## 1 Introduction  
6G wireless communication is a successor of 5G communication. As per [PERSON] et al. [1], it uses a higher frequency than any of its predecessors and provides a higher capacity and lower latency. This helps the technology to integrate communication over land, water, and air into one network with higher speed and reliability. This is a very important prerequisite for the large-scale adoption of the IoT. As stated by [PERSON] [2], the devices connected to IoT infrastructure are expected to reach billions, and this connection will ultimately depend on the speed of connectivity. It should also be noted that, at present, very little information is available on the standard of 6G wireless communication. However, given the rapid scale of the progression of communication from 2G to 5G in the space of a few years, the arrival of 6G communication is inevitable. This will eventually be a potential game-changer, as this technology would disrupt the current state of technology and intelligence. This is discussed by [PERSON] et al. [3], who point to the revolutionary nature of 6G communication, as it can have a wider frequency with greater communication transmission. Given the increasing role of artificial intelligence (AI), it is doubtless that 6G wireless communication will have a very important role to play in the future. This is because, unlike 5G, 6G does not require high power consumption and can be considered highly secure. Security is among the key issues that confront communication and IoT. This is because the current web is built on technology created over 50 years ago. Since then, there has been no major improvement in the web. However, as more devices are connected to the internet, a new challenge has been posed, as academicians and practitioners need to adapt to the changing role of technology. Furthermore, the main limitation of 5G and other previous networks is that they are insufficient to fulfill the connectivity requirements of 2030 and above. For example, 5G is limited to typical scenarios; therefore, villages and motorways are not well-covered, and a transition from classical technologies to 6G is required. Therefore, the main limitations of the previous networks are the security, coverage, and other concerns, which urge the need for 6G communication, especially in smart cities.  
In addition, as the research and markets show [4], there is a need for a critical re-assessment of smart cities in the realm of energy-efficient 6G communication. This should consider IoT infrastructure, market factors that could lead to a faster adoption rate, and strategies that enable the operations of smart cities. Smart cities are built on the principle of increased connectivity; thus, the existing communication infrastructure cannot enable the growth and operation of smart cities. This is one of the core reasons that the world should move towards the faster communication rate provided by energy-efficient 6G communication channels. Hence, it can be concluded that the development of smart cities occurs in tandem with the development of energy-efficient 6G communication. It is also acknowledged in the research and markets [4] that global investment in the infrastructure development of smart cities will exceed USD 3.6B, making it one of the next big things. Under this backdrop, it is important to carve out the technologies, trends, and applications of 6G wireless communication, which will remain the objective of this study.