# Spatial multiplexing MIMO, antenna critical spacing, antenna isolation

How does antenna isolation affect single user spatial multiplexing MIMO performance in an antenna array? Text books talk about a critical antenna spacing of 1/2 of the wavelength provided that the environment is a rich scattering one . Would that be the sole criterion? or would the antenna-antenna isolation rather be the criterion to observe?

Regarding spacing: if the antennas are too close together, then they see essentially the same channel. So, some spacing is needed; the more distance between antennas, the better. The $$\lambda/2$$ antenna spacing is a rule of thumb that may or may not work in practice.