Research On The Key Technologies Of Quality Of Service In Wireless Multimedia Networks

With the development of wireless communication technologies, deploying multimedia services on wireless networks even in mobile environments is becoming reality. However, compared with wired networks, wireless networks have some limitations such as the shortage of the radio spectrum resource, diversity of wireless channels, limited transmit power of terminals and base stations. Furthermore, the mobile terminal has requirement of low power consumption and portability. How to improve radio resources usage, how to guarantee quality of service and allocate resources fairly among users, and how to increase the profit of service providers, are key issues of QoS and system design in wireless multimedia networks.ITU defines quality of service as the collective effect of service performance which determines the degree of satisfaction of a user of the service. There are three distinct, but interrelated notions: intrinsic quality of service, perceived quality of service and assessed quality of service. Intrinsic quality of service is achieved via the technical design of the transport network and terminations, and via provisioning of network accesses, terminations, and communication links. Intrinsic quality of service is the most important portion of quality of service; it is similar to the concept of network performance defined by ITU and the concept of quality of service defined by IETF.There are two typical wireless multimedia networks researched in thisdissertation: UMTS and IEEE 802.11. The research consists of four aspects: the QoS. and radio resource management of UMTS; the improvement of radio resources usagein UMTS; the QoS mechanism of IEEE 802.11; the multi-rate operation and thehandover performance of IEEE 802.11.This dissertation is organized in a top-down manner. Firstly, basic concepts, models and frameworks of QoS and QoS related technologies are introduced. Secondly, QoS related key issues of wireless multimedia networks are pointed out. Finally, main contributions of this dissertation are presented in detail.In chapter 1, basic concepts and models of QoS, as well as IP QoS models, IP traffic classes and IP transfer performance requirements are introduced. Then the policy based QoS and the policy framework are illustrated. At last, QoS related key issues of wireless multimedia networks and main contributions of this dissertation are presented.In chapter 2, after introducing the QoS model and the radio interface protocol architecture of UMTS, the transport block scheduling based uplink load control scheme is proposed and researched carefully. The load control scheme consists of a rate-feeded load control algorithm and two transport block scheduling algorithms. The proposed uplink load control scheme is validated by massive simulation.Chapter 3 studies the improvement of radio resources usage in UMTS. In the first part, an optimized retransmission scheme of UMTS streaming services is proposed to avoid playout interruption caused by RLC retransmission at fixed channel rate. Simulation and analytical results show that the proposed scheme achieves better QoS and decreases 22% of the required average transmit power of the base station. In the second part, the performance of Robust Header Compression applied to UMTS is evaluated, and voice activity detection in the multi-service environment is taken into account. Moreover, the perspective of ROHC is introduced.Chapter 4 researches on QoS of IEEE 802.11 wireless LANs. To maintain a stable system and keep fairness among users, a transmission time based admission control algorithm is proposed and a polling scheme is recommended. Based on the proposed admission control algorithm, performances of real time services in IEEE 802.11a and IEEE 802.11b are evaluated respectively. In order to enhance the polling efficiency, a multi-queue-based single loop polling algorithm is proposed, which has better performances compared with EDCF of IEEE 802. 11e.Chapter 5 focuses on the multi-rate operation and handover performance of IEEE 802.11. The different location of a station leads to different channel condition, so the channel rate may be variable. To increase the throughput of the BSS, a contention window based rate differentiation scheme is proposed. Performances of TCP and UDP traffics are evaluated respectively. According to simulation results, the throughput of the BSS increases significantly and fairness of stations is well...