最新80211ac白皮书汇总
白皮书《802.11ac MU-MIMO：桥接Wi-Fi中的间隙》发布
白皮书《802.11ac MU-MIMO：桥接Wi-Fi中的间隙》发
布
佚名
【期刊名称】《数字通信世界》
【年(卷),期】2015(000)005
【摘要】日前,Qualcomm创锐讯正式发布MU-MIMO白皮书《802.11ac MU-MIMO:桥接Wi-Fi中的间隙》,全面详细讲解了MU-MIMO技术在Wi-Fi网络中的实际需求、技术特性和优势、设计注意事项等内容。
【总页数】1页(P45-45)
【正文语种】中文
【相关文献】
1.如何使用Spirent TestCenter WLAN测试80
2.11ac Wave 2 MU-MIMO [J], 思博伦通信
2.华为发布业界首个《最佳体验的家庭网络Wi-Fi白皮书》 [J], 黄海峰
3.802.11ac wave 2规范发布Wi-Fi连接速度显著提升 [J], 宋向东
4.Wi-Fi黑科技高通MU-MIMO完全技术报告 [J],
5.Qualcomm推出支持MU-MIMO的802.11ac Wi-Fi及先进网络处理解决方案[J],
因版权原因，仅展示原文概要，查看原文内容请购买。
无线局域网的安全技术白皮书
无线局域网的安全技术白皮书一、引言在当今数字化时代，无线局域网（WLAN）已成为人们生活和工作中不可或缺的一部分。
无论是在家庭、办公室、商场还是公共场所，我们都能轻松地连接到无线网络，享受便捷的互联网服务。
然而，随着无线局域网的广泛应用，其安全问题也日益凸显。
未经授权的访问、数据泄露、网络攻击等安全威胁给用户和企业带来了巨大的风险。
因此，了解和掌握无线局域网的安全技术至关重要。
二、无线局域网的基本原理无线局域网是利用无线通信技术在一定范围内建立的网络连接。
它通过无线接入点（AP）将设备连接到有线网络，实现数据的传输和共享。
无线局域网采用的通信标准主要有 WiFi（IEEE 80211）系列，如80211a、80211b、80211g、80211n 和 80211ac 等。
三、无线局域网面临的安全威胁（一）未经授权的访问未经授权的用户可以通过破解无线密码或利用网络漏洞接入无线局域网，获取网络资源和敏感信息。
（二）数据泄露在无线传输过程中，数据可能被窃取或篡改，导致用户的个人隐私、商业机密等重要信息泄露。
（三）网络攻击攻击者可以通过发送恶意数据包、进行拒绝服务攻击（DoS）等方式，使无线局域网瘫痪，影响正常的网络服务。
（四）AP 劫持攻击者可以伪装成合法的无线接入点，诱导用户连接，从而获取用户的信息。
四、无线局域网的安全技术（一）加密技术1、 WEP（Wired Equivalent Privacy）WEP 是早期的无线加密协议，但由于其安全性较弱，已逐渐被淘汰。
2、 WPA（WiFi Protected Access）WPA 采用了更强大的加密算法，如 TKIP（Temporal Key Integrity Protocol），提高了无线局域网的安全性。
3、 WPA2WPA2 是目前广泛应用的无线加密标准，采用了 AES（Advanced Encryption Standard）加密算法，提供了更高的安全性。
802.11n技术白皮书
802.11n技术白皮书傲天动联802.11n技术白皮书目录第1章 802.11n技术介绍 (5)1.1 802.11n标准发展历史 (5)1.2 802.11n关键技术介绍 (5)1.2.1 核心技术—MIMO (5)1.2.2 空口速率提升技术 (6)1.2.3 SNR提升技术-MRC (9)1.2.4 吞吐量提升技术-帧聚合 (9)1.2.5 兼容性-兼容 802.11a/b/g (10)第2章 802.11n组网应用要求 (11)2.1 对频谱的要求 (11)2.2 对无线POE交换机的要求 (11)2.3 对无线控制器的要求 (11)傲天动联802.11n技术白皮书插图目录图1-1 MIMO架构 (5)图1-2 通过MIMO传递多条空间流 (8)图1-3 MIMO利用多径传输数据 (8)傲天动联802.11n技术白皮书802.11n技术白皮书关键词：802.11n摘要：本文介绍了802.11n技术缩略语清单：傲天动联802.11n技术白皮书第1章 802.11n技术介绍1.1 802.11n标准发展历史2003年9月：IEEE成立802.11n任务组，负责创设100+MbpsWLAN标准。
2005年7月：11n草案1获通过.2007年3月：草案2获通过。
2009年9月11日：IEEE标准委员会终于批准通过802.11n成为正式标准。
1.2 802.11n关键技术介绍1.2.1 核心技术—MIMOMIMO是802.11n物理层的核心，指的是一个系统采用多个天线进行无线信号的收发。
它是当今无线最热门的技术，无论是3G、IEEE 802.16e WIMAX，还是802.11n，都把MIMO列入射频的关键技术。
图1-1MIMO架构MIMO主要有如下的典型应用，包括：傲天动联802.11n技术白皮书1) 提高吞吐通过多条通道，并发传递多条空间流，可以成倍提高系统吞吐。
2) 提高无线链路的健壮性和改善SNR通过多条通道，无线信号通过多条路径从发射端到达接收端多个接收天线。
无线局域网技术白皮书
无线局域网技术白皮书目录第1章、前言 (4)第2章、无线网络概述 (4)1．无线网络概述 (4)2．无线网络的特点 (4)3．无线数据网络种类 (6)第3章、无线局域网络 (6)1．无线局域网（WLAN）概述 (6)2．无线局域网络的益处 (9)3．典型的无线局域网络应用 (10)第4章、无线局域网络技术 (11)1．无线局域网标准概述 (11)802.11a标准 (11)802.11g标准 (12)802.11系列新标准 (14)2无线局域网标准进展 (15)3．三种流行无线网络技术的比较 (15)4．下一代无线网络技术：H IPER LAN/2 (17)5．无线局域网频道分配与调制技术 (22)6．无线局域网拓扑结构 (23)7．无线局域网的几个主要工作过程 (24)8．影响无线局域网性能的因素 (25)9．无线局域网络的安全性 (25)1.无线局域网（WLAN）面临哪些威胁？ (25)2．常见的无线网络安全的分类 (25)3．如何保障无线局域网安全 (26)4.保护企业无线网络 (27)第5章、无线局域网络产品的兼容性 (28)第6章、CISCO无线局域网络解决方案 (28)1.思科无线局域网技术指南 (28)下一代无线局域网 (28)无线技术的到来 (28)无线移植方案的选择 (29)802.11a标准 (29)802.11g标准 (30)兼容性 (30)双频Cisco Aironet 1200：全球最佳 (30)今天的无线应用 (30)计算的新纪元 (31)2.思科无线安全解决方案指南 (31)第8章、CISCO AIRONET扩频无线网络产品 (39)一、扩频收发工作站 (39)二、扩频天线馈线系统 (44)第9章、无线网络典型联接方式与实例 (45)一、CISCO AIRONET (46)二、其它无线网案例 (48)第10章、无线联网的现状及发展前景 (49)一、无线网络的需求及实现 (49)二、计算机无线网络的应用现状 (50)三、计算机无线网络目前存在的问题和解决 (50)四、计算机无线网络的标准化 (51)五、计算机无线网络的发展与应用的前景 (51)第11章、计算机无线网技术应用介绍 (51)一、计算机无线网技术适用范围： (51)二、应用介绍 (52)第12章、总结 (54)第八章、无线网络产品选购指南 (54)附录一、无线局域网常用品牌及产品简介 (56)附录一、AIRONET无线网产品安全性说明 (60)附录二、国家无线电委员会对2.4GHZ频段的管理办法 (60)附录三、AIRONET无线网产品参考报价（部分） (62)第1章、前言信息革命到今天，我们越来越离不开计算机网络，无论是信息共享、合作伙伴交流、还是移动用户办公，都有网络价值的体现。
思科802.11ac白皮书
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Contentsபைடு நூலகம்
1. Executive Summary ............................................................................................................................................. 3 2. What Is 802.11ac? ................................................................................................................................................ 4 2.1 Drivers for 802.11ac ...................................................................................................................................... 4 2.2 How Does 802.11ac Go So Fast? ................................................................................................................. 5 2.3 How Do We Make 802.11ac Robust? ........................................................................................................... 7 2.3.1 Technology Overview ........................................................................................................................... 7 2.3.2 Differences Between 802.11ac and 802.11n ........................................................................................ 8 2.3.3 Standards-Based Beamforming ........................................................................................................... 9 2.3.4 RTS/CTS with Bandwidth Indication .................................................................................................. 10 2.3.5 All A-MPDUs ........................................................................................................................................ 12 2.3.6 Channelization and 80+80 MHz .......................................................................................................... 12 2.3.7 Rate at Range ...................................................................................................................................... 15 2.3.8 Regulatory ............................................................................................................................................ 16 2.3.9 MU-MIMO .............................................................................................................................................. 17 2.3.10 802.11ac Project Authorization Request ......................................................................................... 18 3. When Is 11ac Happening? ................................................................................................................................ 18 4. How Does 11ac Affect Me? ............................................................................................................................... 19 4.1 Compatibility ............................................................................................................................................... 19 4.2 When to Upgrade to 802.11ac? .................................................................................................................. 20 4.3 Radio Resource Management and WIPS Effects ..................................................................................... 21 5. Summary ............................................................................................................................................................ 21 Appendix: What Is 802.11n? ................................................................................................................................. 21
WLAN技术白皮书-QOS
WLAN技术白皮书-QOSwlan技术白皮书QOS1.00修订记录日期修订版本修改章节修改描述作者 08/8/5 1.00 第一稿沈翀目录1. Wlan QOS需求背景 (4)2. 名词解释 (4)3. qos背景知识 (5)3.1. 无线qos难点 (5)3.2. PCF介绍 (6)3.3. 802.11协议Qos的局限性 (6)3.4. Qos种类 (7)3.5. 无线qos标准 (7)4. 无线qos帧格式 (8)4.1. Qos Control域 (8)4.2. TID (8)4.3. EOSP (9)4.4. Ack策略 (10)4.5. TXOP限制 (10)5. 无线qos mac功能 (11)5.1. HCF (11)5.2. TXOP (11)5.3. EDCA (11)5.4. HCCA (14)5.5. APSD (15)5.6. TSPEC (16)5.7. 新确认规则 (17)5.8. 直接链路协议 (19)6. 参考文献 (20)7. 附录 WMM介绍 (20)1.Wlan QOS需求背景随着越来越丰富的视、音频业务的出现和无线通信技术的发展，在任何时间、任何地点以各种方式享用服务的议题再次成为人们追求的热点，原来实现于有线和固定网络中的多媒体视、音频实时业务，正日益向无线、移动的趋势发展。
最初人们进行WLAN的协议设计主要是针对数据业务的，对于诸如视频、音频等实时业务应用并没有做充分的考虑。
