Re: Why when I send a complex file with harmonic sequence f1 f2 f3 ...fn, In receiver haromoic sequence gain is changed?

[Marcus Müller]

Hi sp,

yes, *equalization*; **many** approaches to that, and which one you chose depends on many 
systemic factors and channel properties.

I think you're in for a bit of fundamentals; that's not something I could explain in an 
email (though I've really tried).

So, you seem to be concerned with modelling the frequency-selective channel. For that, you 
will need a bit of fundamental theory, or else things will seem very confusing.

On https://wiki.gnuradio.org/index.php/SuggestedReading#Digital_Comms we have collected 
some literature recommendations.
If I was to recommend something that is freely available for you, who needs to understand 
how a channel "works" before becoming able to remove its effect, it would be the book by 
Lapidoth, "A Foundation in Digital Communication"; it's free!
Since you already have seemed to work with digital signals in FPGAs, I think the first 
couple of chapters (1–4) will be easier than for the average person reading this book, as 
you already have a "feeling" for things, but might need some basic notation that helps 
describe and understand what is happening.
Chapter 5 and 6 and 7 are the most important to you. They describe what happens to your 
baseband signal.

Now, you really seem to want to be able to equalize a broadband channel. The right book 
for learning how these channels happen in the real world is Tse and Viswanath's 
"Fundamentals of Wireless Communication", which is also free! However, it really assumes 
you already know why LTI systems can lead to frequency-selective behaviour, so it honestly 
makes more sense reading Lapidoth first.

Best regards,
Marcus

On 08.05.22 12:08, sp h wrote:
> With this description for removing this frequency-selective channel which solution exist 
> in digital communications?
>
> On Sun, May 8, 2022 at 10:36 AM sp h <stackprogramer@gmail.com 
> <mailto:stackprogramer@gmail.com>> wrote:
>
>     Why when I send a complex file (With USRP x300) with harmonic sequence f1 
> f2 f3 ...fn,
>     In receiver (USRP x310) harmonic sequence gain is changed?
>     For example, I have a complex file the FFT of a signal has some harmonic 
> peaks f1 f2 ...fn
>     gain of harmonic peaks in the original file is:
>     f1:2
>     f2:2
>     f3:3
>     f4:4
>     ...
>     fn=3
>
>     But receiver loss or amplify harmonic peaks are not consonant
>     For example, in the receiver we had:
>     f1:5
>     f2:1
>     f3:4
>     f4:7
>     ...
>     fn=.1
>
>     So when I used MatLab to convert complex files to Wav and play file 
> original file and
>     received file is not exactly the same...
>     some higher frequency is suppressed or the sound is more bass. Is this 
> subject related
>     to TDH?
>     In USRP what's TDH?
>     https://en.wikipedia.org/wiki/Total_harmonic_distortion
>     <https://en.wikipedia.org/wiki/Total_harmonic_distortion>
>     can anyone guide me?
>     Thanks in advance

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