ion and is well discussed in the literature. When the information block length increases, the codeword tends to have two different regions, one error free and the other with zero capacity. In such cases, the error-free part can be used for data transmission, and the other region can be predefined to a known value, which is also called frozen bits. In polar encoding, the bit positions are carefully treated as they may belong to one of these two categories depending on the reliability levels of each bit position. In 5G polar codes, each bit posi- tion has a reliability ranking where higher-reliability bits are used to map the information bits, and the rest are set to zero. Also, the construction of polar coding makes the code always operate with powers of two as the output bits. Due to this, polar encoding and decoding always assumes a mother polar codeword size, which is always a power of two. For example, 512 is the maximum mother codeword size in 5G DL control channels, and 1024 is the maximum mother codeword size in 5G UL control channels. Even though these sizes are used in the encoding or decoding, the actual transmissions often require rate matching, and polar coding has good rate matching schemes that can be still applied without loss of significant performance. 6.13.2.1 5G Polar Coding Design There are three different types of polar coding designs in 5G due to the different require- ments identified in 3GPP for DL and UL control channels and for performance in regions with different block sizes. These designs are as follows: DL control: Distributed CRC polar code. UL Control: Parity check (PC) and CRC concatenated polar code: 12-19 bits of UCI CRC concatenated polar code: Above 19 bits of UCI 6.13 Channel Coding with 5G In summary, all these designs are not state-of-art polar coding schemes defined in academia. 5G control channel coding schemes are concatenated codes which use polar coding with CRC and/or PC bits, and these provide much better performance compared to traditional polar coding designs. In DL