WIFI测试技术(好)

1、WIFI测试技术 2013年2月17日硬件测试技术分享会系列目录一WIFI技术概述1. WIFI简介2.WIFI标准3.WIFI调制技术二WIFI架构实现三WIFI性能测试目录一WIFI技术概述1. WIFI简介2.WIFI标准3.WIFI调制技术二WIFI架构实现三WIFI性能测试WIFI简介 Wi-Fi 俗称无线宽带,其实就是 IEEE 802.11b 的别称，是由一个名为“无线以太网相容联盟”（Wireless Ethernet Compatibility Alliance, WECA）的组织所发布的业界术语，中文译为“无线相容认证”,是一种短程无线传输技术。 WIFI的突出优势有三：1

2、.无线电波的覆盖范围广，覆盖半径可达100米，而蓝牙只有15米；2.传输速度快，可以达到54Mbps；3.厂商进入的门槛低，不需网络布线接入。 缺点是：无线通信质量差、数据安全性能比蓝牙差；传输质量也有待改进。WIFI标准 目前常用的标准为：802.11b、802.11a、802.11g、802.11n1. 802.11b 工作频段：2.4GHz 调制技术：DSSS/CCK（直接序列扩频/补码键控） 数据速率：1、2、5.5Mbps/11Mbps 覆盖范围较大，可达100m 产品已发展到第四代或第五代 技术和产品已成熟 1999年被IEEE批准WIFI标准2. 802.11a 工作频段：5GH

3、z 调制技术：OFDM（正交频分多路复用） 数据速率：54Mbps 传输距离在10100m之间 成本高，无法占据市场主导3. 802.11g 工作频段：2.4GHz 调制技术：OFDM（正交频分多路复用） 数据速率：54Mbps 比11a的功耗小、传输距离长、穿透力强 2001年被IEEE批准，2003年正式发布。WIFI标准4. 802.11n 工作频段：2.4/5GHz 调制技术：MIMO OFDM 数据速率：300Mbps甚至600Mbps 采用智能天线技术，覆盖范围可达好几平方公里 高兼容性：当工作在2.4GHz时可向下兼容11b/g 当工作在5GHz时可向下兼容11a 2009年被I

4、EEE批准WIFI调制技术1. DSSS（Direct Sequence Spread Spectrum） 直接序列扩频技术将窄带信息信号扩展成宽带噪声，通过将射频载波和伪噪声（PN）数字信号有效地相乘来执行数据处理。 抑制干扰能力强 功率谱密度低，具有隐蔽性和低的截获概率 具有保密性 抗多径衰落 可高精度测量 对外界的干扰小，固定干扰运行WIFI调制技术2. CCK（Complementary Code Keying） 补码键控CCK 是应用于IEEE802. 11b 中物理层的调制方式。在无线局域网通信中, 它支持两种速率5. 5 Mb/ s 和11 Mb/ s。CCK 的码字有很强的位置

5、对称性和良好的自相关特性, 可以很好地克服多径干扰,所以在雷达和通信中都得到了很好的应用。在数字通信领域, 补偿码被广泛用于正交频分复用OFDM 、多接入和多信道通信等场合。 11Mbps DSSS物理层采用补码键控(CCK)调制模式，CCK具有多信道工作特性，IEEE802.11b通过使用CCK调制技术来提高数据传输速率，最高可达11 Mbit/s。WIFI调制技术3. OFDM（Orthogonal Frequency Division Multiplexing） 正交频分复用技术是将信道分成若干正交子信道，将高速数据信号转换成并行的低速子数据流，调制到每个子信道上进行传输。 频谱效率高

6、带宽扩展性强 抗多径衰落 频谱资源灵活分配 实现MIMO技术较简单u高的峰平比（PAPR）u均衡和同步，受同步误差的影响较大u对频偏和相位噪声敏感目录一WIFI技术概述1. WIFI简介2.WIFI标准3.WIFI调制技术二WIFI架构实现三WIFI性能测试WIFI架构实现2.4G 11M无线网络无线网络AP342无线接入点二AP342无线接入点五AP342无线接入点十二专线热点中心机房PDAAP342无线接入点一数据库WIFI架构实现WIFI架构实现目录一WIFI技术概述1.WIFI简介2.WIFI标准3.WIFI调制技术二WIFI架构实现三WIFI性能测试WIFI性能测试测试的涵义测试的关

