Abstract

As spectrumscarcity is a big problem cognitive radio is an efficient solution to thisproblem. Orthogonal frequency division multiplexing (OFDM) is a potentialtechnology providing many advanced functionalities in terms of power band ratecontrol for cognitive radio networks (CRNs). Power allocation for CRNs is animportant part for reduction of interference. In this paper we compare twowater filling algorithm geometric water filling and dynamic channel sensingalgorithm. This algorithm is optimized in a way to maximize the sum rate ofsecondary users by allocating power more efficiently, while constraining the 1)total transmit power, 2) individual sub channel transmit power as well as 3)individual subcarrier peak power of secondary users, for a given interferencelevel to the primary users. Numerical results show that these algorithmsprovide better utilization of power resources thus maximizes the sum rate thanthe existing algorithms. And the power allocation is optimal. Geometric waterfilling is a dynamic power distribution process. The state of this process isthe difference between the individual peak power sequences and the currentpower distribution sequence obtained by the Algorithm GWF and dynamic channelsensing algorithm provide optimal solution in terms of power is allocatedintelligently and with less complexity.

Keywords:-geometric water filling, conventional water filling, dynamic channelsensing, OFDM system, cognitive radio network.