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A deep dive into why Wi-Fi kind of sucks

arstechnica.com

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Re: A deep dive into why Wi-Fi kind of sucks

#191

Post by dzhiurgis »

willidiots wrote: post #9

I build public Wi-Fi networks, you've probably used one of them. AMA if you have Wi-Fi questions. To say it "sucks" is a bit harsh. It's delivering multiple hundreds of Mbps to you via an unlicensed contention-based medium. The air interface is like sending packets over a noisy Ethernet hub; it's impressive it works as well as it does. That said, this article's a good primer on some of the protocol's fundamental chal…

At my townhouse there are times that 2.4 GHz network dies completely in main floor. Usually its evenings, sometimes feels its periodic. Latency sky rockets even when I am 1 meter from the router.

What are the practical ways to find interference? The tools I have is openwrt router and a macbook.

I normally use 5GHz anyway, but wireless music device is still 2.4GHz which is incredibly annoying once it dies.

Re: A deep dive into why Wi-Fi kind of sucks

#192

Post by hchenji »

Filligree wrote: post #3

This article is all about unwrapping the marketing copy and explaining why it sucks. That's still valuable, but I was hoping for a more technical view on it. Anyone have an article that explains why the systems are as limited as they are?

See my comment https://news.ycombinator.com/item?id=13793876 .

I suggest reading Andrea Goldsmith's or Pramod Vishwanath's book on Wireless Communication. If not, Intro to Communication Systems by Madhow is recommended.

Re: A deep dive into why Wi-Fi kind of sucks

#193

Post by [deleted] »

phil21 wrote: post #138
bsenftner wrote: post #10

My day to day happiness quotient shot up the day I ditched my wireless wifi and ran Ethernet cables through my spaces. I'd realized I was constantly noticing wifi issues, and an apple mbp I use for email seems to drop wifi every half hour. But no longer, with them all wired up! Realizing there are USB3 to Ethernet gadgets really hits home how our modern technology is market-driven-dumb and anti-consumer: all modern l…

I think a lot of this is the 2004 model of plopping an integrated router/access point/modem in a single location in their house simply doesn't work any longer. At least for any sort of Urban deployment. You are seeing many large companies also realizing this and trying to bring products to market. You can get very solid wireless in your house if you are willing to spend some money on it, and of course the time on the…

[deleted]

Re: A deep dive into why Wi-Fi kind of sucks

#194

Post by pedalpete »

This statement is points to why it doesn't suck for most people "In practice, it wasn't a whole lot better than dial-up Internet—in speed or reliability."

At the time of adoption, many people were on dial-up or just moving to slightly faster internet speeds and they were accessing the internet via wifi, so they didn't notice a drop in performance. Wifi speed increased along with access to faster internet.

Is it as fast as it can possibly be? No, but it's like having a Ferrari in highway traffic. Most people can't take advantage of the technical capabilities of anything that would be considered better.

Re: A deep dive into why Wi-Fi kind of sucks

#195

Post by freyr »

hchenji wrote: post #186

The article misses out on explaining WHY we cannot get the promised bitrates. The answer is Shannon's limit on channel capacity, which mandates that you pay in either bandwidth or high power or low noise (SNR) to get higher capacity. Now these WiFi devices have internal rate adaptation algorithms that choose a particular modulation and coding scheme (MCS) index based on the measured SNR. A higher MCS index means bett…

> interference is considered as noise, which means that SNR simply drops

You're arguing that PHY data rates are low because SNR is low, and SNR is low because interference is high. In my experience, this is not the case. PHY rates can be quite high, but the overall throughput is low due to inefficient channel access at the MAC layer.

Wi-Fi doesn't consider interference as noise. Since it uses CSMA/CA to manage channel access, a device can only transmit if no other interfering device is transmitting, or if background interference is very low. This is why your device can be operating at a high MCS, but actual throughput will be so much lower. If your devices are using a low MCS, it's more likely that they're getting a weak signal from the access point.

Re: A deep dive into why Wi-Fi kind of sucks

#196

Post by ioquatix »

dzhiurgis wrote: post #191
willidiots wrote: post #9

I build public Wi-Fi networks, you've probably used one of them. AMA if you have Wi-Fi questions. To say it "sucks" is a bit harsh. It's delivering multiple hundreds of Mbps to you via an unlicensed contention-based medium. The air interface is like sending packets over a noisy Ethernet hub; it's impressive it works as well as it does. That said, this article's a good primer on some of the protocol's fundamental chal…

At my townhouse there are times that 2.4 GHz network dies completely in main floor. Usually its evenings, sometimes feels its periodic. Latency sky rockets even when I am 1 meter from the router. What are the practical ways to find interference? The tools I have is openwrt router and a macbook. I normally use 5GHz anyway, but wireless music device is still 2.4GHz which is incredibly annoying once it dies.

