1. 1 Grid-Based Access Scheduling for Mobile Data Intensive Sensor Networks C.-K. Lin, V. Zadorozhny and P. Krishnamurthy IEEE International Conference on Mobile Data Management, 2008

2. 2 Outline Introduction GLASS protocol description GLASS analysis Simulation results Conclusion

3. 3 Introduction MSN applications have stringent requirements on the response time Minimizing sensor response time and minimizing energy consumption is crucial Even high rate wireless networks (e.g., IEEE 802.11) use best-effort service that can lead to packet loss (from collisions)

4. 4 Grid based Latin Squares Scheduling Access (GLASS) protocol description System model GLASS protocol Time slot assignment

5. 5 System model Sensors are evenly deployed in a field Every sensor transmits or receives on a common carrier frequency Time synchronization is managed by a Base Station (BS) using beacons

6. 6 GLASS protocol Grid searching Transmission frame assignment Time slots assignment

7. 7 Grid searching

8. 8 Transmission frame assignment

9. 9 Transmission frame We define a TF as a group of continuous time slots The length of TF is configured differently for different sensor distributions If the sensors are not evenly distributed, α will increase

10. 10 Time slots assignment Each sensor performs neighborhood discovery to prepare for time slots scheduling We use Latin Squares (LS) to assign time slots for sensors

11. 11 Example 1 4 2 5 3 1 4 2 5 3 14 2 5 3 1 4 2 5 3 14 2 5 3 1 4 2 5 3 1 4 2 5 3 1 4 2 5 3 1 4 2 5 3

12. 12 Collision avoidance near intersection of grids

13. 13 Example 3 2 1 1 4 2 3 1 2 5 6 2

14. 14 GLASS analysis Theorem 3.1: There is no conflicting time slot assignment between any two sensors within any grid cell when the protocol converges. (Proof omitted). Theorem 3.2: There is no conflicting time slot assignment between any two sensors from any two different grid cells when the protocol converges. (Proof omitted). Theorem 3.3: There is no conflicting time slot assignment between any two sensors when the protocol converges. (Proof omitted).

15. 15 Simulation results Simulator: NS-2 Compare the GLASS protocol with the IEEE 802.15.4 CAP mode and DRAND Set the channel data rate to 250 Kbps Set the sensor transmission range to 15 meters The packet size is 70 bytes

16. 16 Distributed Randomized TDMA Scheduling (DRAND)

17. 17 Transmission efficiency(1/2)

18. 18 Transmission efficiency(2/2)

19. 19 Scalable network

20. 20 Overhead evaluation

21. 21 Impact of sensor mobility(1/2)

22. 22 Impact of sensor mobility(2/2)

23. 23 Conclusion GLASS efficiently alleviates conflicting time slots schedules This approach is especially suitable for the mobile data intensive sensor network with frequently changing topology