Sixth Generation (6G) Wireless Networks: Vision, Research Activities, Challenges and Potential Solutions  
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1 Department of Electrical Engineering, College of Electronics and Information Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Korea; [EMAIL_ADDRESS]  
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2 Department of Electrical Engineering and Information Engineering, College of Engineering, Coveant University, Canananland, Ota P.M.B 1023, Ogun State, Nigeria; [EMAIL_ADDRESS]  
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3 Department of Electronics and Communications Engineering, A'Sharatyish University, Ibra 400, Oman; [EMAIL_ADDRESS]  
3 Department of Computer Engineering, Faculty of Engineering and Architecture, Istanbul Gelsim University, Avellar, 34310 Istanbul, Turkey; [EMAIL_ADDRESS]  
3  
[PERSON]  
4 Department of Computer Engineering, Faculty of Engineering and Architecture, Istanbul Gelsim University, Avellar, 34310 Istanbul, Turkey; [EMAIL_ADDRESS]  
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5 Department of Computer Science and IT, University of Lahore, Gujrat Campus 50180, Pakistan; [EMAIL_ADDRESS]  
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6 School of Electrical Engineering, University of Ulsan, Ulsan 446  
including multimedia, online gaming, and high-definition video streaming. The booming mobile Internet technology is the catalyst enabling and propagating various state-of-the-art user-defined services, such as mobile shopping and payment, smart homes/cities, and mobile gaming [1,3]. The standardization of 5G communications has been completed, and the system is being deployed worldwide. Figure 2 shows the 5G commercial network world coverage map (5G field testing/5G trials/5G research). South Korea was the foremost nation to adopt substantial 5G deployment on a large scale for approximately 85 cities with 86,000 5G base stations as of April 2019 [4]. However, 85% of the 5G base stations were located in six cities, including Seoul, Busan, and Daegu, where a 3.5 GHz (sub-6) spectrum in distributed architecture with deployed data rate speed tested speeds in the range of 193 to 430 Mbit/s [5]. In general, close to 65% of the world's population are estimated to gain access to 5G superfast 5G Internet coverage by the end of 2025 [6]. 5G networks will deliver an extensive variety of services comprising enhanced mobile broadband (eMBB), ultra-reliable and low-latency communications (uRLLC), and massive machine type communications (mMTC); for detailed information about the vision, requirements, and core features of 5G wireless cellular mobile communication networks, refer to [2, 7, 8, 9]. However, wireless data traffic volume and the magnitude of connected things are expected to leap to hundredfold of equipment in a given cubic meter. Moreover, data-hungry apps such as sending holographic videos needs a spectrum bandwidth that is currently unavailable in the mm-wave spectrum. This situation presents difficult challenges on an area or a spatial spectral efficiency and the needed frequency spectrum bands for connectivity. Hence, a broader radio frequency spectrum bandwidth has become a necessity and can only be found at the sub-terahertz (THz) and THz bands. Moreover, the recent upsurge of diversified mobile applications, especially those supported by Artificial Intelligence (AI) technology, is spurring heated discussions on the future evolution of wireless communications [10]. These challenges have motivated industry and academia to start conceptualizing the next generation of wireless communication systems (6G) aimed at providing communication services for the future demands  
Figure 1: Major milestones for different generations of communications (1–6G). of the 2030s [11] and maintaining the sustainability and competitiveness of wireless communication systems.