Contents I. Introduction
Consider a space–time coded system with transmit antennas and receive antennas. We assume under the quasi-static Rayleigh fading assumption that the channel is fixed for a duration of symbol transmissions. Let denote the signal alphabet (constellation) and be a space–time code. Each element of the space–time code is thus a matrix. Given that is the transmitted codeword (code matrix), the received signal is given by Y=\sqrt{\rho_t} H S + N\eqno{\hbox{(1)}} where , with being the signal-to-noise ratio (SNR). The components of the noise matrix and the channel fading-coefficient matrix , respectively, are independent and identically distributed, zero-mean, complex Gaussian random variables having common density function f(x) = {{1}\over {\pi}}\, e^{- \vert x\vert^2}.\eqno{\hbox{(2)}} In order to enable to be considered as the SNR, we constrain the components of the signal matrix to satisfy \sum_{q=1}^Q \vert s_{qm}\vert^2 = Q,\qquad {\hbox{for}}\; m=1,\,2,\,\ldots,\, M-1,\, M.
