认知无线电系统中存在载波频偏的OFDM频谱感知技术

OFDM Signal Sensing Scheme for Cognitive Radio in the Presence of Carrier Frequency Offset

提出了一种利用输入检测器数据离散傅里叶变换结果的协方差矩阵的频谱感知技术。分析发现如果没有授权用户信号,协方差矩阵为对角阵;反之为非对角阵。在检测过程中,通过将协方差矩阵中非对角线元素的能量与设定的阈值相比较得出检测结果。理论推导了判决度量在是否存在授权用户信号的两种情况下的分布函数以及算法的阈值和检测概率。仿真结果表明,与已有的方法相比,该算法可以更好地对抗载波频偏,同时具有更优的检测概率。

A spectrum sensing technique using the covariance matrix of the discrete Fourier transform （DFT） output of the detector＇s input vector is proposed. It is found that the covariance matrix is diagonal in the absence of primary user＇s signal and non-diagonal otherwise. Therefore in the detection procedure, the result can be obtained through comparing the power of the non-diagonal elements of the covariance matrix and the predef＇med threshold. The probability of distribution functions（PDFs） of the decision metric as well as the threshold and probability of detection in both hypotheses of the signal presence or absence are derived. The numerical results confurn that the proposed algorithm is more robust to the carrier frequency offset compared with the existing methods, and it also enjoys better detection performance.