fntc community wireless handbook

8/7/2019 FNTC Community Wireless Handbook

1/57

Community Wireless Handbook


Version 1.00

Released: April 18, 2005

Updates of this handbook are always available at:

www.bcwireless.net/~matthewa/handbook/

Copyright (c) 2004, 2005

The First Nations Technology Council

Matthew Asham

The B.C. Wireless Network Society.

Page 1 First Nations Technology Council


2/57

Credits

Many thanks to these people who have reviewed and contributed ideas to the

development of this handbook.

Sue Hanley

Phillip Djwa

Jamie Sterritt

Hans DeBruyn

Mike (aka Reason)

Jamie Campbell

and countless others who have reviewed, critiqued and shared their needs with us.



3/57


Table of Contents

Community Wireless Handbook..........................................................................................1Credits..................................................................................................................................2

Introduction..........................................................................................................................5

What is this handbook about?.........................................................................................6

Sharing your experiences................................................................................................6

Future Versions...............................................................................................................6

What is a network?..........................................................................................................7

What is the Internet?.......................................................................................................8

What is a Community Wireless Network?......................................................................8

What can Wireless networks be used for?.......................................................................8

.........................................................................................................................................8

What is a Wireless network?...........................................................................................9

What are some scenarios a Wireless network would be used?.....................................10

What other (non-wireless) network technologies are available?...................................11

What are the pros and cons of Wireless versus other technologies?.............................12

What are the legal and regulatory implications of using Wireless?..............................13

Are there any health concerns related to using Wireless?.............................................14

We have a satellite up link to the Internet, isn't that a Wireless network?....................15

Anatomy of a Wireless Network........................................................................................16

How information becomes Wireless.............................................................................17Servicing multiple subscribers......................................................................................18

Multiple Access points..................................................................................................19

Linking to a distant community....................................................................................20

Getting started....................................................................................................................21

Range testing and Line of Sight....................................................................................22

Test links that work, but not well..................................................................................24

Site Surveying....................................................................................................................26

Basic radio theory..............................................................................................................28

Example Calculations....................................................................................................34

Examples of common Wireless hardware..........................................................................36WRAP...........................................................................................................................37

Senao ............................................................................................................................37

Soekris...........................................................................................................................38

Tranzeo..........................................................................................................................39

Using PC's, old and new................................................................................................40



4/57

A cheap all-purpose access point for testing.................................................................41

Parts, Accessories .........................................................................................................42

Gear for your surveyor..................................................................................................43

Antennas............................................................................................................................44Parabolic Grids..............................................................................................................45

Setting up client systems to connect to the node...........................................................46

Using Radio Mobile deluxe Software...........................................................................47

Advanced Wireless Networking........................................................................................49

Hotspots.........................................................................................................................49

Non-802.11 back haul...................................................................................................49

Mesh..............................................................................................................................49

Social issues.......................................................................................................................51

Interference....................................................................................................................51

Terminology and other ugly words you need to know......................................................52

Appendix A Free Space Loss tables...............................................................................54

Free Space Loss at 2450 MHz.......................................................................................54

Free Space Loss at 5800 MHz.......................................................................................55

Milliwatt (mW) | Watt (W) | Decibel over a Milliwatt (dBm) conversion chart...............56

Appendix C - Site Survey Worksheet................................................................................57



5/57


Introduction

The use of high speed networks and Internet connections has exploded over the pastdecade. As these communications networks become commonplace tools for conducting

business, delivering education, accessing government, and providing entertainment and

culture, many communities are concerned about falling behind if they can not provide

this technology to their citizens. Small and remote communities tend to lag behind the

major centrers because it is not as profitable for the major communication providers to

expand their network to these areas. This lack of access has become known as the digital

divide the technology gap between communities with high speed communications

networks and those that do not. Many smaller communities have begun to take steps to

develop technology plans and to build broadband and Internet networks as community

projects, hoping to bridge the social and technology gaps themselves.

One network technology commonly used today for community networks is Wireless

broadband. Wireless technology uses radio waves to communicate digital information

and to provide Internet access to subscribers. The use of radio waves means that it is not

necessary to run wire, cable, or fibre optic lines to every home in the community, and

therefore networks can be implemented faster and potentially cheaper in small

communities and remote areas. A number of rural BC communities have successfully

used wireless technology to develop their community networks, so the First Nations

Technology Council (FNTC) has commissioned this handbook to help other small

communities to determine if a wireless network would be appropriate for their area, and

to provide a basic guide for getting started with wireless technology.

The goal for this handbook is to provide basic practical information so that every day

members of a community can setup and maintain a Community Wireless Network.

Although the information presented can also aid a commercial broadband network

operator to deploy a Wireless Internet Service, the target audience is volunteers and

members of the community at large who would like to participate in building a true,

Community Wireless Network.



6/57

What is this handbook about?

This handbook was developed to share our knowledge and experiences with wirelessnetworking and to help you use the technology to connect your community.

We realize information technology can be a complex and overwhelming subject. With

this in mind the author has tried to write this book in an easy, not overtly technical

manner based on real world experiences so that you and others in your community can

build your own Community Wireless Network.

In some parts of this handbook we discuss some of the technical facets behind radio

theory. We do not discuss complex mathematics or other things you would need to know

if you were an engineer, but if you feel overwhelmed feel free to skip the section and

come back to it later.

Wireless networking is much like playing connect the dots. Your end goal as a

wireless networker is to connect people and locations together, and doing so requires each

person to have a common place they can see.

This is the most important thing you, as the reader, need to keep in mind.

Sharing your experiences

If you've undertaken a community wireless project we'd like to hear about it! Send your

story or anything else you'd like to share through this handbook to

[email protected] and it will be included in a future version.

Future Versions

This handbook is updated with new information and resources based on the experiences

of people in our communites. Future versions of this handbook will be released to

http://www.bcwireless.net/~matthewa/handbook/

If you are interested in tracking new releases of this handbook you can subscribe to our

handbook-announce mailing list. http://lists.bcwireless.net/mailman/admin/handbook-

announce



7/57


What is a network?

Networks are links that connect people, places and things together the paths to allowgoods, information, or people to flow from one place to another. To allow this movement

from one place to another, a network must be addressable. This means that an item

travelling on the network must be able to specify a destination or recipients.

Using the example of a road network:

Streets, Highways, alleys and roads are the network paths that material travels

over.

