24-09-2016, 01:03 PM
SPECTRUM SENSING FOR COGNITIVE WIRELESS NETWORKS USING CYCLOSTATIONARY DETECTION METHOD
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ABSTRACT
In wireless communication, demand of the radio spectrum is increasing. Thus the resources of the radio spectrum are not enough to catch the increasing demands of the users. Here cognitive radio formerly known as software radio that can detect the unused spectrum in WRAN and provide an effective utilization of spectrum. Based on this, we use cyclostationary detection method for sensing the unused spectrum. This proposing method has reliable performance even in low signal-to-noise ratio region. It is also found that the increasing number of secondary users can result in improved detection performance, especially at low SNR.
.INTRODUCTION
With the increasing demand in higher data rates, there is a shortage of radio spectrum for the upcoming modern technologies in wireless communications. The spectrum management policies are responsible for the scarcity of the spectrum. Opportunistic spectrum access is a new approach to deal with the shortage of the spectrum problem. Cognitive radio is an important component of the OSA: it can significantly improve the efficient utilization of the radio electromagnetic spectrum. Cognitive radio is an intelligent wireless communication technology, with the following characteristic: it uses different techniques to become aware of the surroundings, have abilities to learn from the outer environment and changes the parameters transmitted data and the receiver to achieve the goal of effective communication without any interference between the primary user and the secondary user. Spectrum sensing is an essential function of the CR. The major challenge for cognitive radio systems is to avoid interference with the licensed user. For this it is necessary for the CR to make faster, and more accurate and reliable sensing of the primary user.
Cooperative spectrum sensing is used to achieve
sensing reliability, but this introduces a cooperative overhead. This problem which can be solved by improving the spectrum sensing efficiency and the role of spectrum-sensing techniques is very vital. The transmitter detection based techniques; Energy detection, Cyclostationary feature detection and Matched filter detection are widely used of spectrum sensing. It has been seen that each transmitter detection technique has a signal to noise ratio threshold, below which these techniques fail to work robustly. The energy detection techniques the simplest and more efficient at higher SNR, but it cannot differentiate between the PU and the SU signal at lower SNR. However the Matched filter detection method also being simple to implement an easily differentiate between a primary user and a secondary user. The cyclostationary feature detection though being comparatively difficult than other two user is able to differentiate between noise and primary user signal. It uses cyclostationary features caused by the periodicity in signal or its statistics like mean and auto correlation.
2. SPECTRUM SENSING IN COGNITIVE RADIO
Spectrum sensing enables secondary users to identify the presence of spectrum holes (spectrum hole is defined as a licensed spectrum band that can be utilized by unlicensed
users),which is a critical element in cognitive radio design. The secondary user can access the licensed spectrum band without interfering with primary user signal. To protect the primary user transmission, the secondary user transmitter needs to perform spectrum sensing to detect whether there is any primary user signs l or not. In general, it is difficult for the secondary user to differentiate the primary user signals from noise and other interfering signal from secondary user. Spectrum sensing involves making observation of the radio frequency spectrum and reporting on the availability of unused spectrum (spectrum hole) for use by the WRAN.
CYCLOSTATIONARY DETECTOR
Cyclostationary detector utilizes the cyclostationary characteristics of transmitted signal for spectrum sensing, which allows it to differentiate the signal from wide-sense stationary noise. It is also known as Feature detector. The transmitted signal exhibits cyclostationary nature (its mean and autocorrelation function exhibit periodicity) due to modulation, pulse spreading sequences and cyclic prefixes, all these operations at transmitter lead to built-in periodicity in transmitted signal.