Adaptive application-driven WLAN power management

In this paper we present an adaptive application-driven power management (AADPM) strategy with online idle period length distribution learning capability for the IEEE 802.11b WLAN. We discuss its design and evaluate the performance in comparison with other power management strategies using the network simulator NS2. We simulated both the single user and multiple user scenarios. Experimental results have shown that, compared with other power management methods examined in this paper, AADPM achieved the highest energy saving in all cases and it demonstrated strong adaptability to network congestion.     

一种功率控制算法的仿真研究

802.11是在Adhoc网络中广泛应用的一种媒体接入控制协议。为了研究功率控制机制对系统带来的影响及其产生的原因,该文对一种能完全兼容802.11的分布式功率控制算法802.11DPC进行了仿真。结果显示:在Adhoc网络中,饱和情况下,根据报文长度不同,802.11DPC在网络吞吐率方面较802.11协议提高17%～20%,平均分组时延降低11%～15%,结点能耗及公平性性能则仅有部分提高。对仿真结果给出了合理的解释,得出了在由笔记本电脑等便携终端构成的Adhoc网络中使用功率控制机制更适合用来提高网络吞吐率的结论,为合理使用功率控制机制提供了参考依据。     

基于功率控制和冲突避免的无线Mesh网络低能耗MAC协议

为了解决IEEE 802.11协议在无线Mesh网络中能量利用效率低的问题,提出一种改进的低能耗MAC协议PCCA。PCCA协议在IEEE 802.11协议的基础上加入两个核心算法,即动态功率控制算法(DPCA)和冲突避免算法(CAA),以此降低能耗。DPCA通过接收节点计算发送节点所需的最佳发射功率,降低数据发送的能耗;CAA利用邻居通信状态表对潜在的冲突进行判断,让可能引起冲突的节点进入休眠以节约能量。仿真结果表明PCCA协议最多可降低约20%的能耗。     

用于传感网功率控制的并行传输MAC 协议

针对无线传感网（WSNs）中节点间不对称的发射功率引起的隐藏节点和暴露节点问题,提出一种用于传感网功率控制的MAC协议（MAC4PC）.该协议采用邻节点向量表对邻节点的状态及当前会话的信息进行记录,并设计了相关的控制帧收发时序和干扰度判断准则,以保证新建立会话与当前会话互不干涉,从而实现暴露节点的并行传输.仿真结果表明,与802.11 DCF协议、SB-FSMA/CA协议以及GLPCB-PMAC协议相比较,MAC4PC协议提高了网络平均吞吐量,降低了节点平均能耗和数据分组的平均传输时延.     

无线传感器网络MAC层能耗与时延的权衡

无线传感器网络节点设计的最重要约束之一就是要求低能耗,这与传统网络依赖持续的能源供应而致力于提供尽可能高的服务质量截然不同.研究了一个结合无线传感器网络的能耗特性而提出的MAC协议S-MAC协议,并在对802.11MAC、S-MAC中的能耗状态与时延特征进行理论和数学分析的基础上,通过仿真实验得出了在模拟网络环境中802.11MAC和S-MAC的能耗和平均时延,S-MAC协议中引入节点周期性睡眠、冲突串音避免和消息传递等新技术,以牺牲时延为代价换取高效的能量利用,提供了一种高效可扩展的在能耗和时延之间进行权衡的方案.     

无源感知网络中能耗和延迟平衡的机会路由协议

部署于野外的感知网络在应用时广泛存在节点能量不足的问题,而新型的使用能量收集技术的节点可以通过周期性地从环境中获取能量来延长网络的生存周期.因此,针对使用能量收集型节点的无源感知网络,能耗不再像有源节点网络那样成为制约网络性能最关键的因素.综合考虑能耗和延迟,可以在使节点获得较长生存周期的同时提高数据到达基站的速度.针对现有应用于无源感知网络的路由协议大多不能兼顾能耗和延迟性能的问题,提出了能耗和延迟平衡的机会路由协议（balance of energy and delay opportunistic routing protocol,简称EDOR）.该协议通过分析节点通信过程来估算节点的预期能耗值,使得节点选择令自己能耗较低的邻居节点作为转发候选.在最终确定转发节点时,该协议通过结合候选节点下一跳邻居节点的占空比信息来进行决策,使得发送节点选择能够更快将数据转发出去的候选节点来降低延迟,从而实现能耗和延迟性能的平衡.最后,该协议还通过设计退避策略来实现转发节点的单一性,减少机会路由过程中产生的不必要的数据包副本数量.     

