网络最大流问题估算sink采用不同路径下的网络寿命并以此为标准进行路径选择,提出了一种基于网络流理论的高效sink路径选择机制。仿真结果表明,本方案同采用固定路径采集及类似解决方案相比,能有效均匀网络能耗,延长网络寿命,取得了较好的网络性能。     

Massive MIMO 下行系统能效资源分配算法

摘 要: 针对无线通信网耗能造成二氧化碳排放量和运营成本日益增加的问题,提出了一种下行大规模天线系统能效最优的资源分配算法。算法在基站端采用最大比合并(MRT)的预编码情况下,考虑各用户最小数据速率、最大发射功率和可容忍的干扰水平约束条件下,以最大化系统能效下界为准则建立非凸优化模型。首先采用一种迭代算法确定每个用户的带宽分配,然后根据分数规划的性质,将能效优化问题的分数形式转化为减式形式,进而利用凸优化方法求解基站端最优的发射天线数和发射功率来获得最优能效。仿真结果表明,所提算法能以较小的迭代次数收敛到最大能效值,并且有较好的系统频谱效率性能,同时算法复杂度得到了显著降低。     

EQOWSN: Evolutionary-based query optimization over self-organized wireless sensor networks

In this paper, a new approach has been introduced that integrates an evolutionary-based mechanism with a distributed query sensor cover algorithm for optimal query execution in self-organized wireless sensor networks (WSN). An algorithm based on an evolutionary technique is proposed, with problem-specific genetic operators to improve computing efficiency. Redundancy within a sensor network can be exploited to reduce the communication cost incurred in execution of spatial queries. Any reduction in communication cost would result in an efficient use of battery energy, which is very limited in sensors. Our objective is to self-organize the network, in response to a query, into a topology that involves an optimal subset of sensors that is sufficient to process the query subject to connectivity, coverage, energy consumption, cover size and communication overhead constraints. Query processing must incorporate energy awareness into the system by reducing the total energy consumption and hence increasing the lifetime of the sensor cover, which is beneficial for large long running queries. Experiments have been carried out on networks with different sensors Transmission radius, different query sizes, and different network configurations. Through extensive simulations, we have shown that our designed technique result in substantial energy savings in a sensor network. Compared with other techniques, the results demonstrated a significant improvement of the proposed technique in terms of energy-efficient query cover with lower communication cost and lower size.     

异构传感器网络的分布式能量有效成簇算法

为了延长网络的生存时间,需要设计能量有效的协议,以适应传感器网络的特点.成簇算法是传感器网络中减少能量消耗的一种关键技术,它能够增强网络的扩展性和延长网络的生存时间.研究了异构传感器网络中成簇算法在节省能量方面的性能,提出一种适应异构无线传感器网络的分布式能量有效的成簇方案.此方案基于节点剩余能量与网络节点的平均能量的比例来选举簇头节点.较高初始能量和剩余能量的节点比低能量节点拥有更多的机会成为簇头节点,从而使网络能量均匀消耗,延长网络的生存时间.模拟实验结果显示,与现有的重要成簇方案相比,新的成簇算法在异构网络下提供了更长的网络生存时间和更大的网络有效吞吐量.     

A cross-layer fault tolerance management module for wireless sensor networks

It is a well-established fact that wireless sensor networks (WSNs) are very power constraint networks, but besides this, they are inherently more fault-prone than any other type of wireless network and their protocol design is very application specific. Major reasons for the faults are the unpredictable wireless communication channel, battery depletion, as well as fragility and mobility of the nodes. Furthermore, as traditional protocol design methods have proved inadequate, the cross-layer design (CLD) approach, which allows for interactions between different layers, providing more flexible and energy-efficient functionality, has emerged as a viable solution for WSNs. In this study we define a fault tolerance management module suitable to the requirements, limitations, and specifics of WSNs, encompassing methods for fault detection, fault prevention, fault management, and recovery. The suggested solution is in line with the CLD approach, which is an important factor in increasing the network performance. Through simulations the functionality of the network is evaluated, based on packet loss, delay, and energy consumption, and is compared with a similar solution not including fault management. The results achieved support the idea that the introduction of a unified approach to fault management improves the network performance as a whole.     

