Theoretical Analysis of Power Saving for Cognitive Radio Systems with Arbitrary Input Distributions

In this paper, an optimal power allocation scheme is derived in cognitive radio systems under the condition of finite symbol alphabet input as used in practical communication systems. The proposed scheme is shown to save transmit power compared to its conventional counterpart, which assumes Gaussian inputs. Numerical results reveal that, for distances between the SU transmitter and the PU receiver ranging between 50m to 100m, the transmit power saving with the proposed algorithm is in the range of 13− 90% depending on the modulation scheme (i.e., M-QAM) used. Furthermore, a theoretical framework is established in this paper for the derivation of the average optimal power allocation and estimation of power saving. Our theoretical analysis is later verified by simulations and proved to be accurate.