# Robust Simulation of Cyber-Physical Systems for Environmental Monitoring on Construction Sites
## 2 Literature Review
### System Robustness  
Researchers in several fields defined robustness with different connotations, while the entry points for previous studies correlated with robustness also vary [28, 29]. Robustness is a crucial attribute in systems' handling of uncertainty problems [30]. Some studies focus on the influencing factors in system robustness and achieving system robustness [31, 32]. Other studies focus on system robustness design. This ensures that the system can achieve robustness by creating control structures or schemes. There are mainly two ways for achieving system robustness in order to respond to environmental changes. Firstly, reaction capabilities can be used to passively respond to environmental changes. Secondly, preemptive capabilities can be used to respond actively. Consequently, some researchers conducted studies from different perspectives. Security defense is a crucial issue in achieving system robustness [33]. In this complicated system, fault tolerance also characterizes a system's robustness under uncertainty conditions such as modeling uncertainty, parametric uncertainty, and unpredictable events. According to the connotation of CPS, individuals such as implementers and decision-makers are also constituent elements since their irrational behaviors are associated with making inappropriate decisions. Some researchers mention that constructing a general fault-tolerance framework for error detection and error handling can enhance the capacity of fault tolerance [34, 35]. Consequently, [PERSON] established a generic guidance framework in order to identify the most robust decision choices and applied a software package to gain intelligent decisions [36].  
In terms of resource failure, an isolation strategy is developed to promote the power system's robustness. In this approach, some typical clusters are separated from the main network, and independent alternative energy sources are used as a power supply [37]. Another method to improve the system's robustness consists in building autonomous nodes that have stripped off the interaction among networks, in order to cope with the damage caused by buffer failures [38]. Although the current studies yield some benefits, the system's robustness still suffers from several limitations. In fact, most of the existing robustness methods are based on specific application scenarios, and they are difficult to migrate to different types of application scenarios. On the other hand, several researchers consider CPS as a technical system while ignoring the fact that E-CPS is a technology-social system, whose robustness results from the interaction of technology, management, and personnel elements.  
The literature review demonstrates that uncertainty is a critical issue that should be paid attention to regarding E-CPS. The existing studies focus on the security defense, resource failure, and fault tolerance of system robustness, while a lack of studies on E-CPS robustness exists. However, E-CPS suffers from more severe problems such as maintaining satisfactory performance when facing uncertain data quality and model specifications. Therefore, it is necessary to extend E-CPS robust design and simulation scenarios according to the actual needs of construction sites, as well as conduct targeted operations within corresponding scenarios.