Connection and advertisement issues in highly reflective environment

[tplux]

Hi

We are developing a system where 2 devices (NRF52840) advertise to each other (and eventually connect) in a highly reflective environment (the cargo hull of a ship). The 2 devices are located on each sides of a metal wall, both looking out into the same cargo hull which is approximately 12 m * 12 m * 20 m. In this environment they are having a very hard time receiving advertisements from each other even though they are less than 10 m apart and the RSSI level is about -55 dBm. If they manage to connect, the connection is lost within one minute. In the same space there are about 30 other BLE devices advertising.

I suspect reflections from all the signals are creating too much noise thereby "scrambling" the signals. Is there a way to "filter out" this noise or somehow live with it?

Thanks.

[Kenneth]

Hi,

Make sure you advertising on all 3 advertisement frequencies here (this is default unless you have tried to manually set specific frequency to use). Also make sure you are either using coded phy or 1Mbps (1Mbps is default), since I suspect 2Mbps can cause problems with fading effects due to reflections. Once they are connected I think it is a bit strange they seem to so easily disconnect, so maybe make sure you are using slave latency (e.g. 6) in the connection parameters and that you can try to enable the softdevice with a lfclk tolerance of 500ppm (just to check the problem is not related to 32kHz lfclk is maringally out of spec and causing any issues).

Kenneth

[haakonsh]

Do you see the same issue outside of this environment, like in free-space, all things being equal? It could be an issue with the clocks. 

[tplux]

No. Outside this environment there is no issue.

[tplux]

We are using all 3 advertisement channels and coded phy. Also we are using 8 dBm power output.

We could try changing slave latency and lfclk tolerance next time we have the opportunity.

[haakonsh]

That's a good idea. I also suggest you measure the accuracy of your LFXO.