【作者】 陈国铭；

【导师】 蒋铃鸽；

【作者基本信息】 上海交通大学 ， 电子与通信工程， 2008， 硕士

【摘要】 无线传感器网络综合了传感器、嵌入式计算、现代网络及无线通信、分布式信息处理等技术,能够通过各类集成化的微型传感器相互协作,实时监测、感知和采集各种环境或监测对象的信息,通过嵌入式系统对信息进行处理,并通过随机自组织无线通信网络以多跳中继方式将所感知信息传送到用户终端,从而真正实现“无处不在的计算”,可以广泛地应用于军事、环境科学、交通监控、智能建筑等领域,具有很大的科学意义和应用价值。目前,无线传感器网络许多相关技术内容仍然处于探索阶段,比如:网络协议设计、能源管理、数据传输安全性和可靠性等问题。因此,无线传感器网络有很大的研究意义。MAC协议控制着通信信道的分配,处于网络协议的底层部分,对网络的性能有较大的影响,是无线传感器网络的研究重点之一。针对无线传感器网络的特点,MAC协议的设计要尽可能地降低能耗来提高网络的生存时间,同时兼顾时延和吞吐量。另一方面,相对于有线网络,无线网络频谱资源有限,存在高误码率。传统的严格分层设计方法不能很好地适应无线通信的特点,没有充分利用网络资源以实现最优的性能。近年来无线传感器网络的跨层优化设计也成为了研究的一个新的热点,不少学者提出利用不同层次间的信息交互设计网络通信协议。本文从无线传感器网络MAC协议和跨层优化的角度出发,进行了如下研究:第一,分析了无线传感器网络区别于其它传统网络的本质不同,无线传感器网络的节点使用电池供电,具有能量受限性质。指出MAC协议设计时要考虑的各个因素,包括网络生存期,能量利用率,端到端时延,吞吐量等。在对已有MAC协议进行分类的同时,指出各个协议的优缺点,从而为设计新的MAC协议打下坚实的基础。第二,分析了无线传感器网络典型的MAC协议-SMAC协议的不足之处,在此基础上,为了减小网络延时,提高能量利用率,提出一种新的无线传感器网络MAC协议-流量自适应的MAC协议(TA-MAC)。SMAC协议采用固定的占空比机制,而TA-MAC以队列中排队的分组数目来预测网络流量的变化,在侦听睡眠周期结构中采用了流量自适应的占空比调整机制。当网络流量较大的时候,把一个长的侦听睡眠周期分成几个短的周期,从而提高占空比,在一个长周期内发送更多的数据。同时利用自适应侦听机制,使一个分组在一个周期内能传送两跳的距离,减小了时延。仿真结果验证,TA-MAC减小了时延,降低了能量消耗。第三,从负载均衡,延长网络生存期的角度出发,提出了一种新的无线传感器网络MAC协议-基于节点剩余能量的无线传感器网络MAC协议(REA-MAC)。该协议改进了SMAC的竞争退避机制,首先是采用了动态竞争窗口调整的方法,节点在发生冲突时扩大竞争窗口大小,在发送成功时恢复到最初的竞争窗口大小,从而可以更好地减小冲突。其次考虑了节点的剩余能量来动态选择竞争退避时间,让剩余能量大的节点获得接入信道的控制权,而让剩余能量小的节点只发送自己采集的数据,尽量避免数据转发的任务,从而使全网负载均衡,延长了网络生存期。仿真结果验证,REA-MAC比SMAC有效地延长了网络生存期。第四,论述了跨层优化的分类和研究进展,并提出对跨层优化研究方向的见解。在此基础上,提出了一种新的跨层优化设计协议,路由层利用物理层剩余能量的信息来进行路由的选择,使剩余能量大的节点尽可能地承担数据转发的任务,从而使全网负载均衡。MAC层利用路由层的信息来判断自己是否是此次通信的下一跳节点,如果不是,就可以直接进入睡眠,从而避免不必要的空闲侦听,达到节省能量的目的。理论分析和仿真结果验证,该跨层优化协议有效地降低了能耗。在最后部分,总结了全文,展望了未来的研究方向。更多还原

