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aged as PC cards (also known as PCMCIA cards). But with the addition of wireless support to
laptops, they™re also readily available in a “mini-PCI” format, which is slightly cheaper and
somewhat smaller.
204 Part III ” Playing with Access Points


When choosing a radio card, you can buy one with more power than a standard laptop wireless
card supplies. Generally, laptop cards output 30“50mW of power, but you can buy cards up to
200 mW which can double your range. One popular brand amongst DIY builders is called
Senao and is made by Engenius. Use a good search engine to find suppliers, or check with the
supplier of your other specialized wireless gear (antenna, pigtails, and so on).

DIY Software
Cool hardware is an expensive (and lousy) boat anchor without software to go with it. Many
consumer access points use Linux underneath, and you can too. There are many free distribu-
tions tailored specifically for building wireless access points. They include:

M0n0wall”www.m0n0.ch/wall
Pebble”http://nycwireless.net/pebble
WISP-Dist”http://leaf-project.org/

There are also some popular commercial suppliers of reasonably priced access point software:

RouterOS”www.mikrotik.com
StarOS”www.star-os.com

More DIY Resources
Many Web sites discuss different aspects of building your own access point. Some starting points:

www.socalfreenet.org/standardap”comprehensive design and description for a
wireless access point used in a community network
www.nycwireless/poe”how to build a PoE adapter from $10 worth of parts for
your existing access point
www.seattlewireless.net”a treasure trove of hardware comparisons, specs, and
vendors
www.socalwug.org”wireless projects, reviews, and vendor presentation videos

There are also many active mailing lists where DIY-related information appears regularly,
including BAWUG and ptp-general from www.bawug.org and www.personaltelco.net/,
respectively.

Related DIY Projects
Consumer access point hardware is hard to beat on price, so some people prefer to improve
them instead of starting from scratch. Some popular access points to hack are:

Linksys wap-11 and wet-11”hacks include replacing the radio card with a more power-
ful version, as well as modifying the hardware to support more PoE options
Apple Airport”the first true consumer access point
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Chapter 8 ” Build Your Own Outdoor Access Point


Linksys WRT54G”this runs Linux, so enthusiasts are hard at work with new firmware
that provides new functionality

Some creative searching online will reveal similarly fascinating projects and ideas. Have fun
hacking!



Summary
Building and installing an outdoor access point can extend your wireless coverage far beyond
what™s possible indoors. This creates exciting opportunities for sharing your coverage with
other people or creating completely new uses.
This chapter provided a lot of information to get you started. You™ve learned how to think
about location. There™s a detailed list of what equipment to buy and the inherent trade-offs that
are necessary. Clever innovations like Power-over-Ethernet simplify your installation.
Putting everything together isn™t as simple as it appears. Planning for cooling, weatherproofing,
and lightning are important to increase the reliability and safety of your installation.
This may just be the beginning of even more ambitious projects. Take some of the ideas from
this chapter and build on them to see how far you can get.
Read on to create the ultimate outdoor wireless access point using solar power. The next
chapter will show how to take a 75 W solar panel and create a completely stand-alone, totally
wireless access point and repeater system. This system can be placed 10 miles or more from the
nearest DSL line and doesn™t require any power lines.
chapter
Building a Solar-
Powered Wireless
Repeater
I
magine placing an access point high up on a hilltop. What a view that
system would have! And now that you have an outdoor wireless system
in this chapter
on your roof, the next question you will have is, “How do I extend the
reach of my network?”
Understanding solar
A wireless repeater can be used to reach out beyond the limits of your power
wired access point. By pulling energy directly from the Sun with a solar
panel, the system can be located out as far as the eye can see.
Setting up your
repeater
Revolutionary advancements in harnessing the Sun™s power to create
energy have flourished over the last decade. Solar power is becoming an
accepted and, in some cases, required component in structural designs of Configuring your
the 21st century.
repeater for solar
power
While once only viewed as a novelty, solar power is quickly becoming an
integral part of powering human requirements. A combination of improved
efficiency coupled with the proliferation of the technology has reduced cost Mounting the
and opened entire new markets for this stable energy source.
system outside
It was only a matter of time before solar power was harnessed to drive
remote networking components. That time has come and as you create the
system described in this chapter (see Figure 9-1), you will be a part of the
energy revolution and a friend to our fragile environment.
Implementing solar can be expensive. Yet, with some creative sourcing and
some do-it-yourself construction, a solar repeater can be put together for
less than you may think.
The items used in this chapter™s project are:
Solar Panel rated at 75 W, 12 V, 4.4 A
Two wireless antennas, one each for downlink and end-user access
Antenna cables and pigtails
Two wireless access points operating in Bridge mode
208 Part III ” Playing with Access Points


One wireless access point operating in Access Point mode
Crossover network cable
Several feet of 10 AWG wire (black and red)
Two 35 ampere-hour (Ah) deep cycle lead-acid batteries
Solar system charge controller
DC-to-AC power inverter rated at 300 W or higher with a modified sine wave output
AC Power strip with no surge suppression circuitry




FIGURE 9-1: A solar-powered wireless repeater.
209
Chapter 9 ” Building a Solar-Powered Wireless Repeater


Galvanized steel outdoor enclosure rated for outdoor operation (NEMA 3R)
Water sealant tape
Adhesive Velcro tape, 2-inch width
Wiring tie downs (optional)
Flexible rubber conduit and end connectors
Galvanized steel angle-iron to construct the solar panel mount
2-inch diameter, 10-foot pole, and concrete

While solar power lends itself to limitless possibilities, this chapter will focus on integrating a
wireless infrastructure. Once we™ve opened your eyes to the potential, we encourage you to har-
ness the Sun™s power to provide a reliable and free source of power for your networking and
computing needs.



