The rapid growth of cellular networks raises enormous constraints to mobile operators, especially due to the limited frequency spectrum allocated to cellular networks. Due to the tremendous increase of mobile equipments like smart phones and the compelling services that offer broadband mobile, frequency reuse that characterizes cellular networks is not sufficient to overcome these issues. The recent discovery of white spaces in the spectrum becomes an open field full of new challenges. Here, the most challenging issue is to use the spare spectrum in a way to allow flexibility between licensed and unlicensed users. In fact, with the discovery of white spaces, licensed users have the preemptive right to access the spectrum when unlicensed users use the idleness of the spectrum to transmit. Cognitive radio technique brings opportunities to the spectrum management. In this thesis, we propose an analysis on the improvement of the spectrum usage. We consider the case of broadband cellular networks in cognitive radio. Our study will bench on three important axis. The first consist on the review of the cognitive radio cycle to make it more dynamic. We will design a cognitive cycle joined to the Radio Resource Management (RRM) to fit with the rapid changes in the spectrum. That will lead us to the second axis, where we will study the spectrum mobility as an important way to optimize spectrum usage. Here, we will concentrate on the spectrum handoff. During that analysis, we will propose a new spectrum handoff sequence based on the PRP M/G/1queuing network model. We will then introduce a new metric that allows better understanding of spectrum handoff sequences. On the third axis we will discuss the FEMTOCELL examining the contributions of FEMTOCELL to actual cellular networks, while minimizing interruptions between them. Additionally, we will analyze present contributions and evaluate the limitations they face. Finally we will propose a discussion topic based on the frequency reuse in FEMTOCELL and cognitive radio capabilities.