Municipal Wi-Fi Network Surveying and Testing: Part II
January 29, 2008
In Part II of our three-part series on muni/metro WLAN testing, we cover the tools you'll need for the job, and guide you through the Pre-Installation Survey phase.
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FurlThe reasoning behind independently testing municipal Wi-Fi networks was covered in the first part of this tutorial series. In that tutorial, we also discussed the three main surveying and testing phases—Pre-Installation Survey, Pilot Testing, and Acceptance Testing. Additionally, we outlined the information and documents that need to be gathered for each phase. In this part of the tutorial series, we will discuss which tools the independent testing team needs and how to perform a Pre-Installation Survey.
Building your Muni Wireless Toolkit
- WLAN analyzer: A WLAN analyzer is a software solution used to show and log information about wireless networks. You’ll need a WLAN analyzer (with a supported radio card) that offers outdoor support with map and GPS integration, such as AirMagnet Survey Pro or Ekahau Site Survey. Be sure the analyzer and radio card support both the client and backhaul bands, usually 2.4GHz (802.11g) and 5GHz (802.11a), respectively. When driving around the city, these software solutions will produce coverage maps of the city’s test or completed network, in addition to existing networks in businesses and homes. Figure 1 shows an example of the map produced during a drive survey, showing signal levels.
Other pertinent information is also recorded, such as SSID (Service Set Identifier), channel, and signal and RF noise levels.
- Laptop: Of course you’ll need a laptop to run the WLAN analyzer, connect to the network, and for other incidental uses. Though the requirements for WLAN analyzers typically only require 512 MB of memory, you should try to get up to at least 1 GB. These analyzers are usually used indoors where you might pick up 25 wireless access points (APs) throughout an office building. But using them outdoors while driving past businesses and homes may reveal hundreds or thousands of APs, bogging out your laptop. If your laptop stops responding you could lose a few hours of work—it has happened to us—so, you should really think about beefing up your laptop.
- GPS unit: So that your WLAN analyzer can map out the signals from AP and mesh nodes, you’ll need a GPS unit that’s supported by the WLAN analyzer.
Figure 1: Drive survey map produced with AirMagnet Survey Pro.
- RF spectrum analyzer: An RF spectrum analyzer receives and records signal information for the given frequency ranges. A spectrum analyzer can be a standalone product or a software and hardware solution (AirMagnet Spectrum Analyzer, Wi-Spy, etc). Though WLAN analyzers also capture signal information, an RF spectrum analyzer can provide much more detailed images of the air waves (see figure 2 for an example) to better identify sources that may cause interference.
Figure 2: RF spectrum image captured with AirMagnet Spectrum Analyzer.
When doing this type of work, we’ve found the following setup to be the most beneficial for our situation:
· AirMagnet Survey Pro using the laptop’s supported built-in Intel PRO/Wireless radio (to save the PCMCIA slot for the AirMagnet Spectrum Analyzer) and interfacing with Microsoft MapPoint for inputting the coverage maps.
· AirMagnet Spectrum Analyzer card inserted in the laptop’s PCMCIA slot.
· Gamin GPSMAP 76CS connected to the laptop.
Performing a Pre-Installation Survey
As discussed in Part I, the purpose of a Pre-Installation Survey is to reveal any technical barriers or issues with setting up a municipal Wi-Fi network, most of which are discovered by a drive survey. Here are the steps of a Pre-Installation Survey:
- Perform the drive survey. While driving in one-mile increments in the intended coverage area you should simultaneously:
- Scan for wireless networks. Setup your WLAN analyzer with a map of the coverage area and make sure it plots your correct location. You should be capturing constantly during the drive.
- Observe mounting assets. While driving keep an eye out for possible mounting assets, such as vertical light poles and horizontal traffic-light poles. Make note of any areas that don’t have sufficient mounting assets to provide adequate coverage. Keep track of the types of light poles you see and note their characteristics. You might even take pictures of some light poles to include in the report.
- Observe the environment. Make notes of the environment that could impact the Wi-Fi network, such as tall buildings and dense foliage or trees. Indicate any highly or lightly populated areas. Note any possible priority areas for the network, such as business districts or high usage areas.
- Observe mounting assets. While driving keep an eye out for possible mounting assets, such as vertical light poles and horizontal traffic-light poles. Make note of any areas that don’t have sufficient mounting assets to provide adequate coverage. Keep track of the types of light poles you see and note their characteristics. You might even take pictures of some light poles to include in the report.
This task requires two people, one to drive (and observe) and another to hold the laptop and observe. The passenger can keep an eye on their current location from the map of the WLAN analyzer and tell the driver where to go in order to keep one-mile increments. Additionally, the passenger can observe and take notes.
- Perform RF spectrum captures. If an RF spectrum analyzer isn’t integrated with your WLAN analyzer and running during the drive, you should stop periodically to do RF spectrum captures. You should have at least one RF spectrum capture for each half-square-mile. Remember to do captures for both the client and backhaul frequency bands.
- Compile the report. Once you’re back at your home office, you can compile a report to state your surveying methodology, observations, and recommendations:
- Existing Signal Levels. Discuss the averages, maximums, and minimums of the noise and signal levels you captured with the WLAN and RF spectrum analyzers. Give your option of the overall impact of these results.
- Existing Wireless LANs. Give the number of wireless LAN access points you found, their pertinent information, and share your thoughts on their co-existence with a municipal Wi-Fi network.
- Environmental Concerns. Share your opinion of any environmental impacts.
- Mounting Assets. Discuss the types, availability, and usability of mounting assets.
- Recommendations. Based upon your WLAN and RF scans, recommend bands for the client and backhaul frequencies. You may also share your recommendation about which mounting assets to use.
You can see an example of a report from the Pre-Installation Survey we participated in for Colorado Wireless Communities—Arvada.
Stay tuned—the next installment will discuss the other testing phases.
Eric Geier is an author of many wireless networking and computing books including Wi-Fi Hotspots: Setting up Public Wireless Internet Access, published by Cisco Press and 100 Things You Need to Know about Upgrading to Windows Vista, published by Que.
