This paper proposes a differential encoding and detection scheme for distributed MIMO system where channel estimation is not needed to know the channel knowledge.At the transmitter

space-time codes are constructed with symbols which are differentially modulated by phase.The phase information is detected using two consecutive received signal vectors.The proposed scheme is evaluated in different channel propagation delay cases

and the simulation results show that the bit error rate (BER) performance is nonidentical in different propagation delay cases:the BER first decreases and then increases as the channel propagation delay changes from 0.1 symbol period to 0.9 symbol period.The BER performance is better when the propagation delay is about 0.6 symbol period

and there exists a delay case when the system achieves better performance.