communi- cations, among others [7]. The expected requirements are the following: Peak transmission rate in the order of 1 Tbps User experienced data rate in the order of 1 Gbps Latency: minimum values in the 10-100us range and consideration of end-to- end delay metrics Mobility: maximum vehicular speeds of up to 1000 km/h Device connectivity density: up to 107 links/km², mainly focused on massive machine-type communications Energy efficiency: reduction in the 10 to 100 times ranges in terms energy efficiency per bit as compared with current 5G metrics Peak spectral efficiency: up to 90 bps/Hz in the downlink and 45 bps/Hz in the uplink Several functionalities within B5G and 6G communication systems are foreseen in order to enable the required capabilities in order to adequately deliver service provision: Extended spectral use: new frequency bands are under consideration in the mm-wave range (up to 300 GHz, with main focus in 60 GHz bands for indoor use), THz range (up to THz, mainly focused on indoor communications, wireless backhaul, stringent QoS applications, Internet of Everything, and ultra- massive machine-type communications), visible light communications (VLC, from 400 to 800 THz, relying on line-of-sight communications, amenable to high-density hot spots, and massive IoT deployments), and optical wireless communications (OWC, spanning from IR range, visible and up to the lower UV wavelengths). The use of this extended frequency range can be further improved by using dynamic spectrum management, supported by cognitive radio and listen-before-talk contention schemes. The use of higher-frequency bands benefits from theoretical higher values of bandwidth and in some cases reduced interference levels as compared with sub 6 GHz. However, given the propagation characteristics, especially in upper mm-wave bands, operation is going to be mainly constrained to line-of-sight links with moderate link distances. Therefore, in the case where coverage extension is required, sub 6 GHz frequency bands will be employed in