摘要：Summary Due to the explosive growth of wireless services with high-speed and better quality-of-services, the demand of spectrum is increasing proportionally. In addition to this, the fixed spectrum allocation scheme of the desired radio frequency bands also creates the spectrum scarcity problem. However, the possible solution of these problems is the cognitive radio (CR) communication technology, which is an emerging area of the wireless communication and relies on the dynamic spectrum access (DSA)/opportunistic spectrum access (OSA) as well as spectrum sharing (SS) techniques. The DSA/OSA allows CR users to access the spectrum opportunistically, when the primary/licensed user (PU) is idle, however the SS allows the CR user to utilize the spectrum in the presence of PU with certain power constraints. The power constraints are applied on the cognitive user/secondary user (SU) transmitter to keep PU's communication impervious. In the CR technology, the user needs to sense its environment and adapt communication parameters on the basis of environmental conditions, which are always random in nature. Therefore, the implementation of cognitive radio with imperfect channel state information is an emerging issue that needs to be analysed. In this technical review, we have presented the potential growth in the area of power allocation strategies in CR communication with perfect and imperfect channel state information. Further, various approaches of the optimal power allocation to cognitive users are presented. Finally, the potential issues of power management in the cognitive radio regime are exploited.
关键词：Channel state information (CSI); Cognitive radio; Dynamic spectrum access; Opportunistic spectrum access; Spectrum sharing;
