RF5G mmWave Technology: A Comprehensive Overview
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5G mmWave technology utilizes millimeter wave frequencies in the fifth generation (5G) of wireless communication networks. Millimeter wave (mmWave) refers to radio frequencies in the range of 30 GHz to 300 GHz, which are higher than the frequencies traditionally used in wireless cellular communication.
About 5G
To meet the demand for higher data rates, aiming for 10 Gbps and beyond, 5G technology has been developed. The specifications are detailed in the 3GPP Release 15 and later.
5G operates across different frequency ranges:
- Sub 6 GHz (optimized for 5G macro cells)
- 3-30 GHz (suitable for 5G small cells)
- 30-100 GHz (designated for 5G Ultra Dense deployments)
About Millimeter Wave
The frequency band between 30 GHz and 300 GHz is known as millimeter wave. This naming comes from the fact that the wavelength of electromagnetic waves at these frequencies is in the millimeter range.
There are both advantages and disadvantages associated with mmWave. The increasing number of mobile data subscribers has led to a demand for larger bandwidth. Since bandwidth is limited in the available mobile frequency spectrum below the mmWave band, operators have explored the millimeter wave band as a mobile frequency spectrum due to its capacity to support larger bandwidths.
While mmWave frequencies suffer from higher penetration loss and cannot easily penetrate walls and certain objects, and are also attenuated by rain, careful consideration of these factors in RF link budget calculations suggests that mmWave has a promising future in the mobile data broadband market.
About 5G Millimeter Wave
5G millimeter wave refers to the millimeter wave frequencies used for 5G mobile technology.
Features
The following table outlines the key features of 5G millimeter wave technology:
| Features | Description |
|---|---|
| Data rate | 10 Gbps or higher |
| Frequency Bands | The bands are split into <40 GHz and >40GHz upto 100 GHz frequency |
| Frequency Bands & Bandwidths | • 10 subcarriers of 100 MHz each can provide 1GHz BW due to carrier aggregation at <40 GHz • 500 MHz to 2 GHz BW can be achieved without carrier aggregation at >40GHz |
| Distance coverage | 2 meters (indoor) to 300 meters (outdoor) |
| Modulation types | CP-OFDMA <40GHz, SC >40GHz |
| Frame topology | TDD |
| Latency | About 1 ms |
| MIMO type | Massive MIMO is supported. Antennas are physically small, allowing for approximately 16 antenna arrays in 1 square inch. Consequently, 5G mmWave compliant eNBs support 128 to 1000 antenna arrays, enhancing both capacity and coverage. |
For frequencies above 40 GHz, Single Carrier modulation is used to improve power amplifier (PA) efficiency and beamforming. It also reduces switching overhead. In Null CP SC type, regular Cyclic Prefixes (CPs) are replaced with null CPs, resulting in a constant envelope in the modulated waveform.
5G Millimeter Wave Frame Structure
Figure 1: Proposed 5G millimeter wave frame structure
As shown in Figure 1, DL (Downlink) refers to transmission from the eNB to UEs, while UL (Uplink) refers to transmission from UEs to the eNB. The separation of control and data planes helps achieve lower latency requirements, as processing of control and data parts can occur in parallel.
5G mmWave Symbol Table (Numerology)
The following table presents probable numerology for two FFT (Fast Fourier Transform) sizes used in 5G millimeter wave technology: 1024, 2048, and 4096.
| FFT Size | 1024 FFT Point (70 GHz) | 2048 FFT Point (3 to 40GHz) | 4096 FFT Point |
|---|---|---|---|
| Carrier Bandwidth | 2000 MHz | 200 MHz | 200 MHz |
| Subcarrier spacing | 1.5 MHz | 120 KHz | 60 KHz |
| Symbol Length | 666.7 ns | 8.335 µs | 16.67 µs |
| Number of syms/frame | 14 | 14 | 14 |
| CP (Cyclic Prefix) duration | 10.4 ns | 0.6 µs | 1 µs |
Advantages of 5G mmWave Technology
The following are the advantages of 5G mmWave technology, positioning it as a strong contender for the future of mobile wireless communication:
- Larger Bandwidth: Accommodates more subscribers due to the increased bandwidth available.
- Smaller Cell Deployment: More favorable for smaller cell deployments due to less bandwidth in millimeter range.
- Viable Scatter Paths: Coverage isn’t limited to line of sight, as first-order scatter paths are viable.
- Channel Sounding: Employs channel sounding to address various losses at mmWave frequencies, ensuring satisfactory 5G network performance. Channel sounding involves measuring or estimating channel characteristics, aiding in the design, development, and deployment of 5G networks with the necessary quality requirements.
- Massive MIMO: Small antenna size allows for a large number of antennas to be packed into a small area, enabling the use of massive MIMO in eNBs/APs to enhance capacity.
- Dynamic Beamforming: Mitigates higher path loss at mmWave frequencies.
- High-Speed Backhaul & Access: Supports multi-gigabit backhaul up to 400 meters and cellular access up to 200-300 meters.
These benefits make 5G mmWave suitable for mobile communication over sub-6GHz wireless technologies.
Disadvantages of 5G mmWave Technology
The following are the disadvantages of the 5G mmWave wireless system:
- Losses and Coverage: Millimeter waves experience various losses (penetration, rain attenuation, etc.), limiting the distance coverage of mmWave in 5G cellular mobile deployments. Path loss at mmWave frequencies is proportional to the square of the frequency. It supports approximately 2 meters indoors and 200-300 meters outdoors, depending on channel conditions and AP/eNB height.
- Line of Sight (LOS) Propagation: Supports only LOS propagation, limiting coverage.
- Foliage Loss: Significant foliage loss at mmWave frequencies.
- Power Consumption: Higher power consumption due to more RF modules and antennas. To address this, hybrid architectures with fewer RF chains than antennas are used at the receiver. Low-power analog processing circuits are designed in mmWave hardware.
These disadvantages must be considered during 5G millimeter wave link budget calculations for successful 5G millimeter wave deployment.
References
Conclusion
5G mmWave technology is designed to meet the demands of densely populated urban areas and locations requiring high data throughput. It complements 5G networks utilizing sub-6 GHz frequency bands, providing a balance between coverage and capacity. The combination of sub-6 GHz 5G and mmWave 5G technologies aims to deliver seamless and high-quality wireless connectivity for various applications.
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