BLE Coded PHY Preamble and Range

[David]

I'm interested in BLE coded phy and am wondering how the improved range is realized given that the preamble is not coded.  In other words, how does the receiver have improved sensitivity when the preamble itself is not actually coded?  Related -- is the RSSI value provided by the softdevice calculated based on the preamble or a packet?  Put differently: should the RSSI value of a coded vs non-coded packet be similar at fixed range holding all other variables constant?

[Simonr]

Hi

The Coded PHY uses the 1MBPS PHYs symbol rate, but represents each bit with more than one symbol, in addition to adding the FEC to the packet. The output power never changes based on what PHY you have selected. and therefore the RSSI shouldn't change either. The RSSI is measured by the receiver and not transmitted by the advertising device, so if should not be different for PHYs at longer ranges either. With Coded PHY however, you have a -103 dBm sensitivity, while the 1MBPS PHY has sensitivity at -95dBm.

The factors that are relevant for the RSSI value are transmit power, the antenna used to transmit, the environment that the signal "travels through" and the antenna used to receive the signal.

Best regards,

Simon

[David]

Understood on the phy/fec and that the the receiver (R) is the one calculating it.

I guess the point is that the SoftDevice exposes fully decoded packets so any RSSI I see from the SoftDevice is reported for a fully decoded packet. So regardless of PHY if I have two links -- only difference is that one is coded and one is not -- and increase distance between them the RSSI should be the same for both links due to exactly what you sated (facepalm moment).  However, at some point the non-coded link will break at increased distance, but the coded link will show RSSI values further decreasing due to the coding/FEC.