Microwave Journal
www.microwavejournal.com/articles/36727-the-evolution-of-cellular-technologies

Early Indications of 6G

September 14, 2021
Charles Schroeder

While 5G deployments are just rolling out, those on the forefront of wireless communications research and standards are already looking toward 6G. Thought leaders from industry and academia are starting to define the vision for 6G and identify target use cases and promising technologies. While lofty goals motivate innovation, early research is critical to begin testing and proving what is achievable. Over the next few years, as many of us start to see 5G technology appear in our daily lives, 6G will be taking shape, first through pre-standards consortia and conferences, then through the 3GPP standardization process.

Over the past 40 years, cellular technology evolution has yielded a new generation of wireless standards approximately every decade and a transformative value proposition every 20 years. 1G and 2G targeted voice, bringing a new level of mobility and reachability to users. 3G and 4G tackled data, delivering the power of the internet, email and apps to handheld devices. Similarly, we expect that the effort and advances of both 5G and 6G will be needed to realize the wireless interconnection of everyone and everything.

5G’s initial release targets the most familiar usage scenario for consumers: enhanced mobile broadband to provide higher data rates for more users to tether or stream video to their phone on the go. The other 5G usage scenarios of massive machine-type communications (mMTC) and ultra-reliable low latency communications (URLLC) will get a boost with follow-on enhancements to enable use cases like industrial IoT and private networks driven by business applications. While these are certainly important technological advances, they have not yet reached the point of transforming peoples’ everyday lives.

WHAT 6G MIGHT LOOK LIKE

So, what’s next? What comes after voice calls and the internet? The aim of 5G is sometimes summarized as “connected everything”connecting billions of devices across vastly different usage scenarios embedded into all aspects of our lives. 6G extends the vision beyond just connections, integrating sensing to deliver truly immersive experiences (see Figure 1). While humans initiated the majority of wireless connections in 1G through 4G to make calls or get information, in 5G and 6G machines will be increasingly initiating these connections as they self-coordinate on our behalf. Terms like tactile internet and wireless cognition may sound like science fiction, but that may not be the case for much longer.

Figure 1

Figure 1 6G applications will require 5G network capabilities to be significantly enhanced.

While highly publicized steps are already bringing us closer to autonomous vehicles, other areas like eHealth and remote surgery, spectroscopy and imaging and centimeter localization to pinpoint a device’s physical position are only just starting to be explored. In addition, the ability to sense the surrounding environment also offers powerful new ways to optimize the network, based on physical position, proximity or other factors, to improve performance and efficiency. Some of these use cases may sound familiar and, in truth, many of them have existed as concepts since the early days of 5G. But the advances of 6G will be needed to make them a reality.

PROMISING ENABLING TECHNOLOGIES

To deliver on this ambitious vision, NI sees four key technology areas gaining broad interest in 6G research:

  • Use of higher (sub-THz) frequencies
  • Evolving multi-antenna techniques
  • Adoption of artificial intelligence (AI) and machine learning (ML)
  • Integration of communications with sensing capabilities.

Combining these technologies offers the potential for faster, higher capacity networks, the latency and sensing capability to enable rich, real-time experiences and the intelligence to optimize for numerous applications and key performance indicators (KPIs).

Moving to higher frequencies has already presented plenty of challenges in 5G mmWave, but the allure of wide swaths of unused sub-THz spectrum is irresistible. While the applications and business cases remain somewhat fuzzy, researchers are working to understand propagation characteristics and determine technical feasibility. A paper published by NYU Wireless researchers paints a surprisingly optimistic view of the potential of sub-THz frequencies for applications in outdoor urban environments, as well as backhaul and non-terrestrial networks. Data from initial channel sounding experiments at 142 GHz show that high propagation loss in the first meter of propagation and diffraction commonly thought to be prominent detractors for non-line-of-sight operation at these frequencies may be mitigated by high gain antennas and stronger reflections from common materials like glass and concrete walls.1

Large antenna arrays with many elements and more precisely directed beams are needed to overcome higher path loss and make sub-THz frequencies usable. In lower frequency bands, enhancements to massive MIMO are being considered to increase cell capacity. One new approach is distributed MIMO, which uses multiple geographically separated radio heads across the cell to improve performance. Given that the sub-6 GHz frequency bands serve most users today, even incremental spectral efficiency gains are extremely valuable.

As we’ve already touched on, the concept of joint communications and sensing is vast, spanning many industries, applications and device types. Different aspects of sensingincluding object detection, analysis of material properties, localization and gesture recognitionare being looked at from both a use case and technology perspective. The Barkhausen Institute is conducting research on joint communications and radar sensing techniques that may benefit several applications, such as Industry 4.0, autonomous driving and, more generally, “radar as a service.” These techniques could, for example, solve radar coordination issues and make beam alignment easier for mmWave communications at the same time. In several published papers, Barkhausen researchers explore the use of a chirped waveform that may be capable of serving both radar and communications, enabled by a single, reconfigurable, co-designed hardware system implementation.2,3 Historically, the primary goal has been the coexistence of radar and communications, but combining them to use the same waveform, spectrum and hardware could enable more flexible, efficient use of resources.

AI and ML will be another key enabler to squeeze every bit of bandwidth out of the available spectrum and optimize the network’s performance. On the RF side, examples include dynamically allocating resources, improving beam management and correcting for RF chain impairments or channel effects. At the application layer, with such a diverse set of use cases, AI and ML could help optimize for application-specific KPIs and make trade-offs between metrics like throughput, latency or energy efficiency. The availability of data is a prerequisite for AI and ML design and adaptation. Large, open datasets to train algorithms are essential for research and development, and additional sensing and data collection will be needed to drive AI-enabled decisions when deployed. Perhaps even more exciting than the wide-ranging possibilities for improving network performance, AI and ML have enormous potential of enabling a vast set of new applications built on top of 6G networks and devices.

While the viability and, ultimately, the value of these technologies remain to be proven, these early explorations provide a window into an exciting new frontier for commercial wireless communications.

CONCLUSION

The first 6G study items are expected to appear in 2025, kicking off the standardization work toward a 2030 rollout, while the evolution of 5G will continue in parallel with early 6G research (see Figure 2). The transformative value that we hope 5G and 6G will deliver is fun to imagine and, inevitably, there will be significant challenges encountered along the way. The data and learnings from these early research efforts are critical inputs for the broader wireless ecosystem to gain consensus on the technologies and use cases around which to build the next generation standard.

Figure 2

Figure 2 6G research occurring in parallel with 5G advancements, with 6G standards beginning by 2025.

References

  1. Y. Xing and T. S. Rappaport, “Propagation Measurements and Path Loss Models for sub-THz in Urban Microcells,” 2021 IEEE International Conference on Communications, June 2021, pp. 16, https://arxiv.org/pdf/2103.01151.pdf.
  2. F. Bozorgi, P. Sen, A. Barreto and G. Fettweis, “RF Front-End Challenges for Joint Communication and Radar Sensing,” 1st IEEE International Symposium on Joint Communications & Sensing, 2021, https://www.barkhauseninstitut.org/fileadmin/user_upload/Publikationen/2021/bozorgi_2021_jc_s.pdf.
  3. A. Barreto, M. T. Pham, S. George, P. Sen and G. Fettweis, “Analysis of a Chirp-Based Waveform for Joint Communications and Radar Sensing (JC&S) Using Non-Linear Components,” European Conference on Antennas and Propagation (EUCAP), 2021, https://www.barkhauseninstitut.org/fileadmin/user_upload/Publikationen/2021/barreto_2021_eucap.pdf.