1. Designing Multi-hop Wireless Backhaul Networks with Delay Guarantees Girija Narlikar, Gordon Wilfong, and Lisa Zhang Bell Lab. Infocom 2006

2. Outline Introduction A generalized link activation framework Routing Scheduling policy Simulation result Conclusion

3. Introduction Multi-hop wireless architecture for backhaul  Multi-hopping can help boost throughput reduce interference  More carefully schedule to reduce interference  Maintain low delays VoIP, video, and interactive applications

4. Introduction Simple generalized link activation framework  Even-Odd framework  Schedule packets over this wireless backhaul network Efficient backhaul routes  Maximize the throughput Interfering links are not simultaneously active

5. A generalized link activation framework Network model  WiMax 802.16 d NLOS technology TDMA  Subchannelization Multiple orthogonal subchannels

6. A generalized link activation framework Two types of interference  Self-interference  Cross-link interference 2 2 32

7. A generalized link activation framework Given the set of routes  Link activation scheme Specify the set of directional links that are active at each timeslot along with the set of subchannels they use  Scheduling policy Determine the set of packets to be transmitted along an active link(s) at each time slot

8. Even-odd Link activation

9. Assign in routing phase

10. Admissible Traffic and Subchannel Assignment Node constraints Link constraint fraction of the subchannels that are allocated to link e total bit rate along link e

11. Admissible Traffic and Subchannel Assignment If node and link constrains has a feasible solution, feasible w(e) Bipartite graph

12. Tackling Interference Self-interference  Simultaneously transmitting and receiving  Even-odd scheme Simultaneously receptions to a single node  Subchannelization

13. Routing ILP  If all demands are scaled by an factor , a feasible routing exists Heuristics routing protocols

14. Routing-ILP

15. x i (e)=1 connection i gets routed on e x(e)=1:e selected by at least one connection 0:even node 1:odd node 0 0 1 each connection remains on a single path

16. Routing-ILP For link 0 0 For link 1 1

17. Routing-Heuristics routing protocols Dijkstra’s algorithm  Distance =1/c(e)  Add the edge which will not interfere with other edge in T’

18. Routing-Heuristics routing protocols  2.algorithm MinMax(minimize the maximum node load)+SP Order the nodes by increasing length of their path to Root 4,0 5,0 3,0 6,0 7,0 8,0 2 3,1 2,1 o e

19. Routing-Heuristics routing protocols  3.algorithm MinMax Similar to previous one Some connections have been routed  Induce the node loads

20. Scheduling policy Assume  No zero propagation delay Scheduling policy determine the order in which packets leave each buffer  Apply any wireline scheduling policy to the even-odd framework  Imaginary wireline network N I

21. No propagation delay Odd link: delay  Even link: no delay

22. Scheduling policy S is well defined for our real system by verifying the following.  Each packet departs from a buffer only when the link is active.  Each packet starts to depart from a buffer after the complete packet has arrived.  Each link services one packet at a time.  No packet misses its departure time.

23. Scheduling policy and Delay analysis Packet arrives at its source  N  N I Packet starts to leave the buffer  N  N I

24. Simulation result Physical layer  Fixed wireless pathloss model in 802.16  Links between AP experience shadow fading   =1 ms  Packet size= 1Kb

25. Routing 15 APs in 5km*5km 5Mbps

26. Subchannelization Penalty

27. End to End Delay

28. Delay v.s. bursk size

29. Conclusion Even-Odd link activation framework  Allows bounded-delay schedulers to be efficiently mapped to our multihop wireless network. WFQ and CEDF