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Introduction to Wireless Ad Hoc and Sensor Networks: From IEEE 802.11 to Berkeley Motes

This informative guide delves into the history, standards, and comparison of wireless LANs like IEEE 802.11 and Bluetooth, as well as Ad Hoc networking principles. Uncover the technological advancements in wireless communication, ranging from Berkeley Motes to the current standards like IEEE 802.11i, and assess the potential of Bluetooth in comparison to well-established standards like 802.11. Dive into the realms of sensor networks and the fascinating world of smart devices like Berkeley Smart Dust and Smart Clothing for a comprehensive view of the wireless technology landscape. Delve deeper into the suitability of IEEE 802.11 for supporting large-scale multihop Ad Hoc networks, examining scalability issues and potential solutions.

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Introduction to Wireless Ad Hoc and Sensor Networks: From IEEE 802.11 to Berkeley Motes

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  1. Introduction toWireless Ad Hoc and Sensor Networks:From IEEE 802.11 to Berkeley Motes Ten-Hwang Lai Ohio State University

  2. Outline Wireless LANs Ad Hoc Networks IEEE 802.11 Bluetooth Berkeley Motes

  3. Wireless LANs IEEE 802.11 Bluetooth HiperLan (Europe)

  4. History of IEEE 802.11 • 802.11 standard first ratified in 1997 • 802.3 LAN emulation • 1 & 2 Mbps in the 2.4 GHz band • Two high rate PHY’s ratified in 1999 • 802.11a: 6 to 54 Mbps in the 5 GHz band • 802.11b: 5.5 and 11 Mbps in the 2.4 GHz band

  5. The Beat Goes On • 802.11d: new support for 802.11 frames • 802.11c: support for 802.11 frames • 802.11e: QoS enhancement in MAC • 802.11f: Inter Access Point Protocol • 802.11g: 2.4 GHz extension to 22 Mbps • 802.11h: channel selection and power control • 802.11i: security enhancement in MAC • 802.11j: 5 GHz globalization

  6. Can Bluetooth Compete with 802.11? • IEEE 802.11 already has been widely accepted. • What’s Bluetooth chance of success stacking against 802.11?

  7. 802.11 BSS Basic Service Set (BSS) --- a basic LAN Infrastructure BSS Independent BSS (Ad Hoc LAN) Access point

  8. 802.11 ESS Extended Service Set (ESS) Distributed System

  9. Bluetooth Piconet & Scatternet Master Master Slaves Slaves S M Piconet Master Slaves Scatternet

  10. Comparison of Bluetooth to 802.11b Parameter Bluetooth 802.11b Bandwidth 1 Mbps 11 Mbps Range 10 meters 100 meters Profiles Almost unlimited AP, STA Current consumption 60mA 300mA Audio PCM channels voice/802.3 Cable replacement Serial, USB, Audio 802.3 Circuit cost (9/2001) $11.00 $46.00 Ad hoc networking multi-hop single-hop

  11. Bluetooth or 802.11?

  12. Can Bluetooth Compete with 802.11? • IEEE 802.11 already has been widely accepted. • What’s Bluetooth chance of success stacking against 802.11? Answer: ? 802.11 --- WLAN Bluetooth-- WPAN

  13. Ad Hoc Networking • BT Scatternet --- multihop? • 802.11 --- single hop? Master Slaves S M Master Slaves

  14. BT Scatternet Formation • Problem: design a protocol that given a set of bluetooth nodes organizes the nodes into a scatternet. • Still an interesting research problem.

  15. A Sensor Node Memory (Application) Processor Network Interface Actuator Sensor

  16. Berkeley Mote: a sensor device prototype • Atmel ATMEGA103 • 4 Mhz 8-bit CPU • 128KB Instruction Memory • 4KB RAM • RFM TR1000 radio • 50 kb/s • Network programming • 51-pin connector • Analog compare + interrupts

  17. Berkeley DOT Mote • Atmel AVR 8535 • 4MHz • 8KB of Memory • 0.5KB of RAM • Secondary store • Low power radio • Power consumption • Active 5mA • Standby 5μA

