achine Type Communications (mMTC) and Ultra-Reliable Low Latency Communications (URLLC) are not part of Release 15's scope. So, let's start. Transport channel coding chains The following figure represents the basic coding scheme for the downlink shared channel. The diagram is very similar to what we have in LTE. A CRC is attached to the transport block, it is segmented onto the code blocks, and then, additional CRSes are attached to each code block: Channel coding schemes TrBlk Transport Block TrBlk Code-Block Segmentation Code-Block Code-Block CRC Code-Block LDPC Channel Coding Coded Bits Rate Matching Rate Matched Bits Interleaver Interleaved Bits Code-Block Concatenation Concatenated Bits Figure 6.14 - Transport channel coding for the downlink shared channel Then, LDPC coding is performed for each code block and the last steps are rate matching, interleaving, and concatenating those code blocks. UL-SCH Transport Block Code-Block LDPC Channel Code-Block CRC Segmentation Coding Code-Block Rate Matching Interleaver Concatenation Data and Control Multiplexing Channel Coding Figure 6.15 - Transport channel coding for an uplink shared channel 5G Air Interface and Physical Layer Procedures - Part 3 The same applies to the uplink with the exception that UCI can be piggybacked on the PUSCH as was the case in LTE. In that case, there is an extra Data and Control Multiplexing operation as shown in the figure here. Data retransmissions Now that we understand the transport channel coding chains in NR, let's compare LTE and NR regarding transport block retransmissions. Code Block Group (CBG)-based retransmissions One of the main differences between data retransmissions in NR and LTE is the addition of CBG-based retransmissions to NR. In NR, it is possible to only retransmit the code blocks that failed at the decoding stage, rather than the entire transport block. This saves resources during retransmission and improves latency since the processing time of the older retransmissions will be shorter because only a few of the or