Physical Uplink Control Channel (PUCCH) :

Similar to LTE, 5G NR PUCCH carriers the Uplink Control Information (UCI) in uplink.

Based on the PUCCH duration and the Payload size, 5G NR defines 5 PUCCH formats, as shown below.

PUCCH format	Length in OFDM symbols	Number of bits
0	1 – 2	≤2
1	4 – 14	≤2
2	1 – 2	>2
3	4 – 14	>2
4	4 – 14	>2

*Short PUCCH format of more than 2 UCI bits frequency multiplex UCI and DMRS

* Long PUCCH formats time multiplex UCI and DMRS

If Intra-slot frequency hopping is configured for PUCCH formats 1,3 or 4, the number of symbols in the first hop is given as |_ PUCCH OFDM symbols/2_|    (Floor of).

UCI can be multiplexed in PUSCH when both UCI and PUSCH transmissions coincide in time. Multiplexing can be done in two ways.

1. Puncturing 

2. Rate Matching

An UCI with 1 or 2 bit HARQ ACK feedback multiplexed by puncturing PUSCH. In rest of the cases multiplexing done by Rate Matching PUSCH.

UCI carries ;

1. CSI (Channel State Information like CQI, PMI, RI, CSI-RS ..etc)

2. ACK-NACK

3. SR (Scheduling Request)

* Transform Precoding is applied to long PUCCH.

Some Important collision cases :

1. If an UE having a PUSCH transmission that overlaps with a PUCCH which includes positive SR, 

    then UE should drop PUSCH.

2. If the UE transmitting PUCCH with CSI reporting with overlapping PUSCH, then UE should multiplex PUSCH with CSI reporting.

3. UE should not multiplex PUSCH transmission with UCI when the SCS of PUSCH is less than SCS of PUCCH.

4. UE should not detect the DL DCI for PDSCH reception or SPS release and indicating PUCCH resource to transmit HARQ-ACK in a slot if the UE already detected a DCI format scheduling PUSCH with HARQ-ACK multiplexing.

5. If an UE multiplex Aperiodic CQI in a PUSCH, and if there is a collision with PUCCH carrying UCI with HARQ-ACK, then UE should multiplex HARQ-ACK with PUSCH and drop PUCCH.

6. UE having multiple PUSCHs configured in a slot on serving cells, the first PUSCH scheduled by DCI 0_0 or DCI 1_0 and the second configured by UL SPS , UE should multiplex UCI on first PUSCH (not on SPS PUSCH).

7. When the UE have multiple PUSCHs in a slot on respective serving cells, UCI is multiplexed in one of the multiple PUSCHs (Aperiodic CQI not multiplexed in any of PUSCHs), the UE should multiplex the UCI in a PUSCH of the serving cell with smallest ServCellIndex (PCELL).

8. If the UE transmits more than one PUSCHs in the slot on the serving cell with smallest ServCellIndex , the UE should multiplex the UCI in the earliest PUSCH that UE transmits in the slot.

9. The DAI field value remain unchanged irrespective of HAR-ACK multiplexing in any PUSCH transmission when the transmission is scheduled by DCI 1_0.