Abstract: After discussing the multi-user differential space-time block coding system, and analyzing the realizability of differential decoding method, we can draw the conclusion that the receiver can not decode the information of various users while the channel is unknown if multiple co-channel users in the system are synchronous. To solve this problem, a new kind of offset system structure is presented. The multiple co-channel users transmit signals nonsynchronously with different offset delays, and the receiver can iteratively subtract to get the equivalent nil-interference result, which can be disposed of with the differential method. While the multi-user system is constructed accordint to the new offset structure, the receiver can easily cancel the interference and decode the signal even if the channel state information is unknown.

Key words: differential space-time block coding, multiple co-channel users, offset construct