远距离无线网状网性能优化和服务质量研究
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摘要
目前世界上超过40%的人口居住在乡村地区，提高这些地区的互联网覆盖率是个亟待解决的问题。传统的网络接入方式（如蜂窝基站、卫星等）存在造价和维护成本高昂等缺点，因此并不适用于这些地区。LDmesh网络（Long Distancewireless mesh networks）由多条长距离WiFi链路组成。该网络通过多跳的形式接入城镇互联网网关节点，可为乡村人口提供低廉、易维护的远程互联网接入方案。在每个村落，由多个（AP，Mesh Router）通信单元组成的本地CSMA/CAMesh网络为村民提供覆盖全村的互联网接入服务（数据流汇聚到该村的LDmesh节点）。然而LDmesh网络并未完善，存在着诸多的问题，如缺乏高效MAC协议、没有端到端QoS路由、缺少节点节能策略等。
音视频应用是LDmesh网络的主要业务。相对Best Effort业务，音视频业务对QoS要求较高。鉴于此，本文首先提出了基于多接口DSR协议的端到端QoS路由协议MQDSR。MQDSR使用MAR带宽约束模型对业务流执行准入控制，从而可以保证音视频业务的端到端吞吐率和可控的端到端延迟。仿真结果表明，对于基于时分复用MAC协议的LDmesh网络，MQDSR能为高优先级（如音频）和一般优先级（如视频）业务提供有保证的端到端QoS。
部署在乡村地区的LDmesh节点往往采用太阳能供电，因此节能是一个亟待解决的问题。本文分析了LDmesh链路的丢包特性和受干扰特性，提出了一个节点速率和功率联合调整算法。该算法通过监测链路干扰变化动态地调整发送速率和功率，从而能够在链路吞吐率和节点能耗间取得较优的平衡。户外实验结果表明，相比固定发送速率和功率的策略，该算法能够在保证链路具有较高投递率的同时有效地降低节点的能耗。
村庄内本地的CSMA/CA Mesh网络提供了可覆盖全村的无线接入。信道化技术（定义为节点自主的选择其物理层速率、发射功率、信道频率和信道宽度）可以提高该网络的容量或改善该网络的公平性。为了降低信道化所需的测量复杂度，本文引入了两个预测模型。针对对称载波侦听的情况，本文通过实验研究了信道化节点的载波侦听半径以及节点间载波侦听关系，扩展了节点发送能力的预测模型。在由6个802.11a节点组成的实验网络中，80%的预测结果所对应的误差小于10%。针对非对称载波侦听的情况，本文提出了相应的节点发送能力概率模型，实验结果表明该模型预测误差不超过8%。
Nowadays more than40percent of the world population is still living in ruralareas. How to increase the Internet penetration rate in those areas remains an issue.Conventional Internet access approaches, such as cellular connections, satellite links,are too expensive to be operational in terms of infrastructure construction andmaintenance. LDmesh (Long Distance wireless mesh) networks consist of multiplelong distant WiFi links, which are routed to the Internet gateways located in urbanareas through multi-hops. It has the capability of providing low cost, easymaintenance Internet access for rural inhabitants. In addition, at each village, thecommunication units (each consists of an AP and a mesh router) form the localCSMA/CA mesh network to provide multiple routes to the local LDmesh node.However, the LDmesh network is not perfect and has a couple of issues, such as thelack of high efficient MAC protocol design, end-to-end QoS routing, node energyefficiency, etc.
The main applications in LDmesh networks are VOIP and video conferencing,which require stringent end-to-end QoS guarantees in the face of fluctuating loss andavailable bandwidth variations. In view of this, we propose a MAR-basedmultiple-interface DSR protocol with end-to-end QoS support: MQDSR. MQDSRintegrates the MAR model and admission control into the multiple-interface DSR toprovide end-to-end throughput and delay guarantees. Simulation results show that inthe operation of the TDMA-type MAC protocol, MQDSR will be in favor of the highand normal priority classes (e.g. VOIP or video conferencing) to support betterend-to-end QoS than that of the best effort class.
LDmesh networks usually use solar energy as nodes are deployed in rural areas.In the dissertation, we at first perform outdoor experiments to understand the link lossand external interference characteristics of LDmesh links and then propose a joint bitrates and transmit power adaptation algorithm. The algorithm is able to achieve areasonable tradeoff between link throughput and energy consumption by dynamicallyadjusting bit rates and transmit power according to the interference fluctuation.Outdoor experiments show that, in comparison to the static bit rates and transmitpower schemes, the proposed algorithm is of great efficiency in energy savings with alittle compromise for link throughput.
Each LDmesh node deployed in a village is connected to a corresponding local CSMA/CA mesh network deployed in the same village. The local mesh networkprovides multiple routes to the corresponding LDmesh node for a complete Internetcoverage of the village. Channelization (defined as the act that each node is free tochoose its bit rates, transmit power, channel frequencies and channel widths) is able toimprove the network capacity or fairness. Two transmission capacity estimationmodels are introduced to further reduce the measurement complexity whenperforming flexible channelization. As for the symmetric carrier sensing, we at firstexperimentally investigate the carrier sensing range and the carrier sensingrelationship among nodes and then extend a transmission capacity model. A6-node802.11a testbed is used for performance evaluations, which show there is less than10%error in prediction for more than80%cases. For the asymmetric carrier sensing, wepropose a probabilistic model for nodes’ transmission capacity estimation showing theprediction error is less than8%by test-bed experiments.
音视频应用是LDmesh网络的主要业务。相对Best Effort业务，音视频业务对QoS要求较高。鉴于此，本文首先提出了基于多接口DSR协议的端到端QoS路由协议MQDSR。MQDSR使用MAR带宽约束模型对业务流执行准入控制，从而可以保证音视频业务的端到端吞吐率和可控的端到端延迟。仿真结果表明，对于基于时分复用MAC协议的LDmesh网络，MQDSR能为高优先级（如音频）和一般优先级（如视频）业务提供有保证的端到端QoS。
部署在乡村地区的LDmesh节点往往采用太阳能供电，因此节能是一个亟待解决的问题。本文分析了LDmesh链路的丢包特性和受干扰特性，提出了一个节点速率和功率联合调整算法。该算法通过监测链路干扰变化动态地调整发送速率和功率，从而能够在链路吞吐率和节点能耗间取得较优的平衡。户外实验结果表明，相比固定发送速率和功率的策略，该算法能够在保证链路具有较高投递率的同时有效地降低节点的能耗。
村庄内本地的CSMA/CA Mesh网络提供了可覆盖全村的无线接入。信道化技术（定义为节点自主的选择其物理层速率、发射功率、信道频率和信道宽度）可以提高该网络的容量或改善该网络的公平性。为了降低信道化所需的测量复杂度，本文引入了两个预测模型。针对对称载波侦听的情况，本文通过实验研究了信道化节点的载波侦听半径以及节点间载波侦听关系，扩展了节点发送能力的预测模型。在由6个802.11a节点组成的实验网络中，80%的预测结果所对应的误差小于10%。针对非对称载波侦听的情况，本文提出了相应的节点发送能力概率模型，实验结果表明该模型预测误差不超过8%。
Nowadays more than40percent of the world population is still living in ruralareas. How to increase the Internet penetration rate in those areas remains an issue.Conventional Internet access approaches, such as cellular connections, satellite links,are too expensive to be operational in terms of infrastructure construction andmaintenance. LDmesh (Long Distance wireless mesh) networks consist of multiplelong distant WiFi links, which are routed to the Internet gateways located in urbanareas through multi-hops. It has the capability of providing low cost, easymaintenance Internet access for rural inhabitants. In addition, at each village, thecommunication units (each consists of an AP and a mesh router) form the localCSMA/CA mesh network to provide multiple routes to the local LDmesh node.However, the LDmesh network is not perfect and has a couple of issues, such as thelack of high efficient MAC protocol design, end-to-end QoS routing, node energyefficiency, etc.
The main applications in LDmesh networks are VOIP and video conferencing,which require stringent end-to-end QoS guarantees in the face of fluctuating loss andavailable bandwidth variations. In view of this, we propose a MAR-basedmultiple-interface DSR protocol with end-to-end QoS support: MQDSR. MQDSRintegrates the MAR model and admission control into the multiple-interface DSR toprovide end-to-end throughput and delay guarantees. Simulation results show that inthe operation of the TDMA-type MAC protocol, MQDSR will be in favor of the highand normal priority classes (e.g. VOIP or video conferencing) to support betterend-to-end QoS than that of the best effort class.
LDmesh networks usually use solar energy as nodes are deployed in rural areas.In the dissertation, we at first perform outdoor experiments to understand the link lossand external interference characteristics of LDmesh links and then propose a joint bitrates and transmit power adaptation algorithm. The algorithm is able to achieve areasonable tradeoff between link throughput and energy consumption by dynamicallyadjusting bit rates and transmit power according to the interference fluctuation.Outdoor experiments show that, in comparison to the static bit rates and transmitpower schemes, the proposed algorithm is of great efficiency in energy savings with alittle compromise for link throughput.
Each LDmesh node deployed in a village is connected to a corresponding local CSMA/CA mesh network deployed in the same village. The local mesh networkprovides multiple routes to the corresponding LDmesh node for a complete Internetcoverage of the village. Channelization (defined as the act that each node is free tochoose its bit rates, transmit power, channel frequencies and channel widths) is able toimprove the network capacity or fairness. Two transmission capacity estimationmodels are introduced to further reduce the measurement complexity whenperforming flexible channelization. As for the symmetric carrier sensing, we at firstexperimentally investigate the carrier sensing range and the carrier sensingrelationship among nodes and then extend a transmission capacity model. A6-node802.11a testbed is used for performance evaluations, which show there is less than10%error in prediction for more than80%cases. For the asymmetric carrier sensing, wepropose a probabilistic model for nodes’ transmission capacity estimation showing theprediction error is less than8%by test-bed experiments.
引文
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