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Wireless & Mobility · Intermediate

System Operating Margin (SOM)

The actual difference between received signal level and the receiver's sensitivity.

Definition

SOM is calculated as received signal strength minus receiver sensitivity and represents how much signal could be lost before the link fails. It should meet or exceed the planned fade margin. It is verified after installation of a bridge link.

Example

Received -60 dBm with -85 dBm sensitivity yields 25 dB SOM.

Exam tip

Compare SOM with fade margin to judge whether a link is robust.

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