Wi-Fi Test Knowledge Twenty: Basic Knowledge of 802.11b (2)
1. 802.11b frame format introduction
802.11b can provide rates of 1Mbit/s, 2Mbit/s, 5.5Mbit/s, 11Mbit/s, and supports long PLCP Preamble and short PLCP Preamble formats. The long PLCP Preamble format must be supported, and the short PLCPPreamble format is optional. . The long PLCP Preamble format and the short PLCP Preamble format are shown in Figure 1 and Figure 2. As can be seen from the figure, the main differences between the two are:
| 帧格式 | Long PLCP Preamble | short PLCP Preamble |
| PLCP Preamble长度 | 144Bit | 72bit |
| PLCP Preamble调制方式 | DBPSK调制 | DQPSK调制 |
| PLCP Preamble速率 | 1Mbit/s | 2Mbit/s |
| PLCP Preamble格式的PSDU域速率 | 1Mbit/s、2Mbit/s、5.5Mbit/s、11Mbit/s | 2Mbit/s、5.5Mbit/s、11Mbit/s |
Table 1 Long PLCP Preamble format
Figure 2 short PLCP Preamble format
2. IEEE 802.11b test
Test item indicators specified by IEEE
| 准备编号 | 测试项目 | 要求 |
| 17.4.7.2 | Transmit power Levels (发射功率） |
Follows national regulatory requirements for2.4GHz ISM band |
| 17.4.7.4 | Transmit spectrum mask (频谱模板） |
Defined limit mask |
| 17.4.7.5 | Transmit center frequency tolerance (中心频率容限） |
±25 ppm |
| 17.4.7.6 | Chip clock frequency tolerance (码片时钟频率容限） |
±25 ppm |
| 17.4.7.7 | Transmit power-on and power-down ramp (上升时间/下降时间） |
< 2us |
| 17.4.7.8 | RF carrier suppression (载波抑制） |
15 dB for unscrambled 10 payload |
| 17.4.7.9 | Transmit modulation accuracy (调制精度） |
<0.35 EVM peak for highest date rate |
| 17.4.8.2 | Receiver minimum input sensitivity (接收机灵敏度） |
11Mbit/s:FER<8% for -76 dBm input. 5.5Mbit/s: FER<8% for -78 dBm input. 2Mbit/s: FER<8% for -80 dBm input. 1Mbit/s: FER<8% for -82 dBm input. |
| 17.4.8.3 | Receiver maximun input level (接收机最大输入电平） |
11Mbit/s:FER<8% for -76 dBm input. 5.5Mbit/s: FER<8% for -78 dBm input. |
| 17.4.8.4 | Transmit adjacent channel rejection (接收机邻道功率抑制） |
ACR>35 dB with FER<8%,25MHz separation |
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