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

To: foundation who wrote (25022)	7/28/2002 12:36:36 PM
From: Clarksterh	Respond to of 196952

Adjacent Channel Interference for W-CDMA - Well golly batman!! This has been a known issue for a long long time. I remember Tero et al saying that W-CDMA was going to be more spectrally efficient than 3x because it made use of more of the band in 5 MHz and it was pointed out back to them that there is a reason for the guard band in 3x (or 1x for that matter). And there were arguments about really steep filters (so the signal drops off very rapidly outside its band) and the cost/complexity/tuning/SNR ... impacts that such a filter involved. Ultimately driving up the cost of W-CDMA and driving down the usable data rate. You would think that they would have researched the **** out of a well known and potentially huge problem. This is a big deal and the only new twist is that it is something that DoCoMo, as the sole operator, won't notice to anywhere near the same extent. Clark

To: foundation who wrote (25022)	8/1/2002 11:21:39 AM
From: RalphCramden	Read Replies (1) \| Respond to of 196952

WCDMA adjacent channel problems are a little overblown. This is a subtle problem and at least two things in the article are wrong, IMHO. The issue is that adjacent channel emission is ~45 dB down from the actual transmit frequency. But signal levels in a cell range from about -25 dBm to -100 dBm, anywhere from 60 to 140 dB of path loss! This path loss is nearly completely due to the distance from the base station doing the radiating. Then if two adjacent channels are radiated from the same base station, they essentially never interfere. Close to the base station, the desired signal is at -25 dBm and the interference is at -70 dBm. Far from the base station the desired signal is at -100 dBm and the interference at -145 dBm. But if the adjacent channels are radiated from different base stations, problems develop when user in system A is near a base station for system B. When this happens, the interference power user in A gets from B can be ~-70 dBm. But then depending on how far user is from BTS in A, his "real" signal is anywhere from -25 to -100 dBm. If his signal is above ~-60 dBm, there is minimal impact from the interference. If his signal is at -70 dBm, then system A must use twice as much RF power to serve this caller. If his signal is much below -70 dBm, he will lose his call on system A due to "jamming" from system B. As you might imagine, this will be a very local problem, local to the respective base stations of the A and B providers. It does not wipe out large areas. Further, it is in BOTH systems interest to cooperate on this issue. If B is adjacent to A, then A is adjacent to B, and if B doesn't help A solve problems, they are nearly guaranteed to have problems with interference from A. ****************** Having said all that, it still seems stupid to go to a channel width that is so large that it makes it hard to do frequency allocations. It remains to be seen what possible performance benefit you will get from this wide channel that you did not already get from the 1.25 MHz channel we all know and love. To the moon, Ralph