Re: [Hackrf-dev] How does the hackrf generate the signals?

[Christopher Howard]

Hi, this page seems very helpful:

http://rfmw.em.keysight.com/wireless/helpfiles/89600b/webhelp/subsystems/wlan-ofdm/Content/ofdm_basicprinciplesoverview.htm

The basic idea is you can add as many sinusoid signals of different
frequencies into one signal as you want, before transmission. It looks
like in DSP applications, this is done with an inverse fast fourier
transform operation, where you start off with all the
frequency/amplitude information you want to send, and mathematically
transform that into a time domain signal. You add guard bands arounds
this "OFDM symbol" and transmit it.

Then on receive end you do the (non-inverse) FFT transform to get the
info back from the different frequencies.

So, really you are only generating one signal, but multiplexed with all
the subcarrier information.

-- 
Christopher Howard
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On Tue, 2020-04-07 at 03:20 +0200, Juan Antonio wrote:
> I've been wanting to understand how an ofdm signal is generated for a
> while and I can't
> 
> The hackrf generates similar signals but I also do not understand how
> it generates them. It seems impossible to generate 8000 carriers at
> the same time, therefore the only thing left is to generate them
> sequentially(to sample), generating a point and passing to the next
> frequency , thus until 8K and then go back to the beginning and go
> the same way.The trick would be to do it so fast that it is not
> noticeable to say it in any way
> 
> Thank  you
> ___
> HackRF-dev mailing list
> HackRF-dev@greatscottgadgets.com
> https://pairlist9.pair.net/mailman/listinfo/hackrf-dev


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Re: [Hackrf-dev] How does the hackrf generate the signals?

[Luis Bernal [n0p]]

Hackrf only works with IQ signals and doesn't "understand" the signal
being transmitted or received.

The OFDM (de)modulation is done on software on the computer. The
specific implementation varies. Try looking at the wikipedia page for
OFDM, it has a few implementation examples:

https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing#Implementation_using_the_FFT_algorithm

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[Hackrf-dev] How does the hackrf generate the signals?

[Juan Antonio]

I've been wanting to understand how an ofdm signal is generated for a while
and I can't

The hackrf generates similar signals but I also do not understand how it
generates them. It seems impossible to generate 8000 carriers at the same
time, therefore the only thing left is to generate them
sequentially(to sample), generating a point and passing to the next
frequency , thus until 8K and then go back to the beginning and go the same
way.The trick would be to do it so fast that it is not noticeable to say it
in any way

Thank  you
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HackRF-dev mailing list
HackRF-dev@greatscottgadgets.com
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