Hardware Design and Construction

Introduction

A CUWiNware network is a mesh of nodes running the CUWiNware software. A node consists of a computer, a wireless NIC, an enclosure, an antenna, and all the necessary cable and mounting equipment. This manual will walk you through all the decisions that need to be made when purchasing and building hardware for a CUWiNware network.

Many of the decisions that you will make will be based on the local circumstances of your community. Topology, budget, available labor, available materials, network type, and network size will all be factors that go into your decisions. One of the biggest tradeoffs is between time and money -- for each option there is generally a way to do it cheaply that takes a lot of time and a way to do it quickly that is more expensive.

Node Placement

Where a node is located can make or break the quality of its connection to the mesh. Ideally, antennas will have a line-of-sight to each other in order to get the best reception. In order to minimize signal degradation, the cabling between the antenna and the wireless receiver card should be as short as possible. This often means that you need to put both the antenna and the rest of the node above as many buildings and trees as possible. On the roof tends to be the standard node placement location.

Isolated Areas

Areas that are isolated from the local mesh can often get a signal from the main mesh by using a well placed directional antenna instead of an omnidirectional antenna. Such isolated areas can then use an omnidirectional antenna to share the connection with neighbors. In this manner, areas that were out of reach to the mesh can become connected satellite meshes. When the mesh extends itself in the future to encompass the satellite, both meshes will merge seamlessly with each-other.

Rural, suburb, and other fringe areas often find themselves without any broadband service provider. These communities can find a donor business or home in a nearby community that has broadband and is willing to share by setting up an Internet gateway node. Once a link is established with the distant community, the mesh can be spread wirelessly among the members of the community that was once isolated. In this manner, communities can equip themselves with both broadband and a municipal network.

Using consumer grade equipment, links of over 50 miles (80.4 km) have been established. See the antenna guide for more information on antennas.

Coverage Requirements

A common question that immediately pops into the minds of people planning a wireless mesh is "How many nodes will be required to cover our area?" Unfortunately, this is one of the hardest to answer because of the variety of aspects involved.

The amount of radio activity in your area is one influential factor. Sources of radio interference can be as powerful as the government and various utility companies. Sources of interference can also be as mundane as a cordless phone or the microwave oven. A wireless signal may be strong in an area, until someone picks up the phone and the reception drops to zero.

The terrain of an area also strongly affects the quality of a signal. Even a few feet of soil will block a signal entirely, so a node that is in a valley will have much worse reception than a node on a hill. If there is a hill between a node and the rest of the mesh, a second node may be needed to route the signal over or around the hill. Similarly, a node that is located at the top of a hill may be able to establish a weak link to very distant nodes. Distance records for longest link are often set by using directional antennas on mountaintops.

Foliage such as trees also play an important role in signal strength. The water in trees and the needles of some types of conifers are fairly effective at absorbing a wireless signal. It is not unheard of for a weak wireless link to be usable in the winter when the leaves are off of trees, but unusable in the summer. There is a similar problem with wet leaves (such as during a rain) blocking a signal.

Buildings will also block a signal as effectively as small hills. Brick, stone, and metal siding are the most opaque building materials, and may need to be routed around. It is far better to place a node on top of a tall building than beside it.

After all this, what would we say are normal coverage requirements? The twin cities of Champaign and Urbana in Illinois, where CUWiNware is being developed, are about as flat as cities get. We don't have particularly tall buildings here, but we have many tall trees, so we should be around average. Currently our longest link is around 400 meters. Of course, if you are planning a new network, it is best to put nodes closer to each-other than 400 meters, 100-200 meters is ideal (depending on the area, as discussed in previous paragraphs).

One of the CUWiNware developers did the calculations for how much a mesh would cost to cover one square mile at $350 per node. If you can reliably obtain one thousand foot links, you only need nine nodes at a total cost of $3150. If you can only obtain two hundred and fifty foot links, you will need one hundred and forty two nodes at a cost of $49700. It should be noted, though, that a long term goal of CUWiN is to run on hardware that costs less than $100. That would move the cost of the setup with two hundred and fifty foot links down to $14200.