Cooperative diversity can enjoy the same benefits of MIMO systems when there is no possibility of carrying multiple antennas on a communication terminal. The main distinction between MIMO and cooperative diversity systems is the inherent asynchronism in the latter. We propose a model to study the effects of carrier frequency offset along with symbol asynchronism. Based on the proposed model, a Viterbi equalizer is utilized as a solution for demodulation. Through simulations, it is observed that such a solution suffers a graceful loss with increasing carrier frequency offset