无线传感器网络同步与接入技术研究
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摘要
鉴于无线传感器网络(WSN, Wireless Sensor Networks)的快速部署、分布式协同工作、成本低廉等特点，学术界和工业界已经对WSN进行了广泛研究。由于节点功耗限制、分布式信息处理以及无线信道等因素的制约，作为WSN关键支撑技术的节点精确时钟同步和高效介质访问控制协议仍未得到很好的解决。如何保证无线传感器节点的有效接入，优化任务分配及提高服务质量便成了首要解决的问题。首先，时钟同步技术是组网及构建协议的基础；其次，随着移动无线传感器网络（MWSN，Mobile Wireless Sensor Networks）受到越来越多的关注，大量节点同时接入网络的增强技术和提升MWSN的移动节点接入效率问题也必须得到很好的解决。
针对上述问题，本文从四个方面研究WSN的同步和接入增强技术：基于分组信令交互式的时钟同步协议设计；基于博弈论的多节点并行接入单信道的控制策略；基于移动性感知的移动节点的接入问题；基于时隙利用率最大化的时隙分配策略。具体研究内容如下：
研究了WSN中的分布式时钟同步问题。考虑无线传感器网络的同步开销以及实现条件，分析比较了现有分布式时钟同步算法存在的问题，在此基础上，提出了一种降低同步开销的分布式时钟同步算法。该算法首先建立一对同步节点，然后通过该对同步节点广播消息，使位于该对节点广播域内的所有节点同步，接着建立一个树形结构（具有双根节点）将算法扩展到整个网络。仿真结果表明所提出的算法能够有效地降低整个网络的同步开销。
研究了单信道内多节点并行传输问题。基于干扰感知的接收信干比模型，将网络中多个节点随机并行接入同一信道的控制决策过程建模为信道接入博弈。随后，求解此博弈的纳什均衡解作为传输门限，并提出一种单信道多节点并行传输策略。仿真结果表明并行传输门限可根据活动节点数、互扰比、传输成本及无线接收机的灵敏度自适应调整。本策略允许多个节点在单信道内并行传输，在提高网络吞吐量的同时降低了能量消耗和通信开销。
研究了WSN中提升移动节点的接入效率问题。为解决移动节点连通性较弱的问题，提出一种提升移动节点连通性的保障时隙(GTS, Guaranteed Time Slot)分配策略。首先，采用卡尔曼滤波预测模型得到用户下一阶段位置；接下来，引入一种考虑速度、方向和相对移动性的节点移动程度界定方法，并在此基础上进行GTS预约优先级的初步确定；随后，根据移动节点对所预约时隙的使用反馈情况自适应调整预约优先级；最后，根据节点的优先级决定GTS时隙的使用顺序及额外预留时隙的使用权。仿真结果显示，提出的分配策略在具有不同移动性节点的网络中，能够提高移动节点接入的成功率，保证较低的分组平均传输时延及较高的分组投递率。此外，采用基于反馈机制的自适应预约优先级调整策略能够显著增加整个网络中已分配时隙的正确使用率。
研究了在中高速情况下节点快速接入路侧单元（RSU，Road Side Unit）的机制，并考虑车载无线传感器节点可持续供电的特点，在与IEEE802.15.4协议族兼容的条件下对传统WSN的超帧结构进行修改，提出使用带有优先级及反馈机制的GTS时隙分配方法，旨在保证车辆无线传感器网络应用环境下节点的快速接入。在给定时延要求、GTS时隙数和接入节点数条件下，分析时隙利用率上限，进一步优化所提出的接入方法。仿真结果表明所提出的算法由于对剩余时隙进行有效分配，实现了时隙的最大利用率，提高了网络吞吐量，并且保证了车载移动网络中业务的时延要求。
Wireless Sensor Networks (WSN), a technology exhibiting the characteristics ofrapid deployment, self-structuring network, and the ability to be remotely controlled,has not only generated much attention academically, but researchers from the public andprivate sectors have all been very interested. Contemporary research and developmentin this field has been rapid and intense. Limited by issues with node power consumptionand widely distributed information processing, accompanied by other issues withchannel mobility, some key supporting technologies of the WSN, such as thenode-precise clock synchronization technology and efficient medium access control(MAC) protocol have not yet been perfected. Therefore, to keep the accessibility ofwireless sensor node, optimize task dispatch and increase the service quality have beenput on the first priority to deal with; Furthermore, as the new technologies of MWSN(Mobile Wireless Sensor Networks) has been becoming increasingly popular, thetechnology of enabling massive nodes connected at the same time and increasing theefficiency of access rate of MWSN have to be developed as well.
