The strength of the signal received by mobile phone from cellular network is called signal strength. Various factors like distance between mobile and cellular tower, weather, obstruction like trees, walls affects the signal strength.
Signal strength of mobiles are generally measured in two ways.
dBm- decibel-milliwatts
The power ratio per one milliwatt is known as dBM.
asu - Arbitrary Strength Unit
The received signal strength is measured in asu. Calculations of asu is different for LTE, GSM etc..
Step 1 : Navigate to "About phone" in your mobile setting.
Step 2 : In "About phone", you can see details regarding phone. Navigate to status for information about IMEI, SIM card and other information.
Step 3 : Navigate to "SIM card status" in status.
Here you can see information regarding your SIM. The signal strength of your respective SIM is displayed under signal strength label.
