| Cooperative transmission, which utilizes the broadcast nature of the wire-less medium and the numerous nodes in a network, is an efficient way to realize the benefits of multi-antenna transmission with only one antenna at each node. Orthogonal Frequency Division Multiplexing (OFDM), which enables the high bit rates demanded by current and emerging applications, has been widely adopted in many current and next generation systems. In this work, we concentrate on using OFDM in a networking context to facilitate cooperation among relay nodes. In particular, obtaining the maximum benefits from cooperation in both single- and multi-source applications, in a well-designed OFDM system with the inherent frequency diversity, is investigated. Moreover, implementation issues, such as centralized and decentralized algorithms, computational complexity, and the required amount of channel state information (CSI), are also considered.;First, cooperative OFDM systems with limited CSI are investigated. Different relay/subchannel management strategies with different levels of CSI are proposed and compared. Then, we study selective relaying strategies for cooperative OFDM systems. Two relaying strategies, selective OFDM relaying and selective OFDMA relaying, are proposed for centralized and decentralized systems, respectively. These approaches are analyzed and compared with different transmission schemes. We also investigate resource allocation in single- and multi-source cooperative OFDM(A) systems. Subchannel permutation is proposed to improve the end-to-end performance. Different resource allocation algorithms with different algorithmic complexities are proposed and compared. Decentralized algorithms are also addressed.;Observing the broadcast nature of wireless transmissions, and the variable quality of wireless channels, we study routing strategies in multihop networks using a realistic channel model. Three routing strategies are designed to fully exploit the diversity gain provided by cooperation among relays with different amounts of communications overhead and with different algorithmic complexity. Later, we extend these three routing strategies to coded OFDM systems. A new metric is proposed to quantize the link quality between nodes, and the three routing strategies are re-designed according to the proposed link metric. |
