Joint space-time code designs for multiple access channels

A joint code design for multiple access channels (MAC) was proposed by Gärtner and Bölcskei, based on the characterization of the error events. In this paper, we propose two new code designs. The first one has a better performance and a higher symbol rate for two-user MAC with two transmit antennas at both users, while the same diversity order is achieved as the design by Gärtner and Bölcskei when both users are in errors. The other one is a systematic design for multiple users and multiple transmit antennas, which achieves the maximum diversity across all the users when errors occur in a group of users.