Selection combining

Various techniques

• Equal-gain combining: All the received signals are summed coherently.
• Maximal-ratio combining is often used in large phased-array systems: The received signals are weighted with respect to their SNR and then summed. The resulting SNR yields ${\displaystyle \sum _{k=1}^{N}SNR_{k}}$ where ${\displaystyle SNR_{k}}$ is SNR of the received signal ${\displaystyle k}$.
• Switched combining: The receiver switches to another signal when the currently selected signal drops below a predefined threshold. This is also often called "Scanning Combining".
• Selection combining: Of the N received signals, the strongest signal is selected. When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be ${\displaystyle \sum _{k=1}^{N}{\frac {1}{k}}}$, expressed as a power ratio. Therefore, any additional gain diminishes rapidly with the increasing number of channels. This is a more efficient technique than switched combining.