Due to the emergence of numerous applications based on wireless applications the problem of spectrum scantiness is increasing day by day. The utilization of spectrum has increased to its maximum level. To tackle this issue the technology named cognitive radio was introduced to the rescue. The cognitive radio is an emerging technology that enables dynamic spectrum access in wireless networks. The cognitive radio is capable of expediently using the obtainable portions of a licensed spectrum to

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... rove the application performance for unlicensed users [1]. The opportunistic use of the accessible channels in the wireless environment requires dynamic channel assignment to efficiently utilize the available resources while minimizing the interference in the network. A lot of work has been reported in the literature so this paper presents a comprehensive survey on the current state-of-the-art, various technologies in which the cognitive radio technology can be used to enhance the performance to get better results are extracted in this paper. Open issues and emerging trends has been brought forward for the researchers working in the fields of wireless communication and network.