The Tradeoff between Channel Capacity and Out-of-Band Interference of Cognitive Radios

Two points need to be considered on power loading policy of Cognitive Radio (CR) systems. The first is to maximize the channel capacity over the given frequency band, which is detected usable for CR systems. The second is the out-of-band interference suppression of the CR systems. In the paper based on the mathematical expression of the interference power caused by MB-OFDM based CR systems, the relationship of the symbols on the sub-carriers can be obtained. To realize the relationship the sub-carrier weighting method can be adopted. With the effect of the weighting factors, the symbols relationship can be satisfied, and simultaneously the maximum channel capacity can be achieved on certain degree. The simulation results of the relationship among the three parameters, channel capacity, interference power and total transmission power, also shows that a better tradeoff can be achieved between the channel capacity and the interference power.