1. Distance ADaptive (DAD) Broadcasting for Ad Hoc Networks

2. Copyright: S. Krishnamurthy, UCR The Paper X. Chen, M. Faloutsos & S.V. Krishnamurthy, “Distance Adaptive Broadcasting for Ad Hoc Networks”, in IEEE MILCOM 2002.

3. Copyright: S. Krishnamurthy, UCR Objective To find a good way to perform effective broadcasting in an ad hoc network such that: Fewer number of rebroadcasts are needed. Achieve a higher coverage Achieve power efficiency Result in a fewer number of collisions

4. Copyright: S. Krishnamurthy, UCR Our Approach Only outmost nodes rebroadcast Outmost nodes are more likely to reach new nodes We achieve a reduction in contention Each node identifies the outmost nodes within its range based on some neighborhood information that is exchanged.

5. Copyright: S. Krishnamurthy, UCR Roadmap Description of problem Metrics of Interest Previous work Our approach Results and Discussion Future work

6. Copyright: S. Krishnamurthy, UCR Broadcasting in Ad hoc network Definition A session in which information is to reach all nodes. Multiple rebroadcasts (local) would be needed Objective Perform broadcasting in an efficient way so as to use fewer rebroadcasts while maintaining the requisite coverage

7. Copyright: S. Krishnamurthy, UCR Metrics and parameters Metrics Coverage – fraction of nodes reached Broadcast Efficiency Broadcast Latency or Duration Parameters Mobility -- speed Node density

8. Copyright: S. Krishnamurthy, UCR Previous work Flooding Expanding Ring Search – application specific. S.Y.Ni, Broadcasting storm problem Probabilistic Scheme wherein a node re-broadcasts a received packet with a certain probability.

9. Copyright: S. Krishnamurthy, UCR General probabilistic broadcast (GEN) Parameter k as the target rebroadcast size When node receives a packet, it randomly generates a number n that is between 0 and its neighborhood size If n < k, it will rebroadcast, otherwise it discards the packet. The protocol attempts to have ‘k’ new rebroadcasts for every broadcast.

10. Copyright: S. Krishnamurthy, UCR Broadcasting and outmost nodes Not every node is needed to rebroadcast It’s more efficient to let the outmost nodes rebroadcast Outmost nodes span the desired area more quickly E.g. outmost nodes 4,5,6,7,8 rebroadcast, it is not necessary for nodes 1,2,3 to rebroadcast.

11. Copyright: S. Krishnamurthy, UCR Our approach Using power level to decide outmost nodes Distance ADaptive: based on local information, a node decides certain number of outmost nodes that are to rebroadcast. Two variants  DAD-NUM, DAD-PER

12. Copyright: S. Krishnamurthy, UCR DAD-NUM Fixed number of outmost nodes performing rebroadcast Node keeps a neighbor table to records the received power level from each neighbor. This table is sorted to decide the threshold power level that identifies the outmost nodes Include this threshold in the broadcast packet When the packet is received, the receiver compares the threshold in the packet and the received power strength to decide whether it should rebroadcast

13. Copyright: S. Krishnamurthy, UCR DAD-NUM State diagram Init_state Pkt_recv. Set timerPkt_Gen Finished Received a packet Time out If receiving power is less than threshold power in packet, ignore packet. Time out Find threshold power and put it in packet, broadcast packet.

14. Copyright: S. Krishnamurthy, UCR DAD-PER Only difference from DAD-NUM: A fixed percentage of total neighboring nodes performing rebroadcast Not good for topologies wherein node density is small or variant.

15. Copyright: S. Krishnamurthy, UCR Simulation results System Setup Glomosim 2.0 802.11 MAC CSMA/CA Hello Message: every 5 seconds Network topology in 3000m x 3000m Transmission radius 223m Result is average on 200 random topologies

16. Copyright: S. Krishnamurthy, UCR Broadcast efficiency DAD-NUM has the highest efficiency DAD-PER is better than GEN when the rebroadcast size is small.

17. Copyright: S. Krishnamurthy, UCR Coverage Bars represent the improvement in coverage of DAD- NUM over GEN. DAD-NUM can achieve up to a 20% increase in coverage.

18. Copyright: S. Krishnamurthy, UCR Efficiency v.s. Coverage DAD-NUM can achieve a better Coverage than GEN while attaining a higher broadcast efficiency.

19. Copyright: S. Krishnamurthy, UCR Latency DAD-NUM takes a short time to complete the broadcast session than GEN Improvement can be up to 21%

20. Copyright: S. Krishnamurthy, UCR Conclusion and future work Conclusion DAD is better than GEN with regards to: Coverage Efficiency Latency Future work Apply DAD to in power-heterogeneous ad hoc networks.

