Dear Pix, thanx for your nice answer and usefull details.
The bad Rxqual is resuilted in bad conditions in the air interface
The the only reason of bad Rxqual is interference
One more question:
Network A: SQI=30, Rxqual=0
Network B: SQI=30, Rxqual=2
Is the quality same for both customers of the two netowrk?
If the answer is YES, I am wondring why engineers take the Rxqual (not the SQI) in the benchmarking ?!