Talk:Convolutional code: Difference between revisions

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== Code Rate 1 ==

Re the recent change to say that code rates could be equal to 1, I don't know of any such codes ever being used in practice, and it certainly doesn't seem very useful...

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Josh Rubin: I second BrettE. The page for Reed-Solomon codes gives a rough but accurate definition;

this page manages to talk about convolutional codes without defining them. A definition of "convolution" as used in mathematics and signal processing is in order too.

:Codes of rate 1 are used in practice I'm quite sure. They would be used in storage media usually to satisfy frequency-related constraints. You can think of these codes as simply transforming information into a different format without changing its rate. [[User:BourkeM|<span style="font-weight:bold"><span style="color:red">Bo</span><span style="color:green">ur</span><span style="color:blue">ke</span><span style="color:red">M</span></span>]] ^{[[User talk:BourkeM|Converse!]]} 05:46, 23 September 2015 (UTC)

== Sequential decoding ==

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: Yes, reg3 does not affect output 1 in direct way - by the argument you describe. However, reg3 affect reg1 : reg1=input+(reg2+reg3), and hence affect output 1 on the next performance cycle. [[User:Alexander Chervov|Alexander Chervov]] ([[User talk:Alexander Chervov|talk]]) 18:42, 8 October 2009 (UTC)

: Another way of looking at constraint length is by the z-exponents; reg3 provides the memory for all <math>z^{-3}</math> terms in the numerator and denominator. If these dropped out of the final transfer functions, then you could argue for a constraint length of 3. --[[Special:Contributions/64.203.138.235|64.203.138.235]] ([[User talk:64.203.138.235|talk]]) 20:24, 30 November 2009 (UTC)

:

: I wonder if the author intended the adder above/between reg1/reg2 to add the encoder input to the reg1 output; this is based on the numerator of the first transfer function. Check my work:

* <math>reg_1=(1+reg_2+reg_3)*z^{-1},\,</math>

* <math>reg_2=reg_1*z^{-1},\,</math>

* <math>reg_3=reg_2*z^{-1},\,</math>

* combining these:

** <math>reg_1=z^{-1}+reg_1*z^{-2}+reg_1*z^{-3}=\frac{z^{-1}}{1-z^{-2}-z^{-3}},\,</math>

** <math>reg_2=\frac{z^{-2}}{1-z^{-2}-z^{-3}},\,</math>

** <math>reg_3=\frac{z^{-3}}{1-z^{-2}-z^{-3}},\,</math>

now, I see the first transfer function from the drawing as:

: <math>H_1=input+reg_2+reg_3+reg_1+reg_3=input+reg_1+reg_2=\frac{1+z^{-1}+z^{-2}}{1-z^{-2}-z^{-3}},\,</math>

[[Special:Contributions/64.203.138.235|64.203.138.235]] ([[User talk:64.203.138.235|talk]]) 19:41, 30 November 2009 (UTC)

== Turbo Code for Planetary Exploration? ==

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: I've now expanded the caption. [[User:Edratzer|Edratzer]] ([[User talk:Edratzer|talk]]) 19:33, 4 December 2008 (UTC)

== Convolutional encoding -> Registers ==

In example 1

"To convolutionally encode data, start with k memory registers"

"The figure below is a rate 1/3 (m/n) encoder with constraint length (k) of 3"

However the figure has 2 registers, m1 should not be a register, it's the input bit

If m1 was was a register, it would output its input on the _next_ clock tick, with its input being what I observe as an unnamed arrow from the left <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/195.251.124.94|195.251.124.94]] ([[User talk:195.251.124.94|talk]]) 18:08, 10 February 2012 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->

:You are right, and the description is wrong: that code has only 4 states, not 8. --[[User:Cantalamessa|Cantalamessa]] ([[User talk:Cantalamessa|talk]]) 20:03, 9 May 2016 (UTC)

== Vandalism ==

Just removed vandalism from 202.184.111.75 (which seems to have a track record of vandalism on other pages : see https://en.wikipedia.org/wiki/User_talk:202.184.111.75)

[[User:SN74LS00|SN74LS00]] ([[User talk:SN74LS00|talk]]) 12:15, 28 January 2014 (UTC)

== MATLAB example code? ==

I'm curious as to what the policy is regarding sample code being written in open/free language/tools. The sample code on this page is not useful for people who don't have MATLAB, and for MATLAB users, it's the kind of thing that likely belongs in a user manual. Would a more open language make more sense to provide a demonstration of this kind of thing?

[[User:XXV|XXV]] ([[User talk:XXV|talk]]) 04:46, 12 September 2014 (UTC)

== k vs. K confusion ==

I had to pull out a textbook to un-confuse myself -- I think later in this article, lower-case k (defined at the top as the output symbol rate) is being re-used at the bottom where it's referred to as 'constraint length'; which was defined as upper-case K at the beginning. Is that correct?

[[Special:Contributions/6450.203205.13821.235122|6450.203205.13821.235122]] ([[User talk:6450.203205.13821.235122|talk]]) 1901:4115, 306 NovemberJuly 20092017 (UTC)