7.2 Downlink shared channel and paging channel

38.2123GPPMultiplexing and channel codingNRRelease 17TS

7.2.1 Transport block CRC attachment

Error detection is provided on each transport block through a Cyclic Redundancy Check (CRC).

The entire transport block is used to calculate the CRC parity bits. Denote the bits in a transport block delivered to layer 1 by, and the parity bits by, where is the payload size and is the number of parity bits. The lowest order information bit is mapped to the most significant bit of the transport block as defined in Clause 6.1.1 of [TS38.321].

The parity bits are computed and attached to the DL-SCH transport block according to Clause 5.1, by setting to 24 bits and using the generator polynomial if ; and by setting to 16 bits and using the generator polynomial otherwise.

The bits after CRC attachment are denoted by , where .

7.2.2 LDPC base graph selection

For initial transmission of a transport block with coding rate indicated by the MCS index according to Clause 5.1.3.1 in [6, TS 38.214] and subsequent re-transmission of the same transport block, each code block of the transport block is encoded with either LDPC base graph 1 or 2 according to the following:

– if , or if and , or if , LDPC base graph 2 is used;

– otherwise, LDPC base graph 1 is used,

where is the payload size in Clause 7.2.1.

7.2.3 Code block segmentation and code block CRC attachment

The bits input to the code block segmentation are denoted by where is the number of bits in the transport block (including CRC).

Code block segmentation and code block CRC attachment are performed according to Clause 5.2.2.

The bits after code block segmentation are denoted by, where is the code block number and is the number of bits for code block number according to Clause 5.2.2.

7.2.4 Channel coding

Code blocks are delivered to the channel coding block. The bits in a code block are denoted by , where is the code block number, and is the number of bits in code block number . The total number of code blocks is denoted by and each code block is individually LDPC encoded according to Clause 5.3.2.

After encoding the bits are denoted by , where the values of is given in Clause 5.3.2.

7.2.5 Rate matching

Coded bits for each code block, denoted as , are delivered to the rate match block, where is the code block number, and is the number of encoded bits in code block number . The total number of code blocks is denoted by and each code block is individually rate matched according to Clause 5.4.2 by setting .

After rate matching, the bits are denoted by, where is the number of rate matched bits for code block number .

7.2.6 Code block concatenation

The input bit sequence for the code block concatenation block are the sequences , for and where is the number of rate matched bits for the -th code block.

Code block concatenation is performed according to Clause 5.5.

The bits after code block concatenation are denoted by, where is the total number of coded bits for transmission.