Adaptive frequency hopping with Bluetooth LE audio broadcast

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

Mathieu Chante — Sat, 18 Jan 2025 05:59:55 GMT

Hello,

When BLE is set to broadcast (no return path), how does frequency hopping work ?

Mathieu

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

SwRa — Tue, 05 Sep 2023 13:08:11 GMT

Hi Miklos,

Sorry for not getting back to you earlier. I heard back from the developers and they mentioned that +20 dBm with BLE is quite tricky due to regulations. We have had previous customers trying to play with channel map to fulfill the regulations, but this is not something that Nordic would suggest.

Regards,

Swathy

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

MKir — Mon, 28 Aug 2023 08:39:27 GMT

Hello Swathy,

Could the RnD get back to you with some answers?

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

SwRa — Tue, 18 Jul 2023 09:03:20 GMT

Hi Miklos,

I have asked this again to the R&D and will get back to you.. However, please expect a delay since we are a bit short staffed, owing to the holiday season here in Norway.

Best Regards,

Swathy

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

MKir — Tue, 11 Jul 2023 13:43:07 GMT

Dear Swathy,

I was asking with this wording because a potential customer came to us with a requirement to "meet ETSI 300 328 requirements for Adaptive Mode" to allow for +20 dBm EIRP. They also explicitely spcecified "support for adaptive frequency hopping" with LE channel selection algorithm #2.

I believe this is what is described in the core specification as channel classification on the LE link layer and channel selection algorithm #2. I am interested in the implementation status of the controller's autonomous channel classification (and channel selection), not the host channel classification. Specifically, the implementation status in the BLE audio network core image.

Vol. 6 Part B of the core specification states the following:

4.4.6.8 Channel indices
Each packet containing a BIS PDU shall be transmitted on the channel index
specified by Channel Selection Algorithm #2 (see Section 4.5.8.3)

4.5.8.1 Channel classification

(different in spec version v5.2 and v5.3/v5.4, this is the content from v5.4)

The Link Layer can classify the general-purpose channels as being unknown,
bad, or good. These classifications are determined individually by the Link
Layer based on local information (e.g., from active or passive channel
assessment methods or from the Host). Information received from other
devices (e.g., via an LL_CHANNEL_MAP_IND) shall not be included in the
channel classification. The Host may provide channel classification information
to the Link Layer. The Link Layer may use the information provided by the
Host.

Kind regards,

Miklos

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

SwRa — Wed, 05 Jul 2023 13:41:44 GMT

Hi Miklos,

This is what I heard back from the developers:

AFH is a term that is only used in the context of BR/EDR support mode only.

Are you looking for Host Channel Classification being done by the Host stack? Or do you want an application from us for it? Both are not currently supported in upstream zephyr Bluetooth host stack or any samples, respectively.

Best Regards,

Swathy

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

MKir — Thu, 29 Jun 2023 07:21:59 GMT

Thank you Swathy.

I got this idea from "The Bluetooth Low Energy Primer" [1]. It states in chapter 7.4 Channel selection:

"One well known example of a spread spectrum technique used in Bluetooth LE is that of adaptive frequency hopping. This involves the radio channel used for packet communication changing at regular intervals. Channels are chosen using a channel selection algorithm and a table of data called the channel map which classifies each channel as either used or unused. Implementations can monitor the quality of communication on each channel and if a channel is found to be performing badly, perhaps due to interference from other sources, the channel map can be updated to set that channel’s classification to unused and this ensures that this channel is no longer selected by the algorithm. In this way, channel selection algorithm adapts to the conditions being experienced and optimizes for the most reliable performance."

Of course, BLE audio broadcasts don't have a feedback channel about reception quality at e.g. a headphone.

[1] Bluetooth_LE_Primer_Paper.pdf

RE: Adaptive frequency hopping with Bluetooth LE audio broadcast

SwRa — Wed, 28 Jun 2023 14:13:03 GMT

Hi Miklos,

I believe it is not possible to use Adoptive Frequency Hopping with LE audio application since BLE is not FHSS.. I will however, confirm this and get back to you.

Regards,

Swathy