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From Smart Dust to Reliable Networks Kris Pister Prof. EECS, UC Berkeley Founder & CTO, Dust Networks Outline • Background – The Science Project • Market – The Hype • Technology – Challenges – Status • Applications • Open Research Problems Grand Challenge A B C Reliably, at low power Smart Dust Goal c. 1997 Smart Dust, 2002 SENSORS ADC PHOTO 8-bits 1V 1-2V FSM RECEIVER 375 kbps 16 mm3 total circumscribed volume TRANSMITTER 175 bps ~4.8 mm3 total displaced volume 1V 1V SOLAR POWER 3-8V 2V OPTICAL IN OPTICAL OUT UCB “COTS Dust” Macro Motes Services David Culler, UCB Networking TinyOS WeC 99 James McLurkin MS Rene 00 Small microcontroller - 10 kbps EEPROM storage (32 KB) Simple sensors Mica 02 Demonstrate scale - 8 kb code, 512 B data Simple, low-power radio Dot 01 Designed for experimentation -sensor boards -power boards NEST open exp. platform 128 KB code, 4 KB data 50 KB radio 512 KB Flash comm accelerators University Demos – Results of 100 man-years of research Motes dropped from UAV, detect vehicles, log and report direction Intel Developers Forum, live demo 800 motes, 8 level dynamic network, and velocity Seismic testing demo: real-time data acquisition, $200 vs. $5,000 per node vs. 50 temperature sensors for HVAC deployed in 3 hours. $100 vs. $800 per node. Sensor Networks Take Off! Industry Analysts Take Off! 800 700 Units (Millions) 600 $8.1B market for Wireless Sensor Networks in 2007 500 400 300 Wi-Fi nodes Handsets Wireless Sensor Nodes 200 100 0 2003 2004 2005 2006 2007 Source: InStat/MDR 11/2003 (Wireless); Wireless Data Research Group 2003; InStat/MDR 7/2004 (Handsets) Wireless Sensor Networking Decision Systems Monitoring Systems Control Systems Enterprise Applications • Significant reduction in the cost of installing sensor networks • Enables new class of services • Increases sensor deployment Analog Sensors and Actuators Digital Sensors and Actuators Physical World Serial Devices WDRG, 2003 $748,000,000 in ‘03 Cost of Sensor Networks Mesh Networking Computing Power Installation, Connection and Commissioning $ Sensors Time Low Data Rate WPAN Applications (Zigbee) security HVAC AMR lighting control access control asset mgt process control environmental energy mgt BUILDING AUTOMATION CONSUMER ELECTRONICS PC & PERIPHERALS INDUSTRIAL CONTROL patient monitoring fitness monitoring TV VCR DVD/CD remote PERSONAL HEALTH CARE RESIDENTIAL/ LIGHT COMMERCIAL CONTROL mouse keyboard joystick security HVAC lighting control access control lawn & garden irrigation Mesh Systems Add: MoteIV, Arch Rock Merged: •Chipcon/Figure8 TI/Chipcon •Integration Associates/CompXs Dust Networks • Founded July 2002 – Angels, In-Q-Tel, ~$1.5M – 28 employees in Jan 04 • Series A Feb 2004 – Foundation – IVP • Series B Feb 2005 – Crescendo – Cargill Network Architecture • Goals – – – – High reliability Low power consumption No customer development of embedded software Customer visibility into all aspects of network operation/status/health – Minimal/zero customer RF/networking expertise necessary • Challenges – 1W emitters in regulated but unlicensed RF bands – Extreme computation and communication resource constraints • MIPS, RAM, bps What do OEMs and SIs want? • • • • ^ and scientists and and engineers and startups and grad students and…. Reliability Reliability Reliability Low installation and ownership costs – No wires; >5 year battery life – No network configuration – No network management • Typically “trivial” data flow – Regular data collection • 1 sample/minute…1 sample/day? – Event detection • Threshold and alarm Reliability • Hardware – Temperature, humidity, shock – Aging – MTBF = 5 centuries • Software – Linux yes (manager/gateway) – TinyOS no (motes) • Networking – RF interference – RF variability Goals • Networks must be – Reliable • count the 9s! – Scalable • thousands to tens of thousands of nodes – Low Power • Self forming, self healing • Zero wires – Flexible • Monitoring, maintenance, log file transfer, … • Battery only or powered infrastructure Challenges • RF environments are dynamic – Time-varying multi-path – Time-varying interference • Sensor Networking is challenging – Traditional traffic models don’t apply • Internet, WiFi • Cell phones – Computational resources are limited Implications of RF Challenges • “Transmit and forget” is unreliable – Lost packets • Single-path networks (trees) are very dangerous – Lost motes • Single-channel networks are fatal – Lost networks RF Solutions • Temporal Diversity – Don’t quit until you get an acknowledgement • Spatial Diversity – Multiple paths from every mote • Frequency Diversity – Frequency hopping in addition to direct sequence spread spectrum IEEE 802.15.4 & WiFi Operating Frequency Bands 868MHz / 915MHz PHY 2.4 GHz PHY 2.4 GHz Gutierrez Channel 0 Channels 1-10 868.3 MHz 902 MHz Channels 11-26 2 MHz 928 MHz 5 MHz 2.4835 GHz 900 MHz cordless phone -50dBm