Multi-input multi-output (MIMO) scheme in communication systems enhances the system performance and capacity. In wireless communications, cooperative networks can provide spatial diversity gain by creating virtual antenna arrays. In this paper, we consider cooperative networks adopting the differential unitary space time code (DUSTC) which bypasses the channel estimation at the receiver. With high signal-to-noise ratio (SNR), the codeword error rate (CER) of these systems is analyzed using both decode-and- forward and amplify-and-forward relaying protocols. The effect of link quality on the error performance is also investigated. Using these results, the comparison between the STC-based and conventional cooperative networks, i.e, repetition-based cooperative system, is addressed.