SocalFreeNet was recently asked to propose a wireless system that could be deployed in Afghanistan by local residents funded by a microloan scheme as a "last mile" solution where phone lines are rare and internet unheard of. This page describes our (evolving) response.
This page is not up to our usual detailed standards due to the recent deployment of several key group members into Mississipi to help with Katrina relief efforts. It will be completed by eary October.
After some consultation, we decided to build a project to satisfy the following criteria.
When pricing out a system, it quickly becomes apparent that the solar panel is the dominant cost with batteries a close second. One easy way to reduce that cost is to reduce the hours of operation. ALthough in most so-called "developed" countries, we expect 24 hr everything (e.g. water, electricity, gas, phone), this not so often the case in other countries even where these facilities are available. If a phone system, say, only worked for 2 hours in the morning and 2 hours at night, that would still be hugely beneficial. And of course services like email are inherently suited to partial connectivity.
Many approaches to providing solutions in remote areas obsess about reliability. For the purposes of this design, we've separated hardware reliability from software reliability. The hardware is expensive and thus should work reliably in the target conditions of heat, variable power and sub-optimal installations. However, if the software is not perfect in ways that are easily circumvented, then this can be a reasonable tradeoff. For example, if the software locks up occaisionally or needs to be restarted at regular intervals, this may be a perfectly reasonable tradeoff against price. Not ideal certainly, but the cost difference between, say, a professional Cisco Access Point at $600-900 and their consumer Linksys branded gear at $60 is arguably worth the occaisonal reboot.
Auto-configuration is highly desirable. One of the appeals of mesh networking is the concept of 'turn it on and walk away'. Unfortunately we're not at the point where this is routinely available, so for now, we're stuck with manually configuring. The next best requirement is a web-based configuration (though an argument can be made for a simple text mode also).
We modified a cheap consumer based access point to function not only as an access point, but also as a client bridge and VOIP server to enable telephone communications. We chose a Linksys WRT54G. It has the following features which make it suitable for this project:
+ retail price is US$60
+ wide availability
+ it runs Linux and has a strong public community developing software addons for it
+ runs on 12V (although 6-18V is ok), so its perfect for powering from commonly available batteries such as car batteries
+ is very power efficient. There are different hardware versions, so values vary, but our 3.1 based hardware used 250mA at 12V, or about 3W. Thus it can easily be powered by a cheap 5W solar panel for as long as the sun is shining. (See also Future Ideas)
The following hardware is required for a single node. Two nodes are needed to make a link.
| Item | Price | Comment |
|---|---|---|
| Linksys WRT54G | $60 | |
| 8-18dBi Antenna | $40 | |
| Outdoor Case | $10 | |
| 12V 5W solar panel | $60 | trickle charge panel |
| 12V 20 amp hour battery | $20 | 10 Amp Hour is enough |
| Misc hardware | $5 | u-bolts or hose clamps, cable |
| PoE | $5 | spiltter and injector |
| Total Price | $180 | |
more detailed info and pictures to come
The Linksys AP is re-flashed with software from www.dd-wrt.com. The test model was built with v.23 beta released on 15 sep. One end of the link was an unmodified Linksys AP. The other end runs the DD-WRT VOIP version. It is configured to run in client-bridge mode.
Need to check:
+ Temperature rating?
+
The power requrements could possibly be halved if the on board switchmode power supply could be eliminated and the box powered directly from a suitable battery (somewhere around 3.3V)
It may also be possible to reduce power consumption by disabling the radio interface at regular intervals (ifdown wi0). We need to make more measurements.
A common strategy for community wireless and rural wireless ISPs is to use single board computers (SBC) as the basis for access points. These can be custom programmed to perform many functions and save cost and increase flexibility. A common approach because of the low power of 802.11b and 802.11a networks is to place the computer on the pole with the antenna to reduce signal loss in the cables. Popular SBCs for wireless use include Soekris, WRAP and MikroTik.
However, while affordable in USA at approx $300-500 each in an outdoor case, it is far more expensive than consumer equipment typically costing $60. Is there a way to have our cake and eat it too? This paper suggests it is.
Many consumer access points are based on reference designs made by computer chip companies. The popular Linksys series use modified designs from Broadcom based around the popular Broadcom radio chips. These boards typically contain a low-power simple computer chip that is different from SBC designs, but still quite powerful.