Agenda Overview Technology –TinyOS; Prof. Phil Levis, Stanford –Energy Scavenging; Prof. Paul Wright, UC Berkeley –Low Power Radios Nate Pletcher, BWRC Ben Cook & Steven Lanzisera, BSAC Applications –Stewart Tansley, Microsoft –Mark Noworolski, Streetline Networks –Joe Polastre, Moteiv –Amy Wang, Mela Networks –Amine Haoui, Sensys Networks –David Culler, Arched Rock

Cost of Sensor Networks Time $ Computing Power Sensors Installation, Connection and Commissioning Mesh Networking

IEEE & WiFi Operating Frequency Bands 868MHz / 915MHz PHY 2.4 GHz MHz Channel 0 Channels 1-10 Channels GHz 928 MHz902 MHz 5 MHz 2 MHz 2.4 GHz PHY Gutierrez

Spatial effect of multipath Plot courtesy Matt Welsh, Harvard

Frequency dependent fading and interference From: Werb et al., “Improved Quality of Service in IEEE Networks”, Intl. Wkshp. On Wireless and Industrial Automation, San Francisco, March 7, 2005.

Network Types Powered mesh infrastructure Star-Mesh Full Mesh Star-connected sensors No infrastructure Mesh-connected sensors Star X X Why not use ?

Radio Reliability in a Crowded Spectrum DSSS doesn’t cut it –Helpful, but only about 10dB +20 dBm doesn’t cut it –Helpful, but expensive in batteries –No guarantee: e.g & cordless phones Must frequency hop –Time synchronization required… …but you probably needed that anyway. –Lots of channels, lots of bandwidth, better scaling, …

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

50 motes, 7 hops 3 floors, 150,000sf >100,000 packets/day

50 motes, 7 hops 3 floors, 150,000sf >100,000 packets/day

Oil Refinery – Double Coker Unit 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 GW 14 unit Network expanded to Expanding to 50+ in ‘06

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/e 2 ) GBA Aloha!

Slotted Aloha Packets sent in time slots –Still collisions, but fewer Requires time synchronization Theoretical throughput limit ~37% (1/e) GBA 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 GBA TX packet ACK A listens to channel: idle  TX TX packet ACK B listens (busy)B listens (idle) ? ??

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/ radios GBA TX packet ACK A listens (idle) TX packet ACK B listens (idle) ? ?

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/ radios GBA TX packet ACK A listens (idle) TX packet ACK B listens (idle) ? ? Collision!

CSMA Challenges A, B both listen, detect a packet At end of packet, both transmit and collide GBA TX packetACK TX packet ACK ? ? X ?? TX packetACK ??? ???

CSMA Challenges A, B both listen, detect a packet At end of packet, both transmit and collide GBA TX packet ACK TX packet ACK ? ? X ?? TX packet ACK ??? ??? Collision!

CSMA Challenges A, B can’t hear each other “Hidden node” or “Hidden terminal” problem In the limit, reduces CSMA to Aloha GBA TX packet ACK ? 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 GBA TX packet ACK ? TX packet ACK ? Collision!

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, …

TDMA TDMA = Time Division Multiple Access Divide time into slots –With , 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 GBA BGBG AGAG CBCBDCDCBGBG

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 – gives ~ (100 slots/s)(16chan) = 1600 cells/sec –Uniquely assigned  no collisions RX need to be scheduled now too No TX, no RX  sleep! GBA AGAG CBCBDCDC BGBG AGAG CBCBDCDC BGBG Ch0 Ch1 Ch2 Ch3

TDMA Challenges Time synchronization –Seems to be an article of faith with some that it’s impossible –Others just do it Sub-microsecond (pairwise) demonstrated in academia Sub-millisecond (entire network) available commercially 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 GBA AGAG CBCBDCDC BGBG AGAG CBCBDCDC BGBG Ch0 Ch1 Ch2 Ch3

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 GBA AGAG CBCBDCDC BGBG AGAG CBCBDCDC BGBG Ch0 Ch1 Ch2 Ch3  A?  E?  D?  F?  A-Z ?  A?  E?  F?  D?

Scalability: Outdoor Test Network 1,100 m 600 m Motes -20 Managers - 32 Acres

Standards Zigbee, Zensys Z-wave Wireless HART, ISA SP-100 LonWorks

Zigbee Great marketing tool, but… –Nothing interoperable yet –“Zigbee” products typically aren’t –Zigbee typically mean proprietary MAC Member survey on requirements for Wireless Sensor Networking due 3/17 Lost industrial automation in 2005 Losing building automation in 2006? Likely winner in home automation

ISA SP A Word from the Chairman –“In working to assure confidence in, and the integrity of, wireless technology, and to provide criteria for implementation in manufacturing automation and control systems, the ISA-SP100 Committee recently launched four project teams. Each team’s goal is to develop documents that will help users make the right decision on industrial wireless implementations.” –Physics of Radio –Interoperability –Requirements –User Guide Update: hijacked by Honeywell

Wireless HART “The Wireless HART working group, an activity of the HART Communication Foundation (HCF), has set an aggressive goal to produce draft specifications for a Wireless HART standard in early 2006.” ABB, Adaptive Instruments, Elpro Technologies, Emerson, Endress+Hauser, Honeywell, Omnex Controls, Phoenix Contact, Siemens, Smar and Yokogawa Update: TDMA network likely to win

~2 mm^2 ASIC Mote on a Chip? (circa 2001) Goals: –Standard CMOS –Low power –Minimal external components uP SRAM Radio ADC Temp Amp inductor crystal battery antenna ~$1

System Cost, 2005 E.g. Chipcon cc2510 –2.4 GHz, 500kbps –8051, AES –Temp sensor One of many single-chip options Single-chip$1.50 Passives$0.20 PCB Assembly & Test$0.20 Battery$0.10 Total$2

Radio Performance 200k Bit rate (bps)100k 300k I RX (mA) X cc1000 Molnar 04 (0.4mA) X cc2420 X Otis 05 (0.4mA) Cook 06 (300  W) X With software: 10 years  D cell With software: 10 years  coin cell

~4 mm^2 ASIC Mote on a Chip Goals: –Standard CMOS –Low power –Minimal external components uP SRAM Radio ADC Temp Amp inductor crystal battery antenna Security Location Time

~4 mm^2 ASIC Mote on a Chip Goals: –Standard CMOS –Low power –Minimal external components uP SRAM Radio ADC Temp Amp Security Location Time Zero Resonant antenna on-chip Demonstrated (e.g. Ken O, U. Florida) RF Inductor on-chip Commercially available Crystal/timing on-chip Demonstrated (many MEMS papers) Solar cell on-chip Commercially available (CMOS cameras ~10% efficient conversion)

Directions <1  W mote 1mm 3 mote True single-chip mote Mobility –Hopping, flying, gliding “Integrated” MEMS sensors –Accelerometers, magnetometers, visible & IR cameras, chem/bio, … Bio-interfacing –Neural, inertial, mechanical, chemical Flexible Platform

Conclusion