International Journal of Computer Applications (0975 – 8887) Volume 87 – No.14, February 2014 23 Dynamic-Double-Threshold Energy Detection Scheme under Noise Varying Environment in Cognitive Radio System Sonam Shrivastava Dept. of Electrical Engg. National Institute of Technology Rourkela, India Ravi Tiwari Dept. of Electrical Engg. National Institute of Technology Rourkela, India Susmita Das Dept. of Electrical Engg. National Institute of Technology Rourkela, India ABSTRACT In cognitive radio, spectrum sensing is a key component for securing the licensed terminal from interference and detects the white spectrum hole to improve the spectrum efficiency. In the existing techniques, the noise uncertainty was either not considered or only detrimental effects are mitigated without much performance improvement. Therefore, a novel dynamic- double-threshold energy detection scheme is proposed under noise uncertainty, and its performance has been studied. Simulation analysis and results show that the proposed scheme improves the performance of detection for smaller values of false alarm probability. It is also found that the detection probability is reached at a satisfactory level, even under varying noise uncertainty. General Terms Cognitive radio, energy detection technique, spectrum sensing. Keywords Cognitive radio, dynamic-double-threshold, noise uncertainty, white spectrum hole, noise variance, energy detection. 1. INTRODUCTION Nowadays, there is a scarcity of the radio spectrum due to advancement in wireless appliances and services as Wi-Fi, Bluetooth, ZigBee, and Wi-MAX etc. Because of this huge demand of radio spectrum cognitive radio gains much attention as it can sense the unused spectrum i.e. spectrum holes under license band and keeping spectrum utilization and quality of service high for the overall system. To meet the excessive demand of the radio spectrum band the cognitive radio (CR) is a very promising technique as it does not cause harmful interference to the licensed terminals. According to a survey performed by Spectrum Policy Task Force (SPTF) within the Federal Communication Commission (FCC), that actual licensed spectrum is inefficiently utilized [1-3]. To utilize the available spectrum up to the full extent it is mandatory to allow the unlicensed terminals to borrow unused licensed band under the condition that it should not cause any harm to the licensed terminals. For this, an intelligent wireless communication system is required, which must be aware of its environment and able to select the spectrum band as well as the parameter (such as carrier frequency, modulation type, Bandwidth, etc.). The cognitive radio is capable of doing this and thus fills the unused licensed spectrum holes also called as white spectrum holes, without causing much interference to the licensed terminals [4]. In order to do so CR must sense the spectrum continuously. The basic spectrum sensing techniques, which already have been proposed, are energy detection technique [5], matched filter detection technique and cyclostationary feature detection technique [6]. In these basic transmitter detection techniques, energy detection is generally used because of its low complexity. The double threshold technique is introduced in [7]. Most of the techniques presented on the basis of invariant noise power, whereas in total noise is present due to various factors like quantization, leakage of signals, thermal noise, etc., thus we can say noise is not perfectly Gaussian also not stationary [8]. Thus, under practical scenario we cannot fix the noise variance of received signal which, results in the noise uncertainty condition. The problem of noise uncertainty is corrected by using the proposed dynamic-double-threshold scheme. Here two varying thresholds has been taken, which will result in high detection probability, while keeping false alarm probability at fixed lower value as in the case of fixed noise condition. The remaining part of the paper is organized as follows. In section II detection model is explained. Double threshold is introduced in section III, and noise uncertainty with dynamic threshold is explained in section IV. The performance improvement is proven with the simulation result in section V. Finally, conclusions are drawn in section VI. 2. DETECTION MODEL Fig. 1 shows the system model for spectrum sensing in cognitive radio (CR). There are two cognitive terminals (CT):   and   , one licensed terminal and one licensed terminal access point. The CTs will sense the spectrum and find the spectrum holes to maximize the radio spectrum utilization. For detection of an unused licensed band of the radio spectrum, the basic transmitter detection techniques are used generally. These techniques can be modeled as a binary hypothesis [9] as follows:                                 