Path names, streets, highway numbers specify the route to be taken.

Addressing of objects on streets (such as your house address or a license plate

number on a car) allows movement to a specific place or person.

Computer networks also have these attributes. There can be many paths for information

to travel over and between networks, and most users and locations on a network have

routes and addresses such as those on a house. Unlike road networks which can move

tangible property such as food or people, computer networks do not yet have the ability to

move physical objects from one place or another, but computer networks can move

digital information very quickly, locally or around the world.

A computer network, sometimes called a data network, moves digital information (codes

and numbers) between computers (and other devices that can read computer information)

in one location to a computer or computers in other location(s). That other location could

be 2 feet away or 10,000 miles away.

Prior to the development of the Internet, if a company or an individual wanted to set up a

data network between two or more computers in different cities they would have to work

with the telephone company to connect each of the locations in the network. For a fee, the

telephone company would set up circuits to interconnect the locations. Those circuits

would be dedicated to your company they formed a private network that no one else

could access.

The Internet was formed by a number of research establishments that wanted to share

information, but did not want to pay for a private network to connect each establishment

to every other establishment. The concept of a shared network between major centrersfunded by national organizations was introduced, and a common data format and a

common set of codes for addressing information was designed.



8/57

What is the Internet?

As this shared network grew in popularity, the applications for the network grew also. At

first the network was used to share technical articles, but as more and more people gainedaccess the concept of electronic mail email took hold. The ability to look at

information on one computer from another remote computer led to the formation of the

worldwide web, and various forms of sharing information on open forums called

newsgroups became common. The Internet now is a worldwide high speed network that

links millions of computers and networks together. For more information about the

Internet look on the Internet at http://www.centerspan.org/tutorial/net.htm !

In order for all these networks and different types of computers to communicate, the

Internet has developed a common language and a means of addressing individual

computers on the network. This common language is called Internet Protocol (IP) or

Transmission Control Protocol / Internet Protocol (TCP/IP), and the address of acomputer on the Internet is described by its Internet Protocol Address (IP Address)

What is a Community Wireless Network?

Unlike the Internet, a Community Wireless Network refers to the network people in a

community use to connect with each other. A Community Wireless Network uses

Internet technology, and may be connected to the Internet through an Internet Point of

Presence (POP) or gateway, and even other non-Internet networks (such as other

networks located in near by regions).

What can Wireless networks be used for?

Wireless networks can be used for the same purposes as the Internet, including web

surfing, email, instant messaging, telephony, and systems used by health centres, schools

and businesses.

Wireless networks can be used to connect people within a community (the first mile or

local loop), connect branch offices and to bridge distant communities or back haul.



9/57


What is a Wireless network?

Wireless networks take many forms. VHF radio, FM/AM radio, Cellular Phones and CB

radios are all forms of Wireless technology but have very specific purposes (usually for

the purpose of communicating verbal information).

When we talk about Wireless networking we talk about a breed of technology that is able

to communicate data. Data can be voice, or Internet, or any other kind of computer

information. This kind of Wireless technology can be used to supplement or even replace

existing Wireless systems.

There are many Wireless technologies suitable for data networking. When the concept of

using radio signals to connect various computers in a building was introduced, theInstitute of Electrical and Electronic Engineers (IEEE) formed a committee to set the

standards for the technology. That committee was called the 802.11 committee, and the

various standards they developed are known as 802.11a, or 802.11b, or 802.11g, etc. This

group of 802.11 standards became known as WiFi technology. Because WiFi

technology quickly became popular, the cost of WiFi equipment has come down rapidly.

Many organizations and Wireless Internet Service providers have started with WiFi.

There are other standards and designs for wireless technologies as well. Many very high

speed or long range solutions are also available and because many use TCP/IP they are

easily integrated into existing networks but for our purposes we will be primarilydiscussing WiFi.



10/57

What are some scenarios a Wireless network would be used?

Wireless can be used for a variety of purposes: To connect households to a community network.

To connect computers within a building in a local area network.

To connect households to a community network.

To provide mobile computing access, such as cellular or radio telephony.

To connect fringe and distant communities quickly and affordably.

To rapidly deploy a network in emergencies and for disaster relief.



11/57


What other (non-wireless) network technologies are available?

There are many other types of technologies available. Each one is capable of transferringany type of binary information, but at different speeds and costs. Some technologies are

built on top of existing technologies while others are independent of others.

ADSL Asymmetric Digital Subscriber Line. ADSL provides high speed

connectivity between a home user and a Central Office. ADSL operates over

telephone lines.

T1 T1 (1.5 megabits per second or Mbps) (sometimes called HDSL). A T1 provides

a single link between two locations. They can be used between a business or home

office and an Internet Service Provider, or from business to business or any other

application where 1.5Mbps of dedicated bandwidth is needed. A T1 is really 23

individual phone lines bonded together.

Cable Modem Cable modems offer anywhere from 512K to 10Mbps of bandwidth.

These are usually used to provide consumers and small offices with high speed

Internet.

T3 A T3 (or often called a DS3) provides up to 45 Mbps of bandwidth and are

usually used as backbone connections. These are provided using telephone lines.

OC3 An OC3 is a 155 Mbps service that is delivered using Fibre Optics.

Fibre Optics - Instead of using copper wires, fibre optics uses laser light to transfer

binary information at very high speeds. Fibre optics can provide up to several Giga-

bits of capacity, but is very expensive to install.



12/57

What are the pros and cons of Wireless versus other

technologies?Cons Pros

Wireless networks use finite resources, a

given geographical area with many wireless

networks will degrade in performance as

more users come on. For example, a

building with 20 competing networks can

cause interference and slow performance

for all users.

Wireless networks are flexible and can be

deployed quickly using inexpensive radio

equipment and antennas. The flexibility of

being able to rapidly deploy a network

means that many networks operating in the

same area can peer, or aggregate

themselves into a larger network with more

capacity to be used by users.

Wireless networks act in a similar manner

to discussing something in a public area. It

can be heard by others in the area with

appropriate equipment.

Security issues are pushed to the users

forcing use of encryption and safe

computing practises that are generally

avoided by the public at large today.

Wireless network speeds does not (yet) fair

against the gigabit speeds achieved by

wired networks such as gigabit Ethernet or

Fibre.

