OK to design a product with RFM95W + LMIC?


(Pomplesiegel) #1

Subjective question here:

Is it OK to design a professional/commercial device using the RFM95W and LMIC at this time? I know that LMIC implements only a portion of the LORAWAN stack, but I believe it currently accomplishes everything I need for my application.

To me the only downsides of LMIC I have noticed are

  • Lack of out-of-the-box OTA firmware upgradability (that I know of)
  • Some open issues regarding the behavior of ADR + setting transmit power… things like that

But it’s still early days, and I’m learning more and more.

What are your thoughts on this approach versus something like the MultiTech xDot?

Thank you!


#2

What’s your thought as a professional/commercial designer on this subject ?
Just seen this topic regarding compliancy, I don’t know if its important to get certification for your endproduct ?


(Pomplesiegel) #3

Great question! For our application we would essentially be making a private network indoors with a dedicated gateway. It’s likely not important that we get certification (I believe). However, we would need to pass FCC emissions testing (USA) with our end product.

I guess part of my question is: Are other people releasing commercial products using LMIC?


(I Connect) #4

:slight_smile: Nice, we have the same thought/question/struggle

I attended the LoraWan conference a week ago and there is a lot of focus on quality and security.

Even though you are using it within a private network the transmitted messages from your devices will still be received by “public” gateways nearby (packets will be dropped though). So they will also affect the public network and it would be good if they “behave” :-). A certification (or at least a confirmation that the used software is compliant as the certification is costly) would be good for all I think, that is where my question came from.

(A plus of the xdot is that it contains the new secure element that securely stores your keys)


(Pomplesiegel) #5

Thanks so much for your response. OK, glad to know I’m not the only one thinking about this :slight_smile: Great point about how our devices will still impact the public, even with a private gateway. That’s always good to remember…

A certification (or at least a confirmation that the used software is compliant as the certification is costly)

What would this sort of confirmation look like without paying for a costly certification? At this moment we’re using the master branch of mcci-catena/arduino-lmic and observing the fair use / duty cycle restrictions.

Overall is the arduino-lmic path a bad idea from a compliance standpoint for a product? I’m not sure what the plans are for maintaining LMIC.

We would gladly change to a standalone LoraWan solution like the RN2903 or xdot if necessary, but our current design is using LMIC + RFM95W. Any guidance would be greatly appreciated, especially if a particular radio chipset has worked well for you.

Thank you!


(I Connect) #6

formal certification can only be done by a recognized test-house like Dekra in NL or IMST in Germany. It means you have to send your device there and they will put it in an RF-silent chamber together with a gateway and test it for for LoRa compliancy. There will need to be a specific test part in your software that they can trigger to have the device respond in a specific way (and overrule the air time restrictions) and then they check the MAC layer implementation running on the End Device. (I can send you the whole test as they sent it to me in an email…)

More general info here

I spoke with an IMST employee during the conference and she mentioned you can do a sort of pre-compliancy check yourself but I have not looked into that yet. I just now sent her an email how this can be done. I will post it when I have more info.

I am no expert but if cost (20-25 eur for xdot) and redesign (new PCB and maybe port software to MBED-OS) is not a big issue and you want to make sure it will be future proof I would go for the xdot, libraries are maintained by the IC vendors, they are working on out of the box differential OTA updates and you have the secure element.

Where LMIC library (the arduino ones on git) and RFM95 do not have any formal support on the LoRa stack and libs are maintained by enthusiasts without any guarantee it will be kept up to date in the future.
(although I hope they will as open source remains a great concept and a bit the whole idea of TTN)

PS, And if you wait for a little bit there will be new modules that have the Semtech SX1261, 1262 or 1268 which are the new Lora IC’s that will also be able to communicate with the satellites TTN is going to launch, which will give you global coverage (while still being able to use regular gateways, you only need to have a different antenna) :slight_smile: :sunglasses:


(Pomplesiegel) #7

Wow, thank you for such an in-depth explanation. This gives us a lot to think about!

Yes, if you could send me the pre-screening procedure when you have it, that would be much appreciated. Thanks again.


(I Connect) #8

Well, got some feedback from IMST.

There is an option to do a pre-certification. If you apply they will send you a gateway for 1 month:

We are loaning this tool to our customers for one month. Of course you may loan it also with a discount for longer periods. It’s simple to use, a gateway is shipped to the client, they connect to the internet (port 22 needs to be accessible) and they can use the https://loratesting.cominterface to run all certification tests. It contains all the test cases from the real certification testing for EU region.

This is the manual for the test: LoRaWAN_Pretest_Service_Instructions_new.pdf (1023.6 KB)

I asked but for now you cannot use your own gateway:

As of today, we offer the pretest with the LGW from IMST and the Semtech Gateway, others are under development.

In the end, we only need to install a modified packet forwarder, but some manufactures will not allow changing their current FW, so we sticked to ours and the Semtech one, first place.

They pointed me to a library that was certified so using it within your own device should not give any issue, but it is not “arduino based IDE” compatible I think:

Git: LoRaMac-node

Not sure how much it differs from other LMIC libs…

Hope this helps