The 'not yet officially defined' 5G standard leads to the consequence that its relevant technological innovation is still widely open. For identifying innovations opportunity, we should discover the specific technical area to contribute to the technological development of 5G. This paper dicusses a framework answering the main question: In which technological area one may contribute to the innovation? The answer shall benefit countries, firms, universities and research institute which intends to contribute to the formulation of official 5G standard. First, we reviewed the key technologies of 5th generation mobile communication technology (5G). Ubiquitous and interoperability of the network are main technical focus. A flat IP-based network concept was reviewed, as well as cognitive radio technology to reach the terminal which have artificial intelligence. BDMA technology was proposed to help achieving system efficiency in terms of multiple access system. Second, we identified technological challenges, focusing on the issues related to security and problems to deal with limited frequency spectrum resources. Subsequently, we mapped the innovation opportunity based on technical area which is recently published in research article. We concluded that innovation opportunities lies on the research regarding security, network, technological implementation and applications issues.