Wireless network technology is rapidly

maturing and new, open standards are

emerging that will provide speeds

comparable to Fibre and other

infrastructures.Many Wireless technologies are

proprietary, resulting in reliance on a

specific vendor and lack of clarity as to an

upgrade path.

Wireless network technologies based on

802.11 and 802.16 standards (ie: WiFi and

WiMax) are not restricted to any one

vendor and can be deployed by anyone

with a basic understanding of the

technology.

Wireless networks are ideal for connecting

many people together without the

expensive of deploying cable and human

resources.

Wireless networks provide mobility and

access to information based on physical

proximity.



13/57


What are the legal and regulatory implications of using Wireless?

Wireless networks use radio frequencies to transmit information. Some wireless

technologies use licensed frequencies, where Industry Canada licenses a specificfrequency range in a specific area to just one use. This ensures that no one else can

interfere with that signal by trying to use the same frequency. Other technologies use

unlicensed frequency bands that have been designed to allow multiple users by

automatically changing frequencies to reduce interference, and by limiting the amount of

power that the radio can put out.

If you use a Wireless technology that is license-exempt (meaning you do not have to pay

a yearly fee to Industry Canada), you are limited by the amount of power your network

can transmit. The power limitations are in place largely to protect users of the unlicensed

radio spectrum from interference.

In practical terms this means you are limited to using as much as you need, provided you

do not interfere with any other wireless systems in the area, however, with thoughtful

planning it is possible to use very low amounts of power while still building a robust

wireless network.

Legally speaking, the limits are based on the radio frequencies and topology of the

network. In a Point to Point network (where only two stations are linked together) an

unlimited amount of antenna gain is permitted, while a Point to Multi Point network (one

central station and many subscribers) is limited to a maximum of 36 dB (4 Watts) emitted

from the antenna.

In all cases the maximum amount of power a transmitter or amplifier (that is, the amountof power going to the antenna) is 30 dBm (1 watt).

We strongly advise against using excessive amounts of power as it will cause more

interference for other users of the shared radio spectrum. In choosing a network

technology careful consideration of the frequency bands being used is also wise.

For example, the 2400 Mhz radio band used by 802.11b and 802.11g devices is very

small in comparison to the 5800 Mhz radio band. In addition many consumer products

(such as cordless telephones, microwave ovens, etc.) use this same frequency band. If

you were to setup a high power radio link in the 2400Mhz band, these devices could be

interfered with.



14/57

Are there any health concerns related to using Wireless?

There is no commonly accepted, Industry sponsored scientific evidence that Wirelesstechnology poses a risk to human health, however, many independent research findings

have linked health risks with high intensity radio systems.

The unlicensed radio band uses a very low amount of power in point to multi point

situations and are considered safe for use near humans, even in the home.

In long distance networks using high gain antennas the effective power output is often in

the 1000-3000 Watt range, and is potentially harmful to any person who stands directly in

the beam.

Licensed radio systems pose a significantly higher risk to human health than unlicensed

systems because they are permitted higher amounts of power. One story describes a

microwave engineer who reportedly brought a twelve pack of beer and a plastic lawn

chair, which he positioned directly in line with the strongest microwave beam. [He] had

not been told about a tenfold boost in microwave power planned that night to handle the

anticipated increase in holiday long-distance calling traffic. . Unfortunately the engineer

did not survive the night.

Although there are risks associated with wireless technology, it is generally safe for

public use but it is advisable to deploy higher power wireless devices in a diligent

manner.

For high gain point to point systems (such as back haul into neighbouring communities)

antennas should be placed on high locations and away from humans. If such networksare deployed in a residential area, it is advisable to keep antennas (up to 24 dB of gain) at

least 10 meters from any person.

Higher gain (30+ dB) antennas such as those employed by Telus Navigata should be

placed even further from people.



15/57


We have a satellite up link to the Internet, isn't that a Wireless

network?Yes, it is. Satellite Internet connections also use radio signals to transmit Internet data,

but the signal has to go back and forth to a satellite orbiting the earth, which is a long

distance. This means that more power is needed to transmit over this distance, which

usually means more expensive equipment, and the distance is long enough that even at

the speed of light the signal takes longer to travel from your computer, up to the satellite,

and back down again this delay can be more than 1 second.

A satellite connection may be a good solution to connect your community to the Internet

if there is no other high speed connection linking the Internet to your community, but it is

not usually the best solution for distributing the Internet signal within your community..



16/57

Anatomy of a Wireless Network

A typical Wireless Network consists of:

An access point

Client wireless radios used by each subscriber

The access point is a central hub device that provides service to 1-100 subscribers.

Multiple access points may be required in larger geographic areas or to serve large groups

of users. An Access Point can be connected to other access points or connected directly to

the network that provides the connection to the Internet in your community.

The access point is typically placed in a central location within view of a group of

subscribers and within view of other access points or with a network link to a POP.

The access point manages the flow of information between subscribers and to other

elements in your network. It broadcasts a networkSSID, or network name, and handles

limited security functions.

When a subscriber links to the community wireless network their subscriber radio is

configured to use the access point's SSID and relevant security parameters. The

subscriber radio then establishes a connection to the Wireless network and a data

connection is created.



17/57


How information becomes Wireless

A computer system is connected to a wireless device using an Ethernet cable.Information sent from the computer (or other computers on the same Ethernet network)

are delivered to the Wireless device:

A transmitter sends radio signals with information to an antenna.

The antenna takes the radio signals and directs them into the air and directs the radio

signal toward a specific physical location.

A receiver hears the radio signals by way of its own antenna, and converts them into a

format your computer can use.

Once the radio signal leaves the transmitter's antenna, it travels through the air and ispicked up by receiving antennas. As the signal travels through the air, it loses its

strength, eventually losing enough power that it cannot be accurately received.

Your objective is to use a combination of antennas and transmitters to deliver enough

radio signal that a reliable wireless link is maintained.



18/57

Servicing multiple subscribers

Wireless is generally what we call line of sight. If you can see from one location toanother, without obstacles, than a wireless connection can see also. This isn't

absolutely true, but is a useful guideline to follow.

When setting up a Wireless network you will need to setup an access point in a

reasonably central location. This location must be visible to those members you wish to

service. As a rule of thumb each access point may service 50-100 users at a time. As

your coverage area expands and usage demand increases, you will want to setup

additional access points and connect them together.



