5G NR PUCCH: Function, Contents, and Physical Layer

This page delves into the 5G NR PUCCH (Physical Uplink Control Channel), covering its function, contents, mapping, and physical layer processing. 5G NR wireless systems support various channels, including:

• Downlink channels: PDSCH (DL shared channel), PBCH (Broadcast channel), PDCCH (DL control channel)
• Uplink channels: PRACH (Random Access Channel), PUSCH (UL shared channel), PUCCH (UL control channel)

5G NR PUCCH Function, Contents, and Mapping

Here’s a look at the function, contents, and mapping of the 5G NR PUCCH:

• The PUCCH channel is used to transport UCI (Uplink Control Information) e.g. HARQ feedback, CSI (Channel State Information), and SR (Scheduling Request).
• 5G NR PUCCH offers flexibility in both the time and frequency domains.
• The PUCCH channel employs five different PUCCH formats.
• PUCCH formats 0 and 2 occupy 1 or 2 OFDM symbols, classifying them as short PUCCH.
• PUCCH formats 1, 3, and 4 occupy 4 to 14 OFDM symbols, categorizing them as long PUCCH.
• PUCCH formats 0 and 1 carry UCI payloads containing 1 or 2 bits.
• The remaining PUCCH formats handle UCI payloads exceeding 2 bits.

PUCCH Format Details

• In PUCCH formats 1/3/4, symbols incorporating DMRS (Demodulation Reference Signal) are time-multiplexed with UCI symbols to minimize PAPR (Peak-to-Average Power Ratio).
• In PUCCH format 2, DMRS is frequency-multiplexed with data subcarriers.
• Multi-user multiplexing on the same time/frequency resources is supported for PUCCH formats 0/1/4 only, achieved through unique cyclic shifts.
• UE (User Equipment) can also be configured for CSI reporting or SR using PUCCH resources.
• For the transmission of UCI + (HARQ-ACK), 4 PUCCH resource sets are used based on UCI size. The first set is used for a maximum of 2 HARQ-ACK bits (i.e., max. 32 PUCCH resources). The other sets are used for 2 bits of UCI (i.e., max. 8 PUCCH resources).
• The 5G NR UE determines the set based on UCI size and also indicates the PUCCH resource within the set based on the DCI’s 3-bit field.

5G NR PUCCH Physical Layer Processing

Here’s a look at the physical layer processing of the 5G NR PUCCH:

The physical layer processing for PUSCH is shown in the figure-1.
The PUCCH channel follows the same modules with modifications as described in the 3GPP TS 38.211, 38.212, 38.213 and 38.214 specifications.