Max packet number per CI for nRF5340

[PengLiu]

Hi, Experts,

We are evaluating BLE throughput (sdk-nrf-2.7.0 throughput sample) using nRF5340DKs. The CI is set to 6 i.e. 7.5ms. The PDU size is set to 251, PHY is 2Mbps.

The measured throughput is around 1040kbps, far less than the theoretical value 1300kbps.

The times include transmitting + IFS + receiving + IFS is 1400us, so the theoretical packet number within 7.5ms is calculated as 7500/1400=5. We suspects packet number of 4 is used instead of 5, thus the actual rate is 80% of theoretical value. Can anyone help confirm whether packet number of 4 is used for this case and for what reason the number is reduced by 1.

Thanks,

Peng,

[PengLiu]

Hi, Hung,

Thanks for the detail information. We don't have a sniffer so can't trace BLE communication. When using Online power profile, I noticed overhead including RF ramp-up, post-processing and standby. Is there any specification about what is the maximum time of RF ramp-up(start radio) and post-processing time?

Another question is that three is a pretty long standby time. I thought this standby time could be reduced if I set more than 1004 byte TX payload per event, but couldn't succeed. (e.g. I set 1100 byte TX payload, the online power profile changed it back to 1004). Is there some criterial to set this payload per event? 

Peng,

  

[Hung Bui]

Hi Peng, 

You can just use any nRF52 DK as the sniffer. You can take a look here: https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-6-bluetooth-le-sniffer/

The reason for a large Standby period is that the scheduler need to be able to fit the maximum payload possible of a pair of TX&RX in to the slot (worst case scenario). Meaning max size TX and max size RX need to fit there otherwise the scheduler will skip them and wait for the next connection event.