Listening to adverts from Broadband providers promising Wi-Fi coverage, you'd be forgiven for thinking that good Wi-Fi only comes from having a very strong signal.
But in an institutional setting, this couldn't be further from the truth.
The airtime available to communicate with an AP is limited, all devices have to take it in turns to transmit their data, and for practical reasons APs and client devices rarely perform to the limits of their specification, so that limits the total available bandwidth.
It is important to make the most of this finite bandwidth, and limiting AP power maximises this bandwidth for the following reasons.
To reduce interference - An AP provides airtime as a cell operating on a particular Wi-Fi channel. The objective is to keep the Wi-Fi channel isolated, so that the airtime can solely be used by devices operating within the AP cell. If the AP power is too strong, devices operating in that cell will leak into other cells on the same channel, forcing cells to share airtime, which can dramatically limit performance. Keeping cell power tuned to that required for the cell size, ensures that the all available airtime can be used by devices in the cell, maximising performance.
Better use of Wi-Fi bands - Wi-Fi currently operates in the UK on two bands 2.4GHz and 5GHz. Wi-Fi signals on the 2.4GHz band tend to travel further, and can be useful in buildings with lots of thick walls. But generally speaking the 5GHz band provides a better quality of signal and more bandwidth. The power of each band needs to be limited for all the other reasons we mention, but at levels (depending on the client device) that devices can attach to, and stepped to favour the best band. This ensures that client devices are encouraged to attach to the best band, to maximise performance.
To implement smaller cells to increase capacity - Using more, or smaller cells, increases capacity. This usually requires the use of specialist antennas and turning down AP power to contain the cells channel. In this way, turning down power, increases capacity and therefore performance.
To balance two-way communication - If the power of an AP is disproportionate to the power of a client device then this causes other problems. If an AP cannot hear an associated client device because its signal strength is weak, then the client device will have to retransmit its data over and over again, until it is heard, wasting valuable airtime. The situation is further worsened by the fact that the client device has to retransmit data at lower and lower rates until it can be heard, and lower and lower rates take up more and more airtime for the same data. So again, tuning the power of the AP to match the behaviour of client devices, increases the performance of the Wi-Fi.
To implement better client device roaming - Another area of client device behaviour that needs to be tuned is roaming. A client device will attach to an AP based on certain initial criteria relating to performance. As we have discovered in testing, some devices only roam when certain criteria thresholds are met, and this can be bad for the quality of the whole Wi-Fi network. So a design that delivers a consistent performance, with AP power levels that are set to promote client device roaming will ensure that a client device does not stay attached to a distance AP, and attaches to its nearest AP that offer s the best signal quality and capacity.
We have written a number of articles to provide more details about Wi-Fi design, and we are adding them to this website.
Tuning AP cell size
Tuning AP Power To Reduce Interference (An explanation of how reducing AP reduces interference and increases the performance of the Wi-Fi)
Tuning AP Power for Better use of Wi-Fi Bands (An example of why it is generally better to set power levels to steer client devices to the 5GHz band)
Tuning AP Power to Balance Two-Way Communication (An example of how Wi-Fi performance is affected when AP power levels are not tuned to client devices)
Tuning AP Power to Implement Better Client Device Roaming (An example of how client roaming can go wrong if AP power and antennas are not configured properly)
Tolerances Required for Polarisation and Other Effects (A demonstration of typical design tolerances that need to be allowed for in the Wi-Fi design)
Example: Tuning AP Power for a Client Device (How AP power may be tuned in practice)
Wi-Fi Capacity and Performance
How Client Devices Limit Your Wi-Fi Performance (How the actual observed behaviour between an AP and its clients, differs from expectations based on specifications)
Channel Width Limitations for Institutional Wi-Fi (How wide channel widths can actually impact the performance of the whole Wi-Fi, and when it is better to avoid them)
Available Airtime for Different Wi-Fi Standards (A deep dive into theoretical total airtime, to help quantify the impact of client devices on total available airtime for capacity planning)
Impact of AP/Antenna position and mounting on performance and design
AP Position/Mounting and Wi-Fi Performance (How APs should be positioned and mounted, and the implications if these positions are compromised.)
Specialist Antennas to Increase Wi-Fi Performance (How specialist antennas can improve Wi-Fi performance)
When APs automatically try to set cell sizes, they do they best they can within the available environment, and to their configured limits.
If the Wi-Fi has not been designed properly, then this will result in problems. To ensure problem-free operation, and excellent performance, you need to design the Wi-Fi properly to take account of the different variables, and position and configure the APs accordingly for your intended applications and devices. Only then is the Wi-Fi system able to fine-tune settings to achieve effective performance.
For a full list of technical and related industry articles click HERE
