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5.9.2003 Gao Chao, Vaasa Polytechnic 1
Energy Sensitive Routing in Ad hoc Networks
Gao Chao, Information Technology Department of Vaasa Polytechnic (www.puv.fi)
In association with Information Technology Department of Vaasa University (www.uwasa.fi)
5.9.2003 Gao Chao, Vaasa Polytechnic 2
Table of Contents
l Introduction to Ad hoc Networks¡Definition¡Physical Layer¡MAC Layer¡Multihop
l Ad hoc Routing¡Proactive Routings¡Reactive Routings
l Energy Consideration in Ad hoc Routingl Q/A and Discussion
5.9.2003 Gao Chao, Vaasa Polytechnic 3
Ad hoc Networks – Wireless without Infrastructure
l Wireless networks work without any central administration.
l Comparing to mobile cellular telephone systems, ad hoc networks have smaller cover range.
l Ad hoc is generally packet-switch system.l IEEE 802.11 standards
5.9.2003 Gao Chao, Vaasa Polytechnic 4
Ad hoc Physical Layer
l Basics:¡2.4G Hz FHSS (Frequency Hopping)¡2.4G Hz DSSS (Direct Sequence)¡Infrared
l 1Mbps or 2Mbps raw data ratel 11Mbps or higher data rate (IEEE 802.11a, IEEE
802.11b)
5.9.2003 Gao Chao, Vaasa Polytechnic 5
Ad hoc MAC layer
l Ad hoc MAC layer uses a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol.
l First the radio interface (carrier) is sensed.l Source node sends (broadcasts) a Request-to-Send
(RTS) packet with the destination node addressl The specified node replies a Clear-to-Send (CTS) packet
5.9.2003 Gao Chao, Vaasa Polytechnic 6
Ad hoc MAC layer
RTS-CTS can eliminate Hidden Node and Expose Node problems
Hidden node
RTS
RTSCTS
CTS
Data
Keep silence
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Multihop Ad hoc Networks
l The devices in Ad hoc network generally have limited power supply
l Ineffective to use high transmission power to cover all nodes in the network
l Data packets are relayed by intermediate nodes – multihop ad hoc network
CA B
Coverage of the node
A 3-hop connectionD
5.9.2003 Gao Chao, Vaasa Polytechnic 8
Energy consumption by Multihop
l For a given threshold receiver power Pr, the minimum transmit power Pt is
l n is the path loss exponent, typically is 4. K is a constant.l With an intermediate node between the source and destination, the
transmit power (energy) is the sum of two hops:
l One can derive that the transmitting energy consumed by two-hop scenario is 1/8 of the single hop if the intermediate node has the same distance to the source and destination
Pt( ) Prnd
dK
=
1 2 1 2Pt'( ) Pt( )+Pt( ) where d d d d d d= = +
5.9.2003 Gao Chao, Vaasa Polytechnic 9
Ad hoc Network Routing
l Routing protocols are necessary in order to find a path between source and destination nodes in multihop ad hoc networks.l Routing is challenged by the dynamic topology
of the network.l Basically there are two classes of routing
algorithms: proactive and reactive.
5.9.2003 Gao Chao, Vaasa Polytechnic 10
Ad hoc Network Routingl In proactive routing, all the nodes maintain and
periodically refresh routes to any other node in the network, even no traffic is carried on a maintained route.l In reactive routing, a route is established on
demand.l Research shows that reactive routing schemes
generate less overhead packets, thus consume less power than proactive ones.
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Reactive Routing Example: Ad hoc On-demand Distance Vector (AODV)
l AODV is a reactive routing algorithml In AODV, there are 4 types of overhead packets
(Routing Signalling):¡ HELLO to notify neighbours¡ RREQ (Routing Request) to initiate a routing procedure¡ RREP (Routing Reply) to confirm a route¡ RERR to indicate a route failure
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AODV – Path Finding (1)
1
6
5
7
4
3
2
RREQ message:Dest: 4Source: 1Seq.No.: 2
The source node broadcasts RREQ message to its neighbours.
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AODV – Path Finding (2)
1
6
5
7
4
3
2
Node 6 forwards RREQ to its neighbors
On receiving RREQ, an intermediate node will broadcast it again.
