Cognitive functions in wireless network nodes are useful for utilizing perplexing trade-offs among EE, performance, and practicality. Nodes combined with these cognitive functionalities, known as \textit{cognitive nodes}, can enhance network execution by environment-aware and self-aware operation capabilities. However, there are intrinsic challenges such as hardware complexity, algorithmic problems, and design trade-offs. These issues can be arranged into two general gatherings: \textit{CR inherent problems}, e.g. efficient sensing and spectrum access, and \textit{interworking issues} involving communications networks themselves and other infrastructural segments such as smart grids \cite{Ref5}. However, it is imaginedbelieved that adaptive and optimal operationoperations via cognitive nodes will benefit the overall ICT and the relevant interconnected systems. In this work, the case of CRs for green wireless communication systems is discussed, and the fundamental tradeoffstrade-offs for greening wireless communications by means of cognitive functions with a specific end goal to pass on the challenges against this objective is outlined.