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Blind Spectrum Sensing for OFDM-Based Cognitive Radio Systems

机译：基于OFDM的认知无线电系统的盲频谱感知

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摘要

Given the ever-growing demand for radio spectrum, cognitive radio has recently emerged as an attractive wireless technology. Since orthogonal frequency-division multiplexing (OFDM) is one of the major wideband transmission techniques, detection of OFDM signals in low-signal-to-noise-ratio scenario is an important research problem. In this paper, it is shown that cyclic prefix (CP) correlation coefficient (CPCC)-based spectrum sensing, which was previously introduced as a simple and computationally efficient spectrum-sensing method for OFDM signals, is a special case of the constrained generalized likelihood ratio test (GLRT) in the absence of multipath. As such, the performance of this algorithm degrades in a multipath scenario, where OFDM is usually implemented. Furthermore, by considering multipath correlation in the GLRT algorithm and employing the inherent structure of OFDM signals, a simple and low-complexity algorithm called the multipath-based constrained-GLRT (MP-based C-GLRT) algorithm is obtained. The MP-based C-GLRT algorithm is shown to outperform the CPCC-based algorithm in a rich multipath environment. Further performance improvement can be achieved by simply combining both the CPCC- and MP-based C-GLRT algorithms. A simple GLRT-based detection algorithm is also developed for unsynchronized OFDM signals, whose performance is only slightly degraded when compared with the synchronized detection in a rich multipath environment.
机译：鉴于对无线电频谱的需求不断增长，认知无线电最近已成为一种有吸引力的无线技术。由于正交频分复用（OFDM）是主要的宽带传输技术之一，因此在低信噪比情况下检测OFDM信号是一个重要的研究问题。在本文中，表明基于循环前缀（CP）相关系数（CPCC）的频谱感知是一种受限的广义似然的特殊情况，该频谱感知先前作为一种简单且计算效率高的OFDM信号频谱感知方法而引入。不存在多径情况下进行比率测试（GLRT）。这样，在通常实现OFDM的多径情况下，该算法的性能会降低。此外，通过在GLRT算法中考虑多径相关性并利用OFDM信号的固有结构，获得了一种简单且低复杂度的算法，称为基于多径的约束GLRT（基于MP的C-GLRT）算法。在丰富的多路径环境中，基于MP的C-GLRT算法的性能优于基于CPCC的算法。通过简单地组合基于CPCC和基于MP的C-GLRT算法，可以进一步提高性能。还为不同步的OFDM信号开发了一种基于GLRT的简单检测算法，与丰富的多路径环境中的同步检测相比，其性能仅稍有下降。

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