in the data to ensure proper modulation detection (compared to the case of sending longer periods of a single constellation point only). - The modulation mapper maps the bits for the modulation in use, from 2 up to 8 bits per symbol (from QPSK to 256-QAM). - The layer mapper maps the code words to different layers, with up to 8 layers sup- ported in 5G Release 15. This is equal to the maximum MIMO order supported, while typically the UE will use only two layers, with the exception of the bands around 2.5 to 3.5 GHz, where four layers are supported as the baseline. - Antenna port mapping to map to the antenna ports in use. There may be more antenna ports available than layers used /supported by the UE. Resource block mapping covers mapping to virtual resource blocks and then further mapping to the physical resource blocks (PRBs) for actual transmission. OFDM signal generation creates the actual OFDM signal to be transmitted. The figure does not cover RF parts such as TX filtering, the power amplifier, or the antenna. Note that with the beamforming operation there are often more antennas than actually antenna ports in the baseband operation (Figure 6.19). Figure 6.18 PDSCH channel encoding. Transport Block CRC Attachment Code Block Segmentation and CRC Attachment LDPC Encoding Rate Matching Code Block Concatenation Codewords (up to 8) 6.8 Uplink User Data Transmission Modulation Scrambling Resource Block Mapping Signal mapper Antenna Codewords Layer generation Antenna mapper Modulation mapping ports Scrambling Resource Block Mapping Signal mapper generation Figure 6.19 PDSCH transmitter chain after encoding. 6.8 Uplink User Data Transmission The user data in the uplink direction is transmitted either with OFDM or with DFT-S-OFDMA (single carrier) transmission depending on the link budget situation. The PUSCH carries user data in the uplink direction. The uplink allocation (uplink grant) is received on the PDCCH, which informs the UE how much resources are allocated for the uplink transmission as well as other trans