Maximum-SNR space-time designs for MIMO channels

We consider a communication scenario involving an m /spl times/ n MIMO linear channel whose input is a symbol stream multiplied prior to transmission by an n x n space-time coding matrix X, and whose output is fed into an m /spl times/ n linear combiner Z. We show how to choose the matrices X and Z to maximize the SNR of the linear combiner output data that are used for detection, under total power constraint (TPC), elemental power constraint (EPC), or total and elemental power constraint (TEPC). The TEPC design (considered here for the first time) is shown to include the TPC and EPC designs (previously considered by the authors) as special cases, and hence to provide a theoretically and practically interesting unifying framework. We make use of this framework to discuss various tradeoffs of the three space-time designs considered, such as transmission rate and requirements for channel status information at the transmission side.