Green framework for future heterogeneous wireless networks

Energy-efficient communication has sparked tremendous interest in recent years as one of the main design goals of future wireless Heterogeneous Networks (HetNets). This has resulted in paradigm shift of current operation from data oriented to energy-efficient oriented networks. In this paper, we propose a framework for green communications in wireless HetNets. This framework is cognitive in holistic sense and aims at improving energy efficiency of the whole system, not just one isolated part of the network. In particular, we propose a cyclic approach, named as energy-cognitive cycle, which extends the classic cognitive cycle and enables dynamic selection of different available strategies for reducing the energy consumption in the network while satisfying the quality of service constraints.     

An energy-efficient task scheduling for mobile devices based on cloud assistant

Mobile cloud computing is an emerging service model to extend the capability and the battery life of mobile devices. Mostly one network application can be decomposed into fine-grained tasks which consist of sequential tasks and parallel tasks. With the assistance of mobile cloud computing, some tasks could be offloaded to the cloud for speeding up executions and saving energy. However, the task offloading results in some additional cost during the communication between cloud and mobile devices. Therefore, this paper proposes an energy-efficient scheduling of tasks, in which the mobile device offloads appropriate tasks to the cloud via a Wi-Fi access point. The scheduling aims to minimize the energy consumption of mobile device for one application under the constraint of total completion time. This task scheduling problem is reconstructed into a constrained shortest path problem and the LARAC method is applied to get the approximate optimal solution. The proposed energy-efficient strategy decreases 81.93% of energy consumption and 25.70% of time at most, compared with the local strategy. Moreover, the applicability and performance of the proposed strategy are verified in different patterns of applications, where the time constraint, the workload ratio between communication and computation are various.     

An energy-efficient MAC protocol with downlink traffic scheduling strategy in IEEE 802.11 infrastructure WLANs

To support mobility, mobile devices are powered by batteries with limited energy. Thus, the good design of energy efficiency becomes one of the most important issues in wireless networks. A well-designed energy-efficient MAC protocols can be realized with both minimum energy consumption as well as maximum data throughput and can be easily implemented in products with de facto standards. Based on IEEE 802.11 infrastructure WLANs, we propose an energy-efficient MAC protocol which employs a novel approach to schedule those to-be-transmitted frames for saving energy by reducing the total waiting time and the collisions of the frames. Fault tolerance issues are also considered in the proposed protocol because frames are transmitted in fading interference wireless environment. Through analyses and simulations, we demonstrate that our protocol presents a better performance than IEEE 802.11 and other protocols not only in energy efficiency but also in aggregate throughput and frame transmission delay.     

Energy-conservation in 802.11 WLANs via transmission-strategy-aware airtime allocation

In a typical 802.11 wireless local area network (WLAN), different wireless stations may communicate with the access point (AP) with different transmission rates, transmit-power levels, and data payload sizes. Such phenomenon is often referred to as transmission-strategy diversity. In this paper, we study the energy-conservation problem in 802.11 WLANs in the presence of transmission-strategy diversity. This problem is addressed from a unique angle – the system-level fairness which is quite different from most of current research that focuses on improving the performance of each individual wireless station. To emphasize fair energy consumption among contending stations, we introduce a new fairness notion, called energy-conservation fairness, which is in sharp contrast to the conventional throughput fairness and airtime fairness. Another contribution of this paper is an energy-efficient scheme that allocates airtime shares to contending stations so as to achieve combined airtime and energy-conservation fairness. Our simulation results show that, when the energy-conservation fairness is considered, both aggregate system throughput and overall system energy-efficiency can be improved significantly with all contending stations consuming a similar amount of energy.     

