Look, Wi-Fi still kind of sucks. And marketing excesses aside, its worst problems all revolve around airtime distribution among multiple devices.

Unlike LTE (the protocol cellular data uses), 802.11 WI-Fi is a protocol with no central management, which leaves all nearby devices duking it out for airtime like angry, unsupervised toddlers. There's only so much you can do to fix this problem without radically overhauling and replacing 802.11 itself—but as new 802.11 protocols emerge, they do their best.

A brief overview of the alphabet soup

If you don't deal with this stuff for a living, it's easy to get lost in all the different Wi-Fi protocols in the ether today. New additions have been released in sort of alphabetical order, but some are backwards-compatible and some aren't. Some are "mainstream" and have broad consumer device support, and some are offshoot technologies rarely to be seen in anything you can buy at a big box store. It's kind of a mess.

If all this isn't bad enough, the Wi-Fi Alliance has not-so-helpfully decided to replace some—not all!—of the 802.11 designations in consumer marketing with a supposedly simpler scheme. 802.11ac, which most of us are using now, becomes "Wi-Fi 5" under this new scheme. 802.11ax will be marketed as "Wi-Fi 6." This new numeric designator conveniently ignores some protocols, unfortunately: neither 802.11ad nor 802.11ay will get "Wi-Fi Numbers" at all.

Designation Spectrum single-MIMO PHY notes 802.11a 5 GHz 54 Mbps There was almost no consumer device adoption; it was prevalent in very early 2000s enterprise. 802.11b 2.4 GHz 11 Mbps 802.11g 2.4 GHz 54 Mbps 802.11n 2.4 GHz / 5 GHz 144 Mbps / 300 Mbps 802.11n devices must have a 2.4 GHz radio; one or more 5 GHz radios are optional. 802.11ac 5 GHz 433 Mbps 802.11ac protocol is 5 GHz only, but in practice all 802.11ac devices also offer a 2.4 GHz 802.11n radio. 802.11ad 60 GHz ~5 Gbps 802.11ax (draft) 2.4 GHz / 5 GHz ~500 Mbps It's a draft protocol scheduled to be ratified in 2019. It covers 2.4 and 5 GHz, with provisional support for 1-6 GHz at a later date. 802.11ay (draft) 60 GHz ~ 40 Gbps

Confused about the PHY column in the table above? You probably should be. PHY is the "PHY"sical transport layer speed of a Wi-Fi connection—but you can't actually move data across the link that fast. Actual data transmission rates can be anywhere from 1/3 to 2/3 of PHY on a completely healthy link in reasonable transmission range. And as you move further away from an access point, you can rapidly see transmission rates falling to 1/10 of PHY or worse.

Ideally, you'll also see the PHY itself fall off as you move further from the nearest access point—a lower QAM means lower PHY and throughput, but longer reliable connection range—but the connections your devices negotiate between themselves frequently aren't optimal.

Adding to the confusion, many of the protocols in this table support varying channel bandwidth settings, with higher bandwidth meaning higher throughput, but fewer available channels and more problems with interference (and multiple MIMO streams as well). The table above assumes a single MIMO stream and the most common (not necessarily the largest) QAM and channel width settings.

About MIMO streams

MIMO is an acryonym for Multiple Input / Multiple Output; it's a way of using multiple antennas to send multiple spatial streams of data from a single radio on a single channel. Broadly speaking, there are two types of MIMO— SU-MIMO, and MU-MIMO. The SU stands for Single-User, and no matter how many streams a device has available, it can only talk to one other device at a time. Got an 8-stream 802.11ac router that's currently talking to a single-stream, non-MU-MIMO 802.11ac device? Tough; you're only getting a single stream worth of transmission to that single device no matter how many other devices you've got clamoring for airtime.

MU-MIMO is Multi-User MIMO, and as the name suggests, it means that an access point can divide up its available MIMO streams between multiple clients. For example, a 4x4:4 access point (four transmit RF chains, four receive RF chains, and four simultaneous data streams possible) can simultaneously "talk" to one 2x2:2 laptop, and two 1x1:1 phones or tablets.

There are quite a few catches with this; the biggest is that all devices currently "talking" must support MU-MIMO. 802.11ac's implementation of MU-MIMO is download only; so while an 802.11ac MU-MIMO router can simultaneously deliver data to several MU-MIMO enabled client devices, any time one of them wants to request data from the router, all other traffic comes to a screeching halt.

All of this MU-MIMO stuff already exists in the real world, but vanishingly few of us have ever benefited from it. MU-MIMO capable routers are increasingly common, but MU-MIMO capable client devices are still rarer than hen's teeth. There's a reason for that, as Chuck Lukaszewski demonstrated in a WLPC presentation from 2016: MU-MIMO requires significantly increased power usage compared to SU-MIMO. And that makes it much less attractive in battery-powered devices.