Description
The Number of Resource Blocks (NRB) is a fundamental parameter in both LTE (E-UTRA) and 5G NR that defines the transmission bandwidth configuration of a carrier. A resource block (RB) is the smallest unit of resources that can be allocated to a user for a transmission time interval. In the frequency domain, one resource block consists of 12 consecutive subcarriers. Therefore, NRB specifies how many of these 12-subcarrier blocks are contiguously allocated within the carrier's channel bandwidth. The value of NRB is directly tied to the channel bandwidth; for example, in LTE, a 10 MHz channel typically corresponds to NRB = 50. The relationship is defined in the specifications, with tables mapping channel bandwidths (e.g., 1.4, 3, 5, 10, 15, 20 MHz for LTE) to their corresponding NRB values, accounting for necessary guard bands at the edges of the allocated spectrum.
Architecturally, NRB is a key input to the physical layer resource grid. The resource grid is a time-frequency matrix where the frequency dimension is defined by NRB * 12 subcarriers. This grid is where physical channels and signals, such as the Physical Downlink Shared Channel (PDSCH), Physical Uplink Shared Channel (PUSCH), and reference signals, are mapped. The base station scheduler uses NRB as a constraint, dynamically allocating subsets of these total resource blocks to different users based on their channel conditions and quality of service requirements. The total number of available resource blocks (NRB) fundamentally limits the peak data rate a carrier can support, as more RBs mean more frequency resources available for data transmission.
In 5G NR, the concept of NRB remains central but is extended with greater flexibility. While an NR resource block also comprises 12 subcarriers, the subcarrier spacing (SCS) can vary (15, 30, 60, 120, 240 kHz). The transmission bandwidth configuration NRB is defined for each SCS and channel bandwidth. Furthermore, NR introduces the concept of bandwidth parts (BWP), where a UE can be configured with a subset of the carrier's total NRB. This allows for power saving and support for devices with different bandwidth capabilities. Therefore, NRB operates at two levels: the overall carrier bandwidth configuration and the per-BWP configuration. The specifications (e.g., 38.101, 38.104) provide extensive tables defining the supported NRB values for every combination of frequency range, SCS, and channel bandwidth, ensuring global interoperability.
Purpose & Motivation
The NRB parameter exists to provide a standardized, scalable, and implementation-friendly way to define and configure the transmission bandwidth of a cellular carrier. Before such standardization, defining bandwidth in raw Hertz (Hz) would be ambiguous due to the need for guard bands and the discrete nature of OFDM subcarriers. NRB abstracts the bandwidth into discrete blocks of resources (12 subcarriers), which aligns perfectly with the scheduling and resource allocation mechanisms of OFDMA (used in downlink) and SC-FDMA (used in LTE uplink). This solves the problem of efficiently partitioning the continuous spectrum into manageable, allocable units for multiple users.
The historical context stems from the design of LTE in 3GPP Release 8, which adopted OFDMA and needed a fundamental resource unit. The resource block, and by extension NRB, was defined as this unit. It provided a common language for specifying UE RF requirements (like channel bandwidths for testing), defining physical channel structures, and implementing scheduling algorithms. As networks evolved to 5G NR, the principle remained vital but required adaptation. NR needed to support a much wider range of frequencies and bandwidths, from narrowband IoT to ultra-wideband millimeter wave channels. The NRB framework was extended with new tables and rules to cover these cases, maintaining backward compatibility in principle while enabling forward-looking flexibility. It addresses the limitation of a one-size-fits-all bandwidth definition, allowing the system to be optimized for diverse use cases from massive IoT to enhanced mobile broadband.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (13 CRs across 4 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-10, normative work from Rel-15.
In Release 15, the NRB function itself was not directly modified in the provided context; however, the release introduced numerous performance requirement updates and corrections for NR physical channels in TS 38.104. These included new or updated demodulation requirements for PUCCH formats 0, 1, 2, 3, and 4, PUSCH for both CP-OFDM and DFT-s-OFDM, and PRACH, alongside clarifications for base station power limits and OTA measurements. The changes also encompassed corrections to co-existence requirements, spurious emissions, and the addition of missing definitions such as EIRP/EIS.