Learning Solar Basics
Photovoltaic power generation systems (also known as solar or PV) are made up of intercon-
nected components, each with a specific function. One of the most attractive features of a PV
system is its modularity. As your requirements change, individual components can be added or
upgraded to provide increased capacity and flexibility. Although your initial components will
vary depending on your application, PV systems generally conform to these specific configura-
tions (see Figure 9-2):

Solar Array: The solar array consists of one or more PV modules that will convert sun-
light into electric energy. The modules can be connected in a series or parallel configura-
tion to provide the voltage and current requirements of your application. Typically the
array will be mounted on a metal post or structure and tilted to face the sun for maxi-
mum exposure.
Charge Controller: Although charge controllers can be purchased with many options,
their main function is to maintain the batteries at the proper charge level, and to protect
them from overcharging, which would damage or reduce life expectancy.
Battery Bank: The battery bank contains one or more deep-cycle batteries, connected in
series or parallel depending on the voltage and current requirements of the application.
The batteries store the power produced by the solar array and discharge it when you
need it.
Inverter: An inverter is required when you want to power AC devices directly from the
solar system. The inverter converts the DC power from the solar array/batteries into AC
power.
AC and DC Loads: These are the appliances or devices that consume the power that you
are generating with your solar array.
210 Part III ” Playing with Access Points


Balance of System: These components provide the interconnections and standard safety
features required for any electrical power system. Included in this group are:
Switches
I

Fuses
I

Circuit Breakers
I

Meters
I

Cabling
I



Several new technologies are emerging, including fuel cells and microturbines that can generate
electric power in a distributed fashion, that is, from locations close to the end-user. However,
solar electric power offers many unique benefits apart from other distributed generation systems.
By crafting a successful solar application, you can reap the benefits that come with using a
renewable energy source. As a direct result of improving technology and declining PV prices,
practical applications for solar cells have steadily expanded from space missions to remote
power and personal electronic devices. Since the mid-1990s, PV has become a practical source
of solar electric generation in the $800 billion electric power industry.
Using solar power in your application creates a highly available wireless network without the elec-
trical delivery costs. A system like the one you will build in this chapter can run for years with lit-
tle more maintenance than the occasional “window cleaning” wipedown of the solar panel.




FIGURE 9-2: Components of a solar system.
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Chapter 9 ” Building a Solar-Powered Wireless Repeater


Setting Up a Wireless Repeater
Before getting in to powering a solar system, you will need to determine where this repeating
network node will be located. Much of this information is covered in Chapters 8 and 13, so
here we will briefly cover how to determine a repeater site.
The concept of a wireless repeater is simple: use a wireless backhaul to beam a signal to an
access point that is accessible by the client. Figure 9-3 shows how this would work. The access
point sits where client devices (i.e., a laptop computer) could connect while the backhaul links
the signal down to the wired Internet.

A backhaul is a point-to-point network link created to maintain a connection between a remote site
and the network base station. The wireless backhaul is meant to carry network traffic from the
repeater station down to the base station. Traffic on the backhaul is generally only between the two
points. The wireless backhaul has an uplink (to the repeater) and a downlink (from the repeater).

The wireless repeater system consists of a total of three Wi-Fi radios. One is set up as an access
point that your users will connect to via their laptop, PDA, or other wireless device. The second
radio is set up in a dedicated bridge mode. The bridge is used to link directly to the network
base station, which is the third radio.

When configuring multiple radios in a single location, as used in the repeater enclosure, it is a
good idea to select channels as far apart as possible, for example, channels 1 and 11 in the
United States. If both radios were on the same channel you would get far too much interference,
even though the antennas are pointed in different directions. This separation helps prevent sig-
nal overlapping because the radios are physically so close together.


Wireless
Access Point


Bridged Backhaul
Downlink




Two-Radio
Repeater




Base Station
Wireless
Uplink
Clients

FIGURE 9-3: Wireless repeater configuration.
212 Part III ” Playing with Access Points



Send to 00:02:AA:BB:11:11
Send to 00:02:AA:BB:00:00
Receive from 00:02:AA:BB:11:11
Receive from 00:02:AA:BB:00:00




Ethernet
Standard Downlink Uplink
Crossover
Access Point Remote Base Station
Cable
00:02:AA:BB:22:22 00:02:AA:BB:11:11 00:02:AA:BB:00:00

Wireless Bridge


FIGURE 9-4: Bridged access points and the MAC address relationship.