Solid mote signal -20dBm Zigbee 1.0 • Single channel networks are built into standard. This will be fatal for reliability. • Tree-based routing recommended by standard will likely not be adopted, especially given the single-channel radio. • No definition of duty cycling routers – Assumes powered routers, battery powered leaf nodes – No explicit prevention of router duty cycling – Zigbee 2.0? Cluster-tree Topology Clustered stars - for example, cluster nodes exist between rooms of a hotel and each room has a star network for control. Full function device Reduced function device Communications flow Techno-Rant • Reduced function devices are a non-starter for most applications • Tree-based routing is fatal • Cluster-tree combines both • Mesh != multi-hop – Mesh = path diversity • Fixed frequency is fatal • Wireless means no wires Radio Reliability in a Crowded Spectrum • UWB? – Unclear potential for duty cycling • DSSS doesn’t cut it – Helpful, but only about 10dB • +20 dBm doesn’t cut it – Helpful, but expensive in batteries – 802.11 & cordless phones • Must frequency hop – Time synchronization required… …but you probably needed that anyway. – Lots of channels, lots of bandwidth, better scaling, … Spatial effect of multipath Beware of static measurements and RF pathloss simulations • Site surveys need to be done over at least 24 hours • Simulation tool results need much more speckle Pictures from www.wirelessvalley.com Path stability vs. Received Signal Strength Distance vs. Received Signal Strength RSSI and distance for Consolidated network 1/R2? 1/R4? Distance [meters] 60 40 20 0 -100 -90 -80 -70 -60 RSSI [dBm] -50 -40 Frequency dependent fading and interference From: Werb et al., “Improved Quality of Service in IEEE 802.15.4 Networks”, Intl. Wkshp. On Wireless and Industrial Automation, San Francisco, March 7, 2005. M Tu W Th F M Tu Real RF links • Indoor propagation – not well modeled by R^k for any k – Attenuation ~ Free space (R2) + Uniform(0,30) dB + rand(t) * uniform(0,30) dB – Not symmetric, time varying • PER is not due to gaussian BER Transmitter efficiency Transmitter efficiency Pout [mW] 1 0 Pin [mW] 20 25 • Transmitter slope efficiency is typically 10—50% but… • Transmitter overhead is typically >10x the max output power, so… • Changing transmit power may be useful for interference reasons, but it has little effect on battery life Energy per packet Energy per packet Etx [uJ] 0 0 Lpayload [bits] 102…103 • Energy spent in turning on the transmitter and sending packet overhead (preamble, start symbol, headers and footers) typically exceeds the energy cost of the payload, often by 10x • The same is true for the receiver, but how do you know when to turn it on? Network Types Star Powered mesh infrastructure X Full Mesh Star-Mesh Star-connected sensors No infrastructure X Why not use 802.11? Mesh-connected sensors Time Diversity • Link-level acknowledgement – Keep trying until you get confirmation of success • Assume packet error rate, PER=20%=0.2 • Try N times • Overall failure probability is (PER)N • Overall success probability is 1- (PER)N N Probability Probability of failure of success 1 0.2 0.8 2 0.04 0.96 3 0.008 0.992 4 0.0016 0.9984 5 0.00032 0.99968 Path diversity • Assume overall reliability is 99% on each of k paths – Probability of success on at least one path is 1 - (1-0.99)k – k=2 99.99% • Path diversity allows smooth recovery from unexpected events – Alarms are generated in network and flow to manager – Manager takes appropriate action (e.g. add bandwidth, new parent, …) Min_Parents = 2 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 B transmits B receives ACK A transmits ACK Expected packet start time Worst case A/B clock skew Packet transmission and acknowledgement Mote Current Radio TX startup Packet TX Radio TX/RX turnaround ACK RX Energy cost: 295 uC Fundamental platform-specific energy requirements • Packet energy & packet rate determine power – (QTX + QRX )/ Tpacket – E.g. (300 uC + 200 uC) /10s = 50 uA Idle listen (no packet exchanged) Mote Current Radio RX startup ACK RX Energy cost: 70 uC 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 Latency reduction • Energy cost of latency reduction is easy to calculate: – Qlisten / Tlisten – E.g. 70uC/10s = 7uA • Low-cost “virtual on” capability • Latency vs. power tradeoff can vary by mote, time of day, recent traffic, etc. A B Tlisten B TX, A ACK Latency reduction • 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 People draw digraphs A A C C B B Graph DiGraph A A C C B B MultiDiGraph MultiGraph Time and Frequency Time One Slot A Freq C B 902.5 MHz B A 903 MHz … B B A C 927.5 MHz One Cycle of the Black Frame •Graphs & Links are abstract, with no explicit time or frequency information. •Frames and slots are more concrete •Time synchronization is required •Latency, power, characteristic data rate are all related to frame length •Relative bandwidth is determined