UNB ECE4253 Digital Communications
Department of Electrical and Computer Engineering - University of New Brunswick, Fredericton, NB, Canada

Convolutional Coder (R=2/3, K=3)

This online tool passes data through this convolutional coder.


For every pair of input bits (C,E) there are three output bits (X,Y,Z), defining a rate two-thirds (R=2/3) encoder. Because output symbols (XYZ) are computed across a history of three bits (the longest shift register being (C-B-A)) this coder has a constraint length K=3. Polynomials can be used to define the XOR connections.

Trellis Diagram

The 3-bit states in the trellis diagram are now the shift registers states as (DBA).

The input bit stream is fed into the circuit as 2-bit pairs (EC) and the 3-bit output symbols (XYZ) are shown as in the circuit diagram.

Input Bits (EC)
trellis
Output Symbols (XYZ)

The initial state (DBA) of the flip flops is assumed to be 000. Three zero dibits are appended to the incoming data to flush the circuit and return to the 000 state at the end.

Input Bits:
Discussion | MATLAB

Try this same data with different encoders:

R=1/2, K=3R=1/2, K=4R=1/3, K=4

2024-05-05 19:29:08 ADT
Last Updated: 2015-02-25 		Richard Tervo [ tervo@unb.ca ] Back to the course homepage...