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

2/24 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

3/24 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 What is the “Sensor Networks”

4/24 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

5/24 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

6/24 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

7/24 Random Delay Mechanism t Processing Time (P) Packet Time G.P node of node X P node of node X node X If child node can restrain from transmitting from time t to t + P + PacketTime, the hidden node problem can be reduced.

8/24 Phase Shift Mechanism Sensor sampling interval is shifted by a random amount in response to transmission failure (Break away from unfortunate synchrony) => Improve bandwidth and fairness X X Channel Node A Node B        tt x

9/24 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

10/24 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 S : current rate if(S is acceptance) { p = p + ; S = S * p; } else { p = p * ; S = S * p ; }

11/24 CSMA schemes

12/24 Utilization and Bandwidth of Channel Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness

13/24 Packet size –30 bytes –Manchester encoding Channel capacity –10 kbps => 20.8 packet/sec 16bit CRC error detection for corrupted packet Experiment Settings

14/24 Simulation Results Summary No backoff mechanism performs good but randomness in the pre- collision phase is essential for robustness

15/24 Energy Efficiency Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness

16/24 Simulation Results -> 10uJ/packet -> 40uJ/packet

17/24 Fairness Constraint - high channel Utilization (bandwidth) - energy efficiency - fairness

18/24 Simulation Results Deviation : 0.25packet/sDeviation : 1packet/s

19/24 Phase Shift Effect deviation : 0.25packet/s

20/24 Empirical Results on single hop

21/24 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 = Total traffic in the busiest cell Network bandwidth

22/24 Empirical Results on Multihop

23/24 Empirical Results on Multihop

24/24 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