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CrazyEyeJoe  ·  1305 days ago  ·  link  ·    ·  parent  ·  post: Wait, are we doing it wrong? [Potential major Hubski experiment]  ·  

Alright, fair enough. If I hurt your feelings back then, I'm sorry that I did, and I certainly didn't intend to.

I'll try to avoid it in the future as well, and hopefully we can have some more productive exchanges.

CrazyEyeJoe  ·  2930 days ago  ·  link  ·    ·  parent  ·  post: ELI5: fourth generation (4G) wireless communications - how do they work?  ·  

I can't give a great answer to all of these, especially since my knowledge of 2G and especially 3G is pretty basic, but I'll give it my best.

    Is speed/quality of connection the only difference between the two generations of communication?

Again that's kind of vague, but the short answer is no. There are many differences. However, what most of these differences are attempting to achieve is better speed and quality. As my experience lies in the physical layer, that's what I can comment most on. The modulation schemes (how the physical signal is transmitted) are different between all three. I started writing about the differences, but it just got too long and complicated. I don't think it would interest you too much anyway, and I wouldn't want to say anything wrong about 2G/3G.

    Are there any particular interesting events connected to the transmission of the signal with 4G (or in general)? I remember seeing something about radio echo while skimming over the Wikipedia article, and it sounded fascinating.

What I think you're getting at here are reflective channels (to put it in layman's terms). When you send a signal over the air, it'll bounce off of all sorts of stuff, like buildings or mountains, etc. Therefore the receiver will receive the same signal several times, with different amplitudes and delays, in very rapid succession. These will overlap, and that of course causes problems. What was really sent, and how can you determine that when what you receive is basically a jumbled mess of reflected versions of the original? Think of it as if you were in a room that had a lot of echo in it. Somebody speaks to you, but the echo is so long that all the words just get blended together in a mush.

The answer, and this is true for 2G, 3G and 4G, is that you periodically (in 4G about 4000 times per second) send a reference signal, a signal that you know what is supposed to be, and you compare that with what you receive. That's the purple blocks in the image in my last post. You take the differences, and use those to make a guess about what happened to the signal between the transmitter and the receiver. This is called channel estimation. Once you have a channel estimate, you use it to correct the received signal.

Another thing that is done is that if you're sending, let's say, 8 bits of data, you will actually send a lot more bits over the channel. Something like (this varies based on channel quality) 24 bits of data. By adding these 16 "redundant" bits, you can retrieve the signal even if some received bits are wrong. This is called channel coding.

    Are there differences in physical structure between the 4G and 3G signal transmitters/accepters (the proper term skips my mind) - as in, are they physically different schemes? I remember reading that 4G is non-backwards-compatible, but does it mean protocols only or the transmitters as well? Can one encode a 4G signal with a 3G transmitter (if there even is such a difference)? Do they have to upgrade the equipment of the cell towers to match the new generation?

Short answer: yes, they are different, and they must be upgraded. Here my knowledge is very limited, but I know that these standards are made in such a way that network providers shouldn't have to completely change all of their equipment to make it work.

To give you a little bit of context, one of my more experienced colleagues at the company told me that when they originally implemented the 4G in the modem I was working on, they did it with a 3G receiver. This shows that it's possible, but he made a point of how impressive it was that they achieved this. I consider this guy to be a straight up genius, so the fact that he found it difficult to do makes me think it was far from the optimal situation.

    How is it possible to remain within the same cell of the station and not tangle up the signal with others?

Modern digital processing. It's what I was talking about in the previous post, with that time/frequency grid. The base station tells you which of the squares are for you, and it tells you which squares you can send on. In 4G, you will actually receive all of those squares, but you will only decode the ones which are for you.

This is made possible by using the Fourier Transform, which is a mathematical operation. The Fourier Transform takes a time domain signal (in this case, some radio wave) and decomposes it into its frequency components. In the picture you see there are 7 symbols in each time slot. That means that you must take the Fourier Transform at 7 different times to get the frequency components of each time instance. This is how you get the grid, which then in fact just becomes a grid of numbers. Those numbers each represent a set of bits. When you know which ones are for you, you can go ahead and decode your data.

    Does different encoding mean that it's simpler/easier/quicker to decode the signal by those of ill intent, thus enabling for easier eavesdropping? Alongside that, does 4G protocols of transmission mean that one would have to catch the required frequency first? is it as easy to do as with 3G communications?

You're confusing channel coding with encryption. Channel coding (which is what I was referring to) is about how you represent bits on a physical signal, it's not about obfuscating the data. In fact, data transmitted over 4G isn't encrypted, although it's not trivial to eavesdrop. I think, however, that if you implement your own base station clone (a very non-trivial task), you'd pretty much be able to listen to anything going on around you. You'd have to know which frequency network operators are using, but this is not exactly secret information.

This turned out fairly long, but I didn't want to be too superficial. I hope this helps.

CrazyEyeJoe  ·  3464 days ago  ·  link  ·    ·  parent  ·  post: Vice: We've Been Had, and We Let It Happen  ·  

I think the reason you never understood Vice is that you were too mature for it, and just not the target demographic at all.

Being young, pissing on everything is a way to make yourself feel above it all. At that stage, one might not realize that boundless negativity is not only something something that doesn't help the world, but also something that makes you feel bad about yourself. Cynicism is a shortcut to feeling like an intellectual. At least it was for me.