what is the CCA?
Clear Channel Assessment (CCA) is one of two carrier sense mechanisms in WLAN (or WiFi). It is defined in the IEEE 802.11-2007 standards as part of the Physical Medium Dependant (PMD) and Physical Layer Convergence Protocol (PLCP) layer. CCA involves two related functions - CCA-CS and CCA-ED.
Carrier Sense (CCA-CS): Ability of the receiver to detect and decode a WiFi preamble. From the PLCP header field, the time duration (in us) for which the medium will be occupied can be inferred and when such WiFi preamble is detected the CCA flag is held busy until the end of data transmission.
Energy Detect (CCA-ED): Ability of the receiver to detect non-WiFi energy in the operating channel and back off data transmission. The ED threshold is typically defined to be 20dB above the minimum Rx sensitivity of the PHY. If the in-band signal energy crosses this threshold, CCA is held busy until the medium energy is below the threshold.
For more info on CCA for the OFDM PHY (802.11a/g/n), you may want to read the CCA Sensitivity section 17.3.10.5 in the IEEE 802.11 standards document.
作者:khldragon
出处:http://www.cnblogs.com/khldragon/
本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。
俗话说,投资效率是最成功的投资。 如果您感觉我的文章质量不错,读后收获很大,感觉能为您提高 10% 的工作效率,不妨小额【赞助】我一下,让我有动力继续写出更多好文章。