Subject: [manet] Preamble length of IEEE 802.11a OFDM PHY

From: [email-masked]
Date: Sat, 7 May 2005 08:51:53 +0800 (CST)

Hi, all!

 In IEEE Std 802.11a-1999 Table 93?OFDM PHY characteristics, I find that aPreambleLength is 20 &micro;s. But now I need to know the preamble length of IEEE 802.11a OFDM PHY measured in bit. In Figure 122?PLCP transmit procedure, PLCP Preamble is 12 symbols. How to understand the meaning of one symbol?
 
 Any information will be appreciated!
 Thanks in advance!
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From: Jim Thompson <[email-masked]>
Date: Fri, 6 May 2005 19:33:45 -1000

The 802.11a (and 802.11g) preamble consists of 12 symbols.  The first 
ten of the symbols are so-called short symbols.  These are followed by 
two long symbols.

The short symbols are typically used for establishing Automatic Gain 
Control (AGC) and the coarse frequency estimate of the carrier signal. 
The receiver uses the long symbols for fine-tuning.

The duration of a short OFDM training symbol in the 802.11a PHY is 800 
ns, the same length as the GI.  The duration of a long training symbol 
is 4us, and there are two GIs between the
short and long training symbols, but the GIis 'counted' as part of the 
long training symbols' duration.   Thus, it takes 16ns (10 * 0.8ns + 2 
* 4ns) microseconds to train the receiver

The entire preamble is sent using BPSK with a 1/2 convolutional coding 
rate.

I'll let you do the math from there.

jim

On May 6, 2005, at 2:51 PM, [email-masked] wrote:

>  Hi, all!
>
>  In IEEE Std 802.11a-1999 Table 93?OFDM PHY characteristics, I find 
> that aPreambleLength is 20 µs. But now I need to know the preamble 
> length of IEEE 802.11a OFDM PHY measured in bit. In Figure 122?PLCP 
> transmit procedure, PLCP Preamble is 12 symbols. How to understand the 
> meaning of one symbol?
>
> ????????????????
> ???????????