Special issue on 6G wireless systems

While 5G is currently being deployed around the globe, research on 6G is under way aiming at addressing the coming challenges of drastic increase of wireless data traffic and support of other usage scenarios. 6G is expected to extend 5G capabilities even further. Higher bitrates (up to Tbps) and lower latency (less than 1ms) will allow introducing new services — such as pervasive edge intelligence, ultra-massive machine-type communications, extremely reliable low-latency communications, holographic rendering and high-precision communications — and meet more stringent requirements, especially in the following dimensions: energy efficiency; intelligence; spectral efficiency; security, secrecy and privacy; affordability; and customization. Artificial intelligence approaches and techniques, such as machine learning (of which deep learning and reinforcement learning are specific examples), and machine reasoning (which includes planning, scheduling, knowledge representation and reasoning, search and optimization), are the new fundamental enablers to operate networks more efficiently, enhance the overall end user experience and provide innovative service applications. Quantum Optics Computing (QOC) and Quantum Key Distribution (QKD) are almost ready for industrial applications. In particular, massive Internet of Things (mIoT), Industrial IoT (IloT), fully automated robotic platforms (which include control, perception, sensors and actuators, as well as the integration of other techniques into cyber-physical systems), vehicles and multisensory extended reality are examples of the new data-demanding applications, which will impose new performance targets and motivate 6G design and deployment.