What is the relationship between RSSI and disconnection?

[Ziyao Zhou]

Hi

I heard about that RSSI has no relationship with disconnection. However, based on my experiments, the connection will break every time I am close to -80dBm.

I am confused about this result, as the RX sensitivity for nRF 52833 -103 dBm sensitivity in 125 kbps. I am using the same Long range code but will break in -103dBm.

So could you help me on clarifying the RX sensitivity, lowest RSSI for communication and disconnection?

[tesc]

Hi,

Received Signal Strength Indicator (RSSI) is exactly that - an indicator of the signal strength (not an exact measure). Basically it measures the energy level detected within the time period of receiving the packet, which may or may not include energy from other signal sources (i.e. noise.)

In order to receive a signal, the signal must also be above the noise floor. Noise floor depend on your environment. In some instances the noise floor might be higher than the RX sensitivity of the device, in which case you will receive the noise (but not be able to detect the signal). Basically, noise floor is the sum of all background radiation within the frequency band you are listening to, including both natural and human sources.

Further, other strong transmissions or noise bursts may interfere with your connection. If there are other transmitters nearby, which uses the same or nearby frequencies, transmissions from those transmitters may interfere with your transmissions, leading to packet loss. This might also be short-lived strong signals, which lead to partial loss of the package and therefore package loss. Such interference may originate also from non-RF equipment, or from RF equipment using different physical layers.

Depending on the type of noise or interference, there are ways to improve packet reception. For BLE, increasing supervision timeout for the connection allows for more packets (and thereby more connection events) to be lost before the connection breaks, which increases the chance of keeping the connection alive. Use of coded PHY might also improve the situation, depending on the cause of the link loss. Coded PHY might flip both ways, though; it improves the link budget through spending more time for each symbol, adding redundancy, which increases the chance of receiving enough information for each symbol to reconstruct the full original message. On the other hand it increases the time needed for transmitting the full packet, so if there are other strong transmitters nearby it increases the chance of packet collision.

Regards,
Terje

[Ziyao Zhou]

Thank you for your information. So that the RX snesitivity is like the minimum RSSI to receive the data?