Welch Periodogram Detector for QPSK Based AWGN Base-Band and Pass-Band Cognitive Radio Systems

The idea of software defined radio was proposed by J. Mittola. It was a radio designed on programmable chips. The idea of SDR was further enhanced in the form of Cognitive radios. It was proposed by the J.Mittola for the solution of the Spectrum Scarcity problem. Cognitive Radio based networks have the two types of users. One type of the users is known as primary users and the other are known as the secondary users. The Primary users are licensed users and the secondary users are the cognitive users(unlicensed) users .The Primary users have the priority of spectrum usage .While the cognitive user have the opportunistic nature of the spectrum usage . Cognitive user can use the primary user’s frequency when the spectrum holes (primary user is not communicating) are available. There are many signal processing operations in the background of the Cognitive Radios. One of these operations is the Spectrum sensing. Signal detection theory is used for the separation and recognition of information from the noise buried background and mitigation of interference. The spectrum sensing (primary user detection in licensed spectrum) is the most important task and fundamental problem in Cognitive Radio systems and networks. This requirement reborn the spectrum sensing as an active research area. Various Parametric and Non parametric Spectrum Sensing techniques are used for the spectrum hole detection. Welch periodogram is the energy based detection technique. It uses the Barlett windowing function. This is an easy to implement, simple real time and fast Spectrum sensing technique. Welch periodogram needs less prior information about the source signal and propagation channel. In this paper, Welch periodogram detector is used for the signal detection in QPSK based Base-band and Passband signal detection through AWGN channel. The technique is successfully implemented up to SNR =-30 dB Welch periodogram provides an easy and simple solution for the detection of spectrum hole and mitigation of noise in cognitive radio systems and networks. Key word: Cognitive radio, Spectrum sensing, Welch periodogram, Windowing, Barlett window