Analysis of Multiuser Stacked Space-time Orthogonal and Quasi-orthogonal Designs

We consider space-time transceiver architectures for multiple access fading channels with K users, each equipped with multiple transmit antennas. Each user employs an orthogonal or a quasi-orthogonal design as an inner code. At the multi-antenna receiver, successive group interference suppression strategies based on the linear zero-forcing or linear MMSE filters are employed in some fixed or channel dependent order. These strategies exploit the specific structure of the inner codes to yield high diversity orders while preserving the decoupling property of the constituent inner codes thereby enabling the use of simple demodulators. Motivated by the special structure of the effective channel matrix induced by the inner codes, we obtain several new results on the QR and eigenvalue decompositions of certain structured random matrices. Using these random-matrix distribution results, we characterize the high-SNR performance limits of the transceiver architectures under consideration by obtaining their diversity- multiplexing tradeoff curves.