Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. Due to high speed of nodes and their frequent disconnections, it is difficult to design a MAC scheme in VANETs that satisfies the quality-of-service requirements in all networking scenarios. In this thesis, we provide a comprehensive evaluation of the mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay, as well as the impact of mobility factors. The study also presents a relation between the mobility factors and the respective medium access behavior. Moreover, a new unfairness problem according to node relative speed is identified for both broadcast and unicast scenarios. To achieve better performance, we propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. Extensive simulation results show the significant impact of mobility on the IEEE 802.11p MAC performance, an identification of a new unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.

Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. Due to high speed of nodes and their frequent disconnections, it is difficult to design a MAC scheme in VANETs that satisfies the quality-of-service requirements in all networking scenarios. In this thesis, we provide a comprehensive evaluation of the mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay, as well as the impact of mobility factors. The study also presents a relation between the mobility factors and the respective medium access behavior. Moreover, a new unfairness problem according to node relative speed is identified for both broadcast and unicast scenarios. To achieve better performance, we propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. Extensive simulation results show the significant impact of mobility on the IEEE 802.11p MAC performance, an identification of a new unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.

本研究以Stroop中文叫色作業，測驗兒童和成人在Stroop作業之練習和刺激向度分離等情形下，其干擾效果的變化情形。共執行兩個實驗，實驗一中的受試者先接受中性刺激和不和諧刺激的測驗，然後對兩類作業練習8日，其後再測驗一次，探討受試者在練習前、後之干擾效果的變化情形。另一組受試接受實驗二中，中性刺激、整合性不和諧刺激和分離性不和諧刺激等作業的測驗，藉以比較整合性干擾和分離性干擾的差異。兩組受試者皆接受文字閱讀的速度測驗。 結果發現，小學二年級兒童的Stroop干擾效果最大，六年級兒童次之，成人最小，這與之前文獻上所載的研究一致，同時也證實，練習確能降低干擾效果，但仍不能使其完全消失，且練習後，三組受試間的干擾效果已無顯著差異。在實驗二的結果顯著，刺激向度分離的干擾效果仍然存在，但比整合性干擾效果小，且受試者間的分離性干擾也沒有顯著差異。而所有受試的閱讀速度均快於叫色速度。 / The study was used the Stroop Chinese task to examine the course of the Stroop interference among second, sixth grade children and adults. Two experiments were conducted. In experiment I, participants were tested with neutral and incongruent tasks and practiced with the same tasks for the following 8 days. They were tested neutral and incongruent tasks again. Then examined the course of the Stroop interference among children of second, sixth grade children and adults, they were test with neutral and incongruent tasks again. Then examine the course of the Stroop interference in between children and adult during before and after practice. The other group of participants took part in experiment II. They were presented with three tasks consist of neutral, integrated and separated incongruent tasks. Then examine the difference of the interference among children of second, sixth grade and adult during integrated and separated incongruent tasks. Two groups of participants were presented word reading speed of task. The finding of the study was Stroop interference increased from the adults through the sixth grade children and finally to the second grade children is in line with previous finding. We have confirmed that although interference decreases with practice, it is very resistant to eradication. After practice, the interference between children and adults is not significant difference. In the experiment II, it was that separated Stroop stimulus showed interference, and the amount was relatively small. The interference of separated Stroop task among children of second, sixth grade and adults were not significant difference. All participants took longer to name color than to read words.