Critique #3 Ø Due: 11/10 (Tuesday) Ø Paper: D. Li, J. Vaidya, M. Wang, B. Bush, C. Lu, M. Kollef and T.C. Bailey, Feasibility Study of Monitoring Deterioration of Outpatients Using Multi- modal Data Collected by Wearables, ACM Transactions on Computing for Healthcare, 1(1), Article 5, March 2020. 1 Demo II Ø In class on 11/17 and 11/19. Ø 15 min per team. Ø Substantial progress à final demo. Ø Send Corey a video before class as backup. 2 WirelessHART Chenyang Lu Applications in Process Industry Ø Process industry q Automotive production q Chemical segments q Food and beverage q Power generation Ø Optimize process, enhance safety, protect environment q Monitor the status of manually operated valves q Monitor safety relief valves to detect venting to avoid accidents q Detect leaks before they lead to environmental problems q Health, Safety, and the Environment (HSE) regulations 4 Process Control Ø Feedback control loop controls physical plants q Example: regulate pressure of a gas container Actuator valve control command Controller sensor data Sensor Reference pressure ut() utˆ() Controller Actuators Plant xtˆ() State ytˆ() yt() Sensors Observer 11/5/20 5 Why Wireless Ø Cost reduction: wiring is economically infeasible Ø Easier installation: inaccessible locations Ø Easier maintenance q Wired networks cannot handle severe heat or exposure of chemicals q A wireless infrastructure can remain in place for many years. Ø Flexibilities and mobility for sensor placement 6 Challenges in Wireless Ø Strict timing requirement Ø Reliable communication despite wireless deficiencies Ø Plant environments are inherently unreliable q Interference, power failures, lightening, storms… Ø High security concerns 7 Wireless Technologies Ø Existing standards fail in industrial environments q ZigBee: static channel q Bluetooth: quasi-static star network Coordinator End Devices star network mesh network Ø WirelessHART q For process measurement and control applications q First open and interoperable wireless standard to address the critical needs of real-world industrial applications 8 History Ø HART (Highway Addressable Remote Transducer Protocol) q Most widely used field communication protocol q 30 million devices worldwide Ø WirelessHART released in Sep 2007 (as a part of HART 7) q Adds wireless capabilities to the HART protocol while maintaining compatibility with existing devices, commands and tools. 9 Wireless for Process Automation Ø World-wide adoption of wireless in process industries • 50,016+ wireless field networks • 16.9+ billion hours Offshore Onshore operating experience Courtesy: Emerson Process Management 10 What is special? Ø Reliable: 99.9% Ø Secure Ø Self-organizing, self-healing Ø Interoperable Ø Supports both star and mesh topologies Ø Built-in time synchronization 11 Network Architecture 12 Network Manager Ø Centralized brain manages the network and its devices q Collect topology information q Routing, scheduling q Generates network management packets to devices q Change when devices/links break q User/administrator interacts with the Network Manager Ø Redundant Network Managers supported (only one active) 13 Field Devices Ø Sensor/actuator/both Ø Connected to the process or plant equipment Ø Combines wireless communication with traditional HART field device capabilities Ø May be line or battery-powered 14 WirelessHART Adapter Ø Enables communication with a non-native device through a WirelessHART network. 15 Gateway Ø A Gateway provides q One or more Host Interfaces connecting the Gateway to backbone networks (e.g., the plant automation network) q One or more Access Points providing the physical connection into the WirelessHART network q A connection to the Network Manager q Buffering and local storage for publishing data, event notification, and common commands q Time synchronization sourcing Ø A Gateway can support up to 80 devices 16 Other Devices Ø Handheld devices q Portable applications used to configure, maintain or control plant assets. q Typically belong to networks of different standards Ø Plant Automation Network q Connects client applications to the gateway Ø Security Manager q Industry standard AES-128 ciphers/keys 17 WirelessHART PHY Ø Adopts IEEE 802.15.4 q Same 16 mutually orthogonal channels q Operates in the 2.4GHz ISM band q Data rate of up to 250 Kbps Ø Radio transceivers q Omni-directional q Half-duplex q 100 meters LOS @ 0 dB q Time to switch between channels: 0.192 ms q Radio turn-on time: 4 ms 18 How to achieve reliability? Ø Time diversity Ø Channel diversity q Channel hopping q Channel