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T L W
K N O W L E D G E
B U L L E T
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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.
https://youtu.be/lP074B-ofyE
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Techlteworld
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