- CR to TS 38.104 on Combined updates from RAN4 #90 This document combines the proposed changes in the following Draft CRs from RAN4 #90: - R4-1900284, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1900763, "Draft CR to TS 38.104: Update of performance requirement numbers for DFT-s-OFDM based PUSCH" - R4-1900876, "Draft CR to TS 38.104: On RX spurious emissions requirement" - R4-1900968, "Draft CR for 38.104: Performance requirements for NR PUCCH format 1" - R4-1901329, "Draft CR to 38.104: Annex C.6 correction" - R4-1901330, "Draft CR to 38.104: Abbreviations addition" - R4-1901387, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1901474, "Draft CR to TS 38.104: Corrections on transmitter co-existence and co-location requirements" - R4-1901483, "Draft CR to TS 38.104: Corrections on general intermodulation requirement" - R4-1902239, "Draft CR to TS 38.104: Addition of missing EIRP/EIS definitions in terminology in clause 3.1" - R4-1902241, "Draft CR to 38.104; clarification of BS power limits" - R4-1902245, "Draft CR to 38.104: Correction to FR2 OTA Interfering signal mean power units" - R4-1902246, "Draft CR to 38.104; Correction to definition of OTA reference sensitivity" - R4-1902260, "draft CR to TS 38.104 - update emissions scaling" - R4-1902338, "Draft CR: Update on FR1 range extension for TS38.104" - R4-1902389, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1902394, "Draft CR to TS 38.104 – PUSCH requirements with CP-OFDM for FR2" - R4-1902396, "CR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1902444, "Draft CR to TS 38.104: Editorial CR for BS demodulation requirements" - R4-1902561, "Draft CR for updating PRACH performance requirements in TS38.104" - R4-1902571, "Corrections to 38.104 Delay profile calculation" - R4-1902642, "Draft CR to TS 38.104: Correction on multi-band operation related requirements" TS 38.104CR0019
In Release 16, the updates for the NRB function included a clarification on the manufacturer's declaration for the number of supported NB-IoT carriers. Furthermore, specifications were updated regarding the synchronization raster to SSB resource element mapping and to provide clarification for the number of interfering signals in testing.
In Release 18, changes to the NRB function primarily involved corrections and alignments of Fixed Reference Channel (FRC) numbers across specifications, including specific corrections for 256QAM configurations. Additionally, a CR addressed the mapping between the channel raster and resource elements. These were technical maintenance updates rather than the introduction of new NRB capabilities or procedures.
- (LTE_NBIOT_eMTC_NTN_req-Perf)CR for TS36.181, Correction on Number of RX antennas in header row of tables for radiated demodulation test requirements TS 36.181CR0021
- Editorial correction to the wrong table number in 36.521-4 annex C TS 36.521CR0001
- Editorial correction to the wrong citation number TS 36.521CR0004
- CR to 38.104: FRC number alignments among specifications TS 38.104CR0616
- CR to 38.104: Correction of FRC numbers for 256QAM, R=682.5/1024 TS 38.104CR0615
- (NR_newRAT-Perf) CR to TS37.145-2: Addition of some missing band numbers TS 37.145CR0376
+ 2 more changes
In Release 19, a specific correction was made to the requirements for Additional Maximum Power Reduction (A-MPR) for eMTC and NB-IoT User Equipment. This change, documented in a Change Request to TS 36.102, aimed to rectify an incorrect subclause reference. The update ensures the accurate application of power reduction rules for these UE categories in the specified technical contexts.
- (LTE_NBIoT_eMTC_NTN_req-Core) CR to 36.102 to correct subclause number for A-MPR requirements for eMTC and NB-IoT UE_R19_CAT_A TS 36.102CR0121
Explore further
Broader topics and technologies where NRB plays a role.
Defining Specifications
3GPP specifications that define or reference NRB, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 25.116 vj00 | LCR TDD Repeater RF Characteristics | Rel-19 |
| TS 25.153 vj00 | LCR TDD Repeater RF Requirements & Testing | Rel-19 |
| TS 32.828 va00 | Study on 3GPP-TMF NRM/SID Alignment | Rel-10 |
| TS 36.102 vj10 | E-UTRA UE Satellite Access RF Requirements | Rel-19 |
| TS 36.104 vj10 | Base Station (BS) radio transmission and reception | Rel-19 |
| TS 36.106 vj00 | E-UTRA FDD Repeater RF Requirements | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.143 vj00 | E-UTRA FDD Repeater RF Testing | Rel-19 |
| TS 36.181 vj30 | E-UTRA RF Test Methods for Satellite Access Node | Rel-19 |
| TS 36.521 vj00 | E-UTRA UE Conformance ICS Proforma | 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 |
| TR 37.900 vj00 | Multi-Standard Radio (MSR) Base Station Requirements | Rel-19 |
| TS 38.101 vj31 | NR User Equipment Radio Transmissions | Rel-19 |
| TS 38.104 vj20 | NR Base Station RF Requirements | Rel-19 |
| TS 38.124 vj00 | NR UE EMC Requirements | Rel-19 |
| TS 38.141 vj20 | NR Base Station RF Conformance Testing Part 1 | Rel-19 |
| TS 38.176 vj20 | IAB Conformance Testing Specification | Rel-19 |
| TS 38.521 vj20 | NR Physical Layer UE Conformance Testing | Rel-19 |
| TS 38.741 vj00 | NTN L-/S-band for NR Technical Specification | Rel-19 |
| TR 38.785 vh00 | UE radio transmission for enhanced NR sidelink | Rel-17 |
| TR 38.786 vi20 | Technical Report for NR Sidelink Evolution | Rel-18 |
| TR 38.846 vi10 | Technical Report | Rel-18 |
| TR 38.921 vj00 | IMT Parameters Study for 6.4-7.1 & 10-10.5 GHz | Rel-19 |