1. On Mitigating the Broadcast Storm Problem with Directional Antennas Sheng-Shih Wang July 14, 2003 Chunyu Hu, Yifei Hong, and Jennifer Hou Dept. of Electrical and Computer Engineering, Dept. of Computer Science University of Illinois at Urbana-Champaign IEEE International Conference on Communications (ICC’03), vol. 1, pp. 104-110, 2003

2. July 14, 2003 Sheng-Shih Wang 2 Outline  Introduction  Directional Broadcast Scheme  Performance Evaluation  Conclusions

3. July 14, 2003 Sheng-Shih Wang 3 Introduction --- Motivation & Objective & Solution  Motivation Broadcast storm problem Too much redundant traffic Frequent contention Transmission collision  Objective Mitigates the Broadcast storm problem  Solution Directional antennas

4. July 14, 2003 Sheng-Shih Wang 4 Introduction --- Directional Broadcast Scheme  Advantage Increase the network capacity with spatial reuse Reduce the interference and contention Increase the number of on-going connections  Drawback Hardware cost

5. July 14, 2003 Sheng-Shih Wang 5 Introduction --- Network Model  For each node One transceiver 4 switched-beam directional antennas  For each directional antenna Span 90 degrees 4 antennas cover all the direction Two operating modes: active and passive Only active antennas are used to transmit or receive

6. July 14, 2003 Sheng-Shih Wang 6 Introduction --- Network Model (cont.)  Assumption The transmission range of both omni-directional and directional antennas are the same MAC layer control of each antenna’s mode learn the angle-of-arrival (AOA) and the strength of incoming signal power All nodes use the same directional antenna patterns

7. July 14, 2003 Sheng-Shih Wang 7 Introduction --- Omni-directional Broadcast Scheme  Idea On receipt of a broadcast packet, a node will forward it to all its neighbors after the random delay timer expire  Advantage Maximize the number of nodes that broadcast packets can reach  Drawback A significant amount of redundant traffic Serious interference/contention Collision

8. July 14, 2003 Sheng-Shih Wang 8 Directional Broadcast Scheme --- On/Off Directional Broadcast Scheme  Idea Only forwards the packet in the directions other than the incoming AOA  Antenna mode setting Passive The incoming antenna AOA The antenna AOA that the same packet is received before the delay time expires Active After the delay timer expires and the channel is sensed idle, only antennas that have not received the packet will be set to active and forward the packet

9. July 14, 2003 Sheng-Shih Wang 9 Directional Broadcast Scheme --- On/Off Directional Broadcast Scheme (cont.)

10. July 14, 2003 Sheng-Shih Wang 10 Directional Broadcast Scheme --- Relay-Node- Based Directional Broadcast Scheme  Idea For each direction, only one relay node to forward broadcast packets The relay node in a direction is the one-hop farthest node

11. July 14, 2003 Sheng-Shih Wang 11 Directional Broadcast Scheme --- Relay-Node- Based Directional Broadcast Scheme (cont.)

12. July 14, 2003 Sheng-Shih Wang 12 Directional Broadcast Scheme --- Location- Based Directional Broadcast Scheme  Idea The relay node should cover the largest extra area that the broadcast packet has not received The delay is not uniform for all the directions Larger extra area  smaller delay The delay for each direction is proportional to the extra coverage ratio The extra coverage ratio is the extra coverage over ¼ of the circle area

13. July 14, 2003 Sheng-Shih Wang 13 Directional Broadcast Scheme --- Location- Based Directional Broadcast Scheme (cont.)

14. July 14, 2003 Sheng-Shih Wang 14 Directional Broadcast Scheme --- Location- Based Directional Broadcast Scheme (cont.) Circle O(0,0): x 2 + y 2 = R 2 Circle S(a,b): (x - a) 2 + (y - b) 2 = R 2

15. July 14, 2003 Sheng-Shih Wang 15 Performance Evaluation --- Simulation Environment  Simulator: QualNet  100 nodes are uniformly distributed in an area of 1500m  1500m  Transmission range: 250m  Transmission rate: 2 Mbps  Simulation time: 300 sec  Packet size: 118/118/134/122 bytes

16. July 14, 2003 Sheng-Shih Wang 16 Performance Evaluation --- Performance Metrics  Coverage (# of nodes) The number of nodes that receive a broadcast packet  Latency (msec) The time span from the instant a broadcast packet is sent till the instant all the nodes receive the packet  Redundancy (# of pkts / node) The total number of duplicate packets received by nodes in a simulation run  Collisions (per node) The number of packets erroneously received because of collision

17. July 14, 2003 Sheng-Shih Wang 17 Performance Evaluation --- Simulation Result in Static Wireless Networks AverageCoverage (# of nodes) Latency (msec) Redundancy (# of pkts/node) Collision (per node) Scheme 075.514.32312.499.2 Scheme 187.714.38200.553.6 Scheme 279.811.0463.978.2 Scheme 388.924.07196.263 1)All three directional schemes outperform the omni-directional scheme 2)Scheme 1  collision Scheme 2  latency and redundancy Scheme 3  coverage 3)Scheme 3 incurs the large latency  one antenna, more carrier sense

18. July 14, 2003 Sheng-Shih Wang 18 Performance Evaluation --- Simulation Result for Mobility The neighbor information is less reliable (relay-node-based scheme)

19. July 14, 2003 Sheng-Shih Wang 19 Conclusions  Proposed solutions On/Off Directional Broadcast Scheme collision Relay-Node-Based Directional Broadcast Scheme Latency, redundancy Location-Based Directional Broadcast Scheme coverage  Future work Power management (sleep and awake periodically)