Date: Mon, 8 May 2000 21:39:04 -0400 (EDT) From: Chuck Robey <chuckr@picnic.mat.net> To: Warner Losh <imp@village.org> Cc: Nate Williams <nate@yogotech.com>, Mike Smith <msmith@FreeBSD.ORG>, hackers@FreeBSD.ORG Subject: Re: [OT] Finding people with GSM phones (was Re: GPS heads up ) Message-ID: <Pine.BSF.4.21.0005082132120.3027-100000@picnic.mat.net> In-Reply-To: <200005081600.KAA77785@harmony.village.org>
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On Mon, 8 May 2000, Warner Losh wrote: > In message <Pine.BSF.4.21.0005071358090.79947-100000@picnic.mat.net> Chuck Robey writes: > : Curious about that, I haven't been following it too closely, but I know > : cdma works on codes, not timing ... how do they get timing (other than bit > : clock recovery)? > > cdma does work on timing. It effectively transmits all the data all > the time. Phones need to know when the start of frame is, which means > they need to know what time it is. They can get that from the last > start of frame, and the rate of start of frames they are seeing. cdma > and tdma are different in some ways, but they both have to know what > time it is to work. ?? I'm a little confused. Most of my direct experience with sequences comes from test equipment. I asked a friend with some recent experience in CDMA, about 2 weeks ago, and that lady told me that they were using the same PN sequences that I was right at home with, and only differentiated one code from another by the offset in the code that the message was synced to. The point being, at least for the PN sequences used in test equipment, syncing isn't done by timing, it's pretty trivially done by a shift register and feedback. Million bit long sequences are synced in 20 bits, no big deal. I'm sure many people on this list (certainly Rod) know this technique, and there isn't any timing factor involved. I'm not trying to tell you you're wrong, but I'm having trouble connecting the dots. Is my lady informant all wet? Or, am I misunderstanding you? > > Warner > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > ---------------------------------------------------------------------------- Chuck Robey | Interests include C & Java programming, FreeBSD, chuckr@picnic.mat.net | electronics, communications, and signal processing. New Year's Resolution: I will not sphroxify gullible people into looking up fictitious words in the dictionary. ---------------------------------------------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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