will be summarized in the following in order to describe the advantages of the new invention time selectivity is induced by transmitting replicas of the same time and frequency variant signal x f t over different antennas the replica on each antenna being multiplied by a time varying complex weight w n t the transmitted signals from antenna n will experience the time and frequency variant channel h n f t and finally all transmitted signals will superimpose at the receive antenna resulting in a received signal y f t according to usually the time varying weights w n t are chosen such that u2211 n 1 n u2062 u2062 uf603 w n u2061 t uf604 2 p u2061 t 2 where p t is the power that would normally have been transmitted on one antenna even when h n f t is static or quasi static over time the time varying weights will introduce time variations in the received signal y f t as long as the different h n f t are sufficiently uncorrelated a simple form of artificial time selectivity u201c doppler diversity u201d is when each antenna transmits with a certain carrier frequency offset u03b4f n frequency selectivity can be introduced in two different ways the simplest being to use delay diversity here the received signal can be expressed as a convolution of the transmitted signal with an effective channel impulse response y u2061 u03c4 t x u2061 u03c4 t u2211 n.