Based on my interpretation from 3GPP Specification 38.212 Rel 15 (Multiplexing and channel coding), i had put together the procedure on how LDPC Base Graph selection and coding happens.
5G-NR DL-SCH Low Density Parity Code (LDPC) Channel coding
- For transmission of a DL transport block , a transport block CRC is first appended to provide error detection, followed by a LDPC base graph selection.
- NR supports two LDPC base graphs, one for small transport blocks and one for larger transport blocks.
- Then transport block is segmented into code blocks and code block CRC attachment is performed.
- Each code block is individually LDPC encoded. The LDPC coded blocks are then individually rate matched.
- Finally, code block concatenation is performed to create a codeword for transmission on the PDSCH. Up to 2 code words can be transmitted simultaneously on the PDSCH.
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