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Does my organisation need a Wireless Site Survey?

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When talking to organisations for the first time about their network and issues, one of the most common topics that comes up is their wireless. Complaints vary from the wireless being slow, to the wireless being so unreliable that people are no longer using it. Typically, the more you talk to users, the more apparent this becomes as many seem to give up on wireless altogether. However, with organisations now becoming more mobile, open-plan, and collaborative, getting wireless right is more important than ever, and a wireless site survey is a key step.

 

There have been a number of misconceptions and fallacies over the years that have resulted in poor wireless performance. I remember hearing of schools that were told, “These Access Points are so powerful you will only need one every 3 or 4 classrooms”. Or businesses that were told, “These Access Points are so smart that you just need to plug them in, they’ll optimise themselves”. Unfortunately, these people often end up with wireless that is temperamental at best, or completely unusable for most. Eventually, it seems that people resign themselves to the fact that this is what wireless is like, and give up on it altogether.

 

There are many factors to consider when deciding to install wireless. ‘Where do I want access?’ is an easy first decision to make. ‘How do I achieve useable access in these locations?’ is a slightly harder question, which is often not properly considered. A wireless site survey can help provide an answer to the latter. 

So what is a Wireless Site Survey?

The fact that wireless signals cannot be seen makes it a difficult technology to understand. At most, the average person might ‘see’ whether there is a connection, and sometimes, how strong or fast that connection is. As I will explain below, even the fact that you are connected and showing a high speed doesn’t necessarily mean that you will receive decent performance. Thankfully, there are tools that can be used to create a visual representation of what is going on, and using these visualisations, make changes that result in wireless performance that people are happy to use.

 

A ‘wireless site survey’ is the process conducted to collect information and produce these visualisations. This is performed by an engineer using a laptop loaded with specialist software and usually covered in various wireless aerials. The software is loaded with a scale map of the building being scanned, and measurements loaded to increase accuracy. The engineer will walk around the entire building, stopping often to mark their position on the map and allow the aerials and software to pick up valuable data about the wireless in that particular position. Once enough data is collected, visualisations often referred to as ‘heat-maps’ can be produced to allow you to see what is going on.

 

Wireless Interference

A heat-map of the wireless site survey allows you to visualise interference. The red areas in this map show a high amount of interference is present.

 

Wireless can be affected by a number of things. For example, walls of different consistencies can attenuate the wireless to varying degrees. Sometimes, especially in older buildings, walls can even completely kill the wireless signal altogether. Wifi can be affected by other devices such as cordless phones, video senders, or even old microwave ovens; it can even be effected simply by people being in the room. This can be partly because people bring additional devices, but also because the human body works well to attenuate radio signals passing through it. These factors are often overlooked. However, the most common issue that I see in organisations is wireless interfering with itself, or other wireless networks nearby.

 

A common term used when explaining how wireless works is ‘airtime’. In its most simple form, a wireless access point sends and receives signals to everyone connected to it, but is only ever talking to one client at any one point in time. It does this by rapidly switching between different clients and sharing its airtime. However, airtime is also shared between access points talking on the same channel. Introduce a new access point nearby on the same channel and, rather than double the capacity, each access point stops and waits for the other. You end up with two access points running at 50% capacity, or even less given the overhead of making this work. Quite often it doesn’t all work this nicely, and this results in far less performance caused by ‘Co-Channel Interference’.

 

Co-Channel Interference

Channel Map of the wireless site survey showing multiple access points sharing common channels.

 

Another common cause of wireless performance issues is when people connect to wireless networks from too far away, or through walls and objects that have reduced the signal strength. As wireless signal strength decreases, so does the speed in which the client can connect. If we refer back to airtime, this client now takes longer to send the same amount of data because it is slower, meaning that it uses more of the access points total airtime. This, in turn, means that other clients have less airtime to share, which means even though they might show as being connected at a high speed, the actual performance they receive is much lower. There are technologies being developed to try and compensate for this, but prevention is always better.

Do I need a Wireless Site Survey?

Without analysing your wireless network and knowing what is going on, interference often goes undiagnosed, and in most cases, people lose faith in wireless technology and go back to their desks and plug into their trusty blue cable. However, alongside a careful review of configurations, the heat-maps that a wireless site survey creates can allow for networks to be fine-tuned through movement of access points, and changes of power and channel settings. I have even helped organisations improve their overall wireless performance by turning some of their access points off or removing them altogether.

 

No matter how advanced and what features access points have, manufacturers still actively promote the use of wireless site surveys to establish and maintain high performing wireless networks. Most even encourage the use of multiple wireless site surveys at different stages of your deployment. A predictive site survey can be performed without an engineer even entering the building. Using a scale map, which is loaded with walls, materials and other available information, virtual access points can be moved around the map to make a prediction of the expected performance. This is a great idea if you have not purchased your system yet and are looking to get a good starting point for what you might need. Commonly this type of survey gets used before a building has been finished, so the network can be incorporated and designed, just like the cabled network or power. A passive site survey is the type talked about above and is great for pre-existing wireless systems, and especially for comparing before and after heat-maps while installing and fine-tuning new systems.

 

With careful analysis of wireless site surveys, dramatic improvements can be made to interference levels. This means greater performance and reliability.

 

Here at Dynamo6 we use tools by New Zealand company TamoSoft as well as MetaGeek hardware to perform predictive and passive site surveys. We have engineers who are experienced and certified with many wireless vendors such as Cisco Meraki, Ruckus, and Aerohive. Whatever stage you are at with your wireless deployment, we would love to chat and discuss how we can help you get the best out of your wireless network.