How long does it take to send a Mesh message?

[Jan]

Hi,

I'm doing research on Bluetooth Mesh for which I built a Mesh system for testing throughput. So currently I am sending messages at the max speed (every 25 milliseconds). Now I was wondering, of those 25 milliseconds, how much time is the devices actually busy sending the message. So for how long is the radio on for sending Mesh messages. 

I am using the Nordic Thingy with Mesh SDK version 1.0.1.

Hope you can help me.

Best regards,

Jan

[Edvin]

Hello Jan,

The mesh messages are based on BLE advertising packets, which are packets up to 31 bytes long. Since parts of the packet is used for headers, and you remain with 0 to 10 bytes of payload, the packet is approximately 20-31 bytes long. 

To see how long an advertising pack is, you can check out the online power calculator:

https://devzone.nordicsemi.com/power/

And set the payload between 20 and 31 bytes, depending on how much payload your messages has. Note that the graph presented is showing advertisements on all three advertising channels, while the Mesh network is only on one channel, so you only need one of the three spikes.

Best regards,

Edvin

[Jan]

Hi Edvin,

Thanks for your quick answer. So, if I am reading the graph correctly, the radio time is less than half a millisecond?

Jan 

[Edvin]

Yes. That is correct. Plus a bit time for changing between RX and TX and back to RX. Of course, this switching is not transmission time, but that is the window that the transmitting node will not be able to listen for incoming packets.

BR,

Edvin