[Make-wifi-fast] [Cerowrt-devel] more well funded attempts showing market demandfor better wifi

David Lang david at lang.hm
Mon Jun 27 03:44:08 EDT 2016

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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