SEEL:无线传感器网络下自适应、低延迟的节能媒质接入控制协议

无线传感器网络有着广泛的应用前景,然而由于传感器节点能量有限,因此传感器网络上运行的协议必须具备能量有效性以获得较长的生命周期.而媒质接入控制子层是节点能量消耗的主要所在,因此无线传感器网络设计的关键问题之一是媒质的接入控制.提出了一种自适应低延迟的节能MAC协议——SEEL协议,根据当前的网络负载自适应地调节竞争窗口的大小,从而减小节点数据传送的碰撞几率和由于碰撞而导致的能量消耗;采用了快速退避机制,减少了节点在退避过程中的空闲监听时间;扩展了RTS/CTS消息机制,可减少节点在每帧活动阶段的时间以及减小数据的延迟,两者都能节约能量的使用.实验结果显示,SEEL协议具有比S-MAC和TEEM协议更好的性能.     

成簇无线传感网中能量高效的协作通信

在成簇无线传感器网络中,会出现极大簇和极小簇并存的现象,从而导致整个网络的能量消耗不均衡,进而降低网络性能。通过采用邻近极大极小簇协作发送的方案,极大地均衡了网络的能量消耗,提高了通信的可靠性。仿真结果表明,基于邻近极大极小簇的协作发送方案是一种高能效协作方案,能够很好地均衡网络能量消耗,在延长网络生存周期方面具有更优越的性能。     

Satisfying the target network lifetime in wireless sensor networks

Generally, the lifetime of a wireless sensor network (WSN) is defined as the duration until any sensor node dies due to battery exhaustion. If the traffic load is not properly balanced, the batteries of some sensor nodes may be depleted quickly, and the lifetime of the WSN will be shortened. While many energy-efficient routing schemes have been proposed for WSNs, they focus on maximizing the WSN lifetime. In this paper, we propose a scheme that satisfies a given ‘target’ lifetime. Because energy consumption depends on traffic volume, the target lifetime cannot be guaranteed through energy-efficient routing alone. We take an approach that jointly optimizes the sensing rate (i.e., controlling the sensor-traffic generation or duty cycle) and route selection. Satisfying the target lifetime while maximizing the sensing rate is a NP-hard problem. Our scheme is based on a simple Linear Programming (LP) model and clever heuristics are applied to compute a near-optimal result from the LP solution. We prove that the proposed scheme guarantees a 1/2-approximation to the optimal solution in the worst case. The simulation results indicate that the proposed scheme achieves near-optimality in various network configurations.     

一种基于功率控制的WSN自适应能量高效传输模式研究

无线传感器网络的能耗决定了网络的生存时间。本文提出了一种基于功率控制WSN自适应能量高效传输模式。分析了在功率控制方案中传输功率损耗与温度之间的关系。使用开环控制去补偿由于温度引起的链路质量的变化。通过结合开环温度感知的补偿与闭环反馈控制,可以在无线传感网络中显著降低传输功率控制的开销。仿真结果表明,与传统的在单一地域最大化增强发送功率来补偿温度的变化相比,该方案能够有效地适应传输链路质量的变化,并且有较少的控制报文开销。     

A detailed review of energy-efficient medium access control protocols for mobile sensor networks

This article reviews the state-of-the-art energy-efficient contention-based and scheduled-based medium access control (MAC) protocols for mobile sensor networks (MSNs) by first examining access schemes for wireless sensor networks (WSNs). Efficient and proper mobility handling in sensor networks provides a window of opportunity for new applications. Protocols, such as S-MAC, reduce energy consumption by putting nodes to sleep after losing to channel contention or to prevent idling. Sleeping is a common method for energy-efficient MAC protocols, but delay depends on sleep duration or frame time, and longer delays lead to higher packet lost rate when nodes are unsynchronized due to network mobility. MS-MAC extends S-MAC to include mobility-awareness by decreasing this sleep duration when mobility is detected. S-MAC with extended Kalman filter (EKF) reduces mobility-incurred losses by predicting the optimal data frame size for each transmission. MMAC utilizes a dynamic mobility-adaptive frame time to enhance TRAMA, a scheduled-based protocol, with mobility prediction. Likewise, G-MAC utilizes TDMA for cluster-based WSNs by combining the advantages of contention and contention-free MACs. Z-MAC also combines both methods but without clustering and allows time slot re-assignments during significant topology changes. All of the above MAC protocols are reviewed in detail.