![Page 1: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/1.jpg)
Low Power Wireless Sensor NetworksLow Power Wireless Sensor Networkshttp://www-mtl.mit.edu/research/icsystems/uamps
Rex Min, Manish Bhardwaj, Seong-Hwan Cho, Eugene Shih, Amit Sinha, Alice Wang, Anantha Chandrakasan
Massachusetts Institute of TechnologyMassachusetts Institute of Technology
![Page 2: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/2.jpg)
Emerging Networked ApplicationsEmerging Networked Applications
Integrated PDAs Home/Office Networking(e.g., Bluetooth)
Medical Monitoring
Equipment MonitoringSensor Networks
Integrated Integrated systemsystem--onon--aa--chipchip to sense, process and to sense, process and collaborate collaborate
![Page 3: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/3.jpg)
The MIT The MIT µµAMPSAMPS ProjectProject
n A universal substrate for power aware data gathering from a massively distributed wireless network
Sensor& A/D StrongARM RF
Tx/Rx
Battery/DC-DC Conversion
µ-OS (Power Aware Control)
Remote Basestation
![Page 4: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/4.jpg)
System RequirementsSystem Requirements
n Sensor Types: Low Rate (e.g., acoustic and seismic)
n Bandwidth: bits/sec to kbits/sec
n Transmission Distance: 5-10m (< 100m)
n Spatial Densityo 0.1 nodes/m2 to 20 nodes/m2
n Node Requirementsn Small Form Factor
n Required Lifetime: > year
n Operational Diversity:
...from the environmento Event arrival
rate/type
o Ambient noise
o Signal statistics
...from network roleso Sensor
o Relay
o Data aggregator
...from user demandso Tolerable latency
o Result SNR
o Pr(Detection)
![Page 5: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/5.jpg)
Integrated SensorIntegrated Sensor--NodeNode--onon--aa--ChipChip
n Integration is the key enabler for massively distributed wireless sensing
µ-PROC&
DSP
MULTIPLEOUTPUTDC-DC
MEMS
MICROBATTERY
A/D
MEMORY
What is the best computation/communication fabric?What is the best computation/communication fabric?How coupled should protocol design be to the fabric?How coupled should protocol design be to the fabric?
RF
![Page 6: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/6.jpg)
n Diversity in operating scenarios: number and type of events, signal statistics, desired quality, latency, etc.
n Cannot achieve Esystem = Eperfect at all pointsoOptimize at important scenarios (Esystemi di is high)
1−
=
∑∑
Scenariosiperfect
Scenariosisystem
PA dE
dE
i
i
η
Scenario
Eperfect
Ene
rgy
Esystemdi
Power AwarenessPower Awareness
![Page 7: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/7.jpg)
Power Aware Node ArchitecturePower Aware Node Architecture
Leakage current Workload variation
Bias currentStart-up time
Standby currentLow duty cycle
Capacity variations
Efficiency variations
Desired result quality variations
Available energyVoltage scheduling
RadioSA-1100A/DSeismic Sensor
Acoustic Sensor
ROMRAM
DC-DC Conversion
Battery
Power
Protocols
Algorithms
µOS
n Graceful energy scalability across a diversity of operating conditions and energy-quality trade-offs
![Page 8: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/8.jpg)
OS Directed Power ManagementOS Directed Power Management
offonsleepsleeps3
offoffsleepsleeps4
rxonsleepsleeps2
rxonsleepidles1
tx, rxonactiveactives0
RadioSensorMemoryARM
Battery and DC/DC converter
Sens
or
A/D
Rad
io
Sensor Node
Memory
StrongARM
µ-OS
• OS must decide suitable transitionpolicy based on observed history
-200
0
200
400
600
800
1000
1200
-10 0 10 20 30 40 50 60
s0
s1
s2s3
s4
Pow
er (m
W)
Transition Latency (ms)
Deeper sleepLower powerMore overhead
![Page 9: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/9.jpg)
Idle Mode Leakage PowerIdle Mode Leakage Power
n Leakage dominates switching energy for low duty cycles
n A major concern for event-driven operation (PDAs, sensors, etc.)
