.7 Channel Coding and Modulation Schemes Channel coding is one of the areas where NR is taking a completely different approach from LTE. In NR, LDPC coding has replaced the turbo coding that was previously used for LTE PDSCH/PUSCH coding and polar codes have replaced the tail biting convolutional codes used previously for LTE PDCCH/PUCCH/PBCH coding, except for very small block lengths where repetition/block coding may be used. Turbo codes generally have a low encoding complexity and high decoding complexity, whereas LDPC codes have more complex encoding and less complex decoding algorithms. Considering eMBB use cases with large code block sizes and the code rates up to 8/9, turbo codes may not meet the implementation complexity required for the decoder. The LDPC codes, on the other hand, have relatively simple and practical decoding algorithms. The decoding is performed by iterative belief propagation (BP). The accuracy of decoding will be improved in each iteration, and the number of iterations is decided based on the requirement of the application, providing a trade-off between the bit error performance, 516 Chapter 4 latency, and complexity. In terms of latency, LDPC codes are parallel in nature, while turbo codes are serial in nature, allowing the LDPC codes to better support low latency applications than turbo codes. Furthermore, the bit error rate (BER) of the turbo codes have higher error floor compared to that of LDPC, and the LDPC matrix can be extended to lower rates than LTE turbo codes, achieving higher coding gains for low-rate applications targeting high reli- ability. As for the polar codes, they were introduced in 2009 and they are among the capacity- achieving codes with low encoding and decoding complexity. They provide full flexibility with very good performance with any code length and code rate without error floor, that is, they do not suffer a decrease in the slope of BLER versus SNR. 4.1.7.1 Principles of Polar Coding In order to describe the polar encoding/decoding concept, let us review 