Multi-Band Sensing: Empowering Industry Applications

China's 5G development has now moved beyond network construction and entered a new phase of application innovation. Building on further evolution and enhancement of 5G network capabilities, the introduction of revolutionary technologies such as integrated sensing and communication (ISAC) can better support scenarios such as low-altitude economy, intelligent driving, and high-end manufacturing.

In November 2023, the International Telecommunication Union Radiocommunication Sector (ITU-R) released the “Framework and Overall Objectives of the Future Development of IMT for 2030 and Beyond”. This recommendation, also known as a global vision for 6G, serves as a blueprint for defining global 6G standards. It defines six major usage scenarios for 6G, three of which are enhanced communication scenarios that build upon 5G's eMBB, URLLC, and mMTC—namely, immersive communication, hyper reliable and low-latency communication, and massive communication. ISAC, AI and communication, and ubiquitous connectivity are three new scenarios introduced by 6G. Among these, ISAC enables 6G mobile communication networks to have dual engines: communication and sensing.

The traditional telecommunications industry has long focused on increasing the amount of information carried by each hertz of electromagnetic waves. Now, it has entered a new phase where electromagnetic waves are directly utilized for sensing purposes, leading to the integration of sensing and communication technologies, and opening a new dimension in the utilization of communication spectrum. Leveraging the abundant communication spectrum and infrastructure resources, a ubiquitous sensing network can be constructed to better support various applications. Sensing capabilities serve as a bridge between the physical and digital world, providing richer content for generative AI models and facilitating the development of digital twins. These advancements represent crucial directions for development from 5G-Advanced (5G-A) towards 6G.

Throughout the evolution of mobile communication networks, both communication and sensing have relied on wireless electromagnetic waves as their medium, making radio spectrum a critical element essential for the survival and growth of mobile communications. Currently, the primary frequency band utilized by 5G systems is in the sub-6 GHz range. In the updated version of China's "Radio Frequency Allocation Regulations", the entire or part of the 6.425–7.125 GHz (U6G) band has been allocated for IMT systems. Additionally, 3GPP has initiated channel modeling research for the FR3 band (7–24 GHz). The use of millimeter wave (mmWave) bands in 5G applications is rapidly growing, and the mmWave bands will undoubtedly play a significant role in 5G-A and 6G systems. All these frequency bands will be crucial in shaping the future of 5G-A and 6G technologies.

This article analyzes the sensing applications in the aforementioned frequency bands and explores methods for collaborative sensing across different bands, aiming to provide insights for enabling sensing capabilities in more frequency bands.

Suitable Sensing Applications for Different Frequency Bands

Sensing is a technology that extracts features of targets or the environment by analyzing the reflections of wireless radios, with applications spanning consumer entertainment, industries, and beyond. Depending on the nature of the sensing targets, applications can be categorized into four major types:

• Monitoring, localization, and tracking applications: These applications detect entities such as pedestrians, UAVs, vehicles, automated guided vehicles (AGVs), animals, and ships in various use cases. They can be further divided into applications focused on detecting a target’s presence, localizing it, and tracking its trajectory.
• Motion monitoring applications: These focus on detecting partial body movements, encompassing use cases like respiratory monitoring, sports monitoring, fall detection, and gesture recognition.
• Environmental monitoring applications: These involve monitoring environmental phenomena, such as rainfall, floods, and landslides.
• Environment reconstruction and imaging applications: These are designed for three-dimensional reconstruction or imaging of environments, including use cases such as 3D mapping, gaming, and network optimization.

Different use cases have varying requirements and correspond to suitable frequency bands. Based on the attributes of different frequency bands, Table 1 illustrates the potentially appropriate bands for each use case.

With the implementation of technologies such as wide bandwidth, multiple antennas, and mmWaves, 5G has acquired the initial sensing capabilities. ZTE, in collaboration with industry partners, is actively exploring 5G-A sensing applications based on sub-6 GHz and mmWave bands. Significant advancements have been made in low-altitude scenarios, where continuous detection and tracking of UAV intrusions have been realized. This technology has already been deployed at scale in commercial operations with carrier partners.

