Energy Efficient Power Allocation in OFDM-Based CRNs with Cyclic Prefix Power Transfer

In this paper, we investigate resource allocation in OFDM based CRNs with cyclic prefix power transfer (CPPT). In this system, the secondary receiver (SR) can extract power from the cyclic prefix (CP) of the received signal and use the harvested energy for its own energy supply. Our objective is to find the optimal power allocation and CP size that maximize the energy efficiency (EE) of the secondary system, under the maximum primary user (PU) interference and the minimum harvested energy constraints. As the CP size will impact the interference constraints, the relationship between optimal power allocation and CP size is hard to be expressed by a function. In this paper, we solve the problem by two steps. First, we propose an efficient iterative algorithm to achieve the optimal power allocation for the EE maximization problem with a certain CP size, and then find the optimal CP size through a full-search method. The influence caused by the CP size on power allocation is illustrated by simulations and numerical results prove CPPT can improve the system utilization greatly compared with traditional methods.