2005年，IEEE 802.11e标准针对实时业务的QOS保证作出补充方案。
2.名词解释CP：contention period，竞争周期。
在竞争周期内，STA通过竞争取得媒介控制权。
CFP：Contention-Free Period，无竞争周期，由中央机制（central authority）控制的周期称为无竞争周期。
TXOP﹕发送时机（transmission opportunity），定义了STA可以发送数据的时间段，包括开始时间和最大持续时间。
WLAN技术白皮书-安全
wlan技术白皮书安全1.00修订记录日期 修订版本 修改章节 修改描述 作者 08/8/1 1.00 第一稿 沈翀目录1. Wlan安全机制 (4)2. 名词解释 (5)3. 无线安全标准历史 (5)3.1. 802.11 (5)3.2. WPA (6)3.3. 802.11i (6)3.4. WAPI (6)3.5. EAP相关RFC (7)4. 无线加密机制 (7)4.1. WEP (7)4.2. TKIP (8)4.3. CCMP (10)5. 无线认证机制 (11)5.1. 开放的无线接入 (11)5.2. 共享密钥 (11)5.3. EAP (12)5.3.1. EAP协议 (12)5.3.2. EAP多种认证方式 (14)5.3.3. 802.1X (16)5.3.4. 无线局域网的802.1X认证 (17)6. 密钥管理机制 (18)6.1. 密钥的产生和管理 (18)6.2. 密钥交互和握手流程 (20)6.2.1. 单播密钥更新的四次握手流程 (20)6.2.2. 广播密钥更新流程 (21)7. 参考文献 (22)8. 附录：一个完整的802.1X认证过程 (23)1. Wlan 安全机制无线局域网相对于有线局域网而言，其所增加的安全问题原因主要是其采用了公共的电磁波作为载体来传输数据信号，而其他各方面的安全问题两者是相同的。
由于无线网络的开放性，为了保证其安全，至少需要提供以下2个机制：1、 判断谁可以使用wlan 的方法—认证机制 2、 保证无线网数据私有性的方法—加密机制因此，早期的无线安全（802.11）包含认证和加密两部分。
为了解决802.11的安全漏洞，802.11i 将无线安全分为4个方面：实际上是把早期的认证机制细分为认证算法（Authentication Algorithm）和认证框架（Authentication Framework）；加密机制则包含了数据加密算法（Data Privacy Algorithm）以及数据完整性校验算法（Data Integrity Algorithm）。
802.11n技术白皮书-wifi
Wi-Fi CERTIFIED™ n：覆盖范围更远，流量更快，多媒体级Wi-Fi®网络2009年9月下文及其所包含的有关Wi-Fi Alliance项目的信息以及预期发布日期有可能在不预先通知的情况下被修改或删除。
本文以“按原样”、“按可用条件”以及“不保证无瑕疵”为基础编写。
WI-FI ALLIANCE不对本文及其所包含信息的有用性、质量、适用性、真实性、准确性或完整性提供任何陈述、保证、前提要求或担保。
摘要Wi-Fi CERTIFIED n可互操作性测试项目认证产品以IEEE 802.11 标准（802.11n）的802.11n修正版本为基础。
802.11n是无线局域网（WLAN）技术的最新发展成果。
本文旨在介绍802.11n的技术概况，详细描述Wi-Fi CERTIFIED n项目。
802.11n修正使Wi-Fi性能获得显著改进。
今天的Wi-Fi CERTIFIED n设备的吞吐量已达到传统802.11技术的五倍以上，覆盖范围达到后者的两倍，且连接更为稳定。
今天，经改进的Wi-Fi技术性能已经而且正在运用于多种产品，满足多元化的市场需求。
随着越来越多的制造商将802.11n关键功能集成于产品之中，802.11n的优势将得到日益明显的体现。
功能全面的Wi-Fi CERTIFIED n 产品能够在房间内传输高清（HD）视频流，同时为多位用户提供高服务质量（QoS）的IP语音（VoIP）流与数据传输服务。
Wi-Fi CERTIFIED n设备还拥有最先进的安全保护性能。
无论是企业网络、校园网络还是城市网络，802.11n都能提供IT管理者孜孜以求的稳健、快速、安全而优质的网络性能。
Wi-Fi CERTIFIED n项目是Wi-Fi CERTIFIED 802.11n 草案 2.0项目的改进版本，后者于2007年6月发布（草案-n项目）。
项目的基准要求未变，更新后的项目增加了对标准包含的部分可选特性的支持。
802.11ac资料整理
无线网络数据速率举例应用数据速率(Mbps)交互式视频会议0.3 8 to 0.5互联网视频流 2.5 to 8高清电视19.4 to 25蓝光播放40无压缩视频, “高” 质量(8-bits/color, 1920x1080p, 24 fps, 4:2:2)796无压缩视频, “最佳”质量(10-bits/color, 1920x1080p, 60 fps, 4:4:4)3730WLAN标准演进频带时间1997 1999 2003 2009 20132.4GHZ 802.112 MbpsDSSS&&FHSS 802.11b11MbpsCCK&&DSSS802.11g54MbpsOFDM&&DSSS802.11n600MbpsOFDM&&MIMO4x4 MIMO20/40MHz5GHZ 802.11a54MbpsOFDM 802.11ac 1.56Gbps OFDM&&MIMO60GHZ 802.11ad>1Gbps(近7Gbps)802.11n回顾功能必选项可选项传输方式OFDM信道带宽20 MHz 40 MHzFFT大小64 128 数据子载波/导频52 / 4 108 / 6 子载波间隔312.5 kHzOFDM 符号持续时间 4 μs (800 ns 保护间隙) 3.6 μs 短保护间隙调制类型BPSK, QPSK, 16QAM, 64QAM前向纠错二进制卷积编码(BCC) 低密度奇偶校验编码(LDPC)编码速率1/2, 2/3, 3/4, 5/6MCS 支持0 到7, 0 到15用于接入点8 到76, 16 到76 用于接入点空间流和MIMO 1, 2 用于接入点直接映射 3 或 4 流发射波束成形, 时空块编码运行模式/ PPDU 格式Legacy/non-HT (802.11a/b/g)Mixed/HT-mixed(802.11a/b/g/n)Greenfield/HT-Greenfield (只在802.11n下)从802.11n 到 802.11ac的扩展功能必选项可选项信道带宽20 MHz, 40 MHz, 80 MHz160 MHz, 80+80 MHzFFT大小64, 128, 256512数据子载波/导频52 / 4, 108 / 6, 234 / 8468 / 16调制类型BPSK(二进制相移键控), QPSK（四相相移键控）, 16QAM（正交幅度调制）, 64QAM256QAMMCS（Modulation and CodingScheme，调制与编码策略）支持0 到78 和9空间流和MIMO 1 2 到8发射波束成形, 时空块编码多用户MIMO (MU-MIMO)运行模式/ PPDU格式极高吞吐率VHT数据速率: 1.56 Gb/s (80 MHz, 4 Tx, MCS9) “合理”情形6.93 Gb/s (160 MHz, 8 Tx, MCS9, short GI) 最佳情形802.11ac 特性总结802.11ac 新的物理层特性包括:• 更宽的通道带宽: 40和80 MHz为必备,160和80+80 MHz为可选• 更高阶的调制: 256QAM支持256QAM调制，更宽的信号，同时需要更好的信号EVM值，增加了设计难度• 更多的空分流和天线:最高8个• 下行多用户MIMO: 最多4个用户,每个用户最多4个流，总共8个流• 发射机和接收机的多数测试与802.11n相同, 增加了新的带宽和调制速率支撑演进的关键技术分析支撑无线传输速率提升的技术分布在物理层和MAC（介质访问控制）层。
华为Wi-Fi 6(IEEE 802.11ax)技术白皮书
白皮书华为Wi-Fi 6(802.11ax)技术白皮书文档版本1.0目录1.Wi-Fi发展简介 (4)2.什么是Wi-Fi 6(802.11ax) (6)2.1Wi-Fi 6速度有多快？ (6)2.2Wi-Fi 6核心技术 (9)2.2.1OFDMA频分复用技术 (9)2.2.2DL/UL MU-MIMO技术 (13)2.2.3更高阶的调制技术(1024-QAM) (15)2.2.4空分复用技术（SR）& BSS Coloring着色机制 (16)2.2.5扩展覆盖范围(ER) (19)2.3其他Wi-Fi 6（802.11ax）新特性 (19)2.3.1支持2.4GHz频段 (19)2.3.2目标唤醒时间（TWT） (20)3.为什么要Wi-Fi 6(802.11ax) (22)4.5G与Wi-Fi 6(802.11ax)的共存关系 (23)5.华为对Wi-Fi 6(802.11ax)产业发展的贡献 (26)6.华为Wi-Fi 6(802.11ax)产品和特性 (28)6.1业界首款商用Wi-Fi 6 AP (28)6.2华为第三代智能天线 (28)6.3三射频& 双5G设计 (29)6.4SmartRadio技术-智能射频调优 (30)6.5SmartRadio技术-智能EDCA调度 (32)6.6SmartRadio技术-智能无损漫游 (33)7.总结 (36)1.Wi-Fi发展简介Wi-Fi已成为当今世界无处不在的技术，为数十亿设备提供连接，也是越来越多的用户上网接入的首选方式，并且有逐步取代有线接入的趋势。
为适应新的业务应用和减小与有线网络带宽的差距，每一代802.11的标准都在大幅度的提升其速率。
1997年IEEE制定出第一个无线局域网标准802.11，数据传输速率仅有2Mbps，但这个标准的诞生改变了用户的接入方式，使人们从线缆的束缚中解脱出来，。
随着人们对网络传输速率的要求不断提升，在1999年IEEE发布了802.11b标准。
IEEE 802.11E技术白皮书
IEEE 802.11E技术白皮书关键词：QoS、WMM摘要：本文介绍了无线局域网中的QoS标准—IEEE 802.11E与WMM标准的公有部分。
缩略语：目录1 概述 (4)2 技术应用背景 (4)2.1 技术优点 (4)2.2 应用限制 (6)3 特性介绍 (6)3.1 相关协议 (6)3.2 协议处理机制 (6)3.2.1 MAC层结构 (6)3.2.2 MAC层数据平面结构 (7)3.2.3 多个接入类 (7)3.2.4 EDCA机制 (8)3.2.5 新增帧类型 (11)4 产品实现的技术特色 (12)4.1 WX5002/WA2110 (12)4.2 WA1208E (12)5 典型组网案例 (13)5.1 全网QoS解决方案 (13)5.2 SVP应用 (14)5.3 WDS组网 (15)6 总结和展望 (15)7 参考文献 (15)1 概述IEEE 802.11E标准定义无线局域网MAC层服务质量，支持语音、视频等多媒体业务在无线局域网中的应用。
IEEE 802.11E扩展了原802.11MAC层DCF和PCF信道接入机制，形成了EDCA和HCCA信道接入规范。
前者增强了DCF机制，区分不同业务应用的优先级，保障高优先级业务的信道接入能力，并在一定程度上保障了高优先业务的带宽。
后者增强了PCF机制，通过QAP的集中控制，以轮询方式为QSTA分配空口资源，提供改善的访问带宽并且减少了高优先级业务的延迟。
由于HCCA机制相比EDCA、PCF机制更加复杂，目前被各厂商束之高阁，没有得到推广。
但EDCA得到了广泛的应用，本文中的机制全部基于EDCA竞争规则，不涉及HCCA的无竞争部分。
除信道接入机制的增强外，IEEE 802.11E标准还引入BLOCK ACK、DLS、No-ACK等多种技术，可以有效地提高无线信道的吞吐量和带宽。
IEEE 802.11E于2005年9月22日通过，但至今尚未完全商用，芯片厂商仅支持其中的少量特性。
Aruba 802.11ax Wi-Fi 6 白皮书说明书
802.11AX—WAIT, DID WE JUST BUILD A WIRELESS SWITCH?
November 2018
Introduction
With the initial versions of 802.11ax (Wi-Fi 6) coming out, some of the most interesting features and enhancements revolve around how it will handle communicating with multiple clients. Currently clients and wireless access points (APs) have to listen to see if someone else is transmitting before they can send traffic. It’s similar to how Ethernet worked in the past with bridges. On a shared medium, more clients mean more fighting over who gets to transmit and longer wait times before each client could send data. Performance is fine with a small number of clients, but as the number of clients increased, the available bandwidth of the network decreases. In a wireless network, an AP with 100 clients can transmit only about 40% of the data that an AP with 10 clients can transmit, as shown in Figure 1.
802-11ac系列无线产品介绍
√
√
√ 2.4G & 5G
1167M 20dBm 内置普通天线
1
√ 2.4G & 5G
600M 23dBm 内置普通天线
1
√
√
胖版有瘦版无电源适配器 胖版有瘦版无电源适配器
WA4320-ACN-D
√ √ 2.4G & 5G 750M 20dBm 内置普通天线 1 √
H3C 802.11ac AP-WA4320系列
属性 产品定位 可管理AP数
可管理AP型号
频段 接入速率：1167M
发射功率 天线类型 千兆接口 标准POE供电和本地供电 自带电源
注：锚AP暂时不支持本地Web管理模式
Anchor AP（WA4320i-ACN-A） 控制器AP 4
WA4320i-ACN-A/WA4320-ACN-SI
2.4G & 5G √
无线配套产品
POE 交换机
百兆 S3110-10TP-PWR
S3110-26TP-PWR
S3100V2-8TP-PWR-EI S3100V2-16TP-PWR-EI S3100V2-26TP-PWR-EI
千兆 S5120-9P-HPWR-SI S5120-28P-PWR-SI S5120-28P-HPWR-SI
WA4330-ACN WA4320i-ACN-A WA4620E-ACN WA4620i-ACN 三叉戟—高密 Anthor系列—锚AP 46系列—高速 46系列—高速
面
室
板
外
型
WA4320H-ACN
型
WA4320X-ACN
11ac产品对比
11ac一共有12款AP，包括普通放装型、室分型、面板、室外型AP。可以全方位的满足一体化组 网的需求。其中4320-C、4320-E、4320-D、4330、4320i-A为新产品
WLAN 身份验证和数据加密白皮书
WLAN身份验证和数据加密白皮书一、概述近年来随着WIFI终端的不断普及，WLAN应用逐渐融入人们的生活，并成为人们即时获取信息的重要途径之一。
由于WLAN采用具有空中开放特性的无线电波作为数据通信媒介，在没有采取必要措施的情况下，任何用户均可接入无线网络、使用网络资源或者窥探未经保护的数据。
因此，在WLAN应用中必须对传输链路采取适当的加密保护手段，以确保通信安全。
由此业界各厂商和相关组织相继开发出各种认证和加密方法，本文仅介绍下列在WLAN中普遍采用的认证加密方式。
z OPEN+WEPz SHARED+WEPz IEEE802.1x+WEPz WPA-PSK（TKIP or CCMP）z WPA2-PSK（TKIP or CCMP）z WPA（TKIP or CCMP）z WPA2（TKIP or CCMP）二、OPEN+WEPOPEN+WEP采用空认证和WEP加密，无线终端无需经过验证，即可与相应的AP进行关联。
具体过程如下：申请者首先发送一个认证请求到AP，如果AP设置了MAC地址过滤功能，则AP对申请者MAC地址进行核实，否则AP直接通过认证请求，认证成功后申请者会向AP发送关联请求，AP回应关联应答，双方建立关联，然后就可以传递数据了。
OPEN模式关联过程该模式只对传输数据进行WEP加密，由于目前使用的无线网卡在硬件上均支持WEP 加密，因此该模式兼容性较强。
WEP 是IEEE 802.11 标准最初指定的加密算法，既可部署用于认证，也可用于加密。
