LoRa receiver / decoder SW for SDR dongles?

[mclane]

Hello,

since we are in the bad weather period, here is a question to the SW gurus within the HAB community:

Currently, as I know, LoRa receivers are based on the LoRa transceiver chips (RFM98 etc.) and just process the decoded information from that chip. I would be interested in an SDR dongle (RTLSDR or FunCube) based decoder SW (with upload possbility to habitat?). I would love to have that integrated into GQRX for example (being a Linux user).

Any feedbck would be appreciated.

Best regards,

--mclane

[Steve Aerospace]

Just point me a the protocol specification and I’ll do it! ;-)

Steve G8KHW

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Steve Randall
Random Engineering Ltd
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[stuart....@catvog.org]

Semtech has not as far as I know said much about how exactly LoRa works.

But out of interest, there must be spread spectrum below noise methods for which the protocol is known, have any of these been decoded with SDR dongles ?

[Ed Moore]

Yes, for example GPS (though I added a pre-amp and filter).

[Leo Bodnar]

There are some initial efforts to reverse-engineer LoRa: https://github.com/hexameron/rtl-sdrangelove/tree/master/plugins/channel/lora

The protocol is reasonably transparent - http://leobodnar.com/balloons/files/LoRa/LoRa-2.gif, you just need to spend some time observing known transmission sequences.

[fabrice faure]

Hello,

Please find below an implementation of LoRa decoder for SDR that I have found :
https://github.com/f4exb/sdrangel/tree/master/plugins/channel/lora

I have not yet succeeded to use it, but I'm sure with some tweaking we can use it with specific LoRa modulation parameters used by the TX (for ex 20.8khz bandwith, SF X, explicit mode),..

Fabrice

2015-12-19 17:14 GMT+01:00 fabrice faure <fab4...@gmail.com>:

Hello,

Please find below an implementation of LoRa decoder for SDR:

[David Brooke]

On Sat, Dec 19, 2015 at 01:41:25AM -0800, mclane wrote:
>
> Currently, as I know, LoRa receivers are based on the LoRa transceiver chips (RFM98 etc.) and just process the decoded information from that chip. I would be interested in an SDR dongle (RTLSDR or FunCube) based decoder SW (with upload possbility to habitat?). I would love to have that integrated into GQRX for example (being a Linux user).

This was mentioned on IRC a while ago:

https://github.com/hexameron/rtl-sdrangelove/blob/master/plugins/channel/lora/lorabits.h

I don't know if it's functional or useful.

David

[MikeB]

I can understand why its worth the development effort to substitute a cheap SDR dongle for a relatively expensive SSB receiver but why repeat this exercise for a LoRa module costing only a few UKP?

There have been a number of suggestions on this forum about how LoRa receivers could be interfaced to HABITAT, including FSK modulating their output to feed into a PC mic input.

[mclane]

Using a LoRa module and uploading to habitat is not the issue, I have that up and running.

I am using a tracker which is transmitting classical RTTY (as a backup) and LoRa intermittendly and I just would like to use one single antenna / receiver (SDR).

I will try the references mentioned and report as soon as I have something to report ;-)

Thanks to every body for the hints.

-- mclane

[stuart....@catvog.org]

On Saturday, December 19, 2015 at 9:41:26 AM UTC, mclane wrote:

I can see that in some circumstances listening to LoRa on a SDR could be useful, and it could be the only receiver you have.

For me the significant benefit of LoRa is that it is two way technology, transmit and receive. So I prefer to use an antenna switch with the antenna going to the LoRa device in one position and the SDR or FT817 in another.

You could use both LoRa TX\RX device and SDR on the same antenna (without a switch) by fitting a limiter on the SDR but you’re going to get signal loss as the signal is split.

I would be interested in knowing how you get on with LoRa on an SDR, in particular how sensitive the SDR is as receiving LoRa. I have some software to test this, a command and control link to a remote LoRa device (can be a HAB tracker) that will allow you to run tests at whatever LoRa modes you choose or standard FSK\AFSK RTTY. I recently used the software to run a comparison of FSK RTTY versus LoRa. This was from the same transmitter setup and with the FSK RTTY being received on a FT817 and the LoRa on a RFM98 with the same antenna (using the antenna switch). The results were that at the same data rate, circa 100baud, the LoRa had a signal advantage of around 7dB, so covering around twice the distance for the same TX power.

One thing does puzzle me, what is the format of the data that the SDR would put out to a PC so it could be sent to Habitat ?