On Mon, 27 Jun 2016, Sebastian Moeller wrote:
On a wireless network, with 'normal' omnidirctional antennas, the signal
drops off with the square of the distance. So if you want to service clients
from 1 ft to 100 ft away, your signal strength varies by 1000 (4 orders of
magnatude), this is before you include effects of shielding, bounces, bad
antenna alignment, etc (which can add several more orders of magnatude of
variation)
The receiver first normalized the strongest part of the signal to a constant
value, and then digitizes the result, (usually with a 12-14 bit AD
converter). Since 1000x is ~10 bits, the result of overlapping tranmissions
can be one signal at 14 bits, and another at <4 bits. This is why digital
processing isn't able to receive multiple stations at the same time.
But, I you add 10 Bits to your AD converter you basically solved this.
Now, most likely this also needs to be of higher quality and of low internal
noise, so probably expensive... Add to this the wide-band requirement of the
sample the full band approach and we are looking at a price ad converter. On
the bright side, mass-producing that might lower the price for nice
oscilloscopes...
well, TI only manufactures AD converters up to 16 bit at these speeds, so 24 bit
converters are hardly something to just buy. They do make 24 and 32 bit ADCs,
but only ones that could be used for signals <5MHz wide (and we are pushing to
160 MHz wide channels on wifi)
also note my comment about walls/etc providing shielding that can add a few more
orders of magnatude on the signals.
And then when you start being able to detect signals at that level, the first
ones you are going to hit are bounces from your strongest signal off of all
sorts of things.
You will also find that noise and distortion in the legitimate strong signal is
going to be at strengths close to the strength of the weak signal you are trying
to hear.
As I said, I see things getting better, but it's going to be a very hard thing
to do, and I'd expect to see reverse mu-mimo (similarly strong signals from
several directions) long before the ability to detect wildly weaker signals.
I also expect that as the ability to more accurately digitize the signal grows,
we will first take advantage of it for higher speeds.
David Lang
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