# A Lookahead Behavior Model for Multi-Agent Hybrid Simulation
## 2 Related Works
### Traditional Agent Behavior Model  
From the structure, an agent consists of the sensor, the actuator, and decision components. The agent uses the sensor to perceive the environment and performs the act determined by the decision components through the actuator, which then affects the environment or other agents. Thus, the agent usually conducts the behavior modeling with the \"sense-think-act\" cycle, as shown in Figure 1[4]. Here, the agent first obtains senses from the environment, then processes these senses and thinks about what to do, and finally acts to affect the environment.  
The Scalable Agents Simulation System (SASSY) [4] and Parallel Discrete Event Simulation for Multi-Agent System (PDES-MAS) [30] are the main hybrid simulation platforms using this original Traditional agent Behavior Model (original TBM). The System for Parallel Agent Discrete Event Simulator (SPADES) [31] framework improves this model by establishing a \"sense-think-act\" delay model (which can be shorted as delayed TBM). In this model, an agent cycle consists of the following three steps: sense, think and act, each with a corresponding delay. These delays can be arbitrary, except for the \"think\" steps, which are not allowed to overlap in two cycles, and different steps of different cycles that can overlap within the delay time, as shown in Figure 2[31]. The \"think\" steps are not allowed to overlap because of the assumption that a typical agent only has one Central Processing Unit (CPU) and cannot think at the same time; this model can perceive the external environment while simulating the thinking of the agent.  
Figure 1: The “sense-think-act” behavior model.  
Figure 2: The agent delay model.  
These two typical TBMs describe the physical agent model intuitively using the cycle formed by the three steps of sense, think, and act. In the war system, the decision cycle based on perception can also be described using this \"sense-think-act\" paradigm. Among them, sense corresponds to the sensor processing, think corresponds to the process of Command and Control (C2), and act contains the implementation process of behaviors including maneuver, attack/defense, logistics management, and communication.  
However, these traditional \"sense-think-act\" models have some shortcomings in simulating the behavior of agents in a continuous process. From the perspective of information processing, the original TBM regards the agent and its behavior as information processing conducted by a device with an input and output (e.g., the agent's perception would be the input and its act would be the output). This type of input/output model is mainly for autonomous agents with intelligent acts. Even with the delayed TBM, the assumption that the \"think\" steps cannot overlap is mainly applicable to agents of the machine type and presents an inability to describe all agent types in a complex system.  
For example, some semi-autonomous entities in military simulation can not only determine and carry out an act required to accomplish a goal by sensing the external environment, but also perform actions by strictly following the order of the superior while under the superior's command and control. In this case, the agent can perform the act without needing to undergo the steps of sensing and thinking.