BWP

Bandwidth Part

Radio Access Network →
Introduced in Rel-15

BWP is a contiguous set of physical resource blocks configured within a channel bandwidth, enabling power-efficient operation by allowing a UE to monitor only a subset of the total bandwidth.

Category
Radio Access Network
Introduced
Rel-15
Where
Radio Access Network › NG-RAN (5G)
Specifications
25 specs
BWP Description Purpose Detected Changes Specifications

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.

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (101 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-15 31 changes

In Release 15, the Bandwidth Part (BWP) function was newly introduced as a core component for flexible spectrum utilization, defined by its subcarrier spacing, cyclic prefix, and location within the carrier's channel bandwidth. The release specified that each cell requires an initial BWP for access and allows for the configuration of additional UE-specific BWPs, which can be managed individually or via BWP sets containing up to four BWPs per link type. Furthermore, the foundational procedures and configurations for BWP operation were established, including the BWP inactivity timer, switching mechanisms, and handling during scenarios like random access and SCell deactivation.

  • 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

+ 25 more changes

Rel-16 13 changes

In Release 16, the BWP function was enhanced with the introduction of a new dormant BWP operation for secondary cells to improve power saving, along with clarifications for common search space on the active BWP. It also introduced support for flexible TRS bandwidth for a BWP of 52 RBs and addressed specific procedures like CSI reporting for non-active BWPs and BWP size restrictions for NR-U operation.

  • 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

+ 7 more changes

Rel-17 19 changes

In Release 17, the BWP function was refined with specific corrections and updates for new UE types and operational scenarios. Key enhancements included dedicated support for Reduced Capability (RedCap) UEs with separate initial BWP configurations and corrections for procedures like SRS transmission and PRS reception outside the initial BWP. The release also introduced corrections for BWP handling during SCG deactivation, BWP switching with PUCCH cell switching, and autonomous UE bandwidth changes during RACH.

  • 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

+ 13 more changes

Rel-18 32 changes

In Release 18, the key new feature for Bandwidth Part (BWP) functionality was the introduction of **BWP operation without restriction**, alongside the formal support for configuring BWPs via **BWP Sets** in the Network Resource Model (NRM). The BWP Set, a new Information Object Class (IOC), allows the network to reference a configured group of up to 12 BWPs (4 DL, 4 UL, 4 SUL) for use by a UE, simplifying management compared to individual BWP references. These enhancements were accompanied by various corrections and maintenance items to ensure robust operation across different scenarios, including positioning and scheduling.

  • 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

+ 26 more changes

Rel-19 6 changes

In Release 19, the BWP function was enhanced to explicitly support the management of RedCap (Reduced Capability) UEs as a distinct device category, including the introduction of a specific `INITIAL_REDCAP` value for the `bwpContext` attribute. Furthermore, the release introduced clarifications and support for new, narrower channel bandwidths below 10 MHz, specifically defining a 7 MHz channel bandwidth option for deployments requiring reduced bandwidth.

  • Rel-19 CR TS 28.541 Enhance NR NRM to support management of RedCap BWP feature TS 28.541CR1469
  • CR to TS 38.176-2: restriction of 7MHz channel bandwidth introduction TS 38.176CR0087
  • Introduction of 7MHz channel bandwidth TS 38.331CR5308
  • (NR_FR1_7MHz_BW-Perf) CR to TS 38.176-2 with clarification for channel bandwidths below 10 MHz TS 38.176CR0094
  • CR to 38.174 with clarification for channel bandwidths below 10 MHz TS 38.174CR0136
  • Correction on the bandwidth of positioning SRS frequency hopping TS 38.331CR5656

Explore further

Broader topics and technologies where BWP plays a role.

Topics
RRC (Radio Resource Control)Spectrum & CoexistenceMEC (Edge Computing)LTE / LTE-Advanced5G NR (New Radio)Lawful Intercept
Technologies
LTE5G

Defining Specifications

3GPP specifications that define or reference BWP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
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