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.
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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 |
