To add VN_433 and VN_923 for Vietnam

[IoTThinks]

This PR is to add VN_433 and VN_923 for Vietnam.

Main document: https://vanban.chinhphu.vn/default.aspx?pageid=27160&docid=204286 In Page 16: https://datafiles.chinhphu.vn/cpp/files/vbpq/2021/10/08-btttt.signed.pdf The accepted frequencies by Vietnam government is

• Item 39: 433.05 - 434.79 MHz <=25 mW ERP
• Item 45: 920 - 923 MHz <=25 mW ERP

[IoTThinks]

This is the related PR in protobufs: meshtastic/protobufs#730
Thanks a lot.

[caveman99]

According to APPENDIX 19 of https://extendmax.vn/vietnam-mic-circular-08-2021-tt-btttt-list-of-equipment-exempt-from-frequency-license devices that want to use more than 10mW need to adhere to a duty cycle of 10% for base stations and 1% for clients. you can not operate meshtastic with these severe restrictions. Unfortunately we have to reject your request in the current form since it will violate local law.

[fifieldt]

Original Appendix 19:

Translated version:

[IoTThinks]

Let me double check and I may use another frequencies.
I will revisit this issue in a few days.
Thanks a lot.

[IoTThinks]

Usually, we follow Singapore's guideline for LPWAN.
So let me compare the proposed VN_923 to SG_923.
This is to find a way and still comply to the local law.

In Meshtastic, SG_923 sets the duty cycle to 100% and power limit to 20dBm.
https://github.com/meshtastic/firmware/blob/master/src/mesh/RadioInterface.cpp#L151

In item 30c for LPWAN, the duty cycle for LPWAN is 1% too. Same as VN_923.

https://www.imda.gov.sg/-/media/imda/files/regulation-licensing-and-consultations/ict-standards/telecommunication-standards/radio-comms/imdatssrd.pdf

Meshtastic allows SG_923 to use 100% duty cycle because may be the proposer used item 30d to have no restriction to the duty cycle?

Then in the same way, VN_923 can use item 44 (instead of item 45) to have 100% duty cycle like SG_923?
https://datafiles.chinhphu.vn/cpp/files/vbpq/2021/10/08-btttt.signed.pdf

Item 44 in https://extendmax.vn/vietnam-mic-circular-08-2021-tt-btttt-list-of-equipment-exempt-from-frequency-license

What do you think?
Thanks a lot and have a nice day.

[fifieldt]

Thanks for the work, I follow the logic.

I guess it depends on the definition of "Short Range Device". Based on what I've seen online, I think our devices could fit that, but I wouldn't be confident to make the call myself :) I'd like to get some more opinions.

[caveman99]

The mentioned 'mitigation techniques' are not qualifierd here, but usually amount to CAD+AFA in other regulatory documents. We do CAD, but not AFA, so this usually does not apply.

[IoTThinks]

If Meshtastic could have some LBT capabilities, then we could avoid a lot of regulation blockers.
Does Meshtastic have LBT (Listen before talk)?