IEEE 802.11 WLAN cannot guarantee the QoS of applications, thus admission control has been proposed as an essen-tial solution to enhance the QoS. Packet delay and throughput are commonly employed as assessment criteri...IEEE 802.11 WLAN cannot guarantee the QoS of applications, thus admission control has been proposed as an essen-tial solution to enhance the QoS. Packet delay and throughput are commonly employed as assessment criterions to determine whether a new connection can be admitted into the WLAN. Considering the real network condition, the analytical model is presented in this paper, which is aimed to evaluate the packet delay and throughput performance of IEEE 802.11 WLAN in nonsaturated conditions, taking into account diverse transmission rates and diverse traffic flows (i.e. flows with different packet sizes and arrival rates) simultaneously. This model is based on Markov chain and the theoretical predictions are verified by simulation in OPNET 14.5. We also analyze the influences of transmission rate diversity and traffic flow diversity on throughput performance. It is observed that, the presence of even one station with lower transmission rate can cause a considerable degradation in throughput performance of all the stations when they have the same packet size and arrival rate. Higher system throughput can be achieved if lower transmission rate stations transmit packets with smaller size or arrival rate.展开更多
In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch mo...In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch model was improved by adding different slow probabilities, turning deceleration rules and modified lane changing rules. The relationship between the saturated flow rate of stretching-segments and adjacent lanes was tested in numerical simulation. The length of stretching-segment, cycle length and green time were selected as impact factors of the cellular automation model. The simulation result indicates that the geometrics design of stretching-segment and the traffic signal timing scenario have major effects on the saturated flow rate of the intersection approach. The saturated flow rate will continually increase with increasing stretching-segment length until it reaches a threshold. After reaching the threshold, the stretching-segment can be treated as a separate lane. The green time is approximately linearly related to the threshold length of the stretching-segment. An optimum cycle length exists when the length of the stretching-segment is not long enough, and it is approximately linearly related to the length of stretching-segment.展开更多
文摘IEEE 802.11 WLAN cannot guarantee the QoS of applications, thus admission control has been proposed as an essen-tial solution to enhance the QoS. Packet delay and throughput are commonly employed as assessment criterions to determine whether a new connection can be admitted into the WLAN. Considering the real network condition, the analytical model is presented in this paper, which is aimed to evaluate the packet delay and throughput performance of IEEE 802.11 WLAN in nonsaturated conditions, taking into account diverse transmission rates and diverse traffic flows (i.e. flows with different packet sizes and arrival rates) simultaneously. This model is based on Markov chain and the theoretical predictions are verified by simulation in OPNET 14.5. We also analyze the influences of transmission rate diversity and traffic flow diversity on throughput performance. It is observed that, the presence of even one station with lower transmission rate can cause a considerable degradation in throughput performance of all the stations when they have the same packet size and arrival rate. Higher system throughput can be achieved if lower transmission rate stations transmit packets with smaller size or arrival rate.
基金Projects(50422283,51208054) supported by the National Natural Science Foundation of China
文摘In order to analyze the impact of stretching-segment on the saturated flow rate of signalized intersection approach, an improved cellular automation model was proposed to estimate its saturated flow rate. The NaSch model was improved by adding different slow probabilities, turning deceleration rules and modified lane changing rules. The relationship between the saturated flow rate of stretching-segments and adjacent lanes was tested in numerical simulation. The length of stretching-segment, cycle length and green time were selected as impact factors of the cellular automation model. The simulation result indicates that the geometrics design of stretching-segment and the traffic signal timing scenario have major effects on the saturated flow rate of the intersection approach. The saturated flow rate will continually increase with increasing stretching-segment length until it reaches a threshold. After reaching the threshold, the stretching-segment can be treated as a separate lane. The green time is approximately linearly related to the threshold length of the stretching-segment. An optimum cycle length exists when the length of the stretching-segment is not long enough, and it is approximately linearly related to the length of stretching-segment.
