TDMA based MAC protocol to assist in Wide area Sensor Network Deployment

1. TDMA based MAC protocol to assist in Wide area Sensor Network Deployment Nuwan Gajaweera

2. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

3. Wireless Sensor Network • Collection of low power computer • With integrated sensors • Networked via short range radio transceivers • Application Areas • Environmental Monitoring • Defense & security • Health • etc

4. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

5. Background • Monitoring of a large area • WSN deployment over a large area • Large number of repeater nodes needed • Alternative • Use a Data Mule • Data Mule – Mobile mote that traverse the area of the sensor network • Random Path: Motes mounted on people, livestock or vehicles • Deterministic Path: Robots

6. Area to be monitored Gateway Background Data Mule

7. Issue • Multiple Data Mules at the Base station • Efficient use of radio resources – i.e. minimize packet collisions • Fair bandwidth allocation to all data mules • Collect maximum data volume from data mule in given time

8. Objectives • Develop suitable MAC protocol • Single hop network • Traffic pattern: data flows from data mule to base station • Maximize throughput • Minimize delay • Develop storage engine • Data collected from leaf nodes should stored so that fast retrieval is possible

9. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

10. Literature Survey • Wireless sensor network platforms • Different MAC protocols in existence

11. Wireless sensor network platforms- Research • TinyOS • Popular event driven OS for deeply embedded systems • SOS • Mantis • Contiki

12. Wireless sensor network platforms- Commercial • Crossbow • Moteiv • Ember Corp • Dust Networks – TDMA-FDMA based MAC TinyOS

13. WSN MAC protocols • Random access schemes • LPL, B-MAC, X-MAC • 802.15.4 MAC • Slotted schemes • S-MAC, S-MAC/AI, T-MAC • TDMA based schemes • Hybrids protocols

14. TDMA MAC protocols • Pros • High channel utilization due to absence of packet collisions • Cons • Complexity in building a scheduling • Need for node synchronization • Inability to handle mobile nodes, due the frequent need to reschedule

15. TDMA MAC protocols • PEDMACS • LMACS • Cluster Based • PACT • EMAC • LEACH – routing protocol • BMA (utilizes LEACH for clustering)

16. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

17. Technology Choices • Wireless Sensor Network Platform • TinyOS • Mote • MICA2 • MAC Protocol • TDMA MAC • Storage engine • Under review

18. Why TDMA? • CSMA • Channel capacity wasted due to packet collisions • TDMA • Channel capacity wasted due to control traffic • Maximize throughput • Energy conservation is a not a priority “Develop demand assigned TDMA MAC Minimizes control traffic”

19. D-Lab Mote • MICA2 Clone Developed at Dialog UoM Lab (D-Lab Mote) • Exact copy of MICA2 • Currently working on developing D-Lab Mote V2 • Small modifications to original MICA2 • GPS, GSM Modules • RTC • Flash Memory (MMC card)

20. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

21. Concept Development Write TinyOS Code Simulate (Arvora) Refine Concept Analyze Results Unsatisfactory Results Satisfactory Results Unsatisfactory Results Analyze Results Execute on MICA2 motes Satisfactory Results Process End Completed In progress To be done MAC protocol development process

22. Transmission Group Radio range of BS Base station (Gateway) TDMA MAC mote #2 mote #3 mote #1 (Data Mule)

23. … Time Transmission period Contention Period TDMA MAC • Contention Periods • Motes contend for membership of the tx group • Transmission Periods • Motes in the tx group transmit data in allocated slot

24. Slot 0 1 2 3 4 5 1 2 3 1 2 3 … … Time Time tx start packet tx start packet tx end packet tx end packet Uplink Downlink Guard period Uplink Downlink Transmission Period Also serves as ack packet

25. Tb,max Tb,max - Max back-off Tp - Packet time Tb - Actual b-off Tp Tb RTS … Time con start packet con end packet + CTS Uplink Downlink Contention Period

26. Contention Period • Motes are only told if they were added to the tx group or not • The time slot is only advertised during the tx start packet • When the membership of the tx group changes, the following tx start packet will carry a uplink map that gives the time slot allocation.

27. TDMA MAC Simulation • Base station wakes up at simulation start • motes wake up after random delay • The motes that are awake contend for membership of the transmission group • After transmitting ‘N’ packets, the mote removes itself from the tx group. • (N = 32, 64, 128, ∞) • The said mote again starts to contend for tx group membership

30. Outline • Wireless Sensor Networks • Background & Objectives • Literature Survey • Technology Choices • TDMA MAC protocol • Remaining Work

31. Storage Engine • Mote will contain • SRAM • Flash Memory (MMC Card) • Mote (Data mule) will collect data from leaf nodes and store data in flash memory • When in range of the base station the mote will read data from the (slow) flash into the SRAM in fixed size blocks • The mote will then attempt to become a member of the tx group and upload this block of data to the base station • Once the block is transferred to the BS, the mote will remove itself from the group and repeat the process

32. Remaining Work • Select/Develop storage engine • Build MICA2 Clone (V2) • Integration of storage engine & TDMA MAC • Uploading base station data to a server

33. Conclusion