When talking to organisations about their network and issues, one of the most common topics that comes up is wireless.
Complaints vary from the wireless is slow, to the wireless is so unreliable that people are no longer using it. Typically, the more you talk to end-users, the more apparent giving up on the WiFi becomes. As organisations become more mobile, open-plan, and collaborative, getting the wireless right is more important than ever. A wireless site survey is a key step in getting it right.
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 got 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. It is often not properly considered. A wireless site survey can help provide an answer to the latter.
what is a wireless site survey?
A wireless site survey is a visual map capturing the radio frequency interference in a given area. It helps to highlight areas where there will be coverage issues.
The fact that wireless signals are not seen makes it a difficult technology to understand. The average person might ‘see’ whether there is a connection and experience strong connectivity.
Even if you’re connected and see a high speed, it doesn’t necessarily mean that you’ll receive decent performance. Thankfully, there are tools that you can use to create a visual representation of what is going on. Using these visualisations you can then make changes that result in wireless performance.
The ‘survey’ part of the process if the physical mapping conducted to collect the information and produce the visualisations. An engineer performs the mapping. They will use a laptop with specialist software and usually covered in various wireless aerials. The engineer loads the software with a scale map of the building that is being scanned. Followed by building measurements to increase accuracy.
The engineer will walk around the entire building. They will stop often to mark their position on the map. This allows the aerials and software to pick up valuable data about the wireless in that particular position. By collecting enough data, visualisations often referred to as ‘heat-maps’ can be produced. They allow you to see what is going on.
how are wireless connections impacted?
Wireless connections 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 completely kill the wireless signal altogether. Other devices such as cordless phones, video senders, or even old microwave ovens can effect WiFi connections.
People being in the room can even affect connections. 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. The most common issues that I have seen in organisations is the wireless interfering with itself or with 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. It 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.
what about adding more access points?
If you were to introduce a new access point nearby on the same channel, 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. This results in far less performance caused by ‘Co-Channel Interference’.
Another common cause of wireless performance issues is when people connect to wireless networks from too far away. Or, through walls and objects that reduce the signal strength. As wireless signal strength decreases, so does the speed in which the client can connect.
Thinking about airtime again, this client passing through an object, now takes longer to send the same amount of data because it is slower. This means that it uses more of the access points total airtime. This, in turn, means that other clients have less airtime to share. Resulting, in a connection which shows high-speed connection, but the real performance is much lower. Other technologies are in development to 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. In most cases, people lose faith in wireless technology and go back to their desks and plug into their trusty blue cable.
Alongside a careful review of configurations, the heat-maps that a wireless site survey creates can allow for networks to be fine-tuned. This is done through the 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. In a few cases 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.
what about predictive site surveys?
A predictive site survey can be performed without an engineer even entering the building. It is done by using a scale map and loading it with walls, materials, and other available information. The map allows you to move the virtual access points around the map to make a prediction of the expected performance of the configurations. This is a great idea if you have not purchased your system yet. It acts as a good starting point to identify what you might need.
Commonly the predictive survey takes place before a building is finished. This is so the network can be incorporated and designed, just like the cabled network or power.
what’s a passive site survey?
A passive site survey is a wireless site survey on pre-existing wireless systems. This survey listens to wireless traffic to detect active access points. It measures signal strength and noise levels. Having predictive and passive heat maps is especially useful while installing and fine-tuning new systems.