Long range, high bandwidth wireless link for quadcopters? - Page 1
Forum section: electronics / beginners

author: skillz21
author_rank: Frequent Contributor
timestamp: October 14, 2017, 09:26:59 am
content: All those quadcopters, like the Mavic Pro, have really long range (about 13km) and yet still manages to get a communication link with enough bandwidth to transmit 4K footage straight from the quadcopter.... how? What sort of communication method do they use? is it possible to replicate something like this yourself? Are there modules or boards that you can buy online for this purpose?Thanks

author: Rerouter
author_rank: Super Contributor
timestamp: October 14, 2017, 09:50:47 am
content: To my knowledge they use a standard wifi link and beam forming with 2 antennas to allow the range to get quite far,As in general people will fly higher off the ground to get a wider shot, the interference from the field interacting with the ground lessen, allowing for lower attenuation, combine that with the beam forming and the signal can get very far before it will suddenly reach its limit and drop off, not resuming communication until far closer than when it was lost.4K video to my knowledge is recorded locally to an SD card, and the video sent to the end device is closer to a heavily compressed 720i stream to keep the latency low,If you actually wanted a near realtime 4K link over several km for your drone, i would suggest using a 4G modem and blasting it out that way, if your both on the same group of towers the network latency can be as low as single digit ms, leaving the level of compression and encoding being the limiting factor to the latency.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 14, 2017, 10:06:49 am
content: Oh yeah check this out:"Inside the Mavic’s pocket-sized remote controller is DJI’s brand new OcuSync transmission technology, with a range of 4.3mi (7km)*, HD 720p long range and Full HD 1080p short range video streaming.*Unobstructed, free of interference, when FCC compliant." From the DJI Website... I should have done some research.Anyway, how can wifi last such a long range though? my wifi at home drops off at about 200m...

author: Rerouter
author_rank: Super Contributor
timestamp: October 14, 2017, 10:23:18 am
content: Your home wifi has to contend with walls, furniture, reflections off the ceiling, multiple other nearby transmitters, things like ceiling fans creating dynamic reflections, walk an access point out to the front of your street, put i on a 3m tall pole and see how far down the road you can get before you run out of signal,Using an older router with wifi-g/b (yes that old), i was able to get a 2.2Km range to my laptop at the time, (I was broadcasting my own wifi over my school as a kid to get around the web filters) using a very similar approach, there was a fairly straight road 1.5km to the school, and as my signal was good enough, i kept walking down the road to see how far it could go.Compare it to flying a drone, you generally will be in a park, or some other area that very few people are nearby to (if your respecting any of the laws regarding them) with line of sight to it, with 1 end being 10+ meters off the ground, with nothing but air in the way.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 14, 2017, 10:32:02 am
content: Fair enough.... it's still hard to imagine that my home AP could transmit a signal that far.... so I could, in theory, put an access point (or just use my phone as an access point...?) in an open area, then connect my quadcopter to it, then fly it for such a long range?

author: Rerouter
author_rank: Super Contributor
timestamp: October 14, 2017, 11:35:38 am
content: You can, this is exactly what there products have always done, just be aware your own solution may not be as well put together as a companies, and using antennas that focus the radiating power to where your flying like a limited field patch antenna can help if you only plan to fly in one direction.

author: David Hess
author_rank: Super Contributor
timestamp: October 14, 2017, 08:57:11 pm
content: Small Wifi access points which use patch antennas can easily do 15km and more. This does not work quite as well with a steerable array but using a directional antenna also allows rejection of other transmitters.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 15, 2017, 08:50:12 am
content: so i could just, say connect and esp32 to my phone's wifi hotspot, connect some ESCs and motors, throw on some flight control software, and use it like that?

author: Rerouter
author_rank: Super Contributor
timestamp: October 15, 2017, 09:06:32 am
content: With a proper extenal antenna model, yes for acting as a command receiver / uncompressed video transmitter, having it handle all that + the actual flight control i would say no, i would hand that side off to a dedicated processor, as its a lot to handle.You would likely need to either have something preformatting the video stream and converting it into QSPI , or a camera module that did that internally, while the ESP32 can have blazing fast transmission rates, any time spent processing rather than shifting would start to chew into that bandwidth, a few projects out there where using I2S at about 10Mbit/s, however that is only 240x320 @ 10fps, as they where not compressing it in any way. with compression you can get a lot more bang per buck for your bandwidth, but then there comes a latency from compressing on one end, not so much for decompressing on the other end.At most you can squeeze about 100Mbit/s UDP out of an ESP32 while doing limited IO shifting, so that would be a 640x480 stream using 16 bits per pixel and 24 frames a second uncompressed if you wanted to go that way.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 15, 2017, 10:01:25 am
content: Quote from: Rerouter on October 15, 2017, 09:06:32 amAre you talking about the ESP32? or my phone? If the ESP32, how would I connect an external processor to it?Edit: also, could you give me an example of an external processor such as this?

author: skillz21
author_rank: Frequent Contributor
timestamp: October 16, 2017, 06:06:48 am
content: Are you suggesting that I use a normal flight controller, and let the ESP32 handle the communication?

author: helius
author_rank: Super Contributor
timestamp: October 16, 2017, 08:12:57 am
content: DJI's link is not wifi. You can see their FCC declarations; the channel frequencies are not the same as wifi channels, although they use the same ISM bands. I don't know if anyone has decoded the details, but I expect it is not IP packet based at all. And I can't see how anyone would expect it to be: a video downlink doesn't benefit in any way from the receiver acknowledging each packet, as is used for wifi unicast.Using advanced modulations and coding schemes, like Turbo codes, you can receive signals that are weaker than the noise level. The systems can be designed to barely skirt the EIRP emissions limits, using the strongest power amplifiers and highest gain antennas allowed.However, if your purpose is to extend the reach of wifi radios, it ispossible. Apparently links of over 300km are in continuous service.

author: skillz21
author_rank: Frequent Contributor
timestamp: October 16, 2017, 08:36:17 am
content: Wow.... can I make one?

author: Rerouter
author_rank: Super Contributor
timestamp: October 16, 2017, 12:22:42 pm
content: I was talking about the esp32, your phone has more than enough grunt for realtime video calls which rely on heavy compression.However the esp wont have that to spare while also doing bandwidth heavy transfers.The chip would be either an FPGA or a video codec if your camera module of choice did not already give the option of a compressed stream output. You would then have the esp send a formatted container and begin the steam. Then from then on it would just be shunting data for the phone or othet device to decompess and show as video.