Bandwidth-efficient linear modulations for multiple-antenna transmission
Some M x T modulation matrices for M transmit antennas and T symbol periods, with M = 2, 3, 4 and T = 2, and M = T = 4 are studied. A transmission rate of M symbols per channel use and a transmit diversity order of min(M, T) are achieved over a quasistatic fading channel when using rotated versions of a multidimensional quadratic amplitude modulation with spectral efficiency 2 bits/symbol. Extension to input constellations with higher spectral efficiencies is then considered. The modulations are then generalized to any number of transmit antennas M and any number of symbol periods T, such that a transmission rate of M symbols per channel use, and a transmit diversity of T are achieved under fast fading (ergodic scenario). By means of signal space diversity, the proposed modulations exploit the degrees of freedom of multiantenna channels and have moderate detection complexity at moderate and large signal-to-noise ratios (SNRs).
modulation constellations diversity methods maximum-likelihood (ml) detection multiple-input multiple-output (mimo) systems