FabFi

FabFi is an open-source, FabLab-grown system using common building materials and off-the-shelf electronics to transmit wireless ethernet signals across distances of up to several miles.

FabFi is a user-extensible long range point-to-point and mesh hybrid-wireless broadband transmission infrastructure. It is based on the simple idea that a network of simple, intelligent, interconnected devices can create reliable networks in unstable environments. FabFi se simple physics to make low-cost devices communicate directionally for very long distances (physics is cool!), and flexible configurations to adapt to a large variety of conditions. For extreme conditions, FabFi is  mounted with commercial wireless routers on fabbed RF (Radio Frequency) reflectors with a wire mesh surface that redirects the RF energy. Reflector gain depends on the materials used and the size of the reflector, but has been measured as high as 15dBi with some of the current designs.

A single wireless link in the FabFi system consists of two reflectors with attached wireless routers. Similarly, two routers can be linked with a wired connection. A single router can be linked to both wired and wireless connections at the same time. The system is configured for individual links to be combined in numerous ways, creating links that cover very long distances or service many users in a small area. A key component of this linking is called “meshing”. A mesh network is one where any device can be connected to one or more other neighbor devices in an unstructured (ad-hoc) manner. Mesh networks are robust and simple to configure because the software determines the routing of data automatically in real-time based on sensing the network topology. Traditional mesh networks are limited in scale because they rely on single radio, wireless-only connections and omni-directional antennas. By using directed wireless links and wired transfers whenever possible, the Fabfi system is optimized for building very large-scale static (as opposed to mobile) mesh networks. With Scale comes the potential for robust digital communities within a region without dependence on high-bandwidth local uplinks, which are expensive and unavailable in many places.

How Reflectors work

FabFi reflectors use the property of parabolic shapes (Y=cX^2) that a when a vector travelling perpendicular to a parabola’s directrix hits the surface of the parabola it is reflected to the parabola’s focal point. By attaching a RF reflective material such as window screen or chicken wire to a frame that forms the shape of a parabola in three dimensions and then attaching our wireless router to the reflector at the focal point we can precisely concentrate and direct the RF energy coming from the router in transmission and efficiently collect RF energy from the paired router in reception.

The Fab Future

Despite te cobbled-together aesthetic, Fabfi has proven incredibly reliable in Afghanistan’s harsh climate (it reaches 130degF in Jalalabad in the summer with regular sandstorms). Beginning in the summer of 2010, we have expanded the fabfi system to provide direct wireless access to client devices and have been running a community-scale wifi ISP. In more than two years of deployment, we can still count the hardware failures on one hand. To our surprise, the biggest challenge so far has been uplink bandwidth. While many countries tout “mobile broadband” as the solution to universal access problems, the ground truth in most places is that mobile devices alone do not provide sufficient performance (or affordable enough prices) to be viable without some help. In Kenya, fabfi provides a value added service to communities where mobile connectivity is the only means of access by decreasing the data throughput per user and making it possible for providers to buy bandwidth in bulk.