Convolutional code: Difference between revisions

Revision as of 05:46, 12 October 2006

Revision as of 16:15, 10 November 2006

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* [[Mars Pathfinder]], [[Mars Exploration Rover]] and the [[Cassini probe]] to Saturn use a ''k'' of 15 and a rate of 1/6; this code performs about 2 dB better than the simpler ''k''=7 code at a cost of 256x in decoding complexity (compared to Voyager mission codes).

===PerforatedPunctured Convolutional Codes===

A ''perforation''"Puncturing" is a technique used to make a ''m/n'' rate code from a "basic" ''1/2'' code. It is reached by deletion of some bits in the decoder output. Bits are deleted according to ''perforationpuncturing matrix''. The following perforationpuncturing matrices are the most frequently used:

{|border=1

| code rate

| perforationpuncturing matrix

| free distance (for NASA standard K=7 convolutional code)

|-

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For example, if we want to make a code with rate 2/3 using the appropriate matrix from the above table, we should take a basic encoder output and transmit every second bit from the first branch and every bit from the second one. The specific order of transmission is defined by the respective communication standard.

The perforatedPunctured convolutional codes are widely used in the [[satellite communications]], for example, in [[INTELSAT]] systems and [[Digital video broadcasting]].

PerforatedPunctured convolutional codes are also called "puncturedperforated".

===Design Issues===