Wireless Sensor Networks Semi-annual update
Kris Pister Professor EECS, UC Berkeley (Founder & CTO, Dust Networks) Outline
Standards Technology Products & Applications
1 Outline
Standards – HART7, WirelessHART – SP100 – IETF – 6LoWPAN, RSN – IEEE – 802.15.4E – Zigbee Technology Products & Applications
2 WirelessHART
HART – Highway Addressable Remote Transducer – Wired standard, ~2 decades old – 25 million sensors deployed – 2-3 million ship per year Industrial Standard – 54% of “field devices” (sensors) – >> $1,000 for installation average Wireless HART – Part of HART7 release – Ratified Sept 7, 2007
3 The De-facto Standard – October 2006
11 manufacturers, 95% of market, all talking w/ pre-HART TSMP
Emerson MACTek
Yokogawa Siemens
Siemens ABB Honeywell Phoenix Contact Smar Endress+ Hauser Pepperl+ Elpro Fuchs
4 5 ISA SP100
Principles of Operation published – Open conflict – Repeat of Fieldbus wars Wireless HART compatibility – Same radio PHY – Same Network and DLL/MAC (TSMP) – Same applications – Same crypto – Same customers But… – Egos & Fortunes Users furious – will it matter?
6 IETF
Internet Engineering Task Force – Folks who standardized IP, TCP, HTTP, … 6LoWPAN – IPv6 over Low power Wireless Personal Area Networks – Draft standard submitted – UCB’s David Culler, Arch Rock heavily involved – Describes header compression for IPv6, TCP, UDP • “only 2 bytes!” RSN – routing in sensor networks – “ok, so now what?” Great start, good community Likely to be the death of Zigbee
7 IEEE 802.15.4E Working Group
From the PAR: “The intention of this amendment is to enhance and add functionality to the 802.15.4-2006 MAC to – better support the industrial markets” – explicitly calls out HART and SP100 elsewhere “Specifically, the MAC enhancements to be considered will be limited to the following: • TDMA: to provide a) determinism, b) enhanced utilization of bandwidth • Channel Hopping: to provide additional robustness in high interfering environments and enhance coexistence with other wireless networks • GTS: to increase its flexibility such as a) supporting peer to peer, b)the length of the slot, and c) number of slots • CSMA: to improve throughput and reduce energy consumption • Security: to add support for additional options such as asymmetrical keys • Low latency: to reduce end to end delivery time such as needed for control applications”
8 TSMP
Time Synchronized Mesh Protocol Basis for – Wireless HART – ISA SP100 – 802.15.4E? – IETF/RSN??
9 Low Data Rate WPAN Applications
Zigbee 20042006Pro
security HVAC TV AMR VCR lighting control DVD/CD access control BUILDING CONSUMER remote AUTOMATION ELECTRONICS
asset mgt mouse process keyboard control INDUSTRIAL PC & joystick environmental CONTROL PERIPHERALS energy mgt patient security monitoring RESIDENTIAL/ HVAC LIGHT lighting control PERSONAL COMMERCIAL access control fitness HEALTH CARE CONTROL monitoring lawn & garden irrigation
10 (… but I heard that it doesn’t work …)
Industrial automation – Decades of false starts Defense – NEST fallout Home, health care, HVAC, security, … – Failed investments in using chips & stacks – “We tried it w/ x, and couldn’t get it to work”
11 How reliable do you need your network to be?
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12 How reliable do you need your network to be?
