Abstract
A fundamental research problem of cooperative half-duplex relaying network is to find its capacity as well as a practical approach in order to achieve the capacity. In this thesis, the state-of-the-art review shows that the achievable rates have been derived as well as a capacity upper bound using max-flow min-cut theorem for the degraded channel with multiple parallel relays. However, the capacity of the relay channel for general case remains unknown. In the literatures, there are several relaying strategies having been developed to push the performance towards the capacity. However, the existing strategies can achieve the desired performance only when the full channel information is available at the source, which causes a large amount of signalling overhead and channel feedback. Another problem for the half-duplex relaying network is that it suffers a loss of spectral efficiency due to the orthogonality requirement for the relay transmission. Half-duplex orthogonal relay often utilizes dedicated resources to help source-to-destination communications, which results in reduced spectral efficiency and underutilization of the allocated bandwidth. The main contributions of this thesis are three-fold: First, we propose a novel relay selection algorithm based on mixed channel information. The proposed selection algorithm aims to reduce the signalling overhead of modulation-adaptive Decode-and-Forward (DF) relaying by exploiting statistical channel information. A novel semi-deterministic approach is proposed to perform joint rate-adaptation and best-relay selection. It is shown that the proposed algorithm can achieve a good trade-off between the spectral efficiency and signalling overhead. Second, to mitigate the error propagation effects of DF relaying, we propose a distributed turbo decoding algorithm exploiting the source-relay correlation with reduced complexity. By iteratively updating the decoding output of the turbo decoders, the proposed decoding algorithm can outperform the conventional selective DF relaying. Third, the relationship between the spectral efficiency and bandwidth dedicated to the relay is theoretically established. It is shown that, with the practical model of users’ channel usage, the spectral efficiency is maximized when the relay does not have any dedicated bandwidth. Moreover, this theoretical result is elaborated through extensive investigation of the DF relay adopting various MAC-layer protocols including round robin resource scheduling, best-user selection, incremental relaying employing type II hybrid automatic repeat request, as well as joint channel and power allocation. Our Monte Carlo simulations show that the DF-relay with coordinated spectrum sharing improves the spectral efficiency by at least 50% in comparison with the relay with dedicated bandwidth allocation.