MAC for Dedicated Short Range Communications in Intelligent Transport System

1. MAC for Dedicated Short Range Communications in Intelligent Transport System Jing Zhu and Sumit Roy University of Washington Presented by Long Vu CS598JH – Fall 07

2. Vehicle to Vehicle Communication through Dedicated Short Range Communication (DSRC) How can we adapt 802.11 MAC to support DSRC Applications?

3. Next… How can we adapt 802.11 MAC to support DSRC Applications? • DSRC and DSRC Applications • Challenges of 802.11 in DSRC Environment • Communication Modes • Blocking Propagation • DCF/PCF over High Mobility • What Do We Expect from Authors? • Summary of 802.11 MAC • Bianchi’s saturated throughput • Fairness • Quality of Service • High-efficiency data transmission

4. DSRC and DSRC Applications • DSRC • 75 MHz in the 5.9 GHz band • Suitable to deliver rich media content at short to medium ranges • Communication modes • Vehicle to Vehicle • Vehicle to Roadside • DSRC Applications • Safety App • Convenience App • Commercial App

5. Next… How can we adapt 802.11 MAC to support DSRC Applications? • DSRC and DSRC Applications • Challenges of 802.11 in DSRC Environment • Communication Modes • Blocking Propagation • DCF/PCF over High Mobility • What Do We Expect from Authors? • Summary of 802.11 MAC • Bianchi’s saturated throughput • Fairness • Quality of Service • High-efficiency data transmission

6. Communication Modes High download rates in short duration Different acceleration among nodes

7. Blocking Propagation

8. DCF/PCF over High Mobility • Vehicle to Roadside • Short communication time, variable rate • High mobility • Vehicle to Vehicle • Cars change speed differently  break connectivity

9. Next… How can we adapt 802.11 MAC to support DSRC Applications? • DSRC and DSRC Applications • Challenges of 802.11 in DSRC Environment • Communication Modes • Blocking Propagation • DCF/PCF over High Mobility • What Do We Expect from Authors? • Summary of 802.11 MAC • Bianchi’s saturated throughput • Fairness • Quality of Service • High-efficiency data transmission

10. What Do We Expect from Authors? • This is a survey paper Summary of 802.11 MAC design Challenges of 802.11 in DSRC Environment How to adapt current 802.11 MAC to support DSRC? Missing block

11. Next… How can we adapt 802.11 MAC to support DSRC Applications? • DSRC and DSRC Applications • Challenges of 802.11 in DSRC Environment • Communication Modes • Blocking Propagation • DCF/PCF over High Mobility • What Do We Expect from Authors? • Summary of 802.11 MAC • Bianchi’s saturated throughput • Fairness • Quality of Service • High-efficiency data transmission

12. Bianchi’s Saturated Throughput – DCF Modeling • Optimal Contention Window Size • Tc: collision duration • n: number of terminals • s: slot time (20 micro sec) • Using RTS/CTS

13. Fairness in 802.11 MAC • Per stream • Each stream is given an equal share of the channel capacity • It is hard to implement in real/distributed systems • Per node • All nodes have the same contention window • Publishing contention window results in overhead • Difficult to apply in DSRC • Highly dynamic: hard to publish contention window • Multi-hop: more overhead

14. QoS Support in 802.11 MAC • Differentiated/Prioritized Services • High priority for real time, bursty and low delay nodes/flows • Best effort nodes/flows • Contention Window Manipulation (CWM) • Short CW to low-delay and real time flows • Apply in DSRC • CWM can be used

15. High-efficiency Data Transmission • Reducing overhead of 802.11 • An RTS/CTS handshake followed by multiple data packets • Reduce overhead of RTS/CTS itself Why RTS/CTS? Why not basic 802.11?

16. Conclusion • Pros • Challenges of 802.11 in DSRC environment • Highly dynamic • Multi-rates • Cons • Miss a very important block Summary of 802.11 MAC design Challenges of 802.11 in DSRC environment How to adapt current 802.11 MAC to support DSRC?