Wi-Fi is a Passion


Overview - Site Survey

Site surveys are must-plan actions in designing and implementing wireless networks. There are to determine the access point locations, to validate an implemented wireless network, or to just get a feeling from the environment to see how the needs of the customer fit in the current situation.

There are different types of site surveys, but there are two main categories: a physical site survey and an RF site survey. The physical site survey is an examination of the physical environment. The RF site survey is the process of examining the current RF activity in the physical space.

With a physical site survey, you check if the physical place can have a wireless network. Consider antenna placement, access point placement, or cable location. If needed, consider how and where to implement the point-to-point links or point-to-multipoint links. It is not that easy to hang up an access point where you want it. There are buildings where the position is based on aesthetics, and for that the architect decides the locations. Sometimes there is a spot that is too far from a wired closet, so you need to create a new wired closet or find a new spot. Questions like this will be answered when visiting the physical location.

The RF site survey is how the RF waves behave in the physical environment. This tells you where to place the access point or antenna the best, but you might know from the physical site survey that the specific spot is not working for whatever reason, so both site surveys are important still today. Here you look at RF coverage in the areas that need coverage. Consider whether the access point will interfere with access points from your own or neighboring wireless network. It is important to know how the RF propagation goes in the physical area to determine the access point placement.

Knowing the types of site surveys, and how to prepare a site survey:
Determine the organizational needs and objectives
Determine the requirements (user, business, technical)
Discover the constraints (budgetary, technical, regulatory)
Define the objectives (business, technical)

How to implement a WLAN that meets the objectives:
Perform the site survey
Document the site survey
Create the implementation plan

I explained the two types of categories, physical and RF survey, but there are three basic types of site surveys as well: manual, predictive, and hybrid.

The manual site survey is the traditional one. You visit the physical location and place one or more access points and walk through the building to test the coverage and the signal strength. After that you move the access points to different spots and repeat it. This survey is also called “access point on a stick” (APoS/APoaS). This is a time-consuming method, but still the most accurate survey when you understand what you measure, since you need to make decisions on the spot based on the results.

The predictive site survey is not a real site survey. It is virtual/theoretical and based on the floorplans. However, it is wise to visit the site to have a feeling before doing the predictive planning. When the floorplan is imported, you need to draw the walls/windows and other building materials that can interfere with the RF propagation. All the objectives are able to entered in the program as well, and based on those and the building type, the program decides where the best locations are for the access points. The tool is quite expensive, and there is a learning curve, but it goes faster for bigger facilities than a manual site survey. For small to medium sized locations, it is better to go for the manual site survey. These tools are from vendors like Ekahau, AirMagnet and Tamosoft.

A hybrid survey is like the name says, hybrid. Hybrid means it is a combination of the other two. You will do some wall attenuation on some floors by a manual site survey, but then that information you can put in the predictive site survey tool and this gives you a more accurate predictive planning.

Beside those three basic survey types you have automated site surveys. This survey relies on the intelligent communication between the access point and the centralized controller. It can adjust the output power and channel selection, also known as radio resource management (802.11k). For this you need some over engineering, placing more access points than needed. This helps the controller to adjust the access points better, and when an access point breaks it adjusts another access point with a higher output power. The assisted site survey is the combination of a manual site survey in combination with an automated survey. You will do some manual measurements and put this in a management software. The software or hardware will analyse the wireless network and make adjustments.

After the surveys, you need to document the findings and results. You write down the customer’s objectives, requirements, and constraints. In addition, you add the floorplans what the coverage areas are, where the access points need to be placed with some notes, the heat maps of the signal strength and signal to noise ratio for example, or even pictures.. Now it is time for the implementation plan, which I’ll cover in other blogs in more detail.

During the placement of the access points, by predictive or manual site survey, it is not only wireless skill that helps. A system analysis needs to be done and future growth needs to be taken into consideration. Consider possibilities such as, if you are going to migrate application from the wired to the wireless how much bandwidth are those consuming, how many users are using this application and is your wireless network ready for that. There needs to be knowledge about QoS, how many throughput is needed and is this possible on the wired network. Consider, which data rate do I need and is there more management overhead on wireless than there is on wired, or is it a changeable environment, and are there specific technologies in use for this vertical (for example VoWLAN in health care). All those questions need to be asked during the requirements analysis, but used during the site survey and access point placement.

Last but not least, site surveys are not only performed for new designs. Site surveys can be executed at locations where a wireless environment is already in place and used for validation or troubleshooting the network.