Mobile P2P Communicator - Part 1

A few weeks ago, I was out on a hike with a couple of my buddies. It was supposed to be a routine hike, albeit in unexpectedly warm conditions. Things didn't turn out as planned. One our way back, we got off-tracked on to a false trail. It kept getting increasingly difficult to push on, with excessive thorny vegetation blocking our path. I felt, we had gone too far to backtrack, and decided to continue pushing further (spoiler: it was a bad idea!).

Update: My attempts at long range wifi

Three hours later, both my arms were bleeding out of a dozen cuts and scrapes. One of the guys had taken several spills and had hurt his back. Sweltering heat and dehydration had got to the third guy. We were in the middle of nowhere. With no supplies or water (it wasn't supposed to be a hike this long; we expected to be back to our car by this time), we were losing daylight fast, and the area was not camp-worthy. We decided to do a 180 and head back. Surely, retracing our steps should be easier.

Wrong, again! Every direction looked the same and we got separated, trying to find our way back. Such dense was the foliage that we had zero visual contact between us. Shouting our lungs out was the only way to communicate (no cell reception!). As we trudged forth, the separation increased, and we were no longer within an earshot of each other.

To cut a long story short, I managed to get to a point with shaky cell coverage. I called for help. We were rescued over the next five hours.


An Idea is Born

Our ordeal got me thinking. What if I could make a communication device to meet these requirements:

  • battery powered, portable
  • P2P
  • voice comm
  • range of 1km+

It would also be good to have: - internet connectivity - satellite maps - GPS location sharing

Initial Thoughts

Instead of building an entire handheld device from scratch, I feel, it is easier to use a smartphone, which, I would already have with me on a hike.

First Draft: Bluetooth Mesh

A Bluetooth PAN would solve many problems. No additional hardware required. All we need is a custom app.

P2P Comm Bluetooth

A quick test exposed the limiting factor - range. Most phones I tested could manage no more than about 30 meters line-of-sight. The range dropped to practically nothing when tested in the midst of foliage and vegetation. Quite the deal-breaker.

Second Draft: Wifi Mesh

After the Bluetooth debacle, I didn't have much hope from wifi, either. Nevertheless, I decided to put it through the hoops. For the range test alone, I kept things simple - started a hotspot on one of the phones and let others join in.

Wifi didn't do much better. I got about the same range as BT. Surprisingly, it fared slightly better in the wild - probably because of no interference. I was able to lock on to the hotspot from about 50 meters away.

None of these solutions come anywhere close to the 1km+ range I require.

Third Draft: High Power, Directional Wifi

My hunch is that a mobile hotspot doesn't put out enough power for the range. I am now toying with the idea of setting up a fixed, 'Wifi Base Station', powered by my car battery. The signal would be beamed forward by a directional antenna.

Some preliminary research indicates that parabolic and yagi antennas can achieve a range of several kilometers! Here's the setup I have in mind:

P2P Comm Wifi

If the base station is set up at a spot with 4G reception, my network would have Internet connectivity, too! As you can see, this is no longer a mesh network. Regardless of the separation between them, as long as hikers are connected to the Base Station, they can communicate with each other.

Hikers get to use their smartphones. There is no additional hardware required at the receiving end. Functionality, such as voice comm and location sharing can be built into a custom app. The separation between hikers doesn't matter as long as they are individually, within the base station's range. This is a star network. Ergo, comms are not P2P, but routed via the base station. The fixed base station can be setup at a location with decent 4G coverage, allowing for internet connectivity. It can be powered off my car battery, or a wall socket, if available. Such an arrangement should let us put out as much power as we need for the range. This, in my opinion, is the clincher!



Well, that's the plan! I gotta get myself a spare router and a directional antenna. Can't wait to start tinkering. More to come!



Update: My attempts at long range wifi