# 6G Cognitive Information Theory: A Mailbox Perspective
## 3 Intelligence Networking for 6G  
### The Evolution of 6G  
After evolution and development, communication technologies have evolved from human-body information transmission to simple signal communication via wired and wireless communication systems. In the current situation of widespread mobile-device usage, data transmission from devices to edge clouds mainly relies on the most widely used wireless/mobile-communication technologies. From the perspective of transmission fusion, existing technologies and related literature can be summarized in terms of which tasks or data are transferred to which computing node, i.e., what, where, how, and when to transmit. The question of how to transmit refers to determining what is currently the most widely used wireless/mobile communication network and technology. The questions of what, where, and when to transmit relates to the fusion and joint optimization of the network communication model and resources. Due to the requirements for power consumption, coverage, transmission rate, cost, number of connected devices, and other related parameters, the IoT wireless communication technology has been a driving force in supporting different application scenarios,including short-range communication, low-power wide-area communication, and mobile cellular network communications. The mentioned communication technologies, with mobile cellular communication as the main research object, are established using multi-scale intelligent sensors all over the heterogeneous IoT where a communication network with the fusion application is gradually forming. As mobile cellular-communication technology continues to evolve towards the sixth generation (6G), wireless access technologies have followed different evolutionary paths. These technologies focus on performance and efficiency in highly mobile environments. With the first generation (1G), the basic mobile voice-communication needs were realized, while for the second generation (2G), capacity and coverage expansion was the main motivation. The third generation (3G) technology opened the door to a mobile broadband experience with higher data-exploration speeds. The fourth generation (4G) technology provided a wide range of telecommunications services, including advanced mobile services provided by mobile and fixed networks. The 4G also supported packet switching with high mobility and high data rates. The fifth generation (5G) technology aimed at changing the world by connecting everything. It not only focused on new frequency bands, but also pursued requirements for higher performance, greater speed, multiple connections, higher reliability, lower latency, higher universality, and specific topological structures in application fields. As for the sixth generation (6G), pervasive AI and edge intelligence will be redefined [23], i.e., an ultra-flexible architecture will be designed and realized to introduce human-like intelligence to all levels of network systems. In recent years, 5G has entered the fast track of commercial deployment, and 3 GPP has released the standard schedule of 5G. 5G has opened a new era of interconnectivity of everything. It has also penetrated a variety of industries, including transportation, agriculture, and energy. The 5G networks can realize ubiquitous information acquisition and meet the requirements for key performance indicators under the scenarios of enhanced mobile bandwidth, large-scale IoT, high reliability, and low latency. With the development of 5G academia, industry, and other research communities have begun to look beyond 5G, and it is expected that the key technologies of the 6G mobile communication networks will be made available in 2023 [6]. 6G will have a brand-new architecture and the capability to support the digitalization of the whole world [24]. Through the reconstruction of people and scenes in the physical world to the digital world, 6G will give IoT cognitive devices and strong intelligence and interactions in ubiquitous interconnection.