The realization of 5G is well on its way with mobile network operators (MNOs) in many cities already deploying the infrastructure in select cities all over the U.S. The inclusion of relatively new technologies including the use of new spectrum blocks in higher frequency ranges, extensive installation of outdoor small cells, a non-terrestrial SATCOM infrastructure, and massive MIMO (mMIMO) base stations along with the densification of macro-cells and the wireless backhaul network, all contribute to meeting the 5G key performance indicators (KPIs) that was originally set in 2015 within the IMT-2020. This, for instance, includes the 1 ms latency in ultra-reliable low latency communications (uRLLC), 10 to 100 times the 4G data rate for enhanced mobile broadband (eMBB), and 10 year battery life for massive machine type communications (mMTC). Parameters such as these along with the strict capacity (1000x), perception of availability (99.999%), and perception of coverage (100%) requirements supports the ever-increasing bandwidth demands put on wireless networks globally.
This, however, is merely a stepping stone for 6G connectivity where near-instant connectivity is anticipated to be achieved in order to support future, bandwidth hungry processes with holographic media, artificial intelligence (AI)/machine learning (ML), smart wearables, autonomous vehicles, commuting reality devices, sensing and 3D mapping. This begs the question: What exactly is 6G and when will it be available? This article aims to provide a basic answer by discussing the differences between these two generations of cellular networks, with detail on the future vision of 6G and its supporting technologies.
5G use cases and some supporting technologies
As early as 2012 there was buzz around the development of 5G with plans of it vastly surpassing 4G LTE speeds and coverage. Serving any and all applications by smartly leveraging multiple radio access technologies (multi-RAT) to better serve customers. As of 2020, there were 26 billion internet-connected devices globally, this is anticipated to increase to almost 40 billion by 2025 and nearly 50 billion by 2030—the year that 6G is expected to begin filling market demands. With the number of connected devices and bandwidth-hungry wireless applications, 5G would likely not be able to meet the speed and capacity requirements to support the number of connected devices. However, similar to how 5G is built upon the 4G infrastructure with additional components, 6G is expected to rely on the established 5G network.
As stated earlier, the 5G vision has been mainly focused on serving three applications: eMBB, uRLLC, and mMTC. These three applications however, require focused network planning around optimizing throughput, latency, and coverage respectively. The eMBB application is particularly challenging in dense urban environments where there is expected to be a massive installation of outdoor small cells as well as an extensive underground fiber optic network to support the traffic and throughput demands from the urban center. Because of this, there has been a major effort around realizing millimeter-wave (mmW) communications technology for mobile networks—a spectrum space that was traditionally exclusively utilized for military and science purposes for radar and imaging.
This has proliferated mmW-based research in antennas, RF transceivers, and fabrication processes so that they are more readily integrated into user equipment. This all comes with the typical power (EIRP) and propagation requirements/considerations that are native to cellular components and networks. This has been particularly challenging considering the path loss at mmW frequencies—the high frequency signal attenuates greatly over distance causing the need for line-of-sight (LoS) links at close distances. Moreover, mmW frequency signals tend to scatter at an obstacle as opposed to its low frequency counterpart that can often diffract around an obstacle.
The uRLLC applications rely upon a highly synchronized network, at low-to-medium throughputs, with a very high device density. Table 1 shows some sample uRLLC scenarios, often in an industrial automation setting. However, public safety and medical applications are also required to have low latency and reliable communications. For instance, in a remote surgery application where a surgeon must be little time delay between the controller and equipment. This type of communications requires a dedicated backhaul backbone, low time errors in the synchronization path/clock chain from the primary reference time clock (PRTC) down to the telecom transparent clock (T-TC), with stringent end-to-end quality of service (QoS) goals.
Table_1_-_uRLLC_applications
The mMTC applications almost directly correspond to the proliferation of IoT devices in industry vertices from commercial to industrial. This is supported by the ever-growing presence of new IoT protocols and the marketplace for IoT development platforms, bringing previously unknown data to the cloud for complex analysis and feedback. The network for this type of communication does not have the bandwidth constraints of eMBB nor the stringent latency requirements of uRLLC, rather, strict battery life/node maintenance expectations along with coverage in the unconnected areas of the globe. Power saving protocols and energy harvesting techniques are used in these compact nodes with smart placement in order to ensure ideal connectivity along with OTA firmware updates for minimal maintenance after installation.
name="_58r6g0udge94">What is 6G expected to support?
The applications have a natural progression to more a ubiquitous virtual experience with AR/VR applications, tactile internet along with intensive predictive analysis/modeling via the proliferation of artificial intelligence (AI) processing within said devices. These push current technologies to the next level. The mixed reality (MR) experience uses 3D objects and AI to provide a seamless, immersive experience with a high integrity 6G connection.
