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Technology Stocks : Qualcomm Moderated Thread - please read rules before posting

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Nov 14 3:59 PM EST

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To: rkral who wrote (23206)	5/30/2002 6:15:02 PM
From: pheilman_	Read Replies (1) of 196654

EOTD....At least Cambridge Positioning Systems didn't try to claim this was new technology. Agreed the frequency reuse will cause problems, but, even without other transmitters, GSM is not very good for doing RF triangulation. It is narrowband. This is why GPS is a spread spectrum transmission, you can time the chips and even sub-chips for accuracy. With a narrowband transmitter and receiver I believe the uncertainty is related to the bandwidth and with GSM at (frantic web search) 200 KHz. The crude method for RF timing is to sample the rising edge and use it crossing a threshold, works poorly as the received power is different at the two BTS. Next step is to use a differential threshold vs. a delayed copy of the signal, works a little better, but notice the edge can never be "faster" than the BW, low bandwidth signal, poor estimate of location. Next clever move is to time off a transmitted timing pattern, still limited by the BW. Now toss in the distant transmitters on the same frequency and it becomes even more difficult to locate a transmitter. Paul

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