A simple recursive scheme for adjusting the contention window size in IEEE 802.11e wireless ad hoc networks

The IEEE 802.11e standard has been introduced recently for providing Quality of Service (QoS) capabilities in the emerging wireless local area networks. This standard introduces a contention window based Enhanced Distributed Channel Access (EDCA) technique that provides a prioritized traffic to guarantee the minimum bandwidth needed for time critical applications. However, the EDCA technique resets the Contention Window (CW) of the mobile station statically after each successful transmission. This static behavior does not adapt to the network state since it reduces the network usage and results in bad performance and poor link utilization whenever the demand for link utilization increases. This paper proposes a new adaptive differentiation technique for IEEE 802.11e Wireless Local Area Networks that takes into account the network state before resetting the contention window. In the new technique, the congestion level of the network is sensed by using previous CW values. Three other enhancement techniques that focus on network adaptation are also discussed. Their main limitations are the high complexity of the implemented algorithms and their slow adaptation to the network state when the channel experiences bursty traffic. The proposed technique is compared to the original differentiation techniques of IEEE 802.11a and IEEE 802.11e standards, as well as to the enhancement schemes. Results show that the proposed adaptive technique outperforms IEEE 802.11e and is comparable to the other enhancement schemes while maintaining relatively low complexity requirements.     

Knowledge,attitude, and behavior of students regarding 'mad cow disease'

The aim of the current study is to assess the knowledge, attitude and behavior of students enrolled at the American University of Beirut (AUB) in Lebanon, towards mad cow disease (MCD). Three hundred and fifty-six students (199 males and 157 females), ranging in age between 17 and 25 years were randomly selected from various majors and were asked to fill out a self-administered questionnaire. It was found that 99.7% of students had heard about MCD and 85.8% knew that the cow is the host for bovine spongiform encephalopathy (BSE). Seventy five percent reported that animals contract the disease through the consumption of meat and bone meal. Thirty-seven percent wrongly believed that MCD cases were reported in Lebanon and 89% were not satisfied with the measures undertaken by the Lebanese government to curb the disease. Eighty four percent were concerned about the disease and 72% stated having modified their eating habits accordingly. Moreover, students majoring in biology and other health-related majors knew significantly more about MCD compared with students majoring in non-health related majors. A surprising finding was that females were more likely to modify their eating habits than males. Hence, this study provides an insight into the knowledge, attitude, and behavior of AUB students towards MCD. A limitation of this study is that our sample is not representative of all university students in Lebanon. Future surveys should also target students enrolled in other universities in the country.