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), lora module 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.

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 4G DTU 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.

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.