CRC bits are appended at the end of the information payload. To circumvent higher overheads at smaller payloads, different regions of the payload use different CRC lengths. When the payload is between 12 to 19 bits, 6 CRC Interleaving <NULL> removing Figure 6.51 Distributed CRC polar coding design with nested property. 6 5G Physical Layer bits are appended with three PC bits. Above 19 bits of information payload, 11 CRC bits are appended. For distributed CRC (DL control) and CRC concatenation (UL control) designs, the same procedure is applied at the polar encoder with the selected mother codeword size. At the polar encoder, the concatenated bits are mapped to the most reliable position (from the ranked positions), and the remaining positions are set to zero. This rank- ing order is known as the polar sequence, which is a nested pattern supporting up to a 1024-bits-long polar codeword. Even though the length can be up to 1024 in UL, the maximum supported polar codeword length for DL is 512. The PC and CRC concate- nated polar codes have minor variations in the parity check bit mapping, which uses a specific mapping mechanism considering the structure of the Kronecker matrix and polarization weights. The polar codeword length used for encoding may not always be the maximum mother codeword size that is supported by 5G. The selection of the polar codeword size depends on the information payload size, rate matching output (i.e. available resources for control channel), and minimum threshold code rate (1/8). A predefined method is used when deriving the exact polar codeword length based on these parameters. Unlike many other coding schemes, rate matching in the 5G control channel has sev- eral sub-steps. First, a sub-block interleaving is performed on the output bit stream to arrange the coded bit stream; next, the coded bits are copied to a circular buffer, and finally, the bit selection is performed depending on the code rate supported in the con- trol channel. If the rate matching output length (based on the code r