Aimed at the resolution of these problems, this report will approach them throughfour aspects of research:(1) Synchronization protocols of clocks based upon packetinteractions or distributed synchronization signal process algorithm;(2) Employing asingle channel control strategy based upon Game Theory’s Multi-node parallel;(3)Resolving the issue based upon mobile perception’s mobile node.(4) A GuaranteedTime Slot (GTS) allocation scheme with delay requirement and slot utilizationguaranteed in vehicular sensor networks. Detailed results of the research report arecontained below.
The first topic of research was conducted on WSN’s distributed clocksynchronization problem. In regards to the synchronization accuracy, energyconsumption and other practical conditions of the clock synchronization mechanism,while making comparisons and analysis on a few existing problems of clocksynchronization algorithm within the field of area broadcasting, we have come across alow cost, multi-hop clock synchronization algorithm. This algorithm utilizes a pair ofnodes that have already been synchronized to transmit information to all peer nodes,thus synchronizing all nodes within the specific physical area. A tree structure with adual root node will be created to spread the algorithm throughout the network. Results from simulations have shown that under circumstances where synchronization accuracyis low and the suggested algorithm is able to effectively reduce the synchronizationcosts of the whole network.
Research was also conducted on problems with single-channel multi-node paralleltransmission. Based on the interface-aware model signal interference ratio, informationmay be assembled from multiple nodes using a stochastic parallel and into a singlechannel control strategy, modeling it into a channel access matrix. Afterwards, the Nashequilibrium of the matrix will be the network’s transmission threshold; this suggests atype of single channel multi-node transmission agreement that transmits all parallelinformation. Simulations have shown that an increase in throughput; transmissionthreshold can also be adjusted according to the activity of nodes, interface ratio,transmission cost and wireless receiver sensitivity. This strategy allows multiple nodesto transmit information in a single channel in parallel: lowing costs while increasingnetwork throughput.
The next topic of research was conducted on problems with accessing mobilenodes in WSNs. To resolve the issue of weak signal within wireless sensor networks, wesuggest utilizations of a network of wireless sensor that contain multiple mobile nodes,in order to widen the GTS of the nodes connectivity. First, by using the Kalman FilterPrediction Model, the location of the user in the next stage of transmission could bedetermined. Next, introducing a type of cognitive speed and taking into considerationthe direction of the transmissions and their respective mobility, to calculate thereservation priority of each signal. The next step is in determining the most appropriatereservation sequences based on the feed backs of the appointed slots of mobile nodes.Lastly, determining the GTS’s order of use based on the priority level of each node, aswell as the utilization of all slack time. Simulations have shown that in a network thatcontains multiple mobile nodes, the suggested allocation strategy is able to improve therate of node successfully accessing the network while keeping failure rate at a lowerlevel even when there is high delay in node group delivery ratio. Furthermore, byutilizing a self adjusting reservation priority strategy based on a feedback mechanism,the accuracy of network time slot reservation priority can be significantly improved.
The final topic of our research was conducted on a GTS allocation scheme withdelay requirement and slot utilization guaranteed in vehicular sensor networks. TheIEEE802.15.4protocol can provide a flexible solution to support both real-time andcontention-based services. When beacon model is enabled, the Guaranteed Time Slot(GTS) scheduling can give a contention-free access to those latency-sensitive services based on time division multiple access mechanism. This characteristic makes IEEE802.15.4the appropriate candidate for vehicular sensor networks in which nodesgenerally should exchange packets with roadside units within given delay limitconsidering their mobility. We first analyze the relation between slots utilization andcorresponding access parameters, such as packets arrival rate, burst size and mobilitylevel etc. Then, for a given number of vehicles ready to access the roadside unit, wepropose a Time-Sensitive Weighted Round Robin scheduler with service delayrequirements, packets arrival rates and vehicles’ mobility levels into account. Bydetailed analysis to our scheduler, the weights setting method and time slots allocationstrategy is presented. Numerical results show the performance of transactions delayrequirement guarantee and GTS utilization maximization in Vehicular Sensor Networks.
