Concatenated Codes and Iterative Decoding

This chapter starts by giving the principles of soft input soft output decoding including the sum-product and forward-backward algorithm for convolutional codes. Next, it describes the low density parity check (LDPC) codes, their encoders and their iterative decoders for erasure channel, binary symmetric channel and additive white Gaussian noise channel. Then, the chapter discusses parallel concatenated convolutional codes or turbo codes and the structure of the associated iterative decoder. It also explains other classes of concatenated codes such as the parallel concatenated block codes (PCBCs), repeat-accumulate (RA) codes, product codes and serial concatenation of convolutional codes. Finally, the chapter gives exercises of soft input soft output decoding of a two-state convolutional code, and soft input soft output decoding of a linear block code for the reader.