Improved design criteria and new trellis codes for space-time coded modulation in slow flat fading channels

The design criteria for space-time code under slow flat Rayleigh fading env ironments are well known to be the rank criterion and the determinant crite rion. However, the derivation of these two criteria is based on the assumpt ion that the signal-to-noise ratio (SNR) is sufficiently high. Hence these criteria are loose when the SNR does not satisfy this assumption. In this l etter, we consider this practical issue and derive tighter design criteria for moderate and low SNRs, Some new space-time trellis codes are found base d on the new criteria through computer search. Simulation results show that these codes outperform existing codes under their designed SNR conditions.