WEP密钥（为专用加密密钥，简称口令）按长度可分为40位和104位两种，其中在40位口令长度的情况下，需要配置5个ASCII字符（或者10个十六进制字符）；在104位口令长度的情况下，需要配置13个ASCII字符（或者26个十六进制字符）。
在WEP中用来保护数据的RC4加密算法（cipher）属于一种对称性（密钥）流加密算法（stream cipher）。
802.11白皮书
White Paper 802.11n: Next-Generation Wireless LANTechnologyThis white paper explains IEEE 802.11n, the newest draft specification for Wi-Fi®. It is designed to provide an overview of the technology, describe new techniques used to achieve greater speed and range, and identify applications, products, and environments that will benefit from the technology.April 2006OverviewDemand for wireless LAN hardware has experienced phenomenal growth during the past several years, evolving quickly from novelty into necessity. As a measure of this expansion, WL AN chipset shipments in 2005 surpassed the 100-million-unit mark, a more than tenfold increase from 2001 shipments of less than 10 million units.Thus far, demand has been driven primarily by users connecting notebook computers to networks at work and to the Internet at home as well as at coffee shops, airports, hotels, and other mobile gathering places. As a result, Wi-Fi®technology is most commonly found in notebook computers and Internet access devices such as routers and DSL or cable modems. In fact, more than 90 percent of all notebook computers now ship with built-in WLAN.The growing pervasiveness of Wi-Fi is helping to extend the technology beyond the PC and into consumer electronics applications like Internet telephony, music streaming, gaming, and even photo viewing and in-home video transmission. Personal video recorders and other A/V storage appliances that collect content in one spot for enjoyment around the home are accelerating this trend.These new uses, as well as the growing number of conventional WL AN users, increasingly combine to strain existing Wi-Fi networks. Fortunately, a solution is close at hand. The industry has come to an agreement on the components that will make up 802.11n, a new WLAN standard that promises both higher data rates and increased reliability, and the IEEE standards-setting body is ironing out the final details. Though the specification is not expected to be finalized before 2007, the draft is proving to be reasonably stable as it progresses through the formal IEEE review process.In the meantime, hardware that conforms to the 802.11n draft is becoming available, so consumers can begin building high-speed wireless networks in anticipation of the standard while ensuring interoperability at high speeds and still supporting their existing WLAN hardware.The purpose of this white paper is to explain the impending 802.11n standard and how it will enable WL ANs to support emerging media-rich applications. The paper will also detail how 802.11n compares with existing WL AN standards and offer strategies for users considering higher-bandwidth alternatives.Wi-Fi® Standards ComparisonThe first WL AN standard to become accepted in the market was 802.11b, which specifies encoding techniques that provide for raw data rates up to 11 Mbps using a modulation technique called Complementary Code Keying, or CCK, and also supports Direct-Sequence Spread Spectrum, or DSSS, from the original 802.11 specification. The 802.11a standard, defined at about the same time as 802.11b, uses a more efficient transmission method called Orthogonal Frequency Division Multiplexing, or OFDM. OFDM, as implemented in 802.11a, enabled raw data rates up to 54 Mbps. Despite its higher data rates, 802.11a never caught on as the successor to 802.11b because it resides on an incompatible radio frequency band: 5 GHz versus 2.4 GHz for 802.11b.Note: All of the WL AN standards provide for multiple transmissionoptions, so that the network can drop to lower (albeit easier tomaintain) data rates as environmental interference challengescommunications. In the most favorable circumstances, 802.11a and802.11b support data rates up to 54 Mbps and 11 Mbps respectively.)In June 2003, the IEEE ratified 802.11g, which applied OFDM modulation to the 2.4-GHz band. This combined the best of both worlds: raw data rates up to 54 Mbps on the same radio frequency as the already popular 802.11b. WLAN hardware built around 802.11g was quickly embraced by consumers and businesses seeking higher bandwidth. In fact, consumers were so eager for a higher-performing alternative to 802.11b that they began buying WL AN client and access-point hardware nearly a year before the standard was finalized.Today, the vast majority of computer network hardware shipping supports 802.11g. Increasingly, as technology improves and it becomes easier and less costly to support both 2.4 GHz and 5 GHz in the same chipset, dual-band hardware is becoming more commonplace. Much of the WLAN client hardware available today, in fact, supports both 802.11a and 802.11g.A similar scenario to the draft 802.11g phenomenon is now unfolding with 802.11n. The industry came to a substantive agreement with regard to the features to be included in the high-speed 802.11n standard in early 2006. And though it will likely be 2007 before the standard is ratified, the specification is stable enough for draft-n Wi-Fi cards and routers to already be making their way to store shelves.802.11n: A Menu of OptionsThe emerging 802.11n specification differs from its predecessors in that it provides for a variety of optional modes and configurations that dictate different maximum raw data rates. This enables the standard to provide baseline performance parameters for all 802.11n devices, while allowing manufacturers to enhance or tune capabilities to accommodate different applications and price points. With every possible option enabled, 802.11n could offer raw data rates up to 600 Mbps. But WL AN hardware does not need to support every option to be compliant with the standard. In 2006, for example, most draft-n WLAN hardware available is expected to support raw data rates up to 300 Mbps.In comparison, every 802.11b-compliant product must support data rates up to 11 Mbps, and all 802.11a and 802.11g hardware must support data rates up to 54 Mbps. Better OFDMIn the 802.11n draft, the first requirement is to support an OFDM implementation that improves upon the one employed in the 802.11a/g standards, using a higher maximum code rate and slightly wider bandwidth. This change improves the highest attainable raw data rate to 65 Mbps from 54 Mbps in the existing standards. MIMO Improves PerformanceOne of the most widely known components of the draft specification is known as Multiple Input Multiple Output, or MIMO. MIMO exploits a radio-wave phenomenon called multipath: transmitted information bounces off walls, doors, and other objects, reaching the receiving antenna multiple times via different routes and at slightly different times. Uncontrolled, multipath distorts the original signal, making it more difficult to decipher and degrading Wi-Fi performance. MIMO harnesses multipath with a technique known as space-division multiplexing. The transmitting WL AN device actually splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end. The current 802.11n draft provides for up to four spatial streams, even though compliant hardware is not required to support that many.Doubling the number of spatial streams from one to two effectively doubles the raw data rate. There are trade-offs, however, such as increased power consumption and, to a lesser extent, cost. The draft-n specification includes a MIMO power-save mode, which