Difference between primary and secondary phy?

Question

In android SDK 28+, Bluetooth Advertising can be performed using the new startAdvertisingSet() methods that integrate Bluetooth 5. One of the parameters, an AdvertisingSetParameters object, has two settable properties in its builder: setPrimaryPhy() and setSecondaryPhy().

I'm wondering what the difference is between the primary and secondary phy - are they used at different times? For different processes? Thanks in advance!

Answer 1

You can use the secondary PHY to talk to other devices supporting the secondary PHY. Why would you want to do that?

• Majority of devices today use the primary PHY, so by moving to a secondary PHY you avoid collisions with the existing primary PHY ecosystem and get improved communication.
• On the secondary PHY the bitrate is double, so it comes with all the advantages of a higher bitrate.

So in principle you should use the secondary PHY anytime you can, i.e., anytime you are very likely to talk to devices that support it.