Date: Wed, 27 Aug 2014 21:05:39 -0700 From: Bart Kus <me@bartk.us> To: freebsd-wireless@freebsd.org Subject: Re: FreeBSD TDMA: Legalizing 440MHz 802.11 modems Message-ID: <53FEAA93.1020505@bartk.us> In-Reply-To: <53FEA94A.3080602@bartk.us> References: <53FE5CF4.1000901@bartk.us> <CAJ-VmokUyrvE-2bgkHDE9sCGJv_3EEffqWVWySvYf=7ra4PfUA@mail.gmail.com> <53FE6513.8040107@bartk.us> <CAJ-VmomNCMy8%2BihYyFFSW1oTVKNQDaaQjXqDxYLxDWCLjb0dDg@mail.gmail.com> <53FE6BDC.5030306@bartk.us> <CAJ-VmonTTPfpHzAF-L95EP4ZXChH1Gb4AKmkPYNC6YE3ymqQ0g@mail.gmail.com> <53FEA94A.3080602@bartk.us>
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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 <me@bartk.us> 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"
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