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Today with increasing development of wireless systems, frequency utilization is limited by the problem of insufficient spectrum. In addition with increasing the implementation of the third generation (3G) and integrated cellular phones that provide high speed packet-switching data transmission, we need more portion of spectrum. On the other hand analogue TV is moving to digital, so after this switch-over, there are some parts of the spectrum which will be free, and may be able to be used for other services. In this study we try to use the technology that is able to sense the spectrums over the DVB-T frequency band (primary system), and detect the existence/absence of primary users, and based on the detection of free spectrum, use that spectrum for LTE system as a secondary system, without harmful interference with primary users defined as Cognitive Radio (CR). Our study has shown that for coexistence and sharing between DVB-T and LTE-OFDM, at the same frequency band (662-742 MHz), the probability of interference is high and a large protection guard distance is needed. However when we apply Cognitive Radio technique, harmful interference can be avoided from secondary systems and improve spectrum efficiency.