A noncoherent receiver based on Semidefinite Relaxation(SDR)approach is proposed for Decode and Forward(DF)cooperative system with distributed orthogonal space-time codes. In the scheme, noncoherent detection is simplified to a Boolean Quadratic Program(BQP), and then, using the SDR approach, the Nondeterministic Polynomial-time hard(NP-hard)BQP problem is transformed into the optimization of a Semidefinite Program(SDP)of polynomial-time hard. Furthermore, a relaying protocol with a combination of channel e...