摘要
IEEE802.11是现在最普及的无线标准之一,它在无线局域网(WLAN)领域已经占据绝对优势。根据IEEE802.11g标准,在2.4GHz频带上可以实现最大54Mbit/s的数据传送,对WLAN的发展起到了很大的推动作用。
本论文的研究是依托国家发改委示范工程项目下一代互联网无线接入终端进行的,本课题的目标是实现IEEE802.11 MAC层基本功能,可以和PHY层联调最终实现无线接入终端。而且研究IEEE802.11协议,对于研究无线局域网技术,开发拥有自主知识产权的无线网络产品具有重要的现实意义。
课题选择嵌入式实时操作系统μC/OS-II作为课题的软件平台,并选用三星公司生产的一款基于ARM920T核的高性能低功耗SOC芯片S3C2410作为MAC层实现的硬件平台。因此,本文对μC/OS-II进行了简单的介绍和分析,并对μC/OS-II在ARM上的移植做了简单介绍。
本文分析了MAC层系统的构成,根据系统框图、各模块功能以及嵌入式系统划分任务的H.Gomma原则,将系统按照发送和接收部分分别划分了6个任务,不同任务之间通过消息队列进行通信。其中发送部分的任务有:MSDU_from_LLC、PrePare_MPDU、PM_Filter_STA、Tx_Coordiantion、Backoff_Procedure和Data_Pump。接收部分的任务分别是:Channel_state、Validate_MPDU、Filter_MPDU、Defragment、Rx_Coordination和MSDU_to_LLC。
根据系统各模块的功能,以及所选嵌入式操作系统μC/OS-II的任务调度机制,给系统划分的任务分配了不同的优先级,并且分别绘制了各模块的软件实现的设计流程图。
出于对整个软件系统的统筹规划以及以后MAC协议系统的整体实现的考虑,将多个任务都会调用的算子函数或是整个系统需要的数据类型单独定义,并按照算子函数的不同功能分类整理编写对应的.C或.H文件。
最后根据任务划分、任务优先级等编写了整个MAC层的程序以及调试程序,并将所有程序移植到ARM上调试。通过串口返回消息,得到程序运行的结果,并分析了结果。从调试的结果可以看出,本文实现了IEEE802.11 MAC层协议的主要功能,为实现整个下一代互联网无线接入终端项目奠定了良好的基础。
IEEE802.11 is now the most popular wireless Standard, it has occupied absolute superiority position in the wireless local area network (WLAN) field.In accordance with IEEE802.11g Standard,in the 2.4 GHz band,we can achieve maximum 54 Mbit / s data transmission rate, it has played a great role in promoting the WLAN Development.
This study is based on the National Development and Reform Commission demonstration‘s project : next generation of wireless Internet access terminal.The project's goal is to implement a basic modules of MAC layer which can be debugged together with the PHY layer implemented by another team of Chongqing University. Research on IEEE802.11 protocol has important practical significance for studying wireless LAN technology and the development of its own intellectual property rights wireless networking products.
RTOSμC/OS-II was chosen as the software platform.,while for the hardware platform, S3C2410,a high-performance low-power SOC chip based on the ARM920T core ,which is a production of Samsung company ,was chosen.Therefore, this paper gives a simple description and analysis forμC/OS-II, and how to transplantμC/OS-II in the ARM was discussed too.
This paper analyses the system of the MAC layer, according to the system diagram, the module functions and H. Gomma principle which is the principle in divding the embedded systems, the system was divided into 6 missions as for both transmission and receptionpart .The 6 missions for transmission are as below: MSDU_from_LLC, PrePare_MPDU, PM_Filter_STA, Tx_Coordiantion, Backoff_Procedure and Data_Pump. While for reception part , the 6 missions are: Channel_state, Validate_MPDU, Filter_MPDU, Defragment, Rx_Coordination and MSDU_to_LLC.
According to the system functional module, and the selected embedded RTOSμC/OS-II‘s task scheduling mechanism, different mission was assigned a different priority, and the software design flow of the module were drawn too.
For the entire software system and the overall planning system the implement of the MAC protocol system, the author defines the data or functions which will be use by multiple tasks solely.And in accordance with the operator function of the different functions the author wrote the corresponding. C or. H documents.
Finally the procedures of all the missions of the MAC layer and the debugging procedures were finished ,and then transplanted into ARM for debugging.The debugging result was sent back by the serial port ,and was analyzed. According to the results, the paper has implemented the principal functions of IEEE802.11 MAC layer, and it was a good foundation for implementing the project :next generation of wireless Internet access terminal
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