Wednesday, April 30, 2014

Building a WiFi “Satellite”

This post is really a companion to my recent post Please read that if possible, before reading the following. It will give you the context in which I write. 

Here, I really mean by “satellite” a device or a system that is remotely located, and performs a communications relay role. It should be designed to withstand pretty harsh environmental conditions and run unattended. It should be self-sustaining in terms of power, depending on solar panels. It does not have to be in earth orbit! It would be sufficient if it is on some tall peak like Doddabetta in Ooty, Mullaiahnagiri in Chikmagalur, Anamudi near Munnar, Perumalmalai peak in Kodaikanal (just to name a few peaks in South India). If there is a tall building visible for miles around, it may even be on top of that building. The harsh environmental conditions that have to be withstood would be rain, lightning, wind force, heat and cold. 

Actually the system does not have to be on the tallest peak or building in the area, but on a well-chosen place that provides effective line of sight with suitable user groups like schools/colleges. The altitude at which it is located should help it to command a large area around. I expect that it would be easy to find many places in India, where one such device would cover a thousand square kilometers within WiFi range! The “satellite” should, of course, be mounted on a tower or something like that to prevent theft!

The system would include a router, several 5.8 GHz radios and directional antennas. It would have maintenance-free storage batteries and solar panels. Designing such a device is an inter-disciplinary engineering activity and I hope students from different disciplines would volunteer to look into the different aspects. Many design issues arise – like should we decide in advance what the user groups should be and fix the directional antennas appropriately? What is the ideal trade-off between simplicity and sophistication? I will leave to readers to find such issues and discuss them.

Srinivasan Ramani 
April 30, 2014

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