As in LTE, in NR as well a huge TB (Transport Block) is split into multiple CBs (Code Block). However, there is a concept that is not in LTE. It is CBG. NR group a multipes of CBs into a CBG and NR can indicate ACK/NACK and retransmit the data in the unit of CBG. CBG is indicated in DCI (Format 0_1, Format 1_1)

Typical structure of TB is illustrated as above. One TB is usually made up of multiple CBG and one CBG is usually made up of multiple CB. But there is possibility of seeing some extreme types as shown below.

In the example shown below, one TB is made up of only one CBG which is made up of multiple CBs.

In following example, you see one TB which is made up of multiple CBG and one CBG is made up of only one CB.

In rare case, you may see a TB made up of CBG as follows. In this case, one TB is made up of one CBG and the CBG is made up of only one CB.

RRC Parameters

PDSCH-ServingCellConfig ::= SEQUENCE {

   codeBlockGroupTransmission        SetupRelease { PDSCH-CodeBlockGroupTransmission } OPTIONAL,

   xOverhead                         ENUMERATED { xOh6, xOh12, xOh18 } OPTIONAL, -- Need S

   nrofHARQ-ProcessesForPDSCH        ENUMERATED {n2, n4, n6, n10, n12, n16} OPTIONAL, -- Need S

   pucch-Cell                        ServCellIndex OPTIONAL , -- Cond

   SCellAddOnly

   ...

}

PDSCH-CodeBlockGroupTransmission ::= SEQUENCE {

    maxCodeBlockGroupsPerTransportBlock        ENUMERATED {n2, n4, n6, n8},

    codeBlockGroupFlushIndicator               BOOLEAN,

    ...

}

Reference

[1]  5G NR - A New Era for Enhanced Mobile Broadband (Mediatek)