他的最新文章
他的热门文章
您举报文章：
举报原因：
原文地址：
原因补充：
(最多只允许输入30个字)无线网络协议802.11a/b/g/n的主要区别
802.11物理层的三种实现方法:
1&FHSS跳频扩频&&&
(适用于频烦移动的场所)
2&DSSS直接序列扩频(适用于相对比较定的场所,如无线局域网)
3&IR 红外线
802.11a/b/g/n，其实指的是无线网络协议，细分为802.11a、802.11b、802.11g、802.11n等。这几种不同的无线协议、都是由802.11演变而来的。802.11是IEEE最早制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中用户与用户终端的无线接入、802.11a工作在5.4G频段、最高速率54M、主要用在远距离的无线连接、802.11b工作在2.4G频段、最高速率11M(逐步被淘汰),802.11g工作在2.4G频段、最高速率54M、802.11n最新无线标准、目前还不成熟、最高速率能到300M。
最大数据传输率
传统 802.11
FHSS 或 DSSS
2.4 或 5 GHz
540 Mbps（理论值）
　　1. 传统 802.11
　　1997 发布
　　两个原始数据率，1 Mbps 和 2 Mbps
　　跳频展频（FHSS）或直接序列展频（DSSS）
　　工业、科技和医疗（ISM）领域内的 <font COLOR="# 个 2.4 GHz
互不重叠频带　　最初定义的载波侦听多点接入/避免冲撞（CSMA-CA）
　　2. 802.11a　　1999 发布
　　各种调制类型的数据传输率： 6, 9, 12, 18, 24, 36, 48 和 54 Mbps
　　带 52 个子载波频道的正交频分复用（OFDM）技术
　　不需要许可证的国家信息基础设施（UNII）频道内的 <font COLOR="# 个 5 GHz 互不重叠频带
　　3. 802.11b
　　1999 发布
　　各种调制类型的数据传输率： 1, 2, 5.5 和 11 Mbps
　　高速直接序列展频（HR-DSSS）
　　工业、科技和医疗（ISM）领域内的 <font COLOR="# 个
2.4 GHz 互不重叠频带
　　4. 802.11g　　2003 发布
　　各种调制类型的数据传输率： 6、9、12、18、24、36、48 和 54 Mbps；
　　可以使用 DSSS 和 CCK 进一步转换为 1、2、5.5 和 11 Mbps
　　带 52 个子载波频道的正交频分复用（OFDM）技术；使用 DSSS 和 CCK 向下兼容 802.11b
　　工业、科技和医疗（ISM）领域内的 <font COLOR="# 个
2.4 GHz 互不重叠频带
　　5. 802.11n　　计划在 2008 年第二季度进行IEEE
认证；但是现在已经出现了早于11n 的接入点（AP）和无线网卡
　　各种调制类型的数据传输率：1、2、5.5、6、9、11、12、18、24、36、48 和54 Mbps
　　采用多输入多输出（MIMO）和频道绑定（CB）的正交频分复用（OFDM）技术　　工业、科技和医疗（ISM）领域内的
3 个 2.4 GHz 互不重叠频带
　　无论有无频道绑定（CB），均为不需要许可证的国家信息基础设施（UNII）频道内的12
个5 GHz 互不重叠频带
已投稿到：
以上网友发言只代表其个人观点，不代表新浪网的观点或立场。2843人阅读
计算机网络（22）
如转载侵犯您的版权，请联系：
802.11a/b/g/n，其实指的是无线网络协议，细分为802.11a、802.11b、802.11g、802.11n等。这几种不同的无线协议、都是由802.11演变而来的。
　　802.11是IEEE最初制定的一个无线局域网标准，主要用于解决办公室局域网和校园网中用户与用户终端的无线接入；
　　802.11a工作在5.4G频段，最高速率54兆，主要用在远距离的无线连接；
　　802.11b工作在2.4G频段，最高速率11兆，由于速率较低，逐步被淘汰；
　　802.11g工作在2.4G频段，最高速率54兆；
　　802.11n最新无线标准，常见速率有108兆、150兆，目前最高速率能到300兆。&
最大数据传输率
传统 802.11
FHSS 或 DSSS
2.4 或 5 GHz
540 Mbps（最高理论&#20540;）
　　1. 传统 802.11&
　　1997 发布&
　　两个原始数据率，1 Mbps 和 2 Mbps&
　　跳频展频（FHSS）或直接序列展频（DSSS）&
　　工业、科技和医疗（ISM）领域内的 3 个 2.4 GHz 互不重叠频带&
　　最初定义的载波侦听多点接入/避免冲撞（CSMA-CA）&
　　2. 802.11a&
　　1999 发布&
　　各种调制类型的数据传输率： 6, 9, 12, 18, 24, 36, 48 和 54 Mbps&
　　带 52 个子载波频道的正交频分复用（OFDM）技术&
　　不需要许可证的国家信息基础设施（UNII）频道内的 12 个 5 GHz 互不重叠频带&
　　3. 802.11b&
　　1999 发布&
　　各种调制类型的数据传输率： 1, 2, 5.5 和 11 Mbps&
　　高速直接序列展频（HR-DSSS）&
　　工业、科技和医疗（ISM）领域内的 3 个 2.4 GHz 互不重叠频带&
　　4. 802.11g&
　　2003 发布&
　　各种调制类型的数据传输率： 6、9、12、18、24、36、48 和 54 Mbps；&
