Saturday, May 4, 2013

Urban testing of Mesh Extender - Part 2

Following the previous test where we placed a mesh extender on a bench in my house, we decided to test again with the mesh extender located in a better, higher location to simulate a purposeful installation.

The first step was to mod our existing prototypes to have the antennae sticking out of the top of their tubs. This reflects our view that the antenna need to stick out to obtain the best performance.  They can be seen here ready to be tested:

One was then promptly installed on our roof:
One thing you will notice is that we have lots of trees in our area that are higher than where we put the Mesh Extender.  So we would continue to suffer from a lack of line-of-sight. Nonetheless, we were confident that we would get substantially better range than in the previous test, but only had a short time window to test in.  This was a bit of an issue, because we would need to cover a few kilo-metres of roads in about twenty minutes.

We thought about driving around, and getting out periodically to measure signal strength, but that didn't sound like fun, and wouldn't give a good idea of real "on the street" coverage, since cars are pretty good shields.  So while it is a situation we should examine, it wasn't the goal of today's test.

Fortunately, I own a Dutch Bakfiets (cargo bike), and one of our developers, was willing to sit in the bike while we rode around.  This worked really well, as we could easily cruise around at about 10km/hour - 15km/hour, and Andrew could read signal strengths off as we went around. You can see him in the bike here, holding his phone to view the signal information, and with the Mesh Extender sitting between his feet.

So how well did it work?

Well, first up, I tested performance around at the local super-market, which we could almost but not quite reach with the Mesh Extender inside my house.  But this time it was possible to get signal about 10m or so into the super-market building.  Here is the Mesh Extender in the fruit-and-veg department showing a solid link of about 10dB:
Then it was time to ride around the neighbourhood and see roughly how far we could get.  Last time we had reliable links to around 200m, and some links to about 260m.  This time we had reliable links to around 500m, spanning about three blocks:
Several hundred dwellings would be within range of this unit. Again, this is the per-hop range, and once we improve the radio firmware to mesh, it will be quite feasible to cover significant distances with multiple hops. 

Part of the rush in this test was that I had to collect Caleb from Childcare. I left the Extender running on the roof, and took the other with me, and came back a different route to see whether we could pick up any signal along Marion Road (the main road running top to bottom in the image).  We did indeed pickup a link along portions of Marion Road at a distance of up to about 850m, including the point shown here:

Not entirely surprisingly the link could be picked up on the further side of Marion Road, but not the nearer side, presumably due to RF shadowing.  

The Mesh Extender in the Bakfiets was less than 1m off the ground, and raising it higher would most likely have improved things, and suggests that distances of a few kilometres might be possible roof-to-roof with good line of sight.

So overall, the range was at least 2.5x better than with the indoor placement.  This is not surprising. It was, however, a pleasant surprise to see urban distances of almost 1km possible -- despite not using advanced error correction and detection schemes in the radio. 

Such a roof-top deployment has the potential to provide coverage over hundreds of dwellings, and it is easy to envisage even a relatively modest mesh of perhaps a dozen or so nodes being able cover an entire suburb, and allow people to make use of mesh services by carrying a small Mesh Extender with them to connect.

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