5G FACT_Code Block & Code Block Group in NR_009 " TLW knowledge bullet "
" TLW Knowledge Bullet "
Some basic Information on Code Block & Code Block Group in NR:
A new feature of the NR HARQ protocol is the possibility for retransmission of code block groups, which is useful for very large transport blocks or when a transport block is partially pre empted by another transmission.
As part of the channel coding operation in the physical layer, a transport block is split into one or more code blocks with channel coding applied to each of the code blocks of up to 8448 bits in order to maintain a reasonable complexity.
In practice and in the presence of burst errors, only a few code blocks in the transport block may be corrupted and the majority of code blocks are correctly received.
In order to correctly deliver the transport blocks to the destination MAC sublayer,it is sufficient to only retransmit the erroneous code blocks.
Also, to avoid the excessive control signaling overhead due to individual code block addressing by HARQ mechanism, code block groups have been defined.
If per-CBG retransmission is configured, feedback is provided per-CBG and only the erroneously received code block groups are retransmitted.
The CBG-based retransmissions are transparent to the MAC sublayer and are handled in the physical layer.
From MAC sublayer perspective, the transport block is not correctly received until all CBGs are correctly received.
It is not possible to mix the CBGs belonging to another transport block with retransmissions of CBGs belonging to the incorrectly received TB in the same HARQ Process.
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