by multiplicity of links Time and Frequency Channel Time BA BA CB BA CB BA BA BA Cycle N Cycle N+1 • Every link rotates through all RF channels over a sequence of NCH cycles • 32 slots/sec * 16 ch = 512 cells/sec • Sequence is pseudo-random CB Cycle N+2 BA A B C 50 channels, 900 MHz 900MHz 930MHz 16 channels, 2.4 GHz 2.4GHz 2.485 GHz Configure, don’t compile TM SmartMesh Console IP Network XML SmartMesh Manager Mote ~100 ft Reliability: 99.99%+ Power consumption: < 100uA average 50 motes, 7 hops 3 floors, 150,000sf >100,000 packets/day Scalability: Outdoor Test Network 1,100 m 3.5 3.5 3.5 te Mo 4 226 Mote 6 157 Mote 6 158 Mote 6 022 Mote 6 023 Mote 6 024 te Mo 4 Mote 6 159 225 4 3 3 Mote Mote Mote Mote 108 Mote 6 155 Mote 6 021 Mote 6 020 Mote 6 019 te Mo 4 223 4.5 Mote 6 154 Mote 107 Mote 6 149 Mote 6 150 Mote 6 016 Mote 6 017 Mote 6 018 6 6 096 4.5 6 6 Mote 6 Mote 6 Mote 6 188 Mote te Mo 6 3 Mote 6 Mote 084 3 085 3 3 086 Mote Mote 4.5 083 Mote 15 082 081 6 Mote 6 Mote 075 6 Mote 076 6 077 Mote 6 Mote 078 6 Mote 079 Mote 148 194 4.5 te Mo 193 Mote Mote 3 3 3 3 3 3 3 6 Mote 6 Mote 072 6 Mote 071 6 070 Mote 6 Mote 069 6 6 Mote 6 Mote 6 Mote 6 Mote 6 Mote 6 Mote 8 064 008 065 007 066 051 Mote 13 4.5 13 Mote Mote Mote 11.5 061 Mote 10 005 Mote 16 006 19 Mote 253 013 Mote 050 8 8 13 13 Mote 4.5 Mote Mote 10 004 Mote 049 Mote 4.5 232 10.5 Mote 250 247 242 8 3 8 001 6 SmartMesh Manager 4.5 Mote Mote Mote 9.5 Mote 1 Mote 4.5 233 Mote 11.5 4.5 4.5 11.5 Mote 4.5 6 264 255 252 027 Interferer (PosC) 246 026 238 025 3 8 Mote 9 287 277 263 8 028 8 8 6 8 Mote 8 3 060 059 Mote 6 038 Mote Mote 4.5 Mote 12.5 Mote 11.5 620 Mote 10 039 Mote 16 621 032 Mote 4.5 4.5 Mote 4.5 Mote 4.5 8 375 Mote 4.5 Mote 4.5 366 Mote 376 4.5 Mote 4.5 Mote 4.5 Mote 362 349 346 333 4.5 Mote Mote 365 377 280 Mote 6 Mote 624 6 Mote 5 041 040 Mote 5 042 Mote 323 332 Mote 7 348 6.5 Mote 4.5 14 3-6m Mote 397 4.5 4.5 422 4.5 Mote 445 460 442 3 9.5 Mote e 635 Mote 5 634 Mote Mote 633 4.5 Mote 16 632 Mote 6 5 Mote 5 643 Mote Mote Mo te Mo te 6 651 3 3 5 650 Mote 6 649 Mot Mote Mote 13.5 Mote 528 648 13.5 Mote 5 Mote 6 044 Mote 5 658 Mote 6 659 Mote 560 Mot SmartMesh Manager 8 Mote 6 3 671 Mote 6 672 M M 673 3 3 4.5 M M 3 683 ot 3-6m 3 3 3 3 3 3 3-6m 3-6m 699 697 ot 57 3 M 57 2 M ot e 58 58 M M 5 ot ot 58 58 ot 59 59 ot 3 61 61 61 5 60 ot e 60 7 e 60 8 9 M 0 ot e 61 8 4.5 M ot e 61 7 4.5 M 2 M 4.5 ot e e ot e 61 6 4 e M ot e 61 5 4 e 61 ot 1 5 4. 5 4. ot 5 m 3-6 e 4 M 4 M 60 M 5 4. 0 ot 6 e ot 5 4. 5 4. 60 ot 4 4.5 M 4 M e 60 e 60 e M 2 ot 4.5 M ot 4.5 e 60 3 M 3 5 4. N 5 4. 4 ot ot 59 4.5 M 1 e 4 5 60 e 60 59 e 4 M 4 ot 59 ot ot e e 6 M 8 M M 59 e 9 ot ot e 7 5 4. Netw ork deployed at 1 Thayer Road, Santa Cruz, CA, on rough pasture. Modifications to Implementation plan due to deployment fit into "thin and hourglass" shape of site (no minimum plan distances compromised). All measurements given in meters, and accurate to w ithin +/-25 centimeters (gopher hole offsets). ot e e 59 M 4.5 M ot 4 M 4 ot 9 4 M 6 M OPEN SPACE DEPLOYMENT 58 8 7 e 58 e e e 4 M ot 4 M ot 4 4 e 58 3 e 4 ot ot 4 e M Forest Edge M 4.5 M 5 4. Mote ot 4 M Mote 1 4.5 Mo te 5 4. 3-6m M Mote 684 6 59 4.5 565 e 0 5 4. 700 6 59 564 5 4. 696 ot 4.5 e 59 Mo te Mo te 2 5 4. Mote Mote ot 4.5 4.5 e 5 4. 3-6m Mote 685 6 5 4. 701 6 695 M 563 566 ot 4.5 M 4.5 Mo te Mo te 551 M 1 567 4.5 4.5 9 5 4. Mote Mote 58 Mo te 550 57 e 2 552 3 e 0 5 4. 3-6m Mote 686 5 58 5 4. 702 5 694 ot 4.5 e 5 4. Mote Mote 5 4. 3-6m Mote 687 6 ot 58 e 537 ot e 5 4. 3 6 693 5 4. 703 Mote M Mot 536 M ot 4.5 M 5 5 4. Mote Mote 688 5 3-6m 5 692 57 4 8 4.5 M e 4 57 e 5 4. Mote 3-6m Mote 689 6 ot 4 e 4 13 3 3 3 698 Mote 5 4. 691 3 57 7 5 4. 6 690 Mote 57 6 5 4. Mote 57 Mo te 5 4. 3 674 6 682 e e e 5 4. Mote ot 571 5 4. 3 3 3 3 3 3 675 6 681 M Mote 5 4. Mote ot 4.5 Mote 16 3 676 5 048 6 5 4. Mote Mote 4.5 562 Mo te 5 4. 677 6 047 6 5 4. Mote Mote Mo te 4.5 549 5 4. 045 5 046 5 5 4. Mote Mote 5 4. 678 6 680 6 5 4. 679 Mote Mote ot 4.5 Mote 3 5 670 3 3 Mote 3 6 669 5 Mo te Mote 5 4. 3 Mote 3 5 4.5 553 538 8 Mo te 3.5 5 h es tM er ar ag Sm Man 661 Mote Mote Mo te 4.5 548 5 4. Mote 668 6 Mo te 568 Mo te e 5 19 9 6 667 Mote 4.5 4.5 554 4 561 662 8 Mote Mo te e 539 Mot 5 5 663 4.5 547 4 3.5 535 Mote 5 6 664 Mote 5 Tree Stump Mote 5 6 665 3 5 666 Tree Trunk Mote 3 3 3.5 3.5 Mote Mo te 660 Mote Mote 4.5 555 Mo te 5 657 16 6 656 5 Mote Mo te 569 4.5 3 3 3 3 3 3 3 Mote 534 6 655 e 540 529 Mote 4.5 4 8 Mote 570 559 Mo te 4 652 Mote Mo te 4.5 546 4 653 5 3 3 Mote Mo te 4.5 556 5 5 654 6 Mo te e 4 Mote 4.5 4.5 545 Mot 541 647 Mo te 5.5 5 533 Mote 16 646 542 Mote 530 Mote 4.5 645 4 6 3 3 3 Mote Tree Stump 4.5 558 16 3 6 644 4 642 3 3 Mote 641 Mo te 557 8 6 640 e 8 Mote 3 3 3 3 6 639 Mot Mote 036 Mote 3 Trees 458 4.5 544 5.5 Mote 4 3 6 4 636 5 4 Mote 4 637 6 4 Mote 4 638 6 Mo te 8 532 Mote 6 543 Mote 035 6 443 378 4 631 3 630 3 629 3 043 3 628 3 627 3 626 Mote M ot e 61 4 524 4.5 Mote 526 