The demand of radio-electric spectrum in cities with high density of users is growing every day. There are many initiatives that aim to meet this demand, one of these initiatives is to insert into wireless communication devices algorithms that alternate their band operation through technology called cognitive radios to allow users to maintain connectivity and transfer data securely in unlicensed bands. Often the study and evaluation of research trying to explore the capabilities of cognitive radios require much financial investment in cases in which the intention is to implement a real experimental network or to perform simulations using proprietary software. Thus, this article presents a case of using modules that are implemented within the framework of network simulator textit 3 (ns-3). The results of this simulation were validated with experimental results of a real cognitive network, which was implemented on CPqD campus in Campinas, Brazil. This simulator creates a variety of opportunities to assess cognition algorithms using an open source tool. The validation of simulations with ns-3 show consistency of results with those which were obtained in cognitive experimental network, thus cognitive radio simulator implemented in ns-3 can be used to evaluate algorithms considering a variety of scenarios without increasing costs.