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Chapter 16 Site Survey Systems and Devices

Chapter 16 Site Survey Systems and Devices. Site Survey defined Site Survey tools Coverage analysis. Exam Essentials. Define spectrum, coverage, and application analysis.

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Chapter 16 Site Survey Systems and Devices

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  1. Chapter 16 Site Survey Systems and Devices • Site Survey defined • Site Survey tools • Coverage analysis

  2. Exam Essentials • Define spectrum, coverage, and application analysis. • Understand why both spectrum and coverage analysis are considered mandatory and application analysis is usually optional. • Identify sources of WLAN interference. • Describe all of the various devices that are potential sources of interference in both the 2.4 GHz ISM and the 5 GHz UNII bands. • Explain RF measurements. • Be able to explain the procedure used while conducting coverage analysis and the different types of RF measurements recorded, including received signal strength and signal-to-noise ratio.

  3. Exam Essentials • Understand AP placement and configuration. • Explain how AP placement, power, and channel settings are part of coverage analysis. • Identify all site survey tools. • Understand the difference between an outdoor and indoor site survey, and identify all the necessary tools. • Explain the three major types of coverage analysis. • Describe the differences between manual, assisted, and predictive site surveys, and explain self-organizing WLAN technology.

  4. Site Survey • Technical Requirements • After you have completed interview and gathered documents • Spectrum Analysis • Coverage Analysis • Placement of APs • Capacity testing • Optional, and depends on needs

  5. Mandatory Spectrum Analysis • Somewhat high cost • Custom equipment • Some options • Spectrum analyzers • Can recognize sources • More than just 802.11 frequencies

  6. Mandatory Spectrum Analysis • Want background noise less than -85dB • Noise will corrupt transmissions • Sources • Microwave ovens • 2.4 GHz cordless phones, DSSS and FHSS • Fluorescent bulbs • 2.4 GHz video cameras • Elevator motors • Cauterizing devices • Plasma cutters • Bluetooth radios • Nearby 802.11, 802.11b, 802.11g, or 802.11n (2.4 GHz) WLANs • Wireless Internet Service Providers ( WISPs)

  7. Mandatory Spectrum Analysis

  8. Mandatory Spectrum Analysis • 5 Ghz sources • 5 Ghz Cordless Phones • Radar • Perimeter sensors • Digital satellite • Nearby 5 GHz WLANs • Outdoor wireless 5 GHz bridges • DFS and TPC are designed to prevent Radar interference

  9. Mandatory Coverage Analysis • Capacity and coverage expectations are reached during interview • Need RF measurements to guarantee that needs are met • Checking received signal strength

  10. Coverage Process Reduce AP power output 1. Place an access point with a power setting of 30 mW in the corner of the building. 2. Walk diagonally away from the access point toward the center of the building until the received signal drops to –65 dBm. This is the location where you place your first access point. 3. Temporarily mount the access point in the first location and begin walking throughout the facility to find the –65 dBm end points, also known as cell boundaries or cell edges. 4. Depending on the shape and size of the first coverage cell, you may want to change the power settings and/or move the initial access point. A good portion of a proper coverage analysis involves starting over and trying again.

  11. Coverage Process

  12. Coverage Process • Think of the cell boundary of the first access point, where the signal is –65 dBm, as the initial starting point. From the first access point, walk parallel to the edge of the building, and place an access point at the location where the received signal is –65 dBm. • Now walk away from this access point, parallel to the edge of the building, until the received signal drops to –65 dBm. • This is the farthest point to place the access point if you do not want cell overlap. • Using the distance from the previous access point and this location, the placement of this next access point should be about 15 to 20 percent (depending on cell overlap requirements) closer to the previous access point. • Move to that location and temporarily mount the access point. Begin walking throughout the facility to find the –65 dBm end points, or cell boundaries.6. Again, depending on the shape and size of the first coverage cell, you may want to change the power settings and/or move this access point.

