What is the difference between CDL and TDL models?

CDL (Clustered Delay Line) is a full spatial channel model with both temporal (delay) and spatial (angle) characteristics. Each cluster has a delay, power, angle of arrival (AoA), angle of departure (AoD), and angular spread. CDL is used for link-level simulations that include beamforming and MIMO. TDL (Tapped Delay Line) is a simplified model with only delay and power per tap, no spatial information. TDL is used for simpler link-level simulations where spatial processing is not modeled. TR 38.901 defines CDL-A through CDL-E and TDL-A through TDL-E profiles with different delay spreads and cluster configurations.

How does the model handle mmWave frequencies?

At mmWave (FR2, 24-100 GHz), propagation differs fundamentally from sub-6 GHz: higher free-space loss (20*log10(f)), more blockage from buildings and foliage, and human body shadowing of 20-35 dB. TR 38.901 models these by: (1) Frequency-dependent path loss with additional blockage loss terms. (2) Higher LOS/NLOS path loss exponents (NLOS exponent 3.5-4.0 vs. 3.0 at sub-6). (3) Oxygen absorption above 60 GHz (15 dB/km at 60 GHz). (4) Spatial consistency procedures that model correlated shadowing as the UE moves. (5) Blockage model that adds random shadowing events from human bodies and vehicles.

mmWave & 5G

3GPP Channel Model

Q: What scenarios does TR 38.901 define?

TR 38.901 defines five propagation scenarios: (1) UMa (Urban Macro): base station at 25m height, ISD 200-500m, for wide-area urban coverage. (2) UMi-Street Canyon: base station at 10m, narrow street environment with strong waveguide effects. (3) UMi-Open Square: base station at 10m, open plaza without canyon effects. (4) InH-Office: indoor office with open plan or mixed layout, ceiling height 3m. (5) RMa (Rural Macro): base station at 35m, ISD up to 5 km, agricultural terrain. Each scenario has LOS and NLOS path loss models, LOS probability functions, and scenario-specific small-scale fading parameters.

The standardized propagation and spatial channel model defined in 3GPP TR 38.901 for 5G NR system-level simulations, covering frequencies from 0.5 to 100 GHz. It provides path loss equations, LOS probability, small-scale fading parameters (delay spread, angular spread, K-factor), and spatial consistency procedures for five deployment scenarios: Urban Macro (UMa), Urban Micro (UMi), Indoor Hotspot (InH), and Rural Macro (RMa). Used universally for 5G performance evaluation, link budget, and beamforming algorithm development.

Category: mmWave & 5G

Specification: 3GPP TR 38.901

Frequency range: 0.5 to 100 GHz

Understanding the 3GPP Channel Model

Accurate channel models are essential for evaluating 5G system performance before deployment. TR 38.901 extends the earlier 3GPP 3D channel model (TR 36.873) to cover frequencies up to 100 GHz, adding mmWave-specific effects like blockage, oxygen absorption, and foliage loss. The model is calibrated against measurement campaigns conducted by multiple organizations worldwide.

The model follows a geometry-based stochastic approach: large-scale parameters (path loss, shadowing, delay spread, angular spread) are drawn from scenario-specific distributions, then small-scale clusters are generated with delays, powers, and angles to create the full spatial channel matrix. This enables realistic simulation of massive MIMO beamforming, beam management, and mobility.

Key Path Loss Models (TR 38.901)

UMa LOS (10m < d < 5km):
PL = 28.0 + 22 log₁₀(d) + 20 log₁₀(f_c) dB

UMa NLOS:
PL = 13.54 + 39.08 log₁₀(d) + 20 log₁₀(f_c) − 0.6(h_UT−1.5) dB

UMi-Street Canyon LOS:
PL = 32.4 + 21 log₁₀(d) + 20 log₁₀(f_c) dB

InH LOS:
PL = 32.4 + 17.3 log₁₀(d) + 20 log₁₀(f_c) dB

f_c in GHz, d in meters. Shadow fading: 4 dB (LOS), 7.8 dB (NLOS) typical.

TR 38.901 Scenario Parameters

Scenario	BS Height	ISD	Delay Spread (median)	Angular Spread (AoD)
UMa LOS	25 m	200-500 m	60 ns	12°
UMa NLOS	25 m	200-500 m	200 ns	30°
UMi-SC LOS	10 m	100-200 m	40 ns	15°
InH LOS	3 m	20-50 m	20 ns	40°
RMa LOS	35 m	1-5 km	30 ns	5°

Common Questions

Frequently Asked Questions

What scenarios does TR 38.901 define?

Five: UMa (25m BS, wide-area), UMi-Street Canyon (10m, narrow streets), UMi-Open Square, InH-Office (3m ceiling), and RMa (35m BS, up to 5 km). Each has LOS/NLOS path loss models and scenario-specific fading parameters.

CDL vs. TDL?

CDL (Clustered Delay Line) includes spatial angles for beamforming simulations. TDL (Tapped Delay Line) has only delay/power, no spatial info. CDL-A through CDL-E and TDL-A through TDL-E are defined with different delay spread profiles.

How does it handle mmWave?

Higher path loss exponents (3.5-4.0 NLOS), blockage model for human/vehicle shadowing (20-35 dB), oxygen absorption above 60 GHz (15 dB/km at 60 GHz), and spatial consistency for correlated fading during UE movement.

Related Terms

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