In CDMA, GSM technology we use antenna system to transmit and receive signals from mobile and from BTS. One of the characteristic of antenna is antenna gain. dBi and dBd is a unit to measure antenna gain with respect to isotropic antenna and dipole antenna respectively.
Dipole has 2.15 dB gain compared to an isotropic antenna, hence
dBi = 2.15 dB + dBd
For example an omni antenna has antenna gain 12.15 dBi or 10 dBd
