Site Survey

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Site Survey
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• To get the best performance out of your wireless
  network, you must both ensure that your access
  points (AP) are in the most optimal locations and
  that other radio emitters, which can cause
  interference, are kept to a minimum.
• This requires you to periodically perform site
  surveys of your wireless spectrum.

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• Depending on the scale of your installation,
  there are a number of tools available for the
  task, such as software that walks you through the
  site survey process.
• But no matter what size network you will have,
  you'll need to follow these basic steps

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Step 1

• Have a blueprint or floor plan(s) of the areas
  you want the wireless network to cover. Some
  software products can work off these floor plans
  directly.
• Look at your plans and identify major building
  obstacles such as walls, halls, elevators and
  floors that will block radio signals. Also note
  where your users will be located -- and where
  they won't -- to determine coverage areas.

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Step 2

• Determine where you can locate APs based on power
  and cabling that you can run to connect the AP to
  the rest of the network.
• Remember that you shouldn't place APs close to
  metal or concrete walls and you should put them
  as close to the ceiling as possible.

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Step 3

• Estimate the total number of APs needed for your
  overall coverage. A good rule of thumb is one AP
  can cover a circle with a 100-foot radius. This
  will give you preliminary AP locations that you
  can use at the beginning of your survey.
• If you already have some APs, note their
  locations on your floor plans.

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Step 4

• Run the survey tool. Make sure to use the same AP
  model for the survey that is used in your actual
  infrastructure.
• See below for recommendations about which tool to
  use.

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Step 5

• Relocate APs and retest, depending on the results
  of your survey.

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Step 6

• Document your findings.
• Record the locations and log your signal readings
  and data rates observed for future reference.

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So, how do you pick the right tool for your
surveying needs? There are three basic types

• First, there are simple Windows-based software
  tools that you can use on a single laptop used
  for recording measurements such as signal
  strength as you walk around your building. You
  just need to buy a single AP and move it around
  to the potential locations that you came up with
  in Step 3. These tools are good for smaller
  installations of, say, one to three APs.

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• They are also good for situations in which you
  don't have a simple open-office plan but rather
  have various corridors and potential radio dead
  spots scattered around multiple floors.
• There are free tools, such as NetStumbler, and
  more capable ones, such as AirMagnet Survey,
  Visiwave, Fluke Networks InterpretAir and Ekahau
  Site Survey, which cost several thousand dollars.

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• Or, there are tools that work in conjunction with
  switched wireless products.
• These tools, from Cisco Systems Inc., Aruba
  Networks and Trapeze Networks, monitor your radio
  coverage and suggest where to locate the APs for
  best coverage.

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• The Aruba Mobility Controller tool is available
  as a free trial and is an integrated part of
  their wireless switch product.
• The Wireless Control System tool from Cisco costs
  4,000, and Trapeze's RingMaster costs an extra
  549.
• If you haven't decided on a wireless
  infrastructure vendor, evaluating the analysis
  tool should be part of your decision process.
• One issue with these tools is that, since they
  use the actual wireless infrastructure to report
  on coverage, they don't do as good a job of
  reporting on dead spots and areas of poor radio
  coverage.
• Depending on your floor plans and the number of
  obstacles, such as thick walls and metal walls,
  you may still need to purchase one of the
  walk-around tools discussed previously.

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• Finally, there are large-scale simulation tools.
  These are useful for multifloor, campus-size
  assessments and are helpful for big deployments
  involving simulations or require the modeling of
  various scenarios.
• These tools include AirTight Networks'
  SpectraGuard Planner, Motorola's Wireless Valley
  LANPlanner, AirDefense Survey and Bluesocket's
  Wireless LAN Planner. Trapeze's RingMaster also
  has the ability to do radio modeling and
  simulation.
• These tools are useful for estimating the total
  number of APs you'll need, and they do a
  relatively good job of simulating the eventual
  environment, but they can't tell you about
  interfering devices or give you a complete
  overview of your wireless networking environment.

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• Remember that doing a wireless site survey once
  is not enough. Rather, they must be done
  periodically. Your radio environment can change
  as Bluetooth keyboards and headsets come and go,
  as microwave ovens turn on and off, and as all
  sorts of other wireless devices pollute the
  802.11 spectrum.
• So, to stay ahead of users who will inevitably
  complain that their signals are too weak and find
  new dead spots in your buildings, be proactive
  and make sure that your surveys are part of
  general network operations.

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Exercise (Manual Coverage Analysis )

• In this exercise, you will test-drive a
  commercial site survey software application
  called Air-Magnet Survey to simulate manual
  coverage analysis.
• After downloading the AirMagnet Survey demo
  software, double-click on the executable file.
  Follow all the installation prompts.
• From the Windows Start menu, under Programs, run
  the AirMagnet Surveyor Demo.
• When prompted to open a sample project, click the
  Yes button.
• In the top-left window of the program, choose
  PassiveSurvey1.svd. Click the Yes button and
  watch the demonstration.
• Observe the colored heat maps that give a
  graphical representation of RF coverage areas.

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• In the top-left window of the program, choose
  ActiveSurvey1.svd. Click the Yes button and watch
  the demonstration.
• In the top-left window of the program, choose
  MergedPassiveActive.svd. Click the Yes button and
  watch the demonstration.
• Test-drive some of the other features on the
  bottom and right menu bars.