Cognitive Radio is proposed as a promising technology to solve the imbalance between spectrum scarcity and spectrum underutilization. In Cognitive Radio, spectrum sensing is done in order to locate the unused spectrum segments. So keeping in view of efficient utilization of the spectrum it is necessary to investigate on the Spectrum Sensing and Spectrum Sharing techniques. So a Comparative Performance Analysis of Cognitive Radio using different Spectrum Sensing techniques, taking in view their Pros and Cons is done. In this Dissertation Non-Cooperative, Cooperative/Dynamic and Fast Spectrum Sensing Techniques have been discussed. Earlier AND and OR Rule being used independently, are combined in this FUSION approach and better result are obtained. Main focus is give on Fast Spectrum sensing using Discrete Wavelet Packet Transform (DWPT). This Wavelet based energy detection technique is based on WRAN, IEEE 802.22 working which reduces the complexity and sensing becomes faster. Stress is given on application areas, where Cognitive Radio techniques are implemented and proved out to have upper-hand than the available Intelligent and Adaptive Radios.