In this paper, we have proposed a framework of cognitive CDMA systems by combining the concept of cognitive radio and code division multiple access. With frequency domain over sample (FDO), the receiver signal is projected to a higher dimension to extract channel diversity in he rent to multi path fading channels . Asa result, the proposed FDO-MMSE receiver design extends cognitive-CDMA’s applications to more severe multipath fading channels, carrier frequency offset and spectrum sensing mismatch. By doing so, cognitive-CDMA systems are of great potential as a transmission technology for internet of things applications