Does Bluetooth Mesh have frequency jumping?

RE: Does Bluetooth Mesh have frequency jumping?

Fridtjof — Tue, 05 Nov 2024 16:37:12 GMT

I think I was able to figure it out using your answer and the official EN 300 328 specification which Norwegian law references.

Bluetooth Mesh does not fulfill the requirements in `EN 300 328`. This spec does not actually define what Frequency Hopping is, but does as you say include a provision that IF you use FHSS THEN you must have at least 5 channels.
The 10mW/MHz is a Spectral Power Density limit, which is relevant for equipment which does NOT jump between frequency channels, but uses some other spread-spectrum method.

So in conclusion, Bluetooth Mesh falls under the general 10mW e.i.r.p. limit for 2.4GHz equipment, and cannot use a higher transmit power despite using several channels.

Thanks again, Edvin!

RE: Does Bluetooth Mesh have frequency jumping?

Edvin — Tue, 05 Nov 2024 14:24:39 GMT

No, it is not DSSS. The channels are spread out through the spectrum (to avoid the WiFi channels). See this figure:

(source: https://academy.nordicsemi.com/courses/bluetooth-low-energy-fundamentals/lessons/lesson-2-bluetooth-le-advertising/topic/advertising-process/ )

The Mesh stack is built on top of the softdevice controller, so it behaves the same as an advertiser and scanner would do in normal BLE applications.

So whenever it sends out a message, it will send it as a packet on all 3 channels, in a burst. The devices that are not transmitting are always listening. I am not sure exactly what parameters they use (scan window and scan interval), but it will have a scan window = scan interval, to get the max RX time, and it will increment the channel on every scan interval.

[quote user="Fridtjof"]and what number I can plug into the 10mW/MHz formula?[/quote]

I am not sure exactly what formula we are talking about here.

Best regards,

Edvin

RE: Does Bluetooth Mesh have frequency jumping?

Fridtjof — Mon, 04 Nov 2024 09:08:55 GMT

Thank you for the answer, Edvin! Do you know how BT Mesh switches between these channels (e.g. is it DSSS?), and what number I can plug into the 10mW/MHz formula?

RE: Does Bluetooth Mesh have frequency jumping?

Edvin — Thu, 31 Oct 2024 14:45:42 GMT

Hello Fridtjof,

Bluetooth Mesh uses the standard Bluetooth LE advertising channels, 37, 38 and 39. As far as I understand, the FHSS requirement is 5 channels, so Bluetooth Mesh does not meet this requirement.

Best regards,

Edvin