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Weakest links for Wi-Fi
- your client devices
- distance/obstacles
Wi-Fi originally meant “wireless fidelity” In 1997 Wifi 1 came out and supported PHY speeds of 1Mbps to 2Mbps in the 2.4 GHz band. In 2002 Wifi 3 came out, increasing speeds from 11Mbps to 54Mbps.
Wi-Fi, spectrum/channels are shared: It is remarkable that Wi-Fi actually works as well as it does, because every device using a particular channel (spectrum) must cooperate and SHARE the time on that channel with every other device using the same channel (you and close neighbors). It is exactly like using a Walkie-Talkie — everyone on the same channel can either talk (Tx) or listen (Rx), but can not do both at the same time. So Wi-Fi works best when all Wi-Fi access points (for you and close neighbors) are evenly spread out across all available channels (not everyone using the same channel).
Analogy: Understanding Modulation/Coding: Imagine that once a second (the ‘symbol rate’ for this channel), you hold up your arms in various positions to convey a message to someone else. If you were only ten feet away from that person, the number of arm positions reliably detected would be very high. But now move 100 feet away. The number of arm positions reliably conveyed would be reduced. Now move 500 feet way. The number of arm positions reliably conveyed might be reduced to just ‘did the arm move at all’. The same thing happens in Wi-Fi. If you are close to the AP/router, a large number of bits can be conveyed ‘at once’ (within each symbol). But as you move away, a smaller and smaller number of bits can be reliably conveyed ‘at once’. So ‘modulation/coding’ is simply how much information can be conveyed at once, and is directly related to distance from the AP/router.
WI.BAT for testing
Sticking to 2x2 MIMO
MOST client devices today are ‘stuck’ at 2×2 MIMO: As can be seen from the tables (right), most client devices today are STILL only 2×2 MIMO. Why haven’t devices switched to 4×4? Because (1) there is (currently) no compelling need for that speed today (there is no app that ‘requires’ 400 Mbps to function) and more importantly (2) the increased speed is not worth the tradeoff in greatly reduced run time for battery powered devices.
MIMO is driving speed increases:
Analogy: Think of MIMO as adding ‘decks’ to a multi-lane highway. More lanes (capacity) are added without using more land (spectrum). 2×2 MIMO is a highway with one more highway deck above it. And 4×4 MIMO is a highway with three more highway decks above it.
Conclusion: I find that most people are surprised to learn that a 100 Watt (incandescent) light bulb kept on for a full year (365×7) would cost around 300 in California) — and have to be replaced nine times (using a ‘typical’ bulb lifespan of 1000 hours)! This alone is a great argument for switching to LED light bulbs! Much longer life span and MUCH lower electrical costs. And you are incurring this cost each and every year.