Channel capacity in fading environment with CSI and interference power constraints for cognitive radio communication system

In this paper, we have numerically computed the channel capacity in fading environment under average interference power constraint with two different adaptation policies for the spectrum sharing in cognitive radio communication systems such as power adaptation and rate and power adaptation for multilevel quadrature amplitude modulation format. However, the small scale fading effect over the transmit power of the secondary transmitter is explored. The rate and power of 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 average interference power constraint.