1. A Rate-Adaptive MAC Protocol for Multi-Hop Wireless Networks By Gavin Holland, Nitin Vaidya and Paramvir Bahl Presented by: Helal chowdhury Telecommunication Laboratory, university of oulu

2. Contents Introduction Receiver Based Auto Rate (RBAR) RBAR implementation Simulation Conclusions References

3. Introduction IEEE802.11 –Supports DSSS, FHSS, and IRDA at the physical layer. –RTS/CTS hand-shake. –Transmission rate 10Mbits/s. Rate Adaption –Rate adaption is the process of dynamically switching data rates to match the channel conditions. There are two aspects to rate adaption: –Channel quality estimation By Sender By receiver-> RBAR(Receiver Based Auto rate) –Rate Selection By Sender ->ARF(Auto rate Fallback) By Receiver -> RBAR(Receiver Based Auto rate) Why receiver based rate adaption –The goal of rate adaption is to provide optimum throughput. The motivations for RBAR Rate selection can be improved by proving more timely and more complete channel quality. Channel quality information is best acquired at the receiver. Transmitting channel quality information to the sender can be costly.

4. RBAR modified DCF Protocol D RTS : Reservation time (IEEE 802.11) D CTS : Reservation time D RSH : Final reservation Time  DCF: To coordinate the transfer of data packet.  NAV: To announce the duration of packet. D RTS : Tentative reservation time (RBAR)

5. RBAR EVENT FLOW S choose a data rate r1, using some heuristic, and sends r1 and the size of the data packet n in the RTS to R. A, overhearing the RTS, uses r1 and n to calculate the duration of the reservation, marking it as tentative. R, having received the RTS, uses some channel quality estimation and rate selection technique to select the best rate r2 for the channel conditions, and sends r2 and n in the CTS to S. B, overhearing the CTS, calculates the reservation using r2 and n. S responds to the CTS by placing r2 into the header of the data packet and transmitting the packet at the selected rate. If r1≠r2, S uses a unique header signaling the rate change. A, overhearing the data packet, looks for the unique header. If it exists, it recalculates the reservation to replace the tentative reservation it calculated earlier. S R B r1, n r2, n ACK A

6. RBAR MAC Header Framl control DurationDest. Address Source Address BSSIDSequnce control BodyFCS Framl control DurationDest. Address Source Address BSSIDSequnce control HCSBodyFCS IEEE 802.11 MAC Header RBAR MAC Header RBAR Reservation SubHeader

7. RBAR RTS/CTS Implementation Frame control DurationDest. Address Source Address FCS IEEE 802.11 RTS RBAR RTS Rate & Length Frame control DurationDest. Address FCS IEEE 802.11 CTSRBAR CTS Rate & Length  In RBAR, instead of carrying the duration of the reservation, the packets carry the modulation rate and the size of the data packet.  If there is rate mismatch between sender and receiver D RTS refer to as tentative reservation.  Final reservations are confirmed by the presence or absence of Reservation SubHeader (RSH).

8. RBAR PLCP Header SyncSFD SignalServiceLengthCRC 802.11 PLCP header Data Rate RSH Rate RBAR PLCP header  In standard 802.11, the PLCP header contains an 8 bit signal field.  In RBAR, the PLCP header has been divided into two 4 bit rate subfields.  Thus, the PLCP transmission protocol is modified as follows: when the MAC passes a packet down to the physical layer, it specifies two rates, one for the subheader and one for the remainder of the packet.

9. Simulation Model Error Model – Fast fading Channel model – Slow Fading Channel model Movement Model –random waypoint mobility pattern Trafic Model – CBR – FTP – ON/OFF Pareto source generating traffic

10. Slow fading Channel

11. Fast Fading Channel

12. Variable Traffic Source

13. Multi-Hop Performance

14. Conclusions Showed that RBAR improve network throughput. RBAR outperforms ARF.

15. References Gavin Holland, Nitin Vaidya, Paramvir Bahl, ” A Rate-Adaptive MAC Protocol for Wireless Networks,” Technical Report TR00-019, Dept. of Computer Science, Texas University. wsl.stanford.edu/~ee360/adaptiveMAC_Jie.ppt B. Sadeghi, V.Kanodia, A.Sabharwal, and E. Knightly,”Opportunistic Media Access for Multirate Ad Hoc Networks”, Department of Electrical and Computer Engineering, Rice University.