A Joint Optimization Framework for Energy Harvesting based Cooperative CR Networks

The energy harvesting cognitive radio networks (EH-CRNs) are expected to play a key role in satisfying the demands of next generation wireless communications. In the underlay CRN, the secondary base station (SBS) is prohibited to transmit at high power to keep the interference temperature within acceptable limits. Thus, the transmission to a secondary user (SU) located far away from SBS may not be possible. In this paper, we investigate cooperative EH-CRNs where an SU close to the SBS harvests the energy and helps in relaying the data of a distant SU. The aim is to maximize the sum rate of the system subject to the limited power budget at the SBS and to the interference constraint of the primary network. We seek a joint optimization framework to distribute power among users at the SBS, power allocation for cooperative transmission, the time slot optimization for transmission of each user, and the power splitting (PS) ratio optimization for energy harvesting (EH) and information decoding (ID). The joint problem under various system constraints results in a non-convex optimization. The problem is first transformed to a convex optimization and then a joint solution is obtained from the duality theory and the simplex method. Further, two solutions, one under uniform power allocation with optimized time and EH while the other with uniform time and optimized power and EH, are also presented. Simulations are provided to validate the proposed optimization model.