mmWave Development and Evolution Overview

Each iteration of communications technology has brought new experiences and opportunities to society. Millimeter wave (mmWave), a high-frequency-band communication technology, plays a vital role in the evolution from 5G-Advanced (5G-A) to 6G, promoting communication technologies to new heights.

mmWave Development in 5G-A

5G-A starts from Release 18 (R18), further advancing and expanding 5G technologies. As one of the key 5G-A technologies, mmWave operates at frequencies from 30 GHz to 300 GHz. Compared with traditional communication frequency bands, mmWave is characterized by short wavelengths and wide frequency bands. This allows more antenna elements to be packed within the same antenna size, providing favorable conditions for the application of large-scale multi-input multi-output (MIMO) technology.

Key mmWave applications in the 5G-A phase include:

• Large, high-density gathering places: mmWave supports huge data traffic demands in places such as large stadiums and commercial centers.
• Industrial internet: In factory workshops, mmWave enables high-precision equipment interconnection and real-time transmission of operational and monitoring data, facilitating intelligent production management and fault prediction.
• XR applications: In XR experience scenarios such as immersive VR games or AR navigation, mmWave ensures fast and stable data transmission, delivering extremely high definition and smooth virtual experiences.
• Live broadcast of HD and 4K videos: mmWave is ideal for live streaming large concerts and sports events. With high-speed transmission capabilities, mmWave base stations ensure the real-time and stable delivery of live HD and even 4K video signals to a wide audience on their devices.

mmWave integrated sensing and communication (ISAC): With its high-precision sensing capabilities, mmWave can be widely used in low-altitude security and logistics. In waterways, mmWave technology enables effective ship detection and tracking, assisting maritime departments in enriching supervision services. In addition, the high-precision feature of mmWave ISAC has been explored for applications such as vehicle-road coordination and micro-deformation detection of bridges and landslides.

mmWave Evolution from 5G-A to 6G

The evolution of mmWave from 5G-A to 6G is marked by continuous upgrades and enhancements, aimed at achieving an intelligent network with higher rates, lower latency and wider coverage.

Frequency Band Expansion: Towards Higher Frequencies

With communication technologies moving towards 6G, mmWave frequency bands will be further extended to higher frequencies. FR2-2, the frequency range beyond

52.6 GHz was introduced in 3GPP R17, and further spectrum expansion is expected in 6G. For example, initial exploration and applications in the 0.1-10 THz frequency range may be involved. Higher frequency bands will offer wider available bandwidth, enabling higher peak rates than those of 5G and 5G-A. This will meet extreme bandwidth requirements of future applications such as holographic communication and ultra-high-definition 8K/16K video transmission.

Technology Integration and Miniaturization

In the 6G era, mmWave communication equipment will evolve towards higher integration and smaller size. Base stations will become more compact and easier to deploy, reducing deployment costs. The continuous advancements in semiconductor and micro-nano processing technologies have enabled the internal components of base stations to be more tightly integrated, significantly reducing the size and weight of the equipment.

Similarly, terminal devices, such as smartphones, intelligent wearable devices, and drone communication modules, will integrate miniaturized mmWave communication modules, improving portability while giving full play to the communication performance of mmWave. This will drive the wide application of the mmWave technology across various terminal devices.

Intelligent Beam Management and Adaptive Communication

To support 6G native AI communication, mmWave in 6G will use more intelligent beam management and adaptive communication technologies. Intelligent beam management can automatically adjust beam characteristics based on complicated environmental conditions—such as dynamically changing obstacles and user distribution—to optimize signal transmission. Base stations (BSs) or UEs can decide which AI algorithm to use.

Fig. 1 shows examples of how the 3GPP standard supports AI-based beam management through the signaling framework, without the need to standardize specific AI algorithms.

• Fig. 1a: The mechanism for UE to provide feedback on its mobility information is standardized so that the information can be used as an input to the neural network at BS for AI-based beam management.
• Fig. 1b: The BS performs AI-based beam management to predict the future beams and sends the future beam indication information with timestamps to the UE via signaling.
• Fig. 1c: The neural network is implemented at the UE side in this case. Feedback is standardized to support AI output results from the UE, such as beam prediction results or recommended demodulation pilot information.
• Fig. 1d: Collaborative AI is done between BS and UE. The BS is responsible for training and downloading the trained neural network to the UE. The UE executes the neural network to generate the final beam prediction result.

Multi-Site Cooperative Communication  

To further enhance the robustness and networking flexibility of 5G mmWave communication, multi-site joint transmission needs to be considered in the first version of 6G mmWave communication, including non-coherent multi-point coordination and coherent multi-point coordination. In addition to the multi-TRP based channel/RS repetition supported in 5G-A, a new topology structure needs to be considered, such as uplink and downlink decoupling. In this new topology, uplink and downlink services can be implemented through different physical sites: Downlink sites can be selected based on the best received signal power or SINR, while uplink sites can be selected based on path loss to achieve the best uplink reception.

Multi-Modal Sensing

In future 6G, ISAC technologies will rely on new frequency bands such as THz and visible light, as well as new technologies such as air-space-ground integration and native AI to endow 6G systems with native sensing capabilities. As an important evolution in sensing technologies, multi-modal sensing integrates multiple sensing technologies and data sources, including mobile communication signals, radars, sensors, cameras, Wi-Fi, ultrasonic waves, Bluetooth, and RFID. Different sensing technologies, combined with data fusion techniques, can significantly improve the accuracy and security of detection, positioning, identification, and estimation.

Key technologies in the future will focus on exploring advanced fusion methods for multi-granularity and multi-modal sensing information, the collaborative application of deep reinforcement learning tools, and the coordinated utilization of multi-source sensing information. The collaborative sensing of multi-modal information will provide powerful support for the wide-area expansion of 6G system capabilities.

Prospects for 6G mmWave Application Scenarios

6G mmWave has a wide range of application scenarios, including immersive communication, holographic communication, greater integration of XR in industrial design, AI perception, and high-precision positioning and tracking.

Holographic Communication and Immersive Experience

With the ultra-high communication rates and bandwidth of 6G mmWave, holographic communication becomes possible. Holographic images can be transmitted in real time over mmWave networks, allowing for remote activities such as holographic conferences and performances, and blurring the boundary between the virtual and real worlds.

Advancing and Expanding XR Applications

In the 6G era, with the further development of mmWave technologies, XR applications will expand further. For example, in building design and industrial maintenance, virtual design solutions or maintenance guidance information can be overlaid onto real-world scenarios or devices through AR/MR applications, improving work efficiency and accuracy.

Deepening and Expanding mmWave Sensing Scenarios

ITU-R has defined IMT-2030 to cover six major application scenarios, including new scenarios such as ISAC, AI and communication, and ubiquitous connectivity. In the future, ISAC systems will leverage a variety of features such as super-large-scale antenna array, large bandwidth, multi-band integration, network multi-point collaboration, AI perception with native computing power, and multi-modal sensing, providing high-precision positioning and tracking, target imaging and reconstruction, action recognition, and agent interaction.  This will empower the  development of intelligent transportation, low-altitude economy, smart factories, and smart medical services, thus promoting industrial transformation and upgrades.

mmWave technology, guided by new technologies such as THz, AI-driven MIMO beams, and air-space-ground integration, will greatly expand its service scope. It will bridge the physical and digital worlds, ushering a new era of ubiquitous sensing, ubiquitous connectivity, and ubiquitous intelligence.