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Re: [Discuss-gnuradio] Scaling down IFFT values

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Scaling down IFFT values
Date: Thu, 16 Oct 2014 14:44:20 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

Hi you!
>Any pointer on where should I make the change?
Yes. Do it before preambling!
The inverse dft is a linear operation; it doesn't really matter whether
you scale before or after. Note though that the IFFT as we use it adds a
sqrt(length_of_fft) factor, so account for that by dividing your scaling
factor by it.


On 16.10.2014 13:35, zealdeal wrote:
> Hi All,
> I need to scale down the OFDM transmission signal in time domain, after IFFT
> is done, so that, all the values are within the range -1 to 1. But, I cant
> simply add one more "scaling" block after cp_adder in
> self.connect(self.preambles, self.ifft, self.cp_adder, self.scale, self) 
> (file: ofdm,py)
> as it will scale down the preamble also, leading to non-recognition of
> packet at receiver end.
> Any pointer on where should I make the change?
> --
> View this message in context: 
> http://gnuradio.4.n7.nabble.com/Scaling-down-IFFT-values-tp50833.html
> Sent from the GnuRadio mailing list archive at Nabble.com.
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