Can they Survive for many Years?
Idea: set MCU in sleep mode
Example: one 16 bit sample per second; idealized channel
Transmission time = 16/(250*1024) s = 62.5 us
Duty cycling
250 * 1024 Bit/s 16 Bit
Wakeup 62.5 us
Transmit Sleep
Can they Survive for many Years?
Tmote sky product description
Processor: 500 uA
Processor sleep@32kHz: 2.6 uA
Radio TX: 17.4 mA
Radio Idle: 365 uA
Radio power down: 1 uA
Processor wakeup: 6 us
Radio oscillator startup: 580 us
10^6 – (6 + 580 + 62.5) usIdle MCU6 us Radio
580 us TX
62.5 us
500 uA
+ 1 uA 500 uA + 365 uA 500 uA
+ 17.4 mA 2.6 uA + 1 uA
Current consumption: Y = 6/10^6 * (500+1) + 580/10^6 * (500+365) +
62.5/10^6 * (500+17400) +
(10^6-6-580-62.5)/10^6 * (2.6+1)
Y = 5.22 uA
Lifetime: 4400 mAh / 0.00522 mA ≈ 842912 h ≈ 35121days ≈ 96years
In practice lifetime of a few years:
• More sources of power dissipation
• Synchronization of communication nodes
• Battery looses current
Übersicht
Beispielanwendungen
Sensor-Hardware und Netzarchitektur
Herausforderungen und Methoden
Limitierender Faktor Batterie
Schlafzyklen
In-Network-Processing
Multihop-Kommunikation
MAC-Layer-Fallstudie IEEE 802.15.4
Energieeffiziente MAC-Layer
S-MAC und T-MAC
B-MAC
X-MAC und Wise-MAC
WSN-Programmierung
Laufzeitumgebungen
Fallstudie TinyOS
MAC-Layer-Programmierung mit der MLA
Where to Process the Data?
Example determine max value
How to reduce communication load on S3?
S3 Sink: compute
max(d1,d2,d3) S1
S2
send(d1)
send(d2)
send(d3)
Data Aggregation
S3 Sink
S1
S2
send(d1)
send(d2)
compute
m = max(d1,d2,d3) send(m)
Übersicht
Beispielanwendungen
Sensor-Hardware und Netzarchitektur
Herausforderungen und Methoden
Limitierender Faktor Batterie
Schlafzyklen
In-Network-Processing
Multihop-Kommunikation
MAC-Layer-Fallstudie IEEE 802.15.4
Energieeffiziente MAC-Layer
WSN-Programmierung
Observation: Energy Efficiency
100 m 100 nJoule/Bit
37
Observation: Energy Efficiency
10 m 1 nJoule/Bit
…
Bluetooth Example
100m in one hop: 100nJ/Bit
100m in ten hops: 10nJ/Bit
Distance
Signal Strength
Broadcast Property
Sender Receiver
Übersicht
Beispielanwendungen
Sensor-Hardware und Netzarchitektur
Herausforderungen und Methoden
MAC-Layer-Fallstudie IEEE 802.15.4
Energieeffiziente MAC-Layer
WSN-Programmierung
Case Study: IEEE 802.15.4 (1/3)
PAN Coordinator
Guaranteed time slots (GTS) Other things
Star topology
v1
v2 v3
v4 v5
v1
v4 v5 v2
ts t
sl2 : v4 sl4 : v1 sl5 : v5 sl7 : v2
Beacon
But how will v3 be able to send data?
not possible
Case Study: IEEE 802.15.4 (2/3)
PAN Coordinator
Contention Access Period (CAP) Super frame Star topology
v1
v2 v3
v4 v5
tnext Beacon
Slotted CSMA with random backoff in CAP
v2 GTS
needs GTS
v3 needs GTS
(Remark: CAP can also be used to send data directly)
Case Study: IEEE 802.15.4 (3/3)
PAN Coordinator
CAP
Star topology v1
v2 v3
v4 v5
t Beacon GTS And what happens here?Nothing ?!?
