A channel estimation method for NC-OFDM systems in cognitive radio context

In orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems, the sub-carriers, which span the spectrum used by licensed users (LUs), should be deactivated to avoid interference. The resulted OFDM system is called non-contiguous OFDM (NC-OFDM) system. For NC-OFDM systems, as no pilot symbols can be transmitted over these deactivated subcarriers, the conventional modified least square channel estimation can not be applied. In this paper, we propose a new channel estimation method to address this issue. In the proposed channel estimation, we use the LS channel estimation to obtain the channel fading coefficients associated with the subcarriers over which the pilot symbols are transmitted. Furthermore, we compute the time domain channel pulse response based on the basic principle of Fourier transform. Then, we adopt inverse discrete Fourier transform (IDFT) based channel estimation noise reduction to improve the channel estimation accuracy. For slow time-varying channel, we also propose to use pilot-block average based channel estimation noise reduction to further improve the channel estimation performance. Simulation results validate our proposed channel estimation method.