Maximum Number of Beacons

[Deepak Gupta]

Hello,

We are working on a Tag and Trace type asset monitoring application, that requires scanning several thousand (>6000) beacons in a closed room of about 15feetx15feet. The application is to the monitor high value items in a locker / storage room. I have multiple questions on this use case.

1. Is this a practically viable use case?

2. what can be the advertising intervals of the beacons? (Quick scanning is not a requirement - even if the beacons are read in several minutes that is acceptable)

3. Can a single nRF52840 based beacon scanner / gateway scan all the beacons? - Will multiple scanners help?

4. The application requires that all the present beacons be scanned without fail - can this be guaranteed somehow?

Any opinions or past experiences on this will also help. TIA. 

[ovrebekk]

Hi Deepak

1) If you can spend some time to receive all the advertisement packets from the beacons then I believe this to be a viable use case. 

2) To reduce chance of packet collisions you would need as high an advertising interval as possible. Most likely setting the advertising interval to 10.2 seconds, which is the maximum supported by the SoftDevice, should keep the amount of packet collisions in check. 

3) A single nRF52840 should be able to scan all the beacons, yes, but you would be able to scan them quicker by using 2 or 3 nRF52840 scanners. 

By default most advertise packets are sent on 3 distinct RF frequencies, and if you can scan on all 3 frequencies at the same time you will be able to read the packets at a higher rate. 

4) Mathematically it is impossible to give a 100% guarantee that all beacons will be scanned, but if you spend enough time scanning you can get pretty close. 

I will have to do some digging, but I did create an Excel sheet a while back that allowed you to calculate theoretical packet reception ratio based on the number of advertising devices and the time spend scanning. 

Best regards
Torbjørn

[Deepak Gupta]

Torbjørn

Thanks for the answer, gives me confidence to carry this forward. Have you come across any comparable use case implemented?

Please share the excel file you mention if and when possible. 

 

[ovrebekk]

Hi 

You will find the excel sheet attached:
PacketLossCalculator.xlsx

It is not the most intuitive excel sheet ever made, but it allows you to experiment with the number of beacons, the length of the beacon packet, and the total time you want to scan for beacons. 

The advertising interval will be set as a percentage of the total scanning time, so if you set the total scanning time to 100000 (100 seconds), then the graphs will plot statistics based on an advertising interval of 1-100 seconds in 1 second intervals. 

The lower graph is probably the most interesting for you. It shows you which advertising interval (in the range 1-100% of the total scanning time) will allow you to receive the most advertise packets if you scan equal to the total time. So if you want to scan for one minute then set the total time to 60000 ms, and you can see which advertising interval would be optimal for this use case. 

Edit: I have gotten questions similar to this before, but I don't know if someone has entered production with solutions based on such a high number of beacons in the same area. 

Best regards
Torbjørn

[Deepak Gupta]

Thanks Torbjørn, I'll give this a try today. 

[Deepak Gupta]

Use it just now. This is just what I was looking for!! Very useful. 

[ovrebekk]

Glad I could help Deepak. The best of luck with your project