6 ms·

Streaming 1080p/60fps up to 20km wirelessly is mind boggling to me. What kind of tech is used to make that happen? seems like it'd require a lot of power.

all2 3y ago
Transmitting long distances lives on a kind of spectrum. On the one end you have MOAR PWER and on the other end you have signals analysis and robust codecs (? I'm not sure "codec" is right. Maybe encoding? Can someone answer this?) that allow for lost information. The signals analysis will clean the incoming signal and the codec/encoding will allow for robust recreation of the captured data. Most wireless transmission technology lives somewhere in-between the extremes of the above spectrum. Signals analysis is quite advanced and codecs/encodings are also quite advanced at this point.
- SSLy 3y ago
  > I'm not sure "codec" is right. Maybe encoding? Numerology
- livueta 3y ago
  My RF knowledge is hobbyist only but I think the word you're looking for is "modulation", e.g. LoRa is able to work over significant distances at low power because of its clever chirp spread spectrum modulation method.
  - brokenmachine 3y ago
    The longest range drone control channel, ELRS, is basically LoRa.
GenerocUsername 3y ago
First off, those numbers are a huge asterisk for perfect atmospheric conditions. In reality you will see about a 2km max in relatively clear conditions, and as few as half a km in even normal suburban/urban conditions.
- steve_adams_86 3y ago
  This is my experience with the mini 3. It’s incredible for sure, but once some trees and/or structures are in the way, it falls apart in a hurry.
  - devit 3y ago
    Is there any system that works for at least 10-20km without line of sight, supporting a video feed usable for guidance, without cell phone network coverage? Maybe something where there are two drones, and one flies high with line of sight to both the user and the low-flying drone so that it can act as a relay like a satellite would? Or something that uses radio frequencies that bounce over the atmosphere, and if bandwidth is not enough uses an automated pilot plus the ability to send photos every few seconds so the user can tell it in which general direction it should fly? Or something that uses Starlink/Iridium/etc. to relay data?
    - hackernewds 3y ago
      why does this read like tech that should not be reasonably legalized for civilian use
      - prmoustache 3y ago
        Don't know about anywhere else but my local laws says you need to see the drone to operate it and you aren't allowed to control it in FPV mode. Local law also say there are very little places I could really use it in 50km radius from home.
      - devit 3y ago
        I think it would be very useful for scouting in woodland/backcountry use including search&rescue. At 50 km/h, it moves 10-20 times faster than a hiker, and at <1000$ it's more than 100x cheaper than a plane or helicopter. But requiring line of sight is a strong limitation because it means that you need to fly over the tree canopy and might not see under it, and you need to fly really high if target is on the other side of a mountain or hill and again you might not see well. And of course cell phone coverage is not guaranteed so you can't use the easiest solution of putting a cell modem on it.
Foivos 3y ago
Keep in mind that this only applies to the FCC regulations. In Europe (CE regulations) the claimed range is 10 km. The mini 3 pro has a CE regulations claimed range of 8 km, but after 2.5 km I pretty much loose connection. If I turn the drone to face my direction, I might be able to fly it a bit further, but at this point it is so hard to control it, that there is no point. Btw, according to regulations, you can not fly it without line of sight. So, in practice the "legal" range is a few hundrend meters. I have yet to see an observer with binoculars. :)
- blindriver 3y ago
  If I claim to see the drone even if it's very far away, can anyone dispute that?
  - akie 3y ago
    Hand me the controls and tell me if I'm steering it left, right, up, or down. If you can, congrats! You can see it. If not...
    - blindriver 3y ago
      Oh damn, when I took my eye off the drone I lost it!
- f3d46600-b66e 3y ago
  You're not allowed to use binoculars.
- SirMaster 3y ago
  Hmm, 2.5km? I've flown the original DJI Mavic Pro to about 4-5km multiple times and never had any real issue with the video feed. I'd be surprised if this much newer gen is worse.
  - Foivos 3y ago
    Which country was that? The drone detects the country through GPS upon startup and limits its transmission power according to the local laws. In the US, the drone can use way higher transmission power (~ 4-20 times more, depending on the drone) .
Aurornis 3y ago
The video quality degrades at longer distances. You can't get the full bandwidth at the maximum distance, but you might see enough to navigate. Communicating with a drone up in the sky is easier than something like your WiFi or your cell phone because you have a nice, clear line of sight to the drone. Fly behind a hill, building, or some trees at distance and the drone will lose connection and go into safety mode. The free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz. If you start with the 1 Watt nominally allowed by regulations, that's +30dBm. Subtract 126dB and you're left with -96dBm. That's a weak signal, but it's actually close to the receive sensitivity of the WiFi card in your laptop, believe it or not. I would guess the DJI gear uses narrower channels than WiFi to achieve a better noise floor than the 20MHz (or wider) channels you get with WiFi. The 20km figure is really an extreme upper limit. Realistically you'd probably need a high-gain antenna pointed in the direction of the drone to achieve it.
- okdood64 3y ago
  Cool stuff. I suspect military communications uses wattage MUCH stronger than what's allowed by regulation in the battle space, correct?
  - exar0815 3y ago
    Lower Frequencies, More power, more directionality, more digital signal Processing are the four ways to increase range. Each has their own disadvantages and advantages, so it's always a tradeoff.
- palata 3y ago
  That's super interesting! Would you have resources to recommend to learn about that? For instance: where do you get that "the free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz"? And why does 1 Watt translate to +30dBm?
  - magnat 3y ago
    https://www.antenna-theory.com/ https://www.antenna-theory.com/ is a good starter for apprentice-level RF voodoo. 30 dBm = 30 decibels wrt to 1 milliwatt. 10 decibels = 1 bel = 10-fold increase of the base quantity, so 30 decibels = 10 x 10 x 10 = 1000x increase, so 30 dBm = 1000x 1 mW = 1 W.
dji4321234 3y ago
DJI OcuSync is based on LTE: https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chipset-its-not-all-that/ https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips... is an example of more information. This is a major advantage DJI and other Chinese drone makers have over US based ones. Technically acquiring an SDR/DSP implemented LTE baseband is not a major difficulty. Getting Qualcomm to let you is quite a challenge. Looking at FCC listings and product pages you can tell that DJI are also throwing power at the problem. The EIRP on DJI devices is very high. They go up to 33dBm (2W EIRP) on the most modern devices like the Mini 4 Pro.
- gruez 3y ago
  > DJI OcuSync is based on LTE: https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips... is an example of more information. Is it using LTE bands? Or just LTE technology on non-licensed bands?