515 505 484 4.5 4.5 4.5 Mote 482 4 Mote 483 Mote 527 3-6m 506 507 457 Mote Mot 4 Mote Mote 423 Mote 6 531 Mote 4 6 4 Mote 4 5 444 9.5 Mote 4 Mote Mote 525 504 4.5 Mote Mote 5 5 14 9.5 Mote Mote 424 398 4 Mote 516 4.5 4.5 425 Mote 5 6 Mote 4.5 Mote 4 481 4.5 4.5 4 Mote 14 514 Mote Mote 4 461 456 4.5 307 4 6 4 485 4.5 9.5 9.5 Mote 282 Mote Mote Mote Mote Mote 441 9.5 Mote 16.5 14 509 Mote 4.5 Mote Mote 6.5 Mote Mote 4.5 4.5 Mote 4 480 4.5 4.5 Mote Mote 3 3 3 3 3 3 3 6 14 503 Mote 4.5 Mote 057 Mote 4 486 4.5 Mote 4 462 Mote 16 622 523 4.5 4.5 363 522 4.5 4.5 Mote 4 479 4.5 4.5 4.5 4.5 Mote Mote 426 421 Mote 14 517 502 4.5 Mote 4 Mote 455 Mote 14 513 Mote 4 487 4.5 Mote 4.5 4.5 Mote 446 Mote 14 510 Mote 463 454 447 Mote 440 427 4.5 399 Mote 14 501 4.5 Mote 4 478 4.5 14 14 4.5 SmartMesh Manager Mote 4 488 4.5 Mote 4 464 Mote Mote 4.5 4.5 Mote Mote 4.5 Mote 14 439 428 4.5 Mote Mote 034 Mote 4.5 Mote Mote Mote 9 10.5 379 6 623 4.5 400 Mote 521 500 4.5 Mote 4 477 4.5 Mote 4.5 4.5 Mote Mote 4 489 4.5 Mote 4 465 429 420 4.5 308 520 4.5 4.5 Mote 419 4.5 4.5 396 4.5 Mote 14 518 512 7 Mote 14 452 453 4.5 3-6m 401 395 380 8 Mote 4.5 Mote 8 Mote Mote 4.5 306 Mote 14 448 4.5 418 402 Mote Mote Mote 14 14 511 4.5 Mote 4 476 4.5 4.5 Mote 4.5 3-6m 4.5 Mote Mote 14 499 4.5 Mote 4 466 4.5 Mote 4.5 4.5 Mote 4.5 394 4.5 364 Mote 14 438 4.5 3 4.5 283 3 10 033 6 625 Mote 16 381 3 258 Mote Mote 417 403 4.5 Mote Mote 14 430 4.5 4.5 4.5 347 Mote Mote 4.5 281 Mote 4.5 Mote 4.5 305 3 3 4.5 Mote 4.5 4.5 404 393 382 4 490 4.5 4.5 4.5 SmartMesh Manager Mote Mote Mote 4 475 Mote 451 431 Mote 4.5 Mote 4.5 Mote 4 467 450 449 437 Mote 14 519 498 4.5 Mote Mote 4.5 4.5 Mote 8 324 Mote 14 6 392 383 Mote 4 491 4.5 4.5 322 309 Mote 14 Mote 4.5 416 4.5 Mote Mote Mote 14 432 415 4.5 Mote 4.5 8 Mote 3 Mote 4.5 Mote 4.5 405 Mote 16 4.5 4.5 4.5 4.5 4.5 Mote 4.5 4.5 4.5 361 350 345 4.5 Mote Mote 325 4.5 284 Mote Mote 4.5 367 360 4.5 Mote 8 3 8 031 6 Mote Mote Mote 259 13 4.5 351 4.5 4.5 406 4.5 4.5 4.5 4.5 Mote 055 13 Mote Mote 4.5 Mote 4.5 391 384 374 368 359 4.5 3 3 Mote 4.5 4.5 260 030 4.5 344 Interferer (PosB) 4.5 4.5 390 Mote Mote 4 474 4.5 4.5 Mote 4.5 3.5 321 Mote 3 304 285 279 3 Mote Mote Mote 19 Mote 058 Mote Mote 16 385 Mote 3-6m 4.5 Mote 257 Mote 8 373 Mote Mote 8 4.5 4.5 4.5 261 3 4.5 335 326 4.5 Mote 3.5 310 4.5 Mote Mote Mote Mote Mote 334 4.5 303 3 3 3 3 8 10.5 244 6 3 Mote 029 245 Mote 236 4.5 331 Mote 4 320 Mote 3.5 4.5 286 278 243 8 8 Mote 235 Mote 4.5 Mote Mote 4.5 4.5 262 256 12.5 Mote 4.5 237 054 8 234 Mote 6 13 13 056 Mote 6 Mote Mote Mote Mote Mote Mote 4 311 3 3 3 3 4 037 Mote 10 4.5 327 3-6m Mote 4.5 468 433 4.5 4.5 Mote 4.5 4.5 4.5 302 Mote 4.5 369 4.5 3-6m 4.5 4.5 4.5 Mote 8 Mote 8 Mote Mote 4.5 319 Mote 4 4.5 4.5 4.5 SmartMesh Manager 4.5 Mote Mote Mote Mote Mote 4.5 358 4.5 Mote 352 Interferer (PosE) 343 328 4.5 Mote 4.5 3-6m 3-6m 336 312 3 3 4 Interferer (PosA) Mote 4.5 301 Mote 4.5 353 4.5 Mote Mote Mote 5 318 4.5 5 Mote 288 276 Interferer (PosD) 3 Mote 4.5 342 4.5 Mote 497 4.5 4.5 4.5 4.5 Mote 5 313 4.5 4.5 4.5 4.5 4.5 Mote Mote Mote Mote Mote Mote 4.5 9.5 337 4.5 4.5 4.5 4.5 4.5 4 10 2 SmartMesh Manager 4.5 619 251 8 8 SmartMesh Manager 9 002 8 Mote 8 8 Mote 8 Mote 5 300 289 4.5 Mote 4 492 4.5 Mote Mote Mote 4.5 414 4.5 4.5 Mote 4 473 4.5 4.5 4.5 Mote 4.5 407 389 Mote 4 469 434 4.5 Mote 4.5 8 372 4.5 4.5 329 4.5 4.5 4.5 275 Mote 5.5 317 4.5 4.5 Mote Mote Mote 4.5 265 Mote 5.5 314 299 4.5 354 Mote 4.5 413 4.5 4.5 Mote 4.5 370 496 4.5 4.5 4.5 Mote 4.5 408 388 386 371 Mote 4.5 357 4.5 4.5 Mote 4.5 Mote 4 493 4.5 4.5 4.5 Mote 4.5 4.5 4.5 5.5 4.5 290 4.5 4.5 4.5 Mote 4.5 356 4.5 Mote 4.5 341 338 316 Mote 8 Mote 6 Mote Mote Mote 274 4 003 3-6m 355 4.5 Mote 4.5 8 4.5 4.5 4.5 Mote 315 298 4.5 4.5 266 254 10.5 Mote 4.5 239 053 3 Mote Mote Mote Mote Mote Mote 6 4.5 291 4.5 4.5 Mote Mote 4.5 273 267 13 248 8 8 Mote Mote Mote 240 231 Mote 3-6m 340 4.5 4.5 Mote 4.5 Mote 3-6m 339 330 297 4.5 4.5 Mote Mote 8 Mote Mote Mote Mote Mote 4.5 292 272 4.5 4.5 Mote 241 8 4.5 4.5 4.5 268 249 Mote Mote Mote 052 Mote 495 4.5 Mote 4 472 Mote 4.5 Mote 4 470 435 4.5 296 Mote 4.5 4.5 Mote 4.5 412 4.5 4.5 Mote 293 271 Mote 4.5 409 4.5 4.5 Mote 4.5 4.5 4.5 8 063 Mote 4.5 387 Mote Mote Mote 014 Mote 16 269 062 Mote 4.5 4.5 4.5 3 3 3 3 3 3 3 Mote Mote Mote 4 494 471 436 4.5 Mote 295 294 270 147 067 Mote 4.5 411 4.5 4.5 4.5 Mote 068 4.5 073 Mote 4.5 410 4.5 Mote Mote Mote Mote Mote Mote 4 8 015 080 8 074 196 195 4.5 te Mo 4.5 187 Mote Mote 198 4.5 197 4.5 te Mo 4.5 te Mo 4.5 190 Mote 4.5 6 3 Mote 3 6 087 3 088 3 089 Mote te Mo 4.5 4.5 203 192 6 201 4.5 te Mo 4.5 te Mo Mote 16 Mote 202 4.5 4.5 16 094 3 010 3 093 3 3 009 3 092 3 091 6 te Mo 4.5 te Mo 4.5 16 Mote 16 Mote 8 4.5 090 Mote 4.5 200 4.5 te Mo 4.5 204 191 Mote 205 te Mo 4.5 199 4.5 te Mo 4.5 Mote 095 3 097 3 3 3 6 098 te Mo 4.5 206 4.5 te Mo 4 8 3 6 099 3 6 100 3 3 101 Brush Pile Tree 4.5 212 14 Mote 207 4.5 te Mo 4 Mote 208 4.5 te Mo 4 211 