Designing a dense environment for Wi-Fi is always a challenge. It takes careful planning and cares to ensure that the RF signal and the user density are taken into consideration. This is done in many ways, but what if we took part of the Wi-Fi standard and adapted it to make designing these environments more predictable?
Starting in Wi-Fi 4 (Wireless N) there was a new feature called transmit beamforming added to the standard. What this was meant to do was optimize the phase of the wave to be at its peak when it reaches the client. The thought behind this was if a wave were to arrive at its peak it could help reduce errors received by the client. How it did this to determine where the client is and start the wave out at a different part of the phase so that when the wave reaches the client the wave will be at a peak.
The reason we can do this is because of QAM modulation. QAM uses both the amplitude modulation and frequency modulation techniques combined to more efficiently transmit data. This means for every bit transmitted multiple bits of usable data can be generated. See the screen capture below from MCSindex.com showing the efficiency of using QAM.[I]
So, why did I bring these pieces of Wi-Fi up? While they were intended to be used with clients in a normal wireless network; we can take them and use their properties in a different way to benefit us when deploying antennas in a non-standard way.
In almost every directional antenna deployment guide it shows that the antenna is to mount to a pole or wall. This is because every antenna has a pole where the wave generates, and the perpendicular pole (90 degrees) is where a magnetic field is generated as a result of the RF wave. Traditionally these antennas were to send a narrower beam of usable signal in a direction, focusing the signal as a passive gain for clients in a specific direction. What if we took this same theory and turned it on its head (figure of speech), but shift the antenna at least 90 degrees?
What I am referring to is instead of deploying a directional antenna horizontally, we deploy it vertically. This can be a solution for highly dense environments, such as auditoriums, convention centers, school lecture halls, etc. We can create the same sectors the directional antennas aim for in these environments, but instead of doing it vertically and having to set power on the AP very carefully, we can deploy it via the ceiling and have a natural traffic cone-shaped coverage. Ekahau even allows us to plan for this in recent versions of their program (see below).
This will divide up the areas that need to be covered to specific APs, limit the clients per AP, and we can better control as clients roam, inadvertently creating overlapping cells/ co-channel or adjacent channel interference. With the cells having a relatively lower power setting when these clients roam the cells do get extended until the clients associate to another AP the range is still very contained.
This works based on the transmit beamforming locating where the client is and adapting the starting phase of the wave so the client will be able to receive the peak and because of QAM using both amplitude and frequency modulation, neither the AP nor the client should notice any difference. Let’s adapt the first chart I made to show a directional antenna deployed on a ceiling facing down. The AP will still adapt its signal to the client; however, it won’t notice how it is deployed only how to optimize it.
As Wi-Fi is now becoming a requirement for shows, events, and everyday life, deploying it in dense environments is always a challenge. Taking this new deployment strategy into account, people that are serious about deploying good quality Wi-Fi can use this method to help.
i http://mcsindex.com/
ii By Chris Watts – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15781908
Bibliography
“MCS Index, Modulation and Coding Index 11n and 11AC.” MCS Index, Modulation and Coding Index 11n and 11ac. Accessed September 27, 2021. http://mcsindex.com/.
Watts, Chris. “File: QAM16 Demonstration.gif.” Wikimedia Commons. Accessed September 27, 2021. https://commons.wikimedia.org/w/index.php?curid=15781908.
