Description
Time Alignment Error (TAE) is a key transmitter characteristic and conformance test requirement defined in the 3GPP specifications for base stations (BS), including NodeB (UTRAN), eNodeB (E-UTRAN), and gNB (NG-RAN). It quantifies the maximum timing difference or misalignment between the radio signals emitted from different transmitter branches, antenna connectors, or antenna ports of the same base station. This misalignment is measured at the air interface relative to a defined reference point. TAE is not an operational signaling parameter but a performance metric used during design, manufacturing, and certification to ensure base station hardware meets stringent timing accuracy requirements. Low TAE is critical because modern base stations employ multiple antennas for technologies like Multiple-Input Multiple-Output (MIMO), beamforming, and carrier aggregation, where precise relative timing between transmitted signals is necessary for these techniques to function correctly.
The measurement of TAE involves analyzing the transmitted waveforms from the base station under test. Specifications such as TS 37.141 (for E-UTRAN and NR conformance testing) define detailed test procedures. Typically, a test setup uses a high-precision signal analyzer to capture the RF signals from multiple transmitter branches simultaneously. The analysis often involves cross-correlation techniques to determine the precise time offset between the measured signals. The TAE limit is specified as a maximum allowable value, often in nanoseconds (ns) or as a fraction of the symbol duration (e.g., Ts). For example, requirements differ for intra-band contiguous carrier aggregation (where signals are on adjacent carriers) versus non-contiguous or inter-band aggregation, with tighter tolerances usually required for contiguous scenarios to prevent interference between component carriers.
TAE impacts several advanced radio features. In MIMO, particularly for spatial multiplexing, timing misalignment between layers can degrade channel estimation at the UE and increase inter-layer interference, reducing throughput. For beamforming, which relies on constructive and destructive interference of waves from multiple antenna elements, timing errors can distort the intended radiation pattern, reducing beam gain or pointing it in the wrong direction. In carrier aggregation, misalignment between the primary and secondary component carriers can complicate UE receiver processing and degrade performance. Therefore, controlling TAE through precise hardware design (e.g., calibrated RF chains, synchronized local oscillators) and digital signal processing is a fundamental aspect of base station implementation. The 3GPP specifications define separate TAE requirements for different base station classes (e.g., wide area, medium range, local area) and deployment scenarios, recognizing that practical tolerances may vary.
Purpose & Motivation
The purpose of defining and testing Time Alignment Error is to ensure the practical realizability and performance of advanced multi-antenna transmission techniques in cellular networks. As 3GPP standards evolved from single-antenna systems (Rel-99 UMTS) to MIMO and beamforming (from HSPA+ and LTE onwards), the theoretical gains of these technologies depended heavily on the physical implementation of the base station transmitter. Without specifying and controlling timing alignment between transmitter paths, the promised benefits of increased data rates, improved coverage, and spectral efficiency could not be guaranteed in real-world deployments.
Historically, for single-carrier, single-antenna transmissions, absolute timing accuracy (relative to a frame clock) was the primary concern. The motivation for introducing TAE specifications arose with the adoption of transmit diversity, MIMO, and later, carrier aggregation in Release 8 (LTE) and beyond. These technologies require multiple coherent RF chains operating in parallel. Any unintentional timing skew between these chains becomes a source of implementation impairment that degrades system performance. The 3GPP standardization effort included TAE to provide a clear, measurable boundary for this impairment, allowing base station vendors to design to a common target and network operators to have confidence in equipment interoperability and performance. It addresses the limitation of assuming ideal transmitter hardware in system simulations and standards development, bridging the gap between theory and practice. By defining TAE, 3GPP ensures that advanced physical layer features perform consistently across equipment from different manufacturers, which is crucial for a competitive and interoperable ecosystem.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (16 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 Time Alignment Error (TAE) function was updated with the removal of Transmit Diversity (Tx Diversity) as a condition for TAE testing, as specified in Change Requests to TR 37.145-2 and TR 37.843. Furthermore, specific TAE requirements for Base Stations (BS) were formally introduced and defined in TS 38.104 through dedicated CRs.