te Mo 14 Mote te Mo 4 210 4.5 te Mo 4 189 Mote 209 4.5 te Mo 4 214 213 152 te Mo 4 te Mo 4.5 te Mo 4 4.5 151 4 216 4.5 215 4.5 4 Mote 6 te Mo 4 224 153 SmartMesh Manager Mote 19 106 Stump "Well" Mote 6 156 3.5 Mote 6 109 3 218 217 4.5 8 3 105 Mote Mote 6 SmartMesh Manager Mote 3.5 Mote 011 6 3.5 6 3.5 6 104 103 Mote 3 102 Mote 110 6 3.5 6 Stump Tree Mote 3.5 Mote 012 6 3.5 6 Mote 6 Mote 111 6 3 6 112 Mote te Mo te Mo te Mo Mote 4 4.5 te Mo 4 222 4.5 160 219 4 221 4.5 3.5 Mote 119 3.5 Mote 6 118 3.5 Mote 6 117 3.5 Mote 3.5 6 3.5 Mote 116 3 3 3 6 115 3.5 Mote 220 4.5 te Mo 3 6 114 3 Mote 3 6 113 3 Mote 4 te Mo te Mo 4.5 4.5 te Mo 4 227 4.5 230 4 228 te Mo 161 3.5 3.5 te Mo 229 4.5 te Mo 4.5 Mote 6 162 4.5 te Mo 174 Mote 6 163 -1400 Motes -20 Managers - 32 Acres 3.5 3.5 3.5 Mote 6 164 Mote 6 173 3.5 Mote 6 165 175 Mote 6 172 3.5 Mote 6 166 3.5 3.5 3.5 3.5 3.5 Mote 6 167 Mote 6 176 Mote 6 171 3.5 Mote 120 3.5 Mote Mote 6 170 186 Mote 6 177 3.5 6 121 Mote 6 169 Mote 6 185 Mote 6 178 3.5 Mote 6 122 Mote 6 168 3.5 Mote 3.5 3.5 133 Mote 6 Mote 6 179 3.5 3 Mote 3 Mote Mote 184 Mote 6 180 3.5 6 6 132 Mote 6 181 134 6 183 3.5 3 3 3 Mote 123 3 3 3 6 124 Mote 6 131 3 Mote Mote Mote Mote 9.5 135 3.5 6 125 Mote 6 136 3 Mote 6 Mote 6 182 146 Mote 6 3 6 126 Mote 130 3 3 3 Mote 6 129 Mote Mote 6 Mote 137 3 Mote Mote 145 6 3 6 128 6 138 3 Mote Mote 3 6 127 Mote 144 6 139 3 Mote 3 3 Mote 6 3 3 6 140 3 Mote 143 Mote 3 6 142 6 141 3 Mote Mote 4 Approaching 8 mote-centuries 459 16 Mote 508 600 m Communication Abstraction • Packets flow along independent digraphs • Digraphs/frames have independent periods • Energy of atomic operations is known, (and can be predicted for future hardware) IP Network XML – Packet TX, packet RX, idle listen, sample, … SmartMesh Manager • Capacity, latency, noise sensitivity, power consumption models match measured data • Build connectivity & applications via xml interface A C Network Services B Configurable Data Filter/Control Analog I/O Digital I/O Serial Port E H G F Multiple graphs Multiple frames Channel Time B A B A C A B A C A B A B A C A B A B A C A B A B C B C C B C B Cycle M of red frame A C A C B Cycle M+1 Frames overlayed Channel Time B A BA B C CB B A CA BA B A C A B A A C B C A B A C B A C C A B A • Packet collisions avoidable with integer-multiple length frames (here Tred = 3Tblack) or • Use mutually prime frame lengths to randomize • Infrequent scheduling collisions will occur - all but RX/RX can be solved by frame priority - mote w/ RX/RX will expect some packet collision Plenty of Time and Frequency Diversity Channel Time GE E C BA FE CB FE GE B C CA F E C A F E A C B E G F C A F E GE F E EC F E E C B A BA B A B A • E C B A F E C B A C C A B A B A GE Many links can share the same time slot (channel diversity) • >1000 links/second in same RF space •~100 payload bytes/link • Path limit: ~3k payload bytes/s • Network limit: ~150k payload bytes/s (w/ no frequency re-use) Subnetworks: single-hop, low latency G C B E H A Black superframe • All motes • 200 slots • Maintains time synch • Data, Health reports up • Control info down Red superframe • Mote F is light switch • Mote A is light • 1 slot, ~30ms latency Blue superframe • Mote H is temp sensor • Mote B is HVAC control point • 30 slots, ~1second latency F Motes A and B are likely powered All frames on all the time All other motes run at <100uA Subnetworks 2: reliable multi-hop control G C B E A H Black superframe • All motes • 10s period • Maintains time synch • Data, Health reports up • Control info down Red superframe • ~2s latency • Mote H is industrial process sensor • Mote A is industrial process controller F Both frames on all the time All motes run at <100uA Subnetworks 3: high speed links A C B E H F Black superframe • All motes • Maintains time synch • Data, Health reports up • Control info down Red superframe • Mote G is a microphone sending real-time compressed voice • 2 slots, 1 payload delivered to A every 2 cycles • ~12kbps Blue superframe G • Mote H is a camera transferring an image • 2 slots, 1 payload delivered to A per cycle • ~25kbps Red & Blue frames are only on occasionally All motes run at <100uA under “normal” conditions Motes on active high speed frames burn 25% to 50% of (Irx+Itx)/2 Zero collisions, zero lost packets Without black graph Subnetworks 3, et cetera W E->C Red frame: 1 packet delivered from G to D every other slot H->B H->C C->A B->A Blue frame: 1 packet delivered from H to A every slot G->E D C->A A F X C B E P H Y G R Q S W->X X->Y Y->Z Gold frame: 1 packet delivered from W to Z every other slot Z H->B H->C C->A B->A Green frame: 1 packet delivered from S to P every slot Many Knobs to Turn • Trade performance and power – Sample & reporting rate – Latency – High bandwidth connections • Tradeoffs can vary with – Time – Location – Events • Use power intelligently if you’ve got it Available data • Connectivity – Min/mean/max RSSI • Path-by-path