When designing commercial WiFi networks, a wireless survey is an essential part of the design process. This can come in many forms but they can be broadly grouped into two main groupings, namely, the more conventional “walk around” style of survey or one done purely on the strength of detailed schematics of the location. It is easy to focus in on the prominent questions of signal strength and bandwidth however this should always be done in the context of the user experience at a given point on a given day with the network in full operational use.
It is almost always the case that designing a commercial grade wifi network involves a good deal of groundwork including asking the users some fairly detailed questions about the location, the structure of the building, existing physical cable plant and associated infrastructure as well as local administrative practices. This information as well as detailed information about the required functionality of the new WIFI network including the key questions of coverage and capacity is fundamental to the creation of an effective rollout plan. It is important too at this stage to bear close account of the types of clients to be used on the eventual production network.
Performing the Survey
When designing a WiFi network, you have to consider how the network is going to look from the point of view of your WiFi clients – all of your clients. Clients come in a very wide variety of shapes, sizes and capabilities. Some may have good quality RF hardware and decent gain antennas, ensuring that they will have few issues in a reasonably well designed network. They should easily be able to connect to deployed APs and achieve SNR levels that ensure low error rates and good throughput.
However, other clients may have miniscule, poorly designed antennas, with low-cost, low quality RF circuitry. Their antennas may often be in a housing partially made of metal. They may have limited power available due to the power demands of a smartphone handset on a very limited battery. The explosion of mobile devices such as tablets and smartphone means that the majority of clients on a network may suffer these limitations . With the proliferation of these ‘less able’ clients, it is often best to be pessimistic about client capabilities when designing a wireless network and design for your ‘worst case’ clients.
We need to take a step back and think about the survey to be performed. What are we measuring? Are signal levels and SNR actually measured with a smartphone or tablet? The answer is: no. We will actually be measuring (in all likelihood) using a laptop with a USB wireless dongle that has very good RF capabilities. Will this survey ‘client’ see the network in the same way as a less capable tablet or smartphone? (The answer is no.)
An Alternative Point of View
In order to understand if this network is going to meet the design criteria laid down, we need to look at the survey data gathered from the point of view of the clients that will be using the network. As mentioned previously, we have to assume the worst, and design for our less able clients.
Back to the Drawing Board
Unfortunately, we now see huge holes in our coverage. We simply cannot meet the design criteria for our agreed limitations for less able devices in this network. We certainly have to add in enough access points, repositioning APs and perhaps winding up our AP transmit powers. There are other considerations that also need to be considered. These include factors such as client transmit power, client sensitivity and the varying CCI view of each client type. The key takeaway from this is that client capabilities need to factored in to design considerations – a survey using raw measurements is generally an invalid approach on today’s “support everything” networks.
In summary, we’ve taken a look at how we need to define design criteria for the type of wireless network that will meet customer requirements. Although we may be able to measure the design criteria using a professional survey tool, we need to be mindful of how the measurements are collected. Survey data gathered with a high-spec wireless NIC is generally going to see RF signals at higher levels than a lower spec mobile device.
When considering how effective our design will be in meeting the design criteria, we have to consider how the gathered RF data will look from the point of view of a actual clients that will use the network. Only then can we be sure of whether we can meet the design criteria and the customers’ requirements.