[JTon]

> That's how shit wifi

Seems like you know a bit about this. Could you indulge my curiosity and elaborate why wifi is shit? I assume some combo of DSP bottleneck (i.e. want to keep hw cheap) and maintaining backwards compatibility with older standards?

[rkangel]

Wifi is improving now. Newer standards like Wifi 6 are doing that basically by taking the good ideas from LTE (4G) and applying them to Wifi. The cellular radio community has been much better about evolving standards, coming up with new technology and rolling it out. Maybe they have it easier because everyone gets a new phone every two years, but they've still had fairly good backwards compatibility support.

Multiple Access - this is the general term for 'multiple devices on the same spectrum'. Cellular divides up the spectrum into frequency bands (Frequency division multiplexing) and time slots in those bands (time division multiplexing). The base station then assigns each device a slot in a band (or potentially several), it also provides the time reference for this scheduling. This makes efficient use of your available spectrum and nothing interferes with or talks over anything else.

Wifi gets none of this. There's no base station planning so two access points can interfere with each other. There's no FDMA (access point runs on one channel of one band), and no TDMA. There's no uplink channel and downlink channel separation. Instead it's "Carrier sense with collision detection". Basically "try not to transmit at the same time as someone else, and if you do come back and try again later". This results in nodes competing, talking over each other, interfering (see "hidden node problem") etc. and makes inefficient use of the spectrum. The problem gets worse as the traffic gets busier. Wifi 6 is bringing in some actual scheduling.

Modulation schemes (the fundamental way that you transmit bits on a radio) - cellular modulation schemes are now incredibly efficient and robust. They use a variety of techniques that allow scaling based on channel conditions so that you can get as close as possible to whatever Shannon currently says you're allows. A lot of wifi uses old-school spread spectrum, and newer standards use OFDM which is a bit better. Wifi 6 is finally moving to the Quadrature Amplitude Modulation stuff that LTE uses.

[MaxikCZ]

Sometimes I work in a factory (full of metal everything) that's a metal plated building with no signal repeaters inside, basically a faraday cage. U can get enormous signal boost by just opening doors trough the wall. Most places inside the building report low signal with no usable internet connectivity, but some special spots provide enough signal to get few KB/s trough both ways. I was always impressed by the amount of work needed to push few KBs of data to cell tower trough such conditions, given a phone is able to establish and hold a connection. With WiFi there would be no hopes of even holding a connection between two points inside the building 30+ meters apart.

[rkangel]

That's an unfair comparison to cellular though as cellular has its own licenced spectrum with nobody else able to interfere, high transmit power limits and potentially a friendlier frequency for the sort of waveguiding you're talking about.

That's why I find the smartsky comparison so interesting - because it's a completely level playing field.

[throwoutway]

Thanks for this information! Do mesh wifi routers do FDMA now? I think my mesh router uses multiple bands

[rkangel]

Not as far as I'm aware. I don't know much about Wifi mesh, but I'm guessing that it has two channels - one for being "master" and one for "slave".

I.e. the master channel is used to serve wifi to the nearby devices, and to the next wifi routers in a chain, whereas the slave channel is used to get wifi from any upstream routers.

We wouldn't describe that approach as FDMA - more that it has a separate channel for backhaul.

[mytailorisrich]

Wifi's use case was, and still largely is, to be a wireless LAN. This means few users, no mobility, static devices, short distances, devices plugged in (not so true now). It started pretty much as exactly that: Just transmit ethernet frames over the radio and everything else is exactly as wired ethernet.

Cellular standards cater for a very different use case and, as a result, as vastly more complex and robust. To manage a lot of moving users and to support mobility is hard, also taking into account that cellular has had to deal with quality of service from the beginning because even if data rate was low voice requires a constant throughput with constrained delays.