info: – TX: attempts, successes – RX: idle, success, bad CRC • Latency (generation to final arrival) • Data maintained – Every 15 min for last 24 hours – Every day for last week – Lifetime • Available in linux log files or via XML IP Network XML SmartMesh Manager Micro Network Interface Card mNIC • No mote software development • Variety of configurable data processing modules • Integrators develop applications, not mesh networking protocols • For compute-intensive applications, use an external processor/OS of your choice. Network Services Configurable Data Filter/Control Analog Digital Serial I/O I/O Port Energy Monitoring Pilot • Honeywell Service: monitor, analyze and reduce power consumption • Problem: >> $100/sensor wiring cost • Solution: – Entire network installed in 3 hours (vs. 3-4 days) – 9 min/sensor – Software developed in 2 weeks (XML interface) – 18 months, 99.99% Chicago Public Health – Dust, Tridium, Teng Temperature and power monitoring Tridium NiagraAX Micro Network Interface Card mNIC • No mote software development • Variety of configurable data processing modules • Integrators develop applications, not mesh networking protocols • For compute-intensive applications, use an external processor/OS of your choice. Network Services Configurable Data Filter/Control Analog Digital Serial I/O I/O Port Sensor uP Perimeter Security Passive IR Passive IR and Camera 1.5 in MEMS and GPS 2.5 in 2.5 in Border Monitoring System, Kirtland AFB SAIC Dust Networks SAIC Dust Networks SAIC Dust Networks SAIC Dust Networks Oil Refinery – Double Coker Unit GW 14 unit Network expanded to 27 -- Expanding to 50+ in ‘06 • Scope limited to Coker facility and support units spanning over 1200ft • Expanded to 27 units, implemented 14 to start • No repeaters were needed to ensure connectivity • Gateway connected via Ethernet port in control room to process control network • Electrical/Mechanical contractor installed per wired practices Applications Public Safety Parking Management Conditioned Maintenance Resource Metering Traffic Monitoring Public Information Basic Enforcement Operation Basic Enforcement Operation 1 Sensor nodes are deployed along streets 2 Sensor nodes detect the arrival, presence and departure of vehicles. 3 Information is collected via the low power mesh, and relayed back to a central database over 4 cellular data networks. The central database maintains an up-to-the-minute map of parking events and violations 5 for the entire city. PCOs are dispatched in 6 efficient routes to ticket violations. Detailed historical and statistical information on parking is used to improve policy and operations over time. Medium Access Approaches • Medium Access (MAC) – How do motes share the radio spectrum? – How many can co-exist? • • • • • • Aloha Slotted Aloha CSMA (sometimes CSMA/CA) CSMA/CD TDMA TDMA/CA Aloha • Simplest MAC protocol – talk when you want to! – Standard for early wireless sensor networks • Fine for very light traffic (5%) • Chaotic collapse above ~10% • Theoretical throughput limit ~18% (1/e2) A G B Aloha! Aloha! Aloha! Aloha! Aloha! Aloha! Aloha! Aloha! Slotted Aloha • Packets sent in time slots – Still collisions, but fewer • Requires time synchronization • Theoretical throughput limit ~37% (1/e) Aloha! Aloha! A G B Aloha! Aloha! Aloha! Aloha! Aloha! Aloha! CSMA • CSMA = Carrier Sense Multiple Access – Listen before talk – Only transmit if the channel is clear – “Carrier” is actually RF energy and/or valid symbols A listens to channel: idle TX A ? TX packet ACK G B listens (busy) B ? B listens (idle) ? TX packet ACK CSMA Challenges • • • • A, B listen at the same time Both detect an idle channel Both begin to transmit, and collide ~10% of packet time w/ 802.15.4 radios A listens (idle) A ? TX packet ACK G B listens (idle) B ? TX packet ACK CSMA Challenges • • • • A, B listen at the same time Both detect an idle channel Both begin to transmit, and collide ~10% of packet time w/ 802.15.4 radios A listens (idle) A TX packet ? ACK Collision! G B listens (idle) B ? TX packet ACK CSMA Challenges • A, B both listen, detect a packet • At end of packet, both transmit and collide A G X B ? ? ? TX packet ? ? ? ? ? TX packet ACK ? TX packet ACK ACK ? CSMA Challenges • A, B both listen, detect a packet • At end of packet, both transmit and collide A G X B ? ? ? TX packet ? ? ? ? ACK ? ? TX packet ACK Collision! ? TX packet ACK CSMA Challenges • A, B can’t hear each other • “Hidden node” or “Hidden terminal” problem • In the limit, reduces CSMA to Aloha A ? TX packet ACK G B ? TX packet ACK CSMA Challenges • A, B can’t hear each other • “Hidden node” or “Hidden terminal” problem • In the limit, reduces CSMA to Aloha A ? TX packet ACK G Collision! B ? TX packet ACK CSMA Solutions • Many approaches – – – – – Random exponential backoff P-persisent CSMA RTS/CTS Slotted CSMA Synchronized CSMA • Hot topic in academia – MACA, B-MAC, S-MAC, T-MAC, … Good packets