7、系测试的现状WIFI性能测试 接 收：灵敏度 距离 EMS：邻道功率抑制 发 射：功率、载频容差 接 收：丢包率无线 质量(WIFI) 发 射：EVM 接 收：接收杂散 EMI 发 射：发射杂散、6dB带宽Definitions1. Extreme test conditions: Temperature: 0C to +55C The frequency range and the e.i.r.p. limit shall not be exceeded. e.i.r.p.(equivalent isotropic radiated power)2. Normal test conditio

8、ns: Temperature: +15C to +35C Relative humidity: 20 % to 75 %3. Test standard: CE: ETSI EN300 328(V1.7.1 (2006-7 10) FCC: FCC Part 15WIFI性能测试4. Data rate:Data rate VS powerWIFI性能测试When IEEE 802.11bs data rate was 2Mbps, IEEE 802.11gs data rate was 6Mbps, the EUT have maximum output power and so all

9、the test was perpormed in this data rate set. 2.4GHz channel VS frequency5. Channel frequency:Channel VS frequencyChannelFrequency(MHz)ChannelFrequency(MHz)Frequency(MHz)Frequency(MHz)124126243711246222417724421224673242282447132472424279245214248452432102457/WIFI性能测试Performance test 1.Carrier frequ

10、ency errorDefinition: The frequency error of the transmitter is the difference between the measured carrier frequency in the absence of modulation and the nominal frequency of the transmitter.Test channel: L/M/H.Test procedure: The transmitter output was connected to an ondometer or a spectrum analy

11、zer, the carrier frequency was measured by an ondometer or spectrum analyzer with 10kHz RBW ,10kHz VBW and 50 - 100kHz sweep bandwidth .Test condition: normal & extreme conditionLimit: 50ppmWIFI性能测试2. Maximum transmit power Definition: The maximum transmit power is defined as the maximum isotrop

12、ic radiated power of the equipment. Test channel: L/M/H. e.i.r.p.(equivalent isotropic radiated power) Test condition: normal & extreme condition Limit: C E： 20dBm(100 mW or -10 dBW ) FCC： 30dBm(1W )WIFI性能测试3.EVM (Error Vector Magnitude)Definition: The EVM is the vector difference between the ac

13、tual transmit signal and the ideal reference transmit signal at a fixed point.WIFI性能测试Perror：the average power for error vectorPreference：the average power for reference sinalEVMdB=20*log(EVM%)SNR= -20LogEVMLimit11g54Mbps, EVM-25dB 11g48Mbps, EVM-22dB 11b : EVM 2.4 GHz and fH 2.4835 GHzWIFI性能测试6. Tr

14、ansmitter spurious emissions Definition: Transmitter spurious emissions are emissions outside the frequency range(s) of the equipment when the equipment is in transmit mode and/or in standby mode. Test channel: L/M/H. Test condition: normal condition Limit: C E：WIFI性能测试6. Transmitter spurious emissi

15、ons Test channel: L/M/H. Test condition: normal condition Limit: FCC：In any 100kHz bandwidth outside the frequency bands in which the spread spectrum intentional radiator in operating, the radio frequency power that is produced by the intentional radiator shall be at least 20dB below that in the 100

16、kHz bandwidth within the band that contains the highest level of the desired power.WIFI性能测试7.6dB bandwidthDefinition: The 6dB bandwidth is defined as the total spectrum the power of which is higher than peak power minus 6dB.Test channel: L/M/H.Test condition: normalTest procedure: The transmitter ou

17、tput was connected to a spectrum analyzer, The bandwidth of the fundamental frequency was measured by spectrum analyzer with 120kHz RBW and 300kHz VBW.Limit(FCC): For direct sequence systems, the minimum 6dB bandwidth shall be at least 500kHz.WIFI性能测试8. Receiver spurious emissions Definition: Receiv

18、er spurious emissions are emissions at any frequency when the equipment is in received mode. Test channel: L/M/H. Test condition: normal Limit(CE):WIFI性能测试9. Receiver sensitivity Definition: The receiver sensitivity is the level of receiver input signal at a specified frequency with specified modula

19、tion that will result in the 8%(for 11b) or 10%(for 11g) PER at the output of the receiver. Test channel: L/M/H. Test data rate: L/H Test condition: normal & extreme condition Limit: -76dBm for IEEE802.11b -65dBm for IEEE802.11gWIFI性能测试10. Maximum receive level Definition: The maximum receive level is the maximum level of receiver input signal