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  Transmitting Three radio modes  Receiving  Standby with power off. AB C 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 ABC

5 RTS PAMAS: Overview(2)  A combination of MACA and using a separate signaling channel A BCD RTS CTS Collision! C does nothing. RTS Collision at B! CTS MACA: Hidden terminal problem

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) ABCD EF

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_response binary search for the longest transmission time Node A wakes up l1l1 Duration of B’s Transmission Duration of C’s Transmission l2l2 l3l3 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 l l/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

10 PAMAS: When a node wants to send a pkt after it wakes up  C sends RTS to notify it will send data RTS ADBC F 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. CTS

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 ADBC F E A can’t send pkt D can’t receive pkt A can send pkt D can receive pkt

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 AB

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: n 1, …, n k is the path that pkt j goes through. T (n i, n i+1 ) denote the energy consumed in transmitting and receiving one pkt over one hop from n i to n i+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 AB 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 AB 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) A B C D

24 Metrics for Power-aware Routing (4)Minimize Cost/Packet  The cost of sending a pkt j from n 1 to n k is : x i represents the total energy expended by node i so far. f i (x i ) denotes the node cost or weight of node i. (reluctance to forward pkts)

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

26 Metrics for Power-aware Routing (4’’)Minimize Cost/Packet (Example) AB 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  Minimize Energy consumed/pkt Associate edge weight (T (n i, n i+1 )) to each edge  Minimize Cost/pkt Associate node weights (f i ) with each node  Combined with shortest-hop routing Implementation of Power-aware 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.