　　可以使用 DSSS 和 CCK 进一步转换为 1、2、5.5 和 11 Mbps&
　　带 52 个子载波频道的正交频分复用（OFDM）技术；使用 DSSS 和 CCK 向下兼容 802.11b&
　　工业、科技和医疗（ISM）领域内的 3 个 2.4 GHz 互不重叠频带&
　　5. 802.11n&
　　计划在 2008 年第二季度进行IEEE 认证；但是现在已经出现了早于11n 的接入点（AP）和无线网卡&
　　各种调制类型的数据传输率：1、2、5.5、6、9、11、12、18、24、36、48 、54、108、150和300 Mbps&
　　采用多输入多输出（MIMO）和频道绑定（CB）的正交频分复用（OFDM）技术&
　　工业、科技和医疗（ISM）领域内的 3 个 2.4 GHz 互不重叠频带&
　　无论有无 CB，均为不需要许可证的国家信息基础设施（UNII）频道内的12 个5 GHz 互不重叠频带。
* 以上用户言论只代表其个人观点，不代表CSDN网站的观点或立场
访问：278280次
积分：4334
积分：4334
排名：第8068名
原创：137篇
转载：47篇
译文：11篇
评论：29条
文章：17篇
阅读：19381
(3)(3)(1)(3)(2)(2)(1)(1)(2)(14)(6)(2)(8)(5)(6)(4)(2)(2)(2)(1)(2)(1)(2)(8)(2)(8)(6)(4)(7)(2)(2)(37)(18)(1)(1)(5)(3)(9)(6)(1)IEEE 802.11g Wi-Fi Tutorial
- the IEEE 802.11g
Wi-Fi / WLAN standard provides data transfer speeds of 54 Mbps data transfer rates using the 2.4 GHz ISM band.
Wi-Fi 802.11 Tutorial Includes
After the introduction of Wi-Fi with the 802.11a and 802.11b standards, the 802.11b standard became the most popular operating in the 2.4 GHz ISM band. This standard proved to be the most popular despite the faster operating speed of the a variant of the standard because the cost of producing chips to operate at 2.4 GHz were much less than ones to run at 5 GHz.
In order to provide the higher speeds of 802.11a while operating on the 2.4 GHz ISM band, a new standard was introduced. Known as 802.11g, it soon took over from the b standard. Even before the standard was ratified, 802.11g products were available on the market, and before long it became the dominant Wi-Fi technology.
802.11g specifications
The 802.11g standard provided a number of improvements over the 802.11b standard which was its predecessor. The highlights of its performance are given in the table below.
IEEE 802.11g Wi-Fi Features
Date of standard approval
Maximum data rate (Mbps)
Modulation
CCK, DSSS, or OFDM
RF Band (GHz)
Channel width (MHz)
802.11g physical layer
Like 802.11b, its predecessor, 802.11g operates in the 2.4 GHz ISM band. It provides a maximum raw data throughput of 54 Mbps, although this translates to a real maximum throughput of just over 24 Mbps.
Although the system is compatible with 802.11b, the presence of an 802.11b participant in a network significantly reduces the speed of a net. In fact it was compatibility issues that took up much of the working time of the IEEE 802.11g committee.
