【作者】 李萌；

【导师】 范亚芹；

【作者基本信息】 吉林大学 ， 通信与信息系统， 2012， 硕士

【摘要】 蓝牙技术作为短距离无线通信技术中的代表性技术，在生产生活中得到了广泛的应用。由于蓝牙技术以低功耗、小体积、便捷互联作为技术特色，其协议中定义的许多技术并不是最先进的，这就使得蓝牙在通信质量不好的情况下数据吞吐量受影响。因此，在蓝牙技术得到大规模应用的背景下，研究改善蓝牙数据吞吐量的方法是很有意义的。本文从介绍蓝牙协议规范入手，详细讲述了蓝牙协议栈的各层要完成的功能，重点分析了基带层和L2CAP的数据传输机制。在此基础上，本文对现有的其他改进方法进行了总结，通过具体的实验验证，对各种方法的优劣进行了总结。针对于现有算法中存在的不足之处，本文在基带层和逻辑链路控制与适配层分别提出了改进策略。在基带层，以不改变蓝牙协议为前提的分组自适应选择策略大都假设信道质量为已知量，但实际应用中该值并不是已知的。之前有相关文献提出了判断信道质量的方案，但本文通过分析发现该方法在估计信道质量时效率不高。本文针对这个问题，提出了一种基于SNR估计的分组自适应选择策略。蓝牙系统接收端通过对接收到的分组进行统计，利用M2M4方式估计信道的当前信噪比。根据信噪比值的大小，接收端可确定当前最适合信道传输的分组类型，并将该分组类型的信息写入L2CAP层的PDU中告知发送端，从而实现了分组的自适应选择。该策略可以实时的监督信道状态，使得收发双方一直使用最佳数据分组，从而取得较高的数据吞吐量。仿真结果证明，接收方只需要几个蓝牙基带层分组就可以估计出信道的信噪比，且估计误差在0.2dB内。在逻辑链路控制与适配层，现有的回退N帧机制在信道质量较差的情况下会因重传过多的数据帧导致吞吐量下降，存在改进空间。在不改变蓝牙协议栈的前提下，可以在该层实现选择重传，能极大的提高数据吞吐量。但经分析发现，选择重传机制需要接收方有很大的缓存区并需要在数据帧中增加一个序号来对分段后的数据帧进行区分，因而给系统带来额外开销。本文针对这个问题，提出了一种动态传输窗口控制方法。通过对回退N帧重传机制的研究，推导了数据吞吐量的表达方式，证明了改变传输窗口可以带来数据吞吐量的提升，并给出了具体的传输窗口选取方法。仿真结果证明，改进后的回退N帧重传机制的吞吐量相对于蓝牙原来的重传机制有较大提升。相对于选择重传机制，该策略几乎不会对蓝牙系统带来额外的开销，因而更具有应用价值。综上，本文在基带层和逻辑链路控制与适配层分别提出了一种策略来改进蓝牙系统的数据传输吞吐量。基带层通过更及时、更准确的判断信道质量来选择最佳传输分组，逻辑链路控制与适配层在几乎不增加系统额外开销的情况下对重传机制进行了改进，两种策略都未对蓝牙协议作出修改，因而在实际应用中不会受到限制。更多还原

【Abstract】 As a typical short-range wireless communication specification, Bluetooth has beenwidely used in a big variety of fields. It has many advantages such as low power, smallsize and convenient to communicat with each other. A Bluethtooth system may performnot well enough in data throughput so even as to cause reduction of the throughput whencommunication quality is not very good. The leading reason of this matter is that theadvantages of Bluetooth mentioned above on the other hand constrain its throughput, ortechnology defined in the Bluetooth specification is not state-of-the-art. Obviously, it isimportant to explore some methodologies to improve throughput between two Bluetoothdevices in bad channel quality condition.This paper firstly introduced the Bluetooth protocol specification, then discussed thefunction of each layer in the procotol stack in detail, especially the data transmissionmechanism in baseband layer and L2CAP layer. Other improvement methods in bothbaseband layer and L2CAP layer were also summarized in this paper. Simulationexperiment was done to illustrate the advantage and the drawbacks of each method aswell. According to the existing problems, the author gave out improvement strategy inboth baseband layer and L2CAP layer.On baseband layer, adaptive packet selection strategy was a sort of approach whichdid not change the Bluetooth procotol stack. But this approach assumed that the channelquality was already known to the system which was in fact unknown in thecommunication of the two Bluetooth devices. Although some literature gave out methodsto change paceket type according to the retransmission times, but most of the researchhad low efficiency.To solve this problem, an adaptive packet selection strategy based onSignal-to-Noise Radio (SNR) estimation was presented in this paper. The receiving sideof Bluetooth system used two-order and four-order moments estimation algorithm toestimate the channel quality, thus the receiver could know which packet type was the bestfor the channel and told this packet type to the transmitting side throuth PDUs in L2CAP layer. This strategy could supervise the channel quality in real-time. Simulation provedthat this strategy could control the estimation errors within0.2dB by using only a fewBluetooth baseband packets.On L2CAP layer, the go-back-N ARQ mechanism could lead to throughputdropping attribute to a lot number of retransmission when the channel quality was not sogood. Selective repeat ARQ mechanism could greatly increase the throughput, but thisstrategy needed enormous buffer size in the receiver and added a sequence number todata frame to discriminate the frame because it might be segmented. So the Bluetoothdevice had to spend extra expense to achieve this strategy.To solve this problem, a dynamic transmission window control method waspresented in this paper. The expression of Bluetooth’s data throuthput under go-back-Nmechanism was put forward, which proved that the change of the transmission windowdid have the function of improving the data throuthput. Furthermore, this expressioncould be used to determine the size of the transmission window. Simulation resultsproved that the throughput of advanced go-back-N ARQ mechanism had improvd datathroughput greater than the previous Bluetooth retransmission mechanism. Moreover,this strategy brought slightly expense to Bluetooth system compared with selective repeatARQ mechanism, so it had more application worth.In summary, methods to improve the data throuthput of Bluetooth system arepresented in both baseband layer and L2CAP layer in this paper. The strategy inbaseband layer is proved to be more efficiency and more accurate than existing methods.The strategy in L2CAP layer can improve the data throughput with little expense addedto the system. Both strategies make no change to the Bluetooth procotol stack, so theyare not restricted to be used to applications.更多还原