MIME-Version: 1.0
In-Reply-To: <4DE82191.3010205@openwrt.org>
References: <BANLkTi=-MDn9eAsRsoXtAetDOZehkMEhJw@mail.gmail.com>
 <201105241627.49201.helmut.schaa@googlemail.com> <BANLkTikcEsKYo=c=ZmzJRbmfgjmrFmx9bg@mail.gmail.com>
 <BANLkTin4MvdbqugTjtXvmjz5N8_TyTY7OA@mail.gmail.com> <BANLkTi=xfv_0C1mVAtO=w5JqyXLvh=vtAQ@mail.gmail.com>
 <BANLkTimMXbZE=vY95C0b2H3hx=4XWdU2Qg@mail.gmail.com> <BANLkTi=rS_kDhB8oKBLsz2Mk2nvRJMu5mg@mail.gmail.com>
 <4DDD5691.2040205@openwrt.org> <BANLkTi=1uj52P208p--5NU=Ow4rDndMkAw@mail.gmail.com>
 <BANLkTimRiU9Pv1B1=VC3XuREbmnpLk3S7w@mail.gmail.com> <4DDE2F5B.3020804@openwrt.org>
 <BANLkTimuaOoV0uvyzs9PbeK_k6vwOG=+YA@mail.gmail.com> <4DDEEEEC.6010800@openwrt.org>
 <BANLkTi=fT-Hdio9ArZKFMZCPX0LGLjGB=A@mail.gmail.com> <BANLkTikhihyTqg+yR8MnR1cp5wJ35sybNA@mail.gmail.com>
 <4DE82191.3010205@openwrt.org>
From: "Luis R. Rodriguez" <mcgrof@gmail.com>
Date: Thu, 2 Jun 2011 22:23:24 -0700
Message-ID: <BANLkTikCqZ65nZU6F+7iktKKTZdUV-Kx6w@mail.gmail.com> (sfid-20110603_072348_326217_D7BB6457)
Subject: Re: Initial automatic channel selection implementation
To: Felix Fietkau <nbd@openwrt.org>
Cc: Matt Smith <smithm@qca.qualcomm.com>,
	Sundar Sankaran <sunsanka@qca.qualcomm.com>,
	Helmut Schaa <helmut.schaa@googlemail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	hostap@lists.shmoo.com
Content-Type: text/plain; charset=UTF-8
Sender: linux-wireless-owner@vger.kernel.org

On Thu, Jun 2, 2011 at 4:49 PM, Felix Fietkau <nbd@openwrt.org> wrote:
> On 2011-06-03 12:36 AM, Luis R. Rodriguez wrote:
>>
>> On Thu, May 26, 2011 at 5:59 PM, Luis R. Rodriguez<mcgrof@gmail.com>
>>  wrote:
>>>
>>>   What I'd like to do is to affect the ratio to nullify it if the noise
>>>   is very low on the channel. Given that noise is logarithmic we'd have
>>>   to use a logarithmic function as well. Working on that now.
>>
>> OK I've figured a way to plug the noise into this, I designed the
>> following function we can use as a factor:
>>
>> 1.1^(x+110)
>>
>> Wolfram|Alpha boring details of this function:
>>
>> http://bit.ly/mJNXE9
>>
>> x,y results of different noise values in dBm, using apcalc:
>>
>> mcgrof@tux ~ $ calc
>> C-style arbitrary precision calculator (version 2.12.3.3)
>> Calc is open software. For license details type:  help copyright
>> [Type "exit" to exit, or "help" for help.]
>>
>> ; define f(x) = 1.1^(x+110)
>> f(x) defined
>>
>> ; f(-130)
>>        ~0.14864362802414368640
>> ; f(-120)
>>        ~0.38554328942953174736
>> ; f(-119)
>>        ~0.42409761837248492210
>> ; f(-118)
>>        ~0.46650738020973341431
>> ; f(-117)
>>        ~0.51315811823070675574
>> ; f(-116)
>>        ~0.56447393005377743132
>> ; f(-115)
>>        ~0.62092132305915517445
>> ; f(-114)
>>        ~0.68301345536507069189
>> ; f(-113)
>>        ~0.75131480090157776108
>> ; f(-112)
>>        ~0.82644628099173553719
>> ; f(-111)
>>        ~0.90909090909090909091
>> ; f(-110)
>>        1
>> ; f(-109)
>>        1.1
>> ; f(-108)
>>        1.21
>> ; f(-107)
>>        1.331
>>
>> So then, we'd use a frequency for initiating beaconing (AP, Mesh, P2P)
>> which uses the lowest value from the following computation:
>>
>> (busy time - tx time) / (active time - tx time) * 1.1^(noise + 110)
>>
>> The 1.1 factor can be modified more accurately to represent the
>> exponential factor of how noise should affect interference decisions,
>> the 110 value here can be modified for any other arbitrary value we
>> find as representative of a regular noise value from a simple AP on
>> the frequency we are observing, my assumption here was -110 dBm.
>
> -110 dBm is not a real noise value. It's an unrealistic, ath9k-specific
> value. I have a patch that changes ath9k to make noise and signal strength
> values more realistic, and I'll submit it soon, as soon as I've made it a
> bit more precise.

Nice. As I noted though this value is arbitrary for now, we can change
it at will. Any other feedback? If not I'll start hacking on it.

 Luis