That architecture diagram is interesting… Then 3DR do not (physically) integrate the hardware so well as Navio. Their architecture (from their diagram) is more like the Navio clones which don’t embed devices directly into the host (RasPi) system/buses, but use “external” connections. Capabilities of Navio should be the same and more then.
In Navio we can run programs directly on the same host which is also “inside” the Pixhawk “box” (in relation to the 3DR diagram) so when we need more integration than MAVLink provides, we can write hooks into APM or customize the build directly to mix-in any other hardware or programs on the host system.
Regarding Wifi this is where it gets proprietary. DJI, Solo and DragonLink have their own “special” (expensive) solutions, most likely based on standard Wifi protocols. I didn’t see any information on “SoloLink” on the 3DR site you linked to, maybe you can discover more in their source if it’s really all open/shared.
Back to standards, we have to pick and choose technologies and antennas. So of course mobile networks are going to be patchy and have a lot of latency compared to a private wifi setup. Longer range could be achieved with private wifi and an antenna tracker, but the laws in most countries don’t permit us to fly out of sight anyway. This is where you need the input from the other guys with more experience.
The “don’t need an RC transmitter/receiver” question is often asked, just search here for many opinions and experience. In short it’s doable but many people just install a cheap/small receiver anyway for backup/landing.
It would be good if somebody could write-up an article/study (any students out there looking for a project for their course?) comparing the different technologies with scientific methods. It’s a burning question I plan to answer for myself if nobody else does it. But I’m way too busy until Q2 next year, working hard on other software stuff for Navio first.
Given that many DIY wifi setups are cheap I’d just experiment yourself with common hardware, then search RC Groups for other more expensive equipment if the cheaper solution does not satisfy your requirements.
To answer your other questions, how it works. It’s basically the same as a local network. You may have some difficulty with the configuration as Linux and Wifi can be a real pain to get right. But once it is running (maybe only buy adapters which have explicit Linux support) it’s the same MAVLink connection. You will connect to the drone for commands over TCP and listen on UDP for status updates. Perhaps use Mission Planner over APM Planner 2 as the GCS, because the joystick support there is more mature.
Moving forwards, if you have compatible Linux drivers, then a “mesh” style network is quite attractive because it makes your drone into a flying hotspot and you can implement concepts like multi-drone communication and re-connects easier. But I found that the mesh mode was not implemented or buggy when trying to configure this on any half-decent network adapter (Linux seems to lag behind here). That’s one reason I was looking at the Windows solution, but even Microsoft are lagging behind on Wifi drivers for the IoT/RasPi even though they already exist on the full desktop build and in theory should run with little or no modification.