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AODV – Path Finding (3)
node 7 also forwards RREQ to 5, but it comes later and discarded.
1
6
5
7
4
3
2
Duplicated RREQ is discarded.
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AODV – Path Finding (4)
1
6
5
7
4
3
2
RREP message:DEST: 4SRC: 1Seq #: xxx
The destination node* replies RREP message when it receives a RREQ.
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AODV – Path Finding (5)
1
6
5
7
4
3
2
In Node 5 a routing entry is established:
Dest Node: 4Next Hop: 4Hop Cnt: 1Seq #: xxx
The RREP will be propagated through inverse path to confirm a route.
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Energy-Conserving Routing Schemes
l Network Device Power Control ¡Adaptive Energy-Conserving Routing (AECR)¡Coordinated Energy-Conserving Routing (CECR))
l Battery-Lifetime Determination¡Time Delay On-Demand Routing (TDOR)
l Battery-Lifetime & Traffic-Load Determination¡EAODV for Optimal Path Discovery* (EAODV)
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Energy-Conserving Routing (1)
l Adaptive Energy-Conserving Routing for Multihop Ad hoc Networks, by Ya Xu, John Heidemann, and Deborah Estrin, http://citeseer.nj.nec.com/310126.html
l The research shows that in receiving/listening mode, the power consumption is still considerable.
l Two algorithms are presented here:¡Basic Energy-conserving Algorithm (BECA)¡Adaptive Fidelity Energy-Conserving Algorithm
(AFECA)l Basically these two algorithms will determine the chance
that a node may participate in a route.
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Energy-Conserving Routing (1)
l In BECA, nodes are in one of three states:¡ Sleeping¡ Listening¡ Active
l When in the sleeping state, radio is turned off to save energy.
l A timer is used to change state when time-out.
Sleeping
Listening
Active
Upon first traffic
After TlWith noTraffic
After Ts
Ta after last traffic
Send Local data
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Energy-Conserving Routing (1)
l In AFECA, a node can improve energy conservation by estimating node populating and increasing sleep time when other nodes are available.
l The sleeping timer is simply set as Tsa, which is
l Here N is the number of neighbours, Ts is the unit sleeping time in BECA.
(1, )SA ST random N T= ×
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Energy-Conserving Routing (2)
l Coordinated Energy Conservation for Ad hoc Networks, by Chavalit Srisathapornphat, Chien-Chung Shen, Communications, 2002. ICC 2002. IEEE International Conference on , Volume: 5 , 2002
l An algorithm called Coordinated Energy Conservation(CEC) for ad hoc was introduced
l A set of backbone nodes are selected to coordinate energy conservation.
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Energy-Conserving Routing (2)
l A backbone node works as a server, which serves a group of clients.
l A server and its clients use Coordinated Energy Conservation Algorithm to collaborate.
l A client sends its states (include intension to transmit, battery remaining, etc) to its server.
l The server replies either a grant to transmit or a duration that the client can turn off the radio interface (sleep).
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Energy-Conserving Routing (2): Network topology and Client Algorithm
ServerClient
Backbone Active
Requesting
Sleeping
Timer expiresOr transmitting
CommunicationActivity
Receive AuthorizationSet timer
IDLE/SendRequest to sleep
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Energy-Conserving Routing (3)
l Implementation of an Energy-Efficient Routing Protocol: Time Delay On-Demand Routing Algorithm (TDOR), Tran Minh Trung and Seong-Lyun Kim, Proc. IEEE Conference on Mobile and Wireless Communications Networks, Stockholm, Sweden, 2002
l In TDOR, a node holds the RREQ packet for some times, inversely proportional to its own residual battery capacity.
ti
tii C
CT1
)( =
5.9.2003 Gao Chao, Vaasa Polytechnic 25
Energy-Conserving Routing (3)s
B:9
A:9
D:7
C:8F:6
E:9
d
G:9
T1
T1
T2
T2T5
T6T4
T4T8
T5
s
D
C
B
A
F
E d
G d
d
T0 T1 T2 T3 T4 T5 T6 T7 T8
A Path is Found with Maximum Battery Residual
5.9.2003 Gao Chao, Vaasa Polytechnic 26
Optimal Path Routing AODV-Based on Ad hoc research group result at Vaasa University
l In the original AODV, the destination node sends RREP message immediately after receiving the first RREQ message.
l This mechanism cannot guarantee that the optimal path is found.
