Description
A Bandwidth Part (BWP) is a fundamental concept in 5G New Radio (NR) that defines a contiguous subset of the total channel bandwidth allocated to a User Equipment (UE). Unlike LTE where UEs typically operate on the entire carrier bandwidth, NR introduces BWP to provide greater flexibility and efficiency. Each BWP is characterized by its numerology (subcarrier spacing and cyclic prefix), bandwidth (number of PRBs), and frequency location within the carrier. A UE can be configured with up to four downlink BWPs and four uplink BWPs per serving cell, but only one downlink BWP and one uplink BWP can be active at any given time. This configuration allows the network to adapt to different service requirements and UE capabilities dynamically.
The BWP operation is controlled through Radio Resource Control (RRC) signaling for semi-static configuration and through Downlink Control Information (DCI) for dynamic switching. When a UE is configured with multiple BWPs, it monitors the Physical Downlink Control Channel (PDCCH) only within the active BWP, significantly reducing power consumption. The BWP switching mechanism allows the network to move the UE between different bandwidths and numerologies based on traffic conditions, service requirements, or energy-saving considerations. For example, a UE might operate on a narrow BWP for basic connectivity and idle-mode operations, then switch to a wider BWP for high-throughput data sessions.
From an architectural perspective, BWP configuration includes parameters such as the locationAndBandwidth field (indicating the starting PRB and bandwidth in PRBs), subcarrierSpacing, and cyclicPrefix. The initial BWP is configured for initial access procedures including synchronization and random access. The default BWP is used for fallback operation when no data transmission occurs for a configured timer period. BWP inactivity timer triggers switching to the default BWP when the UE hasn't received scheduling for a specified duration, further enhancing power efficiency.
BWP plays a crucial role in supporting diverse spectrum scenarios in 5G NR. It enables operation in wide bandwidth carriers (up to 400 MHz in FR2) while accommodating UEs with limited RF capabilities. The technology supports mixed numerology scenarios where different services (eMMB, URLLC, mMTC) can be multiplexed on the same carrier through different BWPs. BWP also facilitates spectrum sharing between different operators or between 4G and 5G through careful BWP configuration that avoids interference areas.
The implementation of BWP involves coordination between multiple protocol layers. At the physical layer, BWP defines the actual transmission and reception bandwidth. At the MAC layer, BWP switching procedures and timer management occur. RRC handles the configuration and reconfiguration of BWP parameters. This multi-layer approach ensures that BWP operations are synchronized across the protocol stack, maintaining service continuity while optimizing resource usage and power consumption.
Purpose & Motivation
Bandwidth Part was introduced in 5G NR to address several limitations of previous cellular systems, particularly LTE's fixed bandwidth operation. In LTE, UEs typically operated on the entire carrier bandwidth regardless of their actual data requirements, leading to unnecessary power consumption. This became particularly problematic with the introduction of wide bandwidth carriers in 5G (up to 100 MHz in FR1 and 400 MHz in FR2), where requiring all UEs to monitor the full bandwidth would be impractical and power-inefficient.
The primary motivation for BWP creation was to enable power-efficient operation for UEs, especially those supporting wide bandwidth carriers. By allowing UEs to monitor only a subset of the total bandwidth when not engaged in high-throughput activities, BWP significantly reduces power consumption. This is crucial for mobile devices where battery life is a key concern. Additionally, BWP supports diverse UE capabilities by allowing devices with different RF capabilities to operate on the same carrier through appropriately configured bandwidth parts.
Another key problem BWP solves is the efficient support of mixed services and numerologies within the same carrier. 5G NR introduced flexible numerology with different subcarrier spacings (15, 30, 60, 120, 240 kHz) to support diverse use cases. BWP enables different services (e.g., eMBB with wide bandwidth and mMTC with narrow bandwidth) to coexist on the same carrier by assigning them different BWPs with appropriate numerologies. This flexibility was not available in previous generations and represents a significant advancement in spectrum utilization efficiency.
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (78 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the Bandwidth Part (BWP) function was newly introduced as a core component of the NR radio interface, defined as a contiguous set of physical resource blocks configured within a carrier's total bandwidth. Each BWP is characterized by its own subcarrier spacing, cyclic prefix, and specific location and size (startRB and numberOfRBs) within the common resource grid, with an initial BWP being mandatory for downlink, uplink, and supplementary uplink to support UE initial access. The release also established the framework for BWP operation and switching, including procedures for inactivity timers, RRC-triggered reconfiguration, and handling during random access, as detailed in numerous foundational Change Requests.
- Update the inheritance hierarchy figure for NR NRM to include BWP IOC and NRSectorCarrier IOC TS 28.541CR0015
- CR on simultaneous active BWP switching across carriers TS 38.213CR0016
- CR on using CORESET#0 in dedicated DL BWP TS 38.213CR0017
- Correction on HARQ-ACK transmission with BWP change TS 38.213CR0064
- Correction on BWP inactivity timer configuration TS 38.321CR0200
- CR on BWP Inactivity timer TS 38.321CR0254
+ 19 more changes
In Release 16, the BWP function was enhanced with the introduction of a new dormant BWP operation for SCells, allowing for more efficient carrier aggregation with reduced power consumption. The release also introduced flexible TRS bandwidth for a BWP of 52 RBs and provided clarifications and corrections for procedures like CSI reporting on non-active BWPs and the configuration of the common search space on the active BWP. Furthermore, specific capabilities were added, such as enabling dormant BWP switching for multiple SCells and addressing initial UL BWP size restrictions for operation in NR-U.
