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Exploring Network Coding and Opportunistic Routing in Wireless Sensor Networks**

This session delves into advanced topics in networking, focusing on network coding and opportunistic routing. We discuss the efficiency gained through network coding techniques like COPE, which reduce time slots needed for transmission and improve throughput. Key challenges such as poor link quality in traditional routing methods are addressed with solutions like opportunistic routing, EXOR, and MORE, which leverage randomness and enhance packet delivery. Additionally, we explore Analog Network Coding, which utilizes inherent interference for higher efficiency, showcasing practical applications and implications for wireless communication.

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Exploring Network Coding and Opportunistic Routing in Wireless Sensor Networks**

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  1. Cool Topics in Networking CS144 Review Session 8 November 20, 2009 Samir Selman

  2. Announcements • Lab 5 : Due Thursday Dec 3 • Final Exam: Wednesday, December 9 12:15pm - 3:15pm • For those of you submitting late, contact us before your deadline if you need an additional extension. Tell us: • Where you are • How much more time you need

  3. Today’s Cool Topics • Network Coding • Wireless Sensor Networks

  4. Current Wireless C Router

  5. Current Wireless C Router Traditional Routing requires 4time slots

  6. Current Wireless C Router Traditional Routing requires 4time slots

  7. Network Coding C Router = XOR Traditional Routing requires 4 time slots

  8. Network Coding C Router Traditional Routing requires 4 time slots

  9. Network Coding C Router = XOR = XOR Traditional Routing requires 4 time slots With Network Coding need only 3 time slots  Higher throughput

  10. I - COPE • Sachin Katti, Hariharan Rahul, Wenjun Hu, Dina Katabi, Muriel Medard, and Jon Crowcroft, "XORs In The Air: Practical Wireless Network Coding,"ACM SIGCOMM, 2006.

  11. COPE Coding Opportunities

  12. COPE Coding Opportunities

  13. II- Opportunistic Routing • Traditional routing chooses next hop before transmitting a packet. • Poor Link Quality => Probability of chosen next hop receiving packet is low • Solution: Opportunistic Routing allows any node that overhears the transmission and is closer to the destination to participate in forwarding the packet • Challenge: Multiple nodes might hear a packet broadcast and unnecessarily forward the same packet.

  14. EXOR • EXOR solves this issue by tying the MAC to the Routing and imposing a strict schedule on the routers. • The scheduler goes in rounds. Forwarders transmit in order, and only one forwarder is allowed to transmit at a given time. • Other nodes listen to learn which packets were overheard by other nodes. • Problem: This strict scheduling prevents forwarders from exploiting spatial reuse (even when multiple packets can be received by their respective receivers).

  15. MORE • Szymon Chachulski, Michael Jennings, Sachin Katti, and Dina Katabi, "Trading Structure for Randomness in Wireless Opportunistic Routing," ACM SIGCOMM, 2007

  16. MORE • MORE solves the problem with Opportunistic Coding without tying Routing to the MAC. • Instead it uses Network Coding + Randomness. • Basically nodes randomly mix packets before forwarding them. • This ensures the routers hearing the same transmission do not forward the same packet.

  17. MORE - Examples Unicast Case • Src sends P1,P2 • Dest luckily overhears P1. • Router doesn’t know what dest received (P1). • In any case R can forward P1 + 2P2 • Dest now has two received packets • P1 • P1 + 2P2 • Dest can solve 2 eqns with 2 unknowns to retrieve P2. • Conclusion: R only forwarded one packet instead of two =>Higher throughput

  18. MORE - Examples Multicast Case • Without Network Coding, src has to retransmit the union of the lost packets ( 4 pkts ). • With Network coding can retransmit only 2 randomly coded pkts and allow all destinations to decode their respective packets. • Src retransmits pa = p1+ p2 + p3 + p4, and pb= p1 + 2p2 + 3p3 + 4p4.

  19. Analog Network Coding • Sachin Katti, Shyamnath Gollakota, and Dina Katabi, "Embracing Wireless Interference: Analog Network Coding," ACM SIGCOMM, 2007.

  20. Analog Network Coding Analog Network Coding (ANC) Instead of router mixing packets… Exploit that the wireless channelnaturally mixes signals

  21. Analog Network Coding C Router

  22. Analog Network Coding C Router Interference Phil and David transmit simultaneously

  23. Analog Network Coding C Router Phil and David transmit simultaneously Router amplifies and broadcasts interfered signal

  24. Analog Network Coding C Router Phil and David transmit simultaneously Router amplifies and broadcasts interfered signal Phil subtracts known signal from interfered signal

  25. Analog Network Coding C Router Dina and Robert transmit simultaneously Router amplifies and broadcasts interfered signal Dina subtracts known signal from interfered signal • Analog Network Coding requires 2 time slots • Higher throughput

  26. It Is More Than Going From 3 To 2! • Philosophical shift in dealing with interference • Strategically exploit interference instead of avoiding it • Promises new ways of dealing with hidden terminals

  27. Hidden Terminal Scenario C C C C Src R2 R1 Dst

  28. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1

  29. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 Src and R2 transmit simultaneously

  30. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 Src and R2 transmit simultaneously R1 subtracts P1, which he relayed earlier to recover P2 that he wants

  31. Hidden Terminal Scenario C C C C Src R2 R1 Dst P1 P2 • R2 and Src are hidden terminals • Today : Simultaneous transmission  Collision • ANC : Simultaneous transmission  Success!

  32. Hidden Terminal Scenario C C C C Src R2 R1 Dst • Other Benefits of ANC: • First step toward addressing hidden terminals • ANC extends network coding to new scenarios

  33. Wireless Sensor Networks • A sensor network is an Ad-hoc network composed of densely populated tiny electronic sensing devices. • Basic function of the network is to observe some phenomenon. • Characteristics: • Low cost, Low power, Light weight • Densely deployed • Prone to failures • Two ways of deployment: randomly, pre-determined • Objectives: • Monitor Activities • Gather and fuse information • Communicate it to special node “Base Station”.

  34. Computer Revolution Original IBM PC (1981) MICAZ Mote (2005) 4.77 MHz 4 MHz 16-256 KB RAM 128 KB RAM 160 KB Floppies 512 KB Flash ~ $6K (today) ~ $35 ~ 64 W ~14 mW 25 lb, 19.5 x 5.5 x 16 inch 0.5 oz, 2.25 x 1.25 x 0.25 inch

  35. Sensor Node Hardware Platform

  36. Software Platform

  37. WSN Applications

  38. WSN Applications

  39. WSN Applications

  40. WSN Applications

  41. WSN Applications

  42. WSN protocols Protocol Requirements: • Energy Efficient (Maximize node lifetime) • Self Configuring • Scalable • Redundant • Efficient (less computation, less memory requirements, less energy consumption…) • Robust

  43. Energy Efficiency • Sources of Energy Consumption: • Communications (Transmitting & Receiving) • Computations • Sensing • Sources of Energy Wastage in Communications: • Collisions • Overhearing • Idle Listening • Control Packets overhead • Over emitting

  44. WSN Protocol Research

  45. Questions?

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