MAXIMIZING AVAILABLE DIVERSITY IN A MIMO FADING CHANNEL

Abstract

The effects of Rayleigh fading on a wireless communications link and the diversity techniques that are available to combat fading are explored in this thesis. The thesis consists of two main portions; an exploration on the use of spatial diversity and an exploration on the use of space-frequency diversity. In harnessing spatial diversity, the use of space-time coding is proposed to combat fading. Several codes of diversity two and four are explored, including Quasi-Orthogonal (QO) codes that are able to achieve a unity rate. The concept of constellation rotation for QO codes to maximize the available diversity is studied. QO codes are shown by simulation to be able to achieve full diversity, despite the fact that the codes are non-orthogonal. The use of space-time-frequency (STF) code to harness both space and frequency diversity is also explored. Simulations were performed for a variety of channel correlations to simulate varying degrees of frequency-selectivity. Results show that STF codes are very effective when the correlations in frequency response are less than 0.5. STF codes also have a power advantage over space-time codes with comparable diversity and bandwidth efficiency.