Microtalk

What's new in Bluetooth 5.4?

Abhijeet Srivastava

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13:26

EOC 2024

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Abhijeet Srivastava

Abhijeet has been deploying ML algorithms in constrained devices as well as powerful servers to improve the range and efficiency of Bluetooth and 5G. His experience in this unique space makes for some interesting anecdotes that he would like to share with other enthusiasts!

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Microtalk

What's new in Bluetooth 5.4?

Abhijeet Srivastava

13:26 EOC 2024

Abhijeet Srivastava

13:26

Bluetooth 5.4 introduced many new interesting features such as PAwR (Periodic Advertising with Response), and Encrypted Advertising Data. It also introduced the ESL profile which uses these features. Let's dive a little deeper into this and gain a deeper understanding.

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Please log in or create an account to test your knowledge and see the answers.

What specific mechanism in Bluetooth 5.4’s PAwR makes advertising bidirectional so devices can send responses back to the central during an advertising event?

A The central sends an op_sync_subevent_ind and devices wait the mandatory response slot delay, then reply in assigned response slots.

B Each device opens a full GATT connection during the advertising event and sends data over that connection.

C Devices immediately transmit unsolicited advertising packets on the primary channel as soon as they hear the central.

D Devices broadcast their responses on a separate always-on scanning frequency without scheduling.

E Devices use frequency hopping to asynchronously return data whenever a channel is free.

In the ESL profile using PAwR, how does a device determine which response slot to use within its group?

A By reading the index of the command in the array included in the sub-event payload (the command index maps to the response slot).

B By choosing a random slot on each event to avoid collisions.

C By responding in the first available slot on a first-come, first-served basis.

D By deriving a slot number from its MAC address or BLE device address.

E By negotiating a slot number earlier during a full connected GATT session.

Why does PAwR help support large numbers of devices with good battery life and reliability?

A Because it is periodic (reducing duty cycle) and uses all 40 channels plus appropriate PHYs (e.g., LE 1M/LE Coded) to reduce interference and improve per-packet reliability.

B Because it forces every device to maintain a continuous connection to the central, eliminating missed packets.

C Because it uses only the highest-rate LE 2M PHY for everything, minimizing airtime per device.

D Because every packet is duplicated across multiple retransmissions on the same primary channel to guarantee delivery.

E Because devices wake constantly and scan continuously to ensure they never miss an advertisement.

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Upvotes Newest Oldest

KerryWoodbury

Score: 0 | 2 years ago | 1 reply

Hello Abhijeet, can you please send some reference links for the two topics you mentioned in your summary slide:

Encrypted Advertising Data
LE GATT Security Levels Characteristic
Thank you, Kerry Woodbury

AbhijeetSpeaker

Score: 0 | 2 years ago | no reply

Hi Kerry,
This article has an excellent overview of those topics.
https://www.bluetooth.com/bluetooth-resources/bluetooth-core-specification-version-5-4-technical-overview/

Nathan3

Score: 0 | 2 years ago | 1 reply

Is it possible to use PAwR with smartphones (with PAST) ? I looked quickly at the Android Bluetooth API and did not found anything related to PAwR.
I was interested in using PAwR to manage a set of wearable devices

AbhijeetSpeaker

Score: 0 | 2 years ago | 1 reply

Hi Nathan,
I don't know much about how Android can do this. However, I know that Nordic and Zephyr RToS have related examples that you could look into. Checkout Bluez, maybe? https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/bluetooth/periodic_adv_rsp/README.html

Nathan3

Score: 0 | 2 years ago | no reply

Zephyr actually provides examples for both the advertiser and the observer in PAwR. Bluez does not seem to be a viable option of Android app unfortunately.

AliceWang

Score: 0 | 2 years ago | 1 reply

Thanks for the talk! I’d be curious to learn the motivation for adding bidirectional advertising in BT 5.4. I'm inferring that it was added to allow a central to update date on the peripheral w.o pairing.

AbhijeetSpeaker

Score: 0 | 2 years ago | no reply

Hi Alice,
I think you have got the gist of it. I can only guess what could have been the motivation for creating bidirectional advertisement. It is sort of the low-energy version of Bluetooth mesh, which provides support for a 1 to-many topology and is near realtime so, it requires pairing and active scanning. So, it wasn't power-friendly and was meant for devices plugged into a power outlet. PAwR on the other hand is intended for low latency applications and is periodical which helps saves energy.
I hope that gives you an idea :)

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