1. An Adaptive Energy-Efficient And Low-Latency Mac for Data Gathering in Wireless Sensor Networks
Gang Lu
Bhaskar Krishnamachari
Cauligi S. Raghavendra
Department of Electrical Engineering, University of Southern California
Speaker: Yung-Lin Yu

2. Outline Introduction Data Forwarding Interruption Problem
DMAC Protocol Design
Staggered Wakeup schedule
Data Delivery and Duty Cycle Adaptation in Multihop chain
Data Prediction
More-To-Send packet
Performance Evaluation
Conclusion

3. Introduction WSN design features for MAC are
Energy
Latency
Throughput
Fairness
For energy saving, low duty cycle has 3 shortcomings
Sleep latency
Does not adapt to the traffic variation
Fixed sync. may increase collision

4. Introduction(cont.) For reducing sleep delay and more energy-efficient
DMAC
DMAC employs
Staggered active/sleep schedule
Data prediction
More-to-Send packet

5. Data Forwarding Interruption Problem
Packets forwarding across the intermediate
node need waiting until wake up

6. Staggered Wakeup schedule

7. Staggered Wakeup schedule(cont.)
Four advantages
Reducing sleep delay
Request for longer active period can propagated easily
Contention is reduced
Other nodes can still hold low duty cycle

8. Data Delivery and Duty Cycle Adaptation in Multihop chain
A node request to
increase their duty
cycles
Use more data flag
in MAC header

9. Data Delivery and Duty Cycle Adaptation in Multihop chain(cont.)
A node set the more data flag if
Buffer is not empty
Received from previous hop with more data flag
With the slot-by-slot mechanism
DMAC react traffic rate variation to both energy and low latency

10. Data Prediction P Send in Next interval Send packet Ack Ack X
Contention A B

11. Data Prediction (cont)
Sleep 3u,and then wake up
Called additional receiving slot P A B

12. Data Prediction (cont.)
In additional receiving slot if
No data receiving
Go to sleeping and no sending slot
Data receiving
Wakeup again after the current sending slot

13. More-To-Send Packet
A control packet MTS(More-To-Send) to adjust duty cycle under the interference
A node received a request MTS will
Keep waking up periodically every 3u
Send request MTS if
Children does not overhear its parent’s ACK
Received a request MTS from its children
Send clear MTS if
Buffer is empty
All request MTSs received from children are cleared

14. Performance Evaluation
Simulator
NS-2 with CMU wireless extension
3 metrics to evaluate the performance
Energy Cost
Latency
Delivery ratio
The distance between nodes is 200m
source report interval 0.5s

15. Performance Evaluation (cont.)
ENERGY
DELAY
Chain Length(No. of Hops)
Chain Length(No. of Hops)

16. Performance Evaluation (cont.)
50 nodes are in 1000m x 500m
5 source node in the margin and 1 sink in the right bottom corner

17. Performance Evaluation (cont.)
100 nodes are in 1000m x 500m
The number of source which are chosen randomly

18. Conclusion
DMAC achieve both energy efficiency and low latency in data gathering tree structure
Future work is
Implement this MAC on a Mote-based sensor network platform