针对上述问题，本文从四个方面研究WSN的同步和接入增强技术：基于分组信令交互式的时钟同步协议设计；基于博弈论的多节点并行接入单信道的控制策略；基于移动性感知的移动节点的接入问题；基于时隙利用率最大化的时隙分配策略。具体研究内容如下：
研究了WSN中的分布式时钟同步问题。考虑无线传感器网络的同步开销以及实现条件，分析比较了现有分布式时钟同步算法存在的问题，在此基础上，提出了一种降低同步开销的分布式时钟同步算法。该算法首先建立一对同步节点，然后通过该对同步节点广播消息，使位于该对节点广播域内的所有节点同步，接着建立一个树形结构（具有双根节点）将算法扩展到整个网络。仿真结果表明所提出的算法能够有效地降低整个网络的同步开销。
研究了单信道内多节点并行传输问题。基于干扰感知的接收信干比模型，将网络中多个节点随机并行接入同一信道的控制决策过程建模为信道接入博弈。随后，求解此博弈的纳什均衡解作为传输门限，并提出一种单信道多节点并行传输策略。仿真结果表明并行传输门限可根据活动节点数、互扰比、传输成本及无线接收机的灵敏度自适应调整。本策略允许多个节点在单信道内并行传输，在提高网络吞吐量的同时降低了能量消耗和通信开销。
研究了WSN中提升移动节点的接入效率问题。为解决移动节点连通性较弱的问题，提出一种提升移动节点连通性的保障时隙(GTS, Guaranteed Time Slot)分配策略。首先，采用卡尔曼滤波预测模型得到用户下一阶段位置；接下来，引入一种考虑速度、方向和相对移动性的节点移动程度界定方法，并在此基础上进行GTS预约优先级的初步确定；随后，根据移动节点对所预约时隙的使用反馈情况自适应调整预约优先级；最后，根据节点的优先级决定GTS时隙的使用顺序及额外预留时隙的使用权。仿真结果显示，提出的分配策略在具有不同移动性节点的网络中，能够提高移动节点接入的成功率，保证较低的分组平均传输时延及较高的分组投递率。此外，采用基于反馈机制的自适应预约优先级调整策略能够显著增加整个网络中已分配时隙的正确使用率。
研究了在中高速情况下节点快速接入路侧单元（RSU，Road Side Unit）的机制，并考虑车载无线传感器节点可持续供电的特点，在与IEEE802.15.4协议族兼容的条件下对传统WSN的超帧结构进行修改，提出使用带有优先级及反馈机制的GTS时隙分配方法，旨在保证车辆无线传感器网络应用环境下节点的快速接入。在给定时延要求、GTS时隙数和接入节点数条件下，分析时隙利用率上限，进一步优化所提出的接入方法。仿真结果表明所提出的算法由于对剩余时隙进行有效分配，实现了时隙的最大利用率，提高了网络吞吐量，并且保证了车载移动网络中业务的时延要求。
Wireless Sensor Networks (WSN), a technology exhibiting the characteristics ofrapid deployment, self-structuring network, and the ability to be remotely controlled,has not only generated much attention academically, but researchers from the public andprivate sectors have all been very interested. Contemporary research and developmentin this field has been rapid and intense. Limited by issues with node power consumptionand widely distributed information processing, accompanied by other issues withchannel mobility, some key supporting technologies of the WSN, such as thenode-precise clock synchronization technology and efficient medium access control(MAC) protocol have not yet been perfected. Therefore, to keep the accessibility ofwireless sensor node, optimize task dispatch and increase the service quality have beenput on the first priority to deal with; Furthermore, as the new technologies of MWSN(Mobile Wireless Sensor Networks) has been becoming increasingly popular, thetechnology of enabling massive nodes connected at the same time and increasing theefficiency of access rate of MWSN have to be developed as well.
