With the explosion of novel wireless applications

the increasing growth of spectrum requirement has outpaced available spectrum resources.Cognitive Radio Network (CRN) has emerged as a promising solution to address the above dilemma by dynamically sharing spectrum among users.Recently

CRN technology has attracted great research interests as well as efforts.In this paper

we review the state-of-the-art of spectrum allocation techniques in CRNs.We first illustrate the technical background of CRNs

and then analyze the key issues in spectrum allocation algorithms design.Following that we review the design rationale and technical feature of typical allocation models

and further investigate the implementation mechanism of classical algorithms for each model.Finally

we envision the possible issues for future work on spectrum allocation.