What is the relationship between RSSI and datarate?

[Ziyao Zhou]

Hi,

Recently I am studying the relationship between RSSI and datarate. Intuitively, I think lower the RSSI lower the datarete. Is there any physical evidence for this guess,Are they causal or correlated?

I have done some experiments in this ticket, specifically, I notice my two experiments shows different behaviour, but all the enviroment is identical, so could you please clarify me about the relationship between RSSI and datarate?

[Edvin]

Hello,

Are we talking about the datarate in a Bluetooth Low Energy (BLE) connection here?

In general, lower RSSI doesn't affect the datarate, but if you are lowering it enough, so that you will start getting packet loss, then this will again trigger retransmissions of the packets, and this will of course affect the total bandwidth, giving you a lower data rate in the BLE connection. 

I don't know if this answers your question. 

Best regards,

Edvin

[Ziyao Zhou]

Hi

Thank you for your information. Yes, I am talking about BLE. Could you please check this ticket, does the change means packet loss?

By the way, I am thinking about tune the RSSI to have the target data rate. Do you think this is feasible physically? Is high RSSI a sufficient condition for high Datarate?

[ketiljo]

RSSI is not related to the datarate at all. RSSI is a measure of the power of the recived signal and will vary with output power, antenna gain and distance only.

[Ziyao Zhou]

Hi,

Thank you for your information!

Can I say that for a specific environment, the noise level is stable, the RSSI is highly related to the data rate. As the C = W log₂(1+S/N) b/s, here the SNR can be tune by increasing transmitter power.

Another question is in my experiment, when the distance become longer, the current will drop. And I consider this to be the packer loss. If it correct, then lower RSSI affect data rate a lot. You may kindly check this ticket.

Edvin said:

In general, lower RSSI doesn't affect the datarate,

[Edvin]

Just to be precise, the RSSI doesn't affect the datarate on air, but it may affect the throughput if you start seeing packet loss. And packet loss is a common thing, and it is increased with more noise, or longer distances, or in other words, a lower Received Signal Strength (indicator). I will look into your other ticket.

Ziyao Zhou said:

As the C = W log₂(1+S/N) b/s, here

This is above my knowledge on the topic, unfortunately.

Best regards,

Edvin