Recently, the Dynamic Spectrum Access (DSA) techniques are proposed to solve the problem of spectrum scarcity and help to use the limited spectrum resource as effectively as possible. The current ongoing spectrum reform opens up the possibilities to exploit the DSA techniques. This paper aims to provide a critical review on the various ongoing efforts towards the use of DSA concept for the frequency management of future wireless communications systems, especially from the Cognitive Radio (CR) perspective. The CR aims for an efficient and dynamic access to the spectrum, and provides a new method of spectrum management. This paper also highlights the various challenges associated with CR in order to realize the concept of DSA.
This chapter specifies a concise review of recent research and development in the context of reconfigurable antenna. An attempt has been made to elaborate the distinct types of the 5G reconfigurable antenna with vital technique of the reconfigurability since from its evolution. Several significant prospects of 5G antennas are described to enhance antenna characteristics. Some basic concepts, theories, advantages, disadvantages, applications, and requirements of the Adaptive and MIMO antenna are discussed along with historical accomplishments. These systems can be the promising candidates for next generation network. This paper also provides a futuristic glimpse of UM-MIMO for 6G purpose.
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