From owner-freebsd-wireless@FreeBSD.ORG Thu Aug 28 07:46:43 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 69869F3B for ; Thu, 28 Aug 2014 07:46:43 +0000 (UTC) Received: from mail-qg0-x22a.google.com (mail-qg0-x22a.google.com [IPv6:2607:f8b0:400d:c04::22a]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 1A8211D86 for ; Thu, 28 Aug 2014 07:46:43 +0000 (UTC) Received: by mail-qg0-f42.google.com with SMTP id a108so392343qge.29 for ; Thu, 28 Aug 2014 00:46:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:sender:in-reply-to:references:date:message-id:subject :from:to:cc:content-type; bh=mS7JbQzIPBwnf765lx8Jg5PrUVEWWso4TCfhnGJF+bI=; b=g1TLsGPzq+bzKb0h0uTryAaBfZji4i5kO952GJH3e0Yvwx1Wm0pGOaElG3f3LJ5f8Z 3rlQWlZMdx5e8KG4futmdUocrdsVw2BijRcVL44n7vCd+889g6BW6O7HExK6wv9QKx1/ dU/DDx4B+EexWrEhVJR1AtkneTOOrcq3TUY9xvx4YTXxfmgHm4FXAiznGgo/Fm8k8QzK YycusilMJ5S8rdeqCkDAhjr+p0JOzLgKiGVRg1EeOkTKhbPsTMOF/beXu89WlfjF4tRI QvmHWnbYp7n2JZxgiMpF25CJYgGVE2iSBepBXAhw/LfC92BedbNY5v26N3vNBBA8q3Ip tXdA== MIME-Version: 1.0 X-Received: by 10.229.38.3 with SMTP id z3mr3772332qcd.17.1409212001988; Thu, 28 Aug 2014 00:46:41 -0700 (PDT) Sender: adrian.chadd@gmail.com Received: by 10.224.39.139 with HTTP; Thu, 28 Aug 2014 00:46:41 -0700 (PDT) In-Reply-To: <53FEA94A.3080602@bartk.us> References: <53FE5CF4.1000901@bartk.us> <53FE6513.8040107@bartk.us> <53FE6BDC.5030306@bartk.us> <53FEA94A.3080602@bartk.us> Date: Thu, 28 Aug 2014 00:46:41 -0700 X-Google-Sender-Auth: M_GZFZInFwZmNl62U3bATZ64lKU Message-ID: Subject: Re: FreeBSD TDMA: Legalizing 440MHz 802.11 modems From: Adrian Chadd To: Bart Kus Content-Type: text/plain; charset=UTF-8 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 07:46:43 -0000 Yup, that's what I thought. I'll go dig it up. The analog filter is something on the front end, just before the transmit/receive RF side. It acts as a filter to ensure (a) decent rejection of adjacent channel signals being received and (b) the transmit spectral mask is being met. -a On 27 August 2014 21:00, 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: > > > > 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 > > >