802.11b 速率

802.11b 支持的速率有: 1Mbps, 2Mbps, 5.5Mbps以及11Mbps,但是这些速率 是如何计算出来的呢?

802.11b速l率是如何计算出来的

The different data rates have different chipping methods, with 1 and 2 Mbps using the Barker code and 5.5 and 11 using CCK. To calculate the total throughput, you have relate chipping method to the bits each data rate sends along with the symbol rate (modulation symbol changes per second) they use. Both run at 11 Mchips/s so the symbol rates look like this:

Barker Code - 11 chip code

Symbol Rate = 11,000,000 / 11 = 1 Msps

CCK - 8 chip code

Symbol Rate = 11,000,000 / 8 = 1.375 Msps

Then you take the Number of Bits each rate transmits and multiply is by the symbol rate:

1 Mbps = 1 bit x 1 Msps

2 Mbps = 2 bits x 1 Msps

5.5 Mbps = 4 bits x 1.375 Msps

11 Mbps = 8 bits x 1.375 Msps

The key here is that the symbol rate is only different between the code types, not the data rates themselves. It's those extra bits being sent over the same rate.