Altunbas, Yasin; Turk, Kadir

Visible light communication (VLC) is a form of short-range wireless optical communication that uses light in the visible band for both communication and illumination. The limited switching frequencies of light-emitting diodes (LEDs), which are mostly preferred as transmitters in VLC systems, adversely affect the speed of communication. Non-orthogonal multiple access (NOMA) as an access method, and multiple-input multiple-output (MIMO) are used in VLC systems to raise the sum rate. Several methods have been proposed in the literature to determine needed power allocation coefficients for indoor MIMO-NOMA based VLC systems. In this study, meta-heuristic optimization algorithms are proposed to determine the power allocation coefficient that are subject to various constraints including fairness. The numeric results demonstrate the superiority of meta-heuristic methods over sum rate performance. In cases where the user signal strength values differ and the number of users increases, or in other words, the solution becomes more complex, the sum rate acquired by traditional methods reduces, whereas the sum rate using the suggested methods almost does not change and stays high.

Ilgin, Fatih Yavuz

As it is known, Energy based detection is widely used in Cognitive Radio and radar systems. In order to reduce the disruptive effects of wireless channels, Energy based sensing method has been used with different combinations. In this study, a new spectrum sensing method is proposed by combining the dual threshold energy based sensing method with Copula functions. The spectrum sensing model is given for the proposed method and the sensing method is explained with theoretical analysis. For simulation studies, OFDM based communication system was used under Rayleigh fading channel. Performance analysis of the proposed method was compared with traditional Energy based detection (both single and double threshold) and a noticeable increase in performance was observed.

Çiflikli, Cebrail; Ilgin, Fatih Yavuz

As is known, eigenvalue based spectrum sensing for multi-antenna cognitive radio systems is a highly preferred method because it requires no priori knowledge concerning the signal to be sensed. The performance of the method depends on the most accurate calculation of the test statistic and the threshold value. Regaining of the threshold values was aimed in this study in order to increase performance in generalized likelihood ratio detection based sensing. While the threshold value was calculated, the probability of false detection (Pfa) and the probability of detection were regained by using a new probability distribution function for Wishart matrices. The simulations were performed under noise uncertainty for MIMO–OFDM systems, and a noticeable performance increase was observed with the new threshold value in comparison with conventional methods.