1
\$\begingroup\$

I've got an unusual use case (optical communications) that would benefit from access to the wifi baseband signal before it is upconverted/modulated at 2.5Ghz. However most modern wifi chips combine baseband encoding and transmission encoding/transceiver functions on a single chip. Are there chips, or chipsets, that split these functions and would allow for custom final encoding - in my case OOK laser diode modulation at << GHz frequencies?

\$\endgroup\$
1
\$\begingroup\$

Your request makes no sense - WiFi baseband is OFDM, and can't be converted to OOK.

None of the things that WiFi does to synchronize would even work with OOK.

It seems to me that you just want the bits going into the modulator. If that's the case: you don't need any hardware - that is exactly what your operating system sends to your WiFi card, and you need just a tap device (Linux networking terminology) to give you access to raw L2 packets.

Based on these, write software that controls youe light source. Later, port that to become a proper network card device driver.

\$\endgroup\$
  • \$\begingroup\$ Ah ok thank you, I think I was misunderstanding how WiFi works. Doing a bit more reading, I think any of the PSK/QAM schemes that WiFi OFDM subcarriers use would also work - the main limitation seems to be accessing them pre upconversion them to 2.4GHz (what I'm reading suggests that this encoding is done pre-upconversion). Does this one make sense or I am still misunderstanding? \$\endgroup\$ – rossmcbee Jul 15 '18 at 21:53
  • \$\begingroup\$ The baseband signal is still OFDM -that means, it consists of 52 (of 64 potentially used) carriers, and they never exist in isolation. Also, I have my doubts regarding you being able to modulate the phase of your light source! \$\endgroup\$ – Marcus Müller Jul 16 '18 at 8:07
  • \$\begingroup\$ Ok, I think I'm getting there. So is the raw bitstream that hits the WiFi card already ODFM modulated, or is that always and forever done in line with the transceiver and is therefore not recoverable? Wouldn't be trying for a light phase modulation (though a en.wikipedia.org/wiki/Electro-optic_modulator can do that) - would just be modulating a sufficient bandwidth but <2.4GHz carrier, say ~100MHz if the 22MHz bandwidth/4us symbol duration listed on wikipedia is accurate. Thanks so much for your help and patience! \$\endgroup\$ – rossmcbee Jul 16 '18 at 16:05
  • \$\begingroup\$ is the raw bitstream that hits the WiFi card already ODFM modulated, or is that always and forever done in line with the transceiver and is therefore not recoverable? OFDM is something that happens in the transceiver hardware, and you won't be able to get the baseband samples out of that. \$\endgroup\$ – Marcus Müller Jul 16 '18 at 16:15
  • \$\begingroup\$ Ok, that's what I was afraid of. Would have been nice to not have to rebuild all of that well-thought-out encoding and error correction if I could skim it before upconversion, but c'est la vie. \$\endgroup\$ – rossmcbee Jul 16 '18 at 17:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.