NB-IoT packet loss

[allard.p]

I'm testing a simple application based on the UDP/CoAP example.  It samples some peripherals and ADC channels, these values are then packed into a CoAP message. This CoAP message is sent trough the socket api (UDP), and the application waits for a response. I've run some tests using different power saving settings. The current version uses PSM in between samples and uses RAI to prevent long time spent in the 'active timer'.

A observation we made after analyzing the logs is the high rate of timeouts/packet loss. We declare a packet lost if the uplink CoAP packet, or the downlink CoAP ACK message is lost. We got a packet loss of around 3% over around 1000 messages (multiple devices, connected to the same cell). Questions:

• I known UDP is a unreliable protocol by design, but I'm wondering what packet loss numbers I should expect? What numbers are other users experiencing?
• Is there some way to identify the cause of these lost packets, using the PCAP/modem log files for example?

The devices all have a Taoglas MFX3 antenna connected, the RSSI is around -85dBm (%CESQ: 54,2,21,3).

[allard.p]

The 3% seems to be consistent between requests and responses. The devices are indoors, in an industrial/office area. The number of  (our) devices connected to the cell are 3 max. at this moment. I did some test with a high rate, a upload every minute, and also tests with a rate of 10 minutes or >30 minutes, all test result in a loss of around 3%.

I know CoAP has retransmissions, but I want to prevent them, the packet loss needs to be lower before I enable the retransmissions, to optimize the power usage. I will take a look at the timing, linking the timeouts to the RCC_MODE's is a good idea, although my timeout is currently longer than the RCC connected time.

I will also setup a test in another area, maybe this cell is just busy, I think the number of NB-IoT devices here in the Netherlands is already quite high.

[Achim Kraus]

Though my modems are usually wake up from PSM, the time to get connected is sometimes large. In fast cases 2-3s, but 10-15s do also occur (not too often), even larger (luckily rare, I usually give up at 60s). 

How long do you wait for your response?

Not that long "waiting time" consumes more power then a retransmission in time.