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Optimal Path Routing AODV
l Meanwhile, the intermediate nodes involved in the established route may be already heavily loaded (traffic consideration) or running out of battery power (energy aware).
l A new approach is considered, in which some Additional (Extended) information is added to the RREQ and RREP packets. It gives the network possibilities to find an optimal route.
l The purpose to let the nodes in ad hoc network equally participate the network activity. Thus energy dissipation is equally decreased and the total network lifetime increases.
5.9.2003 Gao Chao, Vaasa Polytechnic 28
The Extended Message in RREQ
l In the extended message of RREQ, we need route select field (RSF), which is a metric of the node’s battery residual and the traffic load the node has taken recently
Route-select Field
Originator Sequence Number
Originator IP address
Destination Sequence Number
Destination IP address
RREQ ID
Type (8) | reserved bits (5) | others (11) | hop count (8)
32-bit word
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Route Select Field (RSF)
l Noted as
l Battery Lifetime B¡Can be retrieved from OS (Linux)
l Traffic Load L is a historical value. ¡Can be given by the ratio of the number of bits
transmitted by the node in a fixed past time.
0
bNL
T=
RBL
τ =
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The Route Establishment
l The source node initiates a RREQ will maximum RSF.l Every node that has received a RREQ will check the
RSF and calculate its own battery/load metric. If it is lower than the one in RSF, it will replace it by its own.
l The destination node will reply the first arrived RREQ to ensure the minimum latency of route establishment. Meanwhile, it will keep the value of RSF in its cache.
l If another RREQ arrives at the destination, the node will compare the RSF with its cached value. If the new RSF is greater than the cached one, send a RREP and replace the cache by the new value.
l The source node will change its route table if another RREP comes from the same destination.
5.9.2003 Gao Chao, Vaasa Polytechnic 31
The Route Establishment
3
S
5
4
1
8
9
D
Three RREQs Arrive to D
3
S
5
4
2
8
9
D:2
First a less optimalroute selected
RREP
RREP
3
S
5
4
2
8
9
D:4
A more optimalroute selected
RREP
RREP
RREP
The 3rd RREQis dropped
5.9.2003 Gao Chao, Vaasa Polytechnic 32
Advantages & Disadvantages
l Trade-offs:¡ Longer Packet Length of RREQ and RREP¡More than one copy of RREP may be sent out¡ Node load is increased to calculate RSF and more memory
required.l Gains:¡ Energy Conservation¡Optimal Path possibility increase¡ Data packets propagation improved through the better path¡ Compatible with original AODV nodes
5.9.2003 Gao Chao, Vaasa Polytechnic 33
Conclusion
l Routing plays an important role in energy conservation (to select suitable nodes to relay packets).l Energy conservation routing increases the node
complexity and decreases the throughput of the network; meanwhile, it prolongs the network lifetime thus increases overall performance.lQuestions described here are still open
5.9.2003 Gao Chao, Vaasa Polytechnic 34
References
1. Charles E. Perkins. Ad hoc on-demand Distance Vector (AODV) routing. Internet-Draft, draft-ietf-manet-aodv-09.txt, November 2001
2. Y. Xu, J. Heidemann, and D. Estrin. Adaptive Energy-Conserving Routing for Multihop Ad hoc Networks, Tech. Rep. 527, USC/Information Science Institute, Oct.2000
3. Chavalit Srisathapornphat, Chien-Chung Shen, Coordinated Energy Conservation for Ad hoc Networks, Communications, 2002. ICC 2002. IEEE International Conference on , Volume: 5 , 2002
4. Sheetalkumar Doshi, Timothy X. Brown, Minimum Energy Routing Schemes for a Wireless Ad hoc Network, IEEE InfoCom 2002
5. Dmitri D. Perkins, Herman D. Hughes, and Charles B. Owen, Factors Affecting the Performance of Ad Hoc Networks, Communications, 2002. ICC 2002. IEEE International Conference on , Volume: 4 , 2002, Page(s): 2048 -2052 vol.4