How about spread spectrum?

Quote from [1] "Applying spread spectrum technology to RF transmissions is
an extremely effective method of securing both wireless voice and data at
the hardware level. It is a very robust TX/RX technology that is inherently
immune to inter-symbol interference (ISI), reflections, noise and other
environmental factors, as well as jamming."

Spread spectrum transceiver chips are readily available however they
typically will operate either at a higher frequency or lower bandwidth than
you want. A down converter may be necessary to shift things back down to
the frequency range that you want.

[1] http://semiengineering.com/kc/knowledge_center/Spread-Spectrum/225

On Wednesday, December 27, 2017, Forrest Christian (List Account) <
lists@packetflux.com> wrote:

> If I did my calculations right, you're at about 30 meters per half bit.
> Not sure about your environment, but it would seem like 30m isn't far
> enough especially considering possible strong ir reflective surfaces.   M=
y
> guess is that you'd end up with at least some dead areas, possibly a lot =
of
> dead areas, where a simple on off bitstream couldn't be recovered.  This =
is
> even more true if you are relying on reflections to get the ir signal
> through.  If you decide to try this, please report back with your finding=
s
> as I'm kinda curious.
>
> It would be interesting to investigate whether one of the rf digital
> modulation methods (ofdm/qam, psk, etc) could be applied.  Some of these
> are multipath sensitive, some are not so much.
>
> One possible ic resource is the power line modems such as the max2990.
> These are generally ofdm modems in various frequency bands.
>
>
> On Dec 26, 2017 12:26 PM, "Harold Hallikainen" <harold@mai.hallikainen.or=
g
> >
> wrote:
>
> Several years ago I designed a system that transmits audio and data over
> IR. The audio is transmitted as frequency modulated RF over IR. The data
> is transmitted is frequency shift keyed RF over IR. I've been thinking
> about direct digital modulation of the IR. The IR LEDs would be pulsed.
> The bit rate to carry the audio and digital would need to be in the area
> of 5 Mbps. Does anyone have experience, thoughts, or references on this?
> The IR is transmitted in a large room (movie theater auditorium). I'm
> concerned about reflections causing intersymbol interference. What do
> people think would be a good method of encoding the data (async, biphase,
> etc.)? Are such systems existing? Are there any chip sets?
>
> Thanks!
>
> Harold
>
>
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