Description
A Resource Block (RB) is the smallest element of radio resources that can be allocated to a user by the scheduler in the LTE and NR air interfaces. It represents a two-dimensional allocation in the time and frequency domains. In LTE, the definition is fixed: one Resource Block in the frequency domain is 12 consecutive subcarriers, each with a spacing of 15 kHz, resulting in a total bandwidth of 180 kHz. In the time domain, one Resource Block spans one slot, which is 0.5 ms (7 OFDM symbols for normal cyclic prefix). Therefore, the basic LTE Resource Block is a grid of 12 subcarriers x 7 symbols (84 Resource Elements for normal CP). The network scheduler allocates integer numbers of these RBs to different UEs in each 1 ms Transmission Time Interval (TTI), which comprises two slots.
In NR, the concept is more flexible to support diverse spectrum bands and use cases. An NR Resource Block is defined as 12 consecutive subcarriers in the frequency domain. However, the subcarrier spacing (SCS) is not fixed at 15 kHz; it can be 15, 30, 60, 120, or 240 kHz (with 480 and 960 kHz for future study). Therefore, the absolute bandwidth of an NR RB scales with the SCS (e.g., 180 kHz for 15 kHz SCS, 3.84 MHz for 240 kHz SCS). In the time domain, NR scheduling is based on slots, but the slot duration also scales inversely with the SCS (e.g., 1 ms for 15 kHz, 0.125 ms for 120 kHz). The NR physical layer is defined in terms of Resource Grids, composed of Resource Elements (one subcarrier for one OFDM symbol). A Resource Block is the grouping used for resource allocation signaling.
The allocation of RBs is dynamic and performed by the Medium Access Control (MAC) layer based on scheduling algorithms that consider channel quality indicators (CQI), buffer status, QoS requirements, and interference coordination. The Physical Downlink Shared Channel (PDSCH) and Physical Uplink Shared Channel (PUSCH) transport user data mapped onto allocated RBs. The control channels (PDCCH, PUCCH) are also mapped to specific Resource Elements, often at the edges of the carrier bandwidth. The number of RBs in a channel bandwidth defines the channel's transmission bandwidth configuration, which is always less than or equal to the total RF bandwidth to allow for guard bands.
Purpose & Motivation
The Resource Block was created to provide a standardized, granular unit for flexible and efficient spectrum sharing among multiple users in OFDMA-based systems like LTE and NR. Prior technologies like UMTS used code division multiple access (CDMA), where resources were primarily separated by spreading codes, making fine-grained frequency-domain scheduling difficult. The shift to OFDMA required a new fundamental resource unit that could be easily allocated in both time and frequency domains to exploit multi-user diversity and frequency-selective fading.
The RB solves the problem of how to partition the continuous time-frequency resource plane into manageable, allocatable chunks for scheduling, link adaptation, and signaling. It provides the building block for adaptive modulation and coding (MCS selection can be per RB group), interference management techniques like fractional frequency reuse, and carrier aggregation (where RBs can be allocated across multiple component carriers). Its fixed structure in LTE (12 subcarriers) was a design compromise to balance scheduling granularity, control signaling overhead, and implementation complexity. The more flexible RB definition in NR addresses the limitations of the LTE model, allowing efficient operation across a vast range of spectrum from sub-1 GHz to millimeter wave, and for services with vastly different latency and bandwidth requirements, such as massive IoT and ultra-reliable low-latency communications (URLLC).
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (205 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-4, normative work from Rel-15.
In Release 15, the primary new introduction for the Resource Block (RB) function was enhanced resource coordination between E-UTRA and NR cells, as indicated by the CR titles "E-UTRA - NR Cell Resource Coordination" and "Corrections on resource coordination in stage-2." This involved refining the control and configuration of radio resources, including the transmission bandwidth configuration measured in Resource Block units, to support more efficient shared network operations and dual connectivity scenarios.
- Addition of NR bands to E-UTRA co-location blocking requirements TS 36.104CR4801
- E-UTRA - NR Cell Resource Coordination TS 36.300CR1122
- Support maximum 8 SS/PBCH blocks for unpaired spectrum beyond 2.4GHz TS 38.213CR0006
- CR to TS 36.104: Corrections on NB-IoT operating band unwanted emission and blocking requirements (6.6.3.3, 7.6.1.1) TS 36.104CR4790
- Corrections on resource coordination in stage-2 TS 36.300CR1190
- 36.300 CR on Correction of Physical Layer Resource to Cell Resource TS 36.300CR1211
+ 43 more changes
In Release 16, specific refinements to the Resource Block function included corrections to PDSCH PRB bundling notation and enhancements for resource management in multi-TRP scenarios to address PDCCH and PDSCH collisions. The release also introduced clarifications for sidelink resource pool determination based on PSBCH and provided corrections for PUCCH resource determination procedures. These updates focused on improving the integrity and control of radio resources for various transmission and scheduling mechanisms.
