5G NR UCI | Uplink Control Information (UCI) in 5G NR

This page describes 5G NR UCI (Uplink Control Information). It mentions PUCCH formats used to carry various UCI payload sizes in 5G NR uplink.

Introduction:
UCI (Uplink Control Information) is carried by PUCCH channel in 5G NR. UCI consists of HARQ (Hybrid Automatic Repeat Request) feedback, CSI (Channel State Information) and SR (Scheduling Request).

5G NR PUCCH

Refer 5G NR PUCCH >> for more information. There are two types of PUCCH viz. short and long. Various PUCCH formats are mentioned in the following table.

PUCCH Format Length of OFDM symbols Number of Bits
0 (Short) 1-2 <=2
1 (Long) 4 to 14 <=2
2 (Short) 1 to 2 >2
3 (Long) 4 to 14 >2, <N
4 (long) 4 to 14 >N

• 5G NR PUCCH is flexible in time domain and frequency domain.
• The PUCCH channel utilizes five PUCCH formats.
• PUCCH format 0 and 2 occupies 1 or 2 OFDM symbols. It is known as short PUCCH.
• PUCCH format 1, 3 and 4 occupies 4 to 14 OFDM symbols. It is known as long PUCCH.
• PUCCH format 0 and 1 carry UCI payloads having 1 or 2 bits.
• Other PUCCH formats carry UCI payloads having more than 2 bits.
• In PUCCH formats 1, 3 and 4 symbols with DMRS are time division multiplexed with UCI symbols to achieve low PAPR while in PUCCH format 2, DMRS is frequency multiplexed with data subcarriers.

A UE can be configured with PUCCH resources for CSI reporting or SR. For UCI transmission including HARQ-ACK bits, a UE may be configured with up to 4 PUCCH resource sets based on the UCI size. The first set can only be used for a maximum of 2 HARQ-ACK bits (with a maximum of 32 PUCCH resources) and other sets are applicable for more than 2 bits of UCI (each with a maximum of 8 PUCCH resources).

A UE determines the set based on the UCI size. It indicates a PUCCH resource in the set based on a 3-bit field in DCI.

PUCCH format-0 (<=2 bits)

PUCCH Format-0

• PUCCH is based on sequence selection with low PAPR.
• Sequence length is 12 REs.
• Information is delivered by transmitting different sequences/codes.
• It can transmit HARQ-ACK and SR.

Equation-1

PUCCH format-1 (<=2 bits)

PUCCH format-1

• DMRS always occur in every other symbol in the long PUCCH.
• BPSK and QPSK modulations
• Sequence length is 12 REs
• Modulated symbol is spread with a zadoff-chu sequence with OCC in the time domain.

Equation-2

PUCCH format-2 (> 2 bits)

PUCCH format-2

• DMRS is mapped on REs {1,4,7,10} for each PRB.
• DMRS sequence is based on PUSCH
• Contiguous PRB allocation

• PUCCH format-3 (>2 bits, <N bits)
• PUCCH format-4 (>N bits)


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