We had a specific lounge chair, which when you sat in it with a laptop, if someone was using the microwave, the wi-fi would drop out. If you stood up, everything was fine. We took that lounge suite to the holiday house. Good riddance :)

Re: A deep dive into why Wi-Fi kind of sucks

#197

Post by davidcuddeback »

swiley wrote: post #176
davidcuddeback wrote: post #73

Earlier quoted context omitted.

Doppler shift in a radio wave at 10 mph? Wouldn't the Doppler shift be around 36 Hz in that case [1]? That's about 0.015 PPM. Seems temperature would have a bigger impact on frequency stability than that. [1] ∆f = f0 * (∆v/v0) = 2.4 GHz * (4.5 / 3e8) = 36 Hz (using 10 mph = 4.5 m/s) Edit: I'm certainly not an expert in RF. I checked my intuition against the datasheet of a radio module I've been working with (RFM69HCW…

Keep in mind, modern WiFi uses OFDM where the signal is transmitted via a number of simultaneous carriers offset by very small frequencies. So while the center of the 20Mhz band might be shifted just a little the small carries might be shifted far enough onto each other that the signal is unintelligible.

If the individual carriers aren't overlapping in the transmitter, they won't be overlapping in the receiver, either. Each one will be shifted proportionally (∆f/f0=∆v/v0) in the same direction. The signal is still intelligible. It's just shifted.

A radio is a physical device subject to manufacturing variance, temperature fluctuations, and aging effects. It has to be manufactured to tolerate frequency deviations caused by these effects. What I was trying to show in my analysis is that the effect due to Doppler shift at 10 mph is orders of magnitude less than at least one of these effects. If the Doppler shift at 10 mph makes the signal unintelligible, then the other effects I mentioned should as well.

For example, a transmitter with 50 PPM accuracy could cause a 2.4 GHz signal to drift by up to 120 KHz (0.00012 GHz). That's about 3000 times more than the 36 Hz that I calculated for Doppler shift at 10 mph.

Re: A deep dive into why Wi-Fi kind of sucks

#198

Post by tlow »

willidiots wrote: post #9

I build public Wi-Fi networks, you've probably used one of them. AMA if you have Wi-Fi questions. To say it "sucks" is a bit harsh. It's delivering multiple hundreds of Mbps to you via an unlicensed contention-based medium. The air interface is like sending packets over a noisy Ethernet hub; it's impressive it works as well as it does. That said, this article's a good primer on some of the protocol's fundamental chal…

Do you have suggestions for organizing semi-dense apartment complexes such that there aren't more SSIDs than units and are there legal ways to safely share wifi with neighbors? It seems to me that most TOS agreements from ISPs seem to not like the idea that I might share my wifi with my neighbors... Also comments on 20 MHZ v 40 MHZ routers? For high latency, highly attenuated signal situations where varies from .1 Mbps to 3 Mbps, on OSX should one mess with MTU?

Last unrelated tangent, how far are we until we can expect to start seeing widerspread municipal wifi deployments? Is it possible that school districts might expect to see 100% home internet penetration in a non-trivial percentage of American school district areas?

Re: A deep dive into why Wi-Fi kind of sucks

#199

Post by tlow »

FabHK wrote: post #183
mseebach wrote: post #63

Earlier quoted context omitted.

Is there a good suite of tools to actually measure the quality of a wifi connection and/or surface, even help diagnose, problems?

On macOS, someone below recommended "WiFi Signal", USD 5. Not so fully featured, I assume, but free is Wireless Diagnostics. Ignore the popup, and go to Windows -> Info/Scan/Performance (it's in System -> Library -> CoreServices -> Applications, but I start it via Spotlight)

Fing for services and ping?

Re: A deep dive into why Wi-Fi kind of sucks

#200

Post by tlow »

rwmj wrote: post #18
willidiots wrote: post #9

I build public Wi-Fi networks, you've probably used one of them. AMA if you have Wi-Fi questions. To say it "sucks" is a bit harsh. It's delivering multiple hundreds of Mbps to you via an unlicensed contention-based medium. The air interface is like sending packets over a noisy Ethernet hub; it's impressive it works as well as it does. That said, this article's a good primer on some of the protocol's fundamental chal…

Have you ever built "moving" wifi networks (trains, planes), and do those have special challenges?

This was a problem for mobile data ~2008 on Deutsche Telekom networks.
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