A Transmission Control Scheme for Media Access in Sensor Networks

1. A Transmission Control Scheme for Media Access in Sensor Networks A.Woo, D.E. Culler Mobicom’01 2006. 9. 28 Lee, dooyoung AN lab

2. Outline • Introduction • What is the “sensor networks” ? • Characteristic of sensor network • Issues for sensor network • Transmission Control Scheme • Simulation and Empirical results • Single-hop environments • Multi-hop environments • Conclusion

3. What is the “Sensor Networks” • Ad hoc network of sensors • data event traffic • Emerging area of mobile computing • Primary Function • Sensory information • temperature, humidity • Propagate this data block into the infrastructure

4. Characteristics of SN • Unusual application requirements • highly constrained resources • Small packet size • Deep ad hoc multihop dynamic topology • A correlated operating • Short periods the traffic may be very intense • Periodic rendezvous

5. Issues for SN in this paper • Motivation • The design space is different from traditional mobile computer networks • SN needs tight constraints • computational power, Storage, Energy resource • Radio technology • Targets • High channel utilization • Fair bandwidth allocation • Communication efficiency on energy • Propose an adaptive rate control(ARC) mechanism

6. Wireless multiple access protocol • Collision avoidance component • Carrier sensing (listening) mechanism • RTS-CTS-ACKs • For sensor networks where packet size is small, they can constitute a large overhead (up to 40%) • A contention control scheme for sensor networks should use a minimum number of control packets • Contention resolution component • Backoff / Persistence mechanism • To restrain a node from accessing the channel

7. G.P node of node X P node of node X node X t Processing Time (P) Packet Time Random Delay Mechanism If child node can restrain from transmitting from time t to t + P + PacketTime, the hidden node problem can be reduced.

8. t x Phase Shift Mechanism Channel X Node A     X Node B t Sensor sampling interval is shifted by a random amount in response to transmission failure (Break away from unfortunate synchrony) => Improve bandwidth and fairness

9. Rate Control Mechanism • Fairness channel allocation • Channel Capacity / N , where N is total number of node in the entire network • The spontaneous ad hoc of sensor networks make impractical • Proposed transmission rate control mechanism • Linear increase • Multiplicative decrease The adaptive rate control idea is very simple and can be explained with an analogy of metering trac onto a freeway where the route-thru trac is like trac on the freeway and each node originating data is like cars trying to enter. Periodically, a node attempts to inject a packet. If the packet is successfully injected, it becomes part of the route-thru traf- c. As it is routed by the node's parent, it signals that the road still has capacity for more trac and thus, the node can increase its transmission rate. However, if the injection of the packet wasn't successful, it signals that the road is jammed and the node decreases its rate of originating data and backo to achieve a phase change eect. Thyagarajan Nandagopal, Tae-Eun Kim “Achieving MAC layer fairness in wireless packet network”, Mobicom’00

10. S : current rate if(S is acceptance) { p = p + ; S = S * p; } else { p = p * ; S = S * p ; } Rate Control Mechanism • S : application transmission rate • S*p : the actual rate of originating data. p [0, 1] • p : probability of transmission • : a constant • : multiplicative decrease a factor where 0 < < 1 • controls the penalty given a failure of transmission

11. CSMA schemes

12. Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness Utilization and Bandwidth of Channel

13. Experiment Settings • Packet size • 30 bytes • Manchester encoding • Channel capacity • 10 kbps => 20.8 packet/sec • 16bit CRC error detection for corrupted packet

14. Simulation Results Summary No backoff mechanism performs good but randomness in the pre- collision phase is essential for robustness

15. Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness Energy Efficiency

16. Simulation Results -> 40uJ/packet -> 10uJ/packet

17. Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness Fairness

18. Simulation Results Deviation : 0.25packet/s Deviation : 1packet/s

19. Phase Shift Effect deviation : 0.25packet/s

20. Empirical Results on single hop

21. Network bandwidth Total traffic in the busiest cell Multi-hop scenario Under simulation Maximum uniform origination rate  20/24 = 0.83 packet/s (using different encoding scheme, SECDEC) In the implementation, limit origination rate  15.7/24 = 0.66 packet/s Maximum uniform origination rate =

22. Empirical Results on Multihop

23. Empirical Results on Multihop

24. Conclusion • Existing MAC protocol are not suitable in SN networks • Resource limitation, traffic characteristic • Propose new mechanism • Random delay, phase shift • ARC(Adaptive Rate Control) scheme in a multihop network