摘要：
We investigate how to cancel interference by using space time code and codeword space alignment for MIMO Y channel consisting of three users and a relay. All the nodes adopt Alamouti code. During the multiple access stage, two codewords within each reciprocal codeword pair are aligned through pre-coding. The relay decodes the elements of each codeword pair using the orthogonal property of effective channel matrix of Alamouti codeword. During the broadcast stage, the interference between codeword pairs at each user is eliminated by the orthogonal property of effective channel matrix of Alamouti codeword, instead of the interference alignment pre-coding. Thus, channel state information is not required during the broadcast stage, which greatly reduce the amount of feedback.
