Optimal Resource Allocation Scheme for OFDM-based Cognitive Radio System: Correlated Channel

A power allocation algorithm is proposed to share spectrum bandwidth between primary and secondary users under underlay scheme of cognitive radio system. In this scenario, interference power at primary user receiver side has an important role in determining transmission power limit. In conventional water-filling algorithm, main channel gain is used to maximize secondary capacity with total power constraint. In order to adapt this algorithm with cognitive radio scenario, the problem optimization has to solve according to tolerance interference limit at primary receiver. The excess constraint decreases the power efficiency and secondary capacity of water-filling algorithm. As we may know, primary and secondary transceivers have to place in together coverage area to interfere another signal. However, main and interference channels are assumed correlated channel. In this investigation, power allocation algorithm is extended when the main channel coefficient is correlated to the interference channel coefficient. In the proposed algorithm, interference and main channel gain is considered iteratively in two steps. Thus, allocated power into any subcarrier decreases with growing interference channel gain and falling main channel gain. The numerical results show that interference level in primary user receiver side is controlled without decreasing power efficiency.

Keywords:

cognitive radio system , OFDM , power control , channel inversion algorithm , water-filling algorithm