Measure nrf24l01+ RSSI

RE: Measure nrf24l01+ RSSI

Ashish — Fri, 30 Aug 2019 07:42:32 GMT

Thanks for your reply Kenneth.

I will try your suggestions and will let you know.

RE: Measure nrf24l01+ RSSI

Kenneth — Wed, 28 Aug 2019 08:26:29 GMT

I don't understand why 1Mbps is very slow either, because the turn around time is not a big difference, e.g.:

TX 2Mbps 32byte payload with ack: 130us+160us+130us+40us = 460us
TX 1Mbps 32byte payload with ack: 130us+320us+130us+80us = 660us

I do not see any advantage of setting retransmit delay to max (4000), set it to 500us should be fine. It should also increase the speed.

Best regards,
Kenneth

RE: Measure nrf24l01+ RSSI

Ashish — Tue, 27 Aug 2019 12:18:14 GMT

Retransmit count is set to 15 and retransmit delay is at max. The frequencies once set are not changed. On the PRX side, I am using RF24 library (https://tmrh20.github.io/RF24/RPi.html) with raspberry pi, so that handles the PRX pin status. I have tried once with the 1Mbps rate, but that became very slow so didn't test that much.

RE: Measure nrf24l01+ RSSI

Kenneth — Tue, 27 Aug 2019 12:08:27 GMT

What retransmit count and retransmit delay are you using here? Are you changing frequency? Do you on the PRX keep CE high at all times, or do you cycle the CE at any time? Have you tried using 1Mbps instead?

Best regards,
Kenneth

RE: Measure nrf24l01+ RSSI

Ashish — Tue, 27 Aug 2019 11:56:23 GMT

Hi Keneth,

Thanks for your reply.

I understand making a pure sniffer will be difficult, so I have dropped that idea.

Regarding the packet losses, they appear to be random. The transmitter while sending 500+ packets may miss 1 or 2 packets in between. It doesn't happen always though.

Also, the transmitter misses ack packets. I am not using ack payloads, so I guess there will be a ack packet with the PID only. The transmitter sometimes just misses that ack packet and as it is depending upon the ack packet to know whether the receiver has succesfully received the packet or not, it sometimes gets into a stage where the transmitter feels like there were packet drops however the receiver has received all the packets. I have a packet retransmit mechanism on the application side too, but it is dependent on the hardware level ack which are missing for some reason. Right now I am trying to change this, I have implemented a simple ack mechanism on the software side but the results will take some time.

From my initial testings, more the distance, more are the packet loss but it surely happens sometimes with nearby sensor too. I get that there might be interference due to other devices running on same band, so I am still looking into this.

Regarding the PCB layout, we have checked the reference layout and the PCB guidelines and tried to follow them.

If you have any idea on why am I loosing the hardware ack packets, please let me know.

Thanks.

RE: Measure nrf24l01+ RSSI

Kenneth — Tue, 27 Aug 2019 11:02:37 GMT

Hi,

It is not straight forward to make a pure sniffer RX no, but if you know the address and frequency, then you can setup for instance an nRF24L01+ in standard SB mode (clear FEATURE and EN_AA registers), set maximum payload length (32) and disable CRC. Then each time there is an address match, the data will be received by the nRF24L01+, and the payload can be read out by MCU. However, the received payload will then include the 9bit PID field in the beginning of the packet, and actual data is shifted thereby 9bits, also CRC will not be checked in any way, so you will need to check the data entirely by the application firmware on the MCU, data may be erroneous, and random demodulated noise will be at the end of the packet if the payload is shorter than maximum length (32).

I highly doubt measure RSSI will help, I think it will help you can describe a bit more when you experience packet loss. Does it happen independent of distance, is there other 2.4GHz noise in near proximity, what amount of packet loss do you experience, are you using ack payloads, if yes what is the size of the ack payload and retransmit delay? Have you measured the output power on an spectrum analyzer? Have you followed the reference layout carefully and the PCB guidelines in the datasheet?

Best regards,
Kenneth