In order to provide resilience against multipath effects while also being able to carry the high data rates, the main modulation method chosen for 802.11g was that of OFDM - orthogonal frequency division multiplex, although other schemes are used to maintain compatibility, etc..
Note on OFDM:
Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..
Click on the link for an
In addition to the use of OFDM, DSSS - direct sequence spread spectrum is also used.
To provide the maximum capability while maintaining backward compatibility, four different physical layers are used - three of which are defined as Extended Rate Physicals, ERPs.These coexist during the frame exchange so that the sender can use any one of the four, provided they are supported at each end of the link.
The four layer options defined in the 802.11g specification are:
ERP-DSSS-CCK: & This layer is that used with 11b. Direct sequence spread spectrum is used along with CCK - complementary code keying. The performance is that of the legacy 802.11b systems.
ERP-OFDM: & This physical layer is a new one introduced for 802.11g where OFDM is used to enable the provision of the data rates at 2.4 GHz that were achieved by 11a at 5.8 GHz.
ERP-DSSS/PBCC: & This physical layer was introduced for use with 802.11b and initially provided the same data rates as the DSS/CCK layer, but with 802.11g, the data rates have been extended to provide 22 and 33 Mbps. As indicated by the title, it uses DSSS technology for the modulation combined with PBCC coding for the data.
DSSS-OFDM: & This layer is new to 11g and uses a combination of DSSS and OFDM - the packet header is transmitted using DSSS while the payload is transmitted using OFDM
802.11g occupies a nominal 22 MHz channel bandwidth, making it possible to accommodate up to three non-overlapping signals within the 2.4 GHz band. Despite this, the separation between different Wi-Fi access points means that interference is not normally too much of an issue.
IEEE 802.11g Wi-Fi Physical Layer Summary
Physical Layer
Data Rates (Mbps)
1, 2, 5.5, 11
6, 9, 12, 18, 24, 36, 48, 54
1, 2, 5.5, 11, 22, 33
6, 9, 12, 18, 24, 36, 48, 54
802.11g packet structure
It is customary for data packets to be split into different elements. For Wi-Fi systems the data packets sent over the radio interface can be thought of as consisting of two main parts:
Preamble / Header: & As with any other preamble / header, it serves to alert receivers, in this case radios, that a transmission is to start, and then it enables them to synchronise. The preamble consists of a known series of '1's and '0's that enable the receivers to synchronise with the incoming transmission. The Header element immediately follows the pre-amble and contains information about the data to follow including the length of the payload.
Payload: & This is the actual data that is sent across the radio network and can range from 64 bytes up to 1500 bytes. In most cases the preamble/header are sent using the same modulation format as the payload, but this is not always the case. When using the DSSS-OFDM format, the header is sent using DSSS, while the payload uses OFDM.
The initial 802.11 standard defined a long preamble PLCP frame set. In the later 802.11b standard, an optional short
preamble was defined. Then for 802.11g the short preamble PPDU was defined as mandatory.
802.11g ERP-DSSS/CCK PPDU frame
Abbreviations
This is the format into which data is converted by the PLCP for transmission.
This is the PHY Layer Convergence Procedure and it transforms each 802.11 frame that a station wishes to send into a PLCP protocol data unit, PPDU.
& & PDSU: &
This is the Physical Layer Service Data Unit, it represents the contents of the PPDU, i.e., the actual data to be sent.
This field is always set to . The802.11 standard reserves its data and format for future use.
For the ERP-OFDM PHY option an ERP packet must be followed by a 6 &s period of no transmission called the signal extension period. The reason for this that for a 16 &s period was allowed in 802.11a to enable convolutional decode processing to finish before the next packet arrived.
Within 802.11g, the ERP-OFDM modulation scheme still requires 16 &s to ensure that the convolutional decoding process is able to be completed within the overall process timing. To enable this to occur, a signal extension of 6 &s is included. This enables the transmitting station to compute the Duration field in the MAC header. In turn this ensures that the NAV value of 802.11b stations is set correctly and compatibility is maintained.
Share this page
More wireless tutorials
Latest news
& & . . . .
Jeff Hastings | BrightSign LLCJeff Hastings of BrightSign has some interesting ideas on why fans should not be used in digital signage, and how to avoid using them.
Learn the essentials without complex mathematics
Forthcoming Events
& & . . . .
Popular Articles
& & . . . .
Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is (C) Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy}