Abstract:

To make full use of existing spectrum, we study the problem of a joint overlay and underlay resources allocation for the OFDM(Orthogonal Frequency Division Multiplexing) based cognitive radio systems. A new subcarrier and optimal power allocation scheme is proposed under the joint overlay and underlay fashion. This scheme can provide maximum transmission capacity for secondary users while keeping the total power and the interference introduced to the subcarrier below a given threshold. In consideration of the computation complexity of the scheme, the nulling scheme can be used in the proposed method to obtain sub-optimal scheme. Finally,the analysis of the robustness of this power allocation algorithm is presented when considering the uncertainty of
the channel gain between secondary user and primary user in the sense of the Worst-Case. Simulation results show that the proposed schemes demonstrate better performance than the overlay or the underlay resource allocation schemes.

Key words: cognitive radio, orthogonal frequency division multiplexing(OFDM), robust, resource allocation