About wifi signal strength

[professa X]

Ok can someone please explain to me what this signal strength is. I mean i look at it and at full bars its 300 mbps. Why does my internet slow down if i'm farther? I get it that if i'm farther like maybe twice the distance at 300 mbps then i should get 150 mbps. But why would it slow down when my max downstream is capped at 10 mbps by my ISP. whether i'm at 300 mbps or 150 mbps i can only get 10 mpbs so it shouldn't matter about the distance. So can someone explain this please!

[Tsukumo Yuma]

The distance does matter, the farther away you are from your router, the weeker the signel, and the weaker the signal the slower your download and upload speed.

But there is another factor, if there are things blocking the signal, like other wireless equipment or something else that gives out a signal.

The last thing it could be is something is inbetween you and the router, whether it is just piles of paper, a chair, a wall, a lamp, ect, if things are blocking the routerbor are inbetween you and the router, you might get a week signal.

[Dae314]

I'm not a networking expert so I can't explain all of the factors that affect wireless communication, but I can highlight probably the biggest issue for your question:

Noise (EM Interference) If you're an audio engineer or you've ever tried to design a system that needs to pass data over a very long distance, you know exactly what this is. When you send your data over a physical medium (whether that's wifi frequencies or copper wires) you aren't sending your signal into a perfect vacuum. The world is a messy place and there's lots and lots of different things that can affect your signal no matter how well shielded it is. Even when your signal is passing through a wire, you still have some noise buildup. It's part of the reason why different classes/types of wires have different maximum effective lengths. For example, I think cat5 ethernet cable has an advised maximum length of 100m. Other factors play a larger role in cable length limits than noise but we're trying to stay simple here.

Now just think. If there's some noise in a relatively isolated environment like a wire, how much noise would there be if you were sending your signal over the air completely unshielded from environmental interference like wifi is? It's amazing you can even connect at all. Imagine if you were receiving an encrypted file via email on your phone. Lets say there is no error correction at all on the network you're using. Thanks to noise, some of the bits in the original message get flipped (1->0 or 0->1). The way some encryption methods work, even a small change like that could completely corrupt the file you get when you unencrypt it.

Fortunately, there are lots of layers of error correction protecting your data as it crosses a noisy environment at every stage in the OSI network model (see wikipedia). Feel free to look some of these terms up: checksum, cyclic redundancy check, parity bit, error correcting code. You need some math skill to fully understand how some of the more complicated ones work, but you should be able to understand the basics of all of them. Unfortunately, even with the best math can offer, there are still times when your data arrives uncorrectable or corrupted. A good error correction algorithm will at least be able to see that the data is bad though. So the clever network engineers of the past put in a mechanism to request data be resent (at least if you're using the right protocol e.g. TCP) if you find out it's corrupted.

That's great! Now if some data happens to be corrupted, as long as you know it's corrupted you can just rerequest it! Joy. But wait. That's fine if it's just maybe 1 packet (stuff that holds your data) is corrupted out of every say... 1,000,000,000,000 packets you receive. But remember that thing I told you about noise buildup and distance earlier? As you get further from the source of the signal, there is a higher chance that your data will arrive to you corrupted beyond repair and you'll need to ask for it again. And again. And again. So now you're on Wifi and far from the source. Instead of 1/1,000,000,000,000 packets arriving corrupted, you're hitting 1/1,000,000. You're 1,000,000x more likely to need to request a resend. You're obviously not going to be as fast as you were before.

So there's a ton of more information I didn't even mention in this post, and about 95% of it I don't even know about. If you want to learn more, I suggest you pick up a networking book (or heck maybe a physics book about electrical engineering). If this scared you, you probably want to just accept that the network is the way that it is and just thank the networking gurus that things actually work most of the time. I fall into the latter category for now until I have time to pursue a Cisco certification .

Edited June 28, 2014 by Dae314

[professa X]

