Investigations on MAC and Link Layer for a wireless PROFIBUS over IEEE 802.11 von Diplom-Informatiker Andreas Willig aus Berlin von der Fakult¨at IV - Elektrotechnik und Informatik der Technischen Universit¨at Berlin zur Erlangung des akademischen Grades Doktor der Ingenieurwissenschaften - Dr.-Ing. - genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr.-Ing. Gun¨ ter Hommel Gutachter: Prof. Dr.-Ing. Adam Wolisz Gutachter: Prof. Dr.-Ing. Klaus David Tag der wissenschaftlichen Aussprache: 17. Mai 2002 Berlin 2002 D 83 Contents 1 Introduction 20 1.1 Structure of the Thesis . 24 2 Industrial Communication Systems 26 2.1 Requirements for Industrial Communication Systems / Field Buses . 27 2.2 Architectural Characteristics . 28 2.3 Popular Systems . 28 2.3.1 Systems using Token-Passing-MAC's . 29 2.3.2 Other Systems . 29 2.3.3 MAP/MMS . 30 3 Wireless LANs / IEEE 802.11 31 3.1 Wireless LANs . 31 3.1.1 Basics . 31 3.1.2 WLAN Properties Important for MAC Design . 33 3.1.3 WLAN Standards / Systems . 35 3.2 IEEE 802.11 . 36 3.2.1 Architecture . 37 3.2.2 PHY Layer . 37 3.2.3 MAC Layer . 40 4 PROFIBUS and Wireless PROFIBUS 45 4.1 The PROFIBUS Fieldbus System . 46 4.1.1 Architecture . 46 4.1.2 Physical Layer . 47 4.1.3 Link Layer Services . 48 1 4.1.4 MAC- and Data Link Protocol . 52 4.1.5 Important Properties of the PROFIBUS . 56 4.2 Wireless Industrial Communication Systems . 58 4.2.1 Integrated Scenario: General Considerations . 59 4.3 Integrated Scenario for Wireless PROFIBUS . 60 4.3.1 System under Study and Realtime Performance Measures . 60 4.4 Wireless PROFIBUS over IEEE 802.11 MAC . 64 4.4.1 DCF-based approaches . 64 4.4.2 PCF-based approaches . 65 4.4.3 SRD service handling . 65 4.4.4 Final Remarks . 66 4.5 Related Work . 67 4.5.1 Overview of other Work in Wireless Fieldbus Systems . 67 4.5.2 Real-Time Data Transmission with IEEE 802.11 . 69 5 Behavior of the PROFIBUS Protocol under Link Errors 72 5.1 PROFIBUS over Error Prone Links . 72 5.1.1 Major Causes for Ring Instability . 73 5.1.2 Ring Stability Metrics . 74 5.1.3 Analytical PROFIBUS Ring Membership Model . 75 5.1.4 Simulation Results . 82 5.1.5 Improvements . 91 5.2 PROFIBUS over Wireless Links . 99 5.3 Related Work . 101 5.4 Conclusions . 101 6 Error Behavior of Wireless Channels and its Modeling 104 6.1 Sources of Errors . 106 6.1.1 Path Loss . 107 6.1.2 Multipath Fading . 107 6.2 Measurement Setup . 110 6.2.1 IEEE 802.11 / PRISM I PHY . 110 6.2.2 Measurement Setup . 110 2 6.2.3 Format of the Generated Packet-Stream . 112 6.3 Measurement Evaluation Methodology . 113 6.3.1 Indicator Sequences . 113 6.3.2 Trace Evaluation . 114 6.4 Measurement Parameters and Environment . 115 6.4.1 Environment . 115 6.4.2 Parameters . 116 6.5 Measurement Results . 119 6.5.1 Packet-Related Phenomena . 119 6.5.2 Packet Losses . 120 6.5.3 Positions of Bit Errors . 125 6.5.4 Mean Bit Error Rates . 126 6.5.5 Burst Length Statistics . 128 6.5.6 Error Densities and Error Clustering . 131 6.6 Review of other Measurement Studies . 134 6.7 Stochastic Modeling of Bit- and Packet-Errors . 137 6.7.1 Overview of Common Stochastic Models . 137 6.7.2 Bipartite Model for Generating Indicator Sequences . 140 6.7.3 Comparison of Different Models . 142 6.8 Conclusions . 146 6.8.1 Summary of Measurement Results . 146 6.8.2 Stochastic Modeling . 147 6.8.3 Overall Channel Model . 148 6.8.4 Consequences for Design of MAC and Link-Layer Protocols . 149 7 Polling Protocols for Wireless PROFIBUS 151 7.1 System under Study . 153 7.1.1 Description of the System . 154 7.2 Polling-based Protocols . 158 7.2.1 k-limited Round-Robin . 159 7.2.2 Functional Repolling Framework . 160 7.2.3 Relaying . 162 7.2.4 Adaptive Functional Repolling . 165 3 7.3 Realtime-Performance Results . 166 7.3.1 Method of Investigation . 166 7.3.2 Comparison of Round-Robin with PROFIBUS . 168 7.3.3 Comparison of the Polling-protocol Modifications with Round-Robin . 179 7.4 Polling-based MACs for wireless PROFIBUS . 202 7.4.1 Integration Issues . 203 7.4.2 Semantics . 204 7.5 Related Work . 204 7.6 Discussion and Future Work . 205 8 Conclusions and Outlook 209 A Main Characteristics of the Bipartite Model 212 A.1 Asymptotic Behavior . 212 A.2 Distribution of Generated Burst Lengths . 214 A.3 Correlation Properties . 215 B Applicability of Simple FEC Schemes to the Measurement Traces 217 4 List of Figures 2.1 Hierarchy of information flows in manufacturing applications (from [68, p. 13]) . 26 3.1 Hidden terminal scenario . 33 3.2 Exposed terminal scenario . 34 3.3 DSSS PHY PPDU Format . 39 3.4 DSSS PHY Schematic . 40 4.1 PROFIBUS protocol stack . ..