  18. Tightly-Coupled Sensor Array

  19. Artificial Retina

  20. Smart Clothing & Wearable Computing • Smart Underwear • Smart Eyeglasses • Smart Shoes • …

  21. Berkeley Smart Dust • bi-directional communications • sensor: acceleration and ambient light • 11.7 mm3 total circumscribed volume • 4.8 mm3 total displaced volume

  22. Is IEEE 802.11 Suitable for Supporting Large-Scale Multihop Ad Hoc Networks? Ten-Hwang Lai Ohio State University

  23. Approach to the Problem • Now: single-hop, small-scale • Future: multi-hop, large scale? Single-hop, Small-scale Single-hop, Large-scale Multi-hop,Large-scale

  24. Topics • Is IEEE 802.11 (single-hop) scalable? • Time sync in multihop ad hoc networks. • Constructing connected dominating sets by way of clock synchronization.

  25. Is IEEE 802.11 Scalable?

  26. Problem Statement • Can 802.11 support a large-scale ad hoc network? • Large scale – say, a few hundred nodes

  27. 802.11 Timers (Clocks) • Timer: 64 bits, ticking in microseconds. • Accuracy: within + 0.01%, or +100 ppm. • Time synchronization needed for: • Frequency hopping • Power-saving mode • ∆ = max tolerable difference between clocks.

  28. 802.11’s Time Sync Function (I) • Time divided into beacon intervals, each containing a beacon generation window. • Each station: • waits for a random number of slots; • transmits a beacon if no one else has done so. • Beacon: several slots in length. beacon interval window

  29. 802.11’s Time Sync Function (II) • Beacon contains a timestamp. • On receiving a beacon, STA adopts beacon’s timing if T(beacon) > T(STA). • Clocks move only forward. 12:01 12:02 12:01 12:00 12:01 faster slower adopts not adopts

  30. Problems with 802.11’s TSF • Faster clocks synchronize slower clocks. • Equal opportunity for nodes to generate beacons. 1:16 1:17 1:18 1:19 1:21 1:23 1:21 1:22 1:23 1:25 1:28 1:31 1:18 1:18 1:18 1:19 1:21 1:23 1:23 1:23 1:23 1:25 1:28 1:31 1:10 1:11 1:12 1:13 1:14 1:15 1:13 1:13 1:13 1:13 1:14 1:15 +3 +4 +5 +6 +7 +8 +3 +4 +5 +6 +7 +8

  31. The Out-of-Sync Problem When the number of stations increases • More beacon contention • Fastest station send beacons less frequently Stations out of sync

  32. Performance of TSF

  33. How to fix it? • Desired properties: simple, efficient, and compatible with current 802.11 TSF. • Causes of out-of-sync • Unidirectional clocks • Equal beacon opportunity • Single beacon per interval • Beacon contention (collision) 1 n Prob <

  34. Improve fastest station’s chance • Let the fastest station contend for beacon generation more frequently than others.

  35. Adaptive Clock Sync Protocol • Station x participates in beacon contention once every C(x) intervals. • Initially, C(x) =1. Always, 1 < C(x) < Cmax. • Dynamically adjust C(x): x x C(x) +1 faster C(x) -1 slower

  36. Once the protocol converges Fastest station, C(x) =1 Other stations, C(x) = Cmax (Cmax= ?)

  37. What if the fastest node leaves the IBSS? • The previously second fastest now becomes the fastest. Its C(x) will decrease to 1.

  38. What if a new fastest node enters the IBSS? • The previously fastest now no longer the fastest. Its C(x) will increase to Cmax.

  39. Compatible with current TSF • Suppose some nodes do not implement the new protocol.

  40. Performance of Modified TSF

  41. Summary • Showed: the IEEE 802.11 Timing Sync Function (TSF) is not scalable. • Proposed: a simple remedy compatible with the current TFS.

  42. What’s Next? • IBSS: single-hop • MANET: multihop ?? transmission range

  43. Time Synchronization in 802.11-based MANET

  44. Out-of-sync problem in MANETs • More sever than in IBSS because of hidden terminals. • Recall: causes of out-of-sync • Unidirectional clocks • Equal beacon opportunity • Single beacon per interval • Beacon contention(collision)

  45. Select a subset of nodes to generate beacons more frequently than the rest. What subset? Basic Idea fastest node+ (connected) dominating set

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