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IR communication protocol/design for low latency/fast response - ideas?

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ogden:

--- Quote from: pwlps on May 14, 2019, 10:55:48 am ---Again my loose wording. Talking QPSK I had in mind the demodulation technique whatever the actual number of points in the constellation.

--- End quote ---

It's "terms all over the place", not loose wording.


--- Quote ---Quadrature phase-shift keying (QPSK)
Sometimes this is known as quadriphase PSK, 4-PSK, or 4-QAM. (Although the root concepts of QPSK and 4-QAM are different, the resulting modulated radio waves are exactly the same.) QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol
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--- Quote ---There is no ASK vs PSK issue in fast IrDA since it uses a baseband PPM coding without any carrier.

--- End quote ---

Sure. Do you know why? - Because using IR LED you can't modulate phase or frequency of the light, only amplitude!

pwlps:

--- Quote from: ogden on May 14, 2019, 12:23:14 pm ---
--- Quote ---Quadrature phase-shift keying (QPSK)
Sometimes this is known as quadriphase PSK, 4-PSK, or 4-QAM. (Although the root concepts of QPSK and 4-QAM are different, the resulting modulated radio waves are exactly the same.) QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol
--- End quote ---

--- End quote ---

And so what? There is nothing here in contradiction with what I say.


--- Quote ---Sure. Do you know why? - Because using IR LED you can't modulate phase or frequency of the light, only amplitude!

--- End quote ---
Now I should be the one to mark a 'BS' (and a big one :)).   Of course you can, it seems you are completely confusing light frequency (I'm not talking about this) and carrier frequency.  IrDA doesn't use carrier but other IR (or any light) applications can use it, e.g. in the so called multiple frequency phase-shift technique used by laser rangefinders. 

ogden:

--- Quote from: pwlps on May 14, 2019, 02:12:57 pm ---it seems you are completely confusing light frequency (I'm not talking about this) and carrier frequency.

--- End quote ---

Confusement is fully yours  :-DD

Quiz: What do you think is carrier in case of laser rangefinder? - Sound waves, radio waves or light waves?

pwlps:

--- Quote from: ogden on May 14, 2019, 02:27:34 pm ---Quiz: What do you think is carrier in case of laser rangefinder? - Sound waves, radio waves or light waves?

--- End quote ---

Light wave is not really carrier because we don't use it's phase information (except in interferometric devices, but we weren't  talking about this).  Laser rangefinders use carrier frequencies in the range of tens of MHz.  Call it subcarrier if you want, I will not argue on terminology.

ogden:

--- Quote from: pwlps on May 14, 2019, 02:42:26 pm ---Light wave is not really carrier because we don't use it's phase information (except in interferometric devices, but we weren't  talking about this).

--- End quote ---

Right. - That's because using IR LED you can't modulate phase or frequency of the light anyway, only amplitude. Wait.... Didn't I say it before? 8) Whatever are your terminology, IRDA association did not pick phase modulation but PPM instead for a good reason. I did say that as well. No need to reinvent the wheel - just take what is already developed.

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