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
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (468 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, specific enhancements for PUCCH were not the primary focus of the provided change requests. The corrections and introductions detailed instead address adjacent uplink channels and related procedures, such as corrections to the HARQ-ACK bitmap interpretation for FeLAA and clarifications for power control mechanisms. The release also included performance requirements and demodulation requirements for shortened Transmission Time Intervals (sTTI) impacting uplink channels like PUSCH.
- Performance requirements for subslot-PUSCH TS 36.104CR4800
- CR for PUSCH conformance test in TS 36.141 for BS IC TS 36.141CR1080
- Control Plane latency reduction TS 36.306CR1614
- Control Plane latency reduction TS 36.331CR3453
- Introduction of support for MAC PDU containing UE contention resolution identity MAC control element without RRC response message in NB-IoT TS 36.306CR1570
- Introduction of PUSCH demodulation requirements for sTTI TS 36.104CR4803
+ 94 more changes
In Release 16, key PUCCH enhancements were introduced as part of broader Physical Layer Enhancements for NR URLLC, focusing on increased reliability and reduced latency for uplink control signaling. Specific improvements included corrections and refinements to the HARQ-ACK codebook configuration via RRC parameters and enhancements for operation in shared spectrum through corrections on shared spectrum channel access procedures. These updates ensured PUCCH could better support the stringent requirements of ultra-reliable low-latency communication (URLLC) services.
- CR to 36.104 on LTE HST PUSCH conditions TS 36.104CR4873
- CR to TS 36.104: Introduction of PUSCH performance requirements for enhanced HST scenario TS 36.104CR4883
- CR to TS 36.141: Introduction of PUSCH performance requirements for enhanced HST scenario TS 36.141CR1241
- Introduction of Physical Layer Enhancements for URLLC TS 38.202CR0012
- Introduction of Physical Layer Enhancements for NR URLLC TS 38.212CR0026
- Introduction of shared spectrum channel access TS 38.213CR0071
+ 124 more changes
In Release 17, specific enhancements for PUCCH included corrections and clarifications to its resource determination procedure and its operation for new scenarios. These included support for configuring multiple HARQ-ACK codebooks for multicast services and ensuring alignment in related DCI sizes. Furthermore, corrections were made for PUCCH transmission duration in IoT over Non-Terrestrial Networks (NTN) and for its behavior during simultaneous reception with other channels like SDT.
- Introduction of uplink RRC Segmentation capability TS 36.306CR1853
- Introduction of uplink RRC Segmentation capability TS 36.331CR4826
- IoT NTN RRC Correction on PUCCH TX duration TS 36.331CR4936
- Correction on simultaneous reception of SDT and other channels in TS 38.202 TS 38.202CR0026
- CR on DCI size for Rel-17 NTN HARQ in 38.212 TS 38.212CR0116
- CR on the description of the SRS resource set indication for PUSCH repetition TS 38.212CR0117
+ 128 more changes
In Release 18, specific enhancements for PUCCH were not the primary focus of the new work items. The key introductions centered on MIMO evolution for downlink and uplink, network-controlled repeaters, and multi-cell scheduling for PDSCH and PUSCH. The provided grounding context and CR titles do not list any new PUCCH-specific procedures or capabilities for this release.
- Introduction of sidelink channel access procedures for Rel-18 NR sidelink evolution TS 38.201CR0003
- Introduction of Rel-18 network-controlled repeaters TS 38.201CR0004
- Introduction of MIMO evolution for downlink and uplink TS 38.211CR0110
- Introduction of Rel-18 MIMO Evolution for Downlink and Uplink TS 38.212CR0145
- Introduction of Rel-18 network controlled repeaters TS 38.212CR0150
- Introduction of MIMO Evolution for Downlink and Uplink TS 38.213CR0504
+ 78 more changes
In Release 19, the key new PUCCH-related enhancement was the introduction of 32 HARQ process numbers, increasing the capacity for Hybrid Automatic Repeat Request acknowledgments. This change was complemented by corrections to the handling of HARQ Process Number determination for multi-PDSCH and multi-PUSCH scheduling, ensuring proper operation with the expanded process space. Additionally, a change request addressed the multiplexing of UE Inactive-mode Request Information (UEIRI) into the PUSCH, which relates to uplink control signaling procedures.
- CR to TS 38.176-2: restriction of 7MHz channel bandwidth introduction TS 38.176CR0087
- Introduction of 32 HARQ process numbers in Rel-19 [TN32HARQ] TS 38.212CR0222
- Introduction of PDCCH repetitions for Type0-PDCCH CSS set in TNs [Common_PDCCH_Rep_TN] TS 38.213CR0748
- Introduction of control parameters for on-demand posSIB request [OdPosSIB_Req] TS 38.300CR1009
- Introduction of common PDCCH repetition (Rel-19 NTN) for TN [Common_PDCCH_rep_TN] TS 38.300CR1058
- (NR_FR1_7MHz_BW-Perf) CR to TS 38.176-2 with clarification for channel bandwidths below 10 MHz TS 38.176CR0094
+ 14 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 |