Description
The Physical Uplink Control Channel (PUCCH) is a fundamental physical layer channel in both LTE (from Release 8) and NR (5G) radio access networks. It is dedicated to transmitting uplink control information (UCI) from the User Equipment (UE) to the gNB (in NR) or eNB (in LTE). Unlike the PUSCH (Physical Uplink Shared Channel), which carries user data, the PUCCH is specifically designed for signaling that is vital for maintaining the radio link, supporting feedback mechanisms, and enabling efficient dynamic scheduling.
The PUCCH occupies specific resource blocks at the edges of the system bandwidth in LTE, while in NR its location is more flexible and configurable within the bandwidth part. It uses specific formats (PUCCH formats 0-4 in NR, formats 1-5 in LTE) optimized for different payload sizes and reliability requirements. These formats employ different modulation schemes, ranging from simple On-Off Keying for 1-bit ACK/NACK to π/2-BPSK or QPSK for larger CSI reports. The channel coding varies by format, with some using block-based codes and others using Reed-Muller or Polar codes (in NR) for error protection.
The primary types of UCI carried on the PUCCH are: Hybrid Automatic Repeat Request Acknowledgement (HARQ ACK/NACK) for downlink transport blocks, which is crucial for retransmission protocols; Channel State Information (CSI), including Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), and Rank Indicator (RI), which guides downlink scheduling and MIMO configuration; and Scheduling Requests (SR), which the UE uses to indicate it has data to send and requires uplink resources. The PUCCH is a scheduled channel, but its resources are semi-statically configured via RRC signaling, with dynamic indication for certain formats. Its design involves a trade-off between control overhead, coverage, capacity, and latency, leading to multiple formats tailored for different deployment scenarios and UE capabilities.
Purpose & Motivation
The PUCCH was created to provide a reliable and efficient mechanism for transmitting essential control signaling from the UE to the network in OFDMA-based systems like LTE and NR. Its introduction with LTE Release 8 was motivated by the need for a channel separate from user data to carry time-critical feedback. This solves several key problems: it enables fast HARQ ACK/NACK feedback for downlink packets, which is fundamental to achieving high throughput with low latency; it provides the network with timely CSI to perform channel-dependent scheduling and adaptive modulation and coding, maximizing spectral efficiency; and it gives the UE a means to request uplink resources without needing dedicated scheduled resources beforehand, improving uplink latency for sporadic traffic.
Before dedicated control channels like PUCCH, systems used more integrated or less efficient methods for control signaling. The PUCCH's dedicated design allows for optimized transmission characteristics (power, coding) independent of user data traffic. This separation ensures that critical link maintenance information is transmitted reliably even when the UE has no uplink data to send on the shared channel. It is a cornerstone of the dynamic, feedback-driven operation that defines modern cellular systems, enabling advanced features like carrier aggregation, massive MIMO, and ultra-reliable low-latency communication (URLLC) by providing the necessary low-latency control plane link.
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (62 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, enhancements were introduced for the PUCCH function, including corrections and clarifications to its configuration and operation. Specific changes addressed PUCCH resource set configuration, power control for formats 4 and 5, and deactivation procedures for SCells. The release also defined spatial bundling for PUCCH format 3 with carrier aggregation and provided updates for NR-DC (New Radio Dual Connectivity) and LAA SCells.
- CR for PUCCH Format 1 TS 38.211CR0005
- CR on PUCCH format 1 TS 38.211CR0010
- Correction to last PUCCH resource set configuration TS 38.213CR0019
- CR on the determination of the minimum number of PRBs for PUCCH transmission TS 38.213CR0036
- CR to 38.213 on PUCCH configuration for NR-DC TS 38.213CR0060
- Correction on PUCCH power control TS 38.213CR0061
+ 6 more changes
In Release 16, key enhancements for PUCCH included the introduction of sub-slot based transmissions with specific configurations like `subslotLengthForPUCCH-r16`, along with improved handling for repetitions and overlapping transmissions with different priorities. The release also provided clarifications and corrections for procedures such as HARQ-ACK codebook generation for secondary PUCCH groups, UCI multiplexing with overriding rules, and power control for enhanced codebooks. Furthermore, it addressed timing and collision handling for scenarios including secondary cell activation/deactivation and transmissions overlapping with semi-static downlink symbols or SSBs.
