Limits on linear detector performance for close users in a wireless multipath environment

In multiuser wireless systems using multiple antennas in a multipath environment it has been asserted that whenever users are at least a distance of λ/2 apart, it is possible to recover their respective signals with appropriate signal processing [1]. This paper significantly strengthens this remarkable assertion by: 1) showing explicitly that separability of the users' signals is possible using the simplest class of linear detectors; 2) showing that the λ/2 rule of thumb can be quite conservative with meaningful signal separability achievable at separations around λ/10; and 3) identifying critical geometrical properties, such as position of users and multipath geometry that permit the best separability.