无线接入网《宽带通信网课件-CH6》 - 图文(5)

IEEE 802.11特性列表标准频率（RF）红外线（IR）传输机制最大速率（Mb/s）802.11802.11802.11802.11a802.11b802.11g2.4GHz2.4GHz850-950nmDSSSFHSS222541154Diffuse IR5GHzOFDM2.4GHzDSSS速率与2.4GHzOFDM ,802.11b/a兼容DSSSDiffuse：散播、漫播2013-7-30Dr. ZhanqiXU,National Key Lab on ISN, Xidian University21IEEE在WLAN方面的进展,WWW.Ieee.org, WWW.anywlan.com关注802.16 (称WiMAX :World Interoperability for Microwave Access, Wireless MAN) PHY802.11(1/2 Mbps)MAC802.11/11a/11b MAC802.11e---QoS802.11f--漫游和切换802.11i 安全增强802.11b(5.5/11 Mbps)802.11g(>20 Mbps)802.11a(最大54 Mbps)2013-7-30802.11h 动态频率选择和功能控制Dr. ZhanqiXU,National Key Lab on ISN, Xidian University22二、802.11局域网物理层1、参考模型DataLinkPHYLLCMACPLCPPMD（1）PMD：PMD：PhysicalMediaDependent（物理媒质相关）无线媒质中的数据传输（Modem）（2）PLCP：PhysicalLayerConvergenceProtocol实现MAC-PDU与PMD-PDU间转换，尽量减少MAC与PMD子层间的关联,实现对等PLCP子层间对MACPDU的正确传送(PLCP:物理层汇聚协议）（3）MAC：MediumAccessControl实现共享媒质信道接入(4)LLC:(LogicLinkControl,specifiedbyIEEE802.2),a23Dr. ZhanqiXU,National Key Lab on ISN, Xidian University2013-7-30subsetofHDLC2、PMD传输技术：DSSS、FHSS、OFDM（1）CCK互补键控码：（单载波，M-aryOrthogonalKeyingModulation,I/OModulation,用Barker码字扩频）主要优点是抗多径干扰（2）FHSS：跳频扩频，保密性能好（3）OFDM：正交FDM，传输速率高3、PLCP（1）通用格式2013-7-30Dr. ZhanqiXU,National Key Lab on ISN, Xidian University242013-7-30SYNCSFDSIGNALSERVICELENGTH……PREAMBLEPLCPHeaderMACDataCRCPreamble：与物理层相关的同步前导（解调，bit同步）StartFrameDelimiter：(起始帧定界符）帧定位Signal：指明速率信息Service：指明调制方式等信息Length：MAC-PDU长度Dr. ZhanqiXU,National Key Lab on ISN, Xidian University25