CODEWITHSUNDEEP
bluetooth-lowenergy
Radim955
Radim955

Reputation: 45

BLE advertising with different PHY used

I'd like to ask question about BLE 5.0 advertising. If there are several PHY which can be utilized (Long Range - 125kbps or 500kbps, 1M, 2M), I wonder what PHY is used when device is sending advertising messages on these three advertising channels?

Are all used at once? So if I configure device at Long Range PHY, is it advertising using 125kbps/500kbps and is it only using this rate and modulation? Or does it work the way, devices are using only 1M and only when connection is established, they switch to the other rate & modulation?

Thank you very much. I'm just beginning with BLE standard and there is a lot to learn.

Radim

Upvotes: 3

Views: 3126

Answers (1)

Youssif Saeed
Youssif Saeed

Reputation: 13285

Generally speaking, the normal 1M PHY is used by default for advertising/scanning and connection. This is to retain compatibility with pre Bluetooth v5.0 devices. The device can then take advantage of the 2M, 500kbps, 125kbps through the following mechanisms:-

1- Connection: Once a connection is established, your device can request to switch to a different PHY. This is done by sending a request to the remote device and the remote device should accept this request (if it supports different PHYs). If this happens, only the chosen PHY would be used then. In other words, if the connection is switched to 2M PHY, all the packet exchange will be occurring on the 2M modulation and the 1M/500kbps/125kbps will not be used (see Bluetooth Core Specification v5.2, Vol 4, Part E, section 7.8.49: LE Set PHY Command).

2- Advertising: One of the new features of Bluetooth v5 is the availability of primary advertising channels (these are the default 3 advertising channels that have been used by BLE since version 4.0) and secondary advertising channels (these are the 37 data channels which Bluetooth v5 devices can utilise for advertising). When advertising, your device can choose the PHYs for the primary and secondary channels. For primary advertising channels, you are only allowed to choose between 1M or CODED PHY. For secondary advertising channels, your device can choose 1M, 2M, or CODED PHY. This means that your device can be advertising on 1M and CODED PHY simultaneously (see Bluetooth Core Specification v5.2, Vol 4, Part E, section 7.8.53: LE Set Extended Advertising Parameters command).

3- Scanning: Likewise, when performing a scan for devices, your device can choose the PHY that it wants to perform the scan/advert on for both primary and secondary channels. This means that the device can be performing scans on different channels simultaneously.

So to answer your questions:-

  • I wonder what PHY is used when device is sending advertising messages on these three advertising channels?

Th used PHY depends on the device's preference. It is usually 1MPHY by default, but the device can switch to CODED PHY for its primary advertising channels, or to 2M/CODED PHY for its secondary advertising channels.

  • Are all used at once?

For connections you can only have 1 PHY modulation. For advertising/scanning you can have two types of modulation if you are taking advantage of both primary and secondary channels (e.g. you can be advertising on the 1M PHY on your primary channels and also advertising on the CODED PHY on the secondary channels).

  • So if I configure device at Long Range PHY, is it advertising using 125kbps/500kbps and is it only using this rate and modulation?

If you are only using primary advertising channels then yes, it will only be using this rate and modulation. If you are using both primary and secondary channels, you can have two modulations.

  • Or does it work the way, devices are using only 1M and only when connection is established, they switch to the other rate & modulation?

No, the connection can be established on any PHY if both devices support connection establishment on different PHYs.

Below are some useful links:-

Upvotes: 3

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