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

To: Clarksterh who wrote (23238)	5/31/2002 9:45:31 AM
From: rkral	Read Replies (1) \| Respond to of 196652

And how do you know the framing is right? If the framing isn't right, all is lost. :-( But then, an E911 message won't be received anyway .. so it matters not if the time is incorrect. :-) For EOTD the accuracy of one timing sample and range is at best on the order of 1.5 km ... That's an absolutely horrible number .. 1.5 km is about 5 micro-seconds at the speed of light. Is that coming from the 0.2 MHz bandwidth or from +/-1 GSM bit time? I don't really understand what you mean by "timing sample and range". Range? But remember that the mobile and the LMU are both "reading their accurate clocks" when the same data is received from the same BTS. (That's the assumption at this point.) The difference in these clock readings, along with the known BTS to LMU distance, is then used to calculate the BTS to mobile distance. So the error in "one sample" should be much less than 5 micro-seconds. ... and there is no changing multipath. That's the error source that would really scare me, were I in a position of technical responsibility at a GSM SP in the U.S. with its E911 requirements. And the multipath doesn't even have to be changing for it to be a problem. IMHO, there is already a problem if there is a direct path to the LMU, and a reflected path to the mobile. But A-GPS may have a problem with multipath too. I don't know yet. Ron