21. Copyright: S. Krishnamurthy, UCR Distributed Power Control in Ad Hoc Networks

22. Copyright: S. Krishnamurthy, UCR The Paper S.Agarwal, S.V.Krishnamurthy, R.H.Katz and S.Dao, “Distributed Power Control in Ad-hoc Wireless Networks”, IEEE PIMRC 2001.

23. Copyright: S. Krishnamurthy, UCR The IEEE 802.11 MAC AB C RTS CTS D RTS – CTS – DATA – ACK Solves the hidden and exposed terminal problem in most cases. E

24. Copyright: S. Krishnamurthy, UCR Why is Power Control Hard? No centralized controller as in cellular networks. Distributed decisions on what power to use.

25. Copyright: S. Krishnamurthy, UCR Benefits Energy Conservation Frequency Re-use – more number of simultaneous transmissions possible – translates into an increase in the network capacity.

26. Copyright: S. Krishnamurthy, UCR Transmission Range Models Typically models assume a circular range – 250 meters is the transmission range – within this range, data can be decoded. Interference range – larger than the transmission range – data cannot be decoded – only the interference can be sensed.

27. Copyright: S. Krishnamurthy, UCR Clustering Elect clusterheads for a group of nodes. The clusterhead is responsible for the transmit power for each node within its cluster. Imposing a cellular infrastructure onto an ad hoc framework. Refer to paper for reference.

28. Copyright: S. Krishnamurthy, UCR Power Control Extensions to the IEEE 802.11 MAC Ten Quantized Power Levels The levels vary linearly  the difference between levels is about a tenth of the maximum power level. Implement a power control loop between a communicating pair.

29. Copyright: S. Krishnamurthy, UCR Modifications to control messages RTS/CTS messages modified to include a new field. When a node receives the RTS message it measures received signal strength (There is usually what is called a Received Signal Strength Indicator or RSSI in hardware). The receiver indicates the ratio of the received strength to the minimum acceptable strength in the CTS header.

30. Copyright: S. Krishnamurthy, UCR The Power Loop Closed The transmitter (the originator of data) then does a similar computation with the received CTS message. It then includes a similar ratio in the header of the DATA message. So both the transmitter and the receiver are now aware of the power situation on the link – how well are we doing!

31. Copyright: S. Krishnamurthy, UCR Basic Idea Increase power if the power requirements are not satisfied – packet loss. Decrease power if power requirements are satisfied Maintain table for each neighbor – to know the power level to be used in order to communicate with that neighbor.

32. Copyright: S. Krishnamurthy, UCR Nuances A single power measurement will not suffice. One would need to dampen fluctuations. Once a power level is chosen, ten transmissions at that level (a heuristic parameter). The power control loop is only used for unicast transmissions – routing updates etc. that are broadcast do not use this. For further details – read paper.

33. Copyright: S. Krishnamurthy, UCR Sample Simulation Results Simulations were done in ns 2.0 Various mobility models were considered. TCP Throughput (actually goodput – does not take into account duplicates) is the metric of interest.

34. Copyright: S. Krishnamurthy, UCR Parameters

35. Copyright: S. Krishnamurthy, UCR Sample Simulation Results Througput improvement is due to an increase in capacity – higher frequency re-use.

36. Copyright: S. Krishnamurthy, UCR Sample Simulation Results (Cont). Decrease in overall energy consumption (on average).

37. Copyright: S. Krishnamurthy, UCR Why can performance be worse ? Node 3 is receiving Data from Node 4 Node 2 does not know about the data transfer The high power CTS collides with the Data at Node 3 Node 1 establishes a high power link 1 2 RTS CTS 3 Data4

38. Copyright: S. Krishnamurthy, UCR Power Control leads to Asymmetry There is an inherent asymmetry resulting from power control. Simply changing power levels can lead to unfairness – and collisions and can in some scenarios degrade performance.

39. Copyright: S. Krishnamurthy, UCR Problems at the routing layer Traditional routing protocols may no longer be used. Uni-directional links are formed. How can they be used ? Neighbor discovery a challenge.

40. Copyright: S. Krishnamurthy, UCR Interesting topics for projects Few papers try to do power control Paper by Monks in INFOCOM 2001 Paper by Jung and Vaidya – Mobicom 2002. However, no capacity increase, use highest power for transmission of control signals. We will see these in next class. Open area – tough problems – but opportunities.