Description
Energy Per Resource Element (EPRE) is a core physical layer parameter in 3GPP's LTE (E-UTRA) and NR (New Radio) specifications. It quantifies the average transmit power allocated to a single Resource Element within the Orthogonal Frequency Division Multiplexing (OFDM) time-frequency grid. A Resource Element is the smallest physical resource unit, representing one subcarrier for the duration of one OFDM symbol. EPRE is not a directly measured instantaneous power but a configured and standardized reference level. It is typically defined relative to the total cell transmit power or a reference signal power, such as the Cell-Specific Reference Signal (CRS) in LTE or the Synchronization Signal/Physical Broadcast Channel (SS/PBCH) block in NR.
The parameter is crucial for downlink power allocation and UE receiver operation. The network configures power ratios, such as the ratio of PDSCH EPRE to CRS EPRE (ρ_A and ρ_B in LTE) or the power allocation for various channels and signals relative to an SSB. The UE uses these signaled or predefined ratios to estimate the effective signal power for the data channel (PDSCH) and control channels (PDCCH), which is essential for accurate channel estimation, demodulation, and decoding. The concept ensures that power is distributed predictably across the bandwidth and time, managing the trade-off between coverage for cell-edge users (needing higher power) and capacity/interference for cell-center users.
EPRE settings are integral to Radio Resource Management (RRM) and link adaptation. They influence key performance indicators like throughput and block error rate (BLER). For example, a higher PDSCH EPRE relative to a reference signal improves the Signal-to-Interference-plus-Noise Ratio (SINR) for data reception, potentially allowing the use of a higher-order modulation and coding scheme (MCS). Network algorithms dynamically adjust these ratios based on UE feedback (CQI), scheduling decisions, and interference conditions. Specifications like 36.213 (LTE) and 38.213 (NR) detail the power control procedures and formulas that govern how EPRE-related parameters are determined and applied.
Purpose & Motivation
EPRE was introduced to provide a standardized and granular method for defining and controlling transmit power distribution in the OFDM-based air interface of LTE (from Release 8 onwards). Prior cellular systems often used more aggregate power metrics. The shift to OFDMA required a fine-grained power model because resources are allocated in small time-frequency blocks to multiple users simultaneously. Without a clear definition like EPRE, it would be ambiguous how much power is devoted to a user's specific data symbols versus cell-wide reference signals, leading to inconsistent receiver performance and inefficient interference coordination.
Its primary purpose is to enable accurate link budget analysis, predictable UE receiver operation, and effective network planning. By defining power per fundamental resource element, engineers can precisely calculate the received signal strength for any channel, ensuring UEs can correctly set their automatic gain control and demodulation thresholds. It solves the problem of power ambiguity in a shared channel environment, which is critical for advanced features like Coordinated Multi-Point (CoMP) and enhanced Inter-Cell Interference Coordination (eICIC), where precise knowledge of neighboring cell transmit power levels is necessary. EPRE provides the foundational building block for all downlink power control formulas specified in 3GPP.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (129 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, the EPRE function itself was not newly introduced; instead, the release included corrections and clarifications to related physical layer procedures that impact power allocation and resource element utilization. These changes involved corrections to PUSCH and PDSCH resource allocation, including for transmissions scheduled by a RAR UL grant and with SP CSI. Furthermore, clarifications were made regarding PDSCH processing capability and procedures for handling overlapping grants and collisions with SPS PDSCH.
- Correction to last PUCCH resource set configuration TS 38.213CR0019
- Correction on CRC assumption for multi-CSI resource selection and CSI report(s) selection TS 38.213CR0041
- Clarification of reference to PDSCH processing capability 1 in TS 38.213 TS 38.213CR0042
- Correction on uplink resource allocation type 1 TS 38.214CR0010
- Correction on determination of the resource allocation table for PUSCH with SP CSI TS 38.214CR0011
- Correction on PUSCH resource allocation TS 38.214CR0012
+ 12 more changes
In Release 16, the EPRE function itself was not directly modified in the provided context. The release primarily introduced corrections and clarifications to related physical layer procedures, including enhancements for PDSCH reception with multi-TRP deployments, refinements to PUCCH resource determination and HARQ-ACK codebook reporting, and specific handling for SPS PDSCH and PDSCH repetitions. These updates ensured accurate power control and reliable reception by clarifying the conditions and timelines for associated signals and channels.
