## 1 Introduction  
Cyber-physical systems (CPS) represent the tight integration of physical systems with computing and networking capabilities. Networked control systems (NCS) are an important class of CPS, in which physical processes are controlled using networked sensors, controllers and actuators. Thus, the performance of these CPS directly depends on the predictability of the quality of the communication flows. Especially if such CPS are part of an industrial control and sensor application, the requirement of a very low packet drop rate under bounded communication delays is imposed on the networks.  
As of today, the typical state-of-the-art real-time wireless networks are much more predictable than their more general, contention-based counterparts, owing to their static topology and, in general, pre-planned routing and scheduling mandated by the respective standards. A very well-established example of such an approach is WirelessHART [1], a widely-used wireless industrial control/sensor protocol that offers real-time guarantees for delay-sensitive applications. However, such wireless standards do not mandate specific algorithms for performance-critical tasks, such as scheduling of nodes and/or physical layer resources in the link layer or providing an end-to-end routing. In these cases, system designers are free to choose and implement their preferred algorithms and to take competitive advantage of their more sophisticated designs. Thus, it is indispensable for system designers to verify their proposed approaches over a broad range of scenarios with realistic network sizes in order to ensure the resilience and scalability of their algorithms and designs.  
Verification of systems in general is a complex and involved procedure [2]. In our context, verification of the design choices can be done either by measurement on test beds or by simulations. The deployment of realistic testbeds is generally expensive. Moreover, even large testbeds cannot always accurately capture all of the possible channel conditions that a deployed system might encounter, e.g., fading over different channels. On the other hand, simulators are more flexible in this respect, but detailed packet-level simulators exhibit a high computational complexity, which results in limited scalability.  
In this paper, we propose a novel simulation framework, which overcomes the above-mentioned limitations. This framework can simulate a centralized wireless real-time mesh network efficiently. Moreover, it provides a high accuracy network simulation and especially includes a realistic model of the physical layer with multi-channel frequency-hopping mesh networks. We have evaluated the proposed framework by implementing a system simulator for WirelessHART-based NCS.  
The paper is organized as follows. In Section 2, we outline the challenges in the performance evaluation of wireless real-time mesh networks in the cyber-physical context. Section 3 describes the simulation framework and presents the general modeling techniques, especially with regard to the modeling of the performance of wireless links. Section 4 describes the implementation of the simulator and shows validation results. In Section 5, we present a specific system simulator design for WirelessHART-based industrial control networks to demonstrate the usefulness of our proposed approach.