PowerAware Routing in Mobile Ad Hoc Networks

1
Power-Aware Routing in Mobile Ad Hoc Networks

• S. Singh, M. Woo and C. S. Raghavendra
• Presented by Shuoqi Li
• Oct. 24, 2002

2
Two foci

• A power-aware MAC protocol PAMAS
• Basic radio modes
• PAMAS Approach
• Performance
• Metrics for power-aware routing
• Motivation
• New Metrics
• Validation

3
Three radio modes

• Transmitting

• Receiving

C
A
B

• Standby with power off.

• e.g
• Proxim RangeLAN2 2.4GHz 1.6Mbps PCMCIA
  1.50.750.01
• Lucent 15dBm 2.4GHz 2Mbps WaveLAN PCMCIA
  1.851.800.18

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PAMAS Overview(1)

• Power off nodes that are not transmitting or
  receiving

A
B
C
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PAMAS Overview(2)

• A combination of MACA and using a separate
  signaling channel

MACA Hidden terminal problem
Collision! C does nothing.
Collision at B!
B
C
D
RTS
A
RTS
RTS
CTS
CTS
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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)

E
F
A
B
C
D
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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
Duration of Ds Transmission
Duration of Cs Transmission
Duration of Bs Transmission
t
l2
l
l1
l3
l/2
Node A wakes up

• A sends t_probe(l) over the signaling channel

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

• 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
F
RTS
RTS
RTS
CTS
A
D
B
C
E
CTS

• C sends RTS to notify it will send data

• 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.

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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

F
D cant receive pkt
D can receive pkt
A cant send pkt
A can send pkt
A
D
B
C
E
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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 node Or 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 , ni1) denote the energy consumed in
  transmitting and receiving one pkt over one hop
  from ni to ni1.

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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
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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)

C
A
B
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)

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

• fi can be tailored to reflect a batterys
  remaining lifetime
• Zi is the measured voltage.

3.6V 80capacity has been consumed
2.8V all capacity has been consumed
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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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Implementation of Power-aware Routing

• Minimize Energy consumed/pkt
• Associate edge weight (T (ni , ni1)) to each
  edge
• Minimize Cost/pkt
• Associate node weights (fi) with each node
• Combined with shortest-hop 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 cant 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.