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Power-Aware Routing in Mobile Ad Hoc Networks

S. Singh, M. Woo and C. S. RaghavendraPresented by: Shuoqi Li

Oct. 24, 2002

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Two foci

A power-aware MAC protocol: PAMAS Basic radio modes PAMAS Approach Performance

Metrics for power-aware routing Motivation New Metrics Validation

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Transmitting

Three radio modes

Receiving

Standby with power off.

A B

C

e.g: Proxim RangeLAN2 2.4GHz 1.6Mbps PCMCIA: 1.5:0.75:0.01Lucent 15dBm 2.4GHz 2Mbps WaveLAN PCMCIA: 1.85:1.80:0.18

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PAMAS: Overview(1)

Power off nodes that are not transmitting or receiving

A B C

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RTS

PAMAS: Overview(2)

A combination of MACA and using a separate signaling channel

A B C DRTS

CTS

Collision! C does nothing.

RTS

Collision at B!

CTS

MACA: Hidden terminal problem

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PAMAS: Signaling Channel

RTS-CTS exchange

Query transmitters about the length of remaining transmission

Collision in signaling channel: Binary Exponential Backoff

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PAMAS: Powering off radios(1)

When No pkt to transmit and a neighbor begins

to transmit At least one neighbor is transmitting and

another is receiving (even if queue is not empty)

A B C D

E F

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PAMAS: Powering off radios(2) How long:

New transmissions: duration in RTS/CTS Ongoing transmissions: upon waking up,

No data pkt to send: Can receive when no neighbors are transmitting send t_probe(l) to query the remaining transmission

time Having data to send:

Can send when no neighbors are receiving Can receive when no neighbors are transmitting Send RTS, (when collision) r_probe and t_probe

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PAMAS: t_probe and t_probe_responsebinary search for the longest transmission time

Node A wakes upl1

Duration of B’s Transmission

Duration of C’s Transmission

l2l3

Duration of D’s Transmission

t

•A sends t_probe(l) over the signaling channel•C,D sends t_probe_response(t) over the signaling channel

ll/2

•Collision: A sends t_probe(l/2) over the signaling channel•D sends t_probe_response(l2) back•No collision: A sets timer to sleep for l2 seconds

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PAMAS: When a node wants to send a pkt after it wakes up

C sends RTS to notify it will send data

RTSRTS

A DB C

F

E

RTS

B sends busy tone (including duration r) to C If collision with other busy tone, CTS or RTS:

Send r_probe(l) to probe receivers using the same binary search algorithm (r).

Send t_probe(l) to probe transmitters (t). Set timer to sleep min(r, t) seconds.

CTSCTS

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PAMAS: Power Conserving Performance(1)

Power Savings increase when network connectivity increases and when traffic load decreases

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PAMAS: Power Conserving Performance(2)Power saved in complete networks

Power consumption is reduced by 50%. At low loads, there are less control packet contentions, so the saving is even higher.

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PAMAS: Power Conserving Performance(3)Power saved in line networks

Power consumption is reduced by 7%-20%. This is because fewer nodes are in a position to overhear unintended transmissions.

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PAMAS: No delay or throughput Penalty

Compared to S-MAC: S-MAC: All neighbors of sender and receiver are

powered off PAMAS use a separate channel for control pkts

A DB C

F

E

A can’t send pkt

D can’t receive pkt

A can send pkt

D can receive pkt

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Transition: Why do we need power-aware routing protocols?

PAMAS can save energy by shutting down radios, but it has no idea about the entire pkt transmission path.

If the routing protocol chooses a high power-consuming route, the savings by PAMAS might be sacrificed by this routing ineffienciency in energy.

Conclusion: we need both.

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Metrics used in other (power-unaware) routing protocols

Shortest-hop, Shortest-delay Overusing a small set of “popular” nodes

These nodes die faster than others Possible voids or partitioned network

A B

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Metrics used in other (power-unaware) routing protocols (cont.) Message and Time overhead

Using hierarchy to reduce Routing Table Maintenance

Overusing the “back-bone” nodes Others: Link quality, location stability

Back-bone nodeOr Cluster Head

ordinary node

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Metrics for Power-aware Routing(1)Minimize Energy Consumed/Pkt

Energy consumed for packet j is:

n1, …, nk is the path that pkt j goes through.

T (ni , ni+1) denote the energy consumed in transmitting and receiving one pkt over one hop from ni to ni+1.

1

11, )(

k

iiij nnTe

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Metrics for Power-aware Routing(1’)Minimize Energy Consumed/Pkt

Advantages: Light Loaded: Same as shortest-hop routing

Heavy Loaded: Route around congestion

A B

Shortest-hop routing

Minimized Energy Consumed/pkt routing

1

11, )(

k

iiij nnTe

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Metrics for Power-aware Routing(1’’)Minimize Energy Consumed/Pkt

Disadvantage: Widely differing energy consumption in

different nodes – some nodes die faster

A B

Shortest-hop routing

Minimized Energy Consumed/pkt routing

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Metrics for Power-aware Routing(2)Maximize Time to Network Partition

There is a minimum set of nodes the removal of which will cause the network to partition

Routing load should be balanced among these nodes to maximize the network life

Critical node

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Metrics for Power-aware Routing(2’)Maximize Time to Network Partition

Challenge: Load balancing is very difficult Partitions route packets independently;

global balancing is difficult to achieve. Unknown packet length and future

arrivals

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Metrics for Power-aware Routing(3)Minimize variance in node power levels

Reasons Load sharing: keep unfinished work the same in

every node Fairness among nodes

Approach NP-hard Join the Shortest Queue (JSQ)

A B

C

D

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Metrics for Power-aware Routing(4)Minimize Cost/Packet

The cost of sending a pkt j from n1 to nk is:

xi represents the total energy expended by node i so far.

fi (xi) denotes the node cost or weight of node i. (reluctance to forward pkts)

)(1

1i

k

iij xfc

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Metrics for Power-aware Routing(4’)Minimize Cost/Packet

3.6V: 80%capacity has been consumed

2.8V: all capacity has been consumed

fi can be tailored to reflect a battery’s remaining lifetime

Zi is the measured voltage.

8.21

)(:.

i

ii zzfge

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Metrics for Power-aware Routing(4’’)Minimize Cost/Packet (Example)

A B

Shortest-hop routing

Minimized Energy Consumed/pkt routing

Minimized cost/pkt routing

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Metrics for Power-aware Routing(4’’’)Minimize Cost/Packet

Some benefits Incorporate battery characteristics into

routing Increase time to network partition and

reduce variation in node costs Contention increases node cost, so this

metric incorporates congestion effect .

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Metrics for Power-aware Routing(5)Minimize Maximum Node Cost

Advantages: Node failure is delayed. Variance in node power levels is reduced.

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Minimize Energy consumed/pkt Associate edge weight (T (ni , ni+1)) to

each edge Minimize Cost/pkt

Associate node weights (fi) with each node

Combined with shortest-hop routing

Implementation of Power-aware Routing

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Power Conserving Behavior(1)cost/pkt (Quadratic Battery Cost)

Savings are greater in highly connected networks and increase with load.

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Power Conserving Behavior(2)max cost/pkt (Quadratic Battery Cost)

Savings are greater in highly connected networks and increase with load.

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Delay and throughput Performance

No difference compared with shortest-hop routing

Avoid routing through congestion area

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Summary PAMAS uses a separate channel to

exchange control pkts to address the hidden terminal problem. When a node can’t either send or receive pkt, it shuts down its radio. Two communication channels Binary Search Algorithm

Power-aware metrics for routing protocols can achieve power saving without sacrificing performance.