BLE parameters and channels

[GOAA]

Hello,

I am using the SDK examples with the softdevice. I want to know how is the hop sequence determined. From what I understand the channel map for two devices to communicate can be anything until I blacklist/remove it but how's the hop sequence determined. Does the devices scan for high traffic channels and skip those in the SDK examples.

I am using Private resolvable address and changing the address every 15 minutes. What address is changed every 15 minutes is my question. From the information I gathered, the access address is changed but what is this access address and how it is determined?

Thanks a million

[haakonsh]

Does the devices scan for high traffic channels and skip those in the SDK examples.

No, the SoftDevices uses the standard sudo-random BLE hopping algorithm. The SoftDevices do however have a Quality of Service (QoS) channel survey, that measures the energy level of Bluetooth Low Energy channels. The application can then set an adapted channel map to avoid busy channels. 

what is this access address and how it is determined?

 By default, the access address is static throughout the lifetime of a BLE device, but if you enable the privacy mode (Private resolvable address) you change this address at given intervals using the RNG — Random number generator and a private address. 

The access address is used by the Link Layer to determine which physical device it is talking talking to. With a static address you can identify a device based on its access address alone, but with a private resolvable address you need to also transmit the scrambled private address. 

See this artical for more info: https://www.electronicdesign.com/technologies/communications/article/21801870/ble-v42-creating-faster-more-secure-powerefficient-designspart-2.