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13 Outline
Standards Technology – TSMP Products & Applications
14 Barriers to Adoption
Reliability
Standards
Ease of Use
Power consumption
Development cycles
Node size OnWorld, 2005 0% 20% 40% 60% 80% 100%
15 TSMP Foundations
Time Synchronization – Reliability – Power – Sensor time stamps Reliability – Frequency diversity • Multi-path fading, interference – Spatial diversity • True mesh (multiple paths at each hop) – Temporal diversity • Secure link-layer ACK Power – Turning radios off is easy – Knowing when to turn them back on is tricky
16 Power-optimal communication
Assume all motes share a network-wide synchronized sense of time, accurate to ~1ms For an optimally efficient network, mote A will only be awake when mote B needs to talk
A A wakes up and listens
B transmits B B receives ACK A transmits ACK
Expected packet start time
Worst case A/B clock skew
17 Packet transmission and acknowledgement
Mote Current
Radio TX startup Packet TX ACK RX Radio TX/RX turnaround Energy cost (2003): 295 uC 18 Timing – imperfect synchronization (latest possible transmitter)
A CCA: RX startup, Transmit Packet: Preamble, SS, RX startup Tg RX ACK listen, RX->TX Headers, Payload,MIC, CRC or Tx->Rx ACK Tcrypto
B RX Tg Tg RX packet Verify Verify MAC Calculate ACK Transmit startup CRC MIC MIC+CRC ACK
RX->TX Expected first bit of preamble
TCCA = 0.512ms to be standards compliant – Worst case is a receive slot followed by a transmit slot to a different partner, as radio will be finishing up the ACK TX just as it needs to look for a clear channel, so
– TCCA = TTX->RX + Tchannel assessment + TRX->TX = 0.192ms + 0.128ms + 0.192ms
Tpacket = 4.256ms for a maximum length packet – Preamble+SS+packet = 4+1+128B = 133B = 1064 bits 4.256ms @ 250kbps
Tcrypto is the total time to verify packet MIC and create ACK MIC
TgACK is the tolerance to variation in Tcrypto and/or mote B’s turnaround time from RX to TX
TACK is a function of the ACK length. It is likely to be just under 1ms.
Tslot = TCCA+2*Tg+Tpacket+Tcrypto+TgACK+TACK = 0.512+2+4.256+1+0.1+1 = 9ms
19 Fundamental platform-specific energy requirements
Packet energy & packet rate determine power
– (QTX + QRX )/ Tcycle – E.g. (60 uC + 40 uC) /10s = 10 uA
20 Idle listen (no packet exchanged)
Mote Current
ACK RX Radio RX startup Energy cost (2003): 70 uC
21 Scheduled Communication Slots
Mote A can listen more often than mote B transmits Since both are time synchronized, a different radio frequency can be used at each wakeup Time sync information transmitted in both directions with every packet
A B TX, A ACK
B
Ch 3 Ch 4 Ch 5 Ch 6 Ch 7 Ch 8
QTX , QRX , Qlisten
22 Latency reduction
Energy cost of latency reduction is easy to calculate:
– Qlisten / Tlisten – E.g. 20uC/1s = 20uA Low-cost “virtual on” capability Latency vs. power tradeoff can vary by mote, time of day, recent traffic, etc.
23 Multi-hop routing
Global time synchronization allows sequential ordering of links in a “superframe”
Measured average latency over many hops is Tframe/2
G
T2, ch y
A T1, ch x
B Superframe
24 Link
53
37
A link defines a timeslot and channel offset. A link consumes capacity . Links are directional. Links are associated with graphs. This is the link that uses the blue graph connection from 37 to 53 on slot 4 and offset 7
25 Link types
one destination > one
•Contention free
one
source
•Collisions possible > one
•Unicast •Broadcast •Acknowledged •No ACK
26 Graph
17
47 53
41 37 43
A graph is a collection of connections and the links belonging to them A graph contains both routing and capacity In our implementation, the connections cannot form loops Graphs are activated and deactivated by a management function
Similarities to ATM circuits, flow labels, and Cisco tag switching (MPLS)
27 Superframe
A superframe is a collection of slots that repeat periodically in cycles Binds/implements links from a graph with specific time/channel offset
Superframe
Unallocated Slot Allocated Slot
28 Link = (Time Slot, Channel Offset)
One Slot D Time Chan. A offset BA
C CA DA B BA
BC
E F BE BF All of B’s transmit links are dedicated and won’t collide – B has twice as much bandwidth to A as to C – B can broadcast to E and F, or use that link of a unicast to one or the other D and C share a link for transmitting to A. A backoff algorithm is needed in case of collisions.
