# Advanced Physical-Layer Technologies for Beyond 5G Wireless Communication Networks
###### Abstract  
Fifth-generation (5G) networks will not satisfy the requirements of the latency, bandwidth, and traffic density in 2030 and beyond, and next-generation wireless communication networks with revolutionary enabling technologies will be required. Beyond 5G (B5G)/sixth-generation (6G) networks will achieve superior performance by providing advanced functions such as ultralow latency, ultrahigh reliability, global coverage, massive connectivity, and better intelligence and security levels. Important aspects of B5G/6G networks require the modification and exploitation of promising physical-layer technologies. This Special Issue (SI) presents research efforts to identify and discuss the novel techniques, technical challenges, and promising solution methods of physical-layer technologies with a vision of potential involvement in the B5G/6G era. In particular, this SI presents innovations and concepts, including nonorthogonal multiple access, massive multiple-input multiple-output (MIMO), energy harvesting, hybrid satellite terrestrial relays, Internet of Things-based home automation, millimeter-wave bands, device-to-device communication, and artificial-intelligence or machine-learning techniques. Further, this SI covers the proposed solutions, including MIMO antenna design, modulation detection, interference management, hybrid precoding, and statistical beamforming along with their performance improvements in terms of performance metrics, including bit error rate, outage probability, ergodic sum rate, spectrum efficiency, and energy efficiency. B5G; 6G; physical-layer technologies 20212139710.3390/s2109319710. The B5G/6G networks with technological advantages and demanding disruptive capabilities are expected to provide solutions to the ubiquitous connectivity and spectral demands in 2030 and beyond. The 6G networks would extend the 5G application scenarios (i.e., further-eMBB, ultra-mMTC, enhanced-uRLLC) and introduce new application scenarios, including ultrahigh-density data, ultrahigh-speed low-latency communications, and ubiquitous mobile ultra-broadband. Compared to 5G networks, 6G networks could achieve superior performance and offer new performance metrics. The key features of 6G networks are an uplink data rate of up to 1 Tbps (compared to 10 Gbps in 5G), spectral efficiency of up to 1000 bps/Hz/m\({}^{2}\) (compared to 10 bps/Hz/m\({}^{2}\) in 5G), reliability up to 10\({}^{-9}\) frame error rate (compared to 10\({}^{-5}\) frame error rate in 5G), mobility support of up to 1000 km/h (compared to 500 km/h in 5G), control-plane latency of less than 1 ms (compared to 10 ms in 5G), processing delay of 10 ns (compared to 100 ns in 5G), traffic capacity of up to 1-10 Gbps/m\({}^{2}\) (compared to 10 Mbps/m\({}^{2}\) in 5G), localization precision of 1 cm on 3D (compared to 10 cm on 2D in 5G), uniform user experience of up to 10 Gbps 3D (compared to 50 Mbps 2D in 5G), and full integration of artificial intelligence (AI) [6]. The potential evolutionary services/technologies of 6G networks include joint sensing and communication, reconfigurable intelligent surfaces (RISs), holographic MIMO surfaces and beamforming, free duplexing and spectrum sharing, massive device-to-device (D2D) communication, nonterrestrial communication, E-health and biosensing, automated vehicles and robotics for Industry 4.0 and beyond, tactile Internet, dynamic network slicing, and software-defined networking and network-function virtualization. In addition, the potential of radio signaling and maximal cognitive for intelligent radio transmission can be fully realized through AI-empowered systems with the aid of machine-learning (ML) algorithms. Simultaneously, the potential major challenges of 6G networks include communications in higher bands, device capabilities, network security, and transceiver and antenna designs [7,8]. Abbreviations used in this manuscript are listed in Table 1.  
The rest of the editorial is organized as follows. Section 2 provides the overview of the Special Issue.