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Code Block concept in LTE Physical layer(L1)

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Transport block is divided into smaller size code blocks in LTE, which is referred as code block segmentation before being applied to the channel coding/Rate matching modules in the LTE physical layer.

Code Block segmentation

In LTE there are two sizes defined for code block i.e. minimum and maximum code block size. These block sizes are based on block sizes as supported by the turbo interleaver module of CTC Encoder. They are as follows:

•  40 bits of min. code block size
•  6144 bits of max. code block size

If input transport block length is greater than the maximum code block size as supported by encoder then the input block is segmented into the one supported. This segmented block is referred as code blocks.

Each of these code blocks has a 24 bit CRC attached. This CRC is calculated similar to Transport Block CRC calculation. Filler bits are appended at the start of segment, this helps code block size to match a set of valid turbo interleaver block sizes.

In the case when no segmentation is needed only 1 code block is generated. In the case when input block( B ) is less than min. size, filler bits as zeros are added to the beginning of the code block to get complete set of 40 bits.

Code Block Concatenation

At this point, rate matched outputted code blocks are concatenated back together.

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