Network-Coding based Scheduling And Routing Schemes for Serivce-Oriented Wireless Mesh Networks

1. Jian-Liang Pan Nguyen Thi Mai Phuong Yu-Chen Chang Tai Yang Wu Tai Long Chen Network-Coding based Scheduling And Routing Schemes for Serivce-Oriented Wireless Mesh Networks

2. Talk Outline Introduction & Background - Wireless Mesh Networks Mesh vs. Ad-Hoc Networks Wireless Network Coding Routing Strategies Link Scheduling & Channel Assignment Performance Evaluation 2

3. Wireless Mesh Networks • WMN - Wireless Mesh Network: • Ad-hoc network with a core which has limited mobility • Mesh Router: • A wireless base station with limited or no mobility • Infrastructure of the network • Mesh Clients: • A wireless node which is fully mobile, may also act as a router in some WMNs Image: Indigo Systems – WMN for Environmental Monitoring

4. Hybrid WMN

5. Overview Link Types Node Types Intra-mesh wireless links Stationary client access Mobile client access Internet access links Wireless routers Gateways Printers, servers Mobile clients Stationary clients

6. GW Gateways • Multiple interfaces (wired & wireless) • Mobility • Stationary (e.g. rooftop) – most common case • Mobile (e.g., airplane, busses/subway) • Serve as (multi-hop) “access points” to user nodes • Relatively few are needed, (can be expensive)

7. Wireless Router • At least one wireless interface. • Mobility • Stationary (e.g. rooftop) • Mobile (e.g., airplane, busses/subway). • Provide coverage (acts as a mini-cell-tower). • Do not originate/terminate data flows • Many needed for wide areas, hence, cost can be an issue.

8. Typically one interface. Mobility Stationary Mobile Connected to the mesh network through wireless routers (or directly to gateways) The only sources/destinations for data traffic flows in the network. Users

9. Wired Bus (PCI, PCMCIA, USB) Ethernet, Firewire, etc. Wireless 802.11x Bluetooth Proprietary Point-to-Point or Point-to-Multipoint If properly designed is not a bottleneck. If different from router-to-router links we’ll call them access links User – Wireless Router Links

10. Wireless 802.11x Proprietary Usually multipoint to multipoint Sometimes a collection of point to point Often the bottleneck If different from router-to-user links we’ll call them backbone links Router to Router Links

11. Wired Ethernet, TV Cable, Power Lines Wireless 802.16 Proprietary Point to Point or Point-to-Multipoint We’ll call them backhaul links If properly designed, not the bottleneck Gateway to Internet Links

12. User-Internet Data Flows In most applications the main data flows User-User Data Flows In most applications a small percentage of data flows How it Works

13. Mesh vs. Ad-Hoc Networks Wireless Mesh Networks Ad-Hoc Networks • Multihop • Nodes are wireless, possibly mobile • May rely on infrastructure • Most traffic is user-to-user • Multihop • Nodes are wireless, some mobile, some fixed • It relies on infrastructure • Most traffic is user-to-gateway

14. Abstract • One of critical problem : improve the network throughput - Channel assignment problem • Key technology: Network Coding • Step1: analyze the throughput improvement obtained by wireless network coding schemes in wireless mesh networks. • Step2: develop a heuristic joint link scheduling, channel assignment, routing algorithm

15. Wireless Network Coding

16. Wireless Network Coding • Network coding is a particular in – network data processing technique that exploits the characteristics of the wireless medium (in particular, the broadcast communication channel) in order to increase the capacity or the throughput of the network • (Network Information Flow – Rudolf Ahlswede, Ning Cai, Shou – Yen Robert Li, Senior Member, IEEE, and Raymond W.Yeung, Senior Member, IEEE)

