6. Power Allocation for Optimal Energy Efficiency in MAC Protocol of Cognitive Radio Communication Systems

Energy consumption is a major concern in the present wireless communication scenario. Wireless devices run different services—for example web browsing, gaming, social media, and multimedia downloads—which quickly drain the battery of the user terminal; therefore we need to design an energy-efficient user terminal that provides more battery life. Primary users recurrence rate return to the licensed band also impacts the energy efficiency of the cognitive radio network because it may require a restart of spectrum sensing, channel selection and communication over the control and data channels, consuming additional energy. Further, cognitive users consume a great deal of energy for exchange of control information, and during retransmission if the primary user resumes its transmission. A cognitive user with multiple transceivers achieves higher sensing accuracy, avoids hidden terminal problems, maximizes throughput, and is more spectrum-efficient than a single transceiver user, but it utilizes higher energy. Therefore, there is trade-off in cognitive radio MAC protocol design between the number of transceivers and energy efficiency. This chapter is concerned about the energy efficiency of cognitive radio terminals, and obtains the optimal transmit power for the cognitive terminal at which energy efficiency is at its maximum. We further show that the complexity of the proposed algorithm for computing optimal transmit power is greatly reduced. We consider different scenarios of channel conditions at different channel gains and maximize the energy efficiency of the cognitive radio terminal.