Power-Aware 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: 1.5:0.75:0.01 • Lucent 15dBm 2.4GHz 2Mbps WaveLAN PCMCIA: 1.85:1.80:0.18

4. PAMAS: Overview(1) • Power off nodes that are not transmitting or receiving A B C

5. 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 A RTS RTS RTS CTS CTS

6. PAMAS: Signaling Channel • RTS-CTS exchange • Query transmitters about the length of remaining transmission • Collision in signaling channel: Binary Exponential Backoff

7. 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

8. 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

9. PAMAS: t_probe and t_probe_responsebinary search for the longest transmission time Duration of D’s Transmission Duration of C’s Transmission Duration of B’s 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

10. PAMAS: When a node wants to send a pkt after it wakes up • C sends RTS to notify it will send data F RTS RTS RTS CTS A B C CTS D E • 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.

11. PAMAS: Power Conserving Performance(1) Power Savings increase when network connectivity increases and when traffic load decreases

12. 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.

13. 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.

14. 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 can receive pkt D can’t receive pkt A can’t send pkt A can send pkt A B C D E

15. 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.

16. 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

17. 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

18. 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.

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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)

25. Metrics for Power-aware Routing(4’)Minimize Cost/Packet • fi can be tailored to reflect a battery’s remaining lifetime Zi is the measured voltage. 3.6V: 80%capacity has been consumed 2.8V: all capacity has been consumed

26. Metrics for Power-aware Routing(4’’)Minimize Cost/Packet (Example) A B Shortest-hop routing Minimized Energy Consumed/pkt routing Minimized cost/pkt routing

27. 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 .

28. Metrics for Power-aware Routing(5)Minimize Maximum Node Cost • Advantages: • Node failure is delayed. • Variance in node power levels is reduced.

29. Implementation of Power-aware Routing • 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

30. Power Conserving Behavior(1)cost/pkt (Quadratic Battery Cost) Savings are greater in highly connected networks and increase with load.

31. Power Conserving Behavior(2)max cost/pkt (Quadratic Battery Cost) Savings are greater in highly connected networks and increase with load.

32. Delay and throughput Performance • No difference compared with shortest-hop routing • Avoid routing through congestion area

33. 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.