Bandwidth Control Based on Wireless LAN for Applications in Multi-robot Cooperative System

在多群組機器人系統裡，同一時間將可能被分成數個子群體，而各個子群體所執行任務的可行性與流暢度取決於通訊品質的好壞，過大的資料傳遞延遲將可能使的任務合作失敗或執行效果不如預期，因此，依現今的無線網路架構下，提出了一個網路頻寬控制的機制，此一網路頻寬控制機制將可動態地依據任務或是各個群體的需求有效率地分配有限的網路資源，使的多群組機器人系統之合作可以有效率地被完成。在網路控制系統裡(NCS)的資料包括系統狀態與控制命令皆是以週期性的方式產生，此一周期性的資料傳遞特性將是在設計網路頻寬控制機制時最重要的效能指標。 在此網路頻寬控制機制裡，所有機器人的資料傳遞時機皆由一個網路控制器所控制，每隔一個網路控制器的週期時間，機器人所得到的頻寬將會依據任務的優先權與子群體的需求而被重新分配。而在每個機器人裡的封包排程器裡依據網路控制器的分配對每個資料流以週期性為指標做封包排程。透過模擬，此一網路頻寬控制機制成功的在網路控制系統下將多倒單擺控制良好。最後，經由實地測試可以驗證此一網路頻寬控制機制在無線網路系統中之可行性與效果。In multi-robot systems, mobile robots may be separated into several cooperative sub-groups. The smoothness and reliability of task execution in respective sub-groups rely on the quality of communication. Too large transmission latency may cause the failure of successful execution of given tasks or lower effectiveness in cooperation than being expected. This thesis mainly focuses on building a network bandwidth control scheme (NBCS) based on the existing Wireless LAN systems. This NBCS can dynamically allocate the valuable network bandwidth to cooperative sub-groups according to the overall assigned tasks. With the feed back packets interval, the NBCS forms a typical control system and fuzzy control theory is adapted in the network controller. In the NBCS, data transmission in each robot is managed by a Network Controller. The bandwidth for each robot will be reallocated by the Network Controller in accordance to its assigned tasks’ priority or the demands of the cooperative sub-groups. The packet schedulers in each robot will arrange the transmitting order for each data flow with the crucial property, “periodicity”. In the simulation, the multiple inverted pendulum system can be controlled well by the NBCS. Through experiments, the effectiveness of this scheme can be verified under Wireless LAN framework.摘要 I ABSTRACT II CONTENTS III CHAPTER1. INTRODUCTION 1.1 MOTIVATION 1 1.2 MULTI-ROBOT COOPERATIVE SYSTEMS 2 1.3 OVERVIEW OF NETWORKS FOR CONTROL. 3 1.4 ORGANIZATION OF THE THESIS. 3 CHAPTER2. BACKGROUND AND RELATED WORKS 2.1 CONTROL NETWORKS 9 2.2 OVERVIEW OF WIRELESS LOCAL ACCESS NETWORK 11 2.2.1 CONFIGURATIONS IN WIRELESS LAN 11 2.2.2 COORDINATION FUNCTIONS 13 2.3 BEST EFFORT TRANSMISSION AND RELATED WORKS IN ETHERNET 17 2.3.1 BASICS OF TCP/IP 17 2.3.2 RELATED WORKS FOR QOS IN ETHERNET 21 2.4 TRAFFIC SMOOTHER 22 2.5 RELATED SCHEDULERS 24 2.5.1 FIFO QUEUE 24 2.5.2 FAIR QUEUE 25 2.5.3 ROUND ROBIN SCHEDULER 26 2.5.4 WEIGHTED ROUND ROBIN SCHEDULER 27 2.5.5 WEIGHTED FAIR QUEUE 27 CHAPTER3 NETWORK SYSTEM STRUCTURE AND CONTROLLER DESIGN 3.1 WIRELESS NETWORK CONFIGURATION IN MULTI-ROBOT TEAMS 31 3.2 NETWORK RESOURCE ALLOCATION IN COOPERATION-ROBOT SUB TEAMS 33 3.3 MODEL OF NETWORK SYSTEMS 36 3.4 PRIORITY TRANSMISSION SCHEME 39 3.5 REGULATING SCHEDULER 44 3.6 CONTROL STRATEGY 50 3.7 NETWORK CONTROLLER DESIGN 53 CHAPTER4 SIMULATION AND EXPERIMENTAL RESULTS 4.1 NETWORK BANDWIDTH CONTROL FOR ONE DATA FLOW 57 4.1.1 DESIGN PRINCIPLES OF MEMBERSHIP FUNCTION AND RULE TABLE 58 4.1.2 COMPARISON BETWEEN FIVE AND SEVEN MEMBERSHIP FUNCTIONS 60 4.1.3 CONTROL RESULTS OF INSTANT PACKETS INTERVAL 63 4.2 DESCRIPTION OF SIMULATION ENVIRONMENT 65 4.2.1 3D SIMULATION SCENARIO 66 4.2.2 MODEL OF INVERTED PENDULUM 67 4.2.3 CONTROLLER OF INVERTED PENDULUM 69 4.3 NETWORK BANDWIDTH CONTROL FOR MULTI-ROBOT GROUP 71 4.3.1 TASK MAXIMUM BANDWIDTH THRESHOLD 76 4.3.2 DATA LOOP TIME 77 4.3.3 RESPONSE OF INVERTED PENDULUMS IN MULTI-ROBOTS TEAM 79 4.3.4 MULTI TEAMS WITH PRIORITY TASKS 82 4.4 EXPERIMENT 84 4.4.1 EXPERIMENT TEST RESULTS 84 4.4.2 EXPERIMENTAL SCENARIO DESCRIPTION 86 4.4.3 EXPERIMENTAL RESULTS 89 CHAPTER5 CONCLUSION AND FUTURE WORK 5.1 CONCLUSION 93 5.2 FUTURE WORK 94 REFERENCES 9