Over the past few decades there has been massive increase in wireless applications usage and subsequently in allocation of available spectrum. The available spectrum is getting scarce because of this surge in wireless link usage. The scarcity is not only the physical shortage of spectrum but there is an inefficient and inflexible spectrum usage. In order to address the problem of underutilization of spectrum the cognitive radio network (CRN) technology has implemented. According to CRN technology radio users could have the cognitive capacity and adaptability according to different transmission environments what makes them able to transmit through the spectrum holes dynamically and opportunistically. Since in CRN the effective decision making plays a major role to maintain the QoS towards the users, we introduced the effective decision making systems here. In this book we combine Fuzzy logic Mathematical modeling tools with CRN for efficient spectrum usage. To challenge our analysis with real time conditions, we validate the system in multiple propagation environments and channel fading conditions. We implement OFDM technology in CRN to improve the data rate in emergency situation