Hi,
RSSI, or "Received Signal Strength Indicator", is a measurement of how well your device can hear a signal from an access point or router. It's a value that is useful for determining if you have enough signal to get a good wireless connection.
Note: Because an RSSI value is pulled from the client device's WiFi card (hence "received" signal strength), it is not the same as transmit power from a router or AP.
RSSI Equation: Actual RSSI + Antenna Gain = Displayed RSSI
For more RSSI information, You can refer to What is RSSI.
