Thus, the 6G communication systems are expected to provide a large coverage that allows subscribers to communicate with one another everywhere with a high data rate speed due to the unconventional technologies that will be adopted by 6G communication systems, such as an extremely large bandwidth (THz waves) and high AI that include the operational and environmental aspects as well as the services of the networks. Figure 3 presents the timeline of 6G communication. The first ever 6G wireless cellular mobile communications symposium took place in March 2019 and can be framed into one big vision statement of ubiquitous wireless intelligence [13]. The 6G system is expected to witness an unparalleled revolution that would significantly distinguish it from the existing generations and will drastically re-shape the wireless evolution from \"connected things\" to \"connected intelligence.\" Specifically, 6G will transcend mobile Internet and will be required to support ubiquitous AI services from the core to the end devices of the network. Quintessentially, AI will be the driving force in designing and optimizing 6G architectures, protocols, and operations [11; 14]. The current study aims to present the latest state-of-the-art developments in relation to the vision, challenges, and potential solutions as well as the research activities for 6G communications. Figure 3: Timeline of 6G wireless networks [11]. Figure 2: 5G commercial network world coverage map (December 2019) [12]. Accordingly, it attempts to integrate many likely solutions. Given the size constraint, this study thoroughly examined thought-provoking research areas by detailing their specific sub-domains to achieve precise, concrete, and on-the-spot deductions. The major contributions of this study are summarized as follows:  
* This work presents a comprehensive overview of controversial research topics on 6G communications covering the recent industry development in the context of the main areas of services, difficulties, and major actors. We summarize the core domains of the research topics as (i) vision and key features; (ii) challenges and potential solutions; and (iii) research activities. These areas were rigorously investigated on the basis of their respective sub-domains to achieve a precise, concrete, and concise conclusion;
* The challenges associated with 6G communications stem from five key components including the provision of network security and data privacy enforcement, attaining a cost-effective approach toward rapid network deployment and expansion with emphasis on remote and stand-alone areas, reduction in the price of mobile communications' utilization, approaches to extend mobile equipment battery life longevity, and attaining a high data rate buoyed with an end-to-end, ultra-reliable, low latency regime. Notably, satisfying all features is impossible. Nonetheless, tradeoffs between these features should exist, thereby leading to a delicate balance between needs and wants. This study highlights a set of tradeoffs including the key challenges and potential solutions for 6G communications;
* For researchers, this article will contribute significantly to opening new horizons for future research directions by providing several new references that could support the pursuit of enabling 6G communication. Figure 4 illustrates the outline of the paper. Section 2 presents a detailed vision of 6G communication with a focus on key features. Section 3 provides a detailed discussion of a set of tradeoffs, including key challenges and potential solutions for 6G communications. Section 4 highlights the current progress of research activities. Finally, Section 5 concludes the work. Figure 4: Schematic map of the structure of this paper.