Cooperative relay design for energy efficient cell capacity improvements

The effect of relaying in terms of energy efficiency is an important and interesting issue in cellular communications. In this paper, two relaying schemes for uplink are analyzed and compared in the context of cellular systems: Simple relaying (SR), where a user is served either by a relay node or the base station, and Cooperative Relaying (CR), where a user is served by the relay node, the base station or both in a cooperative manner. For the relaying a specific relay network topology is proposed where the relay nodes are deployed at the edge of each cell. The two schemes are analyzed in terms of cell capacity, provided through bit error analysis, and energy efficiency, and are compared to a baseline scheme that is based on a macro network topology with no relays. Based on the proposed relay network topology and the Decode-and-Forward relaying mechanism, this study focuses on finding out the optimal access path between a user and its serving base station. The optimization is performed according to a utility function which targets to maximizing cell capacity and energy efficiency. By choosing the optimal access path while decreasing the energy consumption per user, both cell capacity and energy efficiency of the wireless network are improved. By means of numerical simulations, it is shown that the relay schemes fully outperform the baseline wireless network without relays in both cell capacity and energy efficiency. In all simulation scenarios the CR scheme is the best performing scheme showing a gain around 33% in terms of cell capacity and a gain around 190% in terms of energy efficiency on average over the baseline. Further improvements are expected by utilizing more efficient cooperative relay schemes which will be exploited in the future work.