options. This stage also adds two CRCs: one at TB level and one for each CB. Channel n)Coding-for the shared channel, this is done using LDPC coding. Control signaling is encoded with polar coding. Rate matching-channel coding increases the number of bits transmitted over the wireless channel by 3 X Rate matching is employed to reduce the coding overhead. Interleaving is also implemented in this step. Overall code rate for the channel coding stage is defined as the ratio between useful bits (MAC PDUs or TBs) and total transmitted bit (useful + redundant, post rate matching). This ratio is defined in 3GPP 38.214 using Modulation Coding Scheme (MCS) tables, which pre- define possible coding rate options. Multiple tables are defined, with a complex scheme to determine which table applies. One example is shown for the 256 quadrature amplitude modulation (QAM) table (supporting all code rates up to 256QAM). There are two other tables for systems that only support 64QAM or for low spectral efficiency systems such as URLLC (Table 2-3). In this table, the modulation order Qm defines the number of bits mapped to each IQ car- rier which is defined as 20m or 2 for QPSK, 4 for 16QAM, 6 for 64QAM, and 8 for 256QAM. Selection of the appropriate MCS level is done by the gNB (DU) through the link adaptation algorithm. Typically, these algorithms try to limit the BLock Error Rate (BLER)/HARQ retransmission rate to 10%. Chapter 2 System components, requirements, and interfaces Table 2-3 MCS index table 2 for PDSCH (3GPP 38.214). MCS index MCS Modulation order Qm Target code rate R X [1024] Spectral efficiency 0.2344 0.3770 0.6016 0.8770 1.1758 1.4766 1.6953 1.9141 2.1602 2.4063 2.5703 2.7305 3.0293 3.3223 3.6094 3.9023 4.2129 4.5234 4.8164 5.1152 682.5 5.3320 5.5547 5.8906 6.2266 6.5703 6.9141 916.5 7.1602 7.4063 Physical channel mapping and modulation (3GPP 38.211) The processing steps in 3GPP 38.211 map the coded TBs to physical resources in the fre- quency domain before they are converted to time domain and readied for transmis