In future heterogeneous cellular networks, cognitive radio compatible with device to device communication technique can be an aid to further enhance system spectral and energy efficiency. The unlicensed smart devices (SDs) are allowed to detect the available licensed spectrum and utilise the spectrum resource which is detected as not being used by the licensed users. In this work, we propose such a system and provide comprehensive analysis of the effect of selection of SDs' frame structure on the energy efficiency, throughput and interference. Moreover, uplink power control strategy is also considered where the licensed users and SDs adapt the transmit power based on the distance from their reference receivers. The optimal frame structure with power control is investigated under high-signal-to-noise ratio (SNR) and low-SNR network environments. The impact of power control and optimal sensing time and frame length, on the achievable energy efficiency, throughput and interference are illustrated and analysed by simulation results. It has been also shown that the optimal sensing time and frame length which maximizes the energy efficiency of SDs strictly depends on the power control factor employed in the underlying network such that the considered power control strategy may decrease the energy efficiency of SDs under very low-SNR regime.
Tang, W., Shakir, M. Z., Imran, M. A., Tafazolli, R., Qaraqe, K. A., & Wang, J. (2016). Spectral and energy efficient cognitive radio-aided heterogeneous cellular network with uplink power adaptation. Wireless Communications and Mobile Computing, 16(14), 2144-2162. https://doi.org/10.1002/wcm.2673