Matched filter bound for equalization and antenna diversity over mobile radio channels

We propose a theoretical evaluation of the performances of L-branch spatial and/or polarization diversity in a selective Rayleigh multipath environment. We consider the case of a perfect receiver which ideally equalizes the channel and also maximises the diversity gain (i.e. matched filter and maximal ratio combining). The theoretical model is based on Karhunen-Loeve expansion. While many previous approaches of this kind have been presented in the past, we propose the most general and elegant one. Indeed, our model accounts for the correlations between the L branches and between the channel taps within each branch. It also accounts for the local mean energy mismatch of the branches. The usefulness of our approach is shown through two sample studies. First we compare the benefits of a two branches receiver (L=2) using spatial or polarization diversity for GSM and DCS1800 systems. Then, focusing on polarization diversity, we use our theoretical model to demonstrate that, contrary to the general belief, diversity gain is invariant by spatial rotation of the receiver antennas