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Looking Forward to 6G

Looking Forward to 6G
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by Barry Manz, President, Manz Communications

With 5G deployments sprouting throughout the U.S., the conversation has moved on, even though wide 5G coverage is primarily available via low- and mid-band frequencies, nationwide coverage is spotty and unavailable in many areas, and almost all of 5G’s promises remain to be fulfilled. Nevertheless, although 6G is about a decade away, it is already making its presence felt, proof of which can be found in the IMS 2021 technical program. So, it’s a good time to take a look at how 6G is taking shape.

However, before we look ahead to 6G, we first need to explore what is coming before it, which is GPP Release 17. It is moving through the lengthy approval process, and formal release was predicted for the first quarter of this year, but the pandemic delayed that. The new release date is the end of next year. 3GPP Release 17 is more than a gap filler between the fifth and sixth generations (Figure 1).

Figure 1: Release 17 adds many capabilities beyond those within Release 16 Source: 5Gradio.com

Release 17 includes a long list of enhancements. There will be a greater focus on Machine Type Communication (MTC) using Low Power Wide Area Networks (LPWAN) for IoT communication, which is based on LTE-M and NB-IoT. Typical applications include smart metering, parking, building management, and controlling smart city lights. By increasing support for LPWANs such as LoRaWAN, 3GPP is effectively giving increased attention to the primary competitor of the major wireless carriers, as although its metrics are different, they compete directly with “cellular” for delivering IoT connectivity.

Ultra-Low-Latency Communication (URLLC) was designed to meet the latency and other challenges for robotics and manufacturing, but a new type of device type within a category loosely called New Radio (NR) Light should be created within Release 17 to support industrial wireless sensor networks. 5G NR Light will focus on end-user devices that have low RF output power (less than 200 mW), low data rates, and a channel bandwidth of 10 MHz to 20 MHz rather than 100 MHz for enhanced mobile broadband (eMBB) that provides greater data-bandwidth complemented by moderate latency improvements on both 5G and 4G LTE. It will use half-duplex transmissions, a simplified RF chain, smaller packaging, frequency hopping, and longer low-power modes to increase battery life.

Figure 2: Massive MIMO is one of the key enablers of 5G and will be even more important in 6G Source: Bell Labs Technical Journal

Massive MIMO (Figure 2), which has already become a critical technology for achieving capacity and overage, will continue to evolve in Release 17 based on what has been learned with current deployments. Integrated Access and Backhauling (IAB), introduced in Release 16, will further evolve to provide increased efficiency and support additional use cases. IAB allows multi-hop backhauling using the same frequencies as user equipment or a dedicated frequency. It builds on the spectral efficiencies of 5G, and the increased capacity afforded by the higher bands to provide an alternative to fiber for cell site backhaul. It can be employed as a short-term alternative to fiber or as a permanent option for more isolated antennas or those without right of way access. For instance, in disaster scenarios, it can be critical to enable the support of ad hoc and temporary IAB nodes. In addition, autonomous vehicles could use it for the distribution of information about road conditions delivered by traffic signs, lights, and various types of sensors.

5G has tip-toed into the millimeterWave region and Release 17 will expand this to frequencies above 52.6 GHz for dramatically increasing capacity for delivering broadband services indoors, in dense urban scenarios, and in other areas. These bands offer an immense amount of available unlicensed spectrum that while likely to be used in the next few years, but will ultimately become essential for ensuring high data rates, low latencies, and reliable service for real-time applications.

Moving on Up

When the details of 5G were first revealed, it was obvious that it was massive in scope and technical challenges, and it was widely promoted as being achievable, eventually. At the moment it has not been, but these are early days since 5G deployment only began less than a year and a half ago. Between now and when 6G is released, it is certain many of the challenges will have been solved, every smartphone and many tablets and laptops will have new bands, including those at the lower millimeterWave frequencies, and the networks will have transitioned from hardware-centric to defined mostly in software.

Figure 3: New generations of wireless technology appear about once per decade, with generations overlapping each other

It is important to keep in mind that, as shown in Figure 3, a new wireless generation appears every ten years with generations overlapping. The current generation continues to evolve while the early deployments of the next generation begin. 6G will take the same path. However, as 6G is every bit as complex as 5G, if not more so, it could be decades before everything in this generation is fully realized.

One of the most important advances in 5G that will be further improved in 6G is location positioning. Although a major benefit of the capability is for tracking in general, first responders will finally be able to locate the position where a 911 call was placed from a smartphone. This is currently not possible with the current approach that relies on the triangulation of macro base stations with some help from GPS.

What’s been missing is the ability to locate the caller in the Z-axis (vertically), so if the call is placed inside a multi-story apartment building, for example, first responders can identify the building but not the floor or the specific apartment. As they rush through the building, they have no way to know the exact apartment or even the floor. With 6G (and to some extent in 5G), this will finally be possible (Figure 4).

