Meshtastic

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Sal@mander.xyz

what kind of speed can LoRa really do? (lemmy.zip)

submitted 3 days ago by shortwavesurfer@lemmy.zip to c/meshtastic@mander.xyz

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scenario: In the future, it is possible to update your node on your 200-foot tower by simply sending the firmware file directly to the node with a zero hop direct connection

I know short fast can get about 10kbps (1KB/s) across the link, but thats just too slow to send a 1.5MB firmware update. I know that short turbo is illegal in some places, and I believe it's because it's using a bandwidth of 500KHz instead of the 250KHz of short fast.

So if you turn the error correction way down to almost off what is about the maximum bandwidth you could hope to possibly get out of the LoRa connection at 250KHz?

Even if you could pull off 125kbps (12.5KB/s) that would only require two minutes to send the firmware file from your node to the receiving node up on the tower.

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[–] muntedcrocodile@hilariouschaos.com 2 points 3 days ago (1 children)

Us bandwidth restrained by law cos frequency ranges are limited?

[–] Sal@mander.xyz 2 points 3 days ago (1 children)

The frequency ranges, power of the transmitter, signal bandwidth, the fraction of time that the transmitter is transmitting (duty cycle), and some other parameters are regulated. LoRa usually transmits in an unlicensed ISM region of the radio spectrum. So, you don't need a license to transmit, but devices still need to comply with the regulations to remain lawful.

I'm not sure about the legal bandwidth limits in different locations. The commonly used LoRa chip (SX1261) can support up to 500 KHz bandwidth, and the OP mentioned 250 KHz as their limit.

[–] muntedcrocodile@hilariouschaos.com 1 points 3 days ago (1 children)

Interesting. So what's the limiting factor for Meshtastic data throughput? Is it legal or technological?

[–] Sal@mander.xyz 2 points 3 days ago (1 children)

Is it legal or technological?

Bandwidth is a resource that limits the amount of information that you can transfer per unit time. You can get a higher throughput if you can increase the information density or by using more bandwidth. Physically, both are possible. Increasing bandwidth of a 868 MHz radio signal is primarily limited by law, not technology. Increasing the information density is limited by the technology of the receiver, transmitter, and modulation.

As for Meshtastic, they often rely on the SX1261/2 chips that have a bandwidth limit by design. The people who manufacture that chip could design it to support a wider bandwidth, but it makes more sense for them to optimize the specs in a way that falls within the legal boundaries of the target applications. This comes from the chip's datasheet:

So... It is both, legal and technological. The technology is designed considering the law. But it is not limited by the laws of physics.

And there is an additional layer of constraints that are imposed by the Meshtastic firmware itself.

[–] muntedcrocodile@hilariouschaos.com 2 points 3 days ago

Thanks for the info.