WCDMA phone coverage bars

[m121]

Hi,
I am interested in understanding how in 3G systems phones are calculating how many bars to show in given RF conditions? Maybe somebody knows is this specified in 3GPP specifications and what parameters are affecting it (like min RxLevel and MinQual values like in GSM systems)?
In GSM as far as I know it's involves RxLevMin and signal strength but in UMTS there is also Quality involved.