Trace-orthogonal space-time coding for multiuser systems

In this paper we prove that trace-orthogonal space-time coding provides a necessary and sufficient condition for information lossless coding in a multiple access system, where each user encodes its own symbols independently of the other users. Then, we show that the sub-optimal MMSE decoder can be implemented very simply as a set of scalar decoders and we prove that, under the assumption of using the (sub-optimal) MMSE decoder, the trace-orthogonal design with scaled unitary coding matrices yields minimum BER for each user.