nemo : a high-fidelity noninvasive power meter system for wireless sensor networks
DESCRIPTION
Nemo : A High-fidelity Noninvasive Power Meter System for Wireless Sensor Networks. Ruogu Zhou , Guoliang Xing Department of Computer Science and Engineering, Michigan State University. Wireless Sensor Networks Platforms. Microscopic and inexpensive devices - PowerPoint PPT PresentationTRANSCRIPT
Nemo: A High-fidelity Noninvasive Power Meter System for
Wireless Sensor Networks
Ruogu Zhou, Guoliang Xing
Department of Computer Science and Engineering,Michigan State University
Wireless Sensor Networks Platforms
• Microscopic and inexpensive devices– Densely deployed to increase sensing fidelity
• Ad-hoc deployment– Powered by battery; transmit wirelessly
• Various form factors
2
Node1
Node2
Node3
Node4
Node5
Base Station
xx
x
Scarcity of Power
3
• Small energy reservoir on node– Usually 2 AA batteries
• Energy-efficiency is crucial for WSN– Many energy-efficient protocols are proposed– Their effectiveness is hard to verify
• Power outages are common in deployment – Greatly impair sensing fidelity– Exact reasons are usually unknown
In-situ WSN Power Meters• SPOT[IPSN’07], iCount[IPSN’08]• Low sampling rate/resolution
– Cannot capture sleep power consumption or power transients
4SPOT mounts on MicaZ iCount with Telos
In-situ WSN Power Meters• SPOT[IPSN’07], iCount[IPSN’08]• Low sampling rate/resolution
– Cannot capture sleep power consumption or power transients
• Invasive to host node– Require host CPU, RAM , I/O and timer– Installation requires wiring and soldering
5
Nemo: Noninvasive High Fidelity Power Meter
• Retrofit with after-market platforms w/ power metering
• Noninvasive to host node– Standalone meter, plug &play, work with virtually any platform
• High measurement fidelity– 2uA-200mA dynamic range, >5 KHz sampling rate, <1uA
resolution
• Real-time communication with host– Enable real-time monitoring and energy-aware runtime
adaptation
6
TelosB node
Nemo+
Challenges
• Noninvasiveness and real-time communication?– Only connection b/w meter and host is power rail– No dedicated data wires
• High fidelity and low power consumption? – High fidelity usually results in high power consumption– Ex: ADC w/ high dynamic range consumes > 10 mA current
7
Only connection
Outline
• Motivation• Challenges and System design
– Host-meter Communication– High Fidelity Measurement
• System evaluation• Case study• Conclusion
8
Diode
Switch
Voltage Modulator
Power Positive+
Power Ground
Modulation ControlADC
Sensor
Voltage Modulation (Meter->Host)
9
• Modulate supply voltage of host to transmit measurements– Modulator: A Schottky diode controlled by a switch
• Host decodes by sampling supply voltage– Most built-in ADCs can be programmed to measure supply
voltage • Host cannot modulate supply voltage
– Cannot be applied to host-> meter link
010011011100
Current Modulation (Host->Meter)
10
• Modulate own current draw to transmit data to meter– Modulator: Any component that can be switched fast, e.g. LED
• Meter decodes by measuring host current draw
Sensor
Nem
o
Power Positive+
Power Ground
Current
Measurement
Currrent Modulator
010011011100
Outline
• Motivation• Challenges and System design
– Host-meter Communication– High Fidelity Measurement
• System evaluation• Case study• Conclusion
11
Fidelity Requirements
12
• Wide dynamic range– Sleep (~2uA) to Active (~200mA), 5 orders of difference
• High sampling rate– > 5kHz to capture power transients
• High resolution– Monitor sleep power (< 1uA) which determines system life
-2 0 2 4 6 8 10 12 14 160
5
10
15
20
25
30
Time (ms)
Cur
rent
(mA
)
Power transients caused by radio on/off
Current Measurement 101
13
• Shunt resistor (current sensing resistor)– Convert current intensity to voltage signal
• Pre-amplifier– Amplify voltage signal to a proper level
• ADC– Convert analog signal to digital signal– 2uA to 200mA dynamic range and < 1uA resolution 18-bit ADC
Sensor
Power Positive+
Power Ground
ADC
14
• Shunt resistor (current sensing resistor)– Convert current intensity to voltage signal
• Pre-amplifier– Amplify voltage signal to a proper level
• ADC– Convert analog signal to digital signal– 2uA to 200mA dynamic range requires an 18-bit ADC
High dynamic range ADCs are expensive and power hungry!
Current Measurement 101
• High resolution needed only when measuring small current– Small current does not need 0-200mA dynamic range
• Wide dynamic range needed only when measuring large current– Large current does not need <1uA resolution
• Adjust measurement range and resolution dynamically – Large current -> use wide measurement range, low resolution– Small current -> use narrow measurement range, high resolution
Solution: Auto-ranging
15
Implementation of Auto-ranging
16
• Adjust shunt resistor to change measurement range& resolution– Wide (narrow) range, low (high) resolution -> small (large) shunt
resistor• Use low dynamic range low power ADC
– Adjust measurement range according to ADC reading• Shunt resistor switch
– A series of electrically controlled shunt resistors– Adjust resistance by shorting one or more resistors
Sensor
Pwr Positive+
Pwr Ground
ADC
Input OutputResistors
Switches
Outline
• Motivation• Challenges and System design• System evaluation• Case study• Conclusion
17
Implementation & Experiment Setup
• PCB area 1.5 inch by 2.5 inch• System software implemented in C and assembly• Nemo is calibrated using a set of resistors• Agilent 34410A Bench-top digital multi-meter as reference
18
Agilent 34410A benchtop DMM
Agilent DSO2024A Oscilloscope
Extech handheld DMM TelosB Nemo with battery
Measurement Fidelity (I)
19
• TelosB mote running a sense-and-send app as load
0 2 4 6 8 10 12 140
20
40
60
Time (ms)
Cur
rent
(mA
)
0 1 2 3 4 5 6 7 8 9 100
50
100
Relative Error (Percent)
CD
F
CDF
Ground-truthMeasurement
Match ground-truth closely
Average Error: 2.09%
Radio on ADC on
Radio RX on Radio TX on
Radio off ADC off
Measurement Fidelity (II)
20
• Sampling rate: constant 8.192 KHz• Dynamic range: 0.8 uA to 202 mA• Resolution < 1 uA when current is less than 2.5 mA
10-3
10-2
10-1
100
101
10210
-2
10-1
100
101
102
Current (mA)
Res
olut
ion
(uA
)
resolution
0.069 uA
0.68 uA
6.6 uA
48 uA
0.013 uA
Dynamic range0.8 uA to 202 mA
Resolution < 1uA
20 30 40 50 60 70 800
10
20
30
40
50
60
Temperature (Degrees Celsius)
Sle
ep C
urre
nt (u
A)
Mote1Mote2Mote3
Case Study: Sleep Power of Mote
21
• 3 randomly selected TelosB motes running Null app• Nemo is attached as power meter• Surface of mote is heated to 80oC, then cooled down to 0oC
Difference <1uA
5X difference
Conclusions
22
• A noninvasive in-situ power meter for WSN– Plug and play, high measurement fidelity
• Novel communication scheme for host-meter comm. – Voltage¤t modulation for communication over power rails
• Auto-ranging technique for high measurement fidelity– Dynamically configure meter according to measurement
requirements
• Evaluation in real experiments– High dynamic range, high sampling rate, high resolution, low
error
Q/A
23