ss channels. The bit interleaver in 5G channel coding is quite similar to the LTE bit interleaver. In principle, both have block inter- leavers, and the writing is row-wise left to right, whereas reading is from column-wise top to bottom. One difference is that in 5G the number of rows in the block interleaver 1st Transmission 2nd Transmission 3rd Transmission 4th Transmission Figure 6.50 Circular buffer rate matching in 5G. 6 5G Physical Layer is defined by the modulation order used for the transmission. The 5G block interleaver with dimensions defined by the modulation order is called the systematic bit priority ordering interleaver for RV0, where systematic bits of the coded block get somewhat higher reliability compared to parity bits as they are mapped to the most significant bits in the modulation mapping. After the rate matcher, the bits of each coded block are concatenated together, and output is sent to the next level of the physical layer processing. 6.13.2 Channel Coding for Control Channels In 5G, polar coding is adopted as the main coding scheme for both DL and UL control channels except for the very small block lengths. For the very short block sizes, the same codes used by LTE are adopted, which are repetition for 1 bit, simplex codes for 2 bits, and Reed-Muller codes for 3-11 payload bits. The polar code is a relatively new channel coding scheme compared to other codes like LDPC and Turbo, and shows good performance especially when the code block sizes are smaller. The better performance is obtained with code concatenation with CRC and also with the help of successful cancelation list decoders. At least from the algorithm com- plexity point of view, polar codes also showed a lower number such as O(L * N * log (N)), where N is the encoded block length, and L is the list size. These features made polar codes more suitable for control channels and led them to be adopted as the main coding scheme in both downlink and uplink control. The concept of channel polarization is used in polar coding construct