11/14/2012
Wireless Networking
WLAN Site Survey
Module-11
Jerry Bernardini
Community College of Rhode Island
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Presentation Reference Material
•
CWTS Certified Wireless Technology Specialist
Official Study Guide , Chapter-8,9
• CWNA Certified Wireless Network Administration
Official Study Guide
(PWO-104), David Coleman, David Westcott, 2009,
Chapter-15,16
• CWNA Certified Wireless Network Administration
Official Study Guide, Fourth Edition, Tom Carpenter,
Joel Barrett –
– Chapter 6, pages 232-318
• The California Regional Consortium for Engineering
Advances in Technological Education (CREATE) project
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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:
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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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Design goals for a site survey
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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
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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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Project Planning Overview
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User’s Requirements
Budget
Population
Applications
Performance
Security
Coverage Area
Physical & Logical Network
Site Environment
NSF Grant 0202396
Site Survey
• A site survey is very important before you deploy a
wireless network.
• A site survey involves analyzing a site from an RF
perspective.
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Coverage
Interference Sources
Equipment Placement
Power Requirements
Wiring Requirements
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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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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
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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
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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:
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Destination MAC Address
Continuous Link Test
Number of Packets
Packet Size
Data Retries
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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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inSSIDer screenshots
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Airmagnet Site Survey Tool
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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:
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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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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:
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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 Data rate boundaries
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Performing a Site Survey: Performing the
Survey
• Outdoor Surveys (continued):
– Different tools may be required
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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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Preparing for a Site Survey
• Facilities Analysis (Floor Plan, Maps, Satellite
Imagery)
Satellite or Ariel Imagery
Floor Plan – Network
WLAN
Naming Convention
Santa Maria,SM
BLDG-A
BLDG-B
Maps of Campus/Facilities
wlan-sm-bldga-rm12ap3
RM-12-AP3
RM-12-AP4
RM-10-AP2
NSF Grant 0202396
Indoor Survey
65 feet
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42
feet
Utilities
and POP
Ethernet
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RF Field
Gateway
Access Points
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Existing Networks
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Is there already a network in place?
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Wired
Wireless
Wired-Wireless
Topology – Location of existing equipment
Current User’s Requirements
NSF Grant 0202396
Area Usage and Towers
• Indoors, outdoors, or both.
– Indoor
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Building Type
HVAC
Floor Plan
Security
– Outdoor
• Weather
• Towers
• Environmental Obstructions (RF)
Security
Power
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Bandwidth & Roaming
• Bandwidth and Throughput
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802.11 a, b, g, n and Bluetooth
Number of Users
Types of Applications
Environmental changes as a function of
seasons.
Mobility or Roaming needs
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Available Resources
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Project Budget
Time Line
Trained Personnel
Floor Plans, CAD
Existing Site Survey Reports
Access to Equipment and Site Areas
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Site Survey Kit Checklist
• See Site Survey Kit Checklist in the text.
Laptop or PDA
Wireless PC card and AP as needed.
Power Pack
Site Survey Software
Location maps and building diagrams
Cables & Connectors
Proper Clothing
NSF Grant 0202396
Site Survey Kit Checklist
Hand Tools and mounting hardware
Digital Camera
GPS, Terrestrial Telescope, Binoculars
Measuring wheel, tape measure, and level
Appropriate transporting equipment
Documentation and writing materials
Antennas
Anything else you meant to bring.
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Conducting a Site Survey
• Examine the network usage problems the wireless
LAN solves.
• Study blueprints of the proposed wireless LAN site.
• Conduct a physical walk-through and inventory.
• Measure the radio frequency (RF) transmissions.
• Indoor and/or Outdoor Survey.
NSF Grant 0202396
Indoor Survey
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AC Power Outlets and Grounds
Wired Network Connectivity
Potential RF Obstructions (Metal)
Potential Interference Sources
Access to all areas
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Outdoor Survey
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Trees, buildings, lakes, mountains, or other
obstructions between linked sites.
Consider growth and foliage of trees, bushes, and
plants.
Line of Sight and distance between stations.
Weather common to location.
Towers and roofs.
NSF Grant 0202396
RF Information Gathering
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Range and Coverage Patterns
Data Rate Boundaries
Documentation
Throughput Test and Capacity
Interference Sources
Wired Data Connectivity
AC/DC Power Requirements
Outdoor Antennas
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Range and Coverage Patterns
Think Three Dimensional!
AP
NSF Grant 0202396
Range and Coverage Patterns
AP
-47 dB
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-61 dB
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AP
AP
-61 dB
New Coverage Area
- 61 dB
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Range and Coverage Patterns
Dead Spot
Dead Spot
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Dead Spot
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AP
N
Coverage Map
A dead spot is an area or zone where wireless network services are not
available because the signal between the client and the AP is blocked
or
attenuated, usually by terrain, excessive foliage, buildings, or
architectural features.
NSF Grant 0202396
Range and Coverage Patterns
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802.11a
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802.11b/g
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Data Rate Boundaries
AP
Data Rates
Color Code
11 Mbps
5.5 Mbps
2 Mbps
5.5 Mbps
2 Mbps
1 Mbps
AP
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Throughput Test & Capacity
• Live testing of the network with actual data
transfers.
• Traffic congestion, bottlenecks, and future
expansion.
• Document baseline measurements for deliverables,
(User Requirements) and maintenance and
troubleshooting.
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Interference Sources
• Active Interference – 2.4 GHz cordless phones,
Medical Equipment, Microwave Ovens/sources,
Bluetooth, X10 Devices, Other 802.11 Devices…
• Passive Interference – Path Loss, Metal Walls,
Concrete, Brick, Stucco, Foliage, Glass, People,
Vehicles…
• Signal Reflections - Multipath
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Outdoor Antennas
• Temporary Antennas
for a Site Survey.
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Site Survey Report Format
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Title Page
Abstract
User’s Requirements
RF Coverage Area
Throughput
Interference Sources
Problem Areas
Drawings
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Site Survey Report Format
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Installation/Configuration Information
Cost Analysis
Conclusion
Appendices
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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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