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Technology Stocks : Qualcomm Moderated Thread - please read rules before posting -- Ignore unavailable to you. Want to Upgrade?

To: rkral who wrote (23190)	5/30/2002 1:51:55 PM
From: pheilman_	Read Replies (1) \| Respond to of 196646

Re: E-OTD (Enhanced-Observed Time Difference) technology Doesn't work with just two BTS. And doesn't work well with linear arrays. Web site is either intentionally or unintentionally wrong. The case shown is the best possible case for the system, if the mobile is not between the BTS, the error margins do not minimize. The colinear case does not work in general, as they state there are three unknowns, x, y, and time. OK, two stations 10 km apart and a mobile. The mobile transmits, both base stations receive and measure time difference of arrival (t1). Since the exact time of transmission from the mobile is not known, all that can be concluded is the relative distances(?) from the two base stations. d1 = d2 + c*t1. So for your case of two BTS and the mobile in between, the estimated location would be a line perpendicular to the highway, as long as the timing uncertainty between the BTS and the Mobile. The problem is the unknown clock offset at the mobile. (Poor fools probably didn't bother to put GPS in their base stations either.) For a more academic presentation of how DTOA works, check out: multispectral.com This is a paper from 2000 on an ultimate position locating system, using UWB signals and optimal receivers. On page 8 it is clear once the transmitter gets to the same side of all the receivers, the estimate of location degrades, a lot. DTOA has been used in Electronic Warfare for decades, it is not new theory. Paul