Re: [Bloat] sigcomm wifi

[Jonathan Morton <chromatix99@gmail.com>]

On 24 Aug, 2014, at 2:40 am, Steinar H. Gunderson wrote:

> On Sun, Aug 24, 2014 at 02:29:50AM +0300, Jonathan Morton wrote:
>> Multi-target MIMO allows an AP to transmit to several clients
>> simultaneously, without requiring the client to support MIMO themselves.
>> This requires the AP's antennas and radios to be dynamically reconfigured
>> for beamforming - giving each client a clear version of its own signal and
>> a null for the other signals - which is a tricky procedure.  APs that do
>> implement this well are highly valuable in congested situations.
> 
> FWIW; I don't think you're right about the nulls. Beamforming has some gain,
> and there are some “darker spots”, but they're not what the algorithm is
> aiming for (it aims to maximize the signal at the client, not to minimize it
> at all other clients), and it's not -inf dB, more like -10 dB.

That's true of plain beamforming, whose goal is to increase SNR to a particular client.  That's been around since 802.11g days.  But that's not what I'm talking about here.

I'm talking specifically about 802.11ac multi-target MIMO, which *does* attempt to null out the other clients to which it is simultaneously transmitting, purely so that it *can* transmit to them simultaneously.  But that's only two or three other clients to form nulls for, not the hundred others who are not involved in that particular timeslot.

 - Jonathan Morton