Channel Capacity of Cognitive Radio in a Fading Environment with CSI and Interference Power Constraints

Abstract

Channel capacity is used as a basic performance measurement tool for analysis and design of more efficient techniques to improve the spectral efficiency of wireless communication systems. In spectrum sharing systems, channel state information (CSI) is used at the cognitive/secondary transmitter to adaptively adjust the transmission. The knowledge of secondary link CSI and information at the secondary transmitter/cognitive radio transmitter regarding the channel between the secondary transmitter and the primary receiver (PR) are used to obtain the optimal power transmission policy of the secondary user (SU) under the constraints on the peak and average received power at the primary receiver. In this chapter, we numerically compute the channel capacity in the fading environment under average interference power constraints with two different adaptation policies for spectrum sharing in cognitive radio communication systems: power adaptation and rate and power adaptation for multilevel quadrature amplitude modulation format. We explore the small-scale fading effect on the transmit power of the secondary transmitter. The rate and power of the secondary transmitter is varied based upon the sensing information and channel state information of the secondary link. The channel capacity is maximized for these two policies by considering the Lagrange optimization problem for the average interference power constraint.