- Clarification on resource reservation for eMTC TS 36.331CR4358
- Introduction of carrier specific NRSRP thresholds for NPRACH resource selection TS 36.331CR4777
- CR to 38.213 on HARQ-ACK processing timeline for DCI format 1_1 with Scell dormancy indication without scheduling PDSCH TS 38.213CR0135
- Correction of NRU HARQ procedure in the presence of SPS PDSCH TS 38.213CR0163
- Correction on periodicity of resource pool bitmap TS 38.213CR0171
- Type-1 HARQ-ACK for PDSCH repetition with different SCSs in DL and UL TS 38.213CR0180
+ 44 more changes
In Release 17, specific enhancements to the RB (Resource Block) function included the introduction of the upper 700MHz A block, which expanded the transmission bandwidth configuration for new spectrum. Furthermore, several corrections and clarifications were made regarding PUCCH resource determination for HARQ-ACK feedback, particularly for multicast and dynamic scheduling scenarios, and adjustments were specified for RB set size and availability within IAB and shared spectrum operations.
- CR to TS36.104 on introduction of upper 700MHz A block TS 36.104CR4950
- CR to TS36.141 on introduction of upper 700MHz A block TS 36.141CR1325
- CR to TS37.104 on introduction of upper 700MHz A block TS 37.104CR0956
- CR to TS37.105 on introduction of upper 700MHz A block TS 37.105CR0248
- CR to TS37.141 on introduction of upper 700MHz A block TS 37.141CR0998
- CR to TS38.104 on introduction of upper 700MHz A block TS 38.104CR0365
+ 41 more changes
In Release 18, the Resource Block (RB) function saw specific corrections and enhancements for sidelink and multicast operations, including corrections on PSFCH resource mapping for contiguous RB resource pools and on the determination of starting RB sets for PSSCH. It also introduced support for multicast MBS PDSCH bandwidth for eRedCap UEs in the RRC inactive state and included corrections for multi-cell PDSCH/PUSCH scheduling procedures. Furthermore, the release addressed resource allocation details for dedicated spectrum less than 5 MHz and for SL partial sensing with interlaced RB allocation.
- Introduction of multi-cell PDSCH / PUSCH scheduling TS 38.214CR0442
- CR to TS 38.104 on additional narrowband blocking requirement for Band n100 TS 38.104CR0612
- (NR_FR1_lessthan_5MHz_BW-Core) CR to TS38.104 Add NB-IoT RB power dynamic range for 3MHz TS 38.104CR0681
- (NR_NTN_enh-Core) CR for TS 38.108, Correction on OTA out-of-band blocking requirement for SAN type 2-O TS 38.108CR0095
- (NR_NTN_enh-Core) CR for TS 38.181, Correction on OTA out-of-band blocking requirement for SAN type 2-O TS 38.181CR0049
- Correction on PSFCH prioritization for UE incapable of TX in multi-RB sets for SL-U TS 38.213CR0613
+ 38 more changes
In Release 19, specific enhancements to the Resource Block (RB) function included corrections for determining the Transport Block Size (TBS) for SPS PDSCH and enabling Msg4 PDSCH repetition and retransmission. Furthermore, the release introduced clarifications and corrections on the maximum number of simultaneous measurement resource sets for SRS-RSRP and CLI-RSSI. These updates refined the control and integrity of radio resources managed by the Radio Network Controller.
- CR to TS 37.145-2 OTA test reduction for out-of-band blocking requirement TS 37.145CR0411
- CR to TS 38.141-2 OTA test reduction for out-of-band blocking requirement TS 38.141CR0682
- TEI19 Counting of CSI-RS resource referred by N CSI reporting settings [SimCSI_count] TS 38.214CR0681
- TEI19 Simultaneous NZP-CSI-RS resource counting with NES [SimCSI_countNES] TS 38.214CR0689
- CR to TS 38.104 correcction on SBFD BS blocking TS 38.104CR0770
- Clarification on the number of simultaneous L1 CLI-RSSI and simultaneous L1 SRS-RSRP measurement resources TS 38.214CR0745
+ 9 more changes
Explore further
Broader topics and technologies where RB plays a role.
