Cooperation between Networked Multiple Robots for Exploration

In multiple mobile robot system, cooperation among robots usually executes through communication. With the advance in technology nowadays, each robot can be equipped with off-the-shelf wireless device following the standard IEEE 802.11. However, due to the limitation of transmission range as well as the complexity of environment and signal transmission, maintaining connection between a pair of robots while they are executing their tasks becomes difficult. We construct a wireless ad hoc network multi mobile robots system with consideration of continuous connection between two robots, the Leader and any Follower. Also, our algorithm can be applied to a group of mobile robots when we utilize the wireless environment to establish continuous sharing of information among the robots. In order to enhance the system’s performance, we build a communication framework using the multicast technique. By using this framework, one robot can easily exchange its data with others when coordination is needed. Furthermore, when keeping the connection between two robots, we enhanced the teaming stability of the whole system. Finally, with our framework we create a flexible mobile robot system in which every robot can minimize the energy in communication with the rest of team. The overall performance is validated in the simulation system and experiment.Table of Contents Acknowledgments I Abstract III Table of Contents V List of Figures VII Chapter 1 Introduction 1 1.1. Motivation 1 1.2. Brief Literature Review 3 1.3. Contribution 5 1.4. Thesis Organization 6 Chapter 2 Preliminaries 9 2.1. Wireless Network 9 2.1.1. Wireless Local Area Network (Wireless LAN) 9 2.1.2. Wireless IEEE 802.11 Architecture and Protocols 12 2.1.3. Properties of Wireless Transmissions 14 2.2. Ad-hoc Network for Mobile Robots 16 2.2.1. Need for Ad hoc Robotic Network 17 2.2.2. Characteristic Features of Wireless Ad hoc Robot Network 18 2.2.3. Ad hoc Routing Protocol 19 2.2.4. Ad hoc Robotic Network Architecture 22 2.3. Transmission Protocols 24 2.3.1. The TCP Connection 24 2.3.2. Connectionless Transport UDP 25 Chapter 3 Communication in multiple mobile robots 27 3.1. Problems in Communication between Robots 27 3.2. Methods in Maintaining/recovering Communication 29 3.2.1. Rally Point 30 3.2.2. Communication Recovery Behaviors 32 3.2.3. Value-based Communication Preservation (VBCP) 33 3.2.4. Perceived Signal Strength based Method 35 3.3. Mobility Models and the Impact on Connection Stability 37 3.3.1. Mobility Patterns 37 3.3.2. Entity Mobility Models 41 3.3.3. Group Mobility Models 45 3.3.4. Influence of Mobility 48 Chapter 4 Cooperation between Networked Multi-robot System 53 4.1. Coordination for Exploration 53 4.1.1 Frontier Cell and Occupancy Grid Map 54 4.1.2 Cost of Reaching a Target Location 56 4.2 Algorithm to Maintain Communication between Networked Mobile Robot 57 4.2.1 Mobility Prediction 57 4.2.2 Controllable Parameters 59 4.2.3 Threshold Values 60 4.2.4 Strategy for Robot’s Behavior 61 4.2.5 Controller Design 63 Chapter 5 Experiment and Simulations Results 71 5.1 Winsock API and Programming Model 71 5.1.1 Winsock API 71 5.1.2 Winsock Programming Model 73 5.2 Communication Framework built on UDP and Multicast 74 5.2.1 Purpose of Building a Communication Framework 74 5.2.2 Implementation of Building a Communication Framework 75 5.3 Results with the Group of 2 robots 78 5.4 Results with the Group of 3 robots 82 Chapter 6 Conclusion and Future Work 85 6.1 Conclusion 85 6.2 Future Work 86 References 8