19/57


Multiple Access points

As your network grows you may need to setup additional access points to service a widerarea. Here we have a school and health centrer acting as access points for two distinct

areas of the community.

The health centrer and school are linked directly together.

.



20/57

Linking to a distant community

Some communities may have no access to the Internet or another network. Usingwireless we can create a bridge between the distant community and a community serviced

with a POP.

These are just a few examples of common uses for Wireless networking. There are many

other things you can do as your network grows and faces new challenges.



21/57


Getting started..

The easiest way to plan a wireless network in your community is to dive straight intotesting it.

Obtain some test equipment so that you can set up a temporary network to measure

performance in your area and to try different locations in your community for access

points. By testing on a case-by-case basis, you can better understand how your local

environment will affect the performance of your wireless signal, with the added bonus of

gaining experience without annoying subscribers.

You don't need to spend a lot of money on expensive hardware. The purpose of testing is

to get an idea for how well a wireless signal will travel. There's no point spending $2000

on top of the line equipment when $700 will do.

Some equipment you'll need is:

An access point (a low cost consumer access point such as a Linksys

WRT54G: $90 CAD will suffice)

A portable computer such as a laptop or notebook PC ($1000-$1700) along

with a Wireless card (such as an SMC 2532W-B - ~$100).

Various antennas to test with:

9-14 dB Yagi (one each, for the surveyor and access point): $95

each.

19 dBi Wire Grid (for the access point): $95 each.

24 dBi Wire Grid (for the access point): $130 each.

A GPS (global positioning unit) to determine your latitude, longitude and

estimated elevation: $200.

A compass.

Appropriate mounting equipment for the antenna, such as a tripod and 10 foot

metal pole.

A pair of walkie-talkies with at least 3KM range: $70-$150.

This equipment will let you test the range of wireless networks and take accurate

geographical coordinates for mapping. The GPS is especially important since the latitude

and longitude can be used to calculate wireless network coverage using computer

software.



22/57

Range testing and Line of Sight

The goal of the range test is to find optimum antenna aiming to gain maximum signal andtransfer performance. Ideally you should work with at least one other person when doing

a range test.

One person (the access point manager) will set up the access point at the base location.

This person should be able to adjust the access point and antenna orientation if necessary.

Your partner (or partners), will go to other locations with a portable computer and low

gain (9-14 dBi) antennas. These people will range testthe link by aiming the antenna

toward the base station and testing the ability to communicate with it.

As each surveyor roams around the community taking signal measurements, they should

also try to write down where they are making the measurements from. A GPS will

provide accurate latitude and longitude coordinates which can later be used with

computer software, but even a written description (eg: 12 1st

avenue) is fine. You will

want to make a map to visualize the effective coverage area of your network afterwards.


Setting up a 45KM test link over the Juan de Fuca Strait


23/57


Wireless networks are Line of Sight (or LOS). They must have a good view of other

users to be effective. Terrain including hills, mountains, dense trees and buildings will

weaken a wireless signal. Rain and fog are generally not a problem. If you are standing

behind a wide oak tree, don't expect the signal to get through.

The surveyor will need software to display the strength of received signal from the base

station.

Windows users can use a freeware program called Netstumbler from

www.netstumbler.com Windows XP is recommended, as is the use of an Orinoco or

Prism based wireless card such as the SMC 2532W-B available from London Drugs.

Linux Users can use a program called Kismet with Prism based wireless cards (such as

the SMC 2532W-B). In general we find that Netstumbler and Windows XP is easier

to use for network surveying.



24/57

Test links that work, but not well.

One test two BC Wireless members conducted was between two sites approximately 6.9

KM (4.3 miles) away from each

other.

The test sites are labelled Node 1

and Node 2 respectively

Node 1 used a 19 dBi directional

antenna, while Node 2 used a 24

dB antenna.

Both nodes used a portable

laptop.

The signal strength is -76 dB. This is adequate for mid-speed network link but this link

should have achieved a signal level of -61 dB (well above our desired level of -68 dB).


7 KM test link from North Vancouver to UBC

Netstumbler showing signal readings from the North Vancouver test site


25/57


We were so excited that our first link tested worked right away, we forgot to think about

what we were doing. Hindsight showed us several mistakes that were made:

The antennas were not properly aligned. Using binoculars or a spotting scope

we could have properly aligned the antennas.

We used a total of 40 feet of coaxial cable, this along cut the signal strength by

nearly half. In general it is best to minimize the use of coaxial cable, and

many access points and wireless radios do not even use cable (such as the

Tranzeo wireless devices)

Each side of the link must have the antennas oriented in the same manner.

This is called polarity, if one antenna is horizontally aimed while the other is

vertically aimed, the link will lose up to 20 dB of signal.

Each side of the link was approximately 1 meter above sea level. Much of our

radio signal was absorbed by the ocean in between. If we had elevated our

antennas by 10 feet or so, the link could have been much more reliable.



26/57

Site Surveying

The first thing to do when setting up a wireless network is to conduct a site survey. Thesurvey will help you understand the coverage area of your network and identify the types

of equipment you'll need to connect your subscribers into the network.

Using your laptop and 9 dB antenna, walk around the area where your access point is

servicing. Make note of dead spots or locations that have poor signal readings.

You should also go to each potential subscriber's location and take signal readings. Be

sure to note down the following:

The Site's latitude, longitude and if possible, elevation (use a GPS)

The received signal reading and the noise level.

Whether power is available.

Whether the site is readily accessible (for maintenance).

Visibility from the site (what can it see?). Taking pictures of the site is very useful.

Where antennas may be placed, and how they can be mounted

A sample worksheet for recording this information is contained in Appendix C.

If possible (and with permission of the property owner), take digital pictures from each

place where a wireless device could be mounted.

You will need to map out possible locations and areas where your Wireless network

should provide coverage. Keeping track of a locations geographical coordinates using a

GPS is the first step to creating a map.



27/57


Once you've completed your survey, take a map (or use Radio Mobile) and place

markers (stick pins work well if using a paper map and cork board) at each location you

test. Use a different colour pin to indicate the strength of the access point's signal.

Received Signal Level Colour

0 through -65 Green

-65 through -75 Yellow

-75 and lower Red

By colour coding each location based on the signal level, you can get an idea of the

strength of your network and weak points.



28/57

Basic radio theory

This section is by no means in depth or complete. Unlike wireless systems of the past,current wireless technology is designed for people building networks, not radio engineers.