29 Low latency – high reliability
Dedicated bandwidth for first k transmissions Shared bandwidth for next j All transmissions are on different channels DR ~= 1-PERk+aj
e.g. PER=0.1, 4 inputs 100ms max latency K=2, J=4 ~99.9999%
30 Low latency – multiple hops
Color indicates TX slot for mote of that color 5 hops = 5 slots = 50ms Can repeat immediately, or every k slots, according to superframe length. Peak throughput with n motes in a line: 1 payload / (n*10ms) = 100/n payloads/second
31 High throughput – multiple hops
Use multiple channels Odd slots Only need 2 time slots Throughput is 50 packets/second Even slots – independent of n – Limited by worst PER (not combination) Odd slots
Even slots
Odd slots
32 Source routes, broadcast, multicast
Source routing 17 – Contains graph ID – Can transition to flood
Broadcast 47 – Flood along graph – MAC & NET broadcast ID 41 80 Multicast 1 53 – MAC broadcast ID – NET multicast ID 43 81 82 Multicast 2 – Broadcast on graph covering multicast group
33 Performance Limits
Data collection – 100 pkt/s per gateway channel – 16*100 pkt/s with no spatial reuse of frequency Throughput – ~80kbps secure, reliable end-to-end payload bits per second per gateway – 16 * 80k = 1.28Mbps combined payload throughput w/ no spatial reuse of frequency Latency – 10ms / PDR per hop – Statistical, but well modeled Scale – > 1,000 nodes per gateway channel
34 50 motes, 7 hops 3 floors, 150,000sf >100,000 packets/day 36 37 38 RF Path Loss – R2 ? R4 ?
-20
-30
-40
-50
-60
RSSI (dBm) -70
-80
-90
-100 0 50 100 150 200 250 300
distance in feet 39 40 Path Stability by 802.15.4 Channel
2.480 GHz
802.15.4 Channels 802.15.4 802.11bg Channels 802.11bg
2.405 GHz
Each dot is the 15 minute average 41 42 43 44 Oil Refinery – Double Coker Unit
Scope limited to Coker facility and support units spanning over 1200ft No repeaters were needed to ensure connectivity Electrical/Mechanical GW contractor installed per wired practices >5 year life on C-cell
400m
45 Barriers to Adoption
Reliability >99.9%
Standards Wireless HART, SP100
Ease of Use “It just worked”
Power consumption 5-10 years
Development cycles Complete networks
Node size OnWorld, 2005 0% 20% 40% 60% 80% 100%
46 Excerpts from Presentations at the Emerson Process Users Conference September 2007
47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 Conclusion
Wireless Sensor Networks for Industrial Automation about to take off Based on Berkeley/BSAC-dervived TSMP Other markets and standards will follow
62 Multiple Applications in Multiple Markets
Industrial automation Building automation Defense & security Wireless-enabled applications
63 Industrial Monitoring
Emerson’s SmartWireless products based "Wireless promises to on Dust’s products enable us to put more monitoring in the 12 companies representing 90% of the plant at one-tenth the market for industrial field devices cost of wired demonstrated interoperable prototype technology” products based on Dust products John Berra, President
Save up to 90% on installation The cost of wire, Emerson Wireless Engineering Materials additional hardware and 90% Savings Labor labor drives up the cost of Over Wired Installation Other any project, large or small. Wireless solutions enable cost-effective implementation of new measurement points. 0% 10% 100%
64 Oil and Gas
“…this wireless technology enabled us to do things we simply could not do before, either because of cost or physical wiring “Wireless truly is faster and obstacles. Through the trials, we found that Emerson's wireless approach is flexible, cheaper.“ easy to use, reliable, and makes a step- “It just worked!” change reduction in installed costs."
Brandon Robinson Dave Lafferty EnCana BP
Savings of a 5-node installation: 700’ conduit 3000’ wire 2 guys, 2 full days of labor no trenching or surveying for buried cable
65 Predictive Maintenance
"Unscheduled downtime is the largest single factor eroding plant performance. Over $20 Billion, or almost 5 percent of total production, is lost each year in North America alone due to unscheduled downtime."
ARC, 2002
“Electric motors consume approximately 60% of all electricity generated in the United States.“
US DoE, December 2002
Ubiquitous monitoring of motors, pumps, and bearings: Vibration Temperature Acoustic
66 Parking Monitoring
Wireless sensor node Real-time monitoring of parking for: Increased enforcement Dynamic pricing Real-time vacancy location services
67 Perimeter Security
Monitoring for perimeter violations: Ground vibration (footfalls or vehicles) Metal (vehicles) Sound Motion
68