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Re: [Discuss-gnuradio] OFDM Mod Block - how is it working?

From: rear1019
Subject: Re: [Discuss-gnuradio] OFDM Mod Block - how is it working?
Date: Tue, 9 Jul 2019 20:47:41 +0200

On Tue, 09 Jul 2019 at 17:42:11 +0200, lilijobo1 lilijobo1 wrote:
> <div>The thing is that I don&#39;t really get how the parameters 
> &quot;occupied tones&quot; and the &quot;FFT length&quot; work in that case. 
> Is the occupied tones equal to the numer of subcarriers? If yes where do get 
> to know the subcarrier spacing because if I&#39;m right this is different for 
> LTE or 802.11a .</div>
> <div>And what about the parameter &quot;FFT length&quot;?</div>

Occupied tones determines the number of used (occupied) carriers, i.e.
the number of carriers which contain data and pilots. The number of
carriers which can be used at most is determined by the FFT length.

Carrier spacing Δf_c is determined by Δf_c = 1/T_s where T_s is the
length of the OFDM symbol (cyclic prefix not included). Assuming a
sampling rate of f_s you get Δf_c = 1/(N·(1/f_s)) = f_s/N where N is the
required length of the FFT.

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