17. Wireless Network Coding • Let G=(V,E) be a graph (G is the set of nodes of a point – to – point communication, E is the set of edges) with source s and sinks t1,t2, …tL. • R=[Rij,(i,j) E], Rij is the capacity of an edge (i,j) E. • h is the rate of information source • F=[Fij,(i,j) E] is a flow in G from s to tl (l=1,…L) if for all (i,j) E : and for all i V except s and tl:

18. Wireless Network Coding • F is a max-flow from s to tl in G if F is a flow from s to tl whose value is greater than equal to any other flow from s to tl • Max – Flow Min – Cut theorem: Let G = (V,E) be a graph with source s and sinks t1,…,tL, and the capacity of an edge (i,j) be denoted by Rij. (R,h,G) is admissible if and only if the values of a max – flow from s to tl are greater than or equal to h

19. Wireless Network Coding

20. Wireless Network Coding

21. Wireless Network Coding • A total of 9 bits are sent (network coding) • If network coding is not allowed, at least one more bit has to be sent => Saving 10% bandwidth

22. Wireless Network Coding • Using the scheme in fig.8(b), if 2 bits are sent in each edge, then 4 bits can be multicast to all the sinks • If network coding is not allowed: • Let B = {b1,…,bk} be the set of bits to be multicast to all the sinks. • Let the set of bits sent in the edge (s,i) be Bi, where |Bi| = 2, i = 1, 2, 3 • B = Bi Bj for any • We have:

23. Wireless Network Coding • Therefore: • k 3 or if network coding is not allowed, only 3 bits can be multicast to all sinks (if 2 bits are sent in each edge) => Throughput of network can be increased by one-third using a very simple network code

24. Wireless Network Coding

25. Wireless Network Coding

26. Butterfly Network • When two or more signal transmission path of partial overlap ，Encoded to improve the signal transmission rate of the technology can be called 「common path coding」

27. Each arrow indicates assumed to send a signal ， the signal value is 0 or 1，A point given by the two signals x and y，should be sent to the B point and C point. • Let M points x and y send a representative to the similarities and differences of the signal， when the B point to receive this signal and x, can be solved y; Similarly, C-point can also be solved x. • Graph signal x ⊕ y ，x ⊕ y is called 「binary sum」 ，it not only represents a coded form, is also a mathematical "linear" code.

28. Use network coding，the encoding method has three restrictions: • Each encodedpacket must be the linear independence. • The node after the packet encoded into the nodes need to encode packets with each other linearly independent . • Enter the node will be re-encoded packets and transmitted.

29. Linear Network Coding P1，P2 ， ‧ ‧ ‧ ‧ ‧ ‧ Pn the packets for the node S e = {e1, e2, e3 ‧ ‧ ‧ ‧ ‧ ‧ en} is coded coefficients

30. Figure (2), (3) is linear combination of matrix encoding.

31. Linear Network Decoding • The coefficient matrix is converted into an anti-matrix, the re-encoded packet multiplied by the value of the packet can be restored.

33. Network coding of fault tolerance

34. 反矩陣的算法(一) :高斯消去法 • 步驟: • (步驟1) 將單位矩陣In連接於所給矩陣A之後 [A In] • (步驟2) 利用高斯消去法將步驟1中的A矩陣化成單位矩陣In • 求A-1的教學範例: • 求出矩陣A的反矩陣，

37. 反矩陣的算法(二)

38. 伴隨矩陣(adj A)

39. 餘因子(cofactor) Aij:

40. 伴隨矩陣(adj A)的算法

41. Routing Strategies Two types ： • Shortest single-path routing • Optimized single-path routing

42. Shortest single-path routing ● In particular, single-path routing can beobtained by Dijkstra’s algorithm.

43. Dijkstra’s Algorithm Initial

44. Dijkstra’s Algorithm

45. Dijkstra’s Algorithm

46. Dijkstra’s Algorithm

47. Dijkstra’s Algorithm

48. Dijkstra’s Algorithm

49. Dijkstra’s Algorithm

50. Dijkstra’s Algorithm Finish