Hello,
Concerning diversity, there are several types of diversity and all of them to avoid fading. What I mean to say is that the signal transmitted form the mobile is subjected to scattering, reflections, refractions…etc due to the surrounding terrain. These signals may reach the receiver (antenna in our case) either in phase (constructive) which is good or out of phase which is destructive resulting in a zero amplitude signal level (just like to sinusoidal signals shifted by 180 degrees) . So to avoid such phenomena we need to have diversity and in case you have fading on one path the probability to have the same fading on another one is relatively very small. Moreover, you’ll have a gain of 2-3 dBs in the UL direction only.
I hope made it clear…