Loosing radio packets

[Aune]

I have a setup with one transmitter and three receivers. The transmitter (nRF24L01+) sends a message to the receivers (nRF52832, using SDK v15.3.0) every 10 seconds. The receivers are in RX all the time, except when a packet has been received, it will be processed before it returns to RX again.

This is running without any issues for a random amount of time, then suddenly one, two or all of the receivers do not receive the message. If halting the code when the receiver has not received any message, sometimes it reports CRC error (looking inside nrf_esb.c), and sometimes not.

When a given received loses the packet appears to be totally random, so I suspected noise to be the issue, but I would assume that this would affect all three receivers the same ?

Any suggestions ?

[Kenneth]

For this to work you need to disable ack, else a combination of the following case may occur:

2 receives the packet, 1 doesn't receive the packet due to noise or interference

2 receivers ack the packet, 1 now receive the ack

1 ack the ack, 2 now receive the ack

2 ack the ack, 1 receive the ack

..

This may end in an endless loop, can this be the case?

For the nRF24L01+ make sure to check all irq sources for each transmission, since it is possible to receive RX_DR even for a transmitter. Also make sure to always read out the packet length if there is an RX_DR irq, and if the length exceed 32bytes you need to flush the rx fifo before next transmission or reception may occur.

Best regards,
Kenneth

[Aune]

On the nRF24 the EN_AA register is set to 0, disabling auto-ack on all pipes. On the nRF52, selective_autoack is set to true, and in the tx payload, the noack is also set to true, so ACK should be turned off right ?

[Kenneth]

An error in the address due to noise from nearby Wifi or BT can cause the packet not be be received, however this will only occur from time to time. In such case you will not receive any packet, can this be the case?

Best regards,
Kenneth

[Aune]

Yes that is a possibility I agree, but wouldn't this affect all three receives the same way ? Or is it possible, in your opinion, that one receiver misses the payload, while two receives it ? This is the scenario I cannot understand...

[Kenneth]

Aune said:

Or is it possible, in your opinion, that one receiver misses the payload, while two receives it

Yes it is, because the antennas are far from omni-directional. This means that in some directions they can +-20dB gain or attentuation, which of course will impact how much an interference source impact reception. Also the frequency, reflections etc will impact.

Best regards,
Kenneth

[Aune]

Okey, sounds reasonable. Thanks for taking the time to explain. 

[kris_s]

This suggestion was helpful to me as well.  Looking into the ESB example projects, in esb_prx it's done this way (susceptible to this issue):

if (nrf_esb_read_rx_payload(&rx_payload) == NRF_SUCCESS)
{
// Handle packet
}

But in the other one (esb_low_power_prx) it is done this way (better):

while (nrf_esb_read_rx_payload(&rx_payload) == NRF_SUCCESS)
{
// Handle packet
}

Would be nice if there was consistency in the example projects.