Figure 4: NextNav’s Pinnacle technology will make accurate Z-axis positioning possible Source: Bosch

The technologies from NextNav, which has been working to solve this for many years, have finally been adopted. The company’s Pinnacle solution based on its Metropolitan Beacon System (MBS) along with barometric pressure sensors in the phone can locate a caller within ±3 m vertically, exceeding ± 3 m 80% of the time, a requirement mandated by the FCC. It has already been integrated within the nationwide public safety broadband network, FirstNet, being deployed by AT&T, and as of March, NextNav began making it available in 4,400 cities in the U.S., representing the top 105 cellular market areas. By the time 6G arrives, it should be available almost everywhere, and almost certain to reduce the number of deaths associated with long response times.

6G proposes the use of unimaginably high frequencies in the sub-terahertz region, for which the required technologies are currently in the very early stages of development or simply do not exist. For that matter, many of the applications it is designed to serve do not exist either in tangible form. So, it is easy to speculate what all of these will be, but in general, the goal is to allow instantaneous communications between people, devices, vehicles, and the surrounding environment. It will also rely heavily on AI and machine learning to accommodate the needs of everything from autonomous vehicles to high-definition holographic gaming and many other futuristic applications.

Headline specifications are, of course, data rates and latency, as they currently are in 5G, and the projections show downlink data rates of 1 Tb/s, at least 1000 times faster than 5G. This will require 100 channel bandwidths measured in gigahertz rather than megahertz. And to serve the most demanding real-time applications, latency must be vanishingly small, perhaps 1 ms or less. To achieve this, infrastructure will have to be everywhere, indoors and outdoors. 5G will have paved the way for this in the ensuing decade by the deployment of massive numbers of very small cells and increasing use of millimeterWave frequencies.

There are immense challenges that must be overcome before 6G can become a reality, from the intense development of semiconductor technologies such as silicon germanium, silicon-on-insulator, and BiCMOS, and possibly indium phosphide that can produce reasonable amounts of RF power at sub-terahertz frequencies, to electronically-steered, phased-array antennas required to deliver enough gain to overcome the various factors that make communication extremely difficult in this spectral region.

That said, at these frequencies, electronically-steered phased array antennas can be extremely small. For example, an array consisting of 1000 elements can be 4-cm2 at 250 GHz. This number of elements can produce enormous amounts of forward gain, compensating for the low RF power levels likely to be achievable with any viable semiconductor technology. User equipment will be able to integrate these arrays with fewer elements (but still increasing received performance and delivering reasonable RF power).  Not only will they make communication at sub-terahertz possible, but their narrow beamwidths will also reduce interference and jamming. They will also be incorporated into small cell base stations.

Figure 5: The methodology developed by Technikon for the Reindeer project shows how RadioWeaves can be used Source: Institute of Signal Processing and Speech Communication at Graz University of Technology

Coverage extension technology will be necessary to provide services for drones, ships, and spacecraft as their service areas are not fully covered by conventional cellular networks. To remedy this, geostationary, low-earth-orbit satellites (LEO), and high-altitude pseudo-satellites (HAPS) may be employed to cover mountainous and remote areas, sea, and space, and to provide communication services to new areas. HAPS are getting increasing attention because they can be stationed at a fixed location at an altitude of about 20 km, producing wide coverage with a cell radius greater than 50 km on land. In addition, HAPS is a solution for providing backhaul to portable base stations during disasters and possibly for industrial IoT scenarios.

Accurate positioning and direction-finding coupled with superior sensing and imaging will be massively exploited in 6G, and studies show that 6G phones will be able to see behind walls by building maps of the local surroundings and combining the signals received from the environment with the highly directional, steerable antennas on the phone. A 6G smartphone will also provide precise position location accuracy that will be important for navigating robotic vehicles and self-driving cars. Along with these features will be high-definition video and augmented reality applications.

Dozens of novel schemes are being developed to make 6G possible and one of the most interesting is Project Reindeer from the Institute of Signal Processing and Speech Communication at Graz University of Technology’s Horizon 2020 project. They are working to create RadioWeaves technology (Figure 5), an antenna fabric that can be installed in any location of any size, such as wall tiles or wallpaper. Entire wall surfaces could act as antenna radiators. So, the 80,000 people in a sports stadium, all equipped with virtual reality goggles, could simultaneously watch a goal being scored from the perspective of the goal scorer. The antenna could also be used to provide power wirelessly to the VR goggles. The researchers believe it will also be possible to locate thousands of objects in real-time, so goods could be located with accuracy of 10 cm, creating three-dimensional models for production and logistics.

Summary

From a historical standpoint, it might be said 5G is the wireless generation that started the trend of making everything that could be connected, connectable;then 6G will be the one that brings what seems like science fiction today into the realm of reality. This will obviously take more than a few tweaks to devices, circuits, software, signal processing, and systems to realize, but the benefits are transformational. It will make possible data rates of 1 Tb/s, wireless cognition, centimeter-level positioning, and sensors that perform human-like functions in the 2030s and beyond. If 5G lets us download a movie in a few seconds, 6G will download 70 two-hour movies in 1 s. We’ll have to wait for all this to be available, but it will definitely be worth the wait.

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