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In some cases a parity bit is encoded by a second constituent code (serial concatenation), but more typically all or most of the constituent encoding for the LDPC is done in parallel.
In an example using the DVB-S2 rate 2/3 code the encoded block size is 64800 symbols (N=64800) with 42300 data bits (K=43200) and 21600 parity bits ( M=21600). Each constituent code (check node) encodes 16 data bits except for the first party bit which encodes 8 data bits. The first 4680 data bits are repeated 13 times (used in 13 parity codes), while the remaining data bits are used in 3 parity codes (irregular LDPC code).
To compare, classic turbo codes typically use two convolutional codes of moderate depth (v=3 or 4) configured in parallel, each of which encodes the entire input block (K) of data bits. These constituent encoders are combined with a code interleaver which interleaves one copy of the frame to generate the parity symbols.
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