# A Review of Cognitive Control: Advancement, Definition, Framework, and Prospect
## 7 Main Issues, Research Directions, and Development Prospects of Cognitive Control
### Development Prospects of Cognitive Control  
By establishing control systems to conform to the cognition paradigm, cognitive control changes the way to build control systems from an automation perspective. In traditional control systems and general intelligent control systems, there is usually one kind of controller, which is referred to as the physical controller in this article; the physical controller is used to control actuators or the physical systems (when there exist no actuators in the system). In cognitive control systems, there exist two kinds of controllers, i.e., physical controllers and cognitive controllers. The existence of cognitive controllers makes control systems convenient for coping with uncertainties coming from the environment. For example, in [110; 111; 112; 113], the influences of packet drop and time delay in wireless communication are mitigated by using the cognitive controller to change the number of retransmissions of the MAC layer cognitively; in [121; 122; 123], the cognitive controller is employed to select communication channels to avoid the negative influences of cyber-attacks. Hence, we could not make assumptions about uncertainties and design physical controllers that are tolerable to the assumed uncertainties. From this point of view, cognitive control is prospective in systems that operate in unknown or highly uncertain environments. With the popularization of Industry 4.0, the CPS has been widely used in engineering systems, and the uncertainties coming from the environment become non-negligible influences; the performance of the following kinds of control systems could be improved by cognitive control. * Networked control systems (NCSs). In NCSs, the data and information are transmitted through the wired or wireless network, reducing the geographical restrictions on control systems; however, due to the uncertainties, such as packet drop and time delay, and the unexpected influences, such as cyber-attacks, the NCSs face risks. In traditional control systems, the way to address the influences induced by the network is to make the physical controller tolerable to them. As introduced in [110; 111; 112; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123], cognitive control provides a new way to address these uncertainties; in cognitive control systems, the cognitive controller could be used to adjust the parameters of communication to mitigate the effects of the network on control systems. * Distributed control systems (DCSs). The basic thought of distributed control is decentralized control and centralized management. Generally, a DCS contains many subsystems which are coupled with others. When a certain subsystem fails, the topological structure of the DCS needs to be adjusted; in cognitive control systems, the physical controllers are used to control the corresponding subsystems, and it is convenient to use the cognitive controller to adjust the topological structure, which is a difficult task for the physical controller. * Fault-tolerant control systems. Fault-tolerant control is to make the system have the ability to tolerate faults. In the case of a system failure, the basic function of the system can still be realized. When the actuator, sensor, or component failure occurs in the system, the control system can still ensure its own safe operation through fault-tolerant control adjustment and meets certain performance indicators and requirements. One of the research focuses on fault-tolerant control is to control fault systems. Since the kinds of faults are diverse, they are hard to control by using control methods such as reconfiguring controllers and integrity controller design. At the same time, when a fault occurs, the new controller implemented after the system is reorganized is generally difficult to match the dynamic characteristics of the fault system, which will lead to control failure.