mitigates power consumption by using multiple paths only when communication would benefit from the additional performance. The MIMO power-save mode is a required feature in the draft-n specification.Table 1. Major Components of Draft 802.11nFeature Definition Specification StatusBetter OFDM Supports wider bandwidth &higher code rate to bringmaximum data rate to 65 MbpsMandatorySpace-Division Multiplexing Improves performance byparsing data into multiplestreams transmittedthrough multiple antennasOptional forup to fourspatialstreamsDiversity Exploits the existence ofmultiple antennas toimprove range andreliability. Typicallyemployed when the numberof antennas on thereceiving end is higher thanthe number of streamsbeing transmitted. Optional for up to four antennasMIMO Power Save Limits power consumptionpenalty of MIMO by utilizingmultiple antennas only onas-needed basisRequired40 MHz Channels Effectively doubles data ratesby doubling channel widthfrom 20 MHz to 40 MHzOptionalAggregation Improves efficiency byallowing transmissionbursts of multiple datapackets between overheadcommunicationRequiredReduced Inter-frame Spacing (RIFS) One of several draft-nfeatures designed toimprove efficiency. Providesa shorter delay betweenOFDM transmissions than in802.11a or g.RequiredGreenfield Mode Improves efficiency byeliminating support for802.11a/b/g devices in anall draft-n networkCurrentlyoptionalMIMO EnhancementsThere are two features in the draft-n specification that focus on improving MIMO performance, called beam-forming and diversity. Beam-forming is a technique that focuses radio signals directly on the target antenna, thereby improving range andperformance by limitinginterference.Diversity exploits multipleantennas by combining theoutputs of or selecting thebest subset of a largernumber of antennas thanrequired to receive a numberof spatial streams. This isimportant because the draft-n specification supports up tofour antennas, so devices willprobably encounter othersbuilt with a different numberof antennas. A notebookcomputer with two antennas,for example, might connectto an access point with threeantennas. In this case, onlytwo spatial streams can beused even though the accesspoint itself may be capable ofthree spatial streams.With diversity, surplusantennas are put to gooduse. The device with moreantennas uses the extra onesto operate at longer range.For example, the outputs oftwo antennas may becombined to receive onespatial stream to achieve alonger link range. The conceptmay be extended to combinethe outputs of three antennasto receive two spatialstreams for higher data rateand range and so on.Diversity is not restricted to802.11n or even WL AN. Itcan be used to improve anytype of radio communication. In fact, diversity has typically been implemented in some existing 802.11a, 802.11b, and 802.11g hardware through selection of the best of two antennas.Improved Throughput and Higher Data RatesAnother optional mode in the 802.11n draft effectively doubles data rates by doubling the width of a WLAN communications channel from 20 MHz to 40 MHz. The primary trade-off here is fewer channels available for other devices. In the case of the 2.4-GHz band, there is enough room for three non-overlapping 20-MHz channels. Needless to say, a 40-MHz channel does not leave much room for other devices to join the network or transmit in the same airspace. This means intelligent, dynamic management is critical to ensuring that the 40-MHz channel option improves overall WL AN performance by balancing the high-bandwidth demands of some clients with the needs of other clients to remain connected to the network. This paper has covered many of the major mandatory and optional features of the draft 802.11n specification, though coverage is by no means exhaustive. Other optional features that draft-n hardware may support, for example, include high-throughput duplicate mode, which helps extend the network's range, and shortguard interval, which improves efficiency by further limiting overhead.With all the optional modes and back-off alternatives, the array of possible combinations of features and corresponding data rates can be overwhelming. To be precise, the current 802.11n draft provides for 576 possible data rate configurations. In comparison, 802.11g provides for 12 possible data rates, while 802.11a and 802.11b specify eight and four, respectively.Table 2 compares the primary IEEE 802.11 specifications.Table 2. Primary IEEE 802.11 Specifications802.11a 802.11b 802.11g 802.11nStandardApprovedJuly 1999 July 1999 June 2003 Not yet ratifiedMaximum DataRate54 Mbps 11 Mbps 54 Mbps 600 MbpsModulation OFDM DSSS or CCK DSSS or CCKor OFDM DSSS or CCK or OFDMRF Band 5 GHz 2.4 GHz 2.4 GHz 2.4 GHz or 5 GHz Number ofSpatialStreams1 1 1 1, 2, 3, or 4 Channel Width 20 MHz 20 MHz 20 MHz 20 MHz or 40 MHzCoexisting with Today’s WLANsThe draft 802.11n specification was crafted with the previous standards in mind to ensure compatibility with more than 200 million Wi-Fi devices currently in use. A draft-n access point will communicate with 802.11a devices on the 5-GHz band as well as 802.11b and 802.11g hardware on the 2.4-GHz frequencies. In addition to basic interoperability between devices, 802.11n provides for greater network efficiency in mixed mode over what 802.11g offers.Network efficiency is basically the proportion of the available bandwidth that is used to transmit data as opposed to overhead or protocols used to manage network communications. Wireless environments are much more challenging to orchestrate than wired networks, so there is generally more overhead to ensure that data sent is actually received, and that other clients leave the channel open during transmission.The presence of 802.11b nodes makes communications difficult on the 2.4G-Hz band because the older standard does not recognize OFDM, which is employed by 802.11g and draft-n. This means that if OFDM clients want to communicate in the presence of 802.11b clients, they need to use the older standard’s communication protocol at least to protect their higher-rate OFDM transmissions. This drops network efficiency considerably because data packets take far less time to transmit with 802.11g and draft-n than they do under the old 802.11b standard.Some WLAN chipset suppliers, including Broadcom, devised innovative schemes to improve the efficiency of mixed 802.11b/g networks. Fortunately, the issue is addressed directly in the draft-n specification.One of the most important features in the draft-n specification to improve mixed-mode performance is aggregation. Rather than sending a single data frame, the transmitting client bundles several frames together. Thus, aggregation improves efficiency by restoring the percentage of time that data is being transmitted over the network, as Figure 1 illustrates.Figure 1: How Aggregation Improves Efficiency in a Mixed-Mode NetworkIt is much easier for draft-n devices to coexist with 802.11g and 802.11a hardware because they all use OFDM. Even so, there are features in the specification that increase efficiency in OFDM-only networks. One such feature is Reduced Inter-Frame Spacing, or RIFS, which shortens the delay between transmissions.For the best possible performance, the draft-n specification provides for what is called greenfield mode, in which the network can be set to ignore all earlier standards. It is not clear at this stage whether greenfield mode will be a mandatory or an optional feature in the