Re: Ofdm transmitter and receiver

[Marcus Müller]

Hi Sourya,

On 12.03.24 20:09, Sourya Saha wrote:
> I am working with an OFDM transmitter and receiver. Some article says that
> the number of subcarriers decides the SCS. I could not find any formula
> that relates to it.

Is SCS = subcarrier spacing?

In that case, yes,  the number of subcarriers is directly inverse to the subcarrier 
spacing. Remember that OFDM is "just" doing a DFT, so you get the sampling rate divided by 
the number of DFT bins. Which is the number of subcarriers.

You shouldn't be reading "some articles"; OFDM isn't hard when one learns it from a good 
textbook. It *is* hard when one needs to learn it from research articles, spectrum 
analyzer application notes and random blog articles :)

If you have a good basic education in digital communications, Proakis' "Digital 
Communications", I think starting from 4th or 5th edition. In the third edition (which can 
be bought very cheaply used), it's called "An FFT-based Multicarrier System",  but it's 
really OFDM, just without the name. Either way, that chapter would have explained the same 
as I did above!

If you need a slightly gentler entry to OFDM (in the lectures on digital communications 
that I've been part of, we treated it as something rather advanced, because explaining 
*why* it is like it is requires understanding of a lot of channel concepts), you would 
probably *not* want to rely on Proakis.

Instead, you could try the free "Software-Defined Radio for Engineers" by Travis Collins 
et al.,
https://www.analog.com/en/resources/technical-books/software-defined-radio-for-engineers.html

it does come with the motivation, it illustrates the OFDM spectral shape well, and 
introduces the terminology; it is nice and will (mostly) only require you to have 
understood the chapters 2, 4 and 9.

> Also, if I want to operate the OFDM in a frequency
> range of 490Mhz to 680 Mhz for example, how do i make the blocks use that
> frequency range?

None. Because OFDM deal with the radio frequencies at all, it deals with the *equivalent 
baseband*.

You might be really a bit confused about the basics here; I'd recommend "SDR for 
engineers" as quoted above, or the even gentler entry through pysdr.org (but pysdr.org 
doesn't cover OFDM, so you'd need to switch to different material once you're through with 
the content on pysdr.org).

Best regards,
Marcus