Study On The Performance Of Bluetooth ACL Link Based On Retransmission

Bluetooth technique is an open global standard of wireless data and voice communication, which can help to easily implement wireless transmission among personal digital devices. Bluetooth has many advantages, such as low cost, low power consumption, small size, free spectral bandwidth and short communication distance. It can be used for voice communication, data communication, electronic devices connection and information automatic exchange.Although Bluetooth has so many advantages, it is not perfect and still need to be improved. Some techniques in Bluetooth are not the most advanced in the telecommunication area. The goal of Bluetooth is to be universal, cheap and compact in structure, therefore it do not focus on the advanced property of the technologies that are in use. Taking error correction encoding for example, Bluetooth employed 1/3 rate repetition code, 2/3 rate hamming code instead of convolutional codes with which the coding rate is the same, Turbo code and or other more advanced ways of encoding. ARQ are mainly simple "stop and wait " schemes in the baseband. The users always hope to choose more advanced techniques which can utmostly raise the performance.The data flow passes through L2CAP layer, HCI, baseband layer and RF layer step by step when data is transmitted on Bluetooth ACL. The fragmentation and recombination and data transfer between higher layer and lower layer are normally done in the L2CAP layer. The baseband layer is in charge of processing the data flow before transmitting, which can guarantee the reliability of the data. Finally the data is transmitted by RF circuit. The inverse procedure is used to receive the data. The goal of this thesis work is to do research on the data processing in each layer, analyze and correct the existing problems in order to improve the performance of the high data rate Bluetooth transmission.The creativity of the thesis work can be conclude in 3 aspects:1. One method to solve the problem about uncertainty channel quantity is presented. This method is to use the numbers of Retransmission to estimate the Bluetooth physics channel.2. One algorithm about adaptive packet selection is introduced in the baseband layer. The numbers of repeated transmission is used in this algorithm in order to achieve packet selection and real time channel quantity track.3. In the L2CAP layer, a scheme to deploy two L2CAP logical channel for one data flow is presented. A new select repeat scheme that can achieve two L2CAP format coalescent, increase the efficiency of data repeat transmission and reliability of data transmission is also introdruced.The thesis work can be organized in 6 parts:Part 1 is the introduction of the Bluetooth. It introduce the application area and future of the Bluetooth, analyze the current situation and problem of the research work. Finally how to organize the thesis work is presented.Part 2 is the analysis of the Bluetooth protocol standard. It simply analyze the Bluetooth protocol, which can help to deepen the understanding of the core technique of Bluetooth.The first two part is the basic theory of this thesis work.Patr 3 is the study about Bluetooth low layer data transmission. In the chapter, we carefully analyze Bluetooth ACL data transmission and data processing over baseband layer and HCI. The data is transmitted in the format of baseband packet. Bluetooth can define many formats of packet. In the baseband layer, error check, correct and retransmission are used to ensure the reliability of the data.Part 4 is the study on the data transmission in the L2CAP layer and the basics of L2CAP. There are three work formats in L2CAP layer: basic mode, retransmission mode and flow control mode. When working on the basic mode, the L2CAP layer does not ensure the reliability, so this mode is not good for the requirement of the high transmission quantity. Then we also study about the data transmission on retransmission mode and flow control mode in detail. The way to improve repeat of L2CAP is introduced.The Part 3 and Part 4 mainly focus on the process of the ACL link data transmission and analysis of the factors that can affect the transmission performance. These two Parts are the basis of the improvements that will be introduced in the following chapter.Part 5 which is the core part of this thesis work introduces a algorithm that can improve the performance of ACL data transmission. On the basis of the analysis that is presented in the above Parts, Pare 5 introduces a adaptive packet selection scheme that is based on the numbers of repeat and a algorithm about selective repeat in L2CAP layer. First, adaptive packet selection scheme, Bluetooth protocol 1.2 define six formats that is guaranteed for reliability. We analyze the relation between these data packets repeat probability and bit error probability (BER) , derive the average data rate that should be achieved in the case of different BER, and present a adaptive packet selection scheme that is based on the numbers of repeat. This algorithm is to get the numbers of repeat in the decision time and then derive the threshold of the number of repeat for packet type switching. By comparing these two values, we can get the best packet. This algorithm solves the problems that are coused by uncertainty channel quantity and is suitable for unsteady channel. The algorithm implements the transition from theory to practice. The simulation results and analysis are presented to show the validity and simplicity of the algorithm. Then a algorithm about selective repeat in L2CAP layer is introduced. In the algorithm, the feature that Bluetooth L2CAP support several logical channels combine with retransmission mode and flow control mode can configured two logical channels, data channel and repeat channel for one data flow. The data channel is working under flow control mode to transmit the data in order. When the repeat transmission is needed, the data channel is switching to the repeat channel. The repeat channel is working under repeat format which repeat window number is 1. When the repeat transmission is done, the channel is switched to data channel. The cooperation between two channels can achieve selective repeat. The simulation results and analysis also indicate that the algorithm is easy to implement and has good system throughput, then increase the efficiency.Conclusions and possible future research directions are discussed in Part 6. The problems of Bluetooth transmission that need to be solved are presented as well.