1. Dynamic Link Labels for Energy Efficient MAC Headers in Wireless Sensor Networks Sheng-Shih Wang Gautam Kulkarni, Curt Schurgers, and Mani Srivastava IEEE Proceeding of Sensors, vol. 2, pp. 1520-1525, 2002

2. October 13, 2003 Sheng-Shih Wang Outline  Introduction  Spatial Label Reuse Constraints  Assignment Algorithm Label Assignment Label Representation and Selection  Performance Evaluation  Conclusion

3. October 13, 2003 Sheng-Shih Wang Introduction --- Data Communication Problems  Consume the limited battery energy  Data aggregation technique Reduce redundancy Packet overhead is not under consideration MAC address

4. October 13, 2003 Sheng-Shih Wang Introduction --- Short Label Links Technique  Idea MAC addresses are unique only within the transmission neighborhood of a node  Operation Replace the conventional MAC addresses with short link labels Uniquely identify the neighbors of a node Link labels are assigned only on demand  Objective Packet overhead reduction Spatial reuse

5. October 13, 2003 Sheng-Shih Wang Spatial Label Reuse Constraints  Idea Each node must be able to figure out whether or not it is the intended receiver of a particular transmission

6. October 13, 2003 Sheng-Shih Wang Spatial Label Reuse Constraints (cont.) (A-B)  (A-C) (A-B)  (A-D) (A-B)  (A-E) (A-B)  (B-I) (A-B)  (E-F) (A-B)  (E-G) (A-B)  (I-J) (A-B)  (N-M) (A-B)  (L-K) One-hop constraint Two-hop constraint Unidirectional link constraint

7. October 13, 2003 Sheng-Shih Wang Label Assignment Problem  When data communication is restricted to bi-directional links, a link is said to have a valid label assignment when its label is distinct from that of it’s neighboring links and from the neighbors of the neighboring links, with unidirectional links never being assigned a label

8. October 13, 2003 Sheng-Shih Wang Assignment Algorithm --- Message Exchange Neighbors of active node Active nodePassive node Neighbors of passive node HELLO REQUEST BROADCAST REPORT BROADCAST

9. October 13, 2003 Sheng-Shih Wang Assignment Algorithm --- Label Selection and Representation Smaller labels are selected more often than the higher ones  The smallest available label is picked first Replace MAC addresses with variable length codeword by using Huffman encoding technique

10. October 13, 2003 Sheng-Shih Wang Assignment Algorithm --- Control Packet Format HeaderTx ID HELLO HeaderTx ID REQUEST HeaderTx ID BROADCAST HeaderTx ID REPORT HeaderTx ID CONFLICT 4 bits14 bits Rx ID 14 bits Label Neighbor info K(11+1) bits Rx IDLabel Constrained labels K(11+1) bits Rx ID

11. October 13, 2003 Sheng-Shih Wang Simulation --- Parameters  RFM radio at 2.4 kbps [12] Transmission energy R = 20 m  0.18  J/bit R = 80 m  0.94  J/bit Receiving energy  0.04  J/bit  StrongARM SA-1100 processor [11] 1.5 nJ/instr at 150 MIPs 2.2 nJ/instr at 250 MIPS

12. October 13, 2003 Sheng-Shih Wang Simulation --- Parameters (cont.)  The number of nodes ( N )  1000  Network density The average number of neighbors of a node ( )  The number of traffic streams

13. October 13, 2003 Sheng-Shih Wang Simulation --- Results The address overhead is reduced from 28 bits to 2.84 bits 2.84 bits

14. October 13, 2003 Sheng-Shih Wang Simulation --- Overhead vs. Energy Savings  Net energy saving MAC header saving – computational overhead – protocol overhead for bits sent – protocol overhead for bits received

15. October 13, 2003 Sheng-Shih Wang Simulation --- Overhead vs. Energy Savings (cont.)

16. October 13, 2003 Sheng-Shih Wang Conclusion  Limit the MAC address overhead Replace conventional MAC addresses by short link labels  Reduce the energy consumption