nRF52840 scanning on multiple channels.

[Drew]

Hello,

I'm seeking some clarification on a few points to determine the performance of the nRF52840 in high density deployments.  The current intended soft device is S140, though if another version would offer more features, recommendations would be appreciated.

1. When configured for scanning on all primary channels (37,38,39) will packets be received on all channels simultaneously, or is it only possible to scan on one channel at a time, and does the software handle switching between them in the background.

2. Is this hardware capable of scanning on secondary advertising channels?

3. My understanding is that this device is capable of sustaining up to 20 simultaneous connections.  Does scanning reduce the number of connections that can be maintained?  Does scanning on multiple channels reduce that further?

Thanks,

Drew

[Drew]

From digging deeper into this, it seems that the Bluetooth Core Spec says the following, in section 8.3.1 Page scan substate:

In the page scan substate, a device may be configured to use either the standard or generalized interlaced scanning procedure. During a standard scan, a device listens for the duration of the scan window Tw_page_scan (11.25ms default, see HCI [Vol 2] Part E, Section 7.3.20), while the generalized interlaced scan is performed as two back to back scans of Tw_page_scan. If the scan interval is not at least twice the scan window, then generalized interlaced scan shall not be used. During each scan window, the device shall listen at a single hop frequency, its correlator matched to its device access code (DAC). The scan window shall be long enough to completely scan 16 page frequencies.

So it seems that the answer to my first question is most likely that only one channel may be scanned at a time, unless the nRF52840 implments capabilities outside of the core spec.

[Simonr]

Hi

1. You're correct. You can only scan one channel at a time.

2. Yes, it is possible to scan secondary advertising channels using the nRF52840 series devices. Please check out the ble_gap.h header file in the SoftDevice, at C:\...\nRF5_SDK_16.0.0_98a08e2\components\softdevice\s132\headers\ble_gap.h you can see that when extended is set to 1 the scanner will accept extended advertising packets.

3. It will be more like the other way around. Seeing as the nRF52840 only has one radio, the more connections it maintains, the less time it will have for scanning, which means that the scanning windows and durations have to be lower when maintaining multiple connections.

Best regards,

Simon