I'm not a networking expert so I can't explain all of the factors that affect wireless communication, but I can highlight probably the biggest issue for your question:Noise (EM Interference) If you're an audio engineer or you've ever tried to design a system that needs to pass data over a very long distance, you know exactly what this is. When you send your data over a physical medium (whether that's wifi frequencies or copper wires) you aren't sending your signal into a perfect vacuum. The world is a messy place and there's lots and lots of different things that can affect your signal no matter how well shielded it is. Even when your signal is passing through a wire, you still have some noise buildup. It's part of the reason why different classes/types of wires have different maximum effective lengths. For example, I think cat5 ethernet cable has an advised maximum length of 100m. Other factors play a larger role in cable length limits than noise but we're trying to stay simple here.Now just think. If there's some noise in a relatively isolated environment like a wire, how much noise would there be if you were sending your signal over the air completely unshielded from environmental interference like wifi is? It's amazing you can even connect at all. Imagine if you were receiving an encrypted file via email on your phone. Lets say there is no error correction at all on the network you're using. Thanks to noise, some of the bits in the original message get flipped (1->0 or 0->1). The way some encryption methods work, even a small change like that could completely corrupt the file you get when you unencrypt it.Fortunately, there are lots of layers of error correction protecting your data as it crosses a noisy environment at every stage in the OSI network model (see wikipedia). Feel free to look some of these terms up: checksum, cyclic redundancy check, parity bit, error correcting code. You need some math skill to fully understand how some of the more complicated ones work, but you should be able to understand the basics of all of them. Unfortunately, even with the best math can offer, there are still times when your data arrives uncorrectable or corrupted. A good error correction algorithm will at least be able to see that the data is bad though. So the clever network engineers of the past put in a mechanism to request data be resent (at least if you're using the right protocol e.g. TCP) if you find out it's corrupted.That's great! Now if some data happens to be corrupted, as long as you know it's corrupted you can just rerequest it! Joy. But wait. That's fine if it's just maybe 1 packet (stuff that holds your data) is corrupted out of every say... 1,000,000,000,000 packets you receive. But remember that thing I told you about noise buildup and distance earlier? As you get further from the source of the signal, there is a higher chance that your data will arrive to you corrupted beyond repair and you'll need to ask for it again. And again. And again. So now you're on Wifi and far from the source. Instead of 1/1,000,000,000,000 packets arriving corrupted, you're hitting 1/1,000,000. You're 1,000,000x more likely to need to request a resend. You're obviously not going to be as fast as you were before.So there's a ton of more information I didn't even mention in this post, and about 95% of it I don't even know about. If you want to learn more, I suggest you pick up a networking book (or heck maybe a physics book about electrical engineering). If this scared you, you probably want to just accept that the network is the way that it is and just thank the networking gurus that things actually work most of the time. I fall into the latter category for now until I have time to pursue a Cisco certification .

Thanx maan. I'm a computer engineering major taking a networking class and I love it. So every thing you said made sense. But out of all of that the last paragraph explains it all. See what was getting me was the fact that the wifi signal said I should be getting 150 Mbps even though I'm at half my bars. That's still 15 times the rate of my ISP downstream 10 Mbps. So I didn't understand why there would be a degradation in speed when I'm clearly qualified to receive my max down stream of 10mbps. What I didn't know was even though data was arriving at 10mbps like in a torrent I was only able to receive it at the rate I can correct it. So the farther I am the more time it would take since my data is far more likely to be corrupted. Again thanx for the reply and let me know if my assumption is correct.

[Dae314]

Yup your summary of the issue I highlighted is spot on. All of the paragraphs before the end talking about packet corruption were to give background info in case you didn't have any networking background.

There are probably a lot more issues that get more technical as to what happens as you get farther from the source. Since you're a CE major and especially if you pursue a career in networking, you'll probably come across these as you study.

Also note, the resend issue I highlighted is protocol dependent. I'm sure you've heard "TCP/IP" in reference to the internet. Those are 2 protocols that pass a lot of internet data, but there are others. UDP is another popular alternative to TCP, and it does not natively support packet validation. Depending on the type of data you're sending, you may not need to have perfect data transfer. For example, if you're streaming a movie, it's not critical that pixel (1248,103) is exactly a certain color. If that packet comes in a little corrupted who cares? You'd be wasting your time resending that packet for an unnoticable increase in quality. However, with something like a torrent, you do want that data to be exactly the same.

Networking is a very messy topic with lots of variables to consider. That's part of the reason why networking people tend to get paid more for what they do. Computer networks are complex making them difficult to troubleshoot, but if the network goes down you affect a ton of people. Desktop issues are usually fairly straight forward (reboot it!) and will usually only affect a few people.

[Googler123]

Well, the thing is when you are connected to your router you create a local network. The speed of the wireless connection is that inside that

local network. If another computer would connect by wire to your router and you would be on wireless you could transfer files between them

at almost that network speed.  If both would be on wireless then the maximum bandwith  would be split in half. However the internet is a third entity, an external one and is often capped by the ISP to a preset value, often lower that the capabilities of modern routers.

If you have more questions don't hesitate to ask.

[professa X]

thnx all. By the way just finished covering that material. Read it in Computer Networks by A Tanenbaum. Really great resource!