In full disclosure I work at a company that builds WiFi Access Points, routers etc for enterprises and I just put a hotspot on a drone for fun
It is hard to imagine now, but Ethernet as we know it today (802.3) was not the obvious choice for wired performant connections in 1996, many competing technologies like ATM, Token Ring, RS485, 802.4 etc seemed like more reliable choices, but because Ethernet was fast and cheap (among other reasons) it won out - since then it is hard to imagine a new technology displacing it.
Like Ethernet, WiFi is in the process of subsuming all adjacent technologies (802.15.4, Bluetooth, etc) and for all connections beyond the WAN (which will likely be LTE) it has the ability to be lower power, have better range (within reason) and perform better. This is not because WiFi is necessarily better spec'd - in fact it is unnecessarily complicated - it is because the R&D dollars are focused on it rather than competing technologies. A modern 3x3:3 802.11n chip has massive DSP resource and with .11ac we are seeing double the compute inside the mac/baseband. In addition we are seeing huge improvements in frame detection, phased antenna arrays and RF front ends which has the consequence of increasing link budget (link budget is roughly analogous to signal strength).
Okay, so where am I going with this: as a community we should be looking to use WiFi to consolidate our communication paths with our drones rather than 900MHz telemetry, 2.4GHz remote, 5.8GHz analog. Only fully integrated products like the Parrot AR drone use WiFi and I think that is a mistake. Here are a few reasons why WiFi makes sense:
- We put a digital RX with -95 db sensitivity inches away from a video transmitter transmitting at 23 dBm (in my case, or if you go illegal 36dBm) - this desensitizes our RX significantly reducing link budget. While this is one example, putting a high power transmitter next to a high sensitivity receiver is a bad idea always and we do it 3 times on drones.
- We need to deal with varying ranges and qualities of TX/RX pairs, complicated antenna and ground station setups.
- Analog video is incredibly susceptible to multi-path, limiting quality and antenna types. Don't we all want HD?
- Wouldn't it be convenient to just have one communication path? with maybe a remote as a backup.
Because there are naysayers (correctly so) out there, I thought I would point out common arguments against WiFi:
- WiFi requires a much higher SNR than 802.15.4 - this is true, but the quality of receivers and transmitters along with techniques MRC overcomes much of this and gives you a link that has a much lower duty cycle making it less susceptible to interference and provides superior error checking. A distance of 2-4km is totally practical with WiFi assuming good radios and modest antennas (we do a lot further at my company without too much issue)
- Using WiFi requires IP - yup… but does anybody think this isn't inevitable for us?
- WiFi is unreliable - okay, this needs a 2 part answer - WiFi is actually extremely reliable… it offers very good error checking (CRC) and will do 9 retries before dropping a frame at which point the higher level protocol will also send retries. On the flip side, we are often used to the crappy WiFi found in an Acer laptop (not picking on Acer, just mentioning a random pc vendor) where the radio is placed poorly, the analog front end is poorly designed and the antennas are in odd positions - remove those limitations and buy a $20 card from a reputable manufacturer and you will find superior performance.
- WiFi is really hard to integrate, especially when you need connections beyond serial speeds - I actually dont have an argument here. Most WiFi cards today use a soft MAC which means that most of the radio runs in software - replicating that in Arduino is infeasible. This is why the Arduino Yun uses a linux and a SoC to deliver WiFi. The obvious fix would be to put Autopilot on a linux based platform like OpenWRT, Android or Raspberry Pi
I don't think that it is a question of whether WiFi will become prevalent on drones, it is only a question of when. In the meantime I am working on my WiFi drone, I have 4G and WiFi on mine, Telemetry and Video are the next pieces to get working. I will update as I progress.
Comments
I think you are overestimating the impact of interference in WiFi, unless you are flying in Manhattan the airtime consumption that will trigger the WiFi CCA will be lot duty cycle. Yes, there are lots of transmitters out there, but most don't trigger the CCA, and those that do are likely low duty cycle. TCP does better than you think on WiFi mostly because most of the retransmits happen at L2, it is really rare to see a retransmit at L3 (requires 9 retransmits at L2) so the biggest impact on TCP is RTT which will not initiate a slow start. For Video multicast can be used, as multicast frames are not ACK'd in WiFi.
I work in a building with 1AP per 100 Sqft (I work at a WiFi company) and I can get a usable video stream. TDMA seems like a world of pain - the world has standardized on csma/ca and csma/cd, choosing something else means choosing something proprietary or something out of date.
What we need is a light controller or rc receiver that also has a video transmitter built in, this would allow both systems to benefit from long rand or circular polarised antenna whilst lowering consumer costs and flight weight, also reducing the amount of hardware needed and unifying the systems.
The problem is i am unsure if 2.4g has the bandwidth for vide and control which means a special protocall would have to be made to allow them to work together bu tit would be geat if it was a modular system so you could plug your 2.4g with video module into your radio, the radio would power the tx and output power for video glasses or a small display that could plug directly into the module
On the models end you could have video in plug that allows you to connect the camera directly to the receiver making life so much easier!.
.
You must use common ground on both usb ports on the RPi :)
Thank you :)
I guess there has been so much on wifi because there is the xbee with i guess the same initial range. But that's what i will try to increase. I do send the mavlink via tcp/ip at the 3g system, sp that will be the same for wifi.
Hi Monroe. I have been using the Pi for video and telemetry via 3g and it works. But not via wifi only.
At my office downtown 2.4GHz wireless is useless and does not work. There are so many WiFi units around, they are all jamming each other out of the band. The fact that WiFi is everywhere its showing it's limitations already.
You really need a FHSS radio protocol for a reliable onboard comms in a noisy environment. The choice of band is going to give you either preferable range or preferable data rates. (915Mhz using FHSS is great for fully autonomous flights)
I don't see a huge take-up to HD video either for FPV. With the current analogue systems you can get good range and low latency. And that's the killer problem with 3G/4G technologies is that bandwidth is great, but latency is poor. This isn't going to matter if you are watching a flight, but for FPV, its no fun.
I haven't looked into what new technologies are on the horizon. But I will edge my bets and say FHSS tech is the future.
@Tommy, my goal was to run the IP stack natively in the autopilot which I have since incorporated into the UAV Devboard (UDB) autopilot platform. The ardu platform isn't quite as easy to do serious R&D hacking on, it's more of a commercial product at this point. With UDP/IP I have done flight testing for an around-the-world IFR flight which I call "The mother of all IFR Drone flights". It's not quite around the world, but it's 9 time zones away so thats close enough :)
Looking great Tom :)
I'm actually setup my system where i can fly in FBW using a gamepad via 3g now :) Looking at the video hud, map and gauges :-) Now my goal is to do the same via wifi.
@Tommy, You had a similar setup for what I did a few years back but my intent was to actually fly-by-3G instead of just just get telemetry.
Hi folks
I have been running thissolution for a long time. Now i'm looking into a wifi solution with both telemetry and video on the same link. If you read my comment on THIS blog you can see mye plans for the next solution. But since that post i have been talking to Alex Greve (IBCRAZY) about antennas and i would like to try the Pepperbox and mad-mushroom antennas at www.readymaderc.com at my wifi devices :)
I will follow you guys in this blog to learn more and share knowledge along the way :)
-
1
-
2
-
3
of 3 Next