- CR to TS 37.145-2 Removal of referencing error for in-band blocking TS 37.145CR0070
- CR to TR 37.145-2 removal of Tx Diversity for TAE testing TS 37.145CR0127
- CR to TR 37.843 removal of Tx Diversity for TAE testing TS 37.843CR0024
- CR to TR 37.843: Improvement of error contribution decsription for RC in Annex E.5 TS 37.843CR0027
- CR to TR 37.843: adding background information on angular alignment in subclause 10.8.4 TS 37.843CR0037
- CR to TS 38.104 Combined updates from RAN4 #90bis and RAN4#91 From RAN4 #90bis: - R4-1903105, "Draft CR to TS 38.104: Corrections on terminologies and editorial errors" - R4-1903319, "Draft CR to TS 38.104: removal of unused definition: "minimum EIRP level under extreme condition"" - R4-1903320, "Draft CR to TS 38.104: OSDD information correction" - R4-1903457, "Draft CR to TS 38.104: Removal of FFS for FR2 TDD OFF power level requirement in clause 9.5" - R4-1903499, "Draft CR to 38.104: Correction to unwanted emissions mask for bands n7 and n38" - R4-1903836, "Draft CR to TS 38.104: Correction on description on multi-band operation in section 4.8" - R4-1904024, "Draft CR to TS 38.104 Applicability rules for BS demodulation" - R4-1904234, "draftCR: Correlation matrix for 8Rx in TS 38.104" - R4-1904723, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1904726, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1904729, "Draft CR on PRACH performance requirements in TS38.104" - R4-1904734, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1904735, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1904739, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1904745, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1904799, "Draft CR to TS 38.104: FRC update for PUSCH FR1 mapping type B and FR2 DMRS 1+1" - R4-1904816, "Draft CR : Clarification on step 5 and step 6 for delay profiles calculation (38.104)" - R4-1904842, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1905126, "draft CR to 38.104 for TAE requirements" - R4-1905139, "draft CR to TS 38.104 on EVM measurement (Annex B and C)" - R4-1905140, "Draft CR: editorial correction on FR1 spurious emission requirement in TS38.104" - R4-1905143, "Draft CR for TS 38.104: Addition of NOTE for transmitter intermodulation requirements in certain regions" - R4-1905144, "Draft CR to TS 38.104: FRC reference corrections for the Rx requirements" - R4-1905145, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for ACS, blocking and intermodulation requirements" - R4-1905148, "Draft CR to TS 38.104: Corrections on out-of-band blocking requirement" From RAN4 #91: - R4-1906002, "Draft CR to 38.104: Subclause 6.7 and 9.8 transmitter intermodulation – correction of interfering signal type" - R4-1906096, "Draft CR to 38.104: Correction of frequency range for OTA spurious emissions" - R4-1906311, "Draft CR to 38.104: Correction on FRC (Annex A)" - R4-1906346, "Removal of n65 in Rel-15 38.104" - R4-1906915, "Draft CR to TS 38.104: Clarification on application of interfering signal offsets for OTA ACS, blocking and intermodulation requirements" - R4-1906918, "Draft CR to TS 38.104: Clarification on type of interfering signal for ACS, in-band blocking and ICS requirements" - R4-1907110, "Draft CR to TS 38.104: correction of the fundamental frequency limit of 2.55GHz for the spurious emissions" - R4-1907246, "Draft CR to TS 38.104: Update of performance requirements for DFT-s-OFDM based PUSCH" - R4-1907249, "Draft CR to TS 38.104: Correction on the terminology in PUSCH FRC tables" - R4-1907252, "Draft CR to TS38.104: Updates of PRACH performance requirements" - R4-1907255, "Draft CR on NR PUCCH format2 performance requirements for TS 38.104" - R4-1907258, "Draft CR on NR UCI on PUSCH performance requirements for TS 38.104" - R4-1907261, "draftCR: Updates to PUCCH formats 3 and 4 performance requirements in TS 38.104" - R4-1907266, "Draft CR on TS 38.104 Performance requirement for PUCCH format 1" - R4-1907267, "Draft CR on TS 38.104 Performance requirement for multi-slot PUCCH format 1" - R4-1907272, "Draft CR to TS 38.104 BS demodulation PUCCH format 0 