A new low SNR, correlated fading-suited space-time block code based on zero-padding and unitary transforms

Abstract

In recent years, extensive studies have been done to design space-time codes appropriate for communications over fading channels in multiple input-multiple output (MIMO) systems. Most of these designs have been based upon the assumption that the channel fading coefficients are uncorrelated hence independent jointly Gaussian random variables. Naturally the best strategy in such situations that the elements of the channel matrix are independent is to employ diversity techniques to combat the adverse effects of these fading media and thus the most famous space-time codes, i.e. orthogonal and trellis codes have been designed with an eye to realizing the maximum attainable diversity order in a MIMO system. In this paper, we will remove this practically difficult to meet condition and shall introduce a new linear space-time block code based on zero-padding and unitary transforms that due to having some inherent redundancy as well as diversity is better-suited to correlated fading channels. We will discuss the properties of the proposed code, derive its maximum likelihood (ML) decoder and provide simulation results which show its superiority over the highly used orthogonal space-time block codes in a wide range of signal to noise ratios in correlated fading channels.