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Item A study of QoS support for real time multimedia communication over IEEE802.11 WLAN : a thesis presented in partial fulfillment of the requirements for the degree of Master of Engineering in Computer Systems Engineering, Massey University, Albany, New Zealand(Massey University, 2006) Qian, KunQuality of Service (QoS) is becoming a key problem for Real Time (RT) traffic transmitted over Wireless Local Area Network (WLAN). In this project the recent proposals for enhanced QoS performance for RT multimedia is evaluated and analyzed. Two simulation models for EDCF and HCF protocols are explored using OPNET and NS-2 simulation packages respectively. From the results of the simulation, we have studied the limitations of the 802.1 le standard for RT multimedia communication and analysed the reasons of the limitations happened and proposed the solutions for improvement. Since RT multimedia communication encompasses time-sensitive traffic, the measure of quality of service generally is minimal delay (latency) and delay variation (jitter). 802.11 WLAN standard focuses on the PHY layer and the MAC layer. The transmitted data rate on PHY layer are increased on standards 802.1 lb, a, g, j, n by different code mapping technologies while 802.1 le is developed specially for the QoS performance of RT-traffics at the MAC layer. Enhancing the MAC layer protocols are the significant topic for guaranteeing the QoS performance of RT-traffics. The original MAC protocols of 802.11 are DCF (Distributed Coordination Function) and PCF (Point Coordinator Function). They cannot achieve the required QoS performance for the RT-traffic transmission. IEEE802.lle draft has developed EDCF and HCF instead. Simulation results of EDCF and HCF models that we explored by OPNET and NS-2, show that minimal latency and jitter can be achieved. However, the limitations of EDCF and HCF are identified from the simulation results. EDCF is not stable under the high network loading. The channel utilization is low by both protocols. Furthermore, the fairness index is very poor by the HCF. It means the low priority traffic should starve in the WLAN network. All these limitations are due to the priority mechanism of the protocols. We propose a future work to develop dynamic self-adaptive 802.11c protocol as practical research directions. Because of the uncertainly in the EDCF in the heavy loading, we can add some parameters to the traffic loading and channel condition efficiently. We provide indications for adding some parameters to increase the EDCF performance and channel utilization. Because all the limitations are due to the priority mechanism, the other direction is doing away with the priority rule for reasonable bandwidth allocation. We have established that the channel utilization can be increased and collision time can be reduced for RT-traffics over the EDCF protocol. These parameters can include loading rate, collision rate and total throughput saturation. Further simulation should look for optimum values for the parameters. Because of the huge polling-induced overheads, HCF has the unsatisfied tradeoff. This leads to poor fairness and poor throughput. By developing enhanced HCF it may be possible to enhance the RI polling interval and TXOP allocation mechanism to get better fairness index and channel utilization. From the simulation, we noticed that the traffics deployment could affect the total QoS performance, an indication to explore whether the classification of traffics deployments to different categories is a good idea. With different load-based traffic categories, QoS may be enhanced by appropriate bandwidth allocation Strategy.Item Performance study of IEEE 802.11p for vehicle to vehicle communications using OPNET : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Telecommunications and Network at Massey University, Auckland, New Zealand(Massey University, 2011) Sun, NingIEEE 802.11p is the recently finalised protocol located at the bottom of the Dedicated Short Range Communication (DSRC) protocol suite, which supports Intelligent Transportation System (ITS) applications for both road safety and added value communication purposes. It has evolved from widely applied Wireless Local Area Network (WLAN) standards and it cooperates with peculiar higher layer protocols in order to carry out inter-vehicle communication. In this thesis, we focus on the performance study of road safety communication as being the vital application in ITS, which is very necessary not only because IEEE 802.11p is a relatively new protocol but also because it heavily relies on broadcast mode, thus distinguishing itself from other 802.11 counterparts. With the aid of OPNET, a powerful commercial simulator, different scenarios have been deployed in which one or more variable factors are involved, such as vehicle number, data packet size, communication distance, vehicle fleet topology, etc., in order to find out their impacts on DSCR and characteristics of 802.11p. After analysing results data collected from hundreds of simulations, we found out that 802.11p represented a desirable performance in terms of latency and priority-oriented services throughout our simulation scenarios. However, packet collision caused by either media contention or hidden nodes turned out to be a relatively serious issue of vehicle communication and 802.11p seems in shortage of an effective mechanism to deal with it. What we can only hope is that under practical application, the media should always be lightly occupied and that there are few ACs with high priorities trying to contend resources simultaneously at any given time. Meanwhile, our analyses indicate that current 802.11p protocol might still need further modifications in order to address its inherent issues and enhance the communication performance.