vs. attempted transmits, Aloha TDMA • TDMA = Time Division Multiple Access • Divide time into slots – With 802.15.4, a slot is ~10ms – ~100 slots/second • Like Aloha, but with assigned TX time slots – Unique TX slots means no collisions – Many motes can receive if desired A BG G B AG DC CB BG TDMA with multiple channels • Assign each mote a time slot and channel to transmit. – – – – All channels can be used simultaneously Big increase in available bandwidth 802.15.4 gives ~ (100 slots/s)(16chan) = 1600 cells/sec Uniquely assigned no collisions • RX need to be scheduled now too • No TX, no RX sleep! Ch0 DC CB Ch1 BG AG A G Ch2 B Ch3 DC CB BG AG TDMA Challenges • Time synchronization • Cell scheduling • Dynamic Bandwidth Allocation TDMA with CSMA • Backbone TDMA network – Baseline connectivity and time synchronization – Guaranteed bandwidth – ~10% of cells in a 10,000 mote network • All or some of remaining cells are “open listens” – Slotted Aloha by default – Fancier algorithms possible • All motes can listen, or just those with power Ch0 DC CB Ch1 BG AG A G Ch2 B Ch3 DC CB BG AG TDMA with CSMA • Backbone TDMA network – Baseline connectivity and time synchronization – Guaranteed bandwidth – ~10% of cells in a 10,000 mote network • All or some of remaining cells are “open listens” – Slotted Aloha by default – Fancier algorithms possible • All motes can listen, or just those with power Ch0 DC CB A-Z? A-Z? A? D? Ch1 BG AG A-Z? A-Z? DC CB Ch2 A? D? A-Z? A-Z? BG AG Ch3 E? F? A-Z? A-Z? E? F? A G B Flexibility of hybrid TDMA/CSMA • TDMA provides framework – 50 uA baseline current for synchronization and control – Static bandwidth allocated efficiently – Collision free • CSMA or Slotted Aloha for dynamic bandwidth – Accurate timing improves all algorithms • Power/performance tradeoffs in filling the cell matrix – Use powered infrastructure where you find it Technology directions • Reliable – Four 9s today – Moving beyond six 9s • Scalable – Thousands per site today – Tens of thousands per site • Low Power – A decade on a D cell today – >10x reduction in radio power demonstrated in academia • Flexible – Configurable networks today – Dynamically move along optimal power/performance curves Standards • • • • IEEE 802.15.4 Zigbee Wireless HART ISA/SP100 Mote on a Chip? (circa 2001) • Goals: – Standard CMOS – Low power – Minimal external components antenna Temp ~$1 uP SRAM Amp ADC Radio ~2 mm^2 ASIC battery inductor crystal UCB Hardware Results ~2003 • 2 chips fabbed in 0.25um CMOS – “Mote on a chip” worked, missing radio RX – 900 MHz transceiver worked • Records set for low power CMOS – ADC • 8 bits, 100kS/s • 2uA@1V – Microprocessor • 8 bits, 1MIP • 10uA@1V – 900 MHz radio • 100kbps, “bits in, bits out” • 20 m indoors • 0.4mA @ 3V Chipcon cc2430 Chipcon cc2430 • Key Features • 32 MHz single-cycle low power 8051 MCU • 2.4 GHz IEEE 802.15.4 compliant RF transceiver • 32, 64, and 128 kByte in-system programmable flash • Ultra low power: Ideal for battery operated systems • Prevailing development tools • Industry leading ZigBee(TM) protocol stack (Z-Stack) available • 8 kByte SRAM, 4 kByte with data retention in all power modes • RoSH compliant 7 mm x 7 mm QLP48 package • Powerful DMA functionality • Four flexible power modes for reduced power consumption • AES security coprocessor • Programmable watchdog timer • Power on reset/Brown-out detection • One IEEE 802.15.4 MAC timer, one general 16-bit timer and two 8-bit timers • Two programmable USARTs for master/slave SPI or UART operation • True random number generator • Digital RSSI/LQI support • Digital battery monitor • On-chip temperature sensor • Hardware debug support • Reference design with external PA providing +10 dBm output power available 2.4GHz Radio in 0.13um CMOS • Cook et al, ISSCC ’06 • Goal: ISM, frequency hopping, fast startup, lowest power TX Performance NF vs. Power Consumption Measured at RSSI Output CC2420 NF, 55mW Die Photo • 2.2mmx2.2mm • Active Area: 800µm2 Radio Performance 25 X 20 With software: 10 years D cell IRX (mA) cc2420 15 X 10 cc1000 With software: 10 years coin cell 5 Cook 06 (300 mW) Molnar 04 (0.4mA) X Otis 05 (0.4mA) X 100k X 200k 300k Bit rate (bps) Mote on a Chip • Goals: – Standard CMOS – Low power – Minimal external components Zero antenna uP Security Temp Location Amp ADC Radio Time SRAM ~4 mm^2 ASIC battery inductor crystal Die area, power, 20052009 • ADC – 10-12 bits, zero area, zero power • Digital – – – – 32 bit uP 1mm2 0.25mm2 Crypto - ~ uP Dedicated datapath? 