| Summary: | 碩士 === 國立中興大學 === 資訊科學與工程學系所 === 99 === As multimedia applications become more prevalent in wireless networks space, the support as quality of service(QoS) requirements becomes increasingly important. To achieve this issue, 3G mobile communication systems based on Wideband Code Division Multiple Access(WCDMA) was proposed to offer high data capability and variable-rate services. Downlink traffic volume generated by applications in WCDMA systems is often inherently bursty in nature. Downlink-Shared Channels(DSCH) are more appropriate to transmit bursty packets, because it allows many users to share an Orthogonal Variable Spreading Factor(OVSF) code set. Dynamic Priority Assignment(DPA) was presented. It takes into account delay sensitivity of packets and signal interference ratio(SIR) to share the code set, and uses the delay divided by the delay threshold of a packet to be its transmission priority. However, DPA does not consider packet loss rate and bandwidth utilization, and it may waste bandwidth for empty queues.
In this thesis, we propose a Residual-Lifetime-Aware Bandwidth Allocation(RLBA) scheme for WCDMA systems. Through a cross-layer framework, RLBA provides QoS differentiation services based on delay sensitivity, and it is intended to minimize the packet loss probability. It uses the residual lifetime of a packet as transmission priority; we suppose that, for instance, a packet with one-slot delay and two-slot delay threshold should be as urgent as a packet with two-slot delay and three-slot delay threshold. The proposed RLBA scheme considers rate assignment according to the backlogged packets in a queue. It solves the bandwidth waste problem and effectively reduces average packet delay through bandwidth utilization. Simulation results show that RLBA outperforms DPA in terms of packet loss rate and average delay.
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