QoS provisioning in energy-efficient cooperative networks with power assignment and relay deployment planning

The cooperative network is an energy-efficient technology to provide ubiquitous broadband access and quality-of-service (QoS). This paper investigates the tradeoffs among QoS, capacity, and power consumption in the cooperative networks. By adaptively selecting among the direct, relay, and cooperative transmission (TX) modes for users, we can enhance the capacity with lower transmission power. Furthermore, we determine the proper relay location and transmission powers of base station (BS) and relay station, so that more users can exploit the low-power two-hop TX modes to enhance the capacity and reduce the delay. In the real networks, if the packet queue is empty, the BS can be idle without sending (to save energy). Hence, we also properly increase the link capacity and idle probability to further reduce power consumption. We develop an analytical model to evaluate the delay, variance, capacity, idle probability, and actual power consumption in unsaturated traffic conditions. Then, we apply an optimization approach to analytically determine the optimal relay location and transmission powers, aiming to maximize the overall energy efficiency (EE) subject to the delay requirements. Numerical results show that the adaptive TX-mode selection scheme along with the joint power assignment and relay deployment planning can significantly enhance the capacity and reduce the power consumption. Then, the goal of QoS support can be achieved with higher EE.