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Wireless Networking
WLAN Site Survey
Module-07
Jerry Bernardini
Community College of Rhode Island
5/20/2012 Wireless Networking J. Bernardini 1
Presentation Reference Material
• CWNA Certified Wireless Network
Administration Official Study Guide, Fourth
Edition, Tom Carpenter, Joel Barrett –
Chapter 6
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What is a Site Survey?
• Process of planning a WLAN to meet design goals
• When installing a WLAN for an organization, areas of
dead space might not be tolerated
– Ensure blanket coverage, meet per-user bandwidth requirements,
minimize “bleeding” of signal
• Factors affecting wireless coverage goals:
– Devices emitting RF signals
– Building structure (walls, construction materials)
– Open or closed office doors
– Stationary versus mobile machinery/equipment
– Movement of mobile walls (e.g., cubicles)
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What is a Site Survey?
• Factors affecting wireless coverage goals (continued):
– Expansion of physical plant or growth of organization
– Existing WLANs
• Both inside organization, and within nearby organizations
• Site survey: Process of planning a WLAN to meet
design goals
– Effectiveness of a WLAN often linked to thoroughness of the site
survey
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Design goals for a site survey
• Achieve best possible performance from WLAN
• Certify that installation will operate as promised
• Determine best location for APs
• Develop networks optimized for variety of
applications
• Ensure coverage will fulfill organization’s
requirements
• Locate unauthorized APs
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More Site Survey Goals
• Map nearby wireless networks to determine existing
radio interference
• Reduce radio interference as much as possible
• Make wireless network secure
• Survey provides realistic understanding of
infrastructure required for proposed wireless link
• Assists in predicting network capability and
throughput
• Helps determine exact location of APs and power
levels required
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When to perform a site survey
• Before installing a new wireless network
• Before changing an existing wireless network
• When there are significant changes in personnel
• When there are changes in network needs
• After making physical changes to a building
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Physical and RF Site Surveys
• Two major categories of site surveys
• Physical Survey and RF Survey
• Physical Survey
– Examination of physical environment
• RF Survey
– Examination of RF activity
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Questions Answered by Physical Site Surveys
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Questions Answered by RF Site Survey
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Manual RF Site Survey Breakdown
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Obtaining Business Requirements
• Determine business reasons why WLAN being
proposed or extended
– If this step skipped, almost impossible to properly design and
implement the network
– Primary data gathering method is interviewing
– Must determine type of mobility required within organization
– Must determine per-user bandwidth requirements
• May be different “types” of users with different bandwidth requirements
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Overall Business Objectives
• Quality improvement (Better)
• Efficiency improvement ( Faster)
• Cost reduction (Cheaper)
• Increased production (More)
• Organizational continuity (Continue to exist)
• Sarbanes-Oxley (accountability)
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Organization’s Needs and Objectives
• Determine business requirements
• User requirements-bandwidth related
• Functional requirements
• Budgetary Constraints
• Regulatory Constraints
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Site Survey Tools: Wireless Tools
• Most basic tool is AP itself:
– Position AP in various locations, monitor signal as you move
– APs should have ability to adjust output power
– APs should have external antenna connectors
• Test effectiveness of different antenna types in different situations
– May need DC-to-AC converter for testing
• Notebook computer with wireless NIC also essential
for testing
– Previously configured and tested
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Site Survey Tools: Measurement Tools
• Site Survey Analyzers: Specifically designed for
conducting WLAN site surveys
– Software often built into AP
– Receive Signal Strength Indicator (RSSI) value
– Full-featured site survey analyzer software settings:
• Destination MAC Address
• Continuous Link Test
• Number of Packets
• Packet Size
• Data Retries
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Site Survey Tools: Measurement Tools
(continued)
• Site Survey Analyzers (continued):
– Full-featured site survey analyzer software settings (continued):
• Data Rate
• Delay Between Packets
• Packet Tx Type
– Unicast or multicast
• Percent Success Threshold
– Basic survey analyzer software contains far fewer features
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Spectrum Analyzers
• Scan radio frequency spectrum and provides
graphical display of results
– Typically measure signal-to-noise ratio
– Single-frequency analyzers measure signal-to-noise ratio at specified
frequency
– Helpful in identifying interference problems
• Thus, helps properly position/orient AP
• Costly $500 $50,000
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Site Survey Tools:Single-frequency analyzer
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Spectrum Analyzer Measures RF energy
Frequency range: 100kHz - 6 GHz.
Internal preamplifier with frequency range
from 100 kHz - 6 GHz.
Displayed average noise level typ. -135
dBm (RBW 100 Hz).
