Crowded Spectrum in Wireless Sensor Networks

1. Crowded Spectrum in Wireless Sensor Networks Gang Zhou, John A. Stankovic, Sang H. Son Department of Computer Science University of Virginia May, 2006

2. Spectrum Crisis – Single Network Find objects; The position is (x,y); Persons with guns; What are they talking about? (Audio) What are they doing? (Video) Need Higher Throughput! AA…

3. Security WSN Other Devices Health Care WSN Spectrum Crisis – Co-existing Co-existing WSNs & Electric Appliances Need Frequency Management

4. Outline • The Spectrum Crisis • Initial solutions in three dimensions • Single Network Throughput • Cooperative Networks • Non-cooperative Networks and Electric Appliances • Open Challenges • Summary

5. Multi-channel design needed Hardware appearing Software still lags behind • Multi-channel support in MICAz/Telos • More frequencies available in the future • Collision-based: B-MAC • Scheduling-based: TRAMA • Hybrid: Z-MAC Single Network Throughput • Limited single-channel bandwidth in WSN • 19.2kbps in MICA2, 250kbps in MICAz/Telos • The bandwidth requirement is increasing • Support audio/video streams (assisted living, …)

6. State of the Art: Multi-Channel MAC in MANET • Require more powerful hardware/multiple transceivers • Listen to multiple channels simultaneously • [Nasipuri 1999], [Wu 2000], [Nasipuri 2000], [Caccaco 2002] • Frequent Use of RTS/CTS Controls • For frequency negotiation • Due to using 802.11 Examples: [Jain 2001], [Tzamaloukas 2001], [Fitzek 2003], [Li 2003], [Bahl 2004], [So 2004], [Adya 2004], [Raniwala 2005]

7. Basic Problems for WSN • Don’t use multiple transceivers • Cost • Form factor • Packet Size • 30 bytes versus 512 bytes (or larger) in MANET • RTS/CTS • Costly overhead

8. RTS/CTS Overhead Analysis [Zhou INFOCOM’06] • RTS/CTS Controls are too heavyweight for WSN: • Mainly due to small packet size: 30~50 bytes in WSN vs. 512+ bytes in MANET • From 802.11: RTS-CTS-DATA-ACK • From frequency negotiation: case study with MMAC MMAC: • RTS/CTS frequency negotiation • 802.11 for data communication

9. Design Consideration - Frequency Assignment Reception Frequency F8 F7 • Complications • Not enough frequencies • Broadcast F6 F5 F1 F4 F2 F3

10. Design Consideration - Media Access • Issues: • Packet to Broadcast • Receive Broadcast • Send Unicast • Receive Unicast • No sending/no receiving See [Zhou,INFOCOM’06] for our solution F8 F7 F6 F5 F1 F4 F2 F3

11. Co-existing & Cooperative Networks • The Challenges: • QoS Control • Different priorities for different networks, different bandwidths • Map to frequency decision • Space-Dimension Flexibility • Frequency decision depends on node density& network density • Time-Dimension Flexibility • Dynamic frequency adjustment See [Zhou, EmNets’06] for our solution

12. Non-cooperative Networks and Devices • IEEE Standards in 2.4GHz ISM Band • 2.4 GHz Electronic Devices & Electric Appliances 802.11 (1997) 802.11 b 78 channels (1 MHz Distance) 14 channels (5 MHz Distance) 802.15.1 (Bluetooth) 802.15.4 79 channels (1 MHz Distance) 16 channels (5 MHz Distance)

13. Measurement with Spectrum Analyzer • When MICAz operates on 2.45 GHz, 46%~81% PRR • When MICAz operates on 2.42 GHz, PRR not impacted by presenter

14. Deal With the Crowded Spectrum • New challenges: • Interference from a different radio • Measurement & metrics • Interference from electric appliances • Measurement & metrics • Incorporate these into: • Static frequency assignment • Dynamic frequency adjustment • Media access

15. More Open Challenges • What is/are the best place/places to provide spectrum management in WSN communication stack? • More unlicensed frequencies from the FCC? • Tradeoff between #channels and bandwidth: static/dynamic? • More sophisticated radio hardware? • Take advantage of partially-overlapping channels? • A service between MAC and PHY, supporting existing single-channel minded MACs?

16. Summary • Present a vision of crowded WSNs & the spectrum crisis • Initial efforts in three complementary dimensions • Single WSN • Cooperative WSNs • Non-cooperative WSNs

17. Backup Slides

18. Frequency Assignment

19. … ... T T T T c b tran b c tran Media Access Design • Different frequencies for unicast reception • The same frequency for broadcast reception • Time is divided into slots, each of which consists of a broadcast contention period and a transmission period.

20. Media Access Design Case 1: When a node has no packet to transmit

21. Media Access Design Case 2: When a node has a broadcast packet to transmit

22. Media Access Design Case 3: When a node has a unicast packet to transmit

23. Toggle Snooping • During “ “, toggle snooping is used

24. Toggle Transmission • When a node has unicast packet to send • Transmits a preamble • so that no node sends to me • so that no node compete for the same channel • We let

25. Co-existing & Cooperative Networks • The Challenges: • QoS Control • Space-Dimension Flexibility • Node density & network density • Time-Dimension Flexibility • More dynamics

26. Co-existing & Cooperative Networks • The Solutions: • Static frequency assignment • Collect (ID, gID, ) from (two-hop) neighbors • Chained frequency decision: (increasing gID & ID) • The candidate frequency range • Randomly choose one of the least chosen frequencies from the range • Dynamic frequency adjustment • Reassign nodes from crowded frequencies to light ones • Avoid pushing around “hot potatoes”