【作者】 张韬；

【导师】 陈道蓄；

【作者基本信息】 南京大学 ， 计算机软件与理论， 2012， 博士

【摘要】 无线传感器网络将物理世界和信息世界相互联系,极大的丰富了计算机获取信息的方式。在军事、医疗、环境监测、智能家居等领域有着广阔的应用前景,被各方面广泛关注。传感器网络由传感器节点通过自组织形式组成网络,需要有高效的网络通信机制支持。传统自组织网络的研究侧重于提供高质量的服务和高效的带宽利用,其次才是考虑节约能源。而在传感器网络中,节约能源是首要目标。因此,需要提出新的解决方案,以适应传感器网络对低能耗通信的需要。我们在底层设计了MAC层的节能协议,在MAC层和路由层通过跨层设计的方式研究大规模数据采集网络中的节能通信协议,并对建筑安全监控中利用电梯进行数据传输以节约能耗的问题进行了研究,从传感器网络通信的不同层次对节能问题进行了探索。本文在传感器网络低能耗网络通信方面作出如下贡献：(1)针对低功耗MAC协议中的广播策略进行研究,提出适合于无线传感器网络的MAC层低功耗广播协议。各节点采用异步休眠的方式节约能耗。在传输广播数据时,以动态变化的时间间隔进行数据重传。使得邻居节点在唤醒时能够接收到数据传输的同时降低了广播能耗。而每次重传的时间间隔有一定的随机性,可以有效减少由隐藏节点造成的传输冲突,提高广播传输的成功率,大幅降低因报文冲突而造成的报文丢失和额外监听能耗。我们在MICAz节点上实现了本协议的原型,进行了初步验证,并在NS-2模拟环境中进行了深入的实验。实验结果验证了本协议能够有效应对网络中的广播报文冲突问题,提高报文的接收成功率,降低报文冲突造成的额外能量消耗。(2)针对数据采集应用中的高效低能耗传输问题,我们通过MAC层和路由层的跨层设计与优化,提升通信协议整体性能。在MAC层,我们采用低功耗监听策略,令节点以异步的方式定期休眠以节约能耗。我们在MAC层实现了任播机制,任意满足指定条件的节点都可以作为目标节点接收数据,数据将被其中最早唤醒的节点接收。路由层在选择下一跳目的节点时,对各节点到基站的延迟进行估测,在发送数据时选择估测延迟较低的若干节点作为下一跳目标进行发送。基于休眠机制的节能协议的共同点是以一定的延迟换取较好的节能效果。我们对MAC层和路由层进行跨层设计,可以使得付出的延迟代价大幅降低。实验表明,我们的协议能够有效减小延迟代价。并且在越大规模的网络中,能耗和延迟越小。(3)针对高层建筑安全监控的应用,我们提出一种利用电梯移动进行数据采集的传输策略。在电梯上放置一个基站节点,随着电梯的运行移动。每层部署一个传感器节点,在电梯经过或停靠在该楼层时,以较小的功率将采集到的数据传输至电梯基站。在保证数据能够及时传输至基站的条件下,将此问题建模为一个最大化系统寿命的优化问题。当电梯的移动可以完全预测时,该问题可以获得最优解。但是当电梯运行轨迹不可预测时,任意在线算法所生成的调度策略,都不能达到采用最优解的相对近似度。我们对一定时间段内电梯的运行进行预测,根据不同的预测能力进行数据传输的调度,以达到延长网络寿命的目的。通过一系列的模拟实验和MICAz节点平台的实验,对不同条件下的系统性能进行了验证。实验结果表明,相较于传统多跳传输,以及不经过调度简单等待电梯的算法,我们的数据采集算法可以获得较长的系统寿命。更多还原

【Abstract】 Wireless sensor networks bridge the gap between physical world information and digital world, enhance the data collection ability of computer, and open up a broad application prospect for the fields of military, medicine, environment moni-toring, intelligent home system and so on, and cause wide concern. The sensors in the sensor networks are connected wirelessly with ad hoc mode. Efficient communi-cation supports are needed to build network. The researches on traditional ad hoc networks focus on better service quality and higher throughput. The key issue of wireless sensor networks is energy efficiency. So, efficient communication strategies with low energy consumption are required. We design transmission scheme for MAC layer, cross-layer between MAC and route layer, and special scenario in structural health monitoring. In this paper, we make the following contributions to energy efficient communication for wireless sensor networks:(1) We have designed an asynchronous duty cycle based MAC layer broadcast protocol for wireless sensor networks. The sender repeats the broadcast packets with dynamic interval. The repeated transmissions would make the period sleeping neighbors receive the packet when they wake up. The dynamic interval would reduce the packets collision caused by hidden nodes problem. We implement our scheme in MICAz motes to validate the applicability. We also have performed further experi-ments with NS-2simulation environment. The results show that our protocol could deal with packet collision well. The extra power consumption caused by collision is reduced and the data reception ratio is enhanced.(2) We have proposed a cross layer designed communication protocol for data collection in wireless sensor networks. In the MAC layer, we inherit the low power listening approach to save the power consumption. Instead of single target adopted in traditional MAC protocol, the sender could select multi-nodes to be the candidate targets and transmit the data to the node that wakes up first. In the route layer, we evaluate the latency from each node to sink and select the nodes with low latency to be the next hop targets. The sleeping based energy efficient protocol trades high latency for low energy consumption. Our work could achieve lower energy consumption with much less latency introduced. The experiments shows the energy consumption and latency are lower than state of art sleeping based energy efficient protocols. Our protocol is much efficient in large scale network.(3) We have introduced a novel scheme of using the elevators to assist data collection for wireless sensor networks used in structural health monitoring applica-tion. A base station is attached to an elevator. A representative node on each floor collects and transmits the data to the base station using short range communication when the elevator stops at or passes by this floor. We formulate the problem as an optimization problem where the data traffic should be transmitted on time and the lifetime of the sensors should be maximized. We show that if we know the movement pattern of the elevator in advance, this problem can be solved optimally. We then study the online version of the problem and show that no online algorithm has a constant competitive ratio against the offline algorithm. We show that knowledge of the future elevator movement will intrinsically improve the data collection per-formance. We discuss how the information could be collected and develop online algorithms based on different level of knowledge of the elevator movement patterns. A comprehensive set of simulations and MICAz testbed experiments have demon-strated that our algorithm substantially outperforms conventional multi-hop routing and naive waiting for elevator scheme.更多还原