requirements" - R4-1907275, "Draft CR to TS 38.104 BS demodulation CP-OFDM PUSCH FR2 requirements" - R4-1907277, "draftCR for 38.104 on PUSCH requirements with CP-OFDM and FR1" - R4-1907629, "Draft CR to 38.104: Term “reference signal” replacing by term “ideal signal” in EVM context" - R4-1907634, "Draft CR to 38.104: corrections to the EVM annex" - R4-1907659, "Draft CR to TS 38.104 on Spurious emission Category B in FR2" - R4-1907661, "Draft CR to 38.104 Definition of contiguous transmission bandwidth" - R4-1907662, "Draft CR to 38.104: BS TAE requirements" - R4-1907664, "Draft CR to 38.104: Clarification of interferer RB frequency for narrowband blocking" - R4-1907672, "Draft CR for TS 38.104: Correction on EVM" - R4-1907689, "Correction to CA carrier spacing" TS 38.104CR0029
In Release 16, the Time Alignment Error (TAE) function was enhanced with new alignment procedures and corrections for Over-the-Air (OTA) measurements. The updates specifically introduced requirements for angular alignment in TRP (Total Radiated Power) measurements and provided alignments and corrections for Measurement Uncertainty (MU) values, contributors, and derivations. Furthermore, a dedicated correction for OTA TAE was formally specified for NR (New Radio) base stations.
- CR to TS 37.145-2: Additional information about alignment needed for TRP measurements in Annex F.1 TS 37.145CR0224
- CR to TR 37.941: Clause 6.3.3 Angular alignment in TRP measurements TS 37.941CR0004
- CR to TR 37.941: MU and TT values alignments and corrections, Rel-16 TS 37.941CR0016
- CR to TR 37.941: alignments and corrections to the MU contributors and MU derivations, Rel-16 TS 37.941CR0018
- CR to TS 38.104: OTA TAE correction, Rel-16 TS 38.104CR0112
In Release 17, the Time Alignment Error (TAE) function was updated to specify measurement uncertainties for the Over-The-Air (OTA) timing error between an IAB-DU and an IAB-MT. This involved the removal of brackets from the uncertainty definitions in the technical specifications. The change provided clearer requirements for measuring this critical synchronization error in Integrated Access and Backhaul nodes.
- CR to TS 38.176-2 with bracket removal for measurement uncertainties for OTA timing error between IAB-DU and IAB-MT TS 38.176CR0017
In Release 18, the Time Alignment Error (TAE) function was updated through specific changes to base station demodulation requirements for MIMO. The modifications involved technical alignments for FRC (Fixed Reference Channel) numbers across specifications and an alignment with UE specifications concerning frequency bands n30 and n77. These adjustments ensured consistent TAE requirements within the enhanced Rel-18 MIMO framework.
In Release 19, the TAE (Time Alignment Error) function was updated with corrections to errors introduced in the SBFD (Subband Full Duplex) specifications. The specific changes were documented in a Change Request to the 3GPP 38.104 technical specification. This CR focused on rectifying technical inaccuracies within the SBFD framework that impacted TAE requirements and measurements.
- CR to 38.104 for correction of errors in the SBFD introduction TS 38.104CR0752
Explore further
Broader topics and technologies where TAE plays a role.
Defining Specifications
3GPP specifications that define or reference TAE, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 25.104 vj00 | UTRA FDD Base Station RF Characteristics | Rel-19 |
| TS 25.141 vj00 | UTRA FDD Base Station RF Conformance Testing | 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 37.842 vd30 | BS RF Requirements for Active Antenna Systems | Rel-13 |
| TR 37.843 vf70 | AAS BS Radiated RF Requirement Background | Rel-15 |
| TR 37.941 vj20 | RF Conformance Testing Background for Radiated BS Requirements | Rel-19 |
| TS 38.104 vj20 | NR Base Station RF 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 |
| TR 38.808 vh00 | Study on NR above 52.6 GHz to 71 GHz | Rel-17 |
| TS 38.817 | 3GPP TR 38.817 | Rel-8 |
| TS 38.863 vj10 | NR NTN RF and Co-existence Spec | Rel-19 |
| TS 48.061 vj00 | BTS-TRAU Protocol for HR Speech/Data | Rel-19 |