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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