nRF51 beacon high frequency scanning and advertising?

RE: nRF51 beacon high frequency scanning and advertising?

Hung Bui — Fri, 28 Aug 2015 09:16:04 GMT

Hi Luis,

I meant why do you want to have lower than 100ms advertising interval ? It's based on my assumption that you want higher frequency than 10Hz.

Regarding the test, no, we haven't done any test like that. But the time frame needed to transmit 3 advertising packet is around 2ms. The scanner can be scanning all the time (on 3 channels, one by one in turn). I guess you can use Mathlab or other tools to do the simulation and calculate the transmit success rate base on your desired advertising interval.

RE: nRF51 beacon high frequency scanning and advertising?

Luis — Thu, 27 Aug 2015 11:17:36 GMT

Thank you very much for your answers. When you say "the advertising interval should be lower than" I think that is a typo and you meant "higher". I understand that is the Bluetooth Core Spec. So the softdevice won't let me go over that spec and I have to use the two workarounds you noted? Connectable up to 50Hz and stop+restart for higher frequencies? Do you know of any tested case like this? In order to estimate what is the highest advertising/scanning frequency I may reach using 5 beacons and 1 scanner (all with nrf51) in the same room?

RE: nRF51 beacon high frequency scanning and advertising?

Hung Bui — Thu, 27 Aug 2015 11:16:15 GMT

One more thing, since non-connectable advertising will most likely be transmitted all the time ( e.g beacon) having larger advertising interval will reduce the chance of interference between them.

When doing connectable advertising, the device not supposed to advertise all the time, main point is to get connected. So it can have shorter interval.

RE: nRF51 beacon high frequency scanning and advertising?

Hung Bui — Thu, 27 Aug 2015 11:06:47 GMT

@mst: It was defined in the Bluetooth specification. I have the reference to the spec in my answer.

From my point of view the 100ms minimum limitation is due to the requirement to be low power consumption. For connectable advertising the minimum limitation of 20ms is to make sure the connection can be quickly established. It's not the case when doing non-connectable advertising.

No technical reason here, just to make sure the power consumption remains low when using the protocol.

Do you have a reason that the advertising interval of your beacon should be lower than 100ms ? Note that if your beacon running on CR2032 battery, having a 100ms advertising interval or lower, will drain your battery in less than 3 months.

RE: nRF51 beacon high frequency scanning and advertising?

mst — Wed, 26 Aug 2015 14:46:17 GMT

Reading this answer makes me wonder.. What is the main (technical) reason that when using non-connectable advertising, the advertising interval should be at least 100ms, while for connectable advertising it can be at least 20ms? Or is there none, and therefore it can be overruled by stopping and re-starting advertising with an interval lower than 100ms?

RE: nRF51 beacon high frequency scanning and advertising?

Hung Bui — Wed, 26 Aug 2015 13:10:47 GMT

Hi Luis,

Yes, you can use the nRF51 to scan for several beacons with higher than 10Hz frequency.

If you advertise as non-connectable advertising, the advertising interval should be lower than 100ms. ( Section 4.4.2.2 Vol 6 Part B in Bluetooth Core Spec v4.4.2.2)

You can get away from that either by advertise with connectable advertising or you can advertise with non-connectable advertising, but stop and re-start advertising with interval lower than 100ms.

When advertising, there will be an extra delay added, to avoid interference (define at the same place at section 4.4.2.2). So you don't have to worry that all the beacon will advertise at the same time.

The scanner can scan continuously (when you set scan windows= scan interval) however, we have to scan on 3 channels (37, 38, 39) so we will scan on each channel in turn, one by one on one scan window. ( One scan window with channel 37 , next window with channel 38 and so on). Note that when advertising, by default the advertiser advertises in all 3 channels one after each other.