blacklisting Ø Route diversity q Graph routing Ø Power Diversity 19 Time Slotted Channel Hopping (TSCH) Ø Part of IEEE 802.15.4e q WirelessHART q 6TiSCH (IPv6 over the TSCH mode of IEEE 802.15.4e) Ø Switch channel for every time slot to enhance reliability Ø In each10-ms time slot q Sender & receiver set channel q Sender waits for guard time to accommodate clock jitter q Sender transmits the packet q Receiver sends ACK if it receives the packet 20 Shared vs. Dedicated Time Slots Ø A time slot may be shared or dedicated Ø Dedicated slot: only one sender sends to a receiver Ø Shared slot: multiple senders attempt to send to a receiver 21 Shared Time Slots Ø Devices contest for access using a contention-based scheme. q Behave similar to Slotted Aloha q Use collision-avoidance (backoff). Ø Using shared links may be desirable when q Throughput requirements of devices are low q Traffic is irregular or comes in bursts Ø May reduce latency since devices do not need to wait for dedicated slot q True only when chances of collisions are low 22 Channel Hopping Ø Enhances reliability q Avoid interference q Reduce multi-path fading effects Ø Blacklisting restricts hopping to some channels Ø Each device has a channel map (logical to physical) Ø ActiveChannel = (ChannelOffset + ASN) % #Channel 23 Routing Ø WirelessHART supports both Graph and Source routing Ø Graph routing: provides redundant paths Ø Routing graphs q Uplink graph: upstream communication q Downlink graph: Downstream communication q Broadcast graph 24 Scheduling Ø Slots and channel assignment q Each receiver uses a separate channel for reception q A transmission is followed by a retransmission on the same link on a dedicated slot, then again on another link on a shared slot Ø Each network contains exactly one overall schedule that is created and managed by the Network Manager. Ø The schedule is organized into Superframes 25 Superframe A series of time slots defining the communication schedule of a set of devices D Superframe C B Access Point AàB BàC CàD Sleep Sleep A Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 End Devices 26 Superframe Ø All devices must support multiple superframes Ø At least one superframe is always enabled while additional superframes can be enabled or disabled Ø The slot size and superframe length are fixed à a cyclic schedule with a fixed repetition rate 27 Data Link Protocol Data Unit (DLPDU) Ø Five DLPDU types: q Data q ACK q Advertise (periodic) q Keep-Alive (periodic) q Disconnect Ø Devices receiving a packet with an unknown packet type must not acknowledge the packet and shall immediately discard it. 28 Network Initialization Ø Network automatically starts up and self-organize. Ø Before a network can form, a Network Manager and a Gateway must exist. Ø The Network Manager activates the first Superframe. This establishes the system epoch – ASN 0. Ø Once the Network Access Point starts to advertise, devices can begin to join the network. Ø As devices join, the network forms. 29 Network Maintenance Ø Advertise and Keep-Alive DLPDUs assist in building and maintaining the device's neighbor list Ø A Keep-Alive must be transmitted to the neighbor if Last Time Communicated > Keep Alive Interval. Ø Keep-Alive transmissions are repeated until a new DLPDU is received from the neighbor Ø Keep-Alive no more often than once per 30 seconds (if temperature varies 2º C per minute or less). 30 Network Maintenance Ø Path failures are reported to the Network Manager when devices lose connectivity to neighbors. q After the Path Fail Interval lapses, a Path-Down Alarm is generated (by both the sender and the receiver). Ø As each device's Health Report Timer lapses, the devices generate health reports, which include indications of any problems the device is having with a neighbor. q Default period of each devices health report is 15 minutes. 31 Network Maintenance Ø Devices continue trying to reestablish communication until the links between them are deleted by the Network Manager. Ø It is common for broken paths to be restored after a temporary environmental effect passes. Ø If the disruption persists, additional Path-Down Alarms will be generated when the Path Fail Interval lapses again. 32 Best Practices Ø Each field device should have at least three neighbors q The 3rd neighbor will act as a backup if one of the two primary paths is obstructed or unavailable. Ø Devices (antenna) mounted >0.5m from any vertical surface. Ø Devices mounted >1.5m off the ground. Ø 25% of the network devices should have a direct connection to the gateway in large networks. 33.