Recursive and Non-recursive Codes
The encoder on the picture above is a non-recursive encoder. Here's an example of a recursive one:
One can see that the input being encoded is included in the output sequence too (look at the output 2). Such codes are referred to as systematic; otherwise the code is called non-systematic.
Recursive codes are almost always systematic and, conversely, non-recursive codes are non-systematic. It isn't a strict requirement, but a common practice.
Read more about this topic: Convolutional Code
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“We must trust infinitely to the beneficent necessity which shines through all laws. Human nature expresses itself in them as characteristically as in statues, or songs, or railroads, and an abstract of the codes of nations would be an abstract of the common conscience.”
—Ralph Waldo Emerson (1803–1882)