Wireless (radio) signals travel through mediums such as the air, and copper wire. Radio

signals are electrical signals. When an electric current travels through a piece of wire, it

emits a wave in the air around it.

By using a proper combination of wire types, shapes and lengths (such as an antenna), it

is possible to force an electrical signal to travel through the air without any wires. This is

called propagation.

You can visualize a radio signal as a wave (like the wave in a pool of water). Radio

waves can go up and down at varying speeds. This is called the frequency, or thenumber of times a radio wave moves up and down.

There are three frequency bands we can use without requiring licensing from the Federal

Government. These bands are:

Range Advantages Caveats

902 928 MHz Less affected by trees, buildings. Limited number of

frequencies.

Low capacity (under 5

Mbps).

Higher cost of equipment.

Heavily used by cordless

phones and other devices.

2400 2483

MHz

More bandwidth than 900 MHz

band.

Many, many products on the

market.

Cheap antennas and radios.

Higher bandwidths (1-50Mbps).

Line of sight, doesn't like

trees or buildings.

Heavily used by other

devices including cordless

phones. Shared with Microwave

ovens, Amateur Radio

operators and some

television companies.



29/57


Range Advantages Caveats

5200-5800 MHz Much more bandwidth than 900 or

2400 MHz band. Not used by many consumers for

data networks.

Higher antenna gain to make up for

limited range.

Actually consists of three bands

from 5150 to 5200, 5200 5350

and 5725 5825. More channels to

choose from.

Used by cordless phones.

Even less range than 2400and 900 MHz band

Affected by water, snow.

Shared by military and

government systems, and

radar.

Antennas are made to a certain size based on the frequencies, you can not take an antenna

from a 2400 MHz radio and use it on a 5800 MHz radio, or vice versa.

There are not many 900 MHz products on the market, although it is used in some areas

for weather monitoring, traffic control and telephones. The 900 MHz band is especially

useful for shooting through trees and other obstructions, particularly well suited to

heavily treed and rural areas.

The 2400 MHz band is a very commonly used frequency band. Typical wireless

technologies that use this band are 802.11b (1-11 Mbps) and 802.11g (1-50 Mbps).

There are 11 channels in the 2400 MHz band, but only three of them are independent.

The other channels 'overlap', meaning that a user on channel 1 will receive some

interference from users on channels 2 and 3. 2.4 GHz signals will penetrate some light

tree coverage, best to try a sample link to see how much penetration is possible.

The 5200-5800 MHz band is not heavily used by consumer Wireless networking products

today. It is used by some cordless phones, however. The 5200Mhz band has three sub-

bands, the lowest being for indoor home use only, while the 5800Mhz frequencies can be

used for long distance wireless links at very fast speeds (30 100 Mbps).

A common strategy is to use 2400 MHz (802.11b and 802.11g) in residential and home

environments, and 5.8 GHz for network infrastructure (such as longer point to point

links).So we can send an electrical signal out in to the air, but we must make the electrical

signal behave in a way that can transfer information. This is called modulation.



30/57

A Wireless radio takes information from your computer and modulates it. It creates an

electrical signal that is sent along a wire, to an antenna. The antenna is made up of wires

cut to certain lengths based on the frequency of the radio wave. If the length is right, the

signal leaves the antenna and travels through the air.

As the radio signal travels through the air it passes through various objects (such as

oxygen molecules, birds, insects, trees, houses, etc.). All of these things absorb the radio

signal. This is called loss.

Air itself causes loss, but is fairly well known. The amount of loss that happens because

of a signal travelling through the air is called free space loss.

Other objects such as buildings or trees also cause loss.

Ideally you want to send your signal through air and air only. If you can transmit your

signal with no obstructions such as trees or buildings, you have what's called pure line of

sight.

We can tell how far a radio signal will travel, and get an idea of how much information

we can transmit based on:

The amount of power the antenna is transmitting into the air.

The distance between the transmitting and receiving sides.

How much radio signal the receiving radio needs.

What type of obstructions are in the way.

When selecting a radio you need to know:

It's all about the dB

Radio power is measured in decibels, or dB. Sometimes you may hear radio power

talked about as watts. Instead of using watts you can convert wattage to dB. Doing so

lets you calculate radio links using simple addition and subtraction.



31/57


How much power it transmits.

Radio transmitter power is rated in one of two ways. Watts, and decibels. The actual

power is in watts, but decibels (dB) is easier to use.

For example, an average Wireless radio card transmits at 30 mill-watts (or mW). Instead

of 30 mW, we say it has a power output of 15 dBm.

The amount of radio signal it needs to hear.

The radio also needs to be able to hear a radio signal at a certain level. As the radio

signal travels through the air, it weakens (much like shouting at someone from a mile

away). The minimum signal required for a receiver to understand the data is called the

receive sensitivity.

Radios are usually rated in dBm or decibels over a milliwatt. Note that this is the sameunit as the radio's transmission power. You'll see why this is useful in a bit.

When a radio signal leaves the transmitting antenna your dB will be a high number (for

example: 25 dB). As it travels through the air, it loses strength and will drop to a

negative number. This is why the amount of power a receiver needs is often rated as low

as -80 dB.

The use of negative numbers can be confusing at first. Just remember, 20 is higher than

0, and -20 is lower than 0. Thus if you can achieve a signal level of -60 dB and your

radio needs -80, you have 20 dB of extra signal to accommodate interference and other

issues.Many radios support different transmission speeds (eg: 1 through 11 Mbps). Each speed

requires a different amount of radio signal to operate correctly.

Here's an example:

Radio Name 1 Mbps 2 Mbps 5.5 Mbps 11 Mbps

Lucent Orinoco

classic

802.11b radio

-94 dBm -91 dBm -87 dBm -82 dBm

In plain english this means that the Orinoco radio needs to hear at least -82 dBm of radio

signal to operate at 11 Mbps. This is a worst case scenario though, you should try to get

at least 10 extra dBm so instead of thinking it needs -82, say -72 dBm.



32/57

How far it can go.

Now that we know how much power we can put out, and how much we need, we have tofigure out how much radio signal will be available at the receiving end. The way we

figure this out is to determine how much loss is present between the two radios.

Remember, as a radio signal travels through the air it loses power. This is called Free

Space Loss, or the amount of signal lost while travelling through free space.

