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# 802.11a training symbols - some problems

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#### efundas

##### Member level 3
802.11a training symbols

I am working on 802.11a phy. I was having some problem understanding how the training symbols are generated. Can anyone help me with an example.

U can generate it directly refered to the appendix in the standard.Or u can first generate the frequency domain symbol then translate it into time domain via ifft.Note that the cyclic append method is different from other symbol.

I was going through the standard. I found that the duration of short training symbols is 8us. In examples of the appendix it is shown for 160 samples for a duration of 8ms. I am getting confused, as to how many bit are there in the 10 short training symbols. Also what is the wt function that is to be taken etc.

Dear efundas,

You are correct in that the duration of the short preamble is 8us. The sample rate in the Appendix is 20MHz which gives us the number of samples in the short preamble as 8e-6*20e6=160 samples.
Here is an example of how you can generate the short preamble in matlab:

c = 1+1i;
Ws = zeros( 1, 64 );
S = sqrt(13/6)*[ 0 0 c 0 0 0 -c 0 0 0 c 0 0 0 -c 0 0 0 ...
-c 0 0 0 c 0 0 0 0 0 0 0 -c 0 0 0 -c 0 0 0 c 0 0 0 ...
c 0 0 0 c 0 0 0 c 0 0 ];
Ws(7:59) = S;
xs = ifft( fftshift(Ws) );

Please note that you will need to do cyclic extension of xs to get 160 samples.

The function wt is a windowing function that is used to create smooth transitions between symbols. This, in turn, is to avoid creating transients in the time domain which will cause the spectrum of your transmitted signal to exceed the spectrum mask. In the standard an example of such a windowing function is given, but it is not mandatory to use that function. Instead you can use some other windowing function or use time domain filtering after signal generation.

Good luck,
Cyberdome

Dear cyberdome
i'm working on 802.16a standard and i have some problem in MAC section of it i think you have some experence on 802.11 which similar to 802.16a,i want to know if you can help .
reza

Dehbashi@usa.com
cyberdome said:
Dear efundas,

You are correct in that the duration of the short preamble is 8us. The sample rate in the Appendix is 20MHz which gives us the number of samples in the short preamble as 8e-6*20e6=160 samples.
Here is an example of how you can generate the short preamble in matlab:

c = 1+1i;
Ws = zeros( 1, 64 );
S = sqrt(13/6)*[ 0 0 c 0 0 0 -c 0 0 0 c 0 0 0 -c 0 0 0 ...
-c 0 0 0 c 0 0 0 0 0 0 0 -c 0 0 0 -c 0 0 0 c 0 0 0 ...
c 0 0 0 c 0 0 0 c 0 0 ];
Ws(7:59) = S;
xs = ifft( fftshift(Ws) );

Please note that you will need to do cyclic extension of xs to get 160 samples.

The function wt is a windowing function that is used to create smooth transitions between symbols. This, in turn, is to avoid creating transients in the time domain which will cause the spectrum of your transmitted signal to exceed the spectrum mask. In the standard an example of such a windowing function is given, but it is not mandatory to use that function. Instead you can use some other windowing function or use time domain filtering after signal generation.

Good luck,
Cyberdome

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