
The End of Spectrum Scarcity (2004) - apsec112
https://spectrum.ieee.org/telecom/wireless/the-end-of-spectrum-scarcity
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superkuh
Even if we get cognitive radio and share spectrum there are still fundamental
and engineering limits that mean spectrum will remain scarce. You're either
sharing one spectrum with the entire world for HF (because of ionosphere
bouncing) or everything that is in line of sight for the vast majority of the
spectrum. That means a _lot_ of people are using the same 0.1-18 GHz. Once you
get above 18 GHz or so then the propagation gets a lot worse, so it's less
than even line of sight, but engineering problems with phase error start
meaning higher order modulations are much more difficult to achieve.

Spectrum is always going to be scarce. That's why cables and fibers are always
going to be important. Each one allows you to use the entire span all to
yourself.

~~~
user5994461
Agreed. The title is disappointing, especially coming from the IEEE.

Anybody who works on radio quickly understands that the radio spectrum is the
most precious most scarce resource on the planet.

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at-fates-hands
Not knowing much about radio spectrum, but its a finite resource right?
There's no way to expand the spectrum, or do something similar like what they
did in the early days of wireless technology where they transitioned from TDMA
(time division multiple access) to CDMA (code division multiple access) in
order to expand the number of user you can put on a data stream.

Am I right to look at radio spectrum as a finite resource?

~~~
sharpneli
Those examples are ways to use the spectrum more efficiently. But the amount
we have does not change.

It is finite indeed. But it’s also not something that’s consumable. Imagine it
as a fixed sized room. If you move stuff out of a corner you can reuse it
infinitely, but there can only be so much stuff in there on a particular
moment.

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metaphor
DARPA Spectrum Collaboration Challenge[1] spent 3 years exploring this space
with SDR + AI in a gamified way[2] and announced its winner last year[3].

[1] [https://www.darpa.mil/program/spectrum-collaboration-
challen...](https://www.darpa.mil/program/spectrum-collaboration-challenge)

[2]
[https://www.youtube.com/watch?v=-a-N8MiMqz0](https://www.youtube.com/watch?v=-a-N8MiMqz0)

[3] [https://www.darpa.mil/news-events/2019-10-24](https://www.darpa.mil/news-
events/2019-10-24)

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d-sc
If there is more capacity available, people will use it.

For instance, I happily stream videos and FaceTime over cellular quite a bit
now. Even though I was plenty happy without that capability and don’t really
mind when the cell service isn’t good enough for it to work.

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hinkley
How does signal processing change when you know that part of the signal is
much more likely to arrive intact than others? Do you use it for more error
correction, or do you send multiple classes of traffic in each message? Like
the color channels on a black and white TV signal?

I know a little bit of theory but I have a big gap in broad spectrum
scenarios.

~~~
user5994461
Bandwidth is physically bounded by frequency * log(noise ratio). As long as
you've got a great signal, much better than what you can decode, you can
increase the bandwidth.

The most common example is broadband. The 2 MHz band is split in a hundred
independent bands of 20 MHz. Each one of the channel is adjusted independently
to maximize bandwidth.
[https://en.wikipedia.org/wiki/G.992.3](https://en.wikipedia.org/wiki/G.992.3)

~~~
hinkley
We are talking about software defined radio though. How do these facts apply
when there are no bands anymore? When collisions are avoided probabilistically
instead of by partitioning?

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sephamorr
No change. Just because your radio is "software defined," doesn't change
physics and signal processing math. There are 'best' ways to use a given piece
of spectrum, and while a SDR can make your hardware more flexible, it can't
change that the most efficient way to use spectrum is usually to have a dense
set of subcarriers modulating amplitude and phase. By avoiding a strict
multiple-access protocol on a band, everything just gets worse; probabilistic
back off is inefficient vs hard-scheduling. Every wireless system I've worked
on (satellite radio, WiFi, LTE) has been very spectrum constrained, so I dont
really believe in this future where spectrum is cheap.

~~~
petra
In some sense,mesh WiFi doesn't seem spectrum constrained(considering home
use) - just install enough mesh AP's.

~~~
rini17
Won't work unless the AP's scrupulously adhere to protocol to avoid
interference. In practice the 2.4GHz interference has became tragical. In
European high density housing, you are likely to have precipitous speed drop
moving only across the room from the AP or behind one wall.

