OFDM carriers spacing

[panji]

Hi,
I have read tutorial : OFDM
In OFDM , sub carrier frequencies are harmonic to first carrier c1.If n is an integer number so cn=nxc1.
At page 5 and 6 there was an example of OFDM using 4 sub carriers. Frequency of the first carrier was 1Hz and carrier 2 frequency is 2 Hz (harmonic to 1'st carrier) then carrier 3 frequency is equal to 3 Hz and carrier 4 is 4Hz.
If I pick 16QAM as modulation scheme and 5Ghz as carrier freq (like IEEE 802.11 standard) with (for example) 30 sub carriers. Is it meaning that 1'st carrier freq c1=5GHz, carrier 2 C2= 2x5Ghz,c3=3x5Ghz,etc...
I'm not sure about that.
Can you explain to me?

Thanks

[charan langton]

It works like this. Lets say you want to transmit a signal of 10 mbps. This will take app. 12 Mhz of bandwidth. The OFDM you have chosen has 1024 carriers. So the frequency spacing of these carriers will be 12 MHz/1024 = 11,719 Hz. So if you are starting at 5 GHz then you would add 11,719 Hz as your second carriers and same amount until you have 1024 carriers. So the first few carriers will have frequencies of: 5000000000, 5000011719, 5000023438, 5000035156.

And as you can see these carriers differs by an integer number so are suitable for OFDM signalling. Although 5, 6, and 7 GHz certainly are integers, this would be take far too much bandwidth so would not be used.

Charan Langton

[panji]

It's gr8 and very helpful
Thank You