In a previous post I explained the first phase of a wireless deployment, gathering wifi design requirements. From those requirements, we move into the next section, Part II Performing A Wireless Site Survey. There are different approaches to a wireless site survey.
We’ll talk about these approaches and I’ll mention which one I like to use. In addition to wireless site surveys, spectrum analysis should also be done. This is to find any sources of interference in the 2.4 GHz and 5 GHz channel ranges.
What is a wireless site survey?
A wireless site survey is a process. It’s the process of analyzing coverage and capacity based on the requirements gathered in the first phase. It also includes spectrum analysis.
When we talk about site surveys you’re probably thinking of the AP-on-a-stick approach.
Site survey is a loaded term. I prefer to call it a predictive site survey or predictive modeling.
We are predicting how a wireless network will be implemented based on various pieces of information that we gathered in the first phase.
A predictive survey uses a piece of software to model a deployment for you. An example is using Ekahau Site Survey to import a blueprint of the floor plan. Building materials, such as walls and other objects, would be taken into the design consideration.
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Ekahau and other similar software use hardware profiles and algorithms to create a prediction or model. For the most part, this is how many wireless engineers perform a site survey, or more accurately termed, a predictive site survey.
The software places access points on the floor plan and afterwards, the design can be tweaked and modified to meet the realistic needs of the environment.
The same software can be used to perform what is called an active wireless site survey. Your software and hardware actively associates to an access point to gather more information such as ping statistics, layer 1 radio frequency measurements, and any packet loss.
The AP-on-a-stick is an example of an active wireless site survey.
An engineer physically places an access point in a specific location of an office, and using a piece of software such as Ekahau, a survey is done. The process is repeated until coverage and capacity is accurately documented.
The AP-on-a-stick model takes more time and money to perform. It is performed less often than a predictive site survey.
Most wireless engineers are comfortable with using a predictive design that they can tune because as we will discuss later.. a validation of the wireless deployment will be conducted.
With both methods, a site survey will provide us with a model for coverage and capacity based on requirements inserted into the application. The results yield predictive signal strength and cell sizes.
A channel reuse plan is considered in the site survey. After the application has determined the best case scenario, you may change the channel reuse plan, even consider turning of 2.4 GHz channels where possible.
Well known tools used for conducting wireless site surveys:
- Ekahau Site Survey
- Airmagnet Survey
In addition to performing coverage and capacity analysis, spectrum analysis should be performed. This is the process of scanning both 2.4 GHz and 5 GHz ranges.
The goal is to find potential sources of interference that may degrade the performance of your wireless network. An acceptable background noise level should be measured and ensured that it does not exceed, for example, -85 dBm.
Noisy environments cause wireless degradation by corrupting data frames in transit. A common result is excessive retries. This brings throughput down considerably and causes the wireless to be portrayed as unusable.
Some potential sources of interference are:
- Bluetooth headsets
- Wireless video cameras
- Nearby wireless networks
- Large number of wireless devices
There are a number of tools can be used to perform spectrum analysis. A built-in wireless card cannot do this for you. Specialized hardware is used to scan the wireless spectrum. This type of hardware is unable to associate to access points.
Tools for spectrum Analysis
- Metageek InSSIDer or Chanalyzer
This was a general overview of conducting a wireless site survey. Various tools can be used to help create a predictive model which automatically places access points on a floor plan with channel reuse plans, cell size boundaries, and expected data rates.
I mentioned the terminology used to describe site surveys – predictive site surveys and active.
We covered spectrum analysis which is also part of conducting a site survey. In a spectrum analysis, the 2.4 GHz and 5 GHz spectrum is scanned for any sources of interference.
The interference must be mitigated or be considered as part of the deployment plan.
What is holding you back from doing wireless site surveys?