From owner-freebsd-wireless@FreeBSD.ORG Thu Aug 28 04:00:12 2014 Return-Path: Delivered-To: freebsd-wireless@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B7FAFB59; Thu, 28 Aug 2014 04:00:12 +0000 (UTC) Received: from a.mx.bartk.us (173-10-122-205-BusName-Washington.hfc.comcastbusiness.net [173.10.122.205]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 8B7B517AC; Thu, 28 Aug 2014 04:00:11 +0000 (UTC) Received: from [192.168.42.2] (splurge [192.168.42.2]) by a.mx.bartk.us (Postfix) with ESMTP id 8A33E3D004A; Wed, 27 Aug 2014 21:00:10 -0700 (PDT) Message-ID: <53FEA94A.3080602@bartk.us> Date: Wed, 27 Aug 2014 21:00:10 -0700 From: Bart Kus User-Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Adrian Chadd Subject: Re: FreeBSD TDMA: Legalizing 440MHz 802.11 modems References: <53FE5CF4.1000901@bartk.us> <53FE6513.8040107@bartk.us> <53FE6BDC.5030306@bartk.us> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.18-1 Cc: "freebsd-wireless@freebsd.org" X-BeenThere: freebsd-wireless@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "Discussions of 802.11 stack, tools device driver development." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Aug 2014 04:00:12 -0000 Well I'll be damned, looks like 5MHz mode on Mikrotik is just slower signalling! All 52-subcarriers are indeed there, although a little hard to see: If you count peaks left/right of center, you'll get 26. 2*26=52, so that's every sub accounted for. Can you point me at your 5/10MHz docs? And which analog filter you're referring to? --Bart On 8/27/2014 4:47 PM, Adrian Chadd wrote: > On 27 August 2014 16:38, Bart Kus wrote: >> I'm guessing the chip generates its own internal clocks from an external >> reference. Can that PLL be slowed down ahead of timers overflowing? >> Hopefully the PCI clock is generated independently. > Yeah, that's what you're slowing down - you program the PLL. > > The PCI clock is generated separately. > >> Also, I think Mikrotik implements narrower bands by dropping subcarriers >> instead of slowing down their symbol rates. I'll try to get a good spectrum >> picture of their 5MHz mode tonight. Keeping the subcarrier symbol rates >> relatively higher might offset some analog droops, at the cost of OFDM skirt >> sharpness. > Hey cool, if they're doing that then I should likely go digging for > the PHY documentation for the AR5414 and find out. > >> Also, a slight correction. I think you meant the subs are 312.5kHz wide, >> which would result in a 200kHz emission having 3.125kHz wide subs. Or, >> perhaps more realistically, running at 1/128th the speed, 2.44140625kHz >> wide. How can you not love a number like that? :) > Someone else can do better math, I'm busy doing non-wifi at the moment. :) > > But, it really is 20MHz / 64 carriers == each subcarrier width. > >> Does the project have a map of all these clocks + timers which might need >> tweaking for spectrum reduction? I know you can't cite original Atheros >> docs, but perhaps there's been derivative documentation works created? > Not at the moment I'm afraid. I haven't really dug into that level of > detail. I documented what's needed for 5 and 10MHz modes. > > However - there's an analog filter that I don't know if it's > programmable or not. It's used for both transmit and receive > filtering. I know on these chips it can do 5/10/20/40 but I don't know > if it's an arbitrary width. > > > -a