Chapter 16

1. Site Survey Systems and Devices Chapter 16

2. Outline • Site Survey Defined • Mandatory Spectrum Analysis • Mandatory Coverage Analysis • AP Placement and Configuration • Optional Application Analysis • Site Survey Tools • Indoor Site Surveys Tools • Outdoor Site Survey Tools • Coverage Analysis • Manual • Assisted • Predictive • Self-Organizing Wireless LANs

3. Site Survey Defined • Site survey is for determining RF coverage • Including looking for potential sources of interference as well as the proper placement, installation, and configuration of 802.11 hardware • During the coverage analysis process, a determination will be made for the proper placement of access points, the transmission power of the access point radio card, and the proper use of antennas

4. Site Survey Defined • Mandatory Spectrum Analysis • Spectrum analyzers are frequency domain measurement devices that can measure the amplitude and frequency space of electromagnetic signals • The spectrum analyzer will need to capable of scanning both the 2.4 GHz ISM band and the 5 GHz UNII bands • The software-based spectrum analyzer was designed specifically for 802.11 site surveys and can correctly identify specific energy pulses such as a microwave oven or cordless phone • If the background noise level exceeds –85 dBmin either the 2.4 GHz ISM band or 5 GHz UNII bands, the performance of the wireless network can be severely degraded.

5. Site Survey Defined • Mandatory Coverage Analysis

6. Site Survey Defined • Mandatory Coverage Analysis • If the intent of the WLAN is solely coverage and not capacity, a lower received signal of –85 dBmmight be used as the boundary for your overlapping cells. • If throughput and capacity are issues, using a stronger received signal of –65 dBmis recommended. • The SNR is an important value because, if the background noise is too close to the received signal, data can get corrupted and retransmissions will increase. • Many vendors recommended a minimum SNR of 18 dB for data networksand a minimum of 25 dB for voice networks.

7. Site Survey Defined • Mandatory Coverage Analysis

8. Site Survey Defined • Mandatory Coverage Analysis

9. Site Survey Defined • AP Placement and Configuration • The location of all the wiring closets will also be noted on the floor plan, and care should be taken to ensure that the placement of any access point is within a 100 meter (328 feet) cable run back to the wiring closet due to CAT5 cabling distance limitations • Using a uni-directional antenna in areas where there are metal racks, file cabinets, and metal lockers • Using indoor semi-directional antennas to reduce reflections will cut down on the negative effects of multipath, namely the data corruption caused by the delay spread and inter-symbol interference (ISI). • If data corruption is reduced, so is the need for retransmissions, thus the performance of the WLAN is enhanced by the use of semi-directional antennas in the correct situations

10. Site Survey Defined • Optional Application Analysis • Capacity testing using application analysis and throughput verification is not normally part of a standard site survey. However, tools do exist that can perform application stress testing of a WLAN • The virtual client stations can have individual security settings. Roaming performance can also be tested. • The 802.11a/b/g multistation emulator works in conjunction with another component that can emulate hundreds of protocols and generate traffic bidirectionally through the virtual client stations. • A great use of such a device could be to test the performance of a simulated wireless data network along with simulated wireless VoIP traffic.

11. Site Survey Tools • Indoor Site Surveys Tools • Spectrum analyzer • This is needed for frequency spectrum analysis. • Blueprints • Blueprints or floor plans of the facility are needed to map coverage and mark RF measurements. • Signal strength measurement software • You’ll need this for RF coverage analysis. • 802.11 client card • This is used with the signal measurement software. It is a recommended practice to use the vendor client card that is most likely to be deployed.

12. Site Survey Tools • Indoor Site Surveys Tools • Access point • At least one AP is needed, preferably two. • Battery pack • Binoculars • They can also be handy for looking at things in the plenum space above the ceiling. • Walkie-talkies or cellular phones • Antennas • A wide variety of both omni-directional and indoor semi-directional antennas is a must in every indoor Wi-Fi site survey kit.

13. Site Survey Tools • Indoor Site Surveys Tools • Temporary mounting gear • During the site survey you will be temporarily mounting the access point often high up just below the ceiling. • Digital camera • A digital camera should be used to record the exact location of the placement of the access point. • Measuring wheel or laser measuring meter • A tool is needed to make sure the access point will in fact be close enough for a 100 meter cable run back to the wiring closet. • Colored electrical tape • The colored tape can be used to leave a trail back to where you want to mount the access points. • A color scheme could even be used to track different channel frequencies: red for channel 1, green for channel 6, and blue for channel 11. • Ladder or forklift • Ladders and/or forklifts may be needed to temporarily the mount the access point from the ceiling.