A reference table of common Free Space Losses is included in the Appendix of this

handbook

For example, free space loss at 5 miles is 118.36 dB.

Using the work sheet below we can estimate the range of our network:

What Add or subtract it The value (all in dB!)

Transmitter power + 15 dBm

Transmitter antenna gain + 14 dBi

Receiver antenna gain + 14 dBi

Transmitter's coaxial cable

loss

- 2 dB

Receiver's coaxial cable loss - 2 dB

Free Space Loss @ 5 miles - 118.36 dB

Total -79.36 dB

Based on the basic math we did, we can guesstimate that a 15 dBm radio hooked into a14 dBi antenna, transmitting 5 miles to another radio hooked up to a 14 dBi antenna will

yield approximately -79 dB of signal.

That's not to bad, enough to get an 11 Mbps connection but it's not ideal. We want to

achieve a signal level of at least 10-20 dB higher than the minimum needed by a radio. In



33/57


this scenario you might use a higher power transmitter, choose a higher gain antenna, or

even setup a dedicated access point to handle subscribers in the 3-5 mile range, leaving

this access point to service subscribers up to 3 miles.



34/57

Example Calculations

The table below lists some sample calculations, the table fields are: tx The transmitter power output in dB.

tx antenna The transmitting sides antenna gain.

rx antenna The receiving sides antenna gain.

tx loss Cable and connector loss on the transmitting sides.

rx loss Cable and connector loss on the receiving sides.

Path loss The amount of signal loss based on the distance of the link and radio

frequency.

Receive Level The total amount of radio signal we expect to hear.

Remember, we're adding up the positive values that add performance to our network link

and subtracting values that take away signal.

tx tx Antenna rx Antenna tx loss rx loss Path Loss

/Distance

Receive

Level

15 24 24 -1 -1

-118.36

(5 miles) -57

15 24 14 -1 -1

-118.36

(5 miles) -67

15 14 14 -2 -1

-104.38

(1 mile) -64

20 18 14 -2 -1

-113.93

(3 miles) -64

20 18 9 -2 -3

-113.93

(3 miles) -71

As we add the transmitter power, antenna gains, the coaxial cable and connector losses,

and the total path loss we come up with a theoretical Receive Level. Ideally we want this

receive level to be at least 10-20 dB higher than what our client radios need to hear.



35/57


Assuming our clients have radios that need -80 dB of signal, an expected receive level of

-67 is well within our comfort range, and even -71 is okay.

Although the calculations can be done quickly by hand, several computer tools can be

used to save time and help visualize how these numbers fit together.

www.bcwireless.net/misc/radio.xls a spreadsheet for OpenOffice and Microsoft Excel,

will do the math for you.



36/57

Examples of common Wireless hardware

There are typically three ways for obtaining a wireless repeater.

Building it yourself using separately obtained parts

Buying pre-assembled equipment from a vendor

Buying integrated all in one devices.

Each of these options comes with unique benefits and trade offs.

Integrated all in one devices save time and help get a specific goal accomplished but at

the sacrifice of flexibility and management tools. Such devices typically run a special

type of software that can not be expanded, and serve only one function.

Building your own equipment can provide many benefits to your community beyond a

wireless infrastructure. The software used on the devices can be expanded by your

community to offer multimedia services to subscribers and tourists. They can also be re-

tasked for other purposes later when they are replaced by newer technologies.

The devices can also be used as a learning and development tool for aspiring hackers in

the community, and provide a means for entrepreneurs to develop innovative software

and services.

Groups such as the BC Wireless Network Society utilize PC based systems because of

their flexibility and design.



37/57


WRAP

The PC Engines WRAP (Wireless

Routing Application Platform) is a low-

profile, low power controller board.

It is capable of running Linux and

several commercially available operating

system and is capable of using one or

two wireless radios.

The picture here shows a WRAP board with one Wireless radio, mounted in a waterresistant case.

The system here is available from Valemount Networks Corporation (www.staros.com),

in Valemount, BC.

Senao

The Senao (pronounced Senn Ay Oh) 2511 is a high power

(23 dBm) access point and is very popular with Wireless

Internet Service Providers. The device is typically housed in a

case similar to the picture shown here. Fully assembledsystems cost approximately $600 USD.



38/57

Soekris

The Soekris (Soh Chris) 4826 is functionally similar to

the WRAP, it offers 2 radio slots and is able to run

Linux based operating systems.

Metrix Communications (www.metrix.net) sells parts

separately and as assembled kits.

Their flag ship product, the Metrix Mark-II is housed in a

water proof container and ships with cables, power

supply and related accessories. The cost for the kit is

approximately $500 USD.



39/57


Tranzeo

Tranzeo (Tranz Zee Oh) manufactures integrated all-in-one radios. These deviceshave a directional antenna built into the radio, allowing for easy roof mounting. No

coaxial cable is needed, power is supplied over an Ethernet cable running from the radio

into your network centrer.

Tranzeo also manufacturers similar systems for point to point

bridge links, as well as subscriber radios.

For more information about Tranzeo's products, visit

www.tranzeo.com



40/57

Using PC's, old and new

PC's can be used for building wireless repeaters as well. Although a PC motherboard isconsiderably larger than a Soekris or WRAP box, many older computers are in need of

recycling and can be used for experimenting with wireless or even setting up permanent

repeaters with.

Here's an example of a repeater we built using a low-power PC motherboard. The device

has radio adaptors (shown in the top part of the picture) each capable of holding two

radios each (that's a total of four wireless radios in one unit!) and a power adaptor to let it

run off a battery or solar panel.

Instead of a hard-drive, we used a special memory module that acts like a hard drive but

has no moving parts. This module runs Linux and controls the repeater's functionality.


Home brew repeater in a solid aluminum case


41/57


A cheap all-purpose access point for testing

The Linksys WRT54G is an affordable, consumer classaccess point that is suitable for testing. You wouldn't want to

build a Community Network infrastructure with it, but for

testing up a survey network the WRT54G is very useful.

The WRT54G has two antennas, capable of being removed

and replaced with external high gain antennas.

The WRT54G is available from many computer stores and costs between $70-$130 CAD.



42/57

Parts, Accessories

If you decide to use a non-all in one system, whether you build it yourself or purchase thedevice pre-assembled you will need to know how the different parts work together.