final 802.11n draft, but it is likely to be an option. Realistically, battery-powered WL AN hardware will continue to be built around 802.11g and even 802.11b for some time. Despite the improved efficiency built into the draft-n specification, however, it is difficult to eliminate all of the obstacles of 802.11b. This means that consumers looking for the best possible network performance may want to consider replacing 802.11b WL AN hardware on their networks.Consumer Applications Demand 802.11nBecause it promises far greater bandwidth, better range, and reliability, 802.11n is advantageous in a variety of network configurations. And as emerging networked applications take hold in the home, a growing number of consumers will come to view 802.11n not just as an enhancement to their existing network, but as a necessity.With most Internet connection speeds below 5 Mbps, it is unlikely that consumers who use WL AN technology simply to pair a single computer with an Internet connection are taxing their existing network, at least when used at close range. Even this class of consumer may be pleasantly surprised by the increase in range and reliability that an upgrade to draft-n WL AN hardware can offer. Some of the current and emerging applications that are driving the need for 802.11n are Voice over IP (VoIP), streaming video and music, gaming, and network attached storage. VoIP is mushrooming as consumers and businesses alike realize they can save money on long-distance phone calls by using the Internet instead of traditional phone service. An increasingly popular way to make Internet calls is with VoIP phones, which are battery-powered handsets that typically connect to the Internet with built-in 802.11b or 802.11g. Telephony does not demand high bandwidth, although it does require a reliable network connection to be usable. Both 802.11b and 802.11g consume less power than 802.11n in MIMO modes, but single-stream 802.11n may become prevalent in VoIP phones. VoIP phones can benefit today from the increased range and reliability of a draft-n access point.As with voice, streaming music is an application that requires a highly reliable connection that can reach throughout the home. Millions of consumers are building libraries of digital music on their personal computers by ripping their CD collections and buying digital recordings over the Internet. In addition, growing numbers are streaming music directly from the Internet.As their digital music collections grow, more consumers find they would like to be able to listen to it through living room stereos or via players in other rooms around the house. Though higher bandwidth is not absolutely necessary, the additional range and reliability that draft-n offers may be better suited to streaming music than older-generation WLAN hardware.Gaming is an application that increasingly is making use of home WLANs, whether users connect wirelessly to the Internet from their computers and portable gaming devices or use the network to compete with others in the home.A growing application that demands all that 802.11n has to offer―high data rates as well as range and reliability―is Network-Attached Storage, or NAS. NAS has become popular in the enterprise as an inexpensive, easy-to-install alternative for data backup. More recently, NAS is taking hold in small offices and even some homes, as users want to safeguard their growing digital photo albums from hard-drive failure, and as the price of self-contained NAS backup systems falls well below $1,000. New, more exciting applications for NAS are emerging, such as video storage centers that demand reliable, high-bandwidth connections to stream prerecorded TV shows, music videos and full-length feature films to televisions and computers throughout the house.Transferring large files such as prerecorded TV shows from a personal video recorder onto a notebook computer or portable media player for viewing outside the home takes planning and patience on an older WLAN. Figure 2 compares the time it would take to transfer a 30-minute video file. At the best data transfer rate, it would take 42 minutes to copy the file using 802.11b, and less than a minute with a two-antenna draft-n client.Figure 2: Time (Best Case) to Transfer 30-Minute HD Video.The enterprise may have the most to gain from the higher raw data rates that the draft-n standard promises. Knowledge workers have grown accustomed to the benefits of WL ANs in the office. They can carry their notebooks to conference rooms, coworkers’ desks, even break areas, and still have access to e-mail, instant messaging, and the Internet, as well as corporate data.But some everyday applications such as transferring large files from a group server, accessing corporate databases, and system backups, can be painstakingly slow on a 54-Mbps WL AN. For such high-traffic applications, many otherwise untethered workers anchor their computers to an Ethernet cable, which connects to the network at 100 Mbps or even 1 Gbps.With draft-n hardware, users can have the best of both worlds: the speed of wired Ethernet and the mobility of WLAN.RecommendationsAs is evident from the previous section, virtually all enterprises could benefit today from higher-bandwidth WLANs. Nevertheless, many large businesses are expected to wait until 802.11n is ratified before initiating large deployments of the new standard. Corporations that are ready to deploy, as well as consumers and smaller businesses anxious to take advantage of the higher data rates and improved range and reliability, should shop carefully. Not all WL AN hardware featuring MIMO, diversity, and other 802.11n-like features can claim to be compliant with the emerging standard. Buyers should look for products that say “IEEE 802.11n Draft Compliant.”Buyers should also keep in mind that there are a host of optional features in the draft-n specification. Many of them, such as channelization and greenfield mode, to name a few, are designed to improve raw data rates, and need to be present on both ends of the link in order to be enabled.There are also differences between how draft-n features are implemented. Some draft-n hardware supporting 40-MHz channelization, for example, is better than others at balancing the demands of high-bandwidth communications for one client with the needs of other users on the network.A good strategy for consumers planning to upgrade the data rates and range of their home WLANs is to start with a draft-n router and purchase one that supports the most spatial streams and optional features that budgets allow. Follow a similar strategy for high-bandwidth file-sharing appliances such as personal video recorders and backup storage devices.For stationary clients that do not need high data rates, for example music players streaming content from a digital home library or the Internet, draft-n may help improve range and reliability.Selecting the right draft-n alternatives for battery-powered devices may be the trickiest item on the shopping list because power consumption is as important a consideration as data rates, range, and cost. VoIP phones, for example, are low-bandwidth devices that might benefit from MIMO techniques in environments where range and reliability are an issue, but at the cost of battery life.Notebook computers may benefit from high-performance features like MIMO, channelization and greenfield mode for file transfers and data backups. Keep in mind that with channelization and MIMO