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Comment by emidoots | Hacker News Reader

FPV today is largely using ExpressLRS[0], an open protocol for running FPV quads' control links (also using esp32 usually)

Video for FPV quads on the other hand is divided: some use analog (mostly because when you lose signal, it's a gradual loss rather than complete loss + a reconnection process), while others use 802.11-based communication which is actually quite competitive. Walksnail Goggles for example use 802.11 for their video links, although not super open/documented people do dig into how it works (see Chris Rosser's work.) Latency is good enough with such setups for fast-paced competitive quad racing, at least

[0] https://www.expresslrs.org

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I will add for those who haven't tried these, as it usually doesn't come across in verbal comparisons:

Digital FPV (like DJI's system) looks vastly better than analog. I think the best comparison is: Digital looks like a modern movie, youtube video etc, and analog looks like CCTV footage from the 80s.

I will also clarify on ELRS: It uses ESP32, but it is a thin wrapper around Semtech LoRa (~915Mhz and 2.4Ghz) SX128x and SX126x chips, which are doing the heavy lifting.

I heard people flying analog also use quite a bit more transmitter power than allowed for non-regulated devices to keep things manageable. Do you have any reference what's possible with digital when staying in the allowed regime?

The bigger advantage with analog is being able to use cheap repeaters to boost the signal back to home.

With digital, you can go from 30-50km with the proper equipment, noise free environment etc... It looks like the video for that has been taken down. But you can find the discussion here: https://greyarro.ws/t/digital-fpv-dji-vs-hdzero-vs-orqa-vs-w...

The "allowed regime" also differs based on where you live. Iirc 25 mW is the maximum permitted power in Europe. Have to double check. That gives you about 100-500 meter range in an open area.

A big advantage with digital video in the US is that some systems, like DJI’s, have FCC approval and can go up to 1 or 2W EIRP legally, so the allowed regime is bigger (there are basically no FCC approved analog video systems, so really you need an amateur radio license and to operate under amateur radio rules for analog video in the US).

Walksnail is not 802.11 based. If anything it is loosely 802.16 based. Likewise DJI OcuSync is more like LTE than anything else.

802.11 is not a good fit for FPV video and trying to use it has held non-proprietary-Chinese video systems back quite a lot.

You mean like OpenHD? What other options do they have while still being able to use COTS hardware?

I think graceless degradation isn't an inherent property of digital radio. You definitely could have some kind of digital modulation that takes advantage of FEC etc. but gracefully degrades.

I'm sure it exists, there probably just not much market for it.

Almost all existing digital FPV systems gracefully degrade as much as they possibly can, both by using FEC and walking down a large number of available MCS as link quality gets worse (and reducing bitrate to match). But when they do eventually fail, re-sync is a much harder problem for them than it is for analog.

Right, but I don't see any reason why that must be the case. It's not a fundamental limitation.

To a great extent you trade statefulness (inter-frame compression, FEC, HARQ, sounding parameters, overhead) for efficiency, so improving link recoverability comes at a cost. There is an existing solution which makes this trade - HDZero. It works amazingly at close range in clean RF environments and has good analog-esque falloff characteristics, but in terms of absolute efficiency it is very bad and therefore does not have the same quality or range as other solutions. Certainly a better hybrid approach is possible but to your point, niche.

> but in terms of absolute efficiency it is very bad

Worse than analogue?

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