Cognitive radio is an encouraging technology for future wireless communication networks. Due to the rapid increase in wireless services, the RF spectrum is going through a scarcity problem. This has forced mobile operators to participate in multi-million dollar auctions to reserve some spectrum resources. Cognitive radio tries to solve this scarcity problem by effectively using the unused portions of the spectrum. FHSS and DSSS are two spread spectrum technologies used for cognitive radios. In this paper, both techniques have been discussed extensively.