Energy Efficiency in
Ad

Hoc Networks
Chien

Jen Huang
& Min Chen
April 22, 2004
EE497A
2
Outline
Introduction
Physical layer design
Routing layer design
Cross

layer design issues
Conclusions
3
Introduction
What is Ad

hoc networks
Energy efficiency is one of the crucial
problems for Ad

hoc
Energy constraint strategy is a global
issue, involving
most
layer stacks in the
network structure
4
Physical layer design

System model
The
whole
transmission period time
The total energy consumption for transmitting bits
The energy

constrained modulation problem finally can be modeled
as
:
Minimize
Subject to
delay constraint
peak

power constraint
tr
sp
on
T
T
T
T
E
L
tr
tr
sp
sp
on
on
T
P
T
P
T
P
E
tr
tr
on
c
t
T
P
T
P
P
)
)
1
((
L
E
E
bit
/
tr
on
T
T
T
max
0
max
)
1
(
0
P
P
P
c
t
tr
tr
sp
sp
on
c
amp
t
T
P
T
P
T
P
P
P
)
(
5
Physical layer design

Energy constraint problem for M

QAM
An upper bound of the symbol error probability for M

QAM in AWGN
channel is given in [5] as
SNR
Free space propagation model
We obtain the lower bound of the transmission energy as
2
1
2
3
)
2
1
1
(
4
)
1
2
3
(
)
2
1
1
(
4
b
e
Q
Pe
b
b
b
f
r
N
B
P
2
2
r
r
t
t
P
G
G
L
d
P
2
2
2
)
4
(
on
d
b
BT
L
f
on
t
t
BT
G
P
N
T
P
E
on
BT
L
on
)
2
1
(
4
ln
)
1
2
(
3
4
2
2
6
Physical layer design

Energy constraint problem for M

QAM
(cont’d)
The total energy consumption per bit as
Peak

power constraint
we can find a lower bound such that all satisfy the
peak

power constraint
Energy consumption optimal problem for M

QAM is modeled as
Minimize
Subject to
The optimal modulation constellation size is obtained from
by
L
T
P
T
P
T
P
E
tr
tr
on
c
on
t
total
/
)
)
1
((
c
t
P
P
P
max
)
1
(
min
T
min
T
T
on
total
E
T
T
T
T
T
tr
on
max
min
*
on
BT
L
b
b
M
2
*
on
T
7
Physical layer design

Numerical results
Fig. 1 versus Fig. 2 versus
T
T
on
/
total
E
total
E
b
8
Physical layer design

Further discussions
M

QAM versus M

FSK
QAM sacrifices transmit power to obtain higher bandwidth
efficiency
FSK sacrifices bandwidth for a reduction in transmit power
Coded versus uncoded modulation
Error control coding can reduce the required SNR for the same
performance requirement
Possible bandwidth expansion caused by error control coding
redundancy, and the extra energy consumption of the encoder
Power Control And
Routing Protocol In
Network Layer
10
Design Rules For Power Control
Routing Protocol
Routing with more
hops can save power
Many short hop may be
better than a few long ones
Routing with more
hops reduces
interference at every
node
hop
BC
AB
BC
AB
hop
Pt
Td
Td
d
d
T
Pt
Td
Pt
CGtGr
T
Td
Pt
d
CGtGr
Pt
2
1
Pr
Pr
)
(
Pr
2
,
Pr
1
1
Pr
Power P required to transmit over a distance d
11
Common Power Routing
Protocol (COMPOW)
Characteristics
Equal transmission power between every
node in the route
The common power is the minimal one which
can keep the connectivity of the route
Compatible to some other protocol
Address resolution protocol (ARP)
DHCP
Reverse ARP
12
COMPOW will be not efficient when the node in
the network is not uniformly distributed
13
Cluster Power Routing Protocol
(CLUSTERPOW)
Characteristic
Use power level clustering the nodes into
groups
The cluster may last for several levels
Every node in the same cluster level transmits
the same power to each other
Designed based on “distance vector routing”
algorithm
14
Property Of CLUSTERPOW
Clusterpow is adaptive to the network
distribution
The route is discovered with a non

decreasing
power levels
COMPOW is the special case of Clusterpow
Clusterpow at every fixed power level is loop
free
Clusterpow is loop free
15
Clusters in the ad hoc network
[7] V. Kawadia and P. R. Kumar, Power Control and Clustering in
Ad Hoc Networks,
IEEE INFOCOM 2003
.
16
Power Efficiency Issue In Cross
Layer
Device power issue
Increase hops number also increase the
device power consumption ( contradict to the
design rule)
Error propagation issue
simply relay case
Data is just amplified without any demodulation or
decoding when passing by the intermediate nodes
between source and destination
17
18
Power Efficiency Issue In Cross
Layer
regenerator case
Data will be demodulated, decoded or some other
processing which can improve the error rate when
passing by the intermediate nodes between source
and destination
Trade off
Use regenerators may decrease the error rate but
also increase the processing power at every node
With error propagation, more hops are not
necessarily good
19
Simulation1:
Compare the cases of directly transmission, simply relay and
regenerator
4

QAM, pass loss exponent=4, dac=5m ,y=0m
2 hops routing, equal error rate in the final nodes
20
Simulation2:
Compare the cases of directly transmission, simply relay and
regenerator
4

QAM, pass loss exponent=4, dac=5m ,y=2m
2 hops routing, equal error rate in the final nodes
21
Conclusion
Optimizing the performance of each layer
is not necessarily optimizing the global
performance
Achieving the global performance, cross
layer issues should be taken into account
22
Questions?
23
References
[1] A. J. Goldsmith and S. B. Wicker, Design Challenges for Energy

constrained Ad Hoc Wireless
Networks,
IEEE Wireless Communications Magazine
, pp. 8

27 Aug. 2002.
[2] A. Y. Wang, S. Chao, C. G. Sodini, and A. P. Chandrakasan, Energy Efficient Modulation and
MAC for Asymmetric RF Microsensor System,”
International Symposium on Low Power
Electronics and Design
, pp. 106

111, 2001.
[3] S. Cui, A. J. Goldsmith, and A. Bahai, Energy

constrained Modulation Optimization under
Energy Constraints,
ICC’03
, Alaska, U.S.A, May, 2003.
[4] S. Cui, A. J. Goldsmith, and A. Bahai, Energy

constrained Modulation, submitted to IEEE
Trans. on Wireless Communications.
[5] J. G. Proakis,
Digital Communications,
4th Ed. New York: MxGraw

Hill, 2000.
[6] S. Hares, H. Yanikomeroglu, and B. Hashem, A Relaying Algorithm for Multihop TDMA TDD
Networks Using Diversity,
IEEE Vehicular Technology Conference 2003 (
VTC'F03
)
, Orlando,
Florida, USA, October. 2003.
[7] V. Kawadia and P. R. Kumar, Power Control and Clustering in Ad Hoc Networks,
IEEE
INFOCOM 2003
.
[8] Vikas Kawadia and P. R. Kumar, A Cautionary Perspective on Cross Layer Design, submitted
to
IEEE Wireless Communication Magazine
. July, 2003.
[9] Z. Sahinoglu and P. Orlik, Regenerator Versus Simple

Relay With Optimum Transmit Power
Control for Error Propagation,
IEEE Communications Letters
,
Vol. 7,
Issue 9,
pp. 416

418,
September 2003.
[10] Z. Sahinoglu,and P. Orlik, Optimum Power Compensation for Error Propagation in Relay
Assisted Wireless Networks,
IEEE Global Telecommunications Conference
, Vol. 1, pp. 382

386,
December 2003.
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