一种功率自适应控制方案在移动自组网的应用

介绍了移动自组网的特点和802．11 DCF传输方式,论述了自组网的动态节能机制,提出了一种通过交换控制信息来预测最小发射功率的功率自适应调整MAC协议。仿真实验证明了该方案能有效降低系统的能量消耗,提高了网络的利用率。     

一种用于WLAN的自适应发射功率控制方案

为降低无线网络中工作站的能量消耗、延长工作时间,在分析IEEE802.11协议的基础上,提出一种用于WLAN的自适应发射功率控制方案。利用IEEE802.11协议中规定的ACK信息,引入效率因子和加权因子,使移动终端根据信道环境自适应地调整发射功率,从而降低能耗。仿真结果验证了该方案的有效性。     

基于802.11ah井下监测传感网的RAW重分组研究

现有的ZigBee、超宽带、WiFi等井下无线传感网通信技术或传输距离短,或传输速率较低,或覆盖范围与接入设备数量受限,而IEEE 802.11ah协议满足井下无线传感网对传输范围、功耗、网络容量、传输速率等的要求,可用于井下监测传感网传输周期性监测数据。针对802.11ah协议中MAC层标准限制接入窗口(RAW)机制在进行传感节点分组时不灵活、易导致组间负载不平衡的问题,提出了一种基于时延优化的RAW重分组方法:根据数据包预计传输时间对所有传感节点重新分组,通过3次分组来减少RAW组内节点碰撞、降低传输时延。为实现RAW重分组,提出了关联标识符(AID)分组重分配方法:采用部分传感节点断开关联的方式,按重分组后的RAW组分批次为节点重新分配AID,并将AID与节点MAC映射,从而减小RAW重分组时间开销,避免AID重分配过程中因数据无法传输而导致网络性能下降。仿真结果表明,随着井下监测传感网中传感节点增多,RAW重分组方法较标准RAW机制的网络时延更小、吞吐量更大、丢包率更低,且重分组过程对网络性能影响较小。     

基于LS-RTS机制和功率可调路由的跨层协议

为了降低线型无线传感网络能耗和传输延时,在改进CLM协议跨层方法的基础上融合其他经典机制,提出了一种适应线型拓扑结构的跨层协议。协议删除中继路由判决以优化原通信判决门限;对节点统一标记链编号形成新LS-RTS机制以提高链路传输率;精简时隙单元和多跳传输时序降低数据传输时延;并引入功率可调路由减少节点路由计算负担以此降低节点能耗。仿真结果表明,相较于CLM和CLR-DCE等两种跨层协议,本文提出的I-CLM跨层协议在降低传输时延的同时整体能耗至少降低了18.75%和7.32%,一定程度上延长了网络生存时间。     

Delay-sensitive routing in multi-rate MANETs

A mobile ad hoc network (MANET) is a collection of mobile hosts, which can communicate by the aid of intermediate mobile hosts without utilizing a fixed infrastructure and centralized administration. Many MANET standards, such as 802.11a, 802.11b, and 802.11g, can be operated at various rates for Quality-of-Service (QoS) constrained multimedia communication to more efficiently use the limited resources of MANETs. Since the radio channel is shared among neighbors in MANETs, calculating one-hop delays and determining delay-sensitive routes using the IEEE 802.11 MAC are still two challenging problems. In this paper, we first exploit the busy/idle ratio of the shared channel to estimate one-hop delay based on varied data rates. Then by the aid of the estimated delay, a multi-rate routing protocol is proposed for selecting data rates and determining a route for admitting a flow with a requested delay. In MANETs, when a host is transmitting data packets, its neighbors are blocked (i.e., forbidden to send packets) since it shares the radio channel with its neighbors. We adopt the strategy by selecting the combination of data rates and a route in order to minimize the total blocking time to all hosts of the network for maximizing the network’s capacity, which is the number of flows admitted by the network. Simulation results show that the proposed method obtains a more precise one-hop delay than a very recent work, and the proposed protocol admits more flows than an existing protocol.     

