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Wrong RSSI value depending on frame counter and SF

Semtech Transceivers
#1

Dear community,

I am a researcher from germany who has conducted several LoRa related studies [1]. Our group recently ran into an issue which we can not explain. We believe this is a very strange bug, which should be further investigated. Here is the situation:

We can conduct reproducible! measurements in a labotory enviroment which show that the reported RSSI by a gateway depends on the value of the FrameCounter. In more detail, if the frame counter is in the range from 256-512 or 768-1024 the repoted RSSI fluctuates heavily while in the range from 0-256 and 512-768 it is stable. Yes, this is a depency modulo 256 :slight_smile: However, only with an SF12!

We have observed this behaviour with the following gateways:

  • TTN Indoor Gateway (Semtech SX1308)
  • DLOS8 Outdoor LoRaWAN Gateway (Semtech SX1301)
  • iC880A-SPI LoRa Concentrator (Semtech SX1301)
  • Multitech MTCDTIP-L4E1-266A-868

Using the following nodes:

  • RAK Wireless RAK4631 (SX1262)
  • Heltec AB01 (SX1262)
  • PyCom LoPy 1.0 (SX1272)
  • Adafruit Feather M0 LoRa (RFM95W (SX1276 LoRa based))

See the following plot as an example of this issue. We have more of these plots, but I am only allowed to post one as a new user.

01_RAKWireless_with_SF12
01_RAKWireless_with_SF121721×713 112 KB

We can not observe this behaviour on a simple self-build single cannel gateway. Therefore, we believe the Gateway is an issue.

So, anybody has an idea?

With kind regards,
Michael

[1] https://scholar.google.de/citations?user=e_bBQ_8AAAAJ&hl=de

#2

Hi Michael,

We observe the exact same behaviour with our gateway. We have a SX1301 communicating over SPI to a linux board. On linux, we have the lora_pkt_fwd package that handles all the communication with the lora concetrator.

What kind of software stack are you using ( or does the gateway use ) ? In your gateway, did you maybe try lora basicstastion ?

Regards,
Thanas