Would the RSSI-value be affected?

[Rilke]

Hello, this might be a stupid question but if I have a Bluetooth 5 module that is advertising and another module getting the RSSI-value without actually being connected to the BT5 module. Would the RSSI-value be affected depending on if the other module support BT 5 or only 4.2?

What I understand is that if the modules actually would connect to each other then they would agree on the latest version that both supports, which would probably affect the signal strength, but in the case above I’m not sure if the RSSI would be affected.

[Sigurd]

Hi,

Q: Would the RSSI-value be affected depending on if the other module support BT 5 or only 4.2?

A: No, if you are using the same antenna-design and tuning, with the same Tx-power(how many milliwatts did the transmitter deliver to its antenna, default is 0 dBm -> 1 milliwatt ), and the same antenna at the receiver, the RSSI itself should not be affected.

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The bottom layer of the BLE stack is called the Physical Layer and is normally referred to as “PHY”. Bluetooth 5 adds two new PHY variants to the PHY specification used in Bluetooth 4. (and also support the “old” PHY used in BLE 4, 1Mbps BLE )

With BLE 5 Long Range mode(Coded physical (PHY) layer, 125kbps BLE), it becomes easier to retrieve data transmissions in surrounding noise. BLE at version 4 does not perform error correction, only error detection. But, Bluetooth 5 long range introduces an error correction capability, called Forward Error Correction (FEC). This improves the receiver sensitivity, and you are able to successfully decode the same transmission at a lower signal strength level. With BLE 5 Coded PHY you have -103 dBm Sensitivity, but with BLE 1Mbps mode(the only PHY available in BLE 4) you have Sensitivity at -95 dBm.

You can read about Bluetooth 5 here and here.

[Rilke]

Thank you so much, that clarified a lot for me. If I understand correctly, the difference between BT 5 Coded and 4.2 will only be that 4.2 will give up at -95 dBm, while 5 Coded can keep up the transmission until -103 dBm? So for example, the new Channel Sequencing Algorithm, or anything else, will also not affect the actual measured RSSI?

Will the measured RSSI always be the same regardless of the version of Bluetooth being used?

[Sigurd]

If I understand correctly, the difference between BT 5 Coded and 4.2 will only be that 4.2 will give up at -95 dBm, while 5 Coded can keep up the transmission until -103 dBm? So for example, the new Channel Sequencing Algorithm, or anything else, will also not affect the actual measured RSSI?

Correct.

Will the measured RSSI always be the same regardless of the version of Bluetooth being used?

Yes, if you are using BLE version 4.2 or BLE version 5, the measured RSSI should be the same. Factors that impact RSSI are generally transmit power, antenna used to transmit, the environment the signal travels through and antenna used to receive the signal.