Resource Element Resource Element Mapper Mapper OFDM Signal OFDM Signal Generation Generation Figure 6.9 - PUSCH processing chain for the CP-OFDM In the downlink, this is not a problem. The gNB has total freedom in defining the precoders and then coordinating them accordingly. However, if freedom was given to the devices in the uplink, that would be impossible. To make uplink transmissions from different devices, we use precoders that enable MU-MIMO. The precoder that a device uses must be explicitly indicated: Uplink physical channels and signals codewords Scrambling Modulation Mapper Layer Mapper layers Transform Transform Precoding Precoding Precoding antenna ports Resource Element Resource Element Mapper Mapper OFDM Signal OFDM Signal Generation Generation Figure 6.10 - PUSCH - processing chain for the DFT-s-OFDM The figure here shows the same coding chain for the DFT-s-OFDM. The transform precoder is inserted between the layer mapper and the precoding. Notice that only one codeword is used in this case. Now that we have covered the PUSCH, PUSCH DMRS, and the processing chain for different OFDM schemes in the uplink, the last physical channel we are going to cover in the uplink is the PUCCH. The PUCCH The PUCCH carries UCI, HARQ feedback, and SR. Two different PUCCHs are defined; long and short. The long PUCCH spans over many OFDM symbols while the short PUCCH uses only one or two OFDM symbols. 5G Air Interface and Physical Layer Procedures - Part 3 PUCCH Format Length in OFDM Symbols Number of Bits 0 (SHORT) 1 (LONG) 2 (SHORT) 3 (LONG) > 2, < N 4 (LONG) In the table presented here, you can see different PUCCH formats divided between long and short PUCCH formats and classified as a function of the supported number of information bits. The short PUCCH Format 0 for the PUCCH is a short PUCCH for up to two information bits. This PUCCH is based on sequence selection, which means that the bits are not modulated in the signal. Instead, four different 12 subcarrier sequences are defined and the sequence that is used