Transmission time minimization of an energy harvesting cognitive radio system

Telecommunication systems consume significant amount of energy from the grid. Energy harvesting wireless systems utilize energy from the environment and provide a green solution. On the other hand, cognitive radio (CR) wireless systems harvest spectrum from licensed users reducing spectrum crunch. These two techniques can be synthesized in an energy harvesting cognitive radio (EHCR) system to efficiently manage precious resources, i.e., power and spectrum. However, since the availability of both spectrum and energy is not deterministic, such a system can suffer from large delay at the transmission stage. This paper aims at providing an exact solution to the transmission time minimization problem of an EHCR system. The challenge comes from the multiple constraints. In addition to the available energy and spectrum constraints, the CR system will have to have peak power constraint to avoid interference to the licensed user. This results in a non-convex mixed-integer optimization problem for which we develop an exact solution using geometric water-filling with peak power constraints (GWFPP). We also use a recursion machinery to solve the delay minimization problem. Such a system will save energy for the power grid and satisfy user with low-latent communication. Numerical example and complexity analysis illustrate exactness and efficiency of our proposed algorithm.