基于Q学习的蚁群优化水声网络协议

针对水声通信中数据传输延时高且动态适应性弱的问题, 提出了一种基于Q学习优化的蚁群智能水声网络路由协议(Q-learning ant colony optimization, QACO). 协议包括路由行为和智能决策部分, 在路发现和维护阶段, 依靠网络智能蚂蚁进行网络拓扑环境的构建和节点之间的信息交换以及网络的维护. 在Q学习阶段, 通过定量化节点能量和深度以及网络传输延时学习特征作为折扣因子和学习率, 以延长网络的生命周期, 降低系统能耗和延时. 最后通过水声网络环境进行仿真, 实验结果表明QACO在能耗、延迟和网络生命周期方面都优于基于Q学习辅助的蚁群算法(Q-learning aided ant colony routing protocol, QLACO)和基于 Q-learning 的节能和生命周期感知路由协议(Q-learning-based energy-efficient and lifetime-aware routing protocol, QELAR)和基于深度路由协议 (depth-based routing, DBR)算法.     

一种基于LEACH的低延迟和低功耗的WSN分簇算法

针对经典分簇LEACH协议的不足,提出了低延迟、低功耗和网络能耗均匀的改进算法。该算法主要从两个方面对LEACH进行了改进:在稳定数据传输阶段采用CSMA机制,降低了数据传输延迟;在能量均衡和能耗方面,混入小部分初始能量高的高级节点,在簇头选举阶段首先对节点进行能量感知,并综合考虑节点剩余能量和平均能量,从而延长了网络的生命周期。文中首先对LEACH协议进行简单介绍,利用平均周期法对LEACH中使用的CSMA机制进行分析,从而得到了改进算法的延迟计算方法;然后对改进算法的数据传输阶段的能耗和算法复杂度进行分析,并对改进算法的簇头选举阈值的计算进行讨论;最后对改进算法的数据传输阶段的延时和功耗进行建模分析,并利用MATLAB进行仿真对比。仿真结果显示,改进算法使得第一个节点死亡的时间延长了31%,全部节点死亡的时间延长了24.7%,并且网络能耗更加均匀,因此,该算法有效地解决了LEACH中的热区问题,改进了实际WSN应用中节点集中死亡带来的区域信息缺失问题。相比于LEACH,改进算法的数据传输延迟平均降低了78.6%,保证了WSN应用中数据的实时性,因此改进算法在延迟、生命周期、网络能耗均匀性以及吞吐量等性能上都得到了优化提升。     

An energy efficient security protocol for IEEE 802.11 WLANs

Security protocols in wired and wireless networks make use of computationally intensive cryptographic primitives and several message exchanges for authenticated key exchange at the session level and data confidentiality and integrity at the packet level. Moreover, changes in connectivity require mobile stations to repeatedly authenticate themselves, thereby expending more energy. In this paper, we propose an energy efficient security protocol for wireless local area networks (WLANs) that employs (a) different cryptographic primitives based on their suitability in terms of energy consumption and security level, (b) different levels of security and types of security services depending on the type of packet in 802.11 WLANs, and (c) a light-weight hashed key chain to reduce the number of expensive authentication transactions due to connectivity losses. We use packet traces from three different networks to compare the performance of the energy efficient security protocol with that of the standard 802.11 WLAN security protocol and show significant reduction in energy consumption.     

一种基于信噪比的自组网功率控制算法

能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,网络在实际应用中的节能效果不好.为了降低网络节点的能量消耗,在媒体接入层802.11协议基础上,,提出一种功率控制算法,以物理层信噪比为基础估计控制帧和数据帧的发送功率.通过OPNET网络仿真软件对算法进行了计算机仿真,仿真结果表明.相比802.11协议,算法有效降低了节点能量消耗,提高了能量利用率,延长了网络的生存时间,同时保持了网络的吞吐量性能,对自组网的理论研究和实际应用提供了一定的参考价值.     

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.     