all2 3y ago

Transmitting long distances lives on a kind of spectrum. On the one end you have MOAR PWER and on the other end you have signals analysis and robust codecs (? I'm not sure "codec" is right. Maybe encoding? Can someone answer this?) that allow for lost information. The signals analysis will clean the incoming signal and the codec/encoding will allow for robust recreation of the captured data. Most wireless transmission technology lives somewhere in-between the extremes of the above spectrum. Signals analysis is quite advanced and codecs/encodings are also quite advanced at this point.

SSLy 3y ago
> I'm not sure "codec" is right. Maybe encoding? Numerology
livueta 3y ago
My RF knowledge is hobbyist only but I think the word you're looking for is "modulation", e.g. LoRa is able to work over significant distances at low power because of its clever chirp spread spectrum modulation method.
- brokenmachine 3y ago
  The longest range drone control channel, ELRS, is basically LoRa.

GenerocUsername 3y ago

First off, those numbers are a huge asterisk for perfect atmospheric conditions. In reality you will see about a 2km max in relatively clear conditions, and as few as half a km in even normal suburban/urban conditions.

steve_adams_86 3y ago
This is my experience with the mini 3. It’s incredible for sure, but once some trees and/or structures are in the way, it falls apart in a hurry.
- devit 3y ago
  Is there any system that works for at least 10-20km without line of sight, supporting a video feed usable for guidance, without cell phone network coverage? Maybe something where there are two drones, and one flies high with line of sight to both the user and the low-flying drone so that it can act as a relay like a satellite would? Or something that uses radio frequencies that bounce over the atmosphere, and if bandwidth is not enough uses an automated pilot plus the ability to send photos every few seconds so the user can tell it in which general direction it should fly? Or something that uses Starlink/Iridium/etc. to relay data?
  - hackernewds 3y ago
    why does this read like tech that should not be reasonably legalized for civilian use
    - prmoustache 3y ago
      Don't know about anywhere else but my local laws says you need to see the drone to operate it and you aren't allowed to control it in FPV mode. Local law also say there are very little places I could really use it in 50km radius from home.
    - devit 3y ago
      I think it would be very useful for scouting in woodland/backcountry use including search&rescue. At 50 km/h, it moves 10-20 times faster than a hiker, and at <1000$ it's more than 100x cheaper than a plane or helicopter. But requiring line of sight is a strong limitation because it means that you need to fly over the tree canopy and might not see under it, and you need to fly really high if target is on the other side of a mountain or hill and again you might not see well. And of course cell phone coverage is not guaranteed so you can't use the easiest solution of putting a cell modem on it.