power-conservation, which enables multiple spatial streams only when they are needed, performance features may end up saving power in some cases because the notebook is active on the WL AN for shorter periods.Figure 3 depicts a number of considerations for choosing draft-n WLAN hardware.Figure 3: Considerations for Choosing Draft-n WLAN HardwareWhy Choose Broadcom for Draft-N?First and foremost, Broadcom’s Intensi-fi TM family of WL AN chipsets is 802.11n draft-compliant. And although the draft-n standard appears to be fairly stable at this stage, the Intensi-fi family is highly programmable, which means it is adaptable to unforeseen and unexpected changes in the specification.Second, due to Broadcom-designed signal processing techniques, Intensi-fi chipsets feature Active Diversity, which gives a network connection between two dual-antenna devices higher performance, range, and reliability without the cost and power consumption of a third antenna on one of the connections.The fidelity of the Intensi-fi TM radio is second to none, which means it can maintain higher data rates at longer distances and in more adverse conditions.With regard to the optional 40-MHz channel mode, the Intensi-fi chipset provides superior balance between performance and the needs of other members of the WL AN. Intensi-fi’s “good-neighbor” approach to channelization includes frequent scans for other network traffic, along with a mechanism to dip quickly back to all-20-MHz channels when other clients need to communicate.The Intensi-fi chipset supports the latest standards to secure WL ANs, including WPA2 and CCX version 4. In addition, Intensi-fi supports SecureEasySetup™, a one-touch push-button security setup that makes it easy to install a secure WLAN.Phone: 949-450-8700 Fax: 949-450-8710E-mail: info@ Web: 802_11n-WP100-R BROADCOM CORPORATION16215 Alton Parkway, P.O. Box 57013Irvine, California 92619-7013© 2006 by BROADCOM CORPORATION. All rights reserved.04/21/06Broadcom®, the pulse logo, Connecting everything®, the Connecting everything logo, Intensi-fi TM, BroadRange™, Secur eEasySetup™, High Speed Mode™, SpeedBooster™, and Broadcom 54g™ are trademarks of Broadcom Corporation and/or its affiliates in the United States, certain other countries and/or the EU. Any other tr ademar ks or tr ade names mentioned ar e theFinally, Intensi-fi supports 125 High Speed Mode™ (also known as SpeedBooster), a proprietary high-speed mode in Broadcom’s 54g™ 802.11g family of chipsets, as well as BroadRange™ signal processing technology that improves the ability of Wi-Fi devices to extend coverage area. A network can take advantage of 125 High Speed Mode if all WLAN devices in the network include Intensi-fi or 54g TM chipsets. BroadRange TM, on the other hand, improves network performance in 802.11g modes regardless of the chipsets inside the other devices on the network.For added assurance of greatest reliability and best range, choose products built with Intensi-fi TM technology.。
NETGEAR 802.11ac千兆WI-FI演进技术白皮书
802.11ac – Evolution to Gigabit WiFiIntroduction: WiFi for the Video-Enabled Home802.11ac is the next progression of WiFi. The latest WiFi standard, 802.11n, ratified in 2009, with the current generation of 802.11n allowing for up to 450 mbps per radio. 802.11ac builds on 802.11n and enables wireless speeds over a gigabit per second (Gbps), almost three times the speeds offered by 802.11.n. The 802.11ac standard is targeted to be certified by theWi-Fi Alliance by the end of 2012.Driven by the growth in mobile devices and streaming video entertainment services such as: Netflix, Hulu and YouTube, the industry will likely see a slew of "draft" pre-standard 802.11a access points/routers for the home starting second-half of 2012. The utility of 802.11ac in the home will become clear as a range of 802.11ac-enabled laptops, tablets and cell phones enter the market in 2013 and onwards; while enterprise adoption of 802.11ac is projected to follow from 2014 onwards.802.11ac is expected to herald the arrival of home video products that will make enjoying streaming Web video as easy as watching cable TV today. The top initial use case for 802.11ac is anticipated to be WiFi-based transport of high-definition video throughout the home. One scenario would be to use 802.11ac for distribution of HD video to multiple televisions. Another would be to utilize 802.11ac to stream HD video from a mobile device to a television.This document is a technical overview of the new capabilities of 802.11ac and summarizes its benefits due to the improvements made by 802.11ac, especially vis-à-vis 802.11n.802.11ac Technology OverviewThe continuing trend of devices and applications transitioning from fixed links to wireless links and the emergence of new wireless applications with ever higher throughput requirements is driving the need for higher performance wireless networks. The 802.11ac protocol has a number of enhancements that will be implemented in a phased manner, which, taken together, have the goal of significantly increasing the throughput and reliability of WiFi networks.•Radio enhancements higher frequency band and enhanced channel width, increased number of spatial streams, and modulation enhancements• Multi-User MIMO (MU-MIMO) with enhanced beamforming• MAC layer enhancements with extended Aggregation MPDU (A-MPDU) and enhanced Request to Send/Clear to Send (RTS/CTS) mechanismsRadio EnhancementsHigher Frequency Band and Wider Channel WidthsEvery WiFi device sends or receives signals over a slice of the radio spectrum or frequency band, the use of which is strictly regulated by international agreements. One problem with current 802.11n WiFi networks is that the 2.4 GHz spectrum that they operate in is congested with many other devices, from Bluetooth headsets to microwave ovens. Because all of these devices are competing for the same restricted bandwidth, everyone's Internet connection slows down; just as the traffic on a highway slows down when too many cars are on the road. In comparison, 802.11ac operates solely in the much less congested 5 GHz spectrum. With less competition for the airwaves from other devices, transmission rates are boosted.A notable feature of the 5GHz band is that it offers more room for radio transmissions compared to the 2.4 GHz band. As a result, the 802.11ac provides for extended bandwidth of the wireless channels compared to 802.11n (the wider the bandwidth channels, the faster the WiFi connections can operate).802.11ac mandates support of 20, 40 and 80 MHz channels (versus 20 and 40 MHz in 802.11n). Optionally, the use of contiguous 160 MHz channels or non‐contiguous 80+80 MHz channels is also allowed. The doubling of the channel bandwidth (from 40 to 80 MHz) is a very efficient way to increase performance in a cost-efficient way. Alternatively, an 80 MHz system can use a lower number of antennas to provide the same performance as a 40 MHz system.The 802.11ac draft specification provides channel allocation for the United States (see figure 1 on the following page) and for Europe, Japan and global operating classes (see figure 2 on the following page). China does not support this band, but the draft will include support for China in the 5.725 to 5.850 GHz range. (Note: Global operating classes are used for operation anywhere in the world and are used in addition to the operating classes for a specific region.)By doubling the bandwidth (from 40 to 80 MHz), each spatial stream can roughly support twice the number of bits per symbol. As such, an 80 MHz single‐stream transmission can provide the same performance as a two‐stream 40 MHz transmission. When enhanced bandwidth is used to deliver the same data rate with fewer RF chains, the power consumption of the device will be lower because of the lower number of RF components. This gives an advantage to the 80 MHz system over a 40 MHz system with two streams from this perspective.Figure 1. US Region Channel AllocationFigure 2. Europe, Japan, and Global Operating Class Channel AllocationHigher Modulation RatesLike the 802.11n wireless specification, 802.11ac uses Orthogonal Frequency‐Division Multiplexing (OFDM) to modulate bits for transmission over the wireless medium. While the modulation approach is identical to that used in 802.11n, 802.11ac optionally allows the use of 256 Quadrature Amplitude Modulation (QAM) in addition to the mandatory Quadrature Phase Shift Keying (QPSK), Binary PSK (BPSK), 16 QAM and 64 QAM modulations. 