Multi-Band Collaboration Approachs

Future ISAC systems will collaborate across multiple frequency bands to perform both communication and sensing functions. There are three ways in which collaboration can occur across multiple bands:

• Different bands can play different roles, such as utilizing sub-6 GHz for communication and mmWave for sensing, as illustrated in Fig. 1 (a). Leveraging the extensive coverage of sub-6 GHz for communication and the high precision of mmWave for sensing, these two functions can be separately realized. However, this approach does not fully exploit the spectrum of both bands and keeps sensing and communication functions compartmentalized. It represents a compromise designed to minimize alterations to existing sub-6 GHz communication networks, which may not be the mainstream or widely deployed method for future integrated communication and sensing systems.
• Multiple bands collaborate to accomplish either sensing or communication tasks through carrier aggregation or multi-link approaches. For example, using a multi-link approach with both sub-6 GHz and mmWave bands to complete either communication or sensing functions, as depicted in Fig. 1 (b). When different bands work together to handle both communication and sensing services, the spectrum resources expand beyond a single band, significantly broadening the available bandwidth. A larger transmission bandwidth offers higher data rates for communication and higher resolution for sensing. However, there are coverage disparities across different bands. Moreover, supporting carrier aggregation or multi-link technologies across these bands increases terminal complexity and power consumption. In addition, multi-band carrier aggregation or multi-link technologies require precise power control and interference coordination mechanisms.
• Different bands assist each other, collaboratively completing a single communication or sensing task, as shown in Fig. 1 (c). For instance, in sensing scenarios, sub-6 GHz's wide beams can be initially used for scanning to roughly pinpoint the location of the sensing target. Subsequently, mmWave's narrow beams can be employed for precise scanning. This approach not only reduces the time required for mmWave beam scanning but also allows for the fusion of sub-6 GHz and mmWave sensing data to enhance overall sensing performance.

Potential Key Technologies

To support sensing capabilities in mobile communication systems, research into several potential key technologies is necessary.

• Waveform, sequence, and pattern design: Research is needed into waveforms, sequences, and patterns that support sensing across multiple bands while accommodating detection, localization, identification, imaging, and reconstruction of object targets—essential for delivering comprehensive sensing services. ZTE pioneered the industry's first solution that supplements linear frequency modulation (LFM) onto OFDM waveforms under the base station mono-static sensing, to address coverage challenges in sensing. This solution has been successfully implemented with favorable outcomes.
• Sensing measurement reporting: There are various levels of sensing measurement reporting involved. For applications such as detection, localization, and tracking, leveraging the computational power of base stations and their management of multiple AAUs enables the fusion of sensing data from multiple AAUs. Processing this data at the base station to derive sensing outcomes can significantly enhance sensing accuracy while reducing transmission overhead.
• Multi-band sensing collaboration: ISAC leverages the strengths and characteristics of different frequency bands to offer comprehensive, optimized solutions, facilitating a broader range of sensing applications and expanding possibilities for both end-users and industry stakeholders. Collaboration across multiple bands can enhance sensing accuracy or extend the sensing range; however, techniques for data fusion, synchronization issues, and beam management require further investigation.

Building on the foundation of technical research, it is necessary to develop communication-sensing prototypes to validate various ISAC technologies, advancing them from research to industry. Efforts should focus on identifying suitable scenarios for each frequency band, conducting effective commercial promotion, fostering related industrial chains, and laying the groundwork for ISAC to thrive in commercial applications by preparing the industrial landscape.

ZTE is actively exploring the applications of sensing across various frequency bands. Together with our operator partners, we have embarked on technical and application explorations for multiple sensing scenarios based on 5G networks in the sub-6 GHz and mmWave bands, encompassing network validation and testing for use cases such as detection and tracking of low-altitude UAVs, vehicles, pedestrians, as well as ship detection and tracking in rivers. These efforts have resulted in commercial deployments in several cities. ZTE is also delving into potential applications in bands like U6G, laying a solid foundation for future exploitation of these new spectrum opportunities.