Research On The QoS And Energy-saving Mechanisms In 802.16/WiMAX Systems

In the past 20 years, broadband wireless access technologies have being developed rapidly. Various advanced tools and methods in the wireless communication field were introduced to it in order to get higher spectrum efficiency and to support more kinds of services as well as to achieve better QoS. The typical broadband wireless access technology is the IEEE 802.16 standards which are proposed for the need of the last mile broadband wireless access. It not only integrates the mobility and flexibility of Wi-Fi, but also possesses high bandwidth features and relatively better QoS as the traditional wire broadband access technologies such as DSL and Cable Modem.One of the important features of IEEE 802.16 standards is the QoS grantee, which can make the network operate-able and manageable. So the IEEE 802.16 standards define a QoS mechanism that can supports different service level in its MAC. But it can't be put into practice directly because it does not indicate a complete solution for access control and packet scheduling. The 802.16e standard becomes to support mobile stations which are usually powered by battery. So the 802.16e standard defines sleep mode to save the mobile station's energy. But it neither indicates how to choose the parameters of the sleep mode nor evaluates the performance of the sleep mode. Therefore, this dissertation presents deeply studies from two aspects: the QoS mechanism and energy-saving mechanism. The main contributions of this dissertation are as follows:(1) Proposed a fair connection access control scheme for 802.16/WiMAX networkThe IEEE 802.16e standard provides Quality of Service (QoS) guarantees for users based on the conception of connection-oriented service. However, fairness has not been considered in existing connection admission control solutions, which is very important for user experience. This dissertation proposes a fair connection admission control scheme (FCAC) to improve the system's fairness on bandwidth allocation to users by setting a dynamic admitting threshold. Simulation results show that FCAC can improve service fairness for users without degrading the performance of the system.(2) Theoretically analyzed the performance of the sleep mode under the scenario the mobile station has both real-time service and non-real-time service, then proposed a Cooperative Power Saving MechanismWhen a mobile station with real-time and non-real-time services enters sleep mode, both Power Saving Class of type I and Power Saving Class of type II are activated. In this dissertation, we theoretically analyze the performance of the sleep mode, and find that due to the asynchrony of the listening windows the efficiency of power saving is very poor. Then we propose a COoperative Power Saving Mechanism (COPS) to resolve this problem. The basic idea behind COPS is to synchronize the listening windows of different power saving classes cooperatively. Furthermore, we analyze the performance of COPS in the multi-service environment and give closed-form expressions of performance metrics. Simulation results validate our analysis and show that COPS not only improves the energy efficiency but also reduces the average frame response time.(3) Proposed an enhanced power saving mechanism for multiple users with real-time services in 802.16eIn the 802.16e system, when multiple Mobile Stations (MSs) with real-time services enter sleep mode, the efficiency of power saving is impacted by the competition of the data scheduling in the overlapping listening windows. This dissertation analyzes the impaction and proposes an enhanced power saving mechanism. The proposed mechanism tries to make the listening windows of different MSs lie dispersedly and balance the system load among OFDM frames by adjusting the start time of sleep mode of the new connection. The simulation result shows the proposed mechanism not only improves the energy efficiency but also decreases the signaling overhead as well as improves the OoS of the network.(4) Analyzed the relation between sleep mode and data scheduling, then proposed an energy efficient scheduling schemeWhen multiple mobile stations (MSs) with real-time services are in sleep mode, the scheduling result of the Base Station (BS) not only determines the QoS of the services, but also impacts the average energy efficiency of the network. This dissertation focuses on this problem and proposes an energy efficient scheduling mechanism. The proposed mechanism first tries to smooth the input of the scheduler by making the listening windows of different MSs lie dispersedly and balancing the system load among OFDM frames. Then it improves the widly used EDF mechanism and promotes the packets'priority of the sleeping MSs. The simulation result shows the proposed mechanism not only improves the energy efficiency but also decreases the signaling overhead as well as grantees the OoS of the network.