Abstract
Due to the capability of the effective usage of the radio frequency spectrum, a concept known as cognitive radio has undergone a broad exploitation in real implementations. Spectrum sensing as a core function of the cognitive radio enables secondary users to monitor the frequency band of primary users and its exploitation in periods of availability. In this work, the efficiency of spectrum sensing performed with the energy detection method realized through the square-law combining of the received signals at secondary users has been analyzed. Performance evaluation of the energy detection method was done for the wireless system in which signal transmission is based on Multiple-Input Multiple-Output—Orthogonal Frequency Division Multiplexing. Although such transmission brings different advantages to wireless communication systems, the impact of noise variations known as noise uncertainty and the inability of selecting an optimal signal level threshold for deciding upon the presence of the primary user signal can compromise the sensing precision of the energy detection method. Since the energy detection may be enhanced by dynamic detection threshold adjustments, this manuscript analyses the influence of detection threshold adjustments and noise uncertainty on the performance of the energy detection spectrum sensing method in single-cell cognitive radio systems. For the evaluation of an energy detection method based on the square-law combining technique, the mathematical expressions of the main performance parameters used for the assessment of spectrum sensing efficiency have been derived. The developed expressions were further assessed by executing the algorithm that enabled the simulation of the energy detection method based on the square-law combining technique in Multiple-Input Multiple-Output—Orthogonal Frequency Division Multiplexing cognitive radio systems. The obtained simulation results provide insights into how different levels of detection threshold adjustments and noise uncertainty affect the probability of detection of primary user signals. It is shown that higher signal-to-noise-ratios, the transmitting powers of primary user, the number of primary user transmitting and the secondary user receiving antennas, the number of sampling points and the false alarm probabilities improve detection probability. The presented analyses establish the basis for understanding the energy detection operation through the possibility of exploiting the different combinations of operating parameters which can contribute to the improvement of spectrum sensing efficiency of the energy detection method.
Highlights
The increased popularity of wireless communication networks raises the need for an improvement of network capacity and the efficiency of spectrum usage
Carlo simulations(pp), signal-to-noise ratio (SNR) simulation range (SNR), length of the Multiple-Input Multiple-Output (MIMO)-OFDM data, dynamic detection threshold (DDT) factor (ρ0), and noise uncertainty (NU) factor (ρ), 2: OUTPUT: Detection probability impacted by detection threshold (DT) adjustment (PdDT ) and Detection probability impacted by NU and DT adjustment (PdNUDT )
The results indicate that for the same number of sampling points used in the energy detection (ED), a better probability of detection will be obtained for the systems with a higher capability of DT adjustments (ρ0 =1.05) during the ED impacted by moderate NU (ρ = 1.03), than the systems with the lower capability of DT adjustments (ρ0 = 1.03) which are impacted by a high NU (ρ = 1.05)
Summary
The increased popularity of wireless communication networks raises the need for an improvement of network capacity and the efficiency of spectrum usage. ED employing the SLC technique represents a simple and efficient concept for the implementation in the MIMO-OFDM CR system, which motivates presenting the results. In this paper, the impact of NU and DT adjustments on the efficiency of the ED employing SLC technique in the SISO and MIMO-OFDM CR systems was analyzed. The development of the explicit analytic mathematical expressions for the performance assessment of ED process employing SLC method impacted by NU and DT adjustments in MIMO-OFDM CR systems.
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