CSE519 Embedded Networks Feb. 5, 2007 Su Jin Kim

1. Energy-Conserving Access Protocols for Identification NetworksBy Imrich Chlamtac, Chiara Petrioli, and Jason RediIEEE/ACM TRANSACTIONS ON NETWORKING, Feb. 1999 CSE519 Embedded Networks Feb. 5, 2007 Su Jin Kim

2. Overviews • Introduction • Current Access Protocols • Proposed Protocols • Energy-Analysis • Simulation Results • Conclusion • References

3. Introduction • Radio Frequency Identification Devices (RFID) and Infrared Identification Devices (IRID) • Small, Inexpensive, resource-limited • IDNET (IDentification NETwork) • Interconnected base stations • Large number of small low-cost wireless tags • Tags contain microprocessor power source, a RF receiver, transmitter, and some support logic. -> Active Tags

4. RFID Systems • Examples: Location tracking of the animals, Supply chain, Health-Care etc. • Characteristics • Scale: large • Cost: inexpensive • Size: small • Traffic: short, simple message → Important issues : Low Energy and Low Delay Requirements

5. Current Access Protocols (1) • Low Power Design • awake & sleep state • Random Access Protocol (Aloha) • The base stations send packets at random times • The tags awakes at random times • The probability of a tag and the base station being awake in the same slot is very low • High the energy consumption and packet delay

6. Current Access Protocols (2) • Classical TDMA • Assign a time slot to each tag • Low energy requirement • awake 1/N slots, N = # of tags in the system • High packet delay • Trade-off: the energy vs. delay • How frequently does a tag awake?

7. Network Model • N tags share a radio channel • Packet-oriented and packet length is constant • The time is slotted and the base station’s transmission is synchronized • Exactly one packet can be transmitting during each slot • Access Protocol • Transmission Scheduling: at the base station • The base station selects a packet for transmission from the arrival queue in each slot • Wake-schedule: at each tag • The tag determines the slots being awake

8. Grouped-Tag TDMA Protocols • Divide tags into m = • N = # of tags in the system • X = # of tags in the group • Assign each slot to one group • Increase the average energy consumption per slot • Decrease the average delay • Drawbacks • Tags continue to wake up cyclically • The packets’ destination distribution is heavily clustered, the performance can degrade severely

9. Directory Protocols • The base station • waits for k packets • Broadcast the directory which lists the destinations of the k packets • Transmit the actual packets • Tags • listen to the directory and find out when they wake up • When there is no group being transmitted, the tags wake up periodically every v slots • Trade-off • Small k, v: Low Delay, but High energy consumption • Large k, v: High Delay, but Low energy consumption

10. Pseudorandom Protocols • All tags • run the same pseudorandom number generator, but each tag has the unique seed • Determine their state (awake or sleep) based on a probability p • Stored state of the random number generator • The base station • Know the seeds of tags • Possible to determine the schedules of tags • Change p based on tags’ expected traffic rates • Good for the heterogeneous traffic patterns

11. Energy Analysis (1) • E: average percentage of slots in which a tag is awake • Grouped-Tag TDMA Protocols • E = • m = # of the groups in the system =

12. Energy Analysis (2) • Directory Protocols • E = • k = # of packets in the group k’ = the slots need for transmitting the directory • Pseudorandom Protocol • E = p

13. Simulation Results • 15,000 packets • N = 1000 tags • Inter-arrival rate, • I = 0.05, 0.2, 0.5 arrivals per slot

14. Classical Access Protocols * Random Access Only when p is high (> I), the system is stable * Classical TDMA Good Energy Consumption (0.001) Extremely Long Delay (≥500 slots)

15. Grouped-Tag TDMA with uniform destination distribution • X = large • High Energy Consumption • Low Delay • X = small • Low Energy Consumption • High Delay • FINDING the OPTIMAL X is IMPORTANT!

16. Directory Protocol with uniform destination distribution • k = large • Low Energy Consumption • High Delay • With given k, v = large • Low Energy Consumption • High Delay • FINDING the OPTIMAL k, v is IMPORTANT!

17. Pseudorandom Protocol with uniform destination distribution • Slightly worse than the grouped-tag TDMA • But, the difference decreases as I increases

18. Energy Conserving Protocols with I = 0.2

19. Energy Conserving Protocolswith wide Gaussian Destination Distribution • The performance of the grouped-tag TDMA degrades rapidly • The performance of the pseudorandom degrades very slightly

20. Energy Conserving Protocolswith narrow Gaussian Destination Distribution • With I = 0.5, the performance of the grouped-tag TDMA is completely unstable

21. Conclusion • Classical TDMA and Random (such as Aloha) Access Protocols are not appropriate for the RFID Systems

22. References • “Energy-Conserving Access Protocols for Identification Networks,” I. Chlamtac, C. Petrioli, and J. Redi, IEEE/ACM Transactions on Networking, Vol. 7, No. 1, Feb. 1999 • “Analysis of Energy-Conserving Access Protocols for Wireless Identification Networks,” I. Chlamtac, C. Petrioli and J. Redi, the Proc. of Int. Conf. on Telecommunication System, March 20-23, 1997 • “Extensions to the pseudo-random class of energy-conserving access protocols,” I. Chlamtac, C. Petrioli and J. Redi, the Proc. 2nd IEEE Int. Workshop Wireless Factory Communication Systems, Oct. 1997, pp. 11-16