Controller Board

The heart of the system is your controller board, this board handles runs a computer

operating system and controls the radios.

Common controller boards include:

The WRAP

Soekris Even an old PC

The Radio(s)

The wireless radio itself plugs into the controller board. Some

boards can handle two or more radios.

Radios come in many shapes and sizes. For WRAP and

Soekris based devices, radios less than the size of a businesscard are used.

Some portable and laptop computers support another type

of radio card, the CardBus radio. These plug into a slot in

the computer and often support attaching an external

antenna.

These radios are very useful for site surveyors and range

testers as they can be removed easily, allowing a tester touse different speed and powers in a range test.


Laptop radio card

MiniPCI Radio Card


43/57


Gear for your surveyor

A Wireless Network Card

Your surveyor will need a Wireless Network card that

supports connecting an external antenna.

The SMC 2532W-B is a high power radio card with a

built in antenna. The antenna can be removed and the

radio can be attached directly to an external antenna using a pigtail.

These cards are 23 dB radios with extremely good receive sensitivity. They function very

well under Linux and Windows.

These cards have been found in computer stores, including London Drugs for

approximately $115 CAD.

A GPS

A GPS (Global Positioning System) is a radio receiver that

can display your geographical coordinates.

A GPS allows a site surveyor to take accurate measurementsand plot network coverage on a map using Radio Mobile.

The Garmin eTrex GPS displayed here is a low end GPS

receiver, available from Canadian Tire for approximately

$150



44/57

Pigtails

A pigtail is connected to the radio, and external antenna

cable (or even the antenna itself). Pigtails often come in a

bulkhead format, which allows you to place the larger

antenna connector through a hole drilled in your case, as

demonstrated here:

Antennas

Antennas are the key part of your wireless system. It doesn't matter how little, or how

much power your transmitter can produce.

Antennas focus the radio energy from a transmitter into a beam. Similar to a flash light

with an adjustable head, the antenna can focus radio energy into a specific direction or

emit it evenly.Antennas that focus energy into one direction are called Directional Antennas. The other

kind of antenna is an Omni directional, meaning the antenna emits radio energy all

around.

Antennas introduce gain into a radio system. Gain is measured in dB, just as a

transmitter is. You can calculate the total effective power being sent from an antenna by

adding the transmitters power output to the gain of the antenna:

15 dBm transmitter + 14 dBi antenna == 29 dB

Antennas also have a beam width. This is literally the width of the radio beam. Beam

width is measured in degrees and has separate horizontal (along the horizon or ground)

and vertical (up and down) beam widths.



45/57


Parabolic Grids

The antenna is an 18 dBi grid parabolic. It

is directional, meaning that it focuses the

radio energy in a specific direction. This

particular antenna has a vertical beam width

of 11 degrees and a horizontal beam width of

17 degrees meaning that at a distance (on

order of centimetres) where the radio signal

has decreased by 3 dB, the beam width of the

signal is 11 x 17 degrees .

This antenna will be used with your access point radio. The access point radio will be

connected to the upstream Internet connection or other local networks. Regardless of the

type of Internet connection (be it a Telus EB1, satellite feed or Microwave hop from

Navigata) we assume that this wireless equipment will be connected to some sort of

Local Area Network using ethernet network cable.



46/57

Setting up client systems to connect to the node.

Client systems may use a variety of types of wireless hardware to connect to the basestation. The hardware may consist of a wireless network card in a desktop PC with

coaxial cable running to a nearby window or roof and antenna.

The type of antenna needed depends on the proximity of the client and the base station.

Distant clients will need a higher gain antenna. Some clients may have special needs or

restrictions, such as strata councils that do not allow antennas. Depending on needs you

may need to help them devise decoy antennas (antennas that look like flag poles, vent

pipes, etc.).

If at all possible you should help the customer deploy a radio system that sits on their

roof and is directly attached to the antenna. A Cat5 network cable can be run into their

house with power supplied over the network cable. Cost for this type of solution can bemore expensive than simply running coaxial cable from the person's PC to roof but

situations differ based on funding sources and performance of the equipment being used.

Antennas mounted to a client's premise should not be hindered by foreign objects such as

trees or other buildings, and should be mounted securely to combat environmental effects

such as wind.

When developing the network you should try to build it in a way that clients are using

low gain antennas such as 9 or 14 dBi antennas. If you need a higher gain antenna,

consider setting up a two radio repeater to extend the range of your access point into

clients local geographical area.



47/57


Using Radio Mobile deluxe Software

Radio Mobile Deluxe is a Windows Freeware utility for designing Radio networks. Itwas written by Roger Coud, VE2DBE.

Radio Mobile can generate maps which reflect the local terrain (topographic maps) using

freely available GIS data. The software can display the visual coverage from a wireless

repeater's location, and calculate radio performance (such as signal strength and

interference) between wirelessly connected radio systems.

The software is an excellent program for plotting long distance point to point wireless

links as well as determining the coverage a repeater has within your community.

The screen shot below shows Radio Mobile displaying a map of the Lower Mainland

including Vancouver and Richmond. Three nodes are displayed, test node 2 and 1 are

directly connected using a Point to Point link and test node 4 and 1 are connected as well.

The yellow blotches in the map are the visual coverage as seen from Test node 4. The

map is topographic, meaning that elevations of buildings and land are taken into account.



48/57

Getting free map data.

Radio mobile can use SRTM (Shuttle Radar Topography Mission) data produced byNASA. If broadband Internet access is available, Radio Mobile can be configured to

download data as needed.

For communities without broadband it may be possible to obtain software as part of a

Wireless Resource kit produced by the BC Wireless Network Society.

A pre-packaged version of Radio Mobile including SRTM data can be downloaded from

the BC Wireless FTP site at ftp://ftp.bcwireless.net/pub/radiomobile/



49/57


Advanced Wireless Networking

Hotspots

Hotspots are wireless networks often run by businesses and individuals. They are called

hotspots, because they provide a small coverage area for people to connect to community

networks and the Internet with.

Popular locations for hotspots include communal areas such as restaurants and cafes.

Hotspots are also powerful tools for supporting tourism. Visitors to a hotspot can be

presented with information about the local community, including upcoming events and

even presentations of local artwork and artisan works.

