Diversity gain
Encyclopedia
In wireless
Wireless
Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

 communications, diversity gain is the increase in signal-to-interference ratio due to some diversity scheme
Diversity scheme
In telecommunications, a diversity scheme refers to a method for improving the reliability of a message signal by using two or more communication channels with different characteristics. Diversity plays an important role in combatting fading and co-channel interference and avoiding error bursts...

, 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 decibel
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

, and sometimes as a power ratio. An example is soft handoff gain.
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 , expressed as a power ratio.
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