- Behaviour for triggered with a CSI report for non-active BWP TS 38.214CR0061
- Introduction of flexible TRS bandwidth for BWP of 52 RBs TS 38.214CR0122
- Introduction of dormant BWP operation and Async CA TS 38.321CR0685
- CR to 38.213 on BWP triggering via SCell dormancy indication TS 38.213CR0134
- Initial UL BWP size restriction for NR-U TS 38.213CR0235
- CR on measurement gap request inside of the active DL BWP for DL PRS measurements TS 38.214CR0199
+ 6 more changes
In Release 17, the BWP function was enhanced with explicit support for RedCap UEs, including the configuration of dedicated initial BWPs for RedCap devices. The release also introduced the new BWP Set (BWPSet) configuration in the NR management model, which groups up to 12 BWPs for a single UE's use. Furthermore, corrections and updates were made for procedures involving BWP switching, SRS transmission, and PDCCH monitoring, particularly for UEs in inactive state or for RedCap-specific test cases.
- Correction of BWP for SRS TS 38.213CR0336
- Correction for HARQ-ACK codebook generation for PUCCH cell switching and UL BWP switching TS 38.213CR0347
- Correction on PDCCH monitoring adaptation and BWP switching TS 38.213CR0424
- CR on broadcast PDCCH monitoring in active DL BWP TS 38.213CR0446
- CR on PRS reception and SRS transmission outside initial BWP TS 38.214CR0305
- Correction on BWP handling for deactivated SCG and the timing requirement for SCG activation TS 38.321CR1439
+ 11 more changes
In Release 18, the primary new feature for Bandwidth Part (BWP) was the introduction of BWP operation without restriction and the formal addition of BWP Set configuration support in the NRM (Network Resource Model). This involved defining a new BWPSet Information Object Class (IOC) that contains references to all BWPs usable by a single UE, supporting up to 4 DL, 4 UL, and 4 SUL BWPs per set. Furthermore, the release included various corrections and clarifications, such as those for BWP switching procedures and support for RedCap UEs.
- Add BWP Set configuration support in NRM (stage 2) TS 28.541CR0755
- Add BWP Set configuration support in NRM (stage 3, YANG) TS 28.541CR0756
- Add BWP set support to NRM (Stage3, YAML) TS 28.541CR0764
- Introduction of BWP operation without restriction TS 38.213CR0510
- Introduction of specification support for BandWidth Part operation without restriction in NR TS 38.214CR0444
- Introduction of support for BWP operation without restriction TS 38.331CR4398
+ 17 more changes
In Release 19, the primary enhancement for the Bandwidth Part (BWP) function was the introduction of specific management support for RedCap (Reduced Capability) UEs. This is reflected in the NR Network Resource Model (NRM) through a new enumerated value, "INITIAL_REDCAP", for the `bwpContext` attribute, allowing the configuration of an initial BWP dedicated for (e)RedCap UE initial access. This update builds upon the existing BWP and BWPSet management framework without altering the core BWP definition or configuration procedures.
- Rel-19 CR TS 28.541 Enhance NR NRM to support management of RedCap BWP feature TS 28.541CR1469
Explore further
Broader topics and technologies where BWP plays a role.
Defining Specifications
3GPP specifications that define or reference BWP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 28.541 vk00 | 5G Network Resource Model (NRM) Stage 2/3 | Rel-20 |
| TR 37.985 vj00 | Overview of V2X features in LTE and NR | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.106 vj20 | NR Repeater Radio Transmission and Reception | 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 38.211 vj10 | NR Physical Channels and Modulation | 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 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.522 vj11 | UE Conformance Test Applicability Statement | Rel-19 |
| TS 38.523 vj20 | 5G NR UE Conformance Testing: Idle/Inactive | Rel-19 |
| TS 38.741 vj00 | NTN L-/S-band for NR Technical Specification | Rel-19 |
| TR 38.808 vh00 | Study on NR above 52.6 GHz to 71 GHz | Rel-17 |
| TR 38.825 vg00 | Study on NR Industrial IoT | Rel-16 |
| TR 38.830 vh00 | NR Coverage Enhancements Study | Rel-17 |
| TR 38.833 vh00 | NR Demodulation Performance Enhancement | Rel-17 |
| TR 38.838 vh00 | Study on XR Evaluations for NR | Rel-17 |
| TS 38.863 vj10 | NR NTN RF and Co-existence Spec | Rel-19 |
| TR 38.864 vi10 | Technical Report on Network Energy Savings for NR | Rel-18 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |
| TR 38.878 vi40 | Technical Report on Advanced Receiver for MU-MIMO | Rel-18 |
