ssible. The logic of non-codebook-based UL transmission is to exploit channel reciprocity more. The following steps are performed: The UE estimates the channel based on CSI-RS, and determines a precoder. The UE transmits one or multiple SRSs, which are precoded with the precoder obtained during the previous step. The gNB selects the best-received SRS and indicates this to the UE, based on the SRI. Further PUSCH transmission occurs based on the indicated SRI (Figure 6.45). Channel Coding with 5G Channel coding is one of the main hardware critical components in 5G, and codes used in 5G are capable of providing good performance gains with a lower implementation 6 5G Physical Layer gNB transmitter CSI-RS DL channel estimation gNB transmitter SRS resource 1 SRS resource 2 UL precoded sounding SRS resource 3 SRS resource 4 SRI, rank Figure 6.45 Non-codebook-based UL transmission procedure. complexity and processing delays compared to its predecessors. In 3GPP Rel-15, different service scenarios were considered in the initial phase of the channel coding discussion; however, the final selection of the channel coding scheme was mainly decided based on the eMBB requirements, which were identified as perfor- mance of the coding scheme, implementation complexity, the latency of encoding and decoding, and the flexibility (e.g. variable code length, code rate, HARQ) of the coding scheme. The coding schemes were separately discussed for the data channel and control channel considering differences in the supported block sizes and code rates. As a result, for the first time in 3GPP, data channels use LDPC codes, and for the first time in any standard, the control channel design is based on polar coding. 6.13.1 Channel Coding for Data Channel LDPC is a very mature coding scheme which has been considered by many other stan- dards. The flexibility that the coding scheme provided in implementations together with competitive performance can be identified as one of the key advantages that LDPC pos- sesses when compared to all other cod