Hi chandrasekhar,
Most commonly used Cellular Antenna Diversities are Space Divsity & Polarization Divsty.
Space Div is to get signal via different paths and therefore to have a gain by combining those signals, & its mainly used for Uplink.
Polarisation diversity means, use of different polarisations (eg. +45/-45) to ensure the optimal coupling at both receiving & transmitting ends.
Rgds