Foivos 3y ago

Keep in mind that this only applies to the FCC regulations. In Europe (CE regulations) the claimed range is 10 km. The mini 3 pro has a CE regulations claimed range of 8 km, but after 2.5 km I pretty much loose connection. If I turn the drone to face my direction, I might be able to fly it a bit further, but at this point it is so hard to control it, that there is no point. Btw, according to regulations, you can not fly it without line of sight. So, in practice the "legal" range is a few hundrend meters. I have yet to see an observer with binoculars. :)

blindriver 3y ago
If I claim to see the drone even if it's very far away, can anyone dispute that?
- akie 3y ago
  Hand me the controls and tell me if I'm steering it left, right, up, or down. If you can, congrats! You can see it. If not...
  - blindriver 3y ago
    Oh damn, when I took my eye off the drone I lost it!
f3d46600-b66e 3y ago
You're not allowed to use binoculars.
SirMaster 3y ago
Hmm, 2.5km? I've flown the original DJI Mavic Pro to about 4-5km multiple times and never had any real issue with the video feed. I'd be surprised if this much newer gen is worse.
- Foivos 3y ago
  Which country was that? The drone detects the country through GPS upon startup and limits its transmission power according to the local laws. In the US, the drone can use way higher transmission power (~ 4-20 times more, depending on the drone) .

Aurornis 3y ago

The video quality degrades at longer distances. You can't get the full bandwidth at the maximum distance, but you might see enough to navigate. Communicating with a drone up in the sky is easier than something like your WiFi or your cell phone because you have a nice, clear line of sight to the drone. Fly behind a hill, building, or some trees at distance and the drone will lose connection and go into safety mode. The free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz. If you start with the 1 Watt nominally allowed by regulations, that's +30dBm. Subtract 126dB and you're left with -96dBm. That's a weak signal, but it's actually close to the receive sensitivity of the WiFi card in your laptop, believe it or not. I would guess the DJI gear uses narrower channels than WiFi to achieve a better noise floor than the 20MHz (or wider) channels you get with WiFi. The 20km figure is really an extreme upper limit. Realistically you'd probably need a high-gain antenna pointed in the direction of the drone to achieve it.

okdood64 3y ago
Cool stuff. I suspect military communications uses wattage MUCH stronger than what's allowed by regulation in the battle space, correct?
- exar0815 3y ago
  Lower Frequencies, More power, more directionality, more digital signal Processing are the four ways to increase range. Each has their own disadvantages and advantages, so it's always a tradeoff.
palata 3y ago
That's super interesting! Would you have resources to recommend to learn about that? For instance: where do you get that "the free space path loss at 20kM is 126dB at 2.4GHz in perfect conditions, or 134dB at 5.8GHz"? And why does 1 Watt translate to +30dBm?
- magnat 3y ago
  https://www.antenna-theory.com/ https://www.antenna-theory.com/ is a good starter for apprentice-level RF voodoo. 30 dBm = 30 decibels wrt to 1 milliwatt. 10 decibels = 1 bel = 10-fold increase of the base quantity, so 30 decibels = 10 x 10 x 10 = 1000x increase, so 30 dBm = 1000x 1 mW = 1 W.

dji4321234 3y ago

DJI OcuSync is based on LTE: https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chipset-its-not-all-that/ https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips... is an example of more information. This is a major advantage DJI and other Chinese drone makers have over US based ones. Technically acquiring an SDR/DSP implemented LTE baseband is not a major difficulty. Getting Qualcomm to let you is quite a challenge. Looking at FCC listings and product pages you can tell that DJI are also throwing power at the problem. The EIRP on DJI devices is very high. They go up to 33dBm (2W EIRP) on the most modern devices like the Mini 4 Pro.

gruez 3y ago
> DJI OcuSync is based on LTE: https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips https://www.suasnews.com/2022/05/the-dji-p1-and-s1-fpv-chips... is an example of more information. Is it using LTE bands? Or just LTE technology on non-licensed bands?