| Summary: | 碩士 === 國立高雄海洋科技大學 === 電訊工程研究所 === 100 === In the past decades, cooperative communications technologies have gained significant attention in wireless networks. With the introduction of relays, an auxiliary channel, the relay channel, to the direct channel between the source and destination can be generated. That is, the relays help forwarding the signal from the source to the destination. As a result, spatial diversity which ameliorates the frame error rate is generated via the help of relay channel. On the other hand, cooperative scheme leads to longer transmission time which can considerably degrade the performance. Thus, there is always a tradeoff between saturation throughput and saturation delay. In order to obtain the optimal system performance, we utilize the cost function which is the ratio of throughput to delay to tradeoff the system performance.
In this thesis, we evaluate the saturation throughput and saturation delay of the Markov chain model with direct/cooperative transmission strategies. Moreover, the cost function is introduced to tradeoff the system performance to determine the optimal strategy for adopting the cooperative transmission, and then we extend the model to support applications with quality of service (QoS) requirements. In order to improve the efficiency, TXOP and Block Ack mechanisms which allow multiple consecutive frame exchanges during the TXOP duration are defined in IEEE 802.11e standard. We show the performance in term of saturation throughput, saturation delay and total throughput of the model. However, there is no assurance that both mechanisms can give a better tradeoff between throughput and delay. Numerical results show that TXOP mechanism is generally suitable for high traffic condition and Block Ack mechanism is suitable for large TXOP duration because it reduces the ACK transmission overheads and aggregating the acknowledgments reduces the control overheads.
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