3 Field busses 3.4 Industrial Wireless Industrial Automation Automation Industrielle Industrielle Automation

Field bus wireless Industrial Automation 2013 Motivation for Industrial Wireless Reduced installation and reconfiguration costs Easy access to machines (diagnostic or reprogramming) Improved factory floor coverage Eliminates damage of cabling Globally accepted standards (mass production)

Field bus wireless Industrial Automation 2013 Wireless Landscape

Field bus wireless Industrial Automation 2013 Wireless IEEE Numbers

Field bus wireless Industrial Automation 2013 Requirements for Industrial Wireless

Field bus wireless Industrial Automation 2013 Wireless for Non Real-Time Applications Remote Control: –Used for remote control of overhead cranes –High security requirements –Long code words to initiate remote control action Machine health monitoring: –Accurate information about status of a process –Local on demand access: PDA or laptop that connects to sensors or actuators –Control room: access point / gateway 6

Field bus wireless Industrial Automation 2013 Wireless for Soft Real-Time Applications Measurements: –For physical process, timestamp values –Ability to reconstruct course of events –Requires clock synchronization; precision dictated by granularity of measurement –E.g. geological or industrial sensors collecting data and transmitting them to base station or control room Media: –Delay and loss rate constraints for user comfort –E.g. voice and video transfer Control loops: –Slow or non-critical operations –Low sample rate –Not affected by a few samples being lost –Delay constraint based on comfort demands –E.g. heat control and ventilation system

Field bus wireless Industrial Automation 2013 Wireless Hard Real-Time Applications Late transmission cannot be tolerated E.g. control loops Assumes fault-free communication channel Wireless: –Error probability cannot be neglected –Sporadic and bursty errors

Field bus wireless Industrial Automation 2013 Challenges and Spectrum of Solutions Wireless Challenges Attenuation Fading Multipath dispersion Interference High Bit Error rate Burst channel errors Application Requirements Reliable delivery Meet deadlines Support message priority Existing Solutions

Field bus wireless Industrial Automation 2013 Radio wave interferes with surrounding environment creating multiple waves at receiver antenna, they are delayed with respect to each other. Concurrent transmissions cause interference too. => Bursts of errors Forward Error Correction (FEC): Encoding redundancy to overcome error bursts Automated Repeat ReQuest (ARQ): Retransmit entire packets when receiver cannot decode the packet (acknowledgements) Reliability for wireless channel

Field bus wireless Industrial Automation 2013 Deadline Dependent Coding Uses FEC and ARQ to improve Bit Error Rate: –Re-transmissions before deadline –Different coding rate depending on remaining time to deadline –Tradeoff between throughput and how much redundancy is needed –Additional processing such as majority voting –Decoder keeps information for future use (efficiency)

Field bus wireless Industrial Automation 2013 Existing protocols- comparison Feature802.11BluetoothZigbee / Interference from other devices --Avoided using frequency hopping Dynamic channel selection possible Optimized forMultimedia, TCP/IP and high data rate applications Cable replacement technology for portable and fixed electronic devices. Low power low cost networking in residential and industrial environment. Energy ConsumptionHighLow (Large packets over small networks) Least (Small packets over large networks) Voice support/SecurityYes/Yes No/Yes Type of Network / Channel Access Mobile / CSMA/CA and polling Mobile & Static / PollingMostly static with infrequently used devices / CSMA and slotted CSMA/CA Bit error rateHighLow Real Time deadlines???

Field bus wireless Industrial Automation 2013 Range 1 m 10 m 100 m 1 km 10 km 0 GHz2 GHz1GHz3 GHz5 GHz4 GHz6 GHz a UWB ZigBee Bluetooth ZigBee b,g 3G UWB

Field bus wireless Industrial Automation 2013 Legal Frequencies

Field bus wireless Industrial Automation 2013 Industrial Example: WirelessHART HART (Highway Addressable Remote Transducer) fieldbus protocol Supported by 200+ global companies Since 2007 Compatible WirelessHART extension

Field bus wireless Industrial Automation 2013 WirelessHART Networking Stack PHY: –2,4 GHz Industrial, Scientific, and Medical Band (ISM-Band) –Transmission power dBm –250 kbit/s data rate MAC: –TDMA (10ms slots, static roles) –Collision and interference avoidance: Channel hopping and black lists Network layer: –Routing (graph/source routing) –Redundant paths –Sessions and broadcast encryption (AES)

Field bus wireless Industrial Automation 2013 WirelessHART Networking Stack Transport layer: –Segmentation, flatten network –Quality of Service (QoS): (Command, Process-Data, Normal, Alarm) Application layer: –Standard HART application layer –Device Description Language –Smart Data Publishing (lazy) –Timestamping –Events –Command aggregation Boot-strapping: –Gateway announcements (network ID and time sync) –Device sends join request –Authentication and configuration via network manager

Field bus wireless Industrial Automation 2013 Design Industrial Wireless Network Existing wireless in plant; frequencies used? Can the new system co-exist with existing? How close are you to potential interferences? What are uptime and availability requirements? Can system handle multiple hardware failures without performance degradation? What about energy source for wireless devices? Require deterministic power consumption to ensure predictable maintenance. Power management fitting alerting requirements and battery replacement goals

Field bus wireless Industrial Automation 2013 Assessment Why is a different wireless system deployed in a factory than at home? What are the challenges of the wireless medium and how are they tackled? How can UWB offer both a costly and high bandwidth and a cheaper and high bandwidth services? Which methods are used to cope with the crowded ISM band? Why do we need bootstrapping?

Field bus wireless Industrial Automation 2013 References Wireless Communication in Industrial Networks, Kavitha Balasubramanian, Cpre 458/558: Real-Time Systems, WirelessHART, Christian Hildebrand, _Seminar_EDS_Hildebrand.pdf WirelessHART TM Expanding the Possibilities, Wally Pratt HART Communication Foundation, Industrial Wireless Systems, Peter Fuhr, ISA,