Continuous-transmit in cognitive radio systems: Spectrum and energy efficiency

Cognitive radio is a promising technology that uses radio spectrum opportunistically and efficiently. In this paper, we propose a general scheme for enhancing the cognitive sources of data transmission and improving the spectrum efficiency to provide "Always Transmit" solution using both underlay and interweave approaches. In addition, the help of the new paradigms, software defined network and cognitive systems, can allow us to do sensing and transmission in the same time and over the same primary band. In this context, we study the optimal power allocation to enhance the energy efficiency and the QoS of cognitive system while respecting the QoS of primary system under different combinations of instantaneous / average transmit and interference power constraints over Nakagami fading channels. We have analyzed and derived the closed form of the outage probability for different phases and states of cognitive transmission. We have shown that the strategy "Always transmit" outperforms others conventional cognitive radio strategies.