Adaptive frequency hopping with Bluetooth LE audio broadcast

[MKir]

We are evaluating the nRF5340 chip for a Bluetooth LE audio broadcast streaming application.

Is it possible to use adaptive frequency hopping with the BLE audio network core image? If yes, how to do it with the audio sample?

[SwRa]

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

[MKir]

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

[SwRa]

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

[MKir]

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

[SwRa]

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