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LTE PUCCH-Physical Uplink Control Channel

This page describes LTE PUCCH channel or Physical Uplink Control Channel with respect to LTE system.

This LTE channel is used to carry UCI(Uplink Control Information). UCI can also be transported using PUSCH channel. An LTE UE can never transmits both PUCCH and PUSCH during the same subframe.

• If UE has application data OR RRC signalling then UCI is carried over PUSCH
• If UE does not have any application data OR RRC signalling then UCI is carried over PUCCH

This is a stand-alone uplink physical channel. This PUCCH control signaling channel comprises following:

•  HARQ ACK/NACK
•  CQI-channel quality indicators
•  MIMO feedback - RI(Rank Indicator),PMI(Precoding Matrix Indicator)
•  scheduling requests for uplink transmission
•  BPSK or QPSK used for PUCCH modulation

LTE PUCCH channel

PUCCH consists of 1 RB/transmission at one end of the system bandwidth which is followed by another RB in the following slot(at opposite end of the channel spectrum). This makes use of frequency diversity with 2dB estimated gain. A PUCCH Control Region comprises every two such RBs.


System BW in MHz 1.25 2.5 5 10 15 20
PUSCCH Control region 1 2 4 8 12 16
No.of resource blocks 2 4 8 16 24 32

The standard specifies 6 LTE PUCCH formats as mentioned in the table-2 below. As mentioned PUCCH format 2a and 2b are not applicable for extended CP.


LTE PUCCH
Format
Modulation
Index
No. of bits
per subframe
No. of REs
occupied(Normal CP)
No. of REs
occupied(Extended CP)
1 - - 48+48=96 OR 48+36=84
1a BPSK 1 48+48=96 OR 48+36=84
1b QPSK 2 48+48=96 OR 48+36=84
2 QPSK 20 120
2a QPSK+BPSK 21 120 Not Applicable
2b QPSK+QPSK 22 120 Not Applicable
Table-2 LTE PUCCH Formats

LTE PUCCH
Format
No. of bits
per subframe
Normal CP Extended CP
1 - Scheduling Request
1a 1 1 x HARQ-ACK OR 1 x HARQ-ACK +SR
1b 2 2 x HARQ-ACK OR 2 x HARQ-ACK +SR
2 20 CQI CQI OR HARQ-ACK+CQI
2a 21 1 x HARQ-ACK + CQI -
2b 22 2 x HARQ-ACK + CQI -
Table-3 Information carried by each PUCCH format

The LTE PUCCH channel is allocated 2 RBs at the edges of channel BW. Each PUCCH transmission occupy 1 RB on each side of the channel bandwidth. These two RBs are distributed across two time slots. RB numbering for PUCCH starts on outside edges and increases inwards.

PUCCH is allocated RBs at the edge of channel BW to avoid fragmenting RBs available to PUSCH.

LTE PUCCH Channel Reference: 3GPP TS 36.211

LTE RELATED LINKS

Difference between SC-FDMA and OFDMA
LTE Cyclic Delay Diversity
LTE eNodeB Physical Layer Measurements
LTE EPC Network Inerfaces
LTE UE Physical Layer Measurements
LTE Bearer types
LTE UE Event Measurement Reporting
LTE RSRP vs RSRQ
LTE Signalling radio bearers
LTE QoS
LTE EPS mobility management states
LTE EPS connection management states
LTE UE cell selection
LTE UE PLMN selection
LTE UE Paging Procedure

RF and Wireless Terminologies


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