An example of this would be holographic communications where conventional video conferences are augmented with a realistic projection for a three-dimensional image. The concept of connected robots and autonomous systems to provide basic services such as mail/package delivery also requires a high-fidelity wireless connection to enable the proper feedback necessary to control the destinations of such equipment.
Other future wireless applications include a brain-computer interface (BCI) where appliances can be controlled via a communication path between the user’s brain and the device's RF front-end. This can be extended to the medical field with medical wearables tracking/monitoring a patient's health while they are in hospice. Entirely automated industrial facilities with intensive computing will require a reliable connection to the cloud in order to perform the complex data analytics necessary for remote control and predictive analysis.
This control can range according the industrial subsystem including real-time location systems (RTLS) for monitoring, actuator controls for robotic-arm, autonomous mobile robots (AMRs) and automated guided vehicles (AGVs) for plant-floor monitoring/maintenance, machine vision (MV) systems for quality assurance, and naturally, the monitoring/control of equipment through extensive wireless sensor networks (WSNs). IoT is expected to proliferate to the internet of everything (IoE) where there is expected to be autonomous coordination among a massive number of remotely connected sensors and devices, all providing feedback on its status to the internet. The five potential use cases for 6G can include the following 1:
- Enhanced mobile broadband plus (eMBB Plus)
- Big communications (BigCom)
- Secure ultra-reliable low-latency communications (SURLLC)
- 3D integrated communications (3D-InteCom)
- Unconventional data communications (UCDC)
These are built upon the three major 5G use cases (eMBB, uRLLC, and mMTC) where eMBB plus is an evolutionary step beyond eMBB. BigCom however, focuses on service ubiquity regardless of location (e.g., dense urban, rural, remote, etc). The use case of uRLLC is built upon with SURLLC for military and industrial communications that require high reliability, determinism and security.
The use case of 3D-InteCom refers to the coverage granted from the integration of non-terrestrial components such as satellites and drones, raising the 2D coverage of the earth to a more 3D space. The application of UCDC is most divergent from traditional cellular use cases as it refers to advanced technologies that are not yet incorporated into everyday life including holographic communications, tactile internet, and BCI.
name="_uhvgepjfk1ag">How will 6G support this connectivity?
The 6G infrastructure is expected to be built upon 5G with some critical additions that diverge from the traditional contemporary cellular technologies. One major aspect of 6G is the incorporation of the terahertz spectrum from 0.1 THz to 10 THz. This massive block of additional spectrum has the bandwidth to support the connectivity needed through the use of photonic and hybrid electronic-photonic transceivers. The benefit of this technology over most mmW technology is that a line-of-sight (LoS) link is not required. A cell-less architecture is called upon to support 6G where user equipment (UE) is connected to the RAN as opposed to a singular cell. This can be realized through the tight integration of difference communication technologies (e.g., sub-6 GHz, mmW, THz, and visible light communications (VLC)) where 6G devices can support all these heterogeneous radios within the device. This eliminates the gaps in coverage that come with handovers.
More 3D coverage of the globe is also envisioned where the current ground coverage is built upon non-terrestrial platforms such as drones, balloons and LEO/MEO/GEO satellites. The concept of network virtualization that was introduced in 5G is anticipated to be realized within 6G with a disaggregated network architecture and the virtualization of the medium access control (MAC) and physical (PHY) layers of the OSI model that typically require dedicated hardware. Table 2 shows some of the major differences in performance and parameters between 5G current and what is 6G is expected to be. As can be seen, the KPIs of 6G differ greatly from 5G and therefore require innovative technologies to support this connectivity.
Table_2_-_Comparing_5G_and_6G
Making 6G a Reality
There are already research initiatives kicked-off in different countries in order to realize 6G. In Finland, the University of Oulu kickstarted Finnish 6G research in 2018. The FCC opened up the 95 GHz to 3 THz spectrum for experimental licenses, opening up research opportunities for optical/photonic communication links in the U.S. As of 2019, South Korea and China began putting together working groups dedicated to 6G research between companies, government departments, and universities. It goes without saying that 6G is very much a nascent platform. However, between the potential new technological solutions and the KPIs, it will become the new goalpost for innovation beyond 5G.
About the author
Aalyia graduated with a bachelor's of science in electrical engineering, with several publications regarding her research of carbon nanotube materials in RF transmission lines. After graduating, Aalyia was employed in mixed signal IC design and layout, before moving back to her native New York City, where she has held RF engineering positions at Mini-Circuits and BAE Systems. She has over five years of experience of engineer-level technical writing and engineering consulting work within the RF and microwave industry.
References
- Dang, S., Amin, O., Shihada, B. et al. What should 6G be?. Nat Electron 3, 20–29 (2020). https://doi.org/10.1038/s41928-019-0355-6
- M. Giordani, M. Polese, M. Mezzavilla, S. Rangan and M. Zorzi, "Toward 6G Networks: Use Cases and Technologies," in IEEE Communications Magazine, vol. 58, no. 3, pp. 55-61, March 2020.
