1. Performance Evaluation and Improvement of an Ad Hoc Wireless Network Takayuki Yamamoto Graduate School of Engineering Science, Osaka University, Japan tak-ymmt@ics.es.osaka-u.ac.jp

2. 31 Jan 2002ICOIN-162 Contents Introduction of Target System - the Flexible Radio Network - Basic Network Performance for Some Different System Parameter Values Suggestions for Performance Improvement Conclusion

3. 31 Jan 2002ICOIN-163 Flexible Radio Network Wireless Ad Hoc Network System developed by Fuji Electric Co. Ltd. Multi-hop Network organized by Stationary Terminals Application Examples Power Consumption Collection in Manufacturing Plants Sales Account Collection from Vending Machines Usage Data Collection from Ski Lift Gates http://www.fujielectric.co.jp/eng/index.html

4. 31 Jan 2002ICOIN-164 System Description Network Configuration Table updated by Periodic Table Exchange Each Node maintains Multiple Routes to All Nodes in the Same Network Route Entry = (Neighbor ID, Hop Count) A E B D C ‥ (B,3)(C,4) 2 ：：： ‥ (C,2)(B,1) 1 ‥ EB Destination Node ID Route entries Network Configuration Table at node A

5. 31 Jan 2002ICOIN-165 Protocol Description Time Division, Slot-based Transmission Packet Maximum Lifetime set in a Source Node decreased by one per slot even when it stays in a buffer Hop-by-Hop Receipt Acknowledgement based on Relay Echo Mechanism Slot 0 1 2 3 4 5 Node A Node B send forward (relay) relay echo Node A eavesdrops node B’s forward transmission. When node A’s first transmission successes, node A can hear the relay echo and delete the packet in its buffer.

6. 31 Jan 2002ICOIN-166 Protocol Description Retransmission Control Slot 0 1 2 3 4 Node A Node B transmission failure × retransmission to node B or another node If no relay echo can be received, node A retransmits the packet.

7. 31 Jan 2002ICOIN-167 Protocol Description ACK from Destination Slot 0 1 2 3 4 Node A Node B Destination Node returns an ACK packet by way of relay echo to B ACK

8. 31 Jan 2002ICOIN-168 Simulation Description for Original System Evaluation Network Simulator - ns-2 with our implementation of FRN Maximum Lifetime = 12, 64 and 128 (slots) Data Collection Network Model

9. 31 Jan 2002ICOIN-169 Original System Evaluation Throughput = Number of Packets received by the Destination per slot Packet Loss Rate = Ratio of unreached Packets to the Destination Load = Average Number of Packets produced per slot L(h) = Maximum Lifetime ( h is described later) Throughput Packet Loss Rate Long Lifetime Packet causes Congestion Short Lifetime Packet causes High Loss Rate for Low Load Environment

10. 31 Jan 2002ICOIN-1610 Performance Improvement Adaptive Maximum Lifetime Source Node calculates the Maximum Lifetime for Each Packet according to the shortest Hop Count to its Destination Methods to Prevent Packet Collision leads to Packet Duplication Random Wait for Retransmission Packet Rejection earlier than its Lifetime expires

11. 31 Jan 2002ICOIN-1611 Adaptive Maximum Lifetime A E B D C F G Example Function: L(h) = 6h+12 ( h is Hop Count of the shortest route) L(h)=18 L(h)=24 L(h)=30

12. 31 Jan 2002ICOIN-1612 Adaptive Maximum Lifetime Low Loss Rate for Low Network Load Long-living Packet can be rejected effectively

13. 31 Jan 2002ICOIN-1613 Packet Duplication Problem Packet Transmission Failure Relay Echo Receipt Failure Packet Retransmission Unique Packet in the Network Packet Duplication Additional Network Load and Performance Degradation

14. 31 Jan 2002ICOIN-1614 Random Wait for Retransmission Reduction of Packet Duplication Repeat Slot 0 1 2 3 4 5 Node X Node A Node B send forward collisio n × echo loss send × echo resend forward × echo loss resend × collisio n echo Packet Collision repeats due to Fixed Wait Duration Case 1: Fixed Wait Duration (3 slots)

15. 31 Jan 2002ICOIN-1615 Random Wait for Retransmission Reduction of Packet Duplication Repeat Slot 0 1 2 3 4 5 Node X Node A Node B send forward collisio n × echo loss send × echo resend forward echo resend echo Probability of repeated echo loss can be reduced by random delay time Case 2: Random Wait Duration

16. 31 Jan 2002ICOIN-1616 Random Wait for Retransmission This Method is effective under Large Maximum Lifetime Setting

17. 31 Jan 2002ICOIN-1617 Early Packet Rejection Packet Rejection earlier than its Lifetime reaches Zero Unreachable Packets cause Useless Collisions (X, D, 2) (source, destination, lifetime) Packet ： (X, D, 1)(X, D, 0) Detect and Reject the unreachable Packet whose Lifetime is shorter than the Shortest Hop Count to its Destination D

18. 31 Jan 2002ICOIN-1618 Early Packet Rejection This Method is effective under Small Maximum Lifetime Setting

19. 31 Jan 2002ICOIN-1619 PLR for All Methods Together

20. 31 Jan 2002ICOIN-1620 Conclusion and Future Work Flexible Radio Network (FRN) system Relay Echo Mechanism, Multiple Route Maintenance for Reliability Maximum Lifetime Calculation with Route Length is capable of increasing Network Reliability Packet Duplication caused by Relay Echo and Retransmission Mechanism Relationship between Maximum Lifetime Setting and Effect of Random Wait Duration, Early Packet Rejection Much Better Performance is achieved by applying All Methods Together Future Works Evaluation for End-to-End Protocol on FRN Implementation into actual FRN Terminals