Spectrum Sensing for OFDM Systems Employing Pilot Tones and Application to DVB-T OFDM
Spectrum Sensing for OFDM Systems Employing Pilot Tones and Application to DVB-T OFDM
复制标题
采用导频音的 OFDM 系统频谱感测及其在 DVB-T OFDM 中的应用
DOI：
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发表时间：
2008
期刊：
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通讯作者：
D. G. Daut
中科院分区：
文献类型：
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作者：
Hou;Wen Gao;D. G. Daut
频谱感知是认知无线电系统的核心技术之一，它为解决无线频谱的稀疏性问题提供了一种可行的方法。目前，OFDM技术被许多现有的或正在发展的无线通信标准所采用。因此，当主信号使用OFDM调制时，非常需要用于OFDM调制信号的鲁棒频谱感知算法来实现CR。基于这一需求，本文提出了一种基于时域符号互相关的频谱感知算法（TDSC方法）。该算法利用了两个OFDM符号的TDSC的平均值不为零的性质，如果他们已经嵌入了相同的频域导频音。本文明确分析了所提出的光谱传感器的统计行为，并推导出误检测概率的理论下限。本文还描述了一种直观的频谱感知方法，该方法利用OFDM调制信号的循环前缀性质（CP方法），作为比较的参考。最后，我们使用DVB-T标准[8]作为应用示例来说明所提出的频谱感知算法。模拟的信道环境是DVB-T标准中定义的莱斯和瑞利信道以及加性白色高斯噪声（AWGN）信道。在DVB-T标准中定义的四个CP比率被仿真为虚警概率等于0.01并且感测时间设置为等于50 ms。仿真结果表明，对于所有四个CP比率，当SNR等于-20.5 dB时，TDSC方法可以实现0.1的误检测概率。TDSC方法在所有情况下都优于CP方法。此外，所提出的方法具有近似相同的检测性能为不同的CP比，而CP方法的检测性能急剧下降时，CP比变小。结果还表明，模拟的性能是非常接近的理论下限，表明下限可以作为一个很好的预测性能。
Spectrum sensing is one of the core technologies of cognitive radio (CR) systems which provide a viable solution to the problem of sparsity of wireless spectrum. Nowadays, OFDM techniques are adopted by many existing or progressing wireless communication standards. Thus, a robust spectrum sensing algorithm for OFDM modulated signals is highly desired to implement CR when the primary signal uses OFDM modulation. Motivated by this demand, a time-domain symbol cross-correlation based spectrum sensing algorithm (TDSC method) is presented in this paper. The algorithm makes use of the property that the mean of the TDSC of two OFDM symbols is not zero if they have embedded the same frequency-domain pilot tones. The statistical behavior of the proposed spectrum sensor is explicitly analyzed and a theoretical lower bound on the misdetection probability is derived in this paper. An intuitive spectrum sensing method which utilizes the cyclic prefix nature of the OFDM modulated signals (CP method) is also described in this paper as a reference for comparison. Finally, we use the DVB-T Standard [8] as an application example to illustrate the proposed spectrum sensing algorithm. The simulated channel environments are the Ricean and Rayleigh channels defined in the DVB-T Standard and the additive white Gaussian noise (AWGN) channel. Four CP ratios defined in the DVB-T Standard are simulated for the probability of false alarm equaling 0.01 and the sensing time set equal to 50 ms. Simulation results show that the TDSC method can achieve a misdetection probability of 0.1 when the SNR equals -20.5 dB for all four CP ratios. The TDSC method outperforms the CP method in all cases. Furthermore, the proposed method has approximately the same detection performance for different CP ratios while the detection performance of the CP method degrades dramatically when the CP ratio becomes small. Results also reveal that the simulated performance is very close to the theoretical lower bound indicating that the lower bound can be used as a good prediction of performance.