JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
COMPUTER ENGINEERING
STUDY OF TRADE-OFFS INVOLVED IN POWER
OPTIMIZATION IN MANET
1
RAKESH G VARMA, 2 SUNIL A BAKHRU, 3 MAYUR M VEGAD
1M.E.
[Computer Engineering] Student,2Asso. Professor,3Asso. Professor,
Department of Computer Engineering, Birla Vishvakarma Mahavidyalaya,
Vallabh Vidyanagar, Anand, Gujarat
rakeshgvarma@yahoo.com, sunilab77@gmail.com, mayurmvegad@bvmengineering.ac.in
ABSTRACT: In basic power control scheme adopted in IEEE 802.11 based wireless ad-hoc network RTS and
CTS are transmitted with maximum power while DATA and ACK with minimum power. Past research work has
shown that this power control scheme is in general very inefficient due to hidden terminal interference. In this
paper we dig more in to this matter and evaluate the performance of basic power control scheme for variation
of different parameters like inter-nodal distance, packet size, packet rate, channel bandwidth and mobility. Our
simulation results show that basic power control scheme consume lesser energy in some situation but degrades
the network throughput.
Keywords— Ad- hoc network, BASIC power control, Energy saving, MAC, AODV,
1. INTRODUCTION
To increase the lifetime of nodes in ad-hoc network
power optimization is required. In mobile ad hoc
networks nodes are operated by batteries which have
some limited energy available. Periodic charging is
required otherwise node will be worn out. In ad hoc
wireless networks energy is an inadequate resource.
Each and every node has a twofold functionality of
router with being either source or destination so
energy consumption is more. Performance of the
network can be corrupted if some nodes may failure.
Movement of nodes confines the size of nodes which
restricts the power reserves available to them. Thus
power conservation is key requirement in ad hoc
network.
IEEE 802.11 MAC [1] protocol uses the same
transmission power during every communication
between sender and receiver. This gives inefficient
usage of energy. Here irrespective of the distance
similar transmission power is utilized. Solution of
this problem is to apply power control technique
which regulates the transmit power during
communication that reduces energy consumption.
Many protocols have been proposed for power
optimization [2-3]. Basic power control protocol [45] has been proposed based on an RTS-CTS
handshake. In this protocol RTS and CTS packets are
transmitted with the maximum power level and
DATA and ACK packets are transmitted with
minimum
power
require
for
successful
communication. From the research work done so far
it has shown that basic power control scheme is
inefficient due to hidden terminal interference that
degrades the network throughput [2]. In this paper to
evaluate the performance of the basic power scheme
in ad-hoc network we have considered novel
parameters like inter-nodal distance, packet size,
packet rate, channel bandwidth and mobility.
The remainder of this paper is organized as
follows, section 2 we discuss basic power control and
discuss various parameters. Section 3 presents the
simulation setup and results of our simulations where
we demonstrate the effect of power optimization in
ad-hoc network.
2. BASIC POWER CONTROL PROTOCOL
Power optimization technique can reduce energy
consumption. With some modification to existing
IEEE 802.11 is to transmit RTS and CTS at the
highest power level and transmit DATA and ACK at
minimum power level required for successful
communication [5].
.
Figure 1 Basic power control method
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JOURNAL OF INFORMATION, KNOWLEDGE AND RESEARCH IN
COMPUTER ENGINEERING
In Figure 1, node 1 sends RTS and node 2 sends CTS
with higher power while DATA and ACK packets
are transmitted with minimum power so that nodes
can save the energy.
In basic scheme, RTS-CTS handshake procedure is
used to decide the transmission power for DATA and
ACK packets. Assume node A wants to send a packet
to node B, A transmits the RTS at maximum power
level Pmax, node B also responds through sending
CTS with Pmax. Source node calculates the
minimum transmission power Ptdata for the DATA
packet based on received power level Pr of CTS as
Ptdata = Pmax / Pr * Rxthresh * C
Similarly, the destination node determines the Ptack
for the ACK packet as
Ptack = Pmax / Pr * Rxthresh * C
Where Rxthresh is the required threshold power of
the receiving node for successful reception of the
packet and C is used to overcome the problem of
unstable link due to channel fluctuations. Even
though we have applied basic power control protocol
to save the power but due to collisions affects the
network throughput. Energy has been saved but
throughput has been reduced. This is the main tradeoffs of power optimization. Here we have used the
basic power control mechanism with AODV protocol
for routing in the MANETs. We have considered
various parameters to observe what are the other
trade-offs after implementing power optimization.
List of various parameters
1) More no. of hops
2) Packet size
3) CBR offered data rate
4) Channel bandwidth
5) Mobility
More no. of hops
When no. of hops in a flow increases, the average
sender-receiver distance for each hop reduces. This
leads to reduced power consumption. Basically
AODV [7] protocol selects a shortest path. Distance
between next hop is more so it consumes more power
for transmission so instead of shortest path we have
change it to longer path and select the nearest next
hop that reduces the distance between neighbouring
nodes and consume lesser power. To reduce
transmission range power of RREQ packet of AODV
protocol compared [8-9] with some predefined fixed
threshold value, based on that next hop has been
selected. In our simulation we have taken threshold
value for the distance of 100 m which will be referred
as Thresh100 for chain topology and the same for the
distance of 200 m as Thresh200 for random topology.
