Appendix B

Spectrum Awareness

B.1 Spectrum Sensing

Sensing based on Energy Detection has been one of the most common approaches due to the reduced computational and implementation complexity this method exhibits. Moreover, it does not require any knowledge of the nature of the primary signal, thus being suitable for general-purpose systems. The signal is detected by comparing the output of the energy detector with a threshold, which depends on the noise floor Urkowitz 1967). The election of an appropriate threshold is not trivial, see for example (Gelabert et al. 2009), and largely impacts the detection errors that come in the form of misdetection (i.e. not detecting a present primary signal) and false alarm (i.e. detecting a nonpresent primary signal). The former error may potentially induce interference between the primary and secondary systems whereas the latter error may cause spectrum underutilization. Despite the versatile operation of the energy detector and its reduced complexity, it reveals a poor performance under low Signal-to-Noise Ratio (SNR) values, see Tang (2005), and for detecting spread spectrum signals (Cabric et al. 2004; Yucek and Arslan 2006). In Sahin et al. (2009) energy detection is considered for the uplink of an Orthogonal Frequency Division Multiple Access (OFDMA) system and compared to ESPRIT (estimation of signal parameters by rotational invariance techniques) algorithms. Results indicate a considerably better performance of the energy detector compared ...

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