near-optimal pilot pattern for cognitiveradio systems based on nc-ofdm

It is critical to understand channel state information (csi) at the receiver in order to recover received signals for wireless networks. to avoid detrimental interference between unlicensed users and licensed users in cognitive radio (cr) systems, licensed users' subcarriers will be disabled. as a result, non-contiguous ofdm (nc-ofdm) is used for data transmission instead of conventional ofdm. as a result, traditional channel estimate approaches based on equidistance pilot symbols will be ineffective for cognitive radio systems. two novel pilot allocation techniques for nc-ofdm systems are proposed in this study. the first technique introduces the equidistance pilot pattern. the channel frequency response will then be determined using interpolation of the frequency response of pilot subcarriers. in the second technique, the ideal pilot pattern will be obtained by applying the searching algorithm that minimizes the mean square error (mse) of channel estimate by utilizing the pilot position of the first suggested pilot pattern and according to the ls estimation. the simulation results showed that the suggested approaches' channel estimation efficiency is extremely close to that of traditional ofdm.