Active period Inactive period
Übersicht
Beispielanwendungen
Sensor-Hardware und Netzarchitektur
Herausforderungen und Methoden
MAC-Layer-Fallstudie IEEE 802.15.4
Energieeffiziente MAC-Layer
S-MAC und T-MAC
B-MAC
X-MAC und Wise-MAC
WSN-Programmierung
Idle Listening Wastes Energy
Psleep Pactive
t P
“Traditional” MAC schemes:
Psleep Pactive
t P
An ideal power minimizing MAC scheme:
Power Consumption
Power Consumption
Power Savings
TX/RX TX/RX TX/RX
TX/RX TX/RX TX/RX
The S-MAC Approach (1/8)
Psleep Pactive
t P
Idea: periodic listen and sleep cycles
Power Consumption Power Savings
TX/RX TX/RX TX/RX
active sleeping …
TX/RX
active sleep
Power Savings:
The S-MAC Approach (2/8)
S
1T
1…
?
Just follow own sleep cycle? Clock drift problem!
The S-MAC Approach (3/8)
S
1T
1…
Idea: synchronizer and follower node
SYNC SYNC
The S-MAC Approach (4/8)
Multihop: (1) Who follows whom? (2) Avoid Synchronization Islands.
SYNC SYNC
s1 s2
The S-MAC Approach (5/8)
(1) Who follows whom?: Contention scheme
SYNC
s1 s2
The S-MAC Approach (6/8)
(2) Avoid Synchronization Islands: Follow all known synchronizers
SYNC(t2) SYNC(t1)
s1 s2
Wakeup Schedule(v)
s t
v
The S-MAC Approach (7/8)
Question: How can u and v communicate? Additional Requirement?
SYNC(t2) SYNC(t1)
s1 s2
v u
The S-MAC Approach (8/8)
Solution: When becoming a follower resend SYNC once
SYNC(t2) SYNC(t1)
s1 s2
v u
Neighbor Table (v)
u t
Neighbor Table (u)
v t2
… …
From S-MAC to T-MAC
Further Reducing Energy Consumption in S-
MAC: the T-MAC approach
wakeup period
Communication in S-MAC: RTS/CTS
s
f1
f2
f3
data
sleep period
no data
no data
no data data for f1
t1 t2 t3
Problem: energy waste at
Contention period Contention period
wakeup period
Sleeping after overhearing CTS
s
f1
f2
f3
data
sleep period
no data
no data
no data data for f1
t1 t2 t3
sleep
sleep
wakeup
wakeup
Problem: energy waste at
Contention period Contention period
wakeup period
Solution: Adaptive Duty Cycle of T-MAC
s
f1
f2
f3
data
sleep period
no data
no data
no data data for f1
t1 t2 t3
Contention period Contention period wakeup
sleep wakeup
sleep
sleep
sleep
sleep
sleep
wakeup period
The Early Sleeping Problem
f1
f2
s
f3
data
sleep period
t1 t2 t3
Contention period Contention period sleep
sleep ???
wakeup
wakeup period
Solution: Future Request to Send
f1
f2
s
f3
data
sleep period
t1 t2 t3
Contention period Contention period sleep
sleep
wakeup
wakeup data
Übersicht
Beispielanwendungen
Sensor-Hardware und Netzarchitektur
Herausforderungen und Methoden
MAC-Layer-Fallstudie IEEE 802.15.4
Energieeffiziente MAC-Layer
S-MAC und T-MAC
B-MAC
X-MAC und Wise-MAC
WSN-Programmierung
B-MAC: Preamble Sampling (1/3)
S
1S
2S
3wakeup/sleep w/s
w/s
w/s w/s w/s w/s
w/s w/s w/s
B-MAC: Preamble Sampling (2/3)
S
1S
2S
3wakeup/sleep w/s
w/s
w/s w/s w/s w/s
w/s w/s w/s
Packet for s1 How to wake up s1?
t1
B-MAC: Preamble Sampling (3/3)
S
1S
2S
3wakeup wakeup
wakeup wakeup
Preamble
t1 t2
sleep again receive packet
Packet(s1)
notes: bmac_power_consumption.pdf
Question: Power over Offered Load
packet arrivals Power [mW]
one packet per packet time
