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

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

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 Task Group (TG) High-Rate (HR) WPAN

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

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 standard

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.

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

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

High-rate WPAN(IEEE ) 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

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

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

Rate-Adaptive MAC protocol for IEEE 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

Rate-Adaptive MAC protocol for IEEE 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.

Rate-Adaptive MAC protocol for IEEE In the IEEE 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

Rate-Adaptive MAC protocol for IEEE 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

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

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

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

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

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

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

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

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

Performance Evaluation

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