In this Paper we review and analyze space time trellis codes with & without ideal beam forming for the free-space optics (FSO) under atmospheric turbulences. Space time trellis code with ideal beam forming at transmitter termed as weighted space. Smart antenna technology provides a wide variety of options, ranging from single-input,multiple-output (SIMO) architectures that collect more energy to improve the signal to noise ratio (SNR) at the receiver, to multiple-input, multiple-output (MIMO) architectures that open up multiple data pipes over a link. Atmospheric turbulence can cause significant performance degradation in free space optical communication systems. An efficient solution could be to exploit the temporal diversity to improve the performance of the FSO- transmission link.