Date: Sat, 06 May 2000 23:49:00 -0600 From: Warner Losh <imp@village.org> To: nate@yogotech.com (Nate Williams) Cc: Mike Smith <msmith@FreeBSD.ORG>, hackers@FreeBSD.ORG Subject: Re: [OT] Finding people with GSM phones (was Re: GPS heads up ) Message-ID: <200005070549.XAA68658@harmony.village.org> In-Reply-To: Your message of "Sat, 06 May 2000 12:50:04 MDT." <200005061850.MAA18384@nomad.yogotech.com> References: <200005061850.MAA18384@nomad.yogotech.com> <200005061840.MAA18274@nomad.yogotech.com> <200005061855.LAA07340@mass.cdrom.com>
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With CDMA, you can get a distance very easily. The phones know what time it is, or CDMA doesn't work at all. That helps a lot. Much of GPS's work is knowing what time it is. Since the phone knows what time it is, they can do all kinds of calculations and round trip things to get the distance. From there, you have a 120degreep arch to worry about. Since CDMA towers have 3 antennas, you likely get use slight phase differences between them to narrow it down further. The CDMA folks at qualcomm tend to be smart (although as they have gotten larger, this tendacy is weaker than it was), so I wouldn't be surprised if they thought real hard and were able to do something simple in the end because it happened to fall out of the equasions. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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