Trellis Modulation

[Pray To Jesus]

Do you have, or can provide, a simple and accurate analogy to explain the invention?

 

[rumpleforeskin]

If coded modulation is your thing this is a good starting point

http://www.amazon.com/Coded-Modulati.../dp/0306472791

Some great information in here with excellent explanations. Its also not too hard of a read given the subject matter

 

[esun]

I haven't studied TCM but this looks like a good read on it:

http://complextoreal.com/wp-content/uploads/2013/01/tcm.pdf

It looks like TCM isn't a particularly simple modulation scheme so it may not be reasonable to expect a simple analogy for it (or at least not an accurate one).

 

[ch424]

(been lurking for a while so thought I'd finally jump in with a first post! Edit: looks like I made a lame post in 2006, oops)

Trellis modulation is a sort-of misnomer. You still have to use it together with other modulation schemes (eg QAM, PSK etc)

It's a way of encoding the data so that if the transmitted data gets corrupted, the receiver can 'guess' what you actually meant. For example, imagine we're playing a strange version of chess where you're allowed to take three moves in one turn.

I decide that I'm going to move my knight from w to z like this:

I then send you the list of positions: B2, C4, E5, C6. However, during transmission, one of the positions is corrupted because of noise, and you actually receive B2, C4, G5, C6, which would look like this:

When you receive this, it's obviously wrong because you know that knights can't move like that. However, because you know the rules, you can pick the most likely move that I was trying to do, and assume that B2, C4, E5, C6 is what I actually sent you and therefore repair the data yourself.

That's conceptually how it works - the actual implementation is quite tricky! It's useful because it means you can turn the transmission rate up, and recover from some of the errors. Without error protection, you have to transmit more slowly so that each bit of information has a high enough chance of getting to the far end without being corrupted. If you're allowed to lose some of the data during transmission, you can transmit much faster and deal with the consequences later.

 

[Pray To Jesus]

I haven't studied TCM but this looks like a good read on it:

http://complextoreal.com/wp-content/uploads/2013/01/tcm.pdf

It looks like TCM isn't a particularly simple modulation scheme so it may not be reasonable to expect a simple analogy for it (or at least not an accurate one).

Yea I went through that already. I was trying to come up with a good analogy but was lazy and didn't want to reinvent the wheel.

I was just using, "It's too complicated" when people ask me what it is.

"It's too complicated" works really well in life. Very efficient time saver. LoL.

 

[Pray To Jesus]

(been lurking for a while so thought I'd finally jump in with a first post! Edit: looks like I made a lame post in 2006, oops)

Trellis modulation is a sort-of misnomer. You still have to use it together with other modulation schemes (eg QAM, PSK etc)

It's a way of encoding the data so that if the transmitted data gets corrupted, the receiver can 'guess' what you actually meant. For example, imagine we're playing a strange version of chess where you're allowed to take three moves in one turn.

I decide that I'm going to move my knight from w to z like this:

I then send you the list of positions: B2, C4, E5, C6. However, during transmission, one of the positions is corrupted because of noise, and you actually receive B2, C4, G5, C6, which would look like this:

When you receive this, it's obviously wrong because you know that knights can't move like that. However, because you know the rules, you can pick the most likely move that I was trying to do, and assume that B2, C4, E5, C6 is what I actually sent you and therefore repair the data yourself.

That's conceptually how it works - the actual implementation is quite tricky! It's useful because it means you can turn the transmission rate up, and recover from some of the errors. Without error protection, you have to transmit more slowly so that each bit of information has a high enough chance of getting to the far end without being corrupted. If you're allowed to lose some of the data during transmission, you can transmit much faster and deal with the consequences later.

Wow! Thank you for the excellent post, even better because it is the 2nd post from a super lurker. Makes me feel special.


Trellis Modulation, why are you so good to me?

 

[ch424]

haha, did my explanation actually help? Are you trying to learn this out of general interest or are you working on something cool?

 

[Pray To Jesus]

haha, did my explanation actually help? Are you trying to learn this out of general interest or are you working on something cool?

Yes, it helped to see how you approach the problem. Your example gave me good ideas on how I can improve my explanations of complicated subject matter.

It started because I wanted to check my memory accuracy re. a specific POTS modem speed. I got sidetracked into reading the history of modems and learned about the history of Trellis Modulation.

It struck me that for years no one was able to overcome the 14.4k barrier. The consensus was that was impossible to go above 14.4k on POTS. It is pretty funny how the guy knew how to do it and sat on it for years before telling the world how to do it. Genius.