From owner-freebsd-wireless@FreeBSD.ORG Thu Aug 28 04:05:40 2014 Return-Path: Delivered-To: freebsd-wireless@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 80D1CD97 for ; Thu, 28 Aug 2014 04:05:40 +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 622951885 for ; Thu, 28 Aug 2014 04:05:39 +0000 (UTC) Received: from [192.168.42.2] (splurge [192.168.42.2]) by a.mx.bartk.us (Postfix) with ESMTP id 7F6A43D004A for ; Wed, 27 Aug 2014 21:05:39 -0700 (PDT) Message-ID: <53FEAA93.1020505@bartk.us> Date: Wed, 27 Aug 2014 21:05:39 -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: freebsd-wireless@freebsd.org Subject: Re: FreeBSD TDMA: Legalizing 440MHz 802.11 modems References: <53FE5CF4.1000901@bartk.us> <53FE6513.8040107@bartk.us> <53FE6BDC.5030306@bartk.us> <53FEA94A.3080602@bartk.us> In-Reply-To: <53FEA94A.3080602@bartk.us> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 04:05:40 -0000 Fixed original email with imgur URL since mailing list strips attachments. --Bart On 8/27/2014 9:00 PM, Bart Kus wrote: > 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: > > http://i.imgur.com/d50zApc.png > > 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 > > _______________________________________________ > freebsd-wireless@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-wireless > To unsubscribe, send any mail to > "freebsd-wireless-unsubscribe@freebsd.org"