# Mapless Collaborative Navigation for a Multi-Robot System Based on the Deep Reinforcement Learning
## 1 Introduction  
Autonomous navigation for mobile robots is one of the most practical and essential challenges in robotics. The navigation systems for mobile robots mainly rely on the localization in a given map and the decision-making system. The relative technique for localization is called Simultaneous Localization and Mapping (SLAM) [1; 2], which can obtain the map of the environment and get the robot poses simultaneously. In addition, the corresponding decision-making system which consists of planning [3; 4; 5; 6; 7] and control [8; 9; 10] would generate a safety trajectory and control the mobile robot to follow it until reaching the goal. The decision-making system plays an important role to connect the preceding localization stage and the following manipulation stage. This paper provides a decision-making method to address the core problem of robot navigation. We particularly focus on dealing with the motion planning and control problems with a navigation method based on the deep reinforcement learning. The traditional decision-making system of the mobile robot can be hierarchically structured into four components, the route planning, the behavioral decision-making, the motion planning and the robot control [11]. For indoor navigation tasks, the decision-making system can be simplified into the motion planning part and the navigation control part. The mobile robot is supposed to plan a trajectory from its current position to the target destination with the specific indoor environment. Then, the motion controller will guide the mobile robot precisely follow the trajectories to the targetposition. The required efficient motion planning strategies and stable motion controllers are mainly based on the mathematical computations and geometric relationships. Although useful in many situations, the applicability of traditional decision-making systems is limited by their flexibility and versatility. The complexity of the environment and the dynamic obstacles can both increase the computational efficiency and decrease the navigation performance. In addition, the errors of each step will be accumulated to the end. Furthermore, most of the traditional methods can't address the mapless navigation tasks in the complex environment. However, there are many practical situations in which the mobile robots can't obtain the accurate map of the environment and only have the relative position relationship between the mobile robots and the targets. Thus, we proposed an end-to-end policy module with the raw sensor inputs to address these issues in mapless navigation tasks. The deep reinforcement learning techniques have been greatly developed and widely applied in various fields of study. This kind of technical training the agent is conducted through the interaction trajectories between the agent and the environment. Intuitively, the character of interactive learning is quite similar to humans. When we consider the mapless navigation tasks, with a given target value and the current position, one person is likely to find the target position heuristically with his intuition. If one person is informed about the relative position values or the polar relationship to the target, he can easily find the target position based on the prior knowledge and the basic navigation strategies in an indoor environment. Compared with the traditional navigation methods, one human has a more efficient way to navigate without computing the precise mathematical module of the unknown environment. In addition, the deep reinforcement learning technique paves the way to accomplish the robot mapless navigation tasks like humans. With the aim of teaching the robot to navigate like humans, this work presents an approach to training the robot to navigate with the human intuition. By utilizing the proposed deep reinforcement learning method, the policy module of the mobile robot can make decisions through the raw 2D lidar sensor data and navigate to the target position in an indoor environment.