【Abstract】 Wireless sensor networks (WSN) are integration of techniques including sensor, embedded computation, networking, wireless communication and distributed computation. The small sensor nodes can collaborate to test, sense, collect and process the information of monitored objects and transfer the processed information to user via multi-hop wireless communication. WSN is regarded as a way to realize“ubiquitous computing”and it has a wide range of applications, such as military, environment monitoring, traffic monitoring, smart building, etc. WSN becomes a new research area and has a bright future in application. However, several technologies related to WSN are still explored, such as networking protocol, energy management, data transmition security and reliability, etc. Therefore, it’s meaningful to make scientific researches on WSN.MAC (Media Access Control) protocol is responsible for channel resource allocation. It is the underlying part of network protocols and plays an important role in the network performance. Therefore, it becomes an important research area in WSN. With regard to the specific feature of WSN, the design of MAC protocol aims to reduce energy consumption as much as possible to prolong the network lifetime. Meantime, end to end delay and throughput should also be taken into consideration. On the other hand, compared to wired network, wireless network has limited spectrum resource and high bit error rate. Traditional layered protocol design can’t meet the demands of wireless communication, since it hasn’t fully utilized network resource to optimize the performance. Recently, the cross-layer optimization of WSN is becoming a hot research topic, the ideas of designing network protocols by sharing information among different layers have been proposed in many works. In this paper, mainly focus on the MAC protocol design and cross-layer design, some discussions and new designs are presented as follows:The main difference between WSN and traditional networks is proposed. The considerations to design MAC protocols are discussed. Sensor nodes use batteries for power supply, so they are power limited. When designing a MAC protocol, several points should be considered, such as network lifetime, energy efficiency, end to end delay, throughput, etc. The existing MAC protocols are classified and both the advantages and disadvantages are analyzed. Finally, some future possible research fields of MAC protocols are proposed.SMAC, the typical MAC protocol in WSN, is analyzed and the disadvantage of SMAC is discussed. Based on SMAC, in order to decrease network delay and improve energy efficiency, a new MAC protocol in WSN named traffic adaptive MAC protocol (TA-MAC) is proposed. SMAC adopts a static duty cycle mechanism, while in TA-MAC, traffic variation is predicted based on the number of packets queued. The traffic adaptive duty cycle scheme in the listen-sleep schedule is adopted. When the network traffic becomes busy, the long listen-sleep cycle is divided into several short cycles, thus the duty cycle is increased and more packets are transmitted during one long listen-sleep cycle. The adaptive listening scheme is also adopted, one packet can be transmitted further to two hops in one basic cycle, and thus the latency is reduced. Simulation results show that TA-MAC can obtain lower latency and reduce energy consumption.Focus on the network load balance, a residual-energy aware MAC protocol (REA-MAC) for wireless sensor networks is proposed. REA-MAC modifies the contention mechanism of SMAC. First, dynamic contention window adjustment mechanism is adopted. The size of contention window is increased when there is a collision and returns to the initial value when the packet is delivered successfully, therefore, the probability of collision is decreased. Second, REA-MAC takes the node’s residual energy into consideration to select the deferring time adaptively and let the nodes that have more residual energy to access the channel with priority. The nodes with less residual energy only need to send the data sensed while avoiding the task of packet delivery, thus the network load is balanced and the network lifetime is prolonged. Simulation results show that, compared to SMAC, REA-MAC can prolong network lifetime effectively.Then, the present research of cross-layer design is discussed and future research fields about cross-layer design are proposed. Based on the analysis, a new cross-layer design is proposed. The residual energy information of physical layer is utilized by routing protocol to select a proper route. The nodes with more energy are selected to handle the task of relaying packets, thus the network load is balanced. The information of routing table is utilized by MAC protocol to judge whether I am the next hop of this communication, if not, go to sleep directly. Thus unnecessary idle listening is avoided and the energy consumption is reduced. Simulation results and theoretical analysis show that this cross-layer scheme can reduce energy consumption effectively.At the last part of this dissertation, the whole work of the dissertation is outlined and the further research issues are discussed.更多还原