一种由接收端发起的无线传感器网络MAC协议

在无线传感器网络(Wireless sensor networks,WSN)中,现有的基于接收节点发起的异步MAC层协议,在计算接收节点唤醒时刻时,多采用维持邻居节点的伪随机唤醒时间表的方法。在网络动态负载条件下,此方法不能动态地改变节点唤醒间隔,从而带来较高的数据传输冲突率及较大的数据传输延时。为了解决此问题,本文提出一种新协议HELD-MAC(High energy efficiency and　low delay MAC),保证节点之间具有不同的唤醒时间,同时能够准确预测接收端唤醒时刻,而且接收端可以根据网络负载情况动态改变唤醒间隔。同时为了减轻能量黑洞问题,协议根据节点的剩余能量,自适应地改变节点的最小唤醒间隔。通过仿真对HELD-MAC进行评估,与RI-MAC,PW-MAC等对比,在数据传输延时、能量消耗、网络吞吐量和传输碰撞方面具有较大优势。     

Mitigating collisions through power-hopping to improve 802.11 performance

In this article, we introduce a power-hopping technique (PH-MAC) that, by alternating between different transmission power levels, aims to deliberately cause packet capture and thereby reduce the impact of collisions in 802.11 WLANs. We first devise an analytical model of the 802.11 protocol with heterogeneous capture probabilities, and show that, depending on the network load, the capture effect can enhance the throughput performance of all nodes. We base the design of PH-MAC on the findings following from this analysis and demonstrate that important performance improvements can be achieved by exploiting the interactions between the MAC and PHY layers to mitigate collisions. Finally, to understand the feasibility of this technique in practical deployments, we present a prototype implementation of PH-MAC which relies on commodity hardware and open-source drivers. We evaluate the performance of this implementation in an indoor testbed under different network conditions in terms of link qualities, network loads and traffic types. The experimental results obtained show that our scheme can provide significant gains over the default 802.11 mechanism in terms of throughput, fairness and delay.     

Leveraging 802.11n frame aggregation to enhance QoS and power consumption in Wi-Fi networks

The Wi-Fi technology, driven by its tremendous success, is expanding into a wide variety of devices and applications. However, many of these new devices, like handheld devices, pose new challenges in terms of QoS and energy efficiency. In order to address these challenges, in this paper we study how the novel MAC aggregation mechanisms developed in the 802.11n standard can be used to enhance the current 802.11 QoS and power saving protocols. Our contribution is twofold. First, we present a simulation study that illustrates the interactions between 802.11n and the current 802.11 QoS and power saving protocols. This study reveals that the 802.11n MAC aggregation mechanisms perform better when combined with the power save mode included in the original 802.11 standard than with the 802.11e U-APSD protocol. Second, we design CA-DFA, an algorithm that, using only information available at layer two, adapts the amount of 802.11n aggregation used by a Wi-Fi station according to the level of congestion in the network. A detailed performance evaluation demonstrates the benefits of CA-DFA in terms of QoS, energy efficiency and network capacity with respect to state of the art alternatives.     

Enhanced AODV routing protocol for Bluetooth scatternet

Bluetooth is one of the most widespread technologies for personal area networks that allow portable devices to form multi-hop Bluetooth ad hoc networks, so called scatternets. Routing is one of the challenges in scatternets because of its impact on the performance of the network. It should focus on reducing the power consumption in the network because most of the nodes are battery-operated portable devices. In this paper, we propose a routing protocol for Bluetooth scatternets that customizes the Ad hoc On-Demand Distance Vector (AODV) routing protocol by making it power-aware and suitable for scatternets. It enhances the AODV flooding mechanism by excluding all non-bridge slaves from taking apart in the AODV route discovery process. In addition, it improves the AODV route discovery phase by considering the hop count, the predicated node’s power, and the average traffic intensity for each node as metrics for best route selection. By removing HELLO packets, our protocol reduces the control packets overhead and the power consumption in network devices. Simulation results show that the proposed protocol achieved considerable improvements over other enhanced AODV protocols by increasing the data delivery ratio by 10.78%, reducing the average end-to-end delay by 8.11%, and reducing the average energy consumption by 7.92%.