nRF52832 notify every 20ms at 50 meters

[StephaneJ]

Hi,

My setup :

• nRF52832
• Soft Device S132 v5
• SDK14.2

My use case involve me to send data to to a central device at 50 meters. I need to send only a small data : one int16_t. I have a timer set up to do a SAADC conversion then send data (sd_ble_gatts_hvx) every 20ms.

It's working great on close range. But as soon as I am further than 5 meters I got a NRF_ERROR_RESOURCES.

Since it's not really a problem if I miss few data, my first try was to ignore it :

/* It's not a problem if we loose few data */
if(retval == NRF_ERROR_RESOURCES){
  retval = NRF_SUCCESS;
}

return retval;

It work great meaning that it does crash the board now and it keep sending data but at a very low speed and multiple packet at a time it looks like on the nRF Connect app log.

So I know that this error means that the queue is full. But why is it related to the distance from the central since it's a notification so we do not expect an acknowledgment or anything!?

Also when I go to ~25 meters (outside) not only I have very slow notification update on my central, but I got disconnect (Timeout).

What are the optimizations I can do to increase my range and keep my transmission speed constant?

Thanks

[MartinBL]

So I know that this error means that the queue is full. But why is it related to the distance from the central since it's a notification so we do not expect an acknowledgment or anything!?
As AmbystomaLabs points out you probably have a HW problem. Notification packets don't require acknowledgments from the application layer, but all BLE packets are actually acknowledged on the Link Layer. If your notification packet doesn't successfully reach the peer, it is retransmitted over and over again until the packet is either received successfully or until the supervision timeout times out and your device disconnects. This is probably why your queue fills up and why your link eventually breaks when you move out of range. 

[StephaneJ]

The designer of the board tells me that there is no HW problem, he is used to work with nRF52 and he advised me to do an antenna tuning to take into account the materials and package surrounding my custom board. How am I suppose to do that?

Also, he tells me that we can optimize the software to the detriment of the battery autonomy to increase the range. Do you know what is he referring to ?

Thanks for your help

[StephaneJ]

They were both on the same surface, wood. But in a closed area with WiFi so this is not representative of the reality but the fact is that they have both the same signal strength. This was the purpose of your this test right ?

Thanks for your help

[AmbystomaLabs]

What was the actual result in dBm of the test?

[StephaneJ]

During my test I measured a degradation from -50dBm to -75dBm. From close range to 5 meter. This is what you are asking isn't it ?