256 QAM increases the number of bits per sub‐carrier from 6 to 8, resulting in a 33% increase in throughput. One point to note, however, is that 256 QAM can only be used in high signal‐to‐noise ratio (SNR) scenarios (across the used spectrum and desired streams); that is, for favorable channel conditions. Increased Number of Spatial Streams802.11ac allows support for up to 8 spatial streams – up from a maximum of 4 streams in 802.11n. Support for more than one spatial stream is optional, however. The increased number of streams are most useful in combination with the new Multi-User Multiple-input multiple-output (MU‐MIMO) capability of 802.11ac (discussed below) with up to 8 spatial streams support in single-user and multi-user MIMO modes, and no more than 4 spatial streams per station in multi-user mode.MU-MIMOMulti-User Multiple-input multiple-output (MU‐MIMO) allows an AP to transmit unique data to multiple client stations simultaneously and are key to enabling 802.11ac networks to achieve Gigabit-level bandwidth. MU-MIMO builds on the single-user MIMO capability of 802.11n and, thus, a review of MIMO basics would be helpful prior to a review of MU-MIMO specifics. MIMO BasicsMIMO means a device with multiple transmitters emitting signals and a device with multiple receivers receiving the signals, is at the heart of 802.11n. A MIMO system is often represented as NxM where N is the number of inputs and M is the number of outputs.Spatial diversity is a MIMO feature that can be achieved either at the transmitter (transmit diversity) or at the receiver (receive diversity) or both. It involves use of multiple antennas separated at enough distance so that the receiver can receive multiple independently fading signal paths. Spatial diversity improves the signal-to-noise ratio (SNR) at the receiver over what would be obtained without diversity (single receive antenna). The improvement in SNR is often termed as “diversity gain.” In theory, the maximum achievable diversity gain is the product of the number of transmit and receive antennas.The goal behind beamforming, an optional feature of the 802.11n standard, is to achieve MIMO transmitter spatial diversity. Beamforming is the process in which a multi-antenna transmitter codes or assigns weights to signals before transmission to maximize the signal-to-noise ratio at the receiver antenna. The weights depend on the transmitter’s estimate of the channel to the receiver. The information to estimate the channel is obtained through implicit feedback. In a nutshell, beamforming allows coherent combining of the multiple independently fading signal paths at the receiver.MU-MIMO OverviewMulti-User Multiple-input multiple-output (MU ‐MIMO) was added to 802.11ac as a technique for boosting AP multi-station throughput capabilities. In MU ‐MIMO, the Access Point (AP) transmits independent data streams to several clients at the same time. MU-MIMO is similar to the 802.11n MIMO capability except the transmissions are to antennas on different receiver devices. The number of spatial streams is limited to the number of transmit chains on the AP . Multi-user MIMO requires enhancements to beamforming and the MAC layer.Compared to the multiple, incompatible, beamforming methods of 802.11n, 802.11ac has honed down the beamforming operation to a single explicit beamforming method in which the receiver side returns the beamforming matrices to the transmitter as a response to a special channel frame sent by the transmitted to elicit the beamforming feedback. The result is an interoperable beamforming capability that maximizes range and coverage of 802.11ac transmissions.Through preprocessing of the data streams at the transmitter (similar to what happens in beamforming), the interference from streams that are not intended for a particular client is eliminated at the receiver of each clients. Therefore, each client receives its data free of interference from the transmissions that are simultaneously directed towards other clients. In MU ‐MIMO, support of multiple spatial streams is used to create independent transmissions to different clients, while in 802.11n single ‐user MIMO,multiple spatial streams is used to increase the throughput from AP to client.In summary, multi-user MIMO should allow significantly improved throughput when multiple single and dual stream clients are connected to the AP , as well as enhanced range and coverage. Most smartphones and tablets are single stream devices (with 802.11n, only 1 single stream device can download at a time).MAC EnhancementsThe 802.11ac standard also implements a number of enhancements to the MAC layer to complement the higher-performance radio and MU-MIMO features.Increased Aggregated MAC Protocol Data Unit PDU (A ‐MPDU) sizeTo reduce communications overhead, 802.11n introduced two methods for frame aggregation: Mac Service Data Units (MSDU)aggregation and Message Protocol Data Unit (MPDU) aggregation. Both aggregation methods reduce the overhead to only a single radio preamble for each aggregated frame transmission.MPDU aggregation translates each Ethernet frame to 802.11n format and then collects the 802.11n frames for a commondestination. The collection does not require wrapping of another 802.11 frame, since the collected frames already begin with an 802.11 MAC header.802.11ac enhances the maximum size of an A ‐MPDU to a maximum of 1,048,575 octets (compared to a maximum of 65,535octets in 802.11n) further reducing communications overhead. The 802.11ac A-MPDU format is an extension of the 802.11n A-MPDU as shown in Figure 3. The extension (shaded in the figure) consists of zero or more delimiters with MPDU length zero and a possible final MAC Pad of less than 4 octets.Figure 3. 