- Correction for PUCCH repetition transmission TS 38.213CR0120
- 38.213 CR Correction on HARQ-ACK codebook for secondary PUCCH group TS 38.213CR0167
- CR on handling overlapping PUCCH/PUSCH transmissions with repetitions and with different priorities TS 38.213CR0178
- Correction on UCI multiplexing with PUCCH overriding TS 38.213CR0183
- CR on Timing for secondary cell activation / deactivation with sub-slot PUCCH TS 38.213CR0197
- Correction on PUCCH resource determination in clause 9.2.1 in TS 38.213 TS 38.213CR0206
+ 12 more changes
In Release 17, key enhancements to PUCCH focused on improving reliability and resource management for new services. This included specific corrections and clarifications for PUCCH resource determination and transmission procedures for multicast HARQ-ACK, SPS configurations, and scenarios involving multiplexing with NACK-only feedback, CSI, and SR. The release also introduced refinements for operations in Non-Terrestrial Networks (IoT NTN), simultaneous transmission with other channels like PRACH and PUSCH, and power control for PUCCH in the FR2-2 frequency range.
- IoT NTN RRC Correction on PUCCH TX duration TS 36.331CR4936
- CR on the clarification of PUCCH resource determination in 38.213 TS 38.213CR0339
- Correction for HARQ-ACK codebook generation for PUCCH cell switching and UL BWP switching TS 38.213CR0347
- Correction of CSI assumptions over multiplexing NCJT CSI reports in PUCCH TS 38.213CR0354
- CR on spatial domain filter for sensing for PUCCH transmission in FR2-2 TS 38.213CR0371
- CR on power control for PUCCH TS 38.213CR0385
+ 18 more changes
In Release 18, the PUCCH enhancements addressed operational refinements and new use cases. Specific updates included clarifications for PUCCH power determination and control, support for multicast HARQ-ACK, and refined handling for simultaneous PUCCH and PUSCH transmission of the same priority, particularly in uplink carrier aggregation and inter-band scenarios. The release also introduced corrections for PUCCH repetition in RedCap UEs and for transmission cancellations due to aperiodic SRS.
- Correction on PUCCH power determination for Type-2 HARQ-ACK codebook TS 38.213CR0524
- CR on PUCCH resources for multicast HARQ-ACK TS 38.213CR0528
- Correction on PUCCH power control parameter determination TS 38.213CR0539
- CR on default pathloss reference signal for SRS and PUCCH TS 38.213CR0548
- CR on Simultaneous PUCCH and PUSCH transmission with same priority in UL CA TS 38.213CR0557
- Correction of PUCCH repetition for RedCap UE with NCD-SSB in TDD TS 38.213CR0566
+ 2 more changes
Explore further
Broader topics and technologies where PUCCH plays a role.
Defining Specifications
3GPP specifications that define or reference PUCCH, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | Rel-19 |
| TS 36.116 vj00 | E-UTRA Relay RF Requirements | Rel-19 |
| TS 36.117 vj00 | E-UTRA Relay RF Test Methods & Requirements | Rel-19 |
| TS 36.133 vj20 | E-UTRA RRM Requirements | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.201 vj00 | LTE Physical Layer General Description | Rel-19 |
| TS 36.211 vj10 | LTE Physical Layer Specification | Rel-19 |
| TS 36.212 vj10 | LTE Multiplexing and Channel Coding | Rel-19 |
| TS 36.213 vj10 | LTE Physical Layer Procedures | Rel-19 |
| TS 36.216 vj00 | LTE Relay Node Physical Layer | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.306 vj00 | E-UTRA UE Radio Access Capability Parameters | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.825 vd00 | Study on Additional LTE TDD Configurations | Rel-13 |
| TS 36.863 vc00 | CRS Interference Mitigation for Homogeneous Networks | Rel-12 |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 |
| TR 37.911 vj00 | 3GPP 5G NTN Self-Evaluation Report | Rel-19 |
| TS 38.133 vj20 | 5G UE Radio Requirements for RRC_IDLE Mobility | Rel-19 |
| TS 38.174 vj10 | NR Integrated Access and Backhaul Radio Spec | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.201 vj00 | NR Physical Layer General Description | Rel-19 |
| TS 38.202 vj00 | 5G NR Physical Layer Services | Rel-19 |
| TS 38.211 vj10 | NR Physical Channels and Modulation | Rel-19 |
| TS 38.212 vj10 | NR Multiplexing and Channel Coding | Rel-19 |
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.523 vj20 | 5G NR UE Conformance Testing: Idle/Inactive | Rel-19 |
| TR 38.808 vh00 | Study on NR above 52.6 GHz to 71 GHz | Rel-17 |
| TS 38.824 vg00 | NR URLLC Physical Layer Enhancements Study | Rel-16 |
| TR 38.830 vh00 | NR Coverage Enhancements Study | Rel-17 |
| TR 38.838 vh00 | Study on XR Evaluations for NR | Rel-17 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |
| TR 38.903 vj00 | Test Tolerances & Measurement Uncertainties | Rel-19 |
| TS 45.820 vd10 | CIoT for Internet of Things | Rel-13 |
