I'm new to BLE, and bluetooth in general, but I'm on a project that includes communication via BT 5. As the BLE communication has to transmit around 2 bytes, to 1 MB at a time, I'm looking for a way to optimize the transmission time. I know the pros n cons for the lower transmission freq (125 kbps), and for the highest transmission freq (2 Mbps), and for the DLE of 251 PDU bytes, but what I see from different forums and articles, the throughput mostly depend on the connection parameters as the connection interval and the packets per connection event. But where does the transmission frequency come in?
I've tried searching this forum for an answer, and several others, and even the BT core specification, but I haven't been able to find a solution for my problem.
If you read my answer at Why is BLE 4.2 faster than BLE 4.1, you can see that there are many components affecting the overall transfer speed.
You first have the radio transmission rate itself, which sets the upper limit.
You then have the overhead between all packets that becomes less apparant as longer packets you have.
The connection interval and length of each connection event can be important if you want the throughout to be high. If there is only one connection and the Bluetooth chip is not too stupid, the connection event length will fill the connection interval and therefore the connection interval doesn't really matter. However, if there are other conflicting radio events scheduled in a way that the connection event must be closed, the transmission cannot continue until the next connection event. So in this case, the throuhput will be higher if you lower the connection interval. So as a summary it highly depends on which Bluetooth stack the chip runs, how it's configured by the host and how many active connections you have.