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PUCCH / UCI
PUCCH is an uplink physical channel that carries UCI (Uplink Control Information). As DCI (Downlink Control Information) is carried by PDCCH, UCI is carried by PUCCH. A big difference between DCI and UCI is that UCI can be carried either by PUCCH or PUSCH depending on situation whereas DCI can be carried only by PDCCH (not by PDSCH in any case).
The contents of UCI is as follows (this is same as LTE). Not all of these are carried by single UCI. Depending on situation, sometimes only CSI is carried, sometimes ACK/NACK only, sometimes SR only and sometimes CSI & ACK/NACK etc.
There are 5 different formats of PUCCH and which one of them is used is determined by how many bits of information should be carried and how many symbols are assigned, as summarized in the following table.
< Based on 38.211 - Table 126.96.36.199-1: PUCCH formats.>
Following is the illustration for the description on 38.213 - 9.2.1 PUCCH Resource Sets
It is possible to enable or disable PUCCH using RRC Parameter PUCCH-frequency-hopping
QPSK or BPSK is used depending on cases as below.
Various types of Channel coding is applied to UCI(Uplink Control Information) depending on the number of bits to be carried.