802.11ac A-MPDU FormatEnhanced Request to Send/Clear to Send (RTS/CTS) operation for wider bandwidthAt the MAC layer, 802.11n devices announce their intent to transmit by sending Request to Send/Clear to Send (RTS/CTS)frames. These frames let nearby 802.11a/g devices sense when the channel is in use to avoid collisions.Because of the wider bandwidth used in 802.11ac and the limited number of 80 MHz channels, hidden nodes on the secondary channels are an important problem that needs to be addressed. The RTS/CTS mechanism has been updated to better detect whether any of the non ‐primary channels are occupied by a different transmission.To this end, both RTS and CTS (optionally) support a “dynamic bandwidth” mode. In this mode, CTS may be sent only on the primary channels that are available in case part of the bandwidth is occupied. The STA that sent the RTS can than fall back to a lower bandwidth mode. This helps to mitigate the effect of a hidden node. Note however that the final transmission bandwidth always has to include the primary channel.variable variable variable 0-3440-3OctetsConclusionThe key benefits of 802.11ac compared to the 802.11n standard are:•Up to triple transmission speeds through wider channel bandwidth and higher modulation rate•Higher reliability due to use of less congested 5 GHz radio spectrum•More coverage and fewer dead zones due to new interoperable beamforming standardAs a result, 802.11ac will allow the WiFi industry to again drive wireless performance to meet the requirements of latest wireless applications. For more information on upcoming wireless products and technologies, please visit NETGEAR, the NETGEAR logo, and Connect with Innovation are trademarks and/or registered trademarks of NETGEAR, Inc. and/or its subsidiaries in the United States and/or other countries. Other brand names mentioned herein are for identification purposes only and may be trademarks of their respective holder(s). Information is subject to change without notice. © 2012 NETGEAR, Inc. All rights reserved.。
WLAN协议技术白皮书-802.11ax技术详解2
802.11ax技术详解（二）前言：上一篇描述了802.11ax新技术的特点，新技术将从PHY层和MAC层两个维度来实现多用户的体验提升，这篇将通过仿真或者软件无线电平台搭建802.11ax物理层实测平台，对场景化下的性能进行分析部分实测验证。
1远距离下性能分析802.11ac 从 64QAM到 256QAM提供了 8/6=1.33 倍增速，802.11ax从256QAM到1024QAM提供了10/8=1.25倍增速。
但在实际实现中，1024QAM对信号发送EVM的要求至少-35dB，相比11ac有3dB的提升，否则在接收端不能解调。
表1.1 802.11ax发送EVM要求Modulation Coding rate Relative constellation error(dB)256‐QAM 3/4 ‐30256‐QAM 5/6 ‐321024‐QAM 3/4 ‐351024‐QAM 5/6 ‐35我们在实际办公室中搭建了802.11ax的物理层软件无线电平台，测试了单流下高阶性能，如表1.4所示，空口4.5m情况下，MCS10/11在接收端不能解调。
MCS10/11适用于传输在近距离下，如2.2m能够良好的解调，解调端EVM能够达到-31dB。
表1.2实测不同距离高阶的解调端EVM测试环境\MCS 891011馈线 ‐41.5dB ‐41.7dB‐42.1dB‐41.8dB空口LOS 0.2M ‐32.3dB ‐31.9dB‐32.4dB‐31.1dB空口LOS 2.2M ‐32.5dB ‐32.2dB‐32.8dB‐32.7dB空口LOS 4.5M ‐24.2dB ‐24.3dB‐24.9dB‐24.4dB1024QAM能够有效提升传输速率，进而提升吞吐，但实测过程中发现，空口4.5m LOS(视距)下性能下降较多，接收端不能解调，1024QAM更适用于在近距离干扰较少的环境，在户外以及远距离下，MCS10/11实用性较差。
无线局域网技术白皮书
无线局域网技术白皮书无线局域网是计算机网络与无线通信技术相结合的产物。
它利用射频(RF)技术，取代旧式的双绞铜线构成局域网络，提供传统有线局域网的所有功能，网络所需的基础设施不需再埋在地下或隐藏在墙里，也能够随需移动或变化。
使得无线局域网络能利用简单的存取构架让用户透过它，达到“信息随身化、便利走天下”的理想境界。
WLAN是20世纪90年代计算机与无线通信技术相结合的产物，它使用无线信道来接入网络，为通信的移动化，个人化和多媒体应用提供了潜在的手段，并成为宽带接入的有效手段之一。
一、IEEE802.11无线局域网标准1997年IEEE802.11标准的制定是无线局域网发展的里程碑，它是由大量的局域网以及计算机专家审定通过的标准。
IEEE802.11标准定义了单一的MAC层和多样的物理层，其物理层标准主要有IEEE802.11b,a 和g。
1.1 IEEE802.11b1999年9月正式通过的IEEE802.11b标准是IEEE802.11协议标准的扩展。
它可以支持最高11Mbps的数据速率，运行在2.4GHz的ISM频段上，采用的调制技术是CCK。
但是随着用户不断增长的对数据速率的要求，CCK调制方式就不再是一种合适的方法了。
因为对于直接序列扩频技术来说，为了取得较高的数据速率，并达到扩频的目的，选取的码片的速率就要更高，这对于现有的码片来说比较困难;对于接收端的R AKE接收机来说，在高速数据速率的情况下，为了达到良好的时间分集效果，要求RAKE接收机有更复杂的结构，在硬件上不易实现。
1.2 IEEE802.11aIEEE802.11a工作5GHz频段上，使用OFDM调制技术可支持54Mbps的传输速率。
802.11a与802.11b 两个标准都存在着各自的优缺点，802.11b的优势在于价格低廉,但速率较低(最高11Mbps);而802.11a优势在于传输速率快(最高54Mbps)且受干扰少，但价格相对较高。
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80211a c白皮书1.概述1.1技术背景在802.11n标准制定后不久，为了获取更高的传输速率，IEEE转入了802.11ac标准的制定当中，目标是在2012年实现千兆级别的无线局域网传输速率，而802.11ac实际上是在802.11a基础上发展起来的。
从2008年上半年开始，IEEE就已经着手802.11ac标准的制定，当时被称为“Very High Throughput”(甚高吞吐量)，目标直接就是达到1Gbps。
到2008年下半年的时候，项目分为两部分，一是802.11ac，工作在6GHz 以下，用于中短距离无线通信，正式定为802.11n的继任者，另一个则是802.11ad，工作在60GHz，市场定位与UWB类似，主要面向家庭娱乐设备。
而到了2012年2月，制定了我们现在看到的D2.0版本。
1.2技术特点802.11ac有如下几个特点：更高的传输速率：802.11ac最高可以支持约7000Mb/s传输速率，这主要得益于OFDM技术以及更高的占用带宽，而MU-MIMO技术提升带宽利用率。
更好的环境适应性：延续使用MIMO技术，增加了空间流的数量。
更好的保证了接收性能。
更少的环境干扰：使用5G频段，减少2.4G公共频段的支持，也就减少了其它信号对自身的干扰，获得更为清洁的频谱环境。
2.名词解释MSDU：MAC Service Data Unit。
可以理解为传输的有效数据，MAC帧的data部分。
MPDU：MAC Protocol Data Unit。
可以理解为经过MAC协议封装的帧，包括MAC帧头。
PLCP：Physical Layer Convergence Procedure。
可以理解为PHY层的编码和封包过程。
PPDU：PLCP Protocol Data Unit。
可以理解为PHY层封装的帧，包括PHY 帧头和MAC帧。
A-MSDU：Aggregate MSDU。
MSDU帧聚合。
A-MPDU：Aggregate MPDU。
MPDU帧聚合。
MIMO：multiple input, multiple output。
一种采用多根天线进行传输的技术。
MU：multiple user。
多个用户STBC：Space-Time Block Code。
空时分组编码，一种可以提高传输质量的编码方式。
MCS：Modulation Coding Scheme。
11ac中规定空间流数目、编码、调制方式和传输速率的一组方案。
CSI：Channel State Information 用于波束成形的一个信息域。
SGI：Short Guard Interval。
11ac引入的短防护间隔，该间隔为400ns。
RIFS：Reduced Interframe Spacing。
11ac引入的短帧间隙，减少传输开销。
CCA：Clear Channel Assessment。
PHY层用于探测信道占用情况的一个功能模块。
VHT：Very High Throughput。
即采用11ac引入的调制编码方式传输，提高了传输速率。
LTF：Long Training Field。
PHY帧头中一个域，用于对接收端进行训练。
Beamformer/Beamformee: beamformer是准备进行波束成形调整的一方，beamformee是辅助对方进行波束成形的一方。
3.技术分析3.1 帧结构变更3.1.1 MPDU帧结构变更802.11ac扩展了802.11n的MAC帧，主要是将帧体扩展到了11426个字节，同时，还对MAC header各部分进行了一定的修改3.1.1.1 Frame Control域增加了NDPA（Null Data Packet Announcement）以及Beamforming Report Poll功能并且从新定义了预留部分3.1.1.2 HT Control域HT控制域格式如下主要控制部分为B1-B29，它可以区分HT以及VHT模式1）HT模式如下而其中 Link Adaption Control域如下：相对于802.11n，其主要变化就是少了B0这个预留字节。
2）VHT模式控制域如下现在对其作出如下说明：MRQ(VHT MCS feedback request)：MCS反馈请求MSI/STBC(MRQ sequence identifier/STBC indication):用于标识MRQ序列以及STBC是否发射。
Unsolicited MFB 为1时结构如下其中STBC indication为1时代表发射STBC，为0时不发射，而CompressedMSI中包含一串数据用于标识特定请求，如果STBC indication为0，他在0-3范围内，1时在0-2之内；而在Unsolicited MFB为0的情况下，如果MRQ为1，那么这整个域有0-6之内的数据用于标识特定请求，而MRQ为0，该域为预留。
MFSI/GID-L(MFB sequence identifier/LSB of Group ID):用于指示MFB序列，以及PPDU的组ID。
MFB(N_STS,MCS,BW and SNR feedback): 结构如下用于指示N_STS，MCS以及带宽和平均信噪比的信息。
GID-H(MSB of Group ID):用于指示群组ID，如果Unsolicited MFB 域为1，而且为MU PPDU确定，那么这里包含最多3个字节的群组ID信息。
Coding Type(Coding Type of MFB response):如果UnsolicitedMFB域为1，那么这个域指示编码信息，0为BCC，1为LDPC。
FB Tx Type(Transmission Type of MFB response):UnsolicitedMFB域为1的情况下，FB Tx Type为0表示MFB来自未经波束成形的VHT PPDU，如果为1，表示MFB来确定为经过波束成形的VHT SU PPDU。
Unsolicited MFB(Unsolicited MCS feedback indicator):为0时表示MFB为一个MRQ的响应，为1则不是。
3.1.2 PPDU帧结构变更802.11ac新定义了一种PHY层帧格式VHT格式，具体格式如下：L-STF: Non-HT Short Training fieldL-LTF: Non-HT Long Training fieldL-SIG: Non-HT SIGNAL fieldVHT-SIG-A: VHT Signal A fieldVHT-STF: VHT Short Training fieldVHT-LTF: VHT Long Training fieldVHT-SIG-B: VHT Signal B fieldData: The Data field includes the PSDU (PLCP Service Data Unit) 其中与VHT相关的域只在VHT PPDU中出现，在VHT NDP中该域就未作定义，而VHT-LTF的数量由空时流的数量确定，可以为1，2，4，6，8。
VHT-SIG-A域中包含了用于诠释VHT格式PPDU的信息，VHT-SIG-A域由两个符号组成，即VHT-SIG-A1和VHT-SIG-A2组成，他们分别如下图所示：VHT-SIG-A1格式VHT-SIG-A2格式而其对应的含义如下：BW:描述工作带宽，0代表20MHz，1代表40MHz，2代表80MHz，3代表160MHz或者80+80MHz。
Reserved：预留位，设为1。
STBC：如果所有用户的所有空间流都有STBC，则设为1，如果任意用户的空间流没有STBC则设为0。
(不允许出现部分用户有STBC)Group ID：分别存在SU PPDU和MU PPDU两种Group ID指示方式。
NSTS/Partial AID：对于MU PPDU，NSTS被分成了4个用户部分，每一块为3位。
对于每一块，0代表0条空时流，1代表1条空时流，2代表2条空时流，3代表3条空时流，5-7为预留；而对于SU PPDU，SU NSTS的值0-7分别对应1-8条空时流，而Partial AID为预期的PSDU接收端提供简单的标识。
TXOP_PS_NOT_ALLOWED：Reserved：预留，设为1。
对于VHT-SIG-A2：Short GI：是否使用短保护间隔，0为不使用，1为使用。
Short GI N SYM Disambiguiation：设为1，代表短保护间隔有使用，并且N SYM(Number of symbol in the Data field)除以10余数为9。
其他情况设为0SU/MU[0] Coding：对于SU PPDU，0代表BCC，1代表LDPC；对于MU PPDU，如果MU[0] NSTS域不为0，那么该位表示用户0的编码方式，0代表BCC，1代表LDPC，如果MU[0] NSTS域为0，那么就预留，并且设为1. LDPC Extra OFDM Symbol：不管是否MU模式，只要LDPC编码过程引入了额外的OFDM符号，该位置1.SU MCS/MU[1-3] Coding：对于SU PPDU 代表MCS的目录；对于MU PPDU B4-B6分别代表MU[1-3] NSTS不为0时，用户1-3的编码方式，0代表BCC，1代表LDPC。
其他情况预留并置为1。
Beamformed：在SU传输中，如果对于波形使用了波束成形控制矩阵，那么该位设为1，其他情况设为0。
对于MU PPDU该位预留，设为1。
Tail：用于终止卷积解码器。
而对于VHT-SIG-B，如下所示，20MHzPPDU包含26位，40MHzPPDU包含27位，80MHz，80+80MHz，160MHz包含29位。
3.2MIMO技术改进3.2.1MU模式的引入802.11ac在原先802.11n的MIMO技术基础上，引入了MU-MIMO概念，通过这个技术，我们可以实现，多个站之间，可以通过相同的信道同时收发多个数据流。
一个支持MU-MIMO的站，他可以生成4个A-PPDUs，并且通过相互独立的空间流，将这些A-PPDUs发给各个接收站，这样就提升了系统的吞吐。
一个MU模式下PPDU发射系统框图如下：与之对应，SU工作模式下PPDU如下图1. 扰码器：将数据扰码，以防止出现长时间的连‘0’或连‘1’，影响后级的编码性能。
2. 编码分配器：将经过扰码的串行数据流分解为个数据流，输出到个FEC编码器中。
分配的算法为Round Robin算法。
3.二进制卷积编码器/低密度奇偶检验码编码器。