ne slot. To support efficient usage of allocated PUCCH resources, CSI content is divided into two parts. The first part of CSI (i.e. rank indicator) has low and fixed payload size to facilitate UCI decoding at gNB without blind decoding. The payload size for the second CSI (i.e. precoding matrix indicator [PMI] is variable and depends on the CSI content transmitted in the first part. Similar to LTE, HARQ-ACK and the first part of the CSI are transmitted on OFDM symbols around DM-RS symbols to provide more reliable transmission, while Figure 3.5.10 PUCCH resource sets. PUCCH resource sets (e.g., selection based on UCI size) PUCCH resources (e.g. selection based on PRI) 3 5G System Overview the remaining resource elements are allocated for the transmission of the second CSI part. To facilitate early decoding of the UCI, mapping of UCI to PUCCH resources is performed in a frequency-first and time-second manner. 3.5.7 Reference Signals In LTE, most of the downlink transmission schemes are based on the always available downlink CRS, which are transmitted by evolved Node B (eNB) irrespective of the actual data traffic. Such an approach for the reference signal transmission has several drawbacks including high overheads, low energy efficiency at the base station, and excessive inter-cell interference. Unlike LTE, NR was designed to support more efficient resource usage and therefore the reference signals are transmitted only when needed. This design enables lower overheads, greater base station power savings, and reduced levels of inter-cell interference. The time and frequency positions of the reference signals in NR are also configurable, which is in contrast to the CRS design in LTE, which only allows for wideband CRS transmission at predetermined positions. The following types of reference signals are supported in NR (3GPP TS 38.211): CSI-RS: for CSI acquisition, beam management, and reporting. DM-RS: reference signals that are UE-specific and designed in the same way for data and control channels; DM-RS transmissio