Packet size
To reduce the power level required to transmit the
packet, it is desirable to use large packet size in
contrast to small packet size which required some
amount of power level. We have chosen various
packet size like 1000, 2000, 3000 and 4000 bytes.
CBR offered data rate
Increase in CBR offered data rate results in
transmission of more no. of packets with keeping the
packet size constant.
Channel bandwidth
To abridge the power level requirement of
transmitted packet channel bandwidth should be
increased.
Mobility
This parameter is used to measure the varying power
level requirements of the dynamic nodes in contrast
to the constant power level required in case of static
nodes.
3. SIMULATION EVALUATION
In this section, we have simulated AODV without
power control, AODV with threshold (100 m / 200 m)
with power control and AODV with threshold (100 m
/ 200 m) without power control and observe the
various trade-offs after applying power optimization.
We have measured following two metrics to evaluate
our research work.
1. Throughput
Throughput means number of successfully
received bits per second. We measure aggregate
throughput of all flows.
2. Energy Efficiency
It is defined as total data delivered by all the
flows divided by per joule of energy consumed.
We have considered only the energy consumed
in packet transmission.
SIMULATION ENVIRONMENT
We have used NS2 (NS-2.34) to evaluate the
performance. UDP/CBR traffic used for each flow in
the network, all simulations results are average of 20
runs. Every simulation runs for 200 seconds of
simulation time.
In our research work we have used both chain and
random topologies.
Chain topology
Regular chain of 5 nodes was setup with
homogeneous distance between adjacent nodes. In
our simulations we have taken distance of 60 m, 70
m, 80 m and 90 m. Thresh100 of 100 m has been taken
for chain topology.
Random topology
It consists of 50 nodes randomly within 1000 x 1000
m2 flat area. Thresh200 of 200 m has been selected.
Total 5 UDP/CBR flows are generated in every
scenario. We simulated 20 different scenarios in our
simulation.
RESULTS OF SIMULATION
Figure 2 and 3 shows the simulation results of 5
nodes with single flow in a chain topology. AODV
without power control provides better throughput but
AODV with 100 m threshold with power control
performs defectively because of dropping of packets.
AODV with power control consumes more energy
because of retransmission of dropped or collided
packets.
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Figure 4 and 5 demonstrates the result of aggregate
throughput and energy efficiency for 8, 10 and 12
nodes in transmission range of source node for
random topology. AODV without power control
gives better throughput compare to others. In case of
AODV without power control, as number of nodes
increases in transmission range energy efficiency
decreases while in AODV with power control, energy
efficiency increases with number of nodes increases
in transmission range.
AODV without power control gives higher
throughput. A minor change occurs in throughput in
other two schemes.
Figure 6 Aggregate throughput Vs Packet size
Figure 2 Throughput Vs Inter-nodal distance
Figure 7 Data Delivered per joule Vs Packet size
Figure 3 Data Delivered per joule Vs Inter-nodal
distance
Figure 8 and 9 illustrates the result of aggregate
throughput and energy efficiency with various packet
rates. In both the scheme (AODV with power control
/ AODV without power control) as the packet rate
increases, throughput also increases, but AODV with
power control poorly performs compare to AODV
without power control.
Figure 4 No. of Nodes Vs Aggregate throughput
Figure 8 Aggregate Throughput Vs Packet rate
Figure 5 No. of Nodes Vs Data Delivered per joule
Figure 6 and 7 shows the result for various packet
sizes. As we increased the packet size in case of
Figure 9 Data Delivered per joule Vs Packet rate
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COMPUTER ENGINEERING
Figure 10 and 11 shows the result of aggregate
throughput and energy efficiency for varying channel
bandwidth. As illustrated with the increased in
channel bandwidth, throughput increases. As
illustrated AODV 200 m threshold with power
control works superior compared to AODV 200 m
threshold without power control. Energy efficiency
increases as channel bandwidth increases.
Figure 10 Aggregate throughput Vs Channel
Bandwidth
Figure 11 Data Delivered per joule Vs Channel
Bandwidth
Figure 12 and 13 shows results of differing speeds of
nodes. As illustrated AODV with threshold with
power control gives better throughput compare to
AODV with threshold without power control. Energy
efficiency is better with AODV threshold with power
control compared to AODV without power control.
Figure 12 Aggregate Throughput Vs Speed of
Nodes
Figure 13 Data Delivered per joule Vs Speed of
Nodes
4. CONCLUSION
In basic power control scheme suggested for IEEE
802.11 based ad hoc networks, RTS and CTS are
transmitted with maximum power while DATA and
ACK are transmitted with minimum power. In
literature, this scheme has been shown to be
ineffective, mainly due to increased interference. In
this work we studied this issue in more detail by
evaluating the performance of this power control
scheme under variation of different parameters like
inter-nodal distance, packet size, offered data rate,
and mobility. In most of the cases it was observed
that, the throughput performance of basic power
control scheme degrades. However, when the
underlying routing protocol is made selective in
choosing the next hop within some specified distance,
the basic power control scheme did show
improvement in general.
REFERENCES
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