low power controller scan

[Hillman007]

Hi,

I have an unusual requirement where the current constraint device needs to the controller and passively scan. My understanding is the best way to estimate the current consumption for this is to use the receive current and that this can be duty cycled with the sleep wait current. 

In my application we would like to successfully detect the beacon within 5 seconds. The beacon isnt power sensitive, and so it can transmit at 20ms for the entire 5 second period.. and beyound. 

For my battery life target the maximum total scan time within 5 seconds is 20ms. I understand that the minimum scan window is 2.5ms, so we'll get eight scan windows - I have assumed that spreading this scan time out is benefical. By my calculations I might expect to see 57 packets in that time - assuming no loss. 

Is this sufficient overhead for me to get a connection within 5 seconds? i.e. they'll controller will need to respond the beacon. 

Thanks,

James

[Kazi Afroza Sultana]

Hello James,

Thanks for your query. Sorry for late reply since it arrived on weekend. 

The examples related to central we have are mostly for longer scan windows/ intervals, scanning most of the time with high current consumption.

There is a good deal of information in the SoftDevice specification, see Suggested intervals and windows. Should be applicable regardless of which SDK that is used really.

For your requirement, you can set the scan window to a multiple of the advertising interval of the beacon to maximize the probability of receiving the advertisement packets. For example, if one beacon advertises at 7.5 ms, then you can set the scan window to N*7.5 ms;  N is the multiplier which could be 3 or larger.

Try this and let us know.

Best Regards,

Kazi Afroza Sultana