Sunday, January 9, 2011

What's the Turbo-code ?


       Turbo coding is a forward error correction (FEC) scheme. Iterative decoding is the key feature of turbo codes. Turbo codes consist of concatenation of two convolution codes. Turbo codes give better performance at low signal to noise ratio (SNR). 

       Interestingly, the name Turbo was given to this codes because of the cyclic feedback mechanism (as in Turbo machines) to the decoders in an iterative manner.The turbo encoder transmits the encoded bits which form inputs to the turbo decoder. The turbo decoder decodes the information iteratively. Turbo codes can be concatenated in series, parallel or in a hybrid manner. Concatenated codes can be classified as parallel concatenated convolutional codes (PCCC) or serial concatenated convolutional codes (SCCC). 

       In PCCC two encoders operate on the same information bits. In SCCC, one encoder encodes the output of another encoder. The hybrid concatenation scheme consists of the combination of both parallel and serial concatenated convolutional codes. The turbo decoder has two decoders that perform iterative decoding. 

we will speak about Encoder next post then Decoder

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