- 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
- Correction for cancellation due to PDSCH/CSI-RS/SFI TS 38.213CR0186
- Correction of Type-3 HARQ-ACK codebook generation for a PDSCH with one transport block for a configuration with a maximum number of two TBs TS 38.213CR0187
+ 27 more changes
In Release 17, the EPRE function itself was not directly modified; however, several related corrections and clarifications were introduced for PUCCH resource determination procedures. These changes specifically addressed the multiplexing of dynamic multicast and SPS unicast HARQ-ACK feedback, as well as resource determination for SPS multicast and for UEs configured with NACK-only feedback modes. Additionally, corrections were made to PDSCH processing timing and multi-PDSCH scheduling validity in shared spectrum and FR2-2 operations.
- CR on the clarification of PUCCH resource determination in 38.213 TS 38.213CR0339
- CR on HARQ-ACK feedback for PDSCH scheduled by DCI format 4_1 TS 38.213CR0389
- CR on PUCCH resource determination of SPS multicast HARQ-ACK TS 38.213CR0400
- CR on PUCCH resource determination for multiplexing dynamic multicast HARQ-ACK and SPS unicast HARQ-ACK TS 38.213CR0401
- CR on PUCCH resource determination of multicast HARQ-ACK TS 38.213CR0432
- CR on PUCCH resource for UE configured with NACK-only mode2 for SPS TS 38.213CR0452
+ 25 more changes
In Release 18, the EPRE function was enhanced to support new network energy saving features and multi-cell PDSCH/PUSCH scheduling. These were introduced alongside corrections to the specification support for network energy saving and maintenance of the related NR mechanisms. The updates aimed to optimize radio resource usage and power control across multiple cells.
- Introduction of network energy savings for NR TS 38.213CR0514
- Introduction of multi-cell PDSCH / PUSCH scheduling TS 38.214CR0442
- Introduction of specification support for network energy saving TS 38.214CR0447
- Maintenance of network energy savings for NR TS 38.213CR0578
- Maintenance of network energy savings for NR TS 38.213CR0599
- Correction on OFDM symbol location for PSFCH transmission in SL-U TS 38.213CR0617
+ 27 more changes
In Release 19, the enhancements for network energy savings introduced new counting procedures for simultaneous CSI-RS resources referred by multiple CSI reporting settings (SimCSI_count) and for simultaneous NZP-CSI-RS resources with Network Energy Savings (SimCSI_countNES). These changes provide more precise control over reference signal transmission power, directly impacting EPRE management. The release also included corrections and clarifications on the maximum number of simultaneous measurement resources for SRS-RSRP and CLI-RSSI to ensure accurate energy-saving configurations.
- Introduction of enhancements of network energy savings for NR TS 38.213CR0706
- Introduction of enhancements of network energy savings TS 38.214CR0688
- 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
- Corrections on enhancements of network energy savings for NR TS 38.213CR0722
- Corrections on enhancements of network energy savings for NR TS 38.213CR0745
+ 8 more changes
Explore further
Broader topics and technologies where EPRE plays a role.
Defining Specifications
3GPP specifications that define or reference EPRE, 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 36.101 vj30 | LTE UE Radio Transmission & Reception Requirements | Rel-19 |
| TS 36.141 vj00 | E-UTRA BS Conformance Testing | Rel-19 |
| TS 36.213 vj10 | LTE Physical Layer Procedures | 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 |
| TR 38.810 vg70 | NR OTA Test Methods Study | Rel-16 |
| TR 38.869 vi00 | Study on low-power wake up signal and receiver for NR | Rel-18 |
| TR 38.884 vi20 | Technical Report | Rel-18 |
| TR 38.889 vg00 | NR-based access to unlicensed spectrum study | Rel-16 |