Transmission Techniques for Future 6G Systems and Beyond

Dear Colleagues,

The future digital society, in the scope of increasing automation, namely the digital society of 2030 and beyond, comprises an increasing number of connected devices (IoT), including sensors, vehicles, aerial drones, data, etc. While 5G supports autonomous vehicles, the increasing number of sensors per vehicle requires higher-speed communications and lower latencies. Society and organizations demand new services to be included in 6G, such as:

• Augmented reality and extended reality;
• Artificial-intelligence-infused applications;
• Wireless brain–computer interactions;
• Holographic services;
• The integration of communications with localization, mapping, and remote control;
• Emerging eHealth applications;
• Improved autonomous vehicles;
• More efficient support of IoT, namely smart cities and smart houses, supporting an extremely high number of low-power devices;
• Support of flying vehicles and increased mobility speed.

The 6G network also aims to have higher energy efficiency and more efficient strategies for use in energy harvesting, so that the autonomy of user equipment can be increased, despite its demanding applications.

These new services and capabilities to be supported by 6G continue to require more efficient networks, such as increased data rates, lower latency, more efficient spectral efficiency, increased energy efficiency, and improved network capacity. Some of the foreseen requirements for 6G include:

• A nomadic peak data rate of at least 1 Tbps (100 times higher than 5G);
• A mobile data rate of 1 Gbps (10 times higher than 5G);
• Energy efficiency 10 to 100 times better than 5G;
• Spectral efficiency 5 to 10 times better than 5G.

While 5G requirements are achieved based on mm-Wave and m-MIMO, 6G must incorporate new concepts such as passive antennas, namely Reconfigurable Intelligent Surfaces (RISs). In order to achieve potential gains (coverage, interference cancellation, secrecy, spectral efficiency, etc.), the channel characteristics must be estimated, and this is difficult to achieve with passive elements. Recently, active antennas, such as Large Intelligent Antenna Systems (LISs), also referred to as Ultra Massive MIMOs (UL-MIMOs) or as Extremely Large Antenna Arrays (ELAAs), have been employed to achieve such gain desiderates, but with their use, the complexity also increases. In terms of frequency bands, 6G is revolutionary, as it includes Visible Light Communications (VLC) and Terahertz bands (100 GHz – 10 THz), enabling data rates in the order of hundreds of Gbps. VLC is a mature communication technique well suited for short-range coverage, although it is susceptible to interferences, such as from the Sun.

This Special Issue, “Transmission Techniques for 6G and Beyond”, will provide an overview of 6G communications and beyond, in terms of networks, services, and requirements, while describing the advancements in transmission techniques foreseen for future versions. All new ideas regarding how the performance, capacity, and/or spectrum efficiency of transmission techniques can be improved for 6G and beyond while keeping computational costs at an acceptable level are most welcome. Contributions to this Special Issue should provide an overview of how the proposed transmission techniques bring added value to the advancements in cellular communications in terms of performance and/or advanced requirements.

Dr. Mario Marques Da Silva
Guest Editor

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• cellular communications
• 6G and beyond
• LIS antenna systems
• RIS antenna systems
• block transmission techniques