how to avoid the collision in BLE 4.0 on smartphone

[kunaal]

I'm working on a solution and facing a few difficulties. well, I have more than 100 smartphones (android and iOS) devices in closed proximity were all the devices are logging each other with say duty cycle of 1. so constant scanning is happening.I read somewhere that when the number of devices increases then the probability of scanning the advertisement falls drastically so will that mean that there would be the possibility of more collision. will all the devices will be able to log each other ? will it also depend on how much time these devices are there together in that crowded space? I also read about the Backoff scheme but as you know android and other OS don't expose that level of control. so what's the way out to ensure maximum logging? what should be the duty cycle optimized for the use? can you please help as the solution is related to the current Covid crisis and a quick reply would be highly appreciated.

[bjorn-spockeli]

Hi Kunaal, 

Nordic's BLE SoCs are not used in any smartphones as far as I am aware. Our SoCs are used in the peripheral devices, i.e. the devices that the smartphones connect to. Your question seems to be related to Android and iOS behavior when many(100+) BLE devices are in close proximity to each other. In general, the more devices that are advertising the more congested the three advertising channels used by BLE will  be, so in short, the more advertising devices the higher the probability of  packet collisions. There is not backoff scheme in Bluetooth Low Energy. 

If you are not using any Nordic SoCs then I suggest that you post this question on a Android and/or iOS developer forum. 

Best regards

Bjørn