The system will require two antennas on the repeater structure, one for the bridged backhaul,
or downlink, and one to link to wireless clients. Depending on distance and interference issues,
the bridge link would usually require a highly directional antenna. The access point would need
an antenna suited to the coverage area.
This configuration requires three wireless devices (not including the clients). Two devices oper-
ate in bridge-mode, while one device acts as an access point. Of course, this is just one configu-
ration of many. It™s conceivable that a wireless signal could be repeated over and over.
Although, in practice, a large number of repeaters cause processing time delays that could cre-
ate synchronization problems with traditional Internet protocols.
A wireless bridge is where two wireless devices are configured to allow connections only to
each other. This is usually done by entering the MAC address of each access point into the
other access point. See Figure 9-4 for an example. Access points in bridge mode will only
accept traffic from the other end of the bridge.
Before getting into the solar installation, configure the wireless equipment in a lab setting. You
will need to configure the bridges individually, and the access point should also be configured
at this point.
The wireless radios used in this chapter are basic off-the-shelf D-Link access points. These are
not necessarily what you would want to run in this type of situation. Considering the money,
time, and effort of integrating a solar system, extra cost on the wireless radio components can be
justified. These radios can vary widely. Any wireless hardware can be used for the repeater section.
Refer to Chapters 8 and 10 for examples of hardware used for providing wireless Internet access.

The D-Link product is one of the few on the market with a built-in repeater mode. This repeater
mode can function well in some environments. However, a single-radio repeater has less than 50
percent of its bandwidth available due to the simultaneous uplink and downlink. Also, the D-Link
product does not work well with two antennas. Indeed, the recent version has only a single antenna
connection. Optimally, two radios are needed for a 100 percent 802.11b bandwidth repeater.

The key to a wireless repeater is the bridge. Some products that support bridging are listed in
Table 9-1. These products should have documentation available with details for bridge config-
uration. Please refer to the documentation of your specific equipment for details.
213
Chapter 9 ” Building a Solar-Powered Wireless Repeater


Table 9-1 Products Supporting Bridge Mode
Vendor Product Name Access Point Mode Bridge Mode

Cisco Aironet 350 series Only on AP model Only on Bridge model
Linksys WAP11 Yes Yes
Linksys WET11 No Yes
D-Link DCS-900 Yes Yes
D-Link DWL-810 No Yes
Proxim Orinoco AP-2500 Yes Yes
Senao/Engenius 2611-CB3 No Yes
Buffalo WLA-L11G Yes Yes
Netgear ME103 Yes Yes




Integrating Solar Power
Aside from the obvious free source of power, there are several other benefits to “solarizing” this
leg of your network infrastructure. First and foremost, having an un-tethered wireless access
point will enable great flexibility in how and where you get network services within the local
region.
Hilltops are no longer out of the equation. By placing a node on a remote hilltop, line-of-sight
and interference issues can be minimal. Additionally, a solar repeater mounted to a tower would
have a commanding view over a low undulating landscape like farmlands, desert, or wilderness
areas.


Understanding Solar Modules
For this application, a 70-watt PV system will be sufficiently adequate. This system will be pre-
configured to 12 V and produce 4.7 A. We recommend using a PV module with a glass surface
that is impact-resistant and allows maximum light transmission.

Choose a single crystalline solar cell, encapsulated and bonded to the glass in multiple layers of
ethylene vinyl acetate (EVA) and laminated with a backing to insure long life in severe condi-
tions. The Shell Solar model SP75, 75-watt solar module fits the bill nicely.



The model we are using (a Shell Solar SP75, see Figure 9-5), uses a proprietary technology
(CIS Thin Film Technology) to efficiently create electricity from the sunlight. This module
is designed for use in 12 V systems. This system™s ability to deliver battery-charge power in
214 Part III ” Playing with Access Points




FIGURE 9-5: A Shell Solar SP75, 75-watt solar panel still carries the Siemens name.

low-light situations makes it particularly effective for specialized applications and in adverse or
changeable environments.

Siemens solar division was acquired by Shell in early 2002. Shell (now Shell Solar) did not begin
renaming the Siemens product line until mid-2003. You will still find products carrying the
Siemens name. The Siemens branded products will eventually disappear from the marketplace as
new products are developed.

These panels are engineered and manufactured for durability and ease-of-use. They are fully
framed in anodized aluminum with pre-drilled, strategically positioned mounting holes to
ensure secure and easy installations. A clamp-type mounting system can be used, so no drilling
is required.
You will also want to use a weather-resistant junction box mounted to the solar module that
will accommodate all wiring. It should include moisture-tight strain relief connectors, electrical
conduit, and a bypass diode. Figure 9-6 shows the junction box on the SP75. Notice the
jumpers and bypass diode. These components connect the panel junction in such a way as to
provide 12 V. This particular solar module can also be configured for 6 V operation.


Solar Power Specifications
Output values of various solar modules are shown in Table 9-2. This is an approximation based
on several manufacturers™ claims for power productivity. Your results may vary depending on
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Chapter 9 ” Building a Solar-Powered Wireless Repeater




FIGURE 9-6: The junction box built in to the Shell SP75 solar module.

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