Abstract

With the increase of different types of wireless devices, the radio frequency (RF) spectrum will not longer large enough to accommodate these increased devices for communication in the future under the traditional fixed spectrum access (FSA) policy. Therefore, cognitive radio (CR), which provides devices flexible spectrum access, has been proposed to solve this scarcity problem in RF spectrum. The ability of CR depends largely on its spectrum sensing since it provides device access to one spectrum band while avoiding interference to other devices. However, the results from single spectrum sensing is not reliable in real communication condition due to various fading effects. Thus, designing an efficient cooperative spectrum sensing scheme a significant task.
In this thesis, two cooperative narrowed spectrum sensing schemes, multi-selective cooperation and selective cooperation, will be proposed. Multi-selective cooperation,
an improved version from selection combining (SC), is based on ordered statistics of the reporting links between the cooperative nodes and fusion center where the links with high signal-to-noise ratios (SNRs) are selected as reliable reporting links. Furthermore, we examine the optimum N-out-of-K rule of our scheme under different detection threshold and SNR. Another new scheme, selective-cooperation, is proposed based on multi-selective cooperation and it selects the links, whose SNRs are larger than fusion center's, as reliable reporting links. The performance of both new schemes are compared to other existing schemes in-terms of the probability of detection and probability of false alarm over independent identity distributed (i.i.d) and independent non-identical distributed (i.n.d) Rayleigh fading channels. Both simulations and analytical results show that the multi-selective scheme outperforms some traditional schemes, i.e. selection combining, general N-out-of-K rule and square-law selection (SLS) under different system parameters. Simulations and analytical results also show that the performance of the selective-cooperation scheme gets further improvement compared with multi-selective scheme and it outperforms some traditional schemes, i.e. square-law combining (SLC), under different communication environments.