Software-defined networking (SDN) is new network architecture that emerges as to implement network virtualization (NV) with vast features, especially when it is applied it in multi-tenant scenarios. The rapid growth of wireless network applications and services, let to adopt NVs into software-defined wireless network (SDWN). This is because wireless networks require specific features that can be hindered of implementing NVs such as updated location information, dynamic channel configuration, and rapid client re-association. This paper presents state-of-the-art NV methods for SDWN with the aim of highlighting issues and challenges of applying NVs techniques of SDN into SDWN. We discuss three SDN techniques that facilitate NV in the cloud, namely proxy-based virtualization, layer two prefixes-based virtualizations and programing language-based virtualization. Moreover, the paper points out the possibility of providing effective VNs in the SDWN architecture. We also taxonomies the SDWN proposed virtualization methods based on hypervisor controller in the different networks. Finally, the potential requirements and challenges and open issues of SDWN NVs are also identified and presented as the future directions in SDWN research.