1. Spatial Backoff in Wireless Networks
Xue Yang
Nitin Vaidya
University of Illinois at Urbana-Champaign
Work-in-Progress Session, Sigcomm 2005

2. Medium Access Control Shared wireless channel
Need mechanisms to resolve contention

3. Temporal Contention Resolution
Transmissions compete for time
Separate transmissions in time B A

4. Traditional View Contention level a given
Adapt behavior to given contention level
Examples: Aloha Ethernet IEEE

5. Alternate View: Spatial Contention Resolution
Transmissions compete for space
Space “occupied” by a transmission can be controlled to control temporal contention

6. Controlling Temporal ContentionB

7. Controlling Temporal Contention
“Space”
occupied
by A A C B
Circular shape
only for
convenience

8. B A

9. Controlling Temporal ContentionB

10. B A
Smaller
occupied
space B A

11. Spatial Contention Resolution
Control occupied space by adapting transmit rate/power/carrier-sensing
Goal:
Occupied space Desired contention level

12. Implementing Spatial Contention Resolution
Example:
Joint adaptation of transmission rate and carrier-sense threshold
Adapting one parameter insufficient to suitably control space

13. www.crhc.uiuc.edu/wireless nhv@uiuc.edu
For more information