  13. Coverage Process

  14. Coverage Process • Avoid too much overlap because of possible roaming issues. • Placement will depend on building layout and materials • they affect RF transmission and change the shape of cells • Also, take measurements: • Received signal strength (dBm), also known as received signal level (RSL) • Noise level (dBm) • Signal-to-noise ratio, or SNR (dB)

  15. Coverage Process • Received Signal needs vary based on type of needs • -85dB is good enough for “coverage” • -65 is better for capacity and throughput • SNR must be large enough for signal to be differentiated from noise

  16. Coverage Process • Can also use data rate measurement • Rates will depend on manufacturer, signal and SNR • Using Received Signal Level (RSL) allows you to compare different vendors

  17. Coverage Process

  18. VoWiFi Coverage • Many manufacturers require received signal of -65dB • Use -60 dB in VoWiFi • Fade margin buffer • SNR for VoWiFi is 25 dB or higher • 15 to 20 % cell overlap • Separation of same channel cells is 20 dB

  19. Coverage

  20. AP Placement • Coverage analysis will help choose placement • Mark locations on floor plan with power levels • Also, semidirectional antennas may be used • Most analysis use dipole/omnidirectional • 2.14dB is standard dipole • Using semidirectionals can help avoid reflections in confined spaces • A good kit has multiple antenna types

  21. AP Placement

  22. Optional Application Analysis • Not normally a part of site survey • Can give important information • Software tools to stress test a network • Simulate multiple clients and lots of traffic

  23. Site Survey Tools • Kit of equipment and software needed for successful survey • Can also buy pre-packaged kits

  24. Indoor Kit • Spectrum Analyzer • Blueprints • Signal Strength Measurement Software • 802.11 client card • Access Point (external antenna) • WLAN Controller • Battery Pack • Binoculars • Walkie-Talkie or cell phone • Antennas • Temporary Mounting Gear • Digital Camera • Measureing Wheel/Meter • Colored electrical tape • Ladder or lift

  25. Outdoor Kit • Topographic Map • Link Analysis software • Calculators • Maximum Tree growth Data • Binoculars • Walkie-Talkie or cell phone • Signal generator or wattmeter • Variable loss attenuator • Inclineometer • GPS • Digital Camera • Spectrum Analyzer • Spotlight or sunlight reflector

  26. Coverage Analysis • Different ways to do survey • Manual • Active • Passive • Assisted • Predictive

  27. Manual Site Surveys • Passive • Radio card collects RF (Signal strength, noise level, SNR) but doesn’t associated to AP • Netstumbler • Active • Associate to AP for layer 2 or 3 connectivity • Measure packet loss and retransmission • Cards sometimes come with basic survey tools • Commercial Tools are also excellent

  28. Manual Site Surveys

  29. Manual Site Surveys • Commercial Tools can import blueprint/floor layout • Take measurements and display on image • Allow for what if

  30. Assisted Site Surveys • WNMS and WLAN controllers can often take RF measurements • Assisted coverage analysis • After installing APs, WNMS server can gather data • Often used to figure final AP placement • WLAN controllers offer radio frequency spectrum management (RFSM)

  31. Predictive Site Surveys • Simulated coverage and information • Software takes information about floor plan, building, etc and plots AP locations and expected coverage • Can Model: • Channel reuse patterns • Coverage cell boundaries • Access point placement • Access point power settings • Number of access points • Data rates

  32. Predictive Site Surveys • Can play out “what if” scenarios • Playing with options takes time • Use as a good first step and then verify during manual site survey

  33. Self Organizing Wireless LANs • Next step from RFSM • Centralized device manages power levels to provide for coverage and correct overlap • Based on the accumulated RF information, the centralized device controls the access points and adjusts their power and channel settings, dynamically changing the RF coverage cells. WLAN capacity needs can also be addressed with RFSM, which utilizes dynamic load balancing of clients between the access points. • When implemented, RFSM provides automatic cell sizing, automatic monitoring, troubleshooting, and optimization of the RF environment, which can best be described as a self-organizing wireless LAN.

  34. Exam Essentials • Define spectrum, coverage, and application analysis. • Understand why both spectrum and coverage analysis are considered mandatory and application analysis is usually optional. • Identify sources of WLAN interference. • Describe all of the various devices that are potential sources of interference in both the 2.4 GHz ISM and the 5 GHz UNII bands. • Explain RF measurements. • Be able to explain the procedure used while conducting coverage analysis and the different types of RF measurements recorded, including received signal strength and signal-to-noise ratio.

  35. Exam Essentials • Understand AP placement and configuration. • Explain how AP placement, power, and channel settings are part of coverage analysis. • Identify all site survey tools. • Understand the difference between an outdoor and indoor site survey, and identify all the necessary tools. • Explain the three major types of coverage analysis. • Describe the differences between manual, assisted, and predictive site surveys, and explain self-organizing WLAN technology.

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