1. A Cross-Layer Architecture to Exploit Multi-Channel Diversity with a Single Transceiver Jay A. Patel, Haiyun Luo, and Indranil Gupta INFOCOM 2007

2. Outline Introduction Scheduling Routing Experiments Conclusion

3. Introduction Multi-channel multi-hop wireless networks Need to synchronize Existing designs are confined to the MAC layer Rendezvous control channel Optimistic synchronization

4. Wireless mesh networks have a scalability problem Contention: single channel Intra-flow interference Inter-flow interference Worsens near gateway(s) Gateway node Introduction

5. Can a single transceiver exploit multi-channel? Neighbors must converge to exchange data While exploiting multiple channels Locally opportunistic channel hopping Multi-channel MAC Seeded Slotted Channel Hopping Limitations Leads to node synchronization problem Introduction

6. Dominion: A cross-layer architecture Spans both the MAC and the network layers Simple MAC + Intelligent routing Deterministic channel hopping MAC protocol Eliminate locally opportunistic behaviour Core logic resides at the routing layer Graph-theoretic model: extensible and flexible Multi-path routing Introduction - Goal

7. Scheduling Subnetwork designation Randomly One-way uniform hashing function EX:SHA1(MacAddress(A)) Spatial reuse Globally optimal assignment Locally based on two-hop neighborhood

8. Frequency Division + CSMA Approach Logical subnetworks: A subnetwork per channel Node n i homed at channel SHA1 (n i ) mod k Creates network and subnetwork partitions f1f1 f2f2 f3f3 Scheduling

9. Key: Periodically converge subnetworks A static and deterministic channel hopping schedule Based on modulo arithmetic Can be generated simply with the parameter k Scheduling

10. Subnetwork A, B, C, D 和 E 是這個 state 中的 32 位元 文字； F 是會變化的非線性函數； <<<n 代表 bit 向左循環移動 n 個位置。 n 因操作 而異。

11. Scheduling For K channels and K subnetworks (K is prime)

12. Scheduling 00000 01234 30241 42031 32104 t 0 t 1 t 2 t 3 t 4 S0S1S2S3S4S0S1S2S3S4

13. Scheduling 00000 01234 30241 42031 32104 t 0 t 1 t 2 t 3 t 4 S0S1S2S3S4S0S1S2S3S4

14. Scheduling 00000 01234 30241 42031 32104 t 0 t 1 t 2 t 3 t 4 S0S1S2S3S4S0S1S2S3S4

15. Scheduling 00000 01234 30241 42031 32104 t 0 t 1 t 2 t 3 t 4 S0S1S2S3S4S0S1S2S3S4 S5S5 Only (K+1)/2 channels are used

16. s2s2 s3s3 s4s4 s5s5 s0s0 s5s5 s2s2 s3s3 s4s4 s4s4 s0s0 s1s1 s5s5 s3s3 s5s5 s4s4 s0s0 s1s1 s2s2 s2s2 s3s3 s5s5 s0s0 s1s1 s3s3 s1s1 s4s4 s2s2 s0s0 s0s0 s1s1 s2s2 s3s3 s4s4 s5s5 t0t0 t1t1 t2t2 t3t3 t4t4 k = 3 f2f2 f3f3 f1f1 Number of subnetworks: 2k Schedule cycle: T= NextPrime(2k - 1) Exactly 2 subnets converge on a channel Every subnet converges every other subnet s1s1 Scheduling

17. DominionIEEE 802.11 Scheduling

18. Routing Utilizing a general purpose routing strategy may yield undesirably high latencies or suboptimal throughput Present an abstract graph model of the physical topology

19. Best route for A -> B? Two routes: AB (direct) and AC -> CB (indirect) Which is the better route? Throughput-wise: AB With multi-path routing A [s 2 ] B [s 3 ] C [s 0 ] t4t4 t2t2 t1t1 Routing

20. Abstraction: Graph-Theoretic Model Convert link state to an abstract model Edge weight assignment ETX ( expected transmissions per packet) Locate shortest route using Dijkstra ’ s Multi-path routing Prune all connectivity edges in route Repeat: until no more routes found A5A5 A0A0 A1A1 A2A2 A3A3 A4A4 C1C1 B4B4 Temporal Edge Connectivity Edge Base Edge A [s 2 ] B [s 3 ] C [s 0 ] t4t4 t2t2 t1t1

21. Experiment Methodology Implementation QualNet v3.9 10 ms timeslots, 80 µ s switching delay Only 11 channels used Topology 100 nodes, 1000m x 1000m Uniform random placement Random assignment of nodes to subnetworks

22. Experiments

23. Distance-normalized aggregate throughput: Dominion vastly better than SSCH (86%) and 802.11 (1813%)

24. Conclusion A cross-layer architecture Dominion exploits k channels with only 1 radio Eliminate locally opportunistic behavior Simple MAC: deterministic schedule Improves the normalized throughput, by 1813% and 86% over 802.11 and SSCH respectively.

25. Thank you!!