top of page

Millimeter Wave Propagation in 5G NR: A Comprehensive Technical Overview

Updated: Jul 4

Millimeter Wave Propagation in 5G NR: A Comprehensive Technical Overview
Millimeter Wave Propagation in 5G NR: A Comprehensive Technical Overview

The millimeter wave (mmWave) spectrum, characterized by frequencies between 30 GHz and 300 GHz, is a cornerstone of 5G New Radio (NR) technology. It offers the potential for ultra-high-speed data transmission due to its capability to support wide channel bandwidths. This article explores the technical aspects of mmWave propagation, focusing on its challenges and the sophisticated models used to address them.


Band Combinations for Dual Connectivity

3GPP has specified band combinations for Dual Connectivity (DC) between multiple NR operating bands. Inter-band NR-DC, combining Frequency Range I (FR1) and Frequency Range II (FR2), is outlined in TS 38.101-3. These combinations are crucial for leveraging the diverse characteristics of different frequency bands to enhance network performance.

Table 1: Supplemental Uplink Band Combinations (FR1)

TDD Band

Supplemental Uplink Band

SUL Band Combination

n78

n80

SUL n78-n80

n78

n81

SUL n78-n81

n78

n82

SUL n78-n82

n78

n83

SUL n78-n83

n78

n84

SUL n78-n84

n78

n86

SUL n78-n86

n79

n80

SUL n79-n80

n79

n81

SUL n79-n81

Characteristics of Millimeter Wave Propagation

The mmWave spectrum is of particular interest due to its potential for wide channel bandwidths and high throughputs. However, mmWave propagation comes with unique challenges, summarized in Figure 1 and detailed below.

Figure 1: Characteristics of mmWave Propagation

Characteristic

Impact

Short Wavelengths (1 to 10 mm)

Increased free space propagation loss

Oxygen Absorption at 60 GHz

Significant absorption and power loss

Water Absorption at 24 GHz

Increased attenuation in humid conditions

Rain Drop Attenuation

Frequency-dependent attenuation, significant in heavy rain

Foliage Attenuation

Substantial loss through dense vegetation

Building Penetration Losses

High attenuation through walls and windows

Lack of Diffraction

Limited ability to bend around obstacles

Increased Scattering

Waves scatter more due to smaller wavelength

Increased Reflections

More reflections from smaller objects

Blocking by Objects

Vulnerable to signal blockage by moving objects

Propagation Models and Path Loss

The fundamental equation for free space path loss between two isotropic antennas is given by:

Free Space Loss (dB)=20log⁡10(distance)+20log⁡10(frequency)+32.4\text{Free Space Loss (dB)} = 20 \log_{10} (\text{distance}) + 20 \log_{10} (\text{frequency}) + 32.4Free Space Loss (dB)=20log10​(distance)+20log10​(frequency)+32.4

Where distance is in kilometers and frequency is in megahertz. This equation serves as a starting point for more sophisticated path loss models, such as those in 3GPP TR 38.900 for urban macro line-of-sight scenarios.

Table 2: Free Space Path Loss at Various Frequencies

Distance (km)

300 MHz

3 GHz

30 GHz

0.5

77.4

97.4

117.4

1.0

83.4

103.4

123.4

1.5

87.4

107.4

127.4

2.0

90.4

110.4

130.4

Specific Attenuation Factors In 5G NR

  1. Oxygen Absorption: Oxygen molecules resonate at 60 GHz, causing significant absorption of radio wave power. This results in higher path loss at frequencies close to 60 GHz, typically quantified in dB/km.

  2. Water Absorption: Water molecules resonate at 24 GHz, leading to increased attenuation. This effect is particularly pronounced in humid conditions and is also measured in dB/km.

  3. Rain Attenuation: Rain drops scatter radio waves, causing frequency-dependent attenuation. For example, a rainfall rate of 5 mm/hour can cause an attenuation of 1 dB/km at 30 GHz and 2 dB/km at 50 GHz.

  4. Foliage Attenuation: The CCIR (now ITU-R) provides an empirical model for foliage loss: Foliage Loss (dB)=0.2×frequency0.3×depth0.6\text{Foliage Loss (dB)} = 0.2 \times \text{frequency}^{0.3} \times \text{depth}^{0.6}Foliage Loss (dB)=0.2×frequency0.3×depth0.6 For instance, at 30 GHz and a foliage depth of 10 meters, the loss is 17.5 dB.

  5. Building Penetration: Building materials significantly affect signal penetration. Brick and stone can attenuate signals by more than 20 dB, while energy-efficient windows can cause more than 30 dB attenuation.


Beamforming and Rapid Handovers

Beamforming is essential in the mmWave band to improve link budgets. The small size of antenna elements allows for the practical implementation of antenna arrays at both the Base Station and the UE. This results in highly directional beams, which can improve signal quality but are also susceptible to blockage. Rapid handovers are necessary to maintain connectivity when the line-of-sight path is obstructed, such as by moving vehicles.


Benefits for Network Deployments

Despite increased propagation losses, mmWave frequencies are advantageous for high-density network deployments. The high path loss helps isolate tightly packed small cells, reducing inter-cell interference and leading to noise-limited rather than interference-limited link budgets.


Conclusion

The millimeter wave spectrum is pivotal for achieving the high data rates and low latency promised by 5G. While it presents unique propagation challenges, sophisticated models and techniques such as beamforming and rapid handovers are employed to mitigate these issues. Understanding the characteristics and propagation behavior of mmWave frequencies is crucial for optimizing 5G network performance.


References

  • 3GPP TS 38.101-1: NR; User Equipment (UE) radio transmission and reception; Part 1: Range 1 Standalone

  • 3GPP TS 38.101-2: NR; User Equipment (UE) radio transmission and reception; Part 2: Range 2 Standalone

  • 3GPP TS 38.101-3: NR; User Equipment (UE) radio transmission and reception; Part 3: Range 1 and 2 Non-Standalone

  • 3GPP TS 38.104: NR; Base Station (BS) radio transmission and reception

  • 3GPP TR 38.900: Study on Channel Model for Frequency Spectrum above 6 GHz

  • Millimeter Wave Propagation: Spectrum Overview

  • ITU-R P.833-9: Attenuation in Vegetation


These references provide a comprehensive understanding of the technical aspects and challenges associated with millimeter wave propagation in 5G networks, offering valuable insights into the deployment and optimization of these high-frequency bands.

5 views0 comments

Comments


bottom of page