Aimed at the resolution of these problems, this report will approach them throughfour aspects of research:(1) Synchronization protocols of clocks based upon packetinteractions or distributed synchronization signal process algorithm;(2) Employing asingle channel control strategy based upon Game Theory’s Multi-node parallel;(3)Resolving the issue based upon mobile perception’s mobile node.(4) A GuaranteedTime Slot (GTS) allocation scheme with delay requirement and slot utilizationguaranteed in vehicular sensor networks. Detailed results of the research report arecontained below.
The first topic of research was conducted on WSN’s distributed clocksynchronization problem. In regards to the synchronization accuracy, energyconsumption and other practical conditions of the clock synchronization mechanism,while making comparisons and analysis on a few existing problems of clocksynchronization algorithm within the field of area broadcasting, we have come across alow cost, multi-hop clock synchronization algorithm. This algorithm utilizes a pair ofnodes that have already been synchronized to transmit information to all peer nodes,thus synchronizing all nodes within the specific physical area. A tree structure with adual root node will be created to spread the algorithm throughout the network. Results from simulations have shown that under circumstances where synchronization accuracyis low and the suggested algorithm is able to effectively reduce the synchronizationcosts of the whole network.
Research was also conducted on problems with single-channel multi-node paralleltransmission. Based on the interface-aware model signal interference ratio, informationmay be assembled from multiple nodes using a stochastic parallel and into a singlechannel control strategy, modeling it into a channel access matrix. Afterwards, the Nashequilibrium of the matrix will be the network’s transmission threshold; this suggests atype of single channel multi-node transmission agreement that transmits all parallelinformation. Simulations have shown that an increase in throughput; transmissionthreshold can also be adjusted according to the activity of nodes, interface ratio,transmission cost and wireless receiver sensitivity. This strategy allows multiple nodesto transmit information in a single channel in parallel: lowing costs while increasingnetwork throughput.
The next topic of research was conducted on problems with accessing mobilenodes in WSNs. To resolve the issue of weak signal within wireless sensor networks, wesuggest utilizations of a network of wireless sensor that contain multiple mobile nodes,in order to widen the GTS of the nodes connectivity. First, by using the Kalman FilterPrediction Model, the location of the user in the next stage of transmission could bedetermined. Next, introducing a type of cognitive speed and taking into considerationthe direction of the transmissions and their respective mobility, to calculate thereservation priority of each signal. The next step is in determining the most appropriatereservation sequences based on the feed backs of the appointed slots of mobile nodes.Lastly, determining the GTS’s order of use based on the priority level of each node, aswell as the utilization of all slack time. Simulations have shown that in a network thatcontains multiple mobile nodes, the suggested allocation strategy is able to improve therate of node successfully accessing the network while keeping failure rate at a lowerlevel even when there is high delay in node group delivery ratio. Furthermore, byutilizing a self adjusting reservation priority strategy based on a feedback mechanism,the accuracy of network time slot reservation priority can be significantly improved.
The final topic of our research was conducted on a GTS allocation scheme withdelay requirement and slot utilization guaranteed in vehicular sensor networks. TheIEEE802.15.4protocol can provide a flexible solution to support both real-time andcontention-based services. When beacon model is enabled, the Guaranteed Time Slot(GTS) scheduling can give a contention-free access to those latency-sensitive services based on time division multiple access mechanism. This characteristic makes IEEE802.15.4the appropriate candidate for vehicular sensor networks in which nodesgenerally should exchange packets with roadside units within given delay limitconsidering their mobility. We first analyze the relation between slots utilization andcorresponding access parameters, such as packets arrival rate, burst size and mobilitylevel etc. Then, for a given number of vehicles ready to access the roadside unit, wepropose a Time-Sensitive Weighted Round Robin scheduler with service delayrequirements, packets arrival rates and vehicles’ mobility levels into account. Bydetailed analysis to our scheduler, the weights setting method and time slots allocationstrategy is presented. Numerical results show the performance of transactions delayrequirement guarantee and GTS utilization maximization in Vehicular Sensor Networks.
引文
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