1. Rate-Adaptive MAC Protocol in High-Rate Personal Area Networks Byung-Seo Kim, Yuguang Fang and Tan F. Wong Department of Electrical and Computer Engineering University of Florida WCNC 2004

2. Agenda Introduction Introduction High-rate WPAN(IEEE 802.15.3) High-rate WPAN(IEEE 802.15.3) Proposed MAC protocol Proposed MAC protocol Performance Evaluation Performance Evaluation Conclusion Conclusion

3. Introduction WPAN Radio range of is around 10 meters Next technology of WPAN is targeted to consumer electronics and portable communication devices Higher data rates Higher data rates IEEE 802.15.3 Task Group (TG) High-Rate (HR) WPAN

4. Introduction HR WPAN Target applications A multimegabyte data file transfer Image and music files Distribution of real-time video and high-quality audio. Up to 55Mbps TDMA-based MAC protocol

5. Introduction HR WPAN Five different data rates Selecting a data rate according to the channel condition. Rate adaptation The mechanism for choosing data rate is not clearly defined in the IEEE 802.15.3 standard

6. Introduction Author proposes A rate adaptive MAC protocol for HR WPAN. A scheme using a constant physical (PHY) frame length Regardless of the data rate Achieving a better performance and an efficient use of channel time.

7. High-Rate WPAN(IEEE 802.15.3) Nodes in HR WPN are Communicating on a centralized and connection-oriented adhoc networking topology Piconet Piconet controller (PNC) Devices (DEVs)

8. High-rate WPAN(IEEE 802.15.3) A TDMA-beasd superframe structure is adopted in the IEEE 802.15.3 standard provide support for multimedia QoS Optional, use for short and non-QoS data and command frames Channel Time Allocation, Assigned by PNC

9. High-rate WPAN(IEEE 802.15.3) Two methods to obtain channel condition information and to select a data rate for transmission. Periodically transmit the channel request command to a target DEV. Evaluated by the presence or absence of ACKs for the transmitted frames

10. Proposed MAC protocol-motivation Using the PHY layer parameter achieves the higher performance gain Evaluated over WLAN environment A source DEV communicates directly with a target DEV Channel estimation and the rate selection have to be done by a pair of DEVs PNC needs to know the selected data rate in order to allocate an optimal channel time

11. Proposed MAC protocol- motivation Frames within a CTA may experience different channel quality Leads to a rate change

12. Rate-Adaptive MAC protocol for IEEE 802.15.3 Data and acknowledgement frames are used for rate adoption Rate-Adaptive Acknowledgement (RA-ACK) frame If the selected rate is not the same as the rate of the received frame Slightly change Rate subfield 101

13. Rate-Adaptive MAC protocol for IEEE 802.15.3 No information of a rate and a channel condition before the first frame transmission Node requests a CTA with an initial data rate May be the lowest rate When the data rate needs to be changed Source DEV and the PNC will hear the first RA-ACK frame from the target DEV.

14. Rate-Adaptive MAC protocol for IEEE 802.15.3 In the IEEE 802.15.3 standard, when the transmission of a data frame fails No ACK frame is sent back to the source DEV. Caused by a channel quality change When the rate needs to be changed even in the case of the transmission failure Target DEV sends the RA-ACK to the source DEV

15. Rate-Adaptive MAC protocol for IEEE 802.15.3 PNC PNC Modifies the currently allocated channel time for the communication link with the updated data rate Hears a RA-ACK frame Broadcast through a beacon frame RA-ACK frame is transmitted with the highest possible power Power control mechanism is applied to the communication of the pair of DEVs

16. Constant PHY frame length varies Using rate adaptation with a fixed MAC frame length, the length of a PHY frame varies according to the data rate In general, it is assumed that a channel is static during one frame transmission The channel is constant even during the transmission of a PHY frame at the lowest data rate More information bits can be transmitted at the higher data rates during the same period as that of a PHY frame transmission at the lowest data rate

17. Constant PHY frame length PHY frame length needs to be kept constant Regardless of the data rate

18. Constant PHY frame length to maintain a constant PHY frame length, the MAC frame payload size at the desired rate R Symbol Rate Frame Check Sequence

19. Constant PHY frame length Using the scheme of uniform PHY frame length reduces Number of PHY frames Overheads are reduced caused by the preamble, PHY/MAC headers, two SIFSs, and ACK frame produced by one data frame transmission

20. Performance Evaluation Assume all DEVs in a piconet have large files to be transferred Size of the file Uniformly distributed over the range from 500K bytes to 3M bytes at each node Each CTA are evenly divided for all DEVs in a superframe All nodes are uniformly distributed in the coverage area of a piconet 10 meter radius

21. Performance Evaluation Throughput comparison Protocol with RA-ACK and constant PHY frame length (RA-ACK-CPF) Protocol with RA-ACK and constant MAC frame length (RA-ACK-CMF) Protocol with fixed data rate (FDR) Once the initial data rate is chosen, a rate change is not allowed until a communication between two DEVs finishes

22. Performance Evaluation K is the strength of the line of the sight component of the received signal.

23. Performance Evaluation Rate of the number of CTAs experiencing the data rate change among total number of CTAs

24. Performance Evaluation

26. Conclusion A rate-adaptive MAC protocol with a constant PHY frame length for HR WPAN is proposed Simulation results show that the proposed protocol gives a 58% throughput gain over the non rateadaptive MAC protocol in IEEE 802.15.3.