Date of Award

Summer 2012

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)



Committee Chair

Shaoen Wu

Committee Chair Department


Committee Member 2

Zhaoxian Zhou

Committee Member 2 Department


Committee Member 3

Nan Wang

Committee Member 3 Department



This thesis proposes a new medium access protocol for IEEE 802.11 wireless local area networks, which is called opp01tunistic medium access. The protocol changes the media access opportunities of nodes by adjusting the contention window dynamically according to the different bit rates. Thereby, the protocol can reduce collision and improve throughput significantly. The n·aditional IEEE 802.11 standards access channel with binary exponential back-off algorithm and all nodes choose the back-off interval from the same initial range. The new protocol in this thesis divides nodes as well as contention windows in proportion to data rate. It offers three methods to group nodes and contention window with different lower boundary or upper boundary. So, nodes can choose their back-off intervals distinguished based on their channel conditions. As a consequence, the nodes with better channel condition will get smaller back-off values, that enables these nodes win the contention with a larger probability. Besides, the protocol takes a data rate normalized average history throughput into the computation of contention window to achieve temporal fairness. The protocol has been implemented based on ath9k wireless driver and the experimental results show that the new protocol gets 20% more throughput compare to the 01iginal IEEE 802.11 n protocol. Besides, in order to verify the perfo1mance in a large network, some simulations conducted in NS-3 which shows proposed protocol have good performance as well.