6, 72, 144, 288} {11, 22, 44, 88, 176, 352} {13, 26, 52, 104, 208} {15, 30, 60, 120, 240} 6 5G Physical Layer Figure 6.48 Use of the base graphs. TB size First, CRC bits are attached to the transport block. This is done separately for smaller TBS and larger TBS. The main motivation for the use of different CRCs is the overhead that can be saved by assuming a shorter CRC length for the smaller TBS. In general, the false alarm rate (FAR) at the receiver side is defined by the length of the CRC attached to the information block. The understanding is that an FAR of 2-4 can be achieved by using an L number of CRC bits. However, unlike the LTE turbo codes, LDPC codes are associ- ated with a parity check mechanism which helps to detect if the code blocks are received without any error or not. In other words, parity check also provides FAR improvements in addition to the CRC bits. This provides a reduction in CRC bits compared to LTE (24 CRC bits). However, the reduction in CRC length is useful only in smaller TBSs where the overhead of CRC is significant. Therefore, 16-bit CRC is used when the TBS is lower than 3824, and 24-bit CRC is used for all other TBSs. After CRC attachment, the input bit sequence can be segmented into more than one code block when certain conditions are satisfied. If the base graph 2 is used, especially when the rate is below 1/4 and the input bit sequence exceeds 3840, the code blocks are segmented assuming 3816 as the maximum code block size (without code block CRC). Otherwise, 8424 is used as the maximum code block size without the code-block-level CRC. In summary, 5G allows two different maximum dimensions for the code block sizes depending on the selection of the base graph. Each code block after the segmenta- tion has a code-block-level CRC of 24 bits (Figure 6.49). After segmentation, the selection of the lifting size to be used in the LDPC encod- ing is decided based on predefined criteria where one value from the set of lifting sizes in Table 6.17 is selected. This lifting value also pro