0.5 dB typ. level accuracy up to 6 GHz.
Resolution bandwidths 100 Hz - 1 MHz, 1
and 3 steps.
Wide range of detectors; sample, max/min
peak, auto peak, RMS.
Cost: $13,500
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Cheep Way to View RF and Stations in
Area
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WiFi Hopper
Website: http://wifihopper.com/overview.html
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Airmagnet Site Survey Tool
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AirMagnet Survey
• AirMagnet Survey
This WLAN planning solution stands apart from other
market planning solutions by enabling enterprises to
collect live signal, packet and spectrum data during
their site surveys. This allows enterprises to simulate
and measure network performance in the most
scientific way possible—with the most accurate
depiction of a real-world user experience-which
ultimately results in a better performing network.
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Site Survey Tools: Measurement Tools
(continued)
• Network Analyzers: Can be used to pick up packets
being transmitted by other WLANs in area
– Provide additional information on transmissions
– Packet sniffers or protocol analyzers
– Not used in placement of AP
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Site Survey Tools: Documentation Tools
• Create a “hard copy” of site survey results
– Make available for future reference
– No industry-standard form for site survey documentation
• Site survey report should include:
– Purpose of report
– Survey methods
– RF coverage details (frequency and channel plan)
– Throughput findings
– Sources of interference
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Site Survey Report Material
• Site survey report should include (continued):
– Problem zones
– Marked-up facility drawings with access point placement
– Access point configuration
• Use plain paper and building layout blueprints as
tools
• Advisable to create database to store site survey
information and generate reports
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Sample site survey form
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Survey Security and Site Documents
• Defining Security Requirements: Consider type of data encryption and type of
authentication that will take place across WLAN
– Consider existing security policies and procedures
• Gathering Site-Specific Documentation:
– Blueprints, facility drawings, and other documents
• Show specific building infrastructure components
– Inspecting the site
• Document changes to blueprints and get visual perspective
– Behind-the-scenes site inspection
• Documenting Existing Network Characteristics: New or expanded WLAN will
“dovetail” into network already in place
– Determine degree to which WLAN will interact with other wired networks
– Legacy systems may require additional equipment to support WLAN
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Performing a Site Survey: Gathering Data
(continued)
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Performing a Site Survey: Performing the
Survey
• Collecting RF Information:
– Note objects in and layout of room
• Use digital camera
– Position AP
• Initial location will depend on antenna type
• Document starting position of AP
– Using notebook computer with site survey analyzer software running,
walk slowly away from AP
• Observe data displayed by analyzer program
– Data rate, signal strength, noise floor, and signal-to-noise ratio
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Position of APs
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Collecting RF Information
• Continue moving until data collected for all areas
• Data collected used to produce:
• Coverage pattern: Area where signal can be received from the AP
• Data rate boundaries: Range of coverage for a specific transmission speed
• Throughput: Number of packets sent and received and data rates for each
• Total transmission range: Farthest distance at which signal can be
received by wireless device
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Survey Coverage Pattern
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Survey Data rate boundaries
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RF Data Collection
• Collecting Non-RF Information:
– Sources of interference can include:
• Wire mesh security windows, Aquariums, Outer walls, Ceramic or marble
floors, Concrete floors or pillars, Security booth bullet-proof glass, Mirrors,
and Elevator shafts or filing cabinets
– Electrical and network connections
• Outdoor Surveys: Similar to indoor surveys, but must
consider climatic conditions, trees, different
possibilities for antenna positions
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Performing a Site Survey: Performing the
Survey
• Outdoor Surveys (continued):
– Different tools may be required
• GPS
• Range finder
• Tape measure
• Lighting beacons, flares, and spotlights
• Finalizing the Survey Documents: Final result is map
of optimal areas of coverage for placement of access
point
– If results unacceptable, must relocate AP and start over
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Creating the Site Survey Report
• Narrative section:
– State customer requirements
– Outline methodology
• Outline all steps taken during survey
– Clearly state results of measurements
• May have tables of measurements
– Recommendations
• Should always address security
• Graphic section:
– Generally includes maps and diagrams of coverage area
• Data rate coverage map
• Signal-to-noise ratio plot
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Table of measurements
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Data rate coverage map
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3-D signal-to-noise ratio plot is the output of
some survey applications
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Summary
• A site survey is an in-depth examination and analysis
of a proposed wireless LAN site to meet design goals
• Three categories of tools used
– Wireless tools include the access point and notebook computers with
a wireless NIC
– Measurement tools include site survey analyzers, spectrum analyzers,
and network analyzers
– Documentation tools create a “hard copy” of the site survey results for
future reference
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