14. Site Survey Tools • Outdoor Site Survey Tools • Topography map • Instead of a building floor plan, a topography map that outlines elevations and positions will be needed. • Link analysis software • Point-to-point link analysis software can be used with topography maps to generate a bridge link profile and also perform many of the necessary calculations, like Fresnel zone and EIRP. • Calculators Software • Calculators and spreadsheets can be used to provide necessary calculations for link budget, Fresnel zone, free space path loss, and fade margin. • Other calculators can provide information about cable attenuation and voltage standing wave ratio (VSWR). • Maximum tree growth data • Trees are a potential source of obstruction of the Fresnel zone, and unless a tree is fully mature, it will likely grow taller.

15. Site Survey Tools • Outdoor Site Survey Tools • Binoculars • Visual line of sight can be established with the aid of binoculars. However, please remember that determining RF line of sight means calculating and ensuring Fresnel zone clearance. • Walkie-talkies or cellular phones • Signal generator and wattmeter • A signal generator is used together with a wattmeter, also known as a Bird meter, to test cabling, connectors, and accessories for signal loss and VSWR. • Variable-loss attenuator • A variable-loss attenuator has a dial on it that allows you to adjust the amount of energy that is absorbed. These can be used during an outdoor site survey to simulate different cable lengths or cable losses. • Inclinometer • This is a device that is used to determine how high obstructions are. This is crucial when making sure that a link path is clear of obstructions

16. Site Survey Tools • Outdoor Site Survey Tools • GPS • Recording the latitude and longitude of the transmit sites and any obstructions or points of interest along the path is important for planning. • Digital camera • You will want to take pictures of mounting locations, cable paths, grounding locations, indoor mounting locations, obstructions, and so on. • Spectrum analyzer • This should be used to test ambient RF levels at transmit sites.

17. Coverage Analysis • Manual • Passive • During a passive manual survey, the radio card is collecting RF measurements, including received signal strength (dBm), noise level (dBm), signal-to-noise ratio (dB), and bandwidth data rates. • The client adapter, however, is not associated to the access point during the survey, and all information is received from radio signals that exist at layer 1. • Active • During an active manual survey, the radio card is associated to the access point and has layer 2 connectively, allowing for low-level frame transmissions. • If layer 3 connectivity is also established, Internet Control Message Protocol (ICMP) ping traffic is sent in 802.11 data frame transmissions. • RF measurements can also be recorded during the active survey, and additional information such as packet loss and retransmission percentages can be measured since the client card is associated to a single access point.

18. Coverage Analysis • Assisted • Some WLAN switches and some centralized wireless network management system (WNMS) applications have the capabilities to conduct assisted coverage analysis. • Most assisted solutions use the information gathered from the access point radio cards, but some solutions can also use a client radio to report information back to the centralized device during a client “walk-through” of the building. • Most WLAN switch solutions that have assisted site survey capabilities also go to the next level and also offer dynamic Radio Frequency Spectrum Management (RFSM) • Although assisted site survey features are an excellent starting point prior to deployment, most professionals still recommend a manual site survey for validation.

19. Coverage Analysis • Predictive • Predicted coverage analysis is accomplished using an application that creates visual models of RF coverage cells, bypassing the need for actually capturing RF measurements. • Projected cell coverage zones are created using modeling algorithms and attenuation values. • Blueprints and floor plans often use vector graphic formats (.dwg, .dwf) and can contain layer information including the type of building materials that are used. • Predictive analysis software supports both vector and raster graphics (.bmp, .jpg, .tif), allowing for the import of building floor plans. • The WLAN design engineer will indicate in the software what materials are used in the floor plan. • The predictive application already has attenuation values for various materials such as drywall, concrete, and glass programmed into the software. The software creates forecast models using the predictive algorithms and the attenuation information.

20. Coverage Analysis • Predictive • The modeling forecast can include the following: • Channel reuse patterns • Coverage cell boundaries • Access point placement • Access point power settings • Number of access points • Data rates

21. Coverage Analysis • Self-Organizing Wireless LANs • 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 be also be addressed with RFSM, which utilizes dynamic load balancing of clients between the access points. • Radio Frequency Spectrum Management provides automatic cell sizing, automatic monitoring, troubleshooting, and optimization of the RF environment, which can best be described as a self-organizing wireless LAN. • Wireless network management systems (WNMSs) can offer RFSM capabilities with fat access points, and WLAN switches or controllers offer RFSM capabilities with thin access points. • Some hardware vendors are also using the client radio cards as scouts to collect RF information to be used in a RFSM environment. • As defined under the 802.11h amendment, transmit power control (TPC) and dynamic frequency selection (DFS) are examples of RFSM technology

22. The END Chapter 16