The Truth About Wi-Fi

THOUGHT LEADERSHIP WHITE PAPER SERIES - IoT CoE Okol Group

revised 3/18/2019 by Okol Group

At some point in time we all heard the famous saying <<We don't need wires, we'll use Wi-Fi>>. This general belief often results in poor network performance and bad client experience. Let's take a moment to understand how Wi-Fi really works and why it is not a full substitute to wires.

History

Wi-Fi stands for Wireless-Fidelity and was released in the late 90s as the 802.11 standard. One particular characteristic of Wi-Fi communication is that it uses unlicensed radio spectrum, which means it can be used by the general population without a license from the administering authorities (in the case of the US, the Federal Communications Commission - FCC). This is why Wi-Fi became so popular. There are basically two RF bands open for Wi-Fi use: the 2.4 GHz and the 5 GHz bands. Since its inception Wi-Fi technology has seen tremendous progress in its ability to transport data over the air without using more radio spectrum. This phenomenon is more known among engineers as "spectrum efficiency". But one thing is certain: the radio spectrum (which is a limited natural resource) remains exactly the same since Wi-Fi was invented. With today's need for each time more speed and users, Wi-Fi's challenge is to handle demand with the exact same amount of bandwidth and number of channels. It is the same as saying that a two-lane highway now needs to handle four times more cars than what it was designed for.

Simplex Operation

The one thing that few people know about Wi-Fi is that it is a "simplex" communication protocol. What that means is that two devices do not communicate simultaneously as cell phones do during a conversation. Take as another example, the walkie-talkie. You press a button to talk, then release the button and wait for the other person to talk, and so on. Wi-Fi works exactly the same manner: it uses only one frequency to communicate with your device, but the simplex exchange occurs several thousands of times a second, only for you not to notice the difference (we call it "air-time"). This is in a perfect world, of course.

Imagine now your Wi-Fi router trying to do the same simplex operation with two persons at a time, then three, four, ten, even twenty. You can easily realize that at this point Wi-Fi needs to split the air-time among 20 clients, not only one. Since we can't buy time, the only solution left is to wait 20 times longer, which decreases speed as per obvious mathematical correlation. This is one of the major limitations that Wi-Fi faces as a popular communication medium.

Too Many Users

Because Wi-Fi runs over unlicensed bands its proliferation is such that the entire radio spectrum is completely saturated. Pull the list of Wi-Fi networks on your laptop and you will understand the magnitude of the problem (assuming you are not in the middle of the country side). Believe it or not, there are only 11 channels available in the 2.4 GHz band (802.11b/g/n), of which only three are fully usable. So if you are in your apartment in NYC chances are you will be sharing three channels with maybe 200 other users around you. The wait-time now increases even more: you not only need to wait for your turn, but you also need to wait for one of the frequencies to free-up in order to send and receive information.

The 2.4 GHz spectrum has only three non-overlapping channels. Picture courtesy of Wikipedia

Too Many Gadgets

What really decreases Wi-Fi performance in today's environment is the lack of wires. Take it for granted: Wi-Fi's #1 enemy is... Wi-Fi itself. Initially developed for mobile devices that can't be hard-wired to a network, nowadays WiFi is being used to replace wires and connect static devices that could otherwise be hard-wired. Take all the myriad of devices at home that do not need mobility: TVs, game consoles, Sonos systems, AppleTVs, stream boxes, printers, you name it. They are static devices that consume Wi-Fi bandwidth, air-time, and throughput that you would otherwise have for use with your mobile phone, tablet, and laptop.

Power, More Power

Another misconception about Wi-Fi is that more power means more coverage and faster speeds. That's absolutely not true. The more power you expel in the environment the more interference you cause, triggering a domino effect from all other Wi-Fi stations around you trying to overcome the interference. This is why careful Wi-Fi planning is a must in order to build a decent Wi-Fi network. In most cases, having three or more low-power Wi-Fi antennas yields much better throughput and coverage than having a powerful access point polluting the radio spectrum.

The Famous "Repeater" from Best Buy

They simply don't work in today's environment. All they do is boost a signal in all directions, which causes even more interference. Interesting enough you will notice a stronger signal on your device, but bare in mind it's pure noise. Repeaters jam the spectrum and reduce throughput capacity by as much as 90%. They should be avoided at all times, except when you plan a point-to-point WLAN or LAN extension over the air.

Understanding spectrum density is key when planning for a multi-cell Wi-Fi network.

Disclaimer: Use of the information provided here is at your own risk. The author makes no warranties of performance or any other claims, and should not be held liable for the use of this information. Readers agree with the terms of use of this website.

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