Diversity gain is the increase in signal-to-interference ratio due to some diversity scheme, or how much the transmission power can be reduced when a diversity scheme is introduced, without a performance loss.
Diversity gain is usually expressed in decibels, and sometimes as a power ratio.
For selection combining N signals are received, and the strongest signal is selected.
When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be
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