Scan response packet sent by beacon without any scan request

[Jusang Kim]

reco_scan_req.PNG

Now i am doing a test of RECO beacon which use a nordic chipset, nrf51822. But something strange came up to me during the test with Ellisys bluetooth analyzer. The problem is that the RECo beacon sends scan response without any scan request. Please take a look of the highlighted area of the attached picture.

Any comments on this ?

My test configuration are as follows;

1. Wireless Test
2. Office environment : There are many Bluetooth scanner in the same room.
3. RECO beacon : the device address(D8 4E 4E E1 CD F9). I used the iBeacon example code.
4. My smart phone plays a role of scanner with the device address(4A F1 E3 4B A0 C2).
5. I used the software filter only to filter the devices. (D8 4E 4E E1 CD F9 & 4A F1 E3 4B A0 C2)

[Stian Røed Hafskjold]

Since you are filtering on the two devices D84E4EE1CDF9 and 4AF1E34BA0C2, maybe the scan request is not shown in the list if the scan request comes from another scanner that is filtered out?

[Jusang Kim]

Thank you for reply. Yes I do filtered only two interesting devices such as D84E4EE1CDF9 and 4AF1E34BA0C2 . But Please take a look the attached picture. And find out the blue colored area which captured the scan response packet. The scan response is for scanner 4AF1E34BA0C2 as you can see. This is waht i am curious about. Ellisys bluetooth analyzer did not capture the scan request from the scanner 4AF1E34BA0C2 on the attached picture. but how does the Ellisys bluetooth analyzer know that the scan response is for the scanner 4AF1E34BA0C2 ?

[Stian Røed Hafskjold]

hmm.. that's a mystery. If the Ellisys does not receive the scan request, it can't possibly know which one is the receiver. Even if there was a bug in the Softdevice that caused the nRF to transmit a scan response without getting a request first, this packet would not contain any recipient information, so the Ellisys would not know which one is the receiver.

I think the only solution to this is that the Ellisys caches the scanner address and uses this as the address when it reports the recipient of the scan response, and that the cached address is not changed until it gets a scan request from another scanner. So I still believe that this is a scan response meant for another scanner that is filtered out.

Are you consistently getting this error? Do you still see this if you turn of the address filtering?

[Jusang Kim]

Thank you for your replay again. It makes me energetic to figure the problem out now.

Anyway, i still meet the error in wireless office environment. It is easy to reproduce the error in wireless office environment. It seems like the Ellisys display the previous scanner's address when it does not receive the scan request. And i believe that the receiver sensitivity performance of the Ellisys is poor. Those two things makes this kind of error on Ellisys. It is my guess. If we use the wired test environment then we can solve what the problem is correctly. What's your opinion on this ?

[Jusang Kim]

One more.... I asked Ellisys how to display the scanner's device address in the scan response when Ellisys does not receive the corresponding scan request. As soon as i get the answer from the Ellisys, I'll let you know.