Spectrum Sensing for OFDM Signals Using Pilot Induced Auto-Correlations
Spectrum Sensing for OFDM Signals Using Pilot Induced Auto-Correlations
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DOI：
10.1109/jsac.2013.130303
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发表时间：
2013-02
影响因子：
16.4
通讯作者：
Yonghong Zeng;Ying-Chang Liang;The-Hanh Pham
中科院分区：
文献类型：
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作者：
Yonghong Zeng;Ying-Chang Liang;The-Hanh Pham
正交频分复用(Ofdm)技术已被广泛应用于各种无线通信系统中。因此，在认知无线电和其他频谱共享系统中，对ofdm信号的检测具有重要意义。在许多流行标准中，ofdm的一个共同特征是一些导频子载波在某些ofdm块之后周期性地重复。本文利用导频的这种重复结构，提出了一种适用于OFDM信号的感知方法。首先，对接收信号的自相关特性进行了识别，并由此推导出最优似然比检验。然而，这种方法需要知道信道信息、载波频偏(CFO)和噪声功率。为了使LRT方法实用化，我们提出了一种不依赖于信道信息和噪声功率的近似LRT(ALRT)方法，因此CFO是ALRT的唯一障碍。为了解决这个问题，我们提出了一种利用接收信号的多抽头AC来估计复合CFO并补偿其在AC中的影响的方法。计算机仿真表明，该方法对频偏、噪声功率不确定性、时延不确定性和信道的频率选择性具有较强的鲁棒性。
Orthogonal frequency division multiplex (OFDM) has been widely used in various wireless communications systems. Thus the detection of OFDM signals is of significant importance in cognitive radio and other spectrum sharing systems. A common feature of OFDM in many popular standards is that some pilot subcarriers repeat periodically after certain OFDM blocks. In this paper, sensing methods for OFDM signals are proposed by using such repetition structure of the pilots. Firstly, special properties for the auto-correlation (AC) of the received signals are identified, from which the optimal likelihood ratio test (LRT) is derived. However, this method requires the knowledge of channel information, carrier frequency offset (CFO) and noise power. To make the LRT method practical, we then propose an approximated LRT (ALRT) method that does not rely on the channel information and noise power, thus the CFO is the only remaining obstacle to the ALRT. To handle the problem, we propose a method to estimate the composite CFO and compensate its effect in the AC using multiple taps of ACs of the received signals. Computer simulations have shown that the proposed sensing methods are robust to frequency offset, noise power uncertainty, time delay uncertainty, and frequency selectiveness of the channel.