RFM98PW with SDR ground station

[sukjinkang]

Wondering if you ever ran into this error when running gr-lora_sdr as a receiver for receiving transmission from RFM98PW.

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xff in position 7: invalid start byte

It seems that I'm receiving and decoding ok. I get the correct payload length and other setup information:

--------Header--------
Payload length: 35
CRC presence: 1
Coding rate: 4
Header checksum valid!

Then it crashes with that Unicode error. When I transmit using gr-lora_sdr from an USRP, receiving on a different USRP, works like a charm. When I transmit from PyCubed to either of those USRP, it crashes with that Unicode error. Anything you can think of that may be causing this?

[maholli]

Can't say I've encountered that one, but like you said it seems to be something to do with the encoding rather than the modulation.

Try this:

• Are you able to demod a short and simple LoRa payload from PyCubed -> USRP? Something like cubesat.radio1.send(b'hello').
• Does your GNUradio LoRa setup have a setting for implicit/explicit header? Make sure it's set to explicit mode (but maybe try both? I'm forgetting the default header config)

[maholli]

@sukjinkang I pulled out my notes and ran a quick gnuradio test. Unfortunately I don't have GNUradio 3.9 built at the moment, so I was limited to 3.8 release. This means gr-lora_sdr wouldn't run, but I was able to demod using rpp0/gr-lora.

Working GNUradio companion script that I used is attached (unzip it to use) and screenshot below. GRC file is already configured for default PyCubed params. Just run script and then pass these two commands to the PyCubed REPL (also pictured below):

from pycubed import cubesat
cubesat.radio1.send(b'hello')

lora_receive_realtime.zip

let me know how it goes
Max

[sukjinkang]

Just reporting back. Summary: success

Situation: I was playing with two versions: gr-lora and gr-lora_sdr. Really needed to get gr-lora_sdr running so I can also transmit via SDR. Problem was, gr-lora was on gnuradio 3.9 and well-working gr-lora_sdr was for 3.8. I just could not get both to work. USRP to USRP works great using gr-lora_sdr. Just could not decode PyCubed using gr-lora_sdr, nor command PyCubed.

Solution: The issue turns out to be the 4-byte header that Radiohead library attaches to the beginning of the packet. PyCubed uses it on Tx and looks for it on Rx. gr-lora_sdr does not. For now, I coded out the RadioHead header portions in pycubed_rfm9x.py on both send and receive, and everything works great. Downside, of course, is that I can't use the to/from codes, but I'll implement that later, if needed.

Thank you for your help!