Defining Specifications
3GPP specifications that define or reference RB, 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 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TS 25.301 vj00 | UE-UTRAN Radio Interface Protocol Architecture | Rel-19 |
| TS 25.323 vj00 | Packet Data Convergence Protocol (PDCP) Specification | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TR 25.912 vj00 | Evolved UTRA and UTRAN Technical Report | Rel-19 |
| TR 25.914 vj00 | 3G UE Radio Performance Test Methods | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TR 25.993 vj00 | UTRA RAB Examples and Radio Interface Mapping | Rel-19 |
| TR 26.935 vj00 | Speech Codec Performance for Packet Switched Multimedia | Rel-19 |
| TS 32.405 vj00 | UTRAN Performance Measurements Specification | Rel-19 |
| TS 33.821 v900 | LTE/SAE Security Threat Analysis and Countermeasures | Rel-9 |
| TS 34.109 vj00 | UE Conformance Test Functions for UMTS | Rel-19 |
| TS 34.114 vc20 | Radiated Performance Test Procedure for UE/MS | Rel-12 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | Rel-19 |
| TS 36.108 vj10 | Satellite Access Node RF Requirements | 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 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.181 vj30 | E-UTRA RF Test Methods for Satellite Access Node | 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 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.745 ve00 | Satellite Protection for LTE Bands 11/21 | Rel-14 |
| TS 36.761 vf00 | Extended-Band 12 Study Report | Rel-15 |
| TS 36.766 vf00 | LTE BS Interference Cancellation Receiver Study | Rel-15 |
| TS 36.790 vf00 | LAA/eLAA for CBRS 3.5GHz Band in US | Rel-15 |
| TS 36.833 | 3GPP TR 36.833 | Rel-4 |
| TS 36.878 vd00 | LTE Performance Enhancements for High Speed Scenarios | Rel-13 |
| TS 36.884 vd10 | MMSE-IRC Receiver Performance for LTE BS | Rel-13 |
| TS 37.104 vj10 | MSR Base Station RF Characteristics | Rel-19 |
| TS 37.105 vj10 | AAS Base Station Transmission & Reception Requirements | Rel-19 |
| TS 37.141 vj10 | RF Test Methods for Multi-Standard Radio Base Stations | Rel-19 |
| TS 37.145 vj10 | AAS Base Station Conducted Conformance Testing | Rel-19 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TS 37.544 vg70 | UE Radiated Performance Test Procedures | Rel-16 |
| TS 37.718 | 3GPP TR 37.718 | Rel-4 |
| TS 37.719 vj00 | 3GPP TR 37.719: Dual Connectivity Band Combinations | Rel-19 |
| TS 37.801 va00 | UMTS/LTE 3500 MHz Band Study | Rel-10 |
| TS 37.802 va10 | MSR BS RF Requirements for Non-Contiguous Spectrum | Rel-10 |
| TS 37.812 vb30 | Multi-band Multi-standard Radio BS Requirements | Rel-11 |
| TR 37.829 vi00 | Technical Report | Rel-18 |
| TR 37.900 vj00 | Multi-Standard Radio (MSR) Base Station Requirements | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TR 37.902 vj00 | OTA TRP/TRS Measurement for LTE Terminals | Rel-19 |
| TR 37.911 vj00 | 3GPP 5G NTN Self-Evaluation Report | Rel-19 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.108 vj20 | NTN NR Satellite Access Node RF Requirements | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | 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 38.181 vj10 | NR Satellite Access Node RF Testing | 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 38.323 vj00 | Packet Data Convergence Protocol (PDCP) | Rel-19 |
| TS 38.809 vg60 | IAB Radio Transmission & Reception Background | Rel-16 |
| TR 38.833 vh00 | NR Demodulation Performance Enhancement | Rel-17 |
| TR 38.864 vi10 | Technical Report on Network Energy Savings for NR | Rel-18 |
| TS 38.870 vj20 | Enhanced OTA Test Methods for NR FR1 TRP/TRS | Rel-19 |
| TR 38.872 vi40 | Technical Report on Sub-1GHz NR Band Combinations | Rel-18 |
| TR 38.877 vi10 | Technical Report | Rel-18 |
| TR 38.878 vi40 | Technical Report on Advanced Receiver for MU-MIMO | Rel-18 |
| TR 38.903 vj00 | Test Tolerances & Measurement Uncertainties | Rel-19 |
| TR 38.921 vj00 | IMT Parameters Study for 6.4-7.1 & 10-10.5 GHz | Rel-19 |
| TR 38.922 vj20 | Study on IMT Parameters for NR in Higher Bands | Rel-19 |
| TS 43.051 vj00 | GERAN Stage 2 Service Description | Rel-19 |
| TS 44.060 vj00 | GERAN RLC/MAC Protocol Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |