4 ms·

The history of orthogonal frequency-division multiplexing (2009)

42 points by teleforce 2y ago

brudgers 2y ago
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5307460 https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=530...
- floam 2y ago
  Neat. Can one resolve the arnumber parameter stamp.jsp takes for articles in general or did that require being logged in?
  - floam 2y 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 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 https://ieeexplore.ieee.org/abstract/document/5307460 Person I replied to clicked the PDF button on the freely-available version.
    - brudgers 2y ago
      I think I remember IEEE making everything available a few years ago…there’s probably an HN discussion if it happened (but it might have been ACM (or both)). If so, this would be an ordinary dark pattern of extracting payment where it is not absolutely necessary. Anyway, I googled the title based on my possibly accurate memory. In fairness my impression is that very few HN members ’give back’ by joining such organizations. It’s not part of today’s startup mindset.
      - Jtsummers 2y ago
        ACM is the one pushing towards open access for everything. IEEE is not as far along with that. It gets really annoying, I'm a member of a couple IEEE societies and find that I have to use my institutional login (GA Tech in my case) to reliably get access to their publications. With ACM, I join a SIG and I pretty much get the entirety of the SIG's digital library (even before the bigger open access push).
Liftyee 2y 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.
- paulgerhardt 2y ago
  I found this playlist to be one of the better explanations: https://www.youtube.com/watch?v=F6B4Kyj2rLw&list=PLx7-Q20A1VYIvtMUWX3yd_sQGbQx1qPGP https://www.youtube.com/watch?v=F6B4Kyj2rLw&list=PLx7-Q20A1V...
drmpeg 2y ago
Stupid OFDM tricks. https://www.youtube.com/watch?v=saac0ZtTeX4 https://www.youtube.com/watch?v=saac0ZtTeX4
- paulgerhardt 2y ago
  Fun. You should link the github in the youtube. I assume it's this one? https://github.com/drmpeg/gr-paint https://github.com/drmpeg/gr-paint
  - drmpeg 2y 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 https://github.com/drmpeg/gr-atsc3
jhallenworld 2y 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 https://www.youtube.com/watch?v=afU9f5MuXr8
- drmpeg 2y ago
  No, that has nothing to do with OFDM.
  - deleted 2y ago
    [deleted]
nakulgarg22 2y 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.
- jjtheblunt 2y 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?
  - layer8 2y ago
    Phase shift isn’t different frequencies?
    - jjtheblunt 2y ago
      Please check out the 3rd paragraph of this article. https://en.wikipedia.org/wiki/Active_noise_control https://en.wikipedia.org/wiki/Active_noise_control
      - layer8 2y ago
        I’m aware of how ANC works. It uses the same frequencies with reverse amplitude. The comment you objected to however was talking about different frequencies.
        01HNNWZ0MV43FF 2y ago
        > reverse amplitude Right? One of my dumb noobie questions has always been why textbooks explain ANC as "180 phase shift" instead of "reverse amplitude". Do they really do an entire DSP pass to break apart a signal and phase-shift it just to get the output that a minus sign could get? There must be something missing from the plum-pudding model.
peterbmarks 2y ago
The codec2 project includes an HF OFDM that can be run from a command line. https://github.com/drowe67/codec2 https://github.com/drowe67/codec2
01HNNWZ0MV43FF 2y 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_multiplexing https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...
- aidenn0 2y 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.

42 points by teleforce 2y ago

https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5307460 https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=530...

floam 2y ago
Neat. Can one resolve the arnumber parameter stamp.jsp takes for articles in general or did that require being logged in?
- floam 2y 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 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 https://ieeexplore.ieee.org/abstract/document/5307460 Person I replied to clicked the PDF button on the freely-available version.
  - brudgers 2y ago
    I think I remember IEEE making everything available a few years ago…there’s probably an HN discussion if it happened (but it might have been ACM (or both)). If so, this would be an ordinary dark pattern of extracting payment where it is not absolutely necessary. Anyway, I googled the title based on my possibly accurate memory. In fairness my impression is that very few HN members ’give back’ by joining such organizations. It’s not part of today’s startup mindset.
    - Jtsummers 2y ago
      ACM is the one pushing towards open access for everything. IEEE is not as far along with that. It gets really annoying, I'm a member of a couple IEEE societies and find that I have to use my institutional login (GA Tech in my case) to reliably get access to their publications. With ACM, I join a SIG and I pretty much get the entirety of the SIG's digital library (even before the bigger open access push).

Liftyee 2y 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.

paulgerhardt 2y ago
I found this playlist to be one of the better explanations: https://www.youtube.com/watch?v=F6B4Kyj2rLw&list=PLx7-Q20A1VYIvtMUWX3yd_sQGbQx1qPGP https://www.youtube.com/watch?v=F6B4Kyj2rLw&list=PLx7-Q20A1V...

drmpeg 2y ago

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

paulgerhardt 2y ago
Fun. You should link the github in the youtube. I assume it's this one? https://github.com/drmpeg/gr-paint https://github.com/drmpeg/gr-paint
- drmpeg 2y 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 https://github.com/drmpeg/gr-atsc3

jhallenworld 2y 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 https://www.youtube.com/watch?v=afU9f5MuXr8

drmpeg 2y ago
No, that has nothing to do with OFDM.
- deleted 2y ago
  [deleted]

nakulgarg22 2y 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.

jjtheblunt 2y 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?
- layer8 2y ago
  Phase shift isn’t different frequencies?
  - jjtheblunt 2y ago
    Please check out the 3rd paragraph of this article. https://en.wikipedia.org/wiki/Active_noise_control https://en.wikipedia.org/wiki/Active_noise_control
    - layer8 2y ago
      I’m aware of how ANC works. It uses the same frequencies with reverse amplitude. The comment you objected to however was talking about different frequencies.
      - 01HNNWZ0MV43FF 2y ago
        > reverse amplitude Right? One of my dumb noobie questions has always been why textbooks explain ANC as "180 phase shift" instead of "reverse amplitude". Do they really do an entire DSP pass to break apart a signal and phase-shift it just to get the output that a minus sign could get? There must be something missing from the plum-pudding model.

peterbmarks 2y ago

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

01HNNWZ0MV43FF 2y 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_multiplexing https://en.wikipedia.org/wiki/Orthogonal_frequency-division_...

aidenn0 2y 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.