Description
A Tapped Delay Line (TDL) is a fundamental channel model used extensively in 3GPP specifications to characterize the time-dispersive nature of radio propagation in multipath environments. It mathematically represents the wireless channel's impulse response as a linear finite impulse response (FIR) filter. The model consists of a series of discrete 'taps,' where each tap corresponds to a distinct propagation path with a specific time delay, average power (attenuation), and phase characteristics. The collective set of taps describes how a transmitted signal is received as multiple delayed and attenuated copies, causing frequency-selective fading.
In operation, the TDL model convolves the transmitted signal with the channel's impulse response. Each tap is defined by parameters including delay (τ), power (P), and a Doppler spectrum shape (e.g., Classical Jakes, Round Robin) that models the time variation due to mobility. The power delay profile (PDP), which lists the power of each tap versus its delay, is a key output. 3GPP has standardized several TDL models (e.g., TDL-A, TDL-B, TDL-C, TDL-D, TDL-E) for different deployment scenarios like urban macro, urban micro, and indoor. These models are derived from extensive channel measurement campaigns and provide a reproducible reference for link-level and system-level simulations.
The TDL model's architecture in simulations involves generating a complex baseband channel filter. For each tap, a complex Gaussian random process with the specified power and Doppler spectrum is generated to represent the time-varying fade. The sum of all taps' contributions, each delayed appropriately, produces the received signal. This model is crucial for evaluating physical layer performance of NR and LTE, including metrics like error vector magnitude (EVM), throughput, and block error rate (BLER) under realistic channel conditions. It allows engineers to test receiver algorithms like equalizers and channel estimators without requiring costly field trials.
Purpose & Motivation
The TDL model exists to provide a standardized, accurate, and computationally efficient method for simulating radio channel impairments in laboratory and software environments. Before such models, system performance evaluation relied heavily on theoretical approximations or expensive drive tests, which were not reproducible and could not cover all possible scenarios. The TDL model solves the problem of needing a common benchmark to compare different vendor equipment and algorithms under consistent, realistic conditions.
Its creation was motivated by the need to specify performance requirements (e.g., in 3GPP TS 38.101 and TS 38.141) for base stations and user equipment. Regulators and operators require evidence that devices perform adequately in typical multipath environments. The TDL model, with its tapped structure, directly addresses the limitation of simpler models (like the additive white Gaussian noise channel) that ignore time dispersion and frequency selectivity. It captures the essential characteristics of multipath propagation, which is critical for designing and testing wideband systems like LTE and 5G NR that use high bandwidths where frequency-selective fading is pronounced.
Historically, channel modeling evolved from simple statistical models to more precise geometry-based stochastic models (GSCM). The TDL model strikes a balance between accuracy and simulation complexity. It is a non-geometric stochastic model that is easier to implement than full ray-tracing but more representative than flat fading models. Its standardization across releases ensures backward compatibility and allows for the evolution of models to support new frequency bands (like mmWave in Rel-15+) and scenarios (like high-speed train in Rel-14).
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (3 CRs across 2 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the specification introduced a standardized procedure for creating simplified Tapped Delay Line (TDL) channel models from the more complex TR 38.901 models, including specific steps for delay scaling, tap quantization, and tap merging. It defined distinct TDL model sets for FR1 (TDLA30, TDLB100, TDLC300) and FR2 (including TDLA10 and TDLD models), each with specified tap delays, powers, and associated Doppler spectra for performance testing. Furthermore, the release provided explicit clarification on the calculation steps for these delay profiles to ensure consistent implementation.
- 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
- 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 19, the key addition for the Tapped Delay Line (TDL) function was the introduction of new delay profiles for the channel models TDLA10 and TDLD10. These new profiles, specifically defined for FR2 with a finer 2 ns delay resolution, expand the set of standardized channel conditions used for performance testing. This update provides enhanced modeling for scenarios with a 10 ns delay spread, complementing the existing TDL models.
- (NR_ext_to_71GHz-Perf, TEI18) Addition of delay profiles for channel models TDLA10 and TDLD10 TS 38.141CR0671
Explore further
Broader topics and technologies where TDL plays a role.
Defining Specifications
3GPP specifications that define or reference TDL, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| 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 38.753 vj00 | Spatial Channel Model Study for NR Demodulation | Rel-19 |
| TR 38.810 vg70 | NR OTA Test Methods Study | Rel-16 |
| TS 38.811 vf40 | Study on NR Support for Non-Terrestrial Networks | Rel-15 |
| TR 38.833 vh00 | NR Demodulation Performance Enhancement | Rel-17 |
| TR 38.878 vi40 | Technical Report on Advanced Receiver for MU-MIMO | Rel-18 |
| TR 38.900 vf00 | Channel Model Study for >6 GHz | Rel-15 |
| TR 38.901 vj10 | Channel Model for 0.5-100 GHz | Rel-19 |
| TR 38.903 vj00 | Test Tolerances & Measurement Uncertainties | Rel-19 |