ETC News
January 24, 2005
The performance of wireless networks is somewhat dependent on the weather conditions. This is particularly true for events that put moisture into the air due to snow or rain. In addition tree foliage coverage (moisture in the leaves) and snow accumulation on tree branches are also a factor. We were curious as to how the mesh network would fare during a blizzard.
Our primary test-mesh network is purposly stretched to the limits, with up to 900 Meters between nodes, using standard antennas. Once there was snow accumulation on the trees, we saw a predictable drop in signal strength, often below a level at which data can be transmitted. In the spring we will fill in the gaps with additional nodes.
Recently we set up a secondary mesh network at a much shorter distance. This is basicaly a node on the second floor of a house, and another node in a basement window down the street. Nothing is optimized about this configuration, and that's the way we wanted it. Basically - Slap up two nodes anywhere and see how it works. The distance is much shorter, only about 150 meters.
Usually we lose the ability to communicate on our mesh networks when the signal strength falls somewhere below -96dBm. This second network has great "fair weather" signal strength hovering somewhere about -80 to -84 dBm, while reporting full "54MBPS" connection rate.
(Note: Every 3dBm difference represents a doubling of output power)
During the severe snowstorm this weekend, the high wind and snow made for a blinding blizzard, at times it was difficult to even see from one house to the next. This was to be a significant test of performance, and honestly I didn't expect the signal to popagate through what was essentially a solid wall of snow. But upon checking the signal strength, I was pleasantly surprised that it had only dropped to only dropped to -90 to -92dBm, and the nodes were still reporting a 22MBPS link.
While not particulary scientifically determined, for future reference I suggest all links in this type of mesh network be installed so that their signal strength during fair weather is -80 to -86dBm, or at least 12dBm above the cutout signal strength. This will of course reduce the maximum distance at which nodes can be placed for outdoor use when network performance is required during poor weather conditions.
Posted by Iain at January 24, 2005 08:50 PMTrackBack URL for this entry: