RSSI, dB, dBm

• RSSI(Received Signal Strength Indicator)

- 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.

- It is usually displayed as a negative dBm value, and closer to 0 dBm, the stronger the signal is. 

- The greater the RSSI value, and the smaller the distance between packet transmitter and packet receiver.

- With these characteristics, RSSI can be used as an indicator of the distance between the transmitter and the receiver.

- RSSI metrics are typically mapped to receive sensitivity thresholds expressed in absolute dBm values.

 

• Get distance between transmitter and receiver with RSSI

$$ R S S I = − 10 n log 10 ( d ) + α $$ $$ d = 10 α − R S S I 10 n $$

- n : Path Loss Index, values range from 2 to 4 depending on the surrounding environment.
If there are no obstacles in the vicinity, the path loss index is 2, which can be 3 or 4, depending on the number of obstacles.

- α : Default RSSI value measured from the receiver at a given distance

- d : distance

 

for example, 

if RSSI=-72

 

if RSSI=-64

 

• dB(Decibel)

- The method of expressing such as weight, length, voltage, etc. in log and the resultant called dB(Decibel).

- The nature of a signal with a frequency quantitatively proportional to the dB scale.

- Sensitive changes at low voltage levels and insensitive changes at large voltage levels.

- If you set all the signal levels on the dB scale, you can do all the calculations by adding and subtracting them very simply.

 

• dBm(Decibel milliwatts)

- It represent the signal strength same as RSSI but it an absolute number representing power levels in mW (milliwatts).

- The closer to 0 dBm, the better the signal is.

- The difference is that RSSI is a relative index, while dBm is an absolute number representing power levels in mW (milliwatts).

•1mW = 0dBm •10mW = 10dBm •100mW = 20dBm •1000mW = 1W = 30dBm =0dB(W)