| Summary: | 博士 === 國立清華大學 === 通訊工程研究所 === 106 === To enhance system throughput and robustness, the concept of multi-resolution services, widely used in broadcast systems, allows the receivers that are located farther away from the source and experience bad channel conditions to receive at least a basic quality of service; the receivers with good channel quality receive a higher quality of service. Hierarchical modulation (HM) is one practical way to achieve multi-resolution services, which consists of multiple transmitted data streams with different degrees of protection based on their importance; that is, the most important information (known as the base bits) can be recovered by all receivers, while the less important information (known as the refinement bits) can be recovered only by receivers with better reception conditions.
In wireless communications, to mitigate fading effect and to extend service coverage, cooperative communication is a promising technology that provides cooperative diversity via the assistance of relay transmission. To meet the growing demand for multimedia communications, it is expected that the incorporation of multi-resolution services and cooperative communication will gradually become the major transmission mechanism in next-generation wireless communication systems. Therefore, in this dissertation, we focus on improving the overall performance of multi-resolution services, especially the reception performance of the refinement bits, for users with poor channel conditions by using relay-assisted transmission. In the first part of the dissertation, motivated by the drawbacks of the existing schemes, we propose the concept of protection level exchanging for the relay node to greatly enhance the protection of the refinement bits, and design the optimal constellation mappings and assign the optimal constellation parameters for the source node and the relay node, respectively. This scheme is referred to as the protection level exchanging with re-mapping (PERM).
Furthermore, signal space diversity (SSD) is also a technique commonly used to combat the fading effect by the additional modulation diversity in wireless communications. Therefore, in the second part of the dissertation, to further enhance overall transmission quality, we incorporate the SSD technique in cooperative networks with HM. Unlike a conventional SSD approach that directly performs the rotation matrix on the superimposed constellation, which leads to a limitation of the selectivity in search of the rotation angle, we propose the concept of multiple-layer rotation (MLR) that each layer, respectively, rotates its own angle on the corresponding constellation before performing constellation superposition to increase the degree of freedom of the rotation angle in the design.
As expected, based on the simulation results, the proposed PERM scheme and MLR scheme can lead to significant improvement gains on the refinement layer.
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