1.1 General Code Types
The most important coding schemes that can be decoded using an iterative (turbo) algorithm can be classified as parallel concatenated codes, serial concatenated codes and low-density parity check (LDPC) codes as indicated in Figure 1.1.
In parallel concatenated codes, the data sequence is encoded by the first constituent encoder. The second constituent encoder encodes an interleaved version of the data sequence. The data bits are sent only once as systematic bits of the concatenated code, whereas only the parity bits of the constituent encoders are transmitted. Usually, recursive systematic convolutional codes are used as constituent codes. However, other code types, for example block codes, can be used and more than two constituent codes can be concatenated with different interleavers. Parallel concatenated convolutional codes (PCCC) ...