Talk:Trellis coded modulation

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Added some discussion. The details of TCM are rather complex for a reader who lacks a PHD in data communications, so I opted to provide a readable (and hopefully understandable) overview.

user:jlpayton 9-Nov-2005

The article uses the term Convolutional code. No one except a telecom expert will know what that word means. Consider having an expert rewrite this article in simpler terms. Invitatious 02:34, 26 May 2006 (UTC)[reply]

18 - July - 2006

Article is fine, if anything it's too simplistic. Anybody who searches for trellis modulation has to know some background. —The preceding unsigned comment was added by 87.203.212.185 (talk • contribs) 19:22, 18 Jul 2006 (UTC)

This link here seems to be offering a description that makes sense to those who don't understand what convolution means: https://sciencegrants.dest.gov.au/SciencePrize/Pages/Doc.aspx?name=previous_winners/Aust1997Ungerboeck.htm (anonymous)

It was CCITT, not ITU in 1980's

Before the ITU, CCITT was the one the standardized the V. standards. Also, there was no CCITT/ITU standard of 19.2 Kbps -- that's a Telebit propritary standard (PEP). Mdrejhon 22:05, 18 January 2007 (UTC)[reply]

Shannon Channel Capacity ?

If the channel in question is the twisted pair cable, I hardly think that the Shannon Channel capacity is 35 kBits/s, considering that standard residential ADSL links utilize the same twisted pair wiring as the POTS line. The Shannon channel capacity for twisted pair wires is much higher, depending on several factors, such as noise power on the channel, length of the twisted pair. It can be as high as a Gbit/s over short runs of cable (several meters) with only thermal noise present. (Anonymous)

The channel in question isn't just the cable, it's the entire POTS infrastructure (for voice), including filters that limit bandwidth to 3 kHz. Combining that with typical noise margins gives you 35 kbit/s. (ADSL bypasses this filtering to achive the higher rates.) 198.99.128.100 (talk) 20:45, 15 January 2013 (UTC)[reply]

Too simplistic

Most definetly too simplistic. Ungerboeck centered rather than topic centered. —Preceding unsigned comment added by Piotroxp (talk • contribs) 07:06, 18 June 2009 (UTC)[reply]

Article definitely too simple. I have no background except college physics. It was hard to understand the actual modulation technique due to lack of detail. I had to infer the actual technique from how it was able to reduce error. InsightSoul (talk) 11:05, 13 December 2013 (UTC)[reply]

Incorrect Terminology

Trellis is a coding method, not a modulation scheme. It does require knowledge of the modulation scheme as if you map the symbols incorrectly, then the point of the error correcting that the trellis coding scheme provides is compromised. For example, ATSC the top bit is passed through, and the low bit is trellis encoded to 2 bits. This results in a 3 bit symbol or code word. In 8VSB, the lower the bit, the less energy it has, and more likely it is to be corrupted/incorrect (and this is why the upper bit is not coded). The trellis encoding scheme allows for max energy difference between code words allowing for a reduced error rate, as the other possible code words are decided to be invalid. See also: Turbo code. 208.87.223.18 (talk) 18:21, 28 October 2015 (UTC)[reply]

Exposition upgrade failure

Here is the core expository block, as the article now stands, in exploded view:

Though hard to visualize in multiple dimensions, a simple one-dimension example illustrates the basic procedure.
Suppose the symbols are located at [1, 2, 3, 4, ...].
Place all odd symbols in one group, and all even symbols in the second group.
(This is not quite accurate, because Ungerboeck was looking at the two dimensional problem, but the principle is the same.)
Take every other symbol in each group and repeat the procedure for each tree limb.
He next described a method of assigning the encoded bit stream onto the symbols in a very systematic procedure.
Once this procedure was fully described, his next step was to program the algorithms into a computer and let the computer search for the best codes.

The 'take and repeat' sentence in bold is the only sentence devoted to business, and it's completely baffling: all this hop-scotch recursive taking, to what end, exactly?

Fine for 2006 as a starting point, dubious a decade later. Even as a starting point, the camera angle jumps around like a pre-production demonstration daily.

And a small thing: it's a bit unseemly to have 'he' refer back to a narrative subject introduced parenthetically. But what this really needs is some TLC from a fresh expert. — MaxEnt 14:07, 17 March 2018 (UTC)[reply]