Joint power assignment and relay location design for cooperative power-efficient networks with adaptive transmission mode selection

Cooperative transmission is a power-efficient transmission technique, with the advantages of diversity and short-range communications. In this paper, we develop joint transmission power and relay location design for the cooperative networks. We investigate the impacts of transmission (TX) mode, transmission power, and relay location on the capacity and power consumption. Besides, we develop TX-mode adaptation schemes for the users to adaptively select a proper TX mode among the direct, relay, and cooperative TX modes. To achieve the goals of saving power and enhancing capacity, we apply an optimization approach to jointly determine the optimal relay location and transmission power of BS and RS; aiming to maximize energy efficiency under the cell capacity and link reliability requirements. We compare the scheme with joint power and relay location design, and the schemes with only transmission power or relay location design. Simulation results show that the scheme with joint optimal design can significantly enhance the energy efficiency, compared to the other two design schemes. We compare the throughput-oriented and signal-strength-oriented TX-mode selection rules. It is shown that the throughput-oriented TX-mode adaptation schemes outperform the signal-strength-oriented schemes.