The BC Wireless Network Society provides a service for Community Wireless Hotspot

Network, more information can be found from http://www.bcwireless.net/hotspot/

Non-802.11 back haul

You may find yourself needing to connect a distant community, or purchasing high

capacity bandwidth from a network service provider. Although WiFi/802.11 wireless

technology can accommodate your needs, higher capacity wireless networking is

available.

Ethernet Bridges that use the 5800 MHz radio spectrum can be used to connect with

distant communities and service providers at speeds of 155 Mbps. These devices are

quite a bit more expensive than WiFi, often $10,000 to $20,000 (USD) but are license

exempt and designed to carry large amounts of information.

Mesh

Mesh Networking is the holy grail of Wireless networking. Mesh refers to many types of

technology that enable wireless systems to automatically find each other and self

configure themselves to route information amongst themselves.Mesh is as organic as networks can get, but is very immature. Several implementations

exist (but are not compatible with each other). Mesh networking should be treated as

experimental, but we strongly suggest that community wireless networks make

provisions for using Mesh technology either during early deployment (where it may turn

out to be stable for the needs of the community) or on an experimental basis.



50/57

Some popular mesh protocols that exist are:

AODV A very common mesh protocol used by commercial and open source

products such as LocustWorld. AODV appears to have many flaws, and is not

necessarily recommended.

RoofNet An experimental protocol from MIT. RoofNet is being tested by

community wireless networks throughout the world, and appears to be very

promising.

Most Mesh products work under the Linux operating system and can use Prism 2.0 and

2.5 devices, or Atheros based radios.



51/57


Social issues

Interference

At first you may be the only wireless network within your region, but as your network

grows and more people get on line you will find yourself competing with new

providers.

Wireless radio spectrum is a finite resource. Many people can use the radio spectrum, but

as more people use wireless networking interference will increase.

In some cases you may even find your competitors actively working to interfere with you.

It is important to adopt a policy early on in your network deployment to work with your

community to resolve interference issues. Network operators should inform each other

when setting up new wireless system.

In fact, if you use licensed wireless devices you mustcoordinate with other wireless

users. Although coordination is not required when using license exempt wireless devices,

it is a best practise to follow.

.



52/57

Terminology and other ugly words you need to know.

Bridge

A bridge connects two paths together directly. Bridges do not decide where information

should be sent, they simply send whatever they hear.

Beam width

Beam Width is literally the width of a radio signal, in degrees. Antennas focus a radio

signal.

ISP

Internet Service Provider. An ISP is a company that provides Internet Services. Thisusually means the ISP has a very large Internet connection (such as T1s, a DS3, OC3,

etc.) and runs servers to provide local Email and Web presence.

Free Space Loss

The amount of radio signal strength lost as the signal travels through a space between two

points. It is called Free Space because the loss does not include foreign sources of loss

such as trees or buildings.

POP

POP means two different things, depending on context.

Email POP is the Post Office Protocol. This is usually known as POP3.

Networks Point of Presence. A POP is a place where a network is available. A bank

machine in a gas station or band office could be thought of being a Point of Presence

because although the Bank itself is not there, it has a presence in the area through the

machine.

Router

A Router is like an intersection of a road. When information is received by a router, the

router decides where it should be sent to next. It does this by looking at where theinformation is destined for, and what paths the router can send it to. The router may

decide to send the information down one of many paths based on network conditions,

cost of a network connection, proximity, etc.



53/57


You might envision a router thinking something like this to itself, I just got a message

from someguy.Internet.com, it's supposed to go to thatotherdude.overthere.com. I'll send

it down via my friend myfriend.thatscloser.tooverthere.com.

TCP/IP

TCP/IP is a protocol. It specifies how information should be sent over an Internet type

network. The Internet refers to many different networks (and technologies).

TCP/IP basically attaches a packing slip onto a packet of information. It includes where

the information comes from, where it is going, how long the information is and options as

to how the information should he handled.

TCP/IP allows information to be passed onto other networks until it finally reaches its

destination.

WiFi

Wireless Fidelity, refers to a commonly used Wireless technology known as 802.11.

WiFi comes in many speeds and uses many frequency bands. Many users use WiFi

within their homes, while service providers often use WiFi to connect subscribers

together.



54/57

Appendix A Free Space Loss tables

Free Space Loss at 2450 MHz

From: https://www.bcwireless.net/moin.cgi/FreeSpaceLossTable

Miles Free Space Loss in dB

1 104.38

2 110.4

3 113.93

4 116.42

5 118.36

6 119.95

7 121.29

8 122.45

9 123.47

10 124.38

11 125.21

12 125.97

13 126.66

14 127.31

15 127.91

16 128.47

17 128.99

18 129.49

19 129.96



55/57


Free Space Loss at 5800 MHz

Miles Free Space Loss in dB

1 111.87

2 117.89

3 121.41

4 123.91

5 125.85

6 127.43

7 128.77

8 129.93

9 130.95

10 131.87

11 132.7

12 133.45

13 134.15

14 134.79

15 135.3916 135.95

17 136.48

18 136.97

19 137.44



56/57

Milliwatt (mW) | Watt (W) | Decibel over a Milliwatt (dBm)

conversion chart.dBm mW W dBm mW W

0 dBm 1 mw 22 dBm 158 mw





5 dBm 3 mw 27 dBm 501 mw6 dBm 4 mw 28 dBm 631 mw


8 dBm 6 mw 30 dBm 1000 mw 1

9 dBm 8 mw 31 dBm 1259 mw 1.259 W

10 dBm 10 mw 32 dBm 1585 mw 1.585 W

11 dBm 13 mw 33 dBm 1995 mw 1.995 W

12 dBm 16 mw 34 dBm 2512 mw 2.512 W

13 dBm 20 mw 35 dBm 3162 mw 3.162 W

14 dBm 25 mw 36 dBm 3981 mw 3.981 W

15 dBm 32 mw

16 dBm 40 mw

17 dBm 50 mw

18 dBm 63 mw

19 dBm 79 mw

20 dBm 100 mw

21 dBm 126 mw



57/57


Appendix C - Site Survey Worksheet

Location Address:

Property Contact:

Latitude and Longitude:

Access point tested against:

Antenna Used:

Signal of access point:

Noise Level:

Power available?

Note: The BC Wireless Network Society maintains a comprehensive locations database

that can be used to store location and placement surveys. You'll need to be a BC

Wireless volunteer to use the database, however, sign up from

https://www.bcwireless.net/signup.php

fntc community wireless handbook

Documents