0.25mW/MHz 50uW/MHz • Memory – ROM & Flash 128kB/mm2 0.5MB/mm2 – RAM 16kB/mm2 64kB/mm2 – ~mW/MHz ~ uW/MHz • RF – 2mm2 1mm2 – 10s of mW 100s of uW • Leakage – 10s uA @ 85C? <1uA @ 85C (circuit solutions; processes get worse) Sago Mine Accident (Jan 2006) • Lack of good sensor information • Limited knowledge of worker location • Wired communication system Worker Location 650 m Explosion Wired phone to surface Bandwidth and Multipath • Increasing BW only helps if 1/BW is similar to path difference RF Geolocation Performance • 1 m of measurement error = 3.3 ns Security Goals • Encryption – Make sure that no one can see the data • Integrity – Make sure that no one can fake the data, fake control packets, screw up the network with replay of old packets, screw up the network with random packets – Make sure that random bit errors don’t screw up the network • Certification – Networks only accept trusted motes – Motes only join trusted networks • Binding – Motes only join the right network Threat models • Easy – No access to hardware – No crypto expertise • Medium – – – – Access to hardware outside the network (demo network) Single PC College students Competitors • Hard – Access to active hardware in the network – PC cluster (~hundreds of 2006 to 2020 vintage PCs) – Theft, sabotage, industrial espionage, hacking • • • • Ocean’s 11 Osama, Putin, Chirac Unocal China David Wagner, UCB People are almost always the weakest link. Public Key & Shared Key • Shared key, or symmetric key – – – – – Encryption of payloads, authentication of headers Block ciphers: AES, DES, XTEA, … In software on 8bit micros ~ 10 ms In hardware on 802.15.4 chips ~ 1us Issues: key storage, key exchange • Public key – – – – Certification of identity of motes, managers Key exchange for shared key systems Seconds to minutes on 8 bit micros Export concerns? Shared-key Encryption & Integrity • Authenticate payload & headers using AES128 CBC-MAC – Generates “secure checksum” Message Integrity Code – 4 or 8 bytes • • Encrypt payload and MIC with AES128 CTR Append a 2 byte checksum – Redundant, less strong, less secure than the MIC – That’s what 802.15.4 forces us to do • A Packet ACK On reception B – Verify CRC – Decrypt payload, MIC – Verify message integrity (calculate MIC over received packet and compare to transmitted MIC) PHY header MAC header NET APP payload header MIC Authenticate integrity Encrypt in place Checksum CRC Public Key Certification - Use Cases • • • • One supplier/integrator One supplier, separate integrator Multiple suppliers, one integrator Multiple suppliers, multiple integrators, multiple neighboring customers Building 2 •HVAC network •Security Network •Fire network •Tenant networks Building 1 •HVAC network •Security Network •Fire network •Tenant networks ? ? ? New mote Simplest public key system for identity certification • Messages encrypted with the private key can only be decrypted with the public key • At manufacture, a mote gets a ‘signed’ copy of its ID – Encrypted with the manufacturers private key • On joining, the mote presents its ID and the signed copy of the ID • The network verifies that the signature is valid by decrypting it with the public key and checking to see if it is the right ID Manufacturer A Secret key Sa --------------------Public key Pa Network/Manager Public key ring: Pa, Pb,… Cy=E(Sa, Y) Mote Y Cy Mote X Cx Y, Cy Verify D(Pa,Cy) = Y ? Verify D(Pb,Cy) = Y ? From manufacture to 3AM join Mote N Manufacturing Protocol version# PC Mote ID Joining Key Signed(ID, JK) Store/ sleep Mote P1 Mote P2 Manager Data/advert packet Data/advert packet Join request Signed(ID,JK) Manager verifies signature Operator accepts new mote Configure? Path key encrypted with JK Mote N key encrypted with JK Activate child Path key encrypted with P1 key Path key encrypted with JK Mote N key encrypted with JK configACK Encrypted with Path Key Add link N->P2 Path key encrypted with P2 key Add link N->P2 Path key encrypted with N key Manager Mores • Prudish – Never • Prudent • Promiscuous – Any mote, anywhere, any time Manager Mores • Prudish – Never • Prudent – meets some combination of criteria: • • • • Mote has valid certificate Mote on access control list Manager accepted this mote before Human/higher-authority approval – Console/web – Button – PDA (RF or cable) • Single-hop from manager w/ specified minimum signal strength • Promiscuous – Any mote, anywhere, any time Key length and security Crypto strength (n) Symmetric Cipher ECC key size RSA key size MIPS-years NIST to crack expiry date 80 Triple DES (80) 160 1024 8x1011 2010 128 AES 128 256 3072 2x1026 >2030 256 AES 256 512 15,000 6x1052 1 million Pentiums running for 1 year is ~ 109 MIPS-years 1 billion (Pentium x1000) running for 1 century is ~ 1017 MIPS-years Open Problems, Hardware • None. Sensors ADC uP Radio RF Ranging Integration Open Problems, Software • Definitions, metrics, and optimization of reliability and power consumption for Academically Dull Applications (low rate data collection and control) – Simple models are fine (until proven otherwise) • Interference, multi-path, radio power, etc. • Start w/ reliability >99.9%, duty cycle <10% and improve • • • • Time synchronization Powered Infrastructure w/ 802.11 Certification, Binding, Commisioning Reducing barriers to access – Interfacing to PDAs, cell phones, web