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.
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