Wireless LAN Site Survey Tools

Anyone who is serious about deploying wireless networks will put together a site survey toolbox with a multitude of products that can aid the site survey process. The main tool of course will be some sort of signal measurement software utility that interfaces with your wireless client card and is used for coverage analysis.

Prepackaged site survey kits are often for sale on the Internet, but most site survey professionals prefer to put together their own kit. Indoor and outdoor site surveys are very different in nature, and we will discuss the different tools that are used in both types of surveys.

Indoor Site Surveys Tools

A spectrum analyzer will be needed for locating potential sources of interference. Your main weapon in your coverage analysis arsenal will be a received signal strength measurement tool.

This tool could be something as simple as the received signal strength meter in your wireless card’s client utility, or it could be a more expensive and complex site survey software package. However, there are many other tools that can assist you when you are conducting the physical site survey.

These are some of the tools that you might use for an indoor site survey:

  • Blueprints - Blueprints or floor plans of the facility are needed to map coverage and mark RF measurements. CAD software may be needed to view and edit digital copies of the blueprints.
  • 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.
  • Access point - At least one AP is needed, preferably two.
  • Battery pack - A battery pack is a necessity because the site survey engineer does not want to have to run electrical extension cords to power the access point while it is temporarily mounted for the site survey.

Not only does the battery pack provide power to the access point, it also provides a safer environment because you don’t have to run a loose power cord across the floor, and it makes it easier and quick to move the access point to a new location.

  • Binoculars - It may seem strange to have binoculars for an indoor sight survey, but they can be very useful in tall warehouses and convention centers. They can also be handy for looking at things in the plenum space above the ceiling.
  • Walkie-talkies or cellular phones - When performing a site survey in an office environment, it is often necessary to be as quiet and unobtrusive as possible. Walkie-talkies or cellular phones are typically preferred over yelling across the room. You must also remember that RF is threedimensional and it is common for one person to be on one floor with the access point while the other person is on another floor checking the received signal.
  • Antennas - A wide variety of both omni-directional and indoor semi-directional antennas is a must in every indoor Wi-Fi site survey kit.
  • Temporary mounting gear - During the site survey you will be temporarily mounting the access point often high up just below the ceiling. Some sort of solution is needed to temporarily mount the AP. Bungee cords and plastic ties are often used as well as good old-fashioned duct tape.

Some professionals will use a tripod and mount the access point on an extending mast. The tripod can then be moved within the building, thereby bypassing the need to temporarily mount the access point.

  • Digital camera - A digital camera should be used to record the exact location of the placement of the access point. Recording this information visually will assist whoever will do the final installation at a later date. Setting the date/time on the pictures may also come in handy when viewing the pictures later.
  • 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. Keep in mind that a 100 meter cable run includes running the CAT5 cabling through the plenum.

A measuring wheel or a laser distance measuring tool could be used to measure the distance back to the wiring closet. A measuring wheel is usually the better tool because the laser devices can often yield bad results.

  • Colored electrical tape - Everyone remembers the fable of Hansel and Gretel and how they used breadcrumbs to leave a trail to find their way home. The colored tape can be used to leave a trail back to where you want to mount the access points.

Leave a small piece of colored electrical tape at the location where the access point was temporarily mounted during the site survey. This will assist whoever will do the final AP installation at a later date. 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.

When conducting a site survey, it is a highly recommended practice to use the same 802.11 access point hardware that you plan on deploying. Keep in mind that every vendor is different and implements RSSI differently.

It is not advisable to conduct a coverage analysis survey using one vendor’s access point and then deploy a completely different vendor’s hardware. Many established site survey companies have put together different vendor site survey kits so that they can offer their customers several options.

Outdoor Site Survey Tools

Outdoor site surveys are conducted using either outdoor access points or mesh routers, which are the devices typically used to provide access for client stations in an outdoor environment.

These outdoor Wi-Fi surveys will use most of the same tools as an indoor site survey but may also use a Global Positioning System (GPS) device to record latitude and longitude coordinates.

Although outdoor 802.11 deployments can be used to provide access, usually a discussion of outdoor site surveys is about wireless bridging. Wi-Fi bridging exists at the distribution layer and is used to provide a wireless link between two or more wired networks.

An entirely different set of tools is needed for an outdoor bridging site survey, and many more calculations are required to guarantee the stability of the bridge link. In earlier, you learned that the calculations necessary when deploying outdoor bridge links are numerous, including the Fresnel zone, earth bulge, free space path loss, link budget and fade margin.

Other considerations may include the intentional radiator (IR) and equivalent isotropically radiated power (EIRP) power limits as defined by the regulatory body of your country. Weather conditions are another major consideration in any outdoor site survey, and proper protection against lightning and wind will need to be deployed.

An outdoor wireless bridging site survey usually requires the cooperative skills of two individuals. The following list includes some of the tools that you might use for an outdoor bridging site survey:

  • 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. The bridge link analysis software is a predictive modeling tool.
  • 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. A chainsaw is not always the answer, and planning antenna height based on potential tree growth might be necessary. The regional or local agricultural government agency should be able to provide you with the necessary information regarding the local foliage and what type of growth you can expect.
  • 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. For links longer than 5 miles or so, this will be almost impossible. A solid understanding of topography and earth bulge is necessary to plan a bridge link.
  • Walkie-talkies or cellular phones - 802.11 bridge links can span many miles. Two site survey engineers working as a team will need some type of device for communicating during the survey.
  • 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. This testing gear is necessary for testing cabling and connectors before deployment.

The testing gear should also be used periodically after deployment to check that water and other environmental conditions have not damaged the cabling and connectors.

  • 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
  • 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.

Antennas and access points are not typically used during the bridging site survey. It is very rare that bridging hardware will be installed during survey since most times a mast or some other type of structure has to be built.

If all the bridging measurements and calculations are accurate, then the bridge link will work. An outdoor site survey for a mesh network will require mesh APs and antennas.