The history of orthogonal frequency-division multiplexing (2009)

https://ieeexplore.ieee.org/abstract/document/5307460

by teleforce • 2 years ago

42 24 2 years ago

ieeexplore.ieee.org

brudgers2• 2 years ago

https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=530...

floam2• 2 years ago

Neat. Can one resolve the arnumber parameter stamp.jsp takes for articles in general or did that require being logged in?

floam2• 2 years ago

Hmm, looking into it myself, it looks not generalizable, short of searching for the document title and hoping you get lucky. This wasn’t a direct paywall bypass.

It looks like this is actually just a version of the document published a different way.

Posted to HN from IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference:

https://ieeexplore.ieee.org/abstract/document/4698465

Same thing but free from IEEE Communications Magazine, vol. 47, no. 11:

https://ieeexplore.ieee.org/abstract/document/5307460

Person I replied to clicked the PDF button on the freely-available version.

Liftyee• 2 years ago

OFDM is one of those technologies that I haven't been able to conceptually grasp. Thinking in a frequency/phase space instead of a (DC) voltage/time space hasn't quite "clicked" for me yet.

paulgerhardt2• 2 years ago

I found this playlist to be one of the better explanations: https://www.youtube.com/watch?v=F6B4Kyj2rLw&list=PLx7-Q20A1V...

drmpeg3• 2 years ago

Stupid OFDM tricks.

https://www.youtube.com/watch?v=saac0ZtTeX4

paulgerhardt2• 2 years ago

Fun. You should link the github in the youtube. I assume it's this one? https://github.com/drmpeg/gr-paint

drmpeg3• 2 years ago

Yes, that's the one. I also have a more useful OFDM project, an ATSC 3.0 transmitter.

https://github.com/drmpeg/gr-atsc3

jhallenworld• 2 years ago

This is a great talk if you want to know how it's implemented:

"Recent Interesting and Useful Enhancements of Polyphase Filter Banks: fred harris"

https://www.youtube.com/watch?v=afU9f5MuXr8

drmpeg3• 2 years ago

No, that has nothing to do with OFDM.

nakulgarg222• 2 years ago

Orthogonality is a beautiful concept.

In physics, different frequencies don’t interfere with each other—they're always independent. However, in digital operations and mathematics, this isn’t automatically true, so we need to carefully select the right frequencies.

OFDM leverages this by ensuring that, in the frequency domain, certain frequencies remain completely separate, meaning changes to one frequency (in amplitude or phase) won't affect the others.

This allows us to capture the maximum information with limited samples.

jjtheblunt3• 2 years ago

In physics, different frequencies don’t interfere with each other—they're always independent.

Are you overlooking harmonics? Are you overlooking the same frequency case of noise cancellation, via phase shift?

layer82• 2 years ago

Phase shift isn’t different frequencies?

nakulgarg222• 2 years ago

You're correct - I oversimplified assuming no doppler effect and a linear time invariant system.

The key is that we can still analyze and manipulate frequency components independently in REAL PHYSICAL WORLD, which enables techniques like OFDM.

peterbmarks• 2 years ago

The codec2 project includes an HF OFDM that can be run from a command line. https://github.com/drowe67/codec2

01HNNWZ0MV43FF2• 2 years ago

Sounds a little bit like CDMA. My professor in college didn't make it obvious why CDMA is any better than just assigning one carrier frequency to each transmitter. [1]

The Wikipedia page for OFDM [2] says something like, if there's interference or attenuation affecting one frequency, it's better to spread that out instead of completely losing one channel. Which kinda makes sense, and would make more sense if I'd ever done RF work. I'd love to do SDR as a hobby some day.

[1] The explanation in the book was something like, "See with 100 frequencies, you can create 100 chips and each user gets 1 chip, so you can support 100 users" which sounded pointless to me.

[2] https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...

aidenn0• 2 years ago

Any spread-spectrum technology has advantages when there is fading only some frequencies (a normal thing to happen in cities with these large surfaces that reflect RF called "buildings").

CDMA has an added advantage that the bit-error-rate is inversely proportional to the number of people communicating. With just giving everybody a single channel (or timeslot for TDMA), you either have enough or you don't. When you give everybody their own code, then you end up with either a small number of very high quality channels (few people communicating) or a large number of much lower quality channels (many people communicating). This was seen as advantageous when cell networks were rapidly growing.

I don't think it's used much for terrestrial anymore, but it is still used in satellites.

The history of orthogonal frequency-division multiplexing (2009)

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