)/(10 SVleakage
TI −∝
![Page 10: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/10.jpg)
Leakage and Switching PowerLeakage and Switching Power
0.13 µ, 15mm die, 1V
1% 2% 3% 5% 8% 11% 15% 20%26%
10
20
30
40
50
60
70
30 40 50 60 70 80 90 100
110
Temp (C)
Po
wer
(Wat
ts)
Leakage
Active80
900.1µ, 15mm die, 0.7V
6% 9% 14% 19%26%
33%41%
49%
56%
10
20
30
40
50
60
70
30 40 50 60 70 80 90 100
110
Temp (C)
Po
wer
(Wat
ts)
80
90LeakageActive
Need to Develop Techniques for Leakage ControlNeed to Develop Techniques for Leakage Control
Courtesy of Vivek De (Intel)
![Page 11: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/11.jpg)
Low Duty Cycle RadioLow Duty Cycle Radio
n Start-up time dominates the energy for small packet sizes
n Innovative radio design required…
10
100
1000
10000
10 100 1000 10000 100000
Packet size (bits)
Ene
rgy
Per
Bit
(nJ)
20mW Electronics Power1mW Transmit power @ 1Mbps
Startup Costs are Fundamental Startup Costs are Fundamental ––Latency not just a function of user requirement Latency not just a function of user requirement
![Page 12: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/12.jpg)
DVS on SADVS on SA--11001100
SA-1100
Control
µOS
VoutController
Power
5 V
Voltage request, 0.9 - 1.6 V
5
1.6V limiter
5
Digitally adjustable DC-DC converter powers SA-1100 core
µOS selects appropriate clock frequency based on workload and latency constraints
SA-1100 requests a voltage appropriate for its clock frequency
MIT DVS PCBMIT DVS PCB
StrongARMEvalualtion
Board
![Page 13: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/13.jpg)
Software Voltage SchedulingSoftware Voltage Scheduling
n Operating system predicts and schedules the voltage
n Adapt power supply to deliver “just enough performance”
Data from StrongARM-1100
StrongArmSA-1100
DC-DC Regulator Controller
5
CP
U C
ore
Po
wer
, 0.9
-1.6
Vo
lts
Buck Regulator
MOSFET control
![Page 14: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/14.jpg)
DVS DemonstrationDVS Demonstration
oUser adjusts number of filter taps
o Frequency/Voltage adjusted appropriately (via eCOS based µOS)
Frequency /Voltage
Workload (filter taps)
![Page 15: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/15.jpg)
Computation vs. CommunicationComputation vs. Communication
Compute, Don’t CommunicateCompute, Don’t Communicate
1E-11
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
1E-04
1E-03
1 10 100 1000 10000
Energy for Electronics + Transmit
R2 Propagation LossLimit (no electronics)Assuming 10pJ/bit/m2
En
erg
y (J
)
Distance (m)
n Computation: 1nJ/op (µ-Processor) and Communication (@10m): 150nJ/bit
n @10 m: ~150 instructions/transmitted bit on a low-power processor
n @10m: > 1Million instructions/transmitted bit using dedicated hardware
![Page 16: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/16.jpg)
Protocol ArchitecturesProtocol Architectures
Source Destination
Router
Multi-hop Routing Example(ignoring electronics)
• 1 hop over 100 m: 100nJ/bit• 10 hops of 10 m:
10 × 1 nJ/bit = 10nJ/bit
n Particular attention must be placed on multiple access schemes
n Scheduled vs. Reactive routing (synchronous vs. asynchronous)
Similar TradeSimilar Trade--off to Onoff to On--chip Interconnectchip Interconnect
![Page 17: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/17.jpg)
Distributed DSP using DVSDistributed DSP using DVS
Ecomp(Vdd=1.5V) = 7 * Efft +Ebf + ELOB
= 27.27 mJ
Parallelizing the FFT means we can reduce the supply voltage and frequency
Ecomp(variable Vdd) = 15.16 mJ
FFT is operated at .9 V
BF & LOB is operated at 1.3 V
n Approach 2 :FFT is done at node and transmitted to C-H
A/D
Sensor 6
FFT
A/D
Sensor 2
FFTA/D
Sensor 1
FFT
Cluster Head
BF LOB
Sensor 7
n Approach 1 : All computation is done at C-H
A/D
Sensor 1A/D
Sensor 2
A/D
Sensor 6
FFT
Cluster Head
BF LOB
Sensor 7
![Page 18: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/18.jpg)
Energy Efficient Link LayerEnergy Efficient Link Layer
0
500
1000
1500
2000
2500
(15,
7,2)
(31,
6,7)
(31,
11,5
)
(31,
16,3
)
(63,
7,15
)
(63,
16,1
1)
(63,
24,7
)
(63,
39,4
)
(63,
45,3
)
EncodeDecode
§ Energy scalability through variation of error-correction scheme
§ Computation-communication tradeoff between coding and Tx power for BER reduction
Energy
Ene
rgy
per b
it (n
J)
![Page 19: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/19.jpg)
n Self-powered operation is a real option if the power dissipation can be scaled to 10’s - 100’s of µW oMechanical vibration (e.g., machine-mounted sensors)o Electromagnetic fields (RF)
n A major opportunity exists in developing energy scavengers(generator and associated electronics) for extracting useful energy from ambient sources
Energy ScavengingEnergy Scavenging
Generator RegulatorVDD
Load Electronics
![Page 20: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/20.jpg)
Energy ScavengingEnergy Scavenging
MEMS Generator
PicoJouleDSP
Power Controller
[Amirthrajah00]
n Scavenge energy from mechanical vibrations to power micropower sensor systems
n Power delivered ~ 10µW
Hardwired Fabrics enable No Power Signal ProcessingHardwired Fabrics enable No Power Signal Processing
![Page 21: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/21.jpg)
Node PrototypeNode Prototype
sensor/processor board radio baseband
n Version 1 prototype with COTS components
n Future nodes will feature custom chipsets
![Page 22: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/22.jpg)
Node and Network APINode and Network API
nn Enable and encourage endEnable and encourage end--user to operate network in a user to operate network in a powerpower--aware manneraware mannero Sufficient abstraction to hide complexity of distributed wireless
network
oGet-optimize-set paradigm to maintain network state
nn Functional interface, object abstractions, and behavioral Functional interface, object abstractions, and behavioral semanticssemanticsoGather and set state of nodes, links, network
o Facilitate data exchange between node and basestation
oRealize a user’s desired operating point for the network
o Visualize network state
oBuilt-in and customizable energy models for energy, delay, etc.
![Page 23: Low Power Wireless Sensor Networks - Semantic Scholar...Low duty cycle Capacity variations Efficiency variations Desired result quality variations Available energy Voltage scheduling](https://reader033.vdocuments.us/reader033/viewer/2022060912/60a68af3bc77a040776a0ac4/html5/thumbnails/23.jpg)
n Just-in-Time computing through supply optimization minimizes energy dissipation
n Leakage is a first order issue – active leakage management at the architecture, circuit, and device levels are critical
n Focus must shift from computation to communication-centric design
n Protocols must be fabric and domain aware o Energy per operation (mW/MIPS) will scale with technologyoCommunication costs (nJ/bit) will not scale at the same rate
SummarySummary
Low Energy Sensor Design Requires a SystemLow Energy Sensor Design Requires a System--level level Approach Approach –– Tight Coupling Between Fabrics, Tight Coupling Between Fabrics,
Algorithms and ProtocolsAlgorithms and Protocols