Feature: Communications
Figure 2: 6G interconnectivity
Technologies to explore When considering 6G, there are at least four promising technologies to examine for their market potential and feasibility:
Joint communication and sensing 6G will require much more environmental sensing and awareness and data collection and processing, underpinned by various communication standards. Autonomous vehicles, for example, have incredibly advanced sensing systems that fuse data from a variety of cameras, lidar and radar sensors using machine-learning algorithms. T ese vehicles depend on cellular networks for streaming infotainment, environment- and performance data, and vehicle-to-everything communications. Sensing researchers are looking to communications
technologies such as orthogonal frequency-division multiplexing (OFDM) or multiple-input, multiple-output (MIMO) phased arrays to improve the 6G experience. In contrast, communications researchers see opportunities for more data bandwidth in the vast swaths of radar-allocated spectrum. Regulatory and technical factors will determine the extent to which these two traditionally distinct functions work together, but their combination may defi ne 6G.
Sub-Terahertz bands Due to the constant demand for more data bandwidth, researchers are exploring the underutilised parts of the spectrum in the sub- THz frequency bands – primarily between 90GHz and 300GHz, which provide many times the amount of spectrum currently used for cellular communications. T e 3GPP has already identifi ed 121.2GHz as a potential 6G frequency. However, one major barrier in moving to the sub-THz bands
is path loss. This could be mitigated by matching a frequency band’s attenuation properties for the application. Using high- attenuation bands for high-security applications, for example, limits how far the signal travels. Furthermore, the inverse relationship between frequency and antenna size provides one method for overcoming path loss. As frequency rises, antenna geometry and spacing shrink, allowing for more elements and thus more gain in the same footprint. Given the delay in 5G mmWave deployments to date, it may
appear a tad premature to discuss moves to the sub-THz bands; still, this move paves a way to increase network capacity.
MIMO Building on popular multi-antenna techniques, MIMO promises potential benefi ts across many diff erent applications and frequency bands. Whilst beamforming is key to overcoming sub-THz path-loss challenges, multi-user MIMO improves spectral effi ciency for the heavily-used sub-8GHz bands. In these bands, where antenna size becomes excessively large, distributed MIMO is especially interesting. T is technique disaggregates the large antenna arrays into multiple, geographically-separated radio heads that are much smaller. T e expansion of MIMO aims to increase cell capacity and provide improved location services.
AI/ML Artifi cial intelligence (AI) and machine learning (ML) are the fourth technology that will play a signifi cant role in 6G. With increasing complexity, the aim of squeezing every bit of bandwidth from the available spectrum becomes crucial. However, with traditional signal- processing approaches, it is becoming increasingly diffi cult to optimise the communication system. One way of dealing with this complexity is to use machine learning. AI/ML-driven design or adaptation to dynamically optimise link performance can provide improvements in areas such as beam management, automatic spectrum allocation and RF non-ideality cancellation. Whereas at the application layer, AI/ML allows the optimisation of Quality of Service (QoS) for factors like latency or energy effi ciency that take into consideration application-specifi c requirements, together with the environment. T e availability of large, open data sets for wireless communications research and training of AI/ML algorithms will play a major role in the development of 6G.
Is there a killer app? 6G will off er many opportunities, some possibly not imagined today; but, looking at it from this stage, is there a killer app? We have relied on connectivity and virtual experiences throughout
recent global events, and many of us have a new appreciation for a reliable, high-speed network. In addition to technology buzzwords like immersive extended reality (XR) and key performance indicators such as 1Tb/s data rates, 6G discussions are beginning to include social and sustainable goals like “connectivity for all”. As 5G is developing to extend beyond enhanced mobile broadband, and as the defi nition of 6G coalesces, it will be just as important to answer the business and social questions as the technical ones.
www.electronicsworld.co.uk September 2021 25
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