WirelessHART: Applying Wireless Technology in Real-Time Industrial Process Control Jianping Song, Song Han, Al Mok University of Texas at Austin Deji Chen, Mike Lucas, Mark Nixon Emerson Process Management Wally Pratt HART Communication Foundation
Outline Background Introduction to WirelessHART Development Challenges and Solutions WirelessHART Demonstration Summary
Future Wireless Plant
WirelessHART: History HART (Highway Addressable Remote Transducer) Bi-directional industrial field communication protocol Used to communicate between field devices and host systems The global installed base of HART-enabled devices is more than 20 million WirelessHART Wireless extension of HART Released in 09/2007
WirelessHART: Designed for Wireless Plant Solutions Real-Time TDMA technology Centralized Network Management Reliability Channel Hopping and Channel Blacklisting Mesh Networking Security Data Integrity on MAC layer Data Confidentiality on the Network layer
Alternative Wireless Standards: Not Suitable for Process Control Zigbee No Channel Hopping or Channel Blacklisting Problem with persistent noises Bluetooth Only supports star type network topology Not scalable for large industrial control systems Wi-Fi No Channel Hopping Power Consumption ISA SP100 Not available yet
Outline Background Introduction to WirelessHART Development Challenges and Solutions WirelessHART Demonstration Summary
WirelessHART Architecture
WirelessHART Architecture Physical Layer (IEEE 802.15.4) Data Link Layer Network Layer and Transport Layer Security Network Manager
Data Link Layer
Timer Module Time is sliced into time slots (starting from 0) Time intervals in a time slot Clock synchronization is critical
Links and Superframes Link: activity in a time slot Neighbor Send/Receive Communication channel Superframe: a group of links Defined by network manager Repeat itself infinitely A device can support several superframes
Data Link Layer State Machine Each run of the state machine 1. Call the link scheduler to determine the next slot to be serviced 2. On receiving the time slot start event, increment the ASN (Absolute Slot Number) by 1 3. When it is time to service the given time slot derived in step 1), execute the associated transaction (SEND/RECV)
WirelessHART Architecture Physical Layer (IEEE 802.15.4) Data Link Layer Network Layer and Transport Layer Security Network Manager
Security Data Link Layer Hop-to-hop data integrity CCM* (Counter with CBC-MAC) mode with AES-128 to generate the MIC Network Layer Public keys: used to generate MICs on MAC layer by joining devices Network keys: used by existing devices in the network to generate MAC MIC s Join keys: used during the joining process to authenticate the joining device Session keys: unique for each end-to-end connection between two network devices
Network Keying Model
WirelessHART Architecture Physical Layer (IEEE 802.15.4) Data Link Layer Network Layer and Transport Layer Security Network Manager
Functions of Network Manager Support devices joining/leaving the network Create routes Schedule communications Adapt the schedule upon network changes
Outline Background Introduction to WirelessHART Development Challenges and Solutions WirelessHART Demonstration Summary
Hardware Platform MC1321x Evaluation Kit by Freescale One 1321x-NCB board, two 1321x-SRB boards 40 MHz 8-bit HCS08 MCU 2.4 GHz 802.15.4 Transceiver Programmable 60 KB Flash and 4KB RAM Multiple 16-bit timers 4 LEDs for demonstrations and monitoring A simple IEEE 802.15.4 Physical Layer Library
Challenge 1: Timer Design Challenge Stringent timing requirements a 10ms time slot further sliced into several time intervals Some tasks are time consuming and may exceed allocated time Solution Use a separate hardware timer for WirelessHART The caller informs the timer module current slot type The timer generates required timer events accordingly
Challenge 1: Timer Design
Challenge 2: Time Synchronization Challenge Synchronize the nodes in a network A new node should derive current time during the joining process Solution A node records the time when the first bit of a frame arrives The receiver calculates the clock drift TsError The receiver includes the drift in the time adjustment field of the corresponding ACK frame When a node receives an ACK from its time source, it will adjust its clock
Challenge 3: Speed Up Security Calculations Challenge The receiver must run CCM* on the received frame and the corresponding ACK frame within TsTxAckDelay (1ms) The lower power HCS08 MCU can not meet the requirement Solution Upon request, Freescale is developing a new chipset with hardware encryption accelerator We propose to execute CCM* as soon as every 16 bytes are received
A WirelessHART demonstration One gateway and two devices: Device 1 and Device 2 The gateway and Device 2 exchange values through Device 1 and show the received values on the LEDs All frames are captured by a sniffer Time slot configuration
A WirelessHART Demonstration A device can synchronize to its time source within 3 time slots A data frame is always ACKed in the same time slot Device 1 acts as a router for the Gateway and Device 2
Conclusions Summary Introduction of the WirelessHART architecture Discussion of the challenges and solutions Demonstration of a prototype WirelessHART network Future Works Full-featured WirelessHART prototype Network Manager Co-existence with ZigBee and Bluetooth
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