[4.10.08]  Wireless Project

Details Image
This project was a joint effort between the RPI electronics club and the watervliet housing authority, to provide a hardware backbone for distributing wireless internet to the buildings in the WHA housing area. The team was composed of a few RPI Electronics club members, who would routinely take trips over to Watervliet, make sure things were up and running and keep the wikipedia pages flowing.
The system architecture, shown right, consisted of a central PF-Sense box [link], running the open source firewall stack, a series of gigabit switches, building switches, building access points, and wireless bridges for spanning roof-to-roof building links.

Diagram made by Andrew Armenia.
An overhead View

The network overlay displayes the housing units and the overall basic structure. We ended up varying the number of access points / building, based on signal propogation
A very basic ray-trace model was used to help make decisions for access point installation location, based on the building's 2d autocad drawings
Power Injection
Because we were using low-cost commercial grade access points, generally tucked up away in the buildings attic spaces, it was fairly difficult to get 120v ac up there. Not to worry!  The access points ran base-100 ethernet, and had  un-used lines, namely 4-5 and 7-8. we fabricated power injectors to pummel 12v DC up to the units and POE adapters for powering the units remotely. At 12v the units only pulled 200mA and the line drop due to impedance was not very significant.
Schematic view of power inejctor
Basement network hardware.
Everything tied up neatly in the basement crawl spaces

Outdoor Hardware
There was a wireless bridge needed to cross a heavily trafficed street. Instead of drilling or digging, we opted for a wifi link, with lightning supression. The beam crossed the street and kept the far building up and connected.

If you have questions or comments, ask below or send over an email.
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Rensselaer Polytechnic Institute 
Electrical & Electrical Power