Hi Parsa48,
Poor uplink quality on U900 could be due to many reasons.
Have you checked dominance in the area.
Is it just one site or cluster of sites.
Check for Scrambling code clashes.
Get it drive tested